{"1": {"fulltext": "", "height": "3764", "width": "2444", "jp2-path": "elementsofphysic00hend_0001.jp2"}, "2": {"fulltext": "Copyrights?\\nCOPYRIGHT DEPOSIT;", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0002.jp2"}, "3": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0003.jp2"}, "4": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0004.jp2"}, "5": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0005.jp2"}, "6": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0006.jp2"}, "7": {"fulltext": "TWENTIETH CENTURY TEXT-BOOKS\\nEDITED BY\\nA. F. NIGHTINGALE, Ph.D.\\nSUPERINTENDENT OF HIGH SCHOOLS, CHICAGO", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0007.jp2"}, "8": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0008.jp2"}, "9": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0009.jp2"}, "10": {"fulltext": "SIE ISAAC NEWTON (1642-1727).\\nGreatest of natural philosophers author of Principia president of Royal\\nSociety twenty five years member French Academy of Sciences knighted 1705.\\nBuried in Westminster Abbey.", "height": "3383", "width": "2346", "jp2-path": "elementsofphysic00hend_0010.jp2"}, "11": {"fulltext": "TWENTIETH CENTURY TEXT-BOOKS\\nELEMENTS OF PHYSICS\\nBY\\nC. HANFORD HENDERSON, Ph.D.\\nPRINCIPAL PRATT HIGH SCHOOL, BROOKLYN\\nAND\\nJOHN F. WOODHULL, Ph D.\\nPROFESSOR OF PHYSICAL SCIENCE, TEACHERS COLLEGE,\\nCOLUMBIA UNIVERSITY, NEW YORK\\nNEW YORK\\nD. APPLETON AND COMPANY\\nIQOO\\nCHhT", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0011.jp2"}, "12": {"fulltext": "47696 QJ\\nLibrary of Congress\\nTwo Copies Received\\nSEP 15 1900\\nFKSTCOPY.\\n2* C*f, Dtfcttal t\u00c2\u00bb\\nORDER DMSKM\\nCopyright, 1900\\nBy D. APPLETON AND COMPANY", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0012.jp2"}, "13": {"fulltext": "PREFACE\\nThe authors have prepared this book in the belief that\\nphysics should be so taught as to be a desirable and even\\nessential subject for every pupil in the secondary schools.\\nIn its preparation they have therefore devoted much study\\nto the conditions which obtain in the schools at the pres-\\nent time, and have endeavored to meet them.\\nThe book is designed to provide a year s work for the\\nclass room, and only such matter has been introduced as\\nis deemed appropriate for pupils of the high-school age\\nand attainments. Laboratory exercises, questions, and\\nproblems given in a text-book are manifestly inadequate\\nand unsatisfactory. The authors have therefore thought\\nit preferable not to follow that course, but to amplify and\\nmake more thorough this part of the study in a separate\\nvolume, which is published under the title Physical Ex-\\nperiments, and is to be used concurrently with the text-\\nbook.\\nThe relations of physics on all sides to human life and\\nhuman interests have been emphasized. A text-book is\\nmuch more readable if the material for the laboratory work\\nis excluded from it. The text-book comprises the infor-\\nmational part of the subject, and the authors in this vol-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0013.jp2"}, "14": {"fulltext": "VI\\nPHYSICS\\nume have imparted to it much warmth and interest. The\\nlaboratory, on the other hand, deals with inductions and\\nverifications, and its chief purpose is to make knowledge\\nreal. Both the laboratory and the class-room work are\\nessential to a correct knowledge of elementary physics,\\nand they should correlate in such a manner as to make\\nthe acquisition of that knowledge interesting as well as\\nthorough. The work has been prepared with these essen-\\ntials in view.\\nIn the text-book the subject has been further human-\\nized by the introduction of a few portraits, with brief\\nsketches of the men who, by their researches, have con-\\ntributed much to our knowledge of physics.\\nA further merit of the work is that the volume is com-\\npact. The subject-matter has been so disposed as to be\\nmost convenient for class exercises and for the arrange-\\nment of a study plan. A supplement in pamphlet form,\\ncontaining helpful suggestions to teachers using the book\\nfor the first time, has been prepared, and will be furnished\\nwithout charge. C. H. H.\\nJ. F. W.\\nAugust, 1900.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0014.jp2"}, "15": {"fulltext": "PROPERTIES OF MATTER AND\\nMECHANICS OF SOLIDS\\nCHAPTER I.\u00e2\u0080\u0094 The Content of Physics\\n1. The Two Elements in Physical Science.\\n2. Matter.\\n3. Three States of Matter.\\n4. The Three States Continuous.\\n5. Radiant Matter.\\n6. Motion.\\n7. Mass Motion and Molecular Motion.\\n8. Force.\\n9. Energy.\\n10. Matter and Motion.\\n11. Physics.\\n12. Metaphysics.\\n13. The Eternal Why.\\nCHAPTER II.\u00e2\u0080\u0094 The Constitution of Matter\\n14. The Province of Physics.\\n15. Simple and Compound Bodies.\\n16. Atoms and Molecules.\\n17. Size of Molecules.\\n18. Mechanical Mixtures and Chemical Compounds. Fig. 1.\\n19. Physical and Chemical Changes. Fig. 2.\\n20. Protyle.\\n21. Doubt.\\n22. The Firm Ground in Physics.\\n23. Table of Elements.\\nCHAPTER III.\u00e2\u0080\u0094 Properties of Matter\\n24. Secondary Properties of Matter.\\n25. Hardness.\\n26. Crystalline Form.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0015.jp2"}, "16": {"fulltext": "viii PHYSICS\\n27. Cohesion. Fig. 3.\\n28. Adhesion.\\n29. Elasticity.\\n30. Malleability\\n31. Ductility.\\n32. Viscosity and Brittleness.\\n33. Divisibility. Figs. 4, 5, and 6.\\n34. Capillarity. Figs. 7 and 8.\\nCHAPTER IV.\u00e2\u0080\u0094 On Measurement\\n35. Science.\\n36. Units.\\n37. Length. Fig. 9.\\n39. Time.\\n40. The C.-G.-S. System.\\n41. The Two Terms in Measurement.\\n42. Methods of Measurement.\\n43. Mathematical Physics.\\n44. Conservation of Matter.\\n45. Conservation of Energy.\\n46. Rationality.\\nCHAPTER V.\u00e2\u0080\u0094 Measurement of Matter\\n47. The Problem.\\n48. Extension in One Direction. Figs. 10, 11, 12, 13, and 14.\\n49. Surveying.\\n50. Extension in Two Directions.\\n51. Extension in Three Directions. Fig. 15.\\nCHAPTER VI.\u00e2\u0080\u0094 Mass and Weight\\n52. Mass.\\n53. Gravitation.\\n54. The Formula of Gravitation.\\n55. Weight.\\n56. Weight as the Measure of Gravitation.\\n57. Measurement of Mass.\\n58. Weighing. Fig. 16.\\nCHAPTER VII.\u00e2\u0080\u0094 Density and Specific Gravity\\n59. Density.\\n60. Specific Gravity.\\n61. Specific-Gravity Bottle. Fig. 17.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0016.jp2"}, "17": {"fulltext": "PROPERTIES OF MATTER i x\\nCHAPTER VIII.\u00e2\u0080\u0094 Measurement of Motion\\n62. Motion.\\n63. Velocity.\\n64. Momentum.\\n65. Xature of the Motion.\\n^6. Path of a Moving Body. Figs. 18 and 19.\\n67. Units of Motion.\\nCHAPTER IX.\u00e2\u0080\u0094 Falling Bodies\\n68. Gravitation.\\n69. The Value of g.\\n70. Falling Bodies.\\n71. Projectiles. Fig. 20.\\n72. Suggestion.\\n73. Vertical Projectiles.\\nCHAPTER X.\u00e2\u0080\u0094 The Pendulum\\n74. Importance of the Pendulum.\\n75. The Simple Pendulum. Fig. 21.\\n76. The Motion of the Pendulum. Fig. 22.\\n77. Formula of the Pendulum.\\n78. Discussion of Formula.\\n79. Time-keeping and the Seconds Pendulum.\\n80. Determination of g by the Pendulum.\\n81. The Compound Pendulum.\\nCHAPTER XI. Composition and Resolution of Motions\\n82. Composition of Motions. Fig. 23.\\n83. Parallelogram of Motions.\\n84. Moments. Fig. 24.\\n85. Parallel Motions. Figs. 25, 26, and 27.\\n86. Resolution of Motions. Fig. 28.\\nCHAPTER XII.\u00e2\u0080\u0094 Work, Power, and Energy\\n87. Work.\\n88. Measure of Work.\\n89. Power.\\n90. Energy.\\n91. Forms of Energy.\\n92. Transfer and Transformation of Energy.\\n93. Xewton s Laws.\\n94. Energy Kinetic and Potential.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0017.jp2"}, "18": {"fulltext": "x PHYSICS\\nCHAPTER XIII.\u00e2\u0080\u0094 Machines\\n95. A Machine.\\n96. Axiom.\\n97. The Principle of Virtual Velocities.\\n98. Simple Machines.\\n99. The Lever. Figs. 29, 30, 31, 32, 33, and 34.\\n100. The Wheel and Axle. Fig. 35.\\n101. The Pulley. Figs. 36, 37, 38, and 39.\\n102. The Inclined Plane. Figs. 40 and 41.\\n103. The Screw. Fig. 42.\\nTables of Contents will also be found on the following pages\\nMechanics of Fluids, 87, 88.\\nHeat, 143, 144.\\nMagnetism and Electricity, 207, 208.\\nLight, 287, 288.\\nSound, 347.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0018.jp2"}, "19": {"fulltext": "PHYSICS: THE SCIENCE OP ENERGY\\nCHAPTER I\\nTHE CONTENT OF PHYSICS\\n1. The Two Elements in Physical Science. Let us call\\nup before us a series of occurrences in the outer world\\nAn express train dashes past us. A waterfall plunges\\nover a precipice. A breath of wind blows against our faces.\\nA bird sings in the branch above us. A tree falls in the\\nforest. A boy throws a ball. A child picks a flower.\\nThese several events are apparently very unlike. They\\nseem at first sight to have nothing in common but when\\nwe look closer and reduce them to their simplest possible\\nterms, we see that they are in reality very much alike. Each\\nevent contains the same two elements, matter and motion,\\nand, from a physical point of view, that is all. Back of the\\nmatter and motion there may be motive and purpose, but\\nwe can only infer these. Our senses make direct report\\nonly of matter and motion. There are different sorts of\\nmatter and different degrees of motion, but the whole event\\nin each case shows only these as the final outer content.\\nThe study of natural events is therefore the study of\\nmatter and motion, and must start out with clear general\\nideas concerning these two elements.\\n2. Matter may be defined for the present as that which\\noccupies space. It naturally prevents anything else from\\noccupying the same space. Hence, the essential properties\\n2 1", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0019.jp2"}, "20": {"fulltext": "2 PHYSICS\\nof matter, or those properties without which we can not\\nconceive matter to exist, are extension and impenetrability.\\nMatter makes itself known to us by the testimony of the\\nsenses. We see it, hear it, smell it, taste it, touch it. But\\nobserve that, after all, this is indirect testimony. These\\nimpressions are all of them simply brain impressions. We\\nsee, hear, smell, taste, touch, in our consciousness .only. We\\ncan not assert, therefore, that matter exists apart from this\\nconsciousness. Science has nothing to say about the ulti-\\nmate nature of matter. Science studies matter simply as a\\nfact of human experience.\\n3. Three States of Matter. Matter manifests itself in\\nthree states as solid, liquid, and gas. These states of mat-\\nter, as well as many of its motions, are best explained by\\nassuming that matter is made up of extremely small par-\\nticles, or units, which are called molecules. We shall study\\nthese later somewhat more in detail.\\nSolids, at the same temperature, have nearly constant\\nvolume and approximately constant form. Their molecules\\nare so bound together that they can not change their rela-\\ntive positions except within very small limits.\\nLiquids, at the same temperature, also have nearly con-\\nstant volume, but take at once the form of the vessels which\\ncontain them. Their molecules are free to move among\\nthemselves, but are not free to fly apart.\\nGases have neither constant volume nor constant form.\\nIn consequence of the perfect mobility of their molecules,\\nthey will occupy any space into which they may be intro-\\nduced, whatever its volume or form.\\nLiquids and gases, on account of the freedom of mo-\\ntion possessed by their molecules, are classed together as\\nfluids.\\n4. The Three States Continuous. It must not be thought\\nfor a moment that matter is sharply divisible into solids,\\nliquids, and gases. On the contrary, these are only names\\nfor typical forms of matter. Within the same state we find", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0020.jp2"}, "21": {"fulltext": "THE CONTENT OF PHYSICS 3\\nwide variations from the type, and even between the three\\nstates themselves we can set np no hard-and-fast lines.\\n5. Radiant Matter. It has been thought that matter\\nmay exist in still a fourth state, and for this the name\\nradiant matter has been proposed. It represents extreme\\ndilution and mobility, and bears somewhat the same rela-\\ntion to gases that gases do to liquids. We shall study it\\nlater, when we come to consider Crooke s tubes.\\n6. Motion is change of position a simple definition, but\\none which involves nearly the whole drama of Nature.\\nThe absence of motion is rest.\\nWe can only know whether a particle is in motion or at\\nrest by comparing it with some other particle whose condi-\\ntion is known. But this in turn can only be known by a\\ncomparison with a third particle, and so on indefinitely. In\\nthe absence of any fixed reference point in the whole uni-\\nverse, we can only know relative motion and relative rest.\\n7. Mass Motion and Molecular Motion. The motion of a\\nbody may be either of the whole, giving us mass motion or\\nit may be of the parts, giving us molecular motion.\\nWhen the motion is of the whole, and not too rapid, as\\nwhen an apple falls to the ground or a ball is thrown through\\nthe air, we can directly watch the change of position. When\\nthe motion is too rapid for that, as in the passage of a can-\\nnon ball, we can still observe indirectly the change of posi-\\ntion by observing the body first in one place and then in\\nanother.\\nIf the motion is confined to the parts, it is more difficult\\nto realize it. The body, as a whole, stands still, and we can\\nnot see the motion of the molecules. But this molecular\\nmotion is quite as important as the mass motion, since it is\\nthe source of all heat and light, and of much that is most\\ninteresting and beautiful in Nature. It is a motion which\\ncan not be observed directly, but nevertheless our knowl-\\nedge of it is almost as definite and accurate as our knowl-\\nedge of the larger visible movements.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0021.jp2"}, "22": {"fulltext": "4 PHYSICS\\n8. Force. The human mind has grown into the habit\\nof hunting for causes back of all events. Motion is a very\\nstriking event. The mind, therefore, following its old\\nhabit, has long hunted for a cause of motion. It has\\nfound none. It has, however, imagined a cause, and called\\nit Force.\\nForce may be denned as that which produces motion or\\npressure.\\nWe shall have occasion from time to time to use the\\nterm Force, but we shall always have in mind the observ-\\nable reality, motion.\\n9. Energy. A body in motion, or a body in such a posi-\\ntion that it is capable of motion, is said to possess Energy.\\nThe motion may be either mass motion or molecular mo-\\ntion the term Energy applies to both.\\nA body can lose energy only by giving its motion to some\\nother body, whose total motion will thus be increased. A\\nbody never loses all of its energy because it never loses all\\nof its motion.\\nThe term energy is not open to the same objection\\nthat force is. It is permissible to speak of the visible\\nuniverse as a manifestation of energy.\\n10. Matter and Motion. It is convenient for the pur-\\npose of study to speak of matter and motion as being the\\ntwo elements in every event. But in ^Nature the two are\\nnot thus separated. Matter is always endowed with motion,\\nand we only know motion as manifested in matter. When\\nwe grow wiser, we shall study the two as one experience.\\nThey are summed up in the term Energy.\\n11. Physics. The study of events in terms of the mat-\\nter and motion involved in them constitutes physical sci-\\nence. If we direct our attention chiefly upon matter, we\\nhave that aspect of physical science known as Chemistry.\\nChemistry is the study of the composition of matter.\\nIf our attention be concentrated upon the motion, we\\nhave that aspect of the science known as Physics.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0022.jp2"}, "23": {"fulltext": "THE CONTENT OF PHYSICS 5\\nPhysics is the study of motion, and deals with matter\\nonly as the carrier of motion.\\nPhysics is sometimes defined as the science of the prop-\\nerties of matter, since these depend upon its motions. It is\\nalso defined as the study of the forces manifested in matter.\\nPerhaps it is best defined as the Science of Energy, or the\\nstudy of matter in motion.\\n12. Metaphysics. Turning back for a moment to the\\nrandom series of events named in the opening paragraph,\\nwe see that in addition to the matter and motion involved in\\nthem, there is in some of them a certain human element,\\nor what we may call a thought element. The express train\\nrepresents a certain amount of matter moving in a certain\\ndirection at a certain rate of speed, but it also represents\\nthe intelligence which shapes and guides it, and the pur-\\npose which prompts the event. It is the same with the boy\\nthrowing the ball, and with the child picking the flower.\\nThis something, outside the matter and motion of the event,\\nwhich we have called the motive, does not fall within the\\nprovince of physics. It belongs to the domain of Meta-\\nphysics.\\nMetaphysics seeks to find a theory of reality. Physics\\ndoes not attempt so difficult a search it limits itself to the\\nstudy of matter in motion, to the study of things as we see\\nthem, and is not at all concerned with the underlying real-\\nity. We are not concerned in physics with what things\\nreally are, but solely with their properties and behavior.\\nPhysics neither offers nor seeks an explanation of the uni-\\nverse. It leaves all such problems to metaphysics.\\n13. The Eternal Why. We shall not, therefore, find\\nin physics any answer to the questions What is matter\\nWhat is motion What is heat, light, electricity Physics\\ndefines them, but it does not tell what they are, for it does\\nnot know. Yet we shall try to show throughout the book,\\nand notably in the concluding chapters, that the whole value\\nof physics is human. It is worth studying, just because it", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0023.jp2"}, "24": {"fulltext": "6 MYSICS\\ndoes make our world larger and more orderly and more\\nbeautiful, and not because physical facts have any value in-\\ndependent of their human application.\\nProblems. 1. Select five events and analyze them into their\\nmatter and motion content.\\n2. Name one event containing a thought element and analyze as\\nbefore. Can the thought element be expressed in terms of matter\\nand motion\\n3. If a monkey sit on top of a pole, and always face a man who\\nwalks around the pole, with his face always turned toward the\\nmonkey, can the man be said to walk around the monkey\\n4. Are the hub and the rim of a carriage wheel relatively in\\nmotion or at rest\\n5. When the dinner bell rings, is it a case of mass or molecular\\nmotion\\n6. Can you name any fact of which you are absolutely sure\\nReference.\\nEmerson s Essay on Nature.\\nFirst Steps in Philosophy William M. Salter.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0024.jp2"}, "25": {"fulltext": "CHAPTEE II\\nTHE CONSTITUTION OF MATTER\\nApparatus Specimens of chemical elements and of simple and compound\\nbodies. and H generators or cylinders. Eudiometer tube. Hoffman\\napparatus for decomposing water, and a suitable battery.\\n14. The Province of Physics. We have defined matter\\nas that which occupies space, and prevents anything else\\nfrom occupying the same space. It is made manifest to us\\nthrough the senses.\\nXow, physics does not deal with matter as such. That\\nis the province of chemistry. But physics does deal with\\nmatter as the carrier or vehicle of motion, and for this pur-\\npose must inquire very carefully into the constitution of\\nmatter.\\n15. Simple and Compound Bodies. We know matter as\\nsolid, liquid, and gas. We can make many substances\\nsuch as water, for example pass through all these three\\nstates. But here our power ends. We can not add or sub-\\ntract anything. The water remains a stubborn fact in\\nwhatever state it exists.\\nWe do observe, however, a marked difference in the be-\\nhavior of substances. Some of them can not by any means\\nnow at our command be separated into different substances\\nor constituents. We can get but one thing out of such a\\nsubstance, and that is itself. Matter which is thus incapa-\\nble of analysis into anything else is called a chemical ele-\\nment. There are about seventy elements so far discovered.\\nA list of them will be found at the end of the chapter.\\n7", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0025.jp2"}, "26": {"fulltext": "8 PHYSICS\\nBut there are other forms of matter which may be sepa-\\nrated into two or more elementary constituents, and are\\ntherefore called compounds. Their number is infinite, but\\nthey all consist of combinations of the seventy elements.\\nThese compounds form nearly all the substances met with\\nin every-day life, such as water, foods, wood, cloth, stone,\\nbrick, etc.\\n16. Atoms and Molecules. We have no direct proof that\\nmatter is built up of distinct particles or units. As far\\nas we can see, it is perfectly continuous, and occupies\\nall of the space that it seems to occupy. But certain\\nconsiderations such as its contraction and expansion, the\\ncapacity of certain liquids to dissolve solids and gases,\\nthe ability of nearly all fluids and of some solids to\\ntransmit light, and many other phenomena which imply\\na large mobility in matter have led to the thought\\nthat matter is made up of definite particles or units, and\\nfor these the names atoms and molecules have been pro-\\nposed.\\nThe atom is the smallest quantity of an element that\\ncan exist. It is indivisible and indestructible. Atoms of\\ndifferent elements have different weights. These are the\\nso-called atomic weights of chemistry.\\nThe molecule contains one or more atoms, and is the\\nsmallest quantity of matter that can have a separate exist-\\nence. When the atoms are all alike, the molecule is ele-\\nmentary, and the substance which it forms is an element.\\nWhen the atoms are unlike, the molecule is compound, and\\nthe substance is known as a compound body.\\n17. Size of Molecules. It is not possible to see a mole-\\ncule, even with the aid of the most powerful microscope.\\nVarious estimates of the size of molecules have been made\\nby different physicists. The illustration given by Lord\\nKelvin is the most familiar. He suggests that if a drop of\\nwater were magnified to the size of the earth, its molecules\\nwould appear as large as tennis balls.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0026.jp2"}, "27": {"fulltext": "THE CONSTITUTION OF MATTER\\n9\\nAccording to Maxwell, the very smallest particle that\\nwe can see contains from sixty million to one hundred\\nmillion molecules.\\n18. Mechanical Mixtures and Chemical Compounds.\\nWhen we mix together two elements or compounds in such\\na way that their molecules remain unchanged, we call the\\nresult a mechani-\\ncal mixture. This\\nis the condition of\\nthe atmosphere.\\nIt consists for the\\nmost part of the\\ntwo gases, oxygen\\nand nitrogen, and\\nthe molecules of\\neach gas remain\\ndistinct and sepa-\\nrate. We speak\\nof them as being\\nfree. When, how-\\never, the sub-\\nstances are so\\nunited that the\\noriginal molecules\\nare broken up and\\nnew ones take\\ntheir place, we call\\nthe result a chem-\\nical compound.\\nThus, for exam-\\nple, when two vol-\\numes of the gas hydrogen are brought into contact with\\none volume of the gas oxygen in the cold, no matter how\\nthoroughly they are shaken up, they remain a simple, me-\\nchanical mixture. But if now an electric spark be passed,\\nor a flame applied, we have an explosion the separate\\nlllllljlllllllll^\\nFig. 1. Eudiometer tube and induction coil.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0027.jp2"}, "28": {"fulltext": "10\\nPHYSICS\\nmolecules of hydrogen and oxygen are broken up, and in\\ntheir place we find molecules of water vapor. We may rep-\\nresent this graphically as follows\\nH 2 H 2 +0 2 H 2 H 2 0.\\nAfter the explosion our three molecules are built into\\ntwo. Consequently, the water vapor occupies only two\\nthirds the volume of the origi-\\nnal gases, and is correspond-\\ningly denser. This may be\\nillustrated by introducing two\\nvolumes of H and one volume\\nof into an eudiometer tube\\nover mercury, and exploding\\nthe mixture by means of a spark\\nfrom an induction coil.\\n19. Physical and Chemical\\nChanges. In terms of the mo-\\nlecular theory we call all\\nchanges in matter physical,\\nwhich leave the molecules the\\nsame and all changes chemi-\\ncal, in which the original mol-\\necules are broken up and new\\nones take their place.\\nThus the passage of water\\nthrough its three states is a\\npurely physical change, while\\nthe decomposition of water into\\nhydrogen and oxygen is a chem-\\nical change. The first is illus-\\ntrated by the melting of ice\\nand evaporation of the result-\\ning water. The second can readily be shown by filling a\\nHoffman apparatus with acidulated water and passing an\\nelectric current through it for some time. Notice that the\\nvolume of the H is twice that of the 0.\\nmm\\nFig. 2. Hoffman apparatu\\ndecomposing water.\\nfor", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0028.jp2"}, "29": {"fulltext": "THE CONSTITUTION OF MATTER H\\n20. Protyle. The atom which we have described above\\nis the chemical atom, and by definition is indestructible.\\nIt is more reasonable to believe, however, that as we have\\nonly one power in the universe manifested in the different\\nforms of energy, known as heat, light, sound, electric cur-\\nrent, etc., so we have only one form of primary matter, and\\nthat the so-called elements are in reality compounds of this\\none primal unit. The name protyle has been suggested for\\nit. According to this view, the chemical atoms are made up\\nof still smaller physical atoms, and are consequently com-\\nposed of the same primal stuff. They differ from one an-\\nother only in their internal architecture, and hence in their\\ncapacities for motion. The difference in the behavior of\\nthe chemical atoms is therefore assumed to depend entirely\\nupon the number and arrangement of the protyle atoms\\nwhich go to make them up.\\nThis view of matter is entirely theoretical. No one has\\never isolated the molecule and atom, much less the physical\\natom of protyle. Nor have we any authentic record of the\\nchange of one chemical element into another. The old\\nalchemists believed in the transmutation of the metals, and\\nspent years in the vain attempt to change base metals into\\ngold. Modern science hardly expects to accomplish this\\ntransformation, even though holding the view that iron and\\ngold are made up of the same primal stuff. It does believe,\\nhowever, that in the mightier laboratory of Nature such a\\nprecipitation of the primal matter into our so-called ele-\\nments may have taken place, is perhaps taking place now\\nin distant suns and stars, and that under suitable condi-\\ntions these so-called elements may resolve again into the\\nprimal element.\\n21. Doubt. We have spoken of molecules and atoms in\\nsome of the preceding paragraphs much as if they really\\nexisted. But modern science believes nothing of the sort.\\nAt best, our molecules and atoms are only shadows of con-\\nditions in matter which we do not yet understand. The", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0029.jp2"}, "30": {"fulltext": "12\\nPHYSICS\\nterms are convenient, and we must often use them, but\\nthey must be understood to be names for our ignorance\\nrather than for our knowledge.\\nProfessor Huxley says The primitive atomic theory,\\nwhich has served as the scaffolding for the edifice of modern\\nphysics and chemistry, has been quietly dismissed. I can\\nnot discover that any contemporary physicist or chemist be-\\nlieves in the real indivisibility of atoms, or in an interatomic\\nmatterless vacuum.\\nAnd Professor Tait says An exact or adequate concep-\\ntion of matter itself, could we obtain it, would almost cer-\\ntainly be something extremely unlike any conception of it\\nwhich our senses and our reason will ever enable us to\\nform. The discovery of the ultimate nature of matter\\nis probably beyond the range of human intelligence.\\n22. The Firm Ground in Physics. The fact that matter\\nand motion must ever remain a profound mystery does not\\nmake the science of physics any less exact. It deals, not\\nwith the ultimate nature of matter and motion, but with\\ntheir every-day manifestations, and these are capable of\\nexact study and measurement.\\n23. Table of Elements.\\nState at\\n2\\nName.\\no\\na\\nusual tem-\\nperature\\nand\\npressure.\\nSource.\\nAtomic,\\nweight.\\nSpecific\\ngravity.\\neg o\\nQ\\nAluminium\\nAl\\nSolid.\\nClay, etc.\\n27.0\\n2.58\\n1828\\nAntimony\\nSb\\na\\nSulphid ores.\\n120.0\\n6.7\\n1450\\n(Stibium).\\nArsenic\\nAs\\n(t cc\\n75.0\\n5.71\\n1694\\nBarium\\nBa\\nHeavy-spar, etc.\\n137.0\\n3.75\\n1808\\nBismuth\\nBi\\nSulphid ores.\\n208.9\\n9.8\\n1450\\nBoron\\nB\\nBr\\nLiquid.\\nBorax.\\nSeaweed, etc.\\n11.0\\n79.95\\n2.6\\n3.19\\n1808\\nBromine\\n1826\\nCadmium\\nCd\\nSolid.\\nZinc ores.\\n112.0\\n8.65\\n1817\\nCcesium\\nCs\\nAlkali salts.\\n132.9\\n1.88\\n1860\\nCalcium\\nCa\\nLimestones, etc.\\n40.0\\n1.7\\n1808\\nCarbon\\nC\\nDiamond, graph-\\nite, coal, etc.\\n12.0\\nUp to\\n3.5\\nAnti-\\nquity", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0030.jp2"}, "31": {"fulltext": "THE CONSTITUTION OF MATTER\\n13\\nTable of Elements (continued).\\nState at\\n.23\\nName.\\nO\\na\\nI\\nusual tem-\\nperature\\nand\\npressure.\\nSource.\\nAtomic\\nweight.\\nSpecific\\ngravity.\\n2b\\nSt\\nP\\nCerium\\nCe\\nSolid.\\nRare earths.\\n140.2\\n6.7\\n1803\\nChlorine\\nCI\\nGas.\\nCommon salt, etc.\\n35.45\\n2.45\\n1774\\nChromium\\nCr\\nSolid.\\nChrome iron ore.\\n52.1\\n7.3\\n1797\\nCobalt\\nCo\\nSulphid ores.\\n59.0\\n8.96\\n1733\\nColumbium\\nCb\\nRare minerals.\\n94.0\\n7.+\\n1801\\nCopper\\nCu\\nNatiYe and sul-\\nphids.\\n63.6\\n8.9\\nAnti-\\nquity\\nErbium\\nEr\\nRare earths.\\n166.3\\n1843\\nFluorine\\nF\\nGas.\\nFluor-spar, etc.\\n19.0\\n1771\\nGadolinium\\nGd\\nSolid.\\nRare earths.\\n156.1\\n1886\\nGallium\\nGa\\nK\\nZinc ores.\\n69.0\\n5!95\\n1875\\nGermanium\\nGe\\nu\\nRare minerals.\\n72.3\\n5.47\\n1886\\nGlueinum\\nGl\\n(1\\nBeryl, etc.\\n9.0\\n1.85\\n1828\\n(Beryllium).\\nGold\\nAu\\nNative.\\n197.3\\n19.3\\nAnti-\\n(Aurum).\\nquity\\nHydrogen\\nH\\nGas.\\nWater, etc.\\n1.0\\n.069\\n1766\\nIndium\\nIn\\nSolid.\\nRare minerals.\\n113.7\\n7.4\\n1863\\nIodine\\nI\\nIr\\nIC\\nSea water, etc.\\nNative.\\n125.85\\n193.1\\n4.95\\n22.4\\n1811\\nIridium\\n1803\\nIron\\nFe\\nOxide ores.\\n56.0\\n8.0\\nAnti-\\n(Ferrum).\\nquity\\nLanthanum\\nLa\\nRare minerals.\\n138.2\\n6.1\\n1839\\nLead\\nPb\\nSulphids, etc.\\n206.95\\n11.36\\nAnti-\\n(Plumbum).\\nquity\\nLithium\\nLi\\nAlkali springs\\nand Li mica.\\n7.02\\n.585\\n1817\\nMagnesium\\nMg\\nLimestones, etc.\\n24.3\\n1.75\\n1829\\nManganese\\nMn\\nOxide ores.\\n55.0\\n7.2\\n1774\\nMercury\\nHg\\nLiquid.\\nNative and sul-\\n200.0\\n13.596\\nAnti-\\n(Hydrargyrum)\\nphid.\\nquity\\nMolybdenum..\\nMo\\nSolid.\\nSulphid.\\n96.0\\n8.6\\n1782\\nNickel\\nNi\\nM\\nSulphids, etc.\\n58.0\\n8.9\\n1751\\nNitrogen\\nN\\nGas.\\nAir and saltpetre\\n14.03\\n.96\\n1772\\nNeodymium\\nNd\\nSolid.\\nRare earths.\\n140.5\\n6.5\\n1885\\nOsmium\\nOs\\nNative.\\n190.8\\n22.48\\n1803\\nOxygen\\nGas.\\nAir, water, and\\nmost minerals.\\n16.0\\n1.1056\\n1774\\nPalladium\\nPd\\nSolid.\\nNative.\\n106.6\\n12.1\\n1804\\nPhosphorus\\nP\\nPhosphate earths\\n31.0\\n1.84\\n1669\\nPlatinum\\nPt\\nk\\nNative.\\n195.0\\n21.5\\n1741\\nPotassium\\nK\\nc{\\nChlorid, etc.\\n39.11\\n.86\\n1807\\n(Kalium).\\nPraseodymium.\\nPr\\nM\\nRare earths.\\n143.5\\n6.5\\n1885\\nRhodium\\nRh\\nM\\nNative.\\n103.0\\n12.1\\n1804", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0031.jp2"}, "32": {"fulltext": "14\\nPHYSICS\\nTable of\\nElements (continued).\\nState at\\nName.\\no\\nS\\nRb\\nusual tem-\\nperature\\nand\\npressure.\\nSource.\\nAtomic\\nweight.\\nSpecific\\ngravity.\\n1\u00c2\u00b0\\nRubidium\\nSolid.\\nAlkali minerals.\\n85.5\\n1.52\\n1860\\nRuthenium\\nRu\\nRare earths.\\n101.6\\n12.26\\n1845\\nSamarium\\nSm\\n150.0\\n1879\\nScandium\\nSc\\na\\na\\n44.0\\n1879\\nSelenium\\nSe\\na\\nWith sulphids.\\n79.0\\n4.5\\n1817\\nSilicon\\nSi\\nQuartz, etc.\\n28.4\\n2.48\\n1823\\nSilver\\nAs\\nNative and ores.\\n107.9\\n10.5\\nAnti-\\n(Argentum).\\nquity\\nSodium\\nNa\\nCommon salt, etc.\\n23.05\\n.97\\n1807\\n(Natrium).\\nStrontium\\nSr\\nCarbonate, etc.\\n87.6\\n2.5\\n1808\\nSulphur\\nS\\nNative, and as\\nmetallic sul-\\nphids.\\n32.06\\n2.07\\nAnti-\\nquity\\nTantalum\\nTa\\nCompound ores.\\n182.6\\n10.+\\n1802\\nTellurium\\nTe\\nWith sulphids.\\n125.0\\n6.23\\n1782\\nTerbium\\nTb\\nt\\nRare earths.\\n160.0\\n1843\\nThallium\\nTl\\n204.18\\n11.19\\n1862\\nThorium\\nTh\\n232.6\\n11.23\\n1828\\nThulium\\nTu\\nK M\\n170.7\\n1879\\nTin\\nSu\\na\\nTinstone.\\n119.0\\n7.25\\nAnti-\\n(Stannum).\\nquity\\nTitanium..\\nTi\\na\\nRare minerals.\\n48.0\\n1789\\nTungsten\\nW\\nu\\nLead and other\\n184.0\\n19.26\\n1781\\n(Wolframium).\\nores.\\nUranium\\nu\\nu\\nOxide ores.\\n239.6\\n18.69\\n1789\\nVanadium\\nV\\na\\nOres of lead, etc.\\n51.4\\n5.87\\n1830\\nYtterbium\\nYb\\nRare oxides.\\n173.0\\n1878\\nYttrium\\nYt\\nU U\\n89.1\\n1828\\nZinc\\nZn\\nZr\\nZinc blende, etc.\\nRare oxides.\\n65.3\\n90.6\\n7.12\\n4.15\\n1520\\nZirconium\\n1824\\nNote.\u00e2\u0080\u0094 The common elements are printed in small capitals, the rare elements\\nin italics, and the remainder in ordinary type. The table follows F. W. Clarke,\\nchemist of the United States Geological Survey.\\nProblems. 1. Select half a dozen common substances, and find\\nout whether they are simple or compound.\\n2. Is brass a mechanical mixture or a chemical compound\\n3. Write out the chemical reaction that will express the decom-\\nposition of water, starting out with two molecules and representing\\nthem by 2H 2 0.\\n4. When a steel bar is magnetized, is the change physical or\\nchemical", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0032.jp2"}, "33": {"fulltext": "CHAPTER III\\nPROPERTIES OF MATTER\\nApparatus A set of minerals, representing the scale of hardness. Crystal\\nmodels and, if possible, common crystallized minerals. Balance and\\nsuspended plate of glass (29). Jars of O and H. Solution of copper sul-\\nphate. Diffusion apparatus (34). Dialyzer. Capillary tubes. Mercury.\\n24. Secondary Properties of Matter. In addition to its\\nessential properties, extension and impenetrability, matter\\nexhibits certain characteristic secondary properties. These\\nare so named because they do not, like the essential prop-\\nerties, apply to all matter, but only to certain forms of\\nmatter. Thus, solids possess hardness, crystalline form,\\ncohesion, adhesion, porosity, flexibility, elasticity, brittleness,\\nmalleability, ductility, and tenacity, while fluids exhibit\\ndiffusibility, viscosity, and capillarity and all bodies solid\\nor fluid separated in space, tend to move toward one an-\\nother, a relation which we express by the word weight.\\nAVe may not say, however, that weight is an essential\\nproperty of matter, since it is rather a relation than an in-\\ndwelling property. A single body, alone in space, would\\nhave no weight.\\nNor may we properly say that inertia is an essential\\nproperty of matter, meaning by inertia the tendency of a\\nbody to remain in motion or at rest unless influenced by\\nsome other body, for this is simply to say that nothing\\nhappens without a cause a statement that goes without\\nsaying.\\nMany of these secondary properties of matter are suf-\\nficiently explained if we simply know the meanings of the\\n15", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0033.jp2"}, "34": {"fulltext": "16 PHYSICS\\nwords themselves. Physics studies only those properties\\nwhich are capable of measurement, or which take some\\nknowable part in the drama of natural events.\\n25. Hardness. By the hardness of a body we mean the\\ndifficulty of penetrating between its particles. We measure\\nhardness by comparing bodies with a series of solids ar-\\nranged by agreement in an ascending scale. That most\\ncommonly in use was proposed by Mohs, and is as follows\\n1. Talc (soapstone). Easily scratched by the finger nail.\\n2. Gypsum. Scratched by the nail.\\n3. Calcite. Easily cut by knife.\\n4. Fluorite. Cut by knife.\\n5. Apatite. Difficultly cut by knife.\\n6. Feldspar. Cut by glass.\\n7. Quartz. Cuts glass.\\n8. Beryl.\\n9. Corundum.\\n10. Diamond.\\nThis scale was meant for the use of mineralogists, and\\nselects natural minerals rather than artificial products,\\npartly because they are better suited to the purposes of\\nmineralogy, and partly because their hardness is more con-\\nstant.\\nThe test of hardness is very important in determining\\nminerals. Thus calcite (crystallized marble, CaC0 3 and\\nquartz (rock crystal, Si0 2 have the same crystal form, and\\noften look much alike. A simple test with the penknife\\nserves to distinguish them.\\n26. Crystalline Form. Many solid bodies exhibit definite\\ngeometric forms or crystals. The study of crystals crys-\\ntallography is a very useful and a very beautiful branch\\nof natural science. It is not known why substances take\\ndefinite crystal forms. In doing so they usually increase\\nin volume, as when water crystallizes into ice, and the pres-\\nsure exerted by their particles is very great pipes of lead,\\nand even of wrought iron, burst with the freezing of the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0034.jp2"}, "35": {"fulltext": "PROPERTIES OF MATTER\\n17\\nwater that they contain the hardest rocks are split and\\ntorn into the tiny fragments which constitute soil, when\\nthe water in their crevices freezes and the delicate lines\\nin our printing types are filled out by the expansion of the\\ncrystallizing type metal.\\nSubstances which have a cystalline structure often show\\na decided tendency to split along planes parallel to well-\\ndefined crystal faces. We call this cleavage. It is well\\nseen in such minerals as mica, calcite, and feldspar.\\nSubstances such as flint and opal, which show no crys-\\ntalline structure, are called amorphous.\\n27. Cohesion is the name given to the bond which holds\\nthe molecules of a body together. It is strongest in solids\\nand least in gases. The varying strength of cohesion gives\\nus the different degrees of rigidity, tenacity, and hardness\\nin bodies. When we break a substance we conceive that\\nthe molecules become so far separated that their cohesion\\nis overcome. Once\\nseparated, cohesion\\ncan only be restored\\nby bringing the mole-\\ncules very close to-\\ngether again by some\\nagent, such as heat.\\nThis is done when\\ntwo pieces of wrought\\niron are welded to-\\ngether. The same\\nthing takes place in\\nthe working of glass.\\nThe strength of\\nmaterials depends up-\\non their cohesion. It\\nis measured by the number of pounds, or kilogrammes, re-\\nquired to break a bar of given cross-section, usually a square\\ninch or a square centimetre. When the weight is applied\\n3\\nFig\\n3. Showing adhesion between glass and\\nwater to be greater than cohesion in water.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0035.jp2"}, "36": {"fulltext": "18 PHYSICS\\nas a pull, we measure the tensile strength of the material.\\nWhen applied as pressure, we measure the compression\\nstrength.\\n28. Adhesion is the general name given to the bond ex-\\nisting between unlike molecules that is, between the mole-\\ncules of different substances. When a glass rod is dipped\\ninto water, a thin film of the liquid spreads itself over the\\nglass, and the attraction between the two is considerable.\\nWe can measure adhesion if we balance a pane of glass so\\nthat its under surface just touches the surface of the water,\\nand then add weights until the glass is pulled away. In the\\nsame manner light articles, such as pieces of tissue paper,\\nfeathers, and the like, will stick to the hand and to one\\nanother.\\n29. Elasticity. When a body has its form altered by\\neither a pull or by pressure, the result is called a strain, and\\nthe pull or pressure itself is spoken of as the stress. If,\\nwhen the stress is removed the strain also disappears, the\\nbody is said to be elastic. Such is the case with rubber,\\nwhalebone, and many other substances. If the strain always\\ndisappears when the stress is removed, no matter how great\\nthe stress may be, the body is said to be perfectly elastic.\\nFluids are the only bodies which fulfill this condition. No\\nsolids are perfectly elastic. The degree of their elasticity is\\nmeasured by the coefficient of elasticity. This is the weight\\nwhich would be required to stretch a bar of unit cross-sec-\\ntion (such as one square centimetre) to twice its original\\nlength, were that possible, and still have the bar regain its\\noriginal length when the stress is removed.\\n30. Malleability. -When the molecules of a body are so\\narranged, or so related to one another, that we may pound\\nthe body into thin sheets without breaking it, we describe\\nthe body as malleable. Gold is probably the most malleable\\nof all substances. It has been beaten into leaves so thin that\\none hundred and twenty thousand were required to make a\\npile one centimetre high.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0036.jp2"}, "37": {"fulltext": "PROPERTIES OF MATTER 19\\n31. Ductility expresses the arrangement of molecules of\\na body which permits it to be drawn into small rods and\\nwire. Platinum possesses this property in a marked de-\\ngree.\\nThe finest wires are obtained by coating a platinum wire\\nwith silver, then drawing it out as fine as possible, and dis-\\nsolving off the silver by means of nitric acid.\\nBoth malleability and ductility depend upon the possi-\\nbility of rearranging the molecules of a body within such\\nnarrow limits that the bond between them that is, their co-\\nhesion will not be broken. This possibility depends upon\\nseveral factors, such as temperature and purity of material.\\nEven small quantities of arsenic or antimony will seriously\\ninterfere with the working of copper and sulphur and phos-\\nphorus have a similar effect upon iron.*\\n32. Viscosity and Brittleness. Xo substances, even among\\nsolids, are perfectly rigid. In all matter the molecules have\\nmore or less ability to change their relative positions, and\\nconsequently the body containing them to change its form.\\nOn the other hand, no substances, even among gases, are\\nperfectly fluid. In all there is more or less retardation of\\nmotion due to an apparent friction among the molecules\\nthemselves.\\nThis property of matter is called viscosity. In solids it\\nmakes permanence of form impossible. A straight glass rod,\\nresting for some time upon two supports, gradually assumes\\na curved form under the stress of its own weight. An iron\\ngirder, between two piers, takes a permanent sag. A cane,\\nstanding in the corner, becomes crooked.\\nIn fluids viscosity comes in as a constant retardation to\\nmotion. Streams do not at once seek their lowest levels,\\nbut take an appreciable time. Waves do not continue in-\\ndefinitely, but finally spend themselves, overcome by the fric-\\ntion of the fluid itself, their motion turned into heat. Fine\\nSee Chemistry.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0037.jp2"}, "38": {"fulltext": "20 PHYSICS\\nparticles remain suspended in water and air for a long time,\\ntheir weight being insufficient to overcome viscosity. Storms\\nfinally spend themselves.\\nWhen a stress acts upon a solid, either as pull or pres-\\nsure, in such a way as to make this rearrangement of mole-\\ncules impossible, the particles separate, and we call the body\\nbrittle.\\n33. Diffusibility. We conceive that the molecules of all\\nmatter are in a constant state of motion. In consequence\\nof this activity, two gases or two liquids capable of mixing,\\nwhen placed in communication with each other,\\nwill become evenly distributed throughout the\\ntotal volume. This diffusion can be shown by\\nseveral simple experiments\\na. Oxygen is. sixteen times as heavy as hydro-\\ngen. When brought together they form\\na highly explosive mixture. If an in-\\n^yfe\u00c2\u00a7\u00c2\u00a3 verted jar of hydrogen be placed above\\nF a^ a jar of oxygen, the glass cover plates\\n7\u00e2\u0080\u009e withdrawn, and the two iars allowed\\nFig. 4.\u00e2\u0080\u0094 Diffusion of _\\noxygen and hydrogen, to stand in communication lor several\\nhours, it will be found that, in spite of\\ntheir differences in weight, the two gases have thoroughly\\ndiffused and each jar contains an explosive mixture. On\\nseparating the jars and applying a match, two almost equally\\nloud reports are heard.\\nb. If clear water be carefully added to the top of a tum-\\nbler already partly filled with colored water, such as a solu-\\ntion of copper sulphate, and the whole allowed to stand for\\nsome time, it will be found that the color distributes itself\\nalmost equally throughout the tumbler.\\nThis diffusion of fluids takes place even when the two\\nare separated by a porous partition. In general, the lighter\\nfluid passes through more quickly than the heavier, as may\\nbe shown by the following experiment\\nc. An inverted porous cup, such as is used in the Daniell", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0038.jp2"}, "39": {"fulltext": "PROPERTIES OF MATTER\\n21\\ncell, has its lower end sealed by a\\ntight rubber stopper, through which\\na long glass tube passes. The free end\\nof the tube dips under the surface of\\na colored liquid in a tumbler below.\\nIf, now, a bell jar filled with hydrogen\\nbe quickly brought over the porous\\ncup, the air inside the cup will be\\nforced down the glass tube and will\\nbubble through the colored liquid.\\nThe hydrogen makes its way through\\nthe porous cup faster than the heavier\\nair can make its way out. When the\\nbell jar is removed, the reverse takes\\nplace. The hydrogen inside the cup\\nescapes faster than the air can take\\nits place, a partial vacuum is pro-\\nduced, and the colored liquid rises in\\nthe tube.\\nd. In the same way liquids diffuse\\ninto each other through unglazed earthenware, parchment\\npaper, and other porous partitions. The action is known as\\nosmose. Dissolved solids have the same power, provided\\nthey are crystallizable. Amor-\\nphous substances, or colloids,\\ndo not diffuse. Chemists some-\\ntimes make use of this dif-\\nference of behavior to sepa-\\nrate some crystallizable poison,\\nsuch as arsenious acid, from\\nthe amorphous contents of the\\nstomach of an animal supposed\\nto have been poisoned. The\\nprocess is known as dialysis,\\nand is easily carried out in the\\nFig. 6.\u00e2\u0080\u0094 Diaiyzer. apparatus (dialyzer) shown.\\nFig\\n5. Diffusion of hy-\\ndrogen through porous\\ncup.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0039.jp2"}, "40": {"fulltext": "22\\nPHYSICS\\nFig. 7.\\n-Capillary elevation and\\ndepression.\\n34. Capillarity. If tubes of very small diameter are partly\\nimmersed in water or other liquid which wets them, it will\\nbe noticed that on withdrawing them in part the leyel of\\nthe liquid in the tubes is con-\\nsiderably above that outside,\\nand is higher as the diameter\\nof the tubes is smaller. In\\ncase of mercury or other liquid\\nwhich does not wet the glass,\\nthere is a depression of level\\nin the tubes in place of ele-\\nvation.\\nThe same appearances may\\nbe seen when solids and liquids\\ncome into contact. The water in a tumbler rises around\\nthe edge, and the surface of the liquid is concave. Mer-\\ncury, on the contrary, would be depressed around the edge\\nof the tumbler, and would present a convex surface. Drops\\nof mercury on a table take the form of globules. Water\\nbehaves in the same way if the table be greasy or dusty.\\nSince these elevations and depressions are most notice-\\nable in hairlike or capillary tubes, the name capillarity has\\nbeen applied to the phenomena. They appear to be strict-\\nly molecular phenomena, and\\nto depend upon the relative\\nstrength of cohesion and adhe-\\nsion. Where the cohesion with-\\nin the liquid is stronger than\\nthe adhesion between the solid\\nand liquid, the resulting strain\\nshows itself as capillary depres-\\nsion but where the adhesion\\nbetween solid and liquid is the stronger, the strain is a\\ncapillary ascension.\\nWe find many illustrations of capillary action in Nature\\nsuch as the rising of oil in the wick of lamps the curi-\\nFig. 8. Capillary curves.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0040.jp2"}, "41": {"fulltext": "PROPERTIES OF MATTER 23\\nous efflorescence of salt over the edge of the tumbler when\\nsalt water evaporates and the wetting of the whole towel\\nwhen one corner is left in a basin of water.\\nExperiments. 1. Try the hardness of such stone and building\\nmaterial as may be convenient marble, brownstone, brick, etc.\\n2. Determine the hardness of pyrite, garnet, graphite, and any\\nother common minerals that may be within reach.\\n3. Let the teacher or pupil, or both, repeat the experiments a, b,\\nc, and d (33), and also those under capillarity (34).", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0041.jp2"}, "42": {"fulltext": "CHAPTER IV\\nON MEASUREMENT\\nApparatus Yardstick, pound weight, quart measure. Metric units,\\nmetre, gramme, and litre. Metric chart. A good scale, weighing up to\\nseveral pounds. English and metric weights.\\n35. Science is exact knowledge. This is only gained\\nby comparison or measurement. We have only so much\\nscience as we have mathematics. The first step, therefore,\\nin the study of practical physics is to learn how to measure.\\nMeasurement involves two processes\\n1. The establishment of a standard or unit of measure-\\nment with which we can compare our unknown quantity.\\n2. The method by which we carry out this comparison.\\n36.* Units. The choice of standard units must naturally\\ndepend upon what we wish to measure, and our units must\\nnecessarily be as numerous as the qualities measured one\\nunit for length, as the yard; another for volume, as the\\ngallon another for weight, as the pound and so on.\\nThe objection to these common English units, however,\\nis that they bear no easily expressed relation to one another,\\nand consequently it is quite inconvenient to translate one\\nunit into another as cubic yards into gallons.\\nThe best system of measurement is that in which the\\ndifferent units are simply related, and are easily deducible\\nthe one from the other. The metric system is such a scheme\\nof measurement, and is therefore always used in scientific\\nwork. In it the unit of mass depends upon the unit of vol-\\nume, and this in turn upon the unit of length. When we\\nestablish the unit of length, therefore, we establish the others.\\n24", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0042.jp2"}, "43": {"fulltext": "ON MEASUREMENT 25\\nMetric Tables.\\nLength.\\n1 millimetre\\n.0393 inches.\\n1 centimetre\\n.3937 10 millimetres.\\n1 decimetre\\n3.9370 10 centimetres.\\n1 metre\\n39.37 10 decimetres.\\n1 kilometre\\n.62137 miles 1,000 metres.\\n1 inch\\n2.54 centimetres.\\nlfoot\\n30.48\\n1 yard\\n91.44\\n1 mile\\n1,609.33 metres.\\nVolume.\\n1 cubic decimetre 1,000 cubic centimetres 1 litre 1.0567 quarts.\\n1 quart .9462 litres 946.25 cubic centimetres.\\nMass.\\n1 gram 15.4323 grains.\\n1 kilogram 1,000 grams 2.2046 pounds (avoirdupois).\\n1 ounce (avoirdupois) 28.349 grams.\\n1 pound =453.5926\\n1 ton =907.185 kilograms.\\nIn physics we measure both matter and motion. Our\\nseries of standards, therefore, must be comprehensive\\nenough to apply to all measurable aspects of matter and\\nmotion. By taking a series of related units it is not diffi-\\ncult to establish even so far-reaching a system as this, for\\nwe find practically that only three fundamental units are\\nnecessary. These are the unit of length, the unit of mass,\\nand the unit of time. They form the basis of all physical\\nmeasurement.\\n37. Length. It is unnecessary to define length. We all\\nunderstand by it the distance between two points, or their\\nseparation in space. The unit of length is the centimetre,\\nthe one hundredth part of the metre. It was originally\\nintended that the metre should be the one forty millionth", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0043.jp2"}, "44": {"fulltext": "26\\nPHYSICS\\npart of the earth s meridian. Practically, it is the length\\nof a standard platinum bar, copies of which are kept in\\nthe national archives at Washington, London, Paris, and\\nBerlin.\\nMost of us are accustomed to thinking of length in\\ninches. It may therefore help us to gain a clear idea of the\\ncentimetre if we remember that it is about four tenths of\\nan inch. As soon as possible, however, it will be well to\\nthink of the centimetre as a unit in itself, and not to trans-\\nlate it into inches.\\n10 Centimeters\\nll lll l ll\\nHlllllil\\nMl\\nllllllll\\nI 6\\nInn\\nl lll l l l l\\nHill\\nT\\n1 1 1 m 1 1 I i 1\\nhi .liiil\\n1.1,1,1,1\\nh li i i 1\\n4 Inches\\nFig. 9. Comparison of centimetres and inches.\\n38. Mass. The mass of a body is the amount of matter\\nit contains. The unit of mass is the gramme. This was in-\\ntended to be the mass of one cubic centimetre of pure dis-\\ntilled water at the temperature of greatest density. Prac-\\ntically, it is the one thousandth part of the standard\\nplatinum kilogramme, copies of which are also kept in the\\nnational archives of the several civilized nations. The\\nkilogramme is about equivalent to two and one fifth pounds\\navoirdupois. The gramme equals .0352 ounces, and one\\nounce equals 28.35 grammes.\\n39. Time. This can not well be defined, but we all know\\nsomething of the meaning of the word. It is our name for\\nthe sequence of events. The unit of time is the second. It\\nis the -g^Joo P ar t \u00c2\u00b0f an average day (mean solar day).\\n40. The C.-G.-S. System. The system of measurement\\nfounded on these three fundamental units is known as the\\ncentimetre-gramme-second system, or, more briefly, as the\\nC.-G.-S. system. The units depending on these fundamen-\\ntals are called derived units, and are capable of expressing\\nall measurable aspects of matter and motion.", "height": "3383", "width": "2123", "jp2-path": "elementsofphysic00hend_0044.jp2"}, "45": {"fulltext": "ON MEASUREMENT 27\\n41. The Two Terms in Measurement. It is to be observed\\nthat every expression of physical magnitude requires two\\nterms One, the numerical term, or coefficient, and the other\\nthe verbal term, or name of the standard unit, as, for ex-\\nample, 10 centimetres, 8 grammes, 60 seconds. The verbal\\nterms are either the fundamental or derived units we have\\nbeen considering, and are agreed upon before beginning the\\nmeasurement. This done, the real process of measurement\\nconsists in finding the coefficient, or the number of times\\nthe standard unit is contained in the unknown quantity to\\nbe measured.\\n42. Methods of Measurement. The comparison between\\nthe standard unit and the quantity to be measured may be\\nmade directly or indirectly.\\nIt is made directly when we apply our foot rule at once\\nto the piece of timber to be measured, or when we pour\\nwater or other liquid into a gallon measure.\\nIn general, however, our measurements are made indi-\\nrectly, as when we find the area of a farm by measuring the\\nlength of its boundaries, or the temperature of a room by\\nobserving the length of a column of mercury in a ther-\\nmometer.\\nIndeed, it seldom happens that quantities can be meas-\\nured directly. In most cases we are forced to resort to in-\\ndirect methods. It is in devising these that physicists show\\ntheir skill and ingenuity.\\nThe measurements most open to the direct method are\\nthose of length, but even here greater accuracy is often ob-\\ntained by indirect methods, as when we find the diameter\\nof a glass tube from the weight of the mercury which is re-\\nquired to fill a given length of the tube, or when we calcu-\\nlate the diameter of a wire from its length and weight.\\n43. Mathematical Physics. We must then consider mod-\\nern physics simply as an interesting branch of applied\\nmathematics. It is a science of measurement, and can be\\nstudied to best advantage in the laboratory. Practical", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0045.jp2"}, "46": {"fulltext": "28 PHYSICS\\nlaboratory work means simply measurement. In the follow-\\ning pages much of our time must be given to the double\\nwork of establishing a suitable system of derived units, and\\nof applying these to the measurement of physical magni-\\ntudes. The student who goes to work in earnest should\\nfirst see that he thoroughly understands the unit, and\\nshould then, as far as possible, make all the measurements\\nfor himself by which the coefficient that is to stand before\\nthe unit is determined. Where the facilities of the school\\ndo not permit the student to make these measurements\\nfor himself, he should at least see them made, and thor-\\noughly participate in working out the subsequent deter-\\nminations.\\n44. Conservation of Matter. It is possible to measure\\nmatter and to reason about it only because of its persist-\\nence. The sum total of matter always remains the same.\\nWe can not create it we can not destroy it. Our experi-\\nence leads to the belief that its mass is absolutely constant.\\nNor can we even think of matter as coming out of nothing-\\nness, or passing into nothingness again. This all-important\\ntruth is known as the conservation of matter, and was only\\ngenerally accepted at the close of the eighteenth century.\\nWe can not prove it by direct experiment, for every method\\nwould have to start out by assuming what we wanted to\\nprove, but reason and general experience are ample proof.\\n45. Conservation of Energy. In like manner it is only\\npossible to measure and study motion because of its persist-\\nence. This is a less obvious truth than the conservation of\\nmatter, for we see on all sides the apparent destruction and\\ncreation of motion. But a more careful examination shows\\nthat the disappearance of motion is always followed by its\\nreappearance in some other form or in some other body,\\nwhile its seeming creation is in reality a similar transforma-\\ntion or transference. We therefore believe that the total\\namount of motion is constant a truth which we define as\\nthe conservation of energy. It is only within the past half", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0046.jp2"}, "47": {"fulltext": "ON MEASUREMENT 29\\ncentury that this truth has been clearly established. It\\nhas made possible the science of modern physics.\\n46. Rationality. We can not overestimate the impor-\\ntance of the recognition of these sister truths, the conser-\\nvation of matter and the conservation of energy. If we\\nlived in a world in which the amount of matter and motion\\nwas constantly changing, we should be unable to reason\\nabout them, or indeed about anything. We should be\\npractically insane, for we should be unable to establish any\\nrelation between the events of life. All would be wild\\nchance and caprice. This is much the position to-day of\\nthose persons who do not realize these fundamental truths.\\nThey live in a world of unreason and chaos. Judged in this\\nway, but a small percentage of the inhabitants of the earth\\nare rational. Civilization is only possible because human\\nexperience is uniform.\\nExperiments. 1. Measure the four dimensions of a sheet of\\npaper in millimetres, and express its area in square centimetres.\\n2. Measure the length of a rod ten times, take the average re-\\nsult, and express the greatest mean error.\\n3. Measure a regular-shaped block of wood in millimetres, and\\nexpress its cubical contents in metres.\\n4. Measure the linear dimensions of the room you are in, and ex-\\npress its volume in litres.\\n5. Put a kilogramme weight on the scale, and find its equivalent\\nin English measure.\\n6. Put a pound weight on the scale, and find its equivalent in\\ngrammes.\\n7. Weigh a quart of water in grammes, and calculate the length\\nof tube, one centimetre in diameter, that this amount of water\\nwould fill.\\nReference.\\nEssay on Measurement William K. Clifford.\\nChapter on Measurement. Practical Physics Glazebrook\\nShaw.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0047.jp2"}, "48": {"fulltext": "OHAPTEE V\\nMEASUREMENT OF MATTER\\nApparatus Spring compass. Calipers. Micrometer screw. Cathetom-\\neter. Measuring engine. Vernier. Surveyor s tape or chain. Transit.\\nGraduated glass jar.\\n47. The Problem. The exact measurement of matter is\\nnecessary in physics in order that matter may be accurately\\nstudied as a carrier of motion. The amount of motion we\\nhave in matter depends upon the amount of matter we\\nhave moving, as well as upon the rate at which it moves.\\nFor this purpose the measurements of matter with which\\nphysics has most to deal are those of extension length,\\narea, and volume of mass and weight, of density and\\nspecific gravity.\\n48. Extension in One Direction. The measurement of\\nlength is of the utmost importance in physical work, not\\nonly for itself, but also because so many other measure-\\nments depend directly upon it. The process involves no\\ntheory. It depends entirely upon the precision of the in-\\nstruments of measurement, and the care with which they\\nare employed. The simplest of these instruments is the\\ndivided scale. For scientific work, its unit is the centi-\\nmetre and its subdivisions. In determining length, we\\nmust first make up our minds as to the degree of accuracy\\nneeded. In comparatively rough work, we apply the scale\\ndirectly, and read off the result with the naked eye, as\\nwhen we measure the length of a line on a drawing, or the\\nlength of a piece of wood or iron,\\n30", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0048.jp2"}, "49": {"fulltext": "MEASUREMENT OF MATTER\\n31\\nBut this direct method involves two sources of error.\\nWe can not be sure that the initial division on the scale\\nexactly coincides with the beginning of the line to be meas-\\nured, nor can we accurately judge of the fractional subdivi-\\nsions of the scale. To avoid one or o ther or both of these\\nsources of error is the purpose of our instruments of preci-\\nsion. It is well to make one s self acquainted with several\\nof the more important of these instruments. b\\nThe spring compass, used in every drawing-room, is\\nsimply a means of transferring a measurement, with great\\naccuracy, from line to scale, or scale to line. Yet even so\\nsimple an instrument is only used accurately after some\\npractice.\\nThe calipers and screw gauge are much alike. Their\\narms, or screw ends encompass the object to be measured,\\nand when placed in close con-\\ntact with it their distance\\nFig. 10.\u00e2\u0080\u0094 Calipers.\\nFig. 11. Micrometer screw.\\napart is reajl off from the little scale attached to the mov-\\nable arm.\\nThe micrometer screiv is used for determining the thick-\\nness of thin sheets of metal, paper, glass, and the like. It\\nconsists of a rigid frame of metal, supported by three fixed\\nlegs. A fourth leg, in the shape of a finely threaded screw,\\nturns in a screw bearing in the center of the frame, and is\\nprovided with a large circular head, accurately divided, so", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0049.jp2"}, "50": {"fulltext": "32\\nPHYSICS\\nthat one may easily read the fraction of a turn made by the\\nscrew. If the head makes one complete turn, the leg moves\\nthrough a distance equal to the\\nscrew thread, and for any smaller\\nturn the motion is proportional.\\nThe micrometer screw may also\\nbe used as a spherometer, an instru-\\nment for finding the curvature of\\nspherical surfaces.\\nThe cathetometer measures accu-\\nrately small vertical distances. It\\nconsists of a rigid upright scale,\\nprovided with a sliding telescope\\ncarrying a second smaller scale. A\\nreading is taken when the cross-\\nhairs of the telescope exactly coin-\\ncide with one end of the distance to\\nbe measured, and a second reading\\nwhen they coincide with the other\\nend. The difference between these\\nreadings equals the distance.\\nThe vernier is a device for help-\\ning the eye to read tiny subdivisions\\nof a given scale. It is used on\\nmany instruments of precision. The\\nprinciple is very simple. A definite\\nlength, say an inch or a centimetre,\\nis divided into ten equal parts. A second length is taken,\\nequal to eleven of these equal parts, and is itself divided\\ninto ten parts. If the two scales be laid alongside of each\\nother, it is very evident that the subdivisions on the longer\\n1 3 3 4\\nFig. 12.\u00e2\u0080\u0094 Cathetometer.\\nIE\\nu_\\ni n i i I\\ni i i i i i i i i i i i i i i\\ni i ii i i i i\\n12 3 4 5 6\\nFig. 13.\u00e2\u0080\u0094 Vernier, set at zero.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0050.jp2"}, "51": {"fulltext": "MEASUREMENT OF MATTER 33\\nscale will overlap those on the shorter scale by just one\\ntenth, as shown in the diagram (Fig. 13). Suppose, now,\\nthat the initial marks on the two scales do not coincide, but\\nthat the shorter one is four tenths of a division ahead of\\nthe longer one, as shown in Fig. 14. We shall know the\\n12 3 4\\n123456789\\nM 1 1 1 1 1 M I 1 1 II 1 1 1 1 MINIMI 1|\\n1 1 1 1 1 1 1 1 1\\n1234 5 6789\\nFig. 14. Vernier, reading four tenths.\\nexact amount by observing that the subdivisions marked\\n4 on both scales now coincide, and this can only occur when\\nthe shorter scale is four tenths ahead.\\n49. Surveying. The instruments already considered\\nserve only to measure very short lengths, such as those met\\nin the laboratory. In measuring greater lengths, as in sur-\\nveying field, or farm, or State, enlarged methods have to\\nbe adopted. In ordinary farm or railroad work it is suffi-\\nciently accurate to measure distance by means of steel or\\nlinen tapes, or iron chains. These are generally one hun-\\ndred feet long. They are divided into feet, and these again\\ninto tenths.\\nIn the case of very, large and accurate surveys, such as\\nthose made by the United States Coast Survey, generally\\nonly one length is measured, and the other distances are\\ncalculated from this. This one line is known as the base\\nline, and is measured as accurately as possible. It is some-\\ntimes several miles long. The ground is cleared and lev-\\neled as carefully as if a road were being constructed. The\\nlength is found by means of rigid measuring rods placed\\nend to end, and the contact observed by means of telescopes.\\n50. Extension in Two Directions. We seldom or never\\nmeasure area directly that is, by applying the unit of area,\\nthe square centimetre, to the surface to be measured. In\\nnearly all cases we measure the linear dimensions and cal-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0051.jp2"}, "52": {"fulltext": "34\\nPHYSICS\\nculate the area from these by means of the simpler propo-\\nsitions in plane geometry. Thus, for example, to get the\\narea of a rectangle, we measure the base and altitude.\\nTheir product equals the area. To find the area of a tri-\\nangle we make the same measurements, knowing that half\\nthe product will be the area. And similarly with other\\nsurfaces.\\n51. Extension in Three Directions. If the volume to\\nbe measured is regular in outline, we measure the linear\\ndimensions and calculate the volume from\\nthese by means of the propositions of solid\\ngeometry. But if the solid be irregular in\\nshape, as is generally the case, we can best\\nfind its volume by immersing it in water or\\nother fluid and determirT-\\n1 1 ing the volume of the fluid\\n3 displaced.\\nExamiple. The volume\\nof an irregularly shaped\\nstone can readily be found\\nby suspending it in a grad-\\nuated jar of water. The\\nrise of water in the jar will\\nindicate the cubical con-\\ntents of the stone. Or,\\nthe jar may be completely\\nfilled with water, the stone\\ncarefully lowered into it,\\nand the overflow of water\\ncaught in a measuring\\nglass, as shown in figure.\\nThe volume of fluids is obtained by measuring the\\ndimensions of the containing vessel, and then calculating\\nits contents. In case the vessel is irregular in form, we can\\nfind its volume by filling it with some liquid, such as mer-\\ncury, weighing the mercury, and then calculating the\\nwmmm\\nn w\\nFig. 15. Measuring the volume of a\\nstone.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0052.jp2"}, "53": {"fulltext": "MEASUREMENT OF MATTER 35\\nvolume by means of the known relation between the weight\\nand volume of the mercury (see Chapter VII).\\nAs every cubic centimetre of mercury weighs 13.56\\ngrammes, we have only to divide the weight of the mercury\\nin grammes by 13.56 to get the volume of the vessel in\\ncubic centimetres.\\nExperiments. 1. Make two dots some distance apart on a sheet\\nof paper. Measure the distance five times by direct application of\\nthe divided scale; take the mean, and see if this corresponds to one\\nmeasurement made by the spring compass.\\n2. Determine the thickness of a glass cover plate by means of the\\nmicrometer screw.\\n3. Determine the thickness of a visiting card by the same instru-\\nment.\\n4. Measure the diameter of a nickel five-cent piece by the cali-\\npers.\\n5. Construct a vernier in stiff paper, making the vernier ji of a\\nsubdivision on a fixed scale. Do the same, making the vernier\\nT 9 o of a subdivision.\\n6. Determine the area of a lot or small field.\\n7. Find the volume of an irregular-shaped stone or mineral by\\nimmersing it in water, and measuring the water displaced.\\n8. Find the volume of a small test tube by weighing the mercury\\nrequired to fill it.\\nNote. Can you from this weight, and the known length of the\\ntest tube, calculate its diameter\\nReference.\\nGillespie s Surveying, or any other standard work.\\nThe Coast Survey in Harper s Monthly for March, 1879, vol.\\nlviii, p. 506.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0053.jp2"}, "54": {"fulltext": "CHAPTEE VI\\nMASS AND WEIGHT\\nApparatus Cubes of the same size, but made out of different material,\\nsuch as cork, wood, clay, metal. A scientific balance, with weights\\nfrom .001 to 50. grammes.\\n52. Mass. We have defined mass as the quantity of\\nmatter in a body. The unit by which it is measured is the\\ngramme.\\nIf we have two spheres of different size but made of the\\nsame material, the larger one will of course contain the\\ngreater mass. In case, however, the material is different,\\nthe smaller sphere may have the greater mass. We say,\\nthen, that mass is independent of volume, and we can not\\njudge of the mass of a body by simply looking at it, or even\\nby measuring its dimensions.\\nSuppose, for example, we have half a dozen cubes, made\\nof cork, wood, marble, iron, silver, and gold, respectively,\\nand each one centimetre in dimension. Their volumes, be-\\ning equal, would be represented by the proportion\\n1:1:1:1:1:1,\\nwhile their masses would be found on experiment to be rep-\\nresented very closely by the proportion\\n1 3 11 30 42 76.\\nThat is to say, a cube of gold has seventy-six times the\\namount of matter contained in a cube of cork of the same\\nsize. But while we can not perceive these differences in\\nmass by the eye, we do perceive them very readily on han-\\ndling the cubes. The greater the mass, the more effort it", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0054.jp2"}, "55": {"fulltext": "MASS AND WEIGHT 37\\ntakes to move or lift them. This is our common method of\\njudging of the mass of bodies that is, by what we call their\\nweight.\\nIn general, the weight of a body is directly proportional\\nto its mass, but we must be very careful in physics not to\\nconfound the two terms. The mass of a body is a constant\\nquantity no matter where the body may be placed while\\nthe weight is a variable quantity depending upon circum-\\nstances. Mass and Weight are therefore two entirely dis-\\ntinct expressions, and must never be used the one for the\\nother. The reason for this will appear still clearer on con-\\nsidering what we mean by weight.\\n53. Gravitation. As far as human experience extends,\\nit is found that all bodies in the universe tend to move\\ntoward one another. We call this tendency gravitation.\\nIts intensity depends upon two factors the quantity of\\nmatter, and the intervening space, or distance. The\\ngravitation between two bodies is greater the larger their\\nmass and the smaller their distance apart. This was first\\nstated by Newton, somewhat as follows\\nEvery particle of matter in the universe tends to move\\ntoward every other particle in a straight line joining the\\ntwo, and with an intensity depending directly upon the\\nproduct of their masses and inversely upon the square of\\ntheir distance apart.\\nW^e have no explanation of gravitation. We do not\\nknow why bodies .tend to move toward one another, and we\\nnever expect to know. The above statement simply ex-\\npresses the observed fact. The name gravitation gives us a\\nconvenient term by which to refer to the action, but it does\\nnot explain it.\\n54. The Formula of Gravitation.\u00e2\u0080\u0094 It is often convenient\\nto sum up our observations in a mathematical expression or\\nformula. This is simply an exact and short-hand way of\\nrepresenting observed facts. Nearly all young students\\nstrongly object to formulas, under the mistaken belief that", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0055.jp2"}, "56": {"fulltext": "38 PHYSICS\\nthey are difficult and obscure. On the contrary, they are\\neasy and clear. No great progress can be made in so exact\\na science as physics without their use, and it would be\\nwell for every student at the very outset to make up his\\nmind to understand and use them. This particularly ap-\\nplies to gravitation, where we sum up the whole matter\\nvery briefly as follows\\nm m\\nG\\nd*\\nin which G stands for gravitation, m and m! for the masses\\nof two bodies, and d for their distance apart. It should\\nperhaps be added that the distance is measured from the\\ncenter of mass, which is commonly spoken of as the center\\nof gravity. In case the body is homogeneous that is, of\\nthe same constitution throughout the center of mass cor-\\nresponds to the center of figure.\\n55. Weight. In harmony with this universal principle\\nof gravitation, all bodies at the surface of the earth tend to\\nmove toward its center of mass with an intensity depending\\nupon their mass and inversely upon the square of their\\ndistance from the center.\\n56. Weight as the Measure of Gravitation. We can now\\nunderstand why weight is a variable quantity, and we can\\nunderstand it still better if we repeat our formula of gravi-\\ntation\\np mm\\nd 2\\nIn this fraction, m\\\\ the mass of the earth, and m, the\\nmass of the body weighed, are constant, while d, the dis-\\ntance from the center of the earth, is constant for any\\none place, but differs for different places. Therefore the\\nweight, depending as it does upon G, depends inversely upon\\nd, and will also differ in different places.\\nAs we pass from the equator to the poles we come thir-\\nteen miles nearer to the center of the earth, and therefore\\nthe weight of bodies increases.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0056.jp2"}, "57": {"fulltext": "MASS AND WEIGHT 39\\nAs we ascend high mountains we pass one, two, three,\\nfour, sometimes over five miles farther from the earth, and\\ntherefore the weight decreases.\\nWe may even imagine conditions such that weight would\\ndisappear entirely. There is a point between the earth and\\nthe moon where the gravitation toward one body is just\\nequal and opposite to that toward the other. A particle at\\nthat point would practically have no weight.\\nBut meanwhile the mass has undergone no change.\\nAt the equator, at the pole, on the high mountain, out in\\nspace, the quantity of matter was the same.\\nWe may therefore say that mass is independent of Aveight\\nas well as of volume.\\n57. Measurement of Mass. We can not measure mass\\ndirectly, since we can not directly compare our standard\\ngramme with the unknown mass to be measured.\\nWe must therefore measure mass indirectly that is, by\\nsome general effect of mass common to all forms of matter.\\nWeight is the most convenient measure of mass, and the\\none commonly employed, since weight, as we have just\\nseen, is directly dependent upon mass, and is constant for\\nany given place on the earth s surface. The practical oper-\\nation of finding the mass of a body consists therefore in the\\nprocess of weighing.\\n58. Weighing. The operation of weighing is carried\\nout by means of very delicate balances and very carefully\\nstandardized weights. It is best learned by practice. It is\\nalways necessary to test such sensitive instruments before\\nusing them, as they are very liable to get out of adjust-\\nment. The weights also must be examined from time to\\ntime and compared with standard weights.\\nTwo methods are in use direct weighing and counter-\\npoise weighing.\\nIn the first, the object to be weighed is put in one scale\\npan and the weights in the other. Where the balance is\\naccurate, it is the more convenient and better method.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0057.jp2"}, "58": {"fulltext": "40\\nPHYSICS\\nIn the second method the object to be weighed is put in\\none scale pan, and fine shot or sand added to the other,\\nuntil the pointer is at zero. The object is then removed,\\nand weights put on the scale pan in its place until the\\nbalance is again even. This method neutralizes any inac-\\ncuracy in the balance itself.\\nThe balance commonly used in physical work will weigh\\nfrom several hundred grammes down to the tenth of a milli-\\ngramme. The weights of one gramme and over are made\\nFig. 16. Balance for accurate weighing.\\nof brass. Those less than a gramme and down to ten milli-\\ngrammes are made of platinum, while the milligramme\\nweights are made of aluminium, in order that they may\\nhave greater volume and consequently be easier to handle.\\nThe fractions of a milligramme are measured by a small\\nplatinum rider which is placed on the arm of the balance.\\nThe farther it is moved from the point of support the\\nlarger value it has.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0060.jp2"}, "59": {"fulltext": "MASS AND WEIGHT 41\\nWhen the right weight has been found, and the pointer\\nstands at zero, the results should be entered in a notebook\\nbefore the weights themselves are disturbed. This saves\\nmany mistakes. It is well to take the reading by noting\\nwhat weights are absent from the box, and then verify the\\nresult when the weights are put back in place.\\nExperiments. 1. Weigh any convenient object first directly\\nand then by counterpoising, and compare the results.\\n2. Weigh the same object with an added fifty-gramme weight\\non each scale pan, and see if the balance is equally sensitive.\\n3. Find the least mass that may be accurately weighed on your\\nbalance, and see if it is the same when the scale pans are each loaded\\nwith one-hundred-gramme weights.\\nProblems. 1. If an object could be carried to the center of\\nthe earth, what would be its weight\\n2. In going toward the center of the earth, weight at first in-\\ncreases and afterward diminishes. Why\\n3. Would a man weigh, more or less, on the moon than on the\\nearth\\nReference.\\nChapters on the Balance and on Weighing, in Practical Physics\\nGlazebrook and Shaw.\\nOther Worlds than Ours, by Richard A. Proctor.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0061.jp2"}, "60": {"fulltext": "CHAPTER VII\\nDENSITY AND SPECIFIC GRAVITY\\nApparatus Hydrostatic balance and weights. Distilled water. Eight-\\nounce beakers. Plunger. Specific-gravity bottle of fifty cubic centi-\\nmetres capacity. Hydrometers. Alcoholometer. Lactometer.\\n59. Density. We speak of bodies as being light or\\nheavy, and by this we mean light or heavy in proportion to\\ntheir size. A small cube of gold contains comparatively a\\nlarge amount of matter, and we speak of gold as being very\\nheavy. A similar cube of cork contains little matter, and\\nwe speak of cork as being very light. This relation be-\\ntween mass and volume is known in physics as density.\\nSince mass is measured by weight, we may define density\\npractically as the weight of a unit of volume of the sub-\\nstance. The unit of volume being the cubic centimetre,\\nand the unit of mass the gramme, we express the density of\\na substance when we state the number of grammes con-\\ntained in one cubic centimetre of the substance.\\nThe following table gives the density of a number of\\ncommon substances\\nTable of Densities.\\nCork 0.240\\nWood 0.434 to 1.330\\nIce 0.917 0.918\\nWax 0.960\\nHuman body 0.987\\nCoal 1 300 to 1 .500\\nSand 1.420\\nClay 1.900\\n42", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0062.jp2"}, "61": {"fulltext": "DENSITY AND SPECIFIC GRAVITY 43\\nTable of Densities {continued).\\nftetort carbon 1 90\\nGraphite 2.17 to 2.33\\nCrown glass 2 52\\nMarble .2.65\\nQuartz 2 65\\nFlint glass 3.00 to 6.00\\nDiamond 3.49 3.53\\nCast iron 7.00 7.70\\nWrought iron 7.80 7.85\\nBronze (Cu and Sn) 8.70 8.90\\nGerman silver (Cu, Zn, and Ni) 8.30 8.40\\nBrass (Cu and Zn) 8.20 8. 70\\nWater 0.99987\\nEther 0. 74000\\nAlcohol 0.80620\\nTurpentine 0. 97000\\nOlive oil 91000\\nSea water 1 02600\\nMilk 1.03200\\nAir 0.001293\\nCarbonic-acid gas 0.001939\\nNote. For specific gravity of single metals and other elements, see\\nTable of Elements, pp. 12-14.\\nIt is to be observed that density varies under different\\nconditions. We may increase density by packing the mole-\\ncules of a body closer together, as when we roll or hammer\\nmetals or compress gases. We may diminish density by\\nallowing the molecules to separate, as when we expand\\nbodies by heat. Hence it is that in stating the density of\\ngases we must mention the temperature and also the .pres-\\nsure to which they are subjected and of solids, the tem-\\nperature and the mode of preparation.\\n60. Specific Gravity is an expression somewhat similar to\\ndensity and yet not quite identical with it. Specific gravity\\nbears much the same relation to density that weight does", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0063.jp2"}, "62": {"fulltext": "44\\nPHYSICS\\nto mass. It is our practical measure of the relation be-\\ntween weight and volume.\\nSpecific gravity may be defined as the ratio between the\\nweight of a given volume of the substance and the weight\\nof the same volume of 9$ second substance taken as a\\nstandard.\\nThis is the same as saying that it is the ratio between\\nthe density of the substance and the density of the standard\\nsubstance.\\nThe specific gravity of solids and liquids is referred to\\nwater as a standard. Since the density of water is about\\n1, the same numbers express both the density and specific\\ngravity approximately of solids and liquids.\\nThe specific gravity of gases is referred to air as a\\nstandard, but since the density of air is only .001293, the\\nnumbers expressing the density and specific gravity of\\ngases are far from being the same.\\nWe shall have nothing to say in this work about meth-\\nods of finding the specific gravity of gases. It will be in-\\nteresting to note, however, what is the specific gravity of a\\nfew of the more familiar ones, as follows\\nAir 1.000\\nHydrogen 0.069\\nOxygen 1.106\\nNitrogen 0.971\\nAmmonia 0.537\\nChlorine 3.440\\nCarbon monoxide 0.967\\nCarbon dioxide 1.529\\nHydrogen sulphide 1.191\\nHydrochloric acid 1.254\\nSulphur dioxide 2.247\\nMarsh gas 0.559\\nThe determination of the specific gravity of solids and\\nliquids is an operation of much importance. It is com-\\nmonly carried out by one of the following methods\\n1. The hydrostatic balance.\\n2. The specific-gravity bottle.\\n3. The hydrometer.\\nThe second method only will be considered here, the\\nfirst and third being deferred until after buoyancy has\\nbeen treated.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0064.jp2"}, "63": {"fulltext": "DENSITY AND SPECIFIC GRAVITY\\n45\\n61. Specific-Gravity Bottle. This is a small glass flask of\\nknown capacity, usually 50 cubic centimetres, or 50 grammes\\nof water. The stopper is accurately ground, so as to fit cor-\\nrectly into the neck of the flask, and has a fine capillary bore,\\nas shown in the figure, through which the excess of liquid\\nmay escape when the stopper is pressed into its seat. A\\nbrass counterpoise is provided which will just balance the\\nflask and stopper. The whole purpose of the bottle is to\\nprovide a means by which we can always measure off pre-\\ncisely the same volume of a liquid. It must be used in con-\\nnection with an accurate\\nbalance. The method\\napplies to both solids and\\nliquids.\\na. Solids. In this\\ncase the solid must be in\\nsmall pieces, or in pow-\\nder, so that it can read-\\nily be put into the bot-\\ntle. A given weight is\\ntaken, generally about\\nfive grammes. The bot-\\ntle is then carefully filled\\nwith distilled water and\\nthe stopper put in place,\\nthe excess of water es-\\ncaping through the capil-\\nlary tube. The whole bot-\\ntle is now thoroughly dried with tissue paper and weighed.\\nThe specific gravity of the solid can easily be calculated.\\nSuppose that just five grammes have been taken, and that\\nthe bottle has a capacity of just 50 grammes of distilled\\nwater at the ordinary temperature of the room. When the\\nsolid is in the bottle, however, the capacity is no longer 50\\ngrammes of water, but is 50 grammes less the weight of the\\nwater displaced by the solid. Eepresenting this by m, we\\nFig. 17. \u00e2\u0080\u0094Specific-gravity bottle.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0065.jp2"}, "64": {"fulltext": "46 PHYSICS\\nshall have 50 5 m weight found w,\\nor m 50 -f- 5 w 55 w,\\nweight in air\\nand specific gravity\\nweight of equal volume of water\\n5 5\\nm 55 w\\nIt is not necessary that the flask should hold just 50\\ngrammes, or that we should take just 5 grammes of the\\nsolid. Indeed, in many cases it is much more convenient\\nthat we should not do so. If, for instance, we are deter-\\nmining the specific gravity of fine wire, and have cut it up\\ninto short lengths, it will be rather difficult to weigh out\\nan even 5 grammes.\\nExample. Silver wire.\\nWeight of silver taken 4.984 grammes.\\nWeight of water in flask 50.168\\nWeight of silver and water above\\nit in flask 54.679 (to)\\nWeight of water displaced by silver\\n50.168 4.984 54.679 .473 grammes (m).\\n4.984\\nSpecific gravity of silver -jno 10.52.\\nb. Liquids. The specific-gravity bottle is especially\\nadapted for the determination of the specific gravity of\\nliquids. The whole process consists in filling the bottle\\ncarefully with the liquid to be determined, drying it as\\nbefore with tissue paper, and weighing it. This weight\\n(omitting, of course, the counterpoise) divided by the\\nweight when filled with water, gives the specific gravity.\\nExample. Milk.\\nWeight of water in flask 50.00 grammes.\\nWeight of milk in flask 51.60\\n51.6\\nSpecific gravity of milk 1.032.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0066.jp2"}, "65": {"fulltext": "CHAPTEE VIII\\nMEASUREMENT OF MOTION\\n62. Motion, we have seen, is a change of position. To\\nstudy and measure motion we must inquire what elements\\nin it are variable. Now, motion is only manifested in bodies.\\nWe will not, therefore, study motion in the abstract, but\\nwe will study moving bodies. To do this completely we\\nshall have to consider\\n1. The space passed over.\\n2. The mass of the moving body.\\n3. The time.\\n4. The nature of the motion, whether uniform or\\nvariable.\\n5. The path of the moving body.\\nThe space is simply the length of the path covered by\\nthe moving body. Where the path is straight that is,\\nwhere the motion is in a straight line the space passed\\nover is simply the length of a straight line joining the\\noriginal position of the body and its final position. Where\\nthe path is a broken or curved line, the space passed over is\\nthe length of this line. In all cases we shall measure the\\nspace in centimetres, and designate it by s.\\nThe mass of the moving body is usually expressed in\\ngrammes and represented by m.\\nThe time is the number of seconds the body is in mo-\\ntion, and is represented by t.\\nThese three quantities, s, m, and t, are all directly\\nmeasurable by tape-line, balance, and clock. They are the\\n47", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0067.jp2"}, "66": {"fulltext": "48 PHYSICS\\nthree fundamental units of measurement in the C.-G.-S. sys-\\ntem (41). There are relations between s and t, and be-\\ntween these two and m, that are highly important. They\\nare denned as velocity and as momentum.\\n63. Velocity. If a body move over a space of 50 metres,\\nthe final result is the same whether the motion takes place\\nin a minute or in an hour. But we have not fully de-\\nscribed the motion unless we have told the time it occu-\\npies. This rate of motion, or speed, is called velocity and\\nis represented by v. We may define velocity as the space\\npassed over by a moving body in one second of time. If\\nthe body be moving uniformly, or if we understand v to\\nrepresent average velocity, we shall have\\ns\\nV T\\n64. Momentum. It evidently makes a great difference\\nwhether the moving body is heavy or light, as we should\\nfind out very quickly if it struck us. A heavy body has\\nmore motion in it than a light body, even though both move\\nat the same velocity. We define the amount of motion as\\nmomentum, and represent it by M. It is the product of\\nthe mass by the velocity\\nM mv.\\nA large body moving with little velocity may still have\\na much greater momentum than a small body moving with\\nhigh velocity, but the effect of the two upon us will be very\\ndifferent. The large, slowly moving body will do us no harm\\nif we, too, are free to move, because by a very slight effort\\nwe can give ourselves the same velocity as the body. But\\nin the case of the small, rapidly moving body, say a bullet,\\nthe injury may readily be fatal. Before the bullet can be\\nrobbed of its momentum, it may penetrate to some vital\\nspot. The velocity is so great that we can not hope to\\nacquire it ourselves, and so repulse the ballet by going\\nalong with it.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0068.jp2"}, "67": {"fulltext": "MEASUREMENT OF MOTION 49\\n65. Nature of the Motion. Further, motion varies with\\nrespect to time that is, is uniform or variable. Motion is\\nuniform when the moving body passes over the same space\\neach second. Motion is variable when the spaces passed\\nover in successive seconds are different.\\nAcceleration. This change of motion may itself be uni-\\nform or variable. It is uniform when the increase or de-\\ncrease in the space passed over in successive seconds that\\nis, the increase or decrease of velocity is the same. In this\\ncase, the uniform velocity added or taken away is called the\\nacceleration. It is usually represented by a. If a body\\nstart from a state of rest, and add a velocity of a centi-\\nmetres each second, it is manifest that its velocity at the\\nend of t seconds will be equal to t X or\\nV=at.\\nWe may also define acceleration as the rate of change of\\nvelocity that is, velocity changes by a centimetres each\\nsecond.\\n66. Path of a Moving Body. A moving body may trace\\nany path whatever. The simplest path is, of course,\\na straight line. A boat moving without vibration over\\nthe surface of still water may trace an almost perfectly\\nstraight line. But the actual path of bodies is usually\\nvery much more complex than this. The path of the\\nmoon is an example. The moon moves around the earth\\nin a constantly shifting path. She also moves with the\\nearth around the sun. Further, she is probably, along\\nwith the sun and the rest of the solar system, mak-\\ning a grand tour through space around some other cen-\\nter. The actual path of the moon must be considered\\nas compounded of these three and many other separate\\nmotions.\\nWe shall consider only the paths described by bodies\\nmoving in simple straight or curved lines in one plane, and\\nthe paths described by rotating bodies.\\n5", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0069.jp2"}, "68": {"fulltext": "50\\nPHYSICS\\nCurvilinear Path. A body moving in a straight line\\nwould go on moving in a straight line forever, unless some\\nsecond motion were compounded with the first, and so\\nchanged the path. We conceive that every curvilinear path\\nis the result of compounding two or more motions. The\\nmost familiar example is that of a projectile of any kind\\nthrown into space. Suppose it to be a ball and to be thrown\\nPROJECTILE FORCE\\nSUN\\nFig. 18.\u00e2\u0080\u0094 Motion of earth (E) around the sun.\\nhorizontally. As we all know, it will approach nearer and\\nnearer to the earth, and will finally strike. We explain this\\ncurvilinear path by saying that the ball has two motions\\none in a horizontal direction, given by the throw and an-\\nother in a vertical direction, due to the weight of the ball\\nthat is, to gravitation. We may represent this graph-\\nically by the diagram shown in Fig. 19, and this is a very\\nconvenient way of studying such curvilinear paths. In the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0070.jp2"}, "69": {"fulltext": "MEASUREMENT OF MOTION 51\\ncase of all projectiles the path is a parabola, the curve pro-\\nduced when we pass a plane through a cone parallel to one\\nof the elements of the cone that is, to one of the lines\\njoining the apex of the cone ,._-\\nwith some point on the base, N\\nand lying in the surface of the Nk\\ncone. \\\\j\\\\\\nIn the same way the earth\\nmay be conceived as having\\ntwo separate motions one, its\\noriginal projectile motion, if\\nwe may use such an expression\\nand the other its motion of con-\\nStantly falling toward the SUn. Fig. 19.\u00e2\u0080\u0094 Motion of ball on end\\nBy the compounding of these\\ntwo motions, we get a curve, which repeats itself each year,\\nand is known as the path or orbit of the earth. This is an\\nellipse, the curve produced when a cone is cut by an oblique\\nplane meeting all the elements.\\nSimilarly a ball or other heavy object attached to the end\\nof a string may be twirled around so as to describe a circu-\\nlar path. Here the motion of the ball is constantly com-\\npounded with the pull exerted by the string. The ball,\\nbeing kept at constant distance (the length of the string)\\nfrom a fixed point (your hand), is forced to describe a circle,\\nsince a circle is the locus of all points in a plane at a fixed\\ndistance from a given point.\\nThese three paths circle, ellipse, and parabola are all\\ncomparatively simple, but they represent only a few out of\\nmany possible paths. The study of more complex paths re-\\nquires a somewhat full mathematical knowledge, and will\\nbe found in larger works on mechanics.\\nRotating Bodies. We have so far assumed that the\\nbodies we have been studying were moving freely in space.\\nA special case of great practical importance is presented\\nwhen one point of the body is fixed, and the only possible", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0071.jp2"}, "70": {"fulltext": "52 PHYSICS\\nmotion is one of rotation, as, for example, a carriage wheel\\nor the fly-wheel of a steam engine. Here a series of points\\nis fixed, what we call the axis of the wheel, and rotation\\ntakes place about this straight line. We can not speak of\\nthe velocity of such a rotating body, since all particles at\\ndifferent distances from the axis move with different veloci-\\nties. The usual method of measuring such motion is to\\nstate the number of rotations per minute. A good average\\ndynamo may make 1,200 rotations per minute.\\n67. Units of Motion. We can evidently measure these\\nseveral aspects of motion in the C.-G.-S. system.\\nUnit velocity is a velocity of 1 centimetre per second.\\nUnit momentum is a mass of 1 gramme moving with unit\\nvelocity that is, 1 gramme moving 1 centimetre per second.\\nUnit acceleration is unit velocity added or subtracted\\neach second that is, 1 centimetre per second, each second.\\nUnit force (F= ma) is a change of unit momentum per\\nsecond, or a change per second of 1 gramme moving 1 centi-\\nmetre per second. This unit is known as the dyne, and is\\nof great importance among physical units. It is commonly\\ndefined as that force which, acting for one second on 1\\ngramme of matter, imparts to it an acceleration of 1 centi-\\nmetre per second.\\nProblems. 1. What is the velocity in centimetres per second of\\na boy riding a bicycle at the rate of twelve miles an hour If the\\nroad be level and straight, what is his path\\n2. What is the average velocity of an ocean steamer which re-\\nquires six days to run from New York to Liverpool Express in\\ncentimetres per second.\\n3. Assuming the boy to weigh 120 pounds, and the steamer\\n10,000 tons, compare the momentum of the two bodies.\\n4. What is the acceleration of a body which starts from a state\\nof rest, and after moving for five seconds has a velocity of 160 feet\\nper second If, at the end of the five seconds, the same accelera-\\ntion, but negative, acted on the body, when would it come to rest\\n5. A stone attached to the end of a string is twirled around the\\nhand. If the string break, what path will the stone describe", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0072.jp2"}, "71": {"fulltext": "MEASUREMENT OF MOTION 53\\n6. The fly-wheel of a large pumping engine is making 120 rota-\\ntions per minute. If the wheel be twelve feet in diameter, what\\nwill be the velocity, in centimetres per second, of any point on the\\ncircumference\\n7. If the body in problem 4 weighed ten grammes, what force in\\ndynes was acting upon it\\n8. Why does a man running down a beach into the water invaria-\\nbly pitch head foremost\\n9. What path does the rash man describe who jumps from a\\nmoving street car\\nReference.\\nElements of Mechanics, by Oliver J. Lodge.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0073.jp2"}, "72": {"fulltext": "CHAPTER IX\\nFALLING BODIES\\n68. Gravitation (53-56). All bodies near the surface of\\nthe earth will, if unsupported, fall toward the surface of\\nthe earth, or if supported will exert a pressure on the sup-\\nport equal to their weight. The term gravitation includes\\nboth the direct motion of falling bodies and the pressure\\nor weight exerted by bodies at re^t. We have already, in\\nChapter VI, considered gravitation as weight it remains\\nfor us to consider it as motion.\\nEven Sir Isaac Newton, who investigated gravitation\\nwith a scientific thoroughness that has left little for subse-\\nquent inquirers to find out, declined to assign any cause\\nfor gravitation, and seems to have believed that it is beyond\\nhuman ken to discover the cause. He was very explicit,\\nhowever, in stating that action at a distance between two\\nbodies is unthinkable that is, he believed that two bodies\\nin space can not attract each other across a perfect vacuum,\\nand that no one with a philosophical mind would ever think\\nsuch a thing. Our inability to conceive attraction between\\ntwo totally unconnected bodies that is, our inability to\\nexplain action at a distance has made it necessary to fill\\nall space with some medium which might serve as a common\\ncarrier for gravitation and all forms of radiant energy;\\nthat is, all forms of energy which, like radiant heat and\\nlight, travel through space in straight lines. This medium,\\nthe Ether, is supposed to fill all free space and also the\\nintermolecular regions of all gases, liquids, and solids.\\n54", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0074.jp2"}, "73": {"fulltext": "FALLING BODIES 55\\nThere is not a single physical fact which bears direct testi-\\nmony to the existence of the ether, but nevertheless it is\\ncoming to figure more and more prominently in all physical\\ndiscussions, because it enables us to deal with undoubted\\nphysical facts which we should otherwise be unable to\\nhandle. The present tendency is to regard gravitation as\\na strain in the ether by which bodies are pushed together,\\nrather than as a mutual pull exerted by the bodies them-\\nselves.\\nThe cause of gravitation has naturally aroused the\\ncuriosity of all thinking minds, but most men, like Newton,\\nhave put it aside as unknowable. Still, if you go to any\\ngreat scientific library, you will find a few slender volumes\\nwhich venture to discuss the problem.\\n69. The Value of g. Every one knows that the farther a\\nbody falls the faster it goes. We do not hestitate to jump\\nfrom the top of a fence, but no one is so foolish as to jump\\nfrom a third-story window. Gravitation as motion that\\nis, the actual velocity is not uniform, but is found by ex-\\nperiment to increase uniformly in all falling bodies. We\\ntherefore speak of gravitation as an acceleration (68), and\\nsince it is a special and very important acceleration, we\\nrepresent it by a special symbol, g. This is the velocity\\nadded to a falling body each successive second.\\ng is not a constant at the equator, at sea level, the\\nvalue of g is 978.1 centimetres at the poles, at sea level, it\\nis 983.1 centimetres. This is partly due to the fact that at\\nthe poles one is about 21-J- kilometres nearer to the center of\\nthe earth, and partly due to the fact that at the equator the\\nearth s rotation tends to diminish g. If the earth turned\\nseventeen times as fast as it does now, g would become\\nzero if faster than this, objects at the equator would be\\nthrown off into space g also varies with the altitude,\\nbeing greater at sea level, and less on top of mountains.\\nThe value of g for all places near the fortieth parallel of\\nlatitude may be taken as 980 centimetres (about 32 feet).", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0075.jp2"}, "74": {"fulltext": "56 PHYSICS\\nIt is the same for all bodies, light or heavy, and only ap-\\npears different on account of the unequal resistance offered\\nby the air. In a vacuum all bodies fall with the same\\nspeed.\\n70. Falling Bodies. The velocity of a falling body de-\\npends directly upon the length of time it has been falling.\\nSince the acceleration g is added each second, the velocity\\nat the end of t seconds must be t times g.\\nv gt\\nTaking g as 32 feet, we should have\\nVelocity at end of 1st second 32 feet.\\n2d 64\\n3d 96\\n4th 128\\n5th 160\\nThe space passed over by a falling body is evidently the\\naverage velocity, multiplied by the time. The body, start-\\ning from rest, has an initial velocity of zero, and at the end\\nof t seconds a final velocity of gt, and the average velocity\\nwill be the mean of these two\\n(ft\\nv i gt.\\nSubstituting this value, we get\\ns igtx t igt*.\\nThis gives the total space passed over in seconds. The\\nspaces passed over in successive seconds are as follows\\nDuring the 1st second 16 feet.\\n2d 48\\n3d 80\\n4th 112\\n5th 144\\nThe formulas give us a ready means of calculating all\\nthe elements involved in falling bodies.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0076.jp2"}, "75": {"fulltext": "FALLING BODIES 57\\n71. Projectiles. We have seen (69) that the motion of\\na projectile is compounded of two motions, the original\\nprojectile motion and the vertical motion of gravity. If\\nwe suppose a cannon ball to be fired horizontally from the\\ntop of a tower, its path would be represented as follows\\nTop of Tower I 2 3 4\\n1 second 1 second 1 second 1 second\\nFig. 20.\u00e2\u0080\u0094 Path of a cannon ball.\\nIf the tower were 400 feet high, the cannon ball would reach\\nthe earth in just 5 seconds. Had it simply been dropped\\nfrom the top of the tower, it would have reached the earth\\nin precisely the same time. This seems curious and at first\\nsight impossible but a moment s reflection will make the\\nmatter clear. In succeeding seconds the ball drops 16, 48,\\n80, 112, and 144 feet respectively, and this whether it is\\nmoving horizontally or not hence in 5 seconds the ball must\\nstrike the earth. In practice, therefore, the cannon must be\\naimed at a considerable angle above the horizontal in order\\nthat the ball may carry any great distance. It is in this way\\nthat modern guns are able to throw a ball 13 miles and over.\\n72. Suggestion. In the preceding paragraph the curva-\\nture of the earth was neglected. The surface was assumed\\nto be plane. But, as we know, the surface is spherical, and\\nin long-distance surveying this fact must always be taken\\ninto consideration. If, therefore, we could fire a cannon\\nball with sufficient speed to have the curvature of the earth\\njust neutralize the fall due to gravity, and if there were no\\nloss of speed by reason of the resistance of the air, and no\\ninterruption from mountains or other obstacles, our camion\\nball would pass completely around the earth, and would be-\\ncome a satellite of the earth.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0077.jp2"}, "76": {"fulltext": "58 PHYSICS\\nWhat speed would we have to give the cannon ball?\\nIn 1 second the ball falls 16 feet. To be at the same dis-\\ntance above the earth as when it started, the ball must in\\n1 second have reached a point where the curved surface of\\nthe earth is 16 feet below the horizontal line drawn through\\nthe starting place. This is the case at places five miles\\napart. Hence, our cannon ball to become a satellite of the\\nearth would require a velocity of 5 miles a second that\\nis, 26,400 feet per second and would pass around the earth\\nin 1 hour, 23 minutes, and 20 seconds.\\n73. Vertical Projectiles. If a body is thrown straight up\\nin the air, its velocity becomes constantly less until finally\\nthe body comes to rest. Neglecting the resistance of the\\nair, it is easy to calculate just how far up the body will\\ngo. Suppose its initial velocity to be 160 feet per second.\\nThen, knowing that gravitation will rob it of 32 feet each\\nsecond, we can readily see that at the end of 5 seconds the\\noriginal impulse will be completely neutralized, and the\\nbody will momentarily come to rest. It is now 400 feet up\\nin the air (s gt 2 and starts immediately to fall back\\ntoward the earth. The return journey also takes 5 seconds,\\nand the final velocity will be the same as the initial velocity\\n160 feet per second. The entire excursion requires 10\\nseconds, and the velocity at any point is always the same,\\nwhether the body be going up or down.\\nProblems. 1 With what velocity would a man strike the water\\nin falling from a bridge 150 feet high\\n2. How far would a body fall in 10 seconds\\n3. Through what distance does a body fall during the sixth\\nsecond\\n4. A stone is thrown upward with a velocity of 100 feet per sec-\\nond what velocity has it when 100 feet high", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0078.jp2"}, "77": {"fulltext": "CHAPTEE X\\nTHE PENDULUM\\n74. Importance of Pendulum. We shall devote a whole\\nchapter, though a short one, to the pendulum alone, be-\\ncause of its importance in the study of mo-\\ntion and of gravity and its application in time-\\nkeeping.\\nWe can best study the pendulum by means\\nof an ideal instrument known as the simple\\npendulum. While this is purely imaginary,\\nthe results obtained from such a study may\\neasily be applied to the real instrument by\\nthe addition of a few inconveniences.\\n75. The Simple Pendulum. This consists\\nof a heavy metallic bob, M, so homogeneous\\nthroughout as to have its centre of figure and\\ncentre of gravity at the same point. We con-\\nceive the entire mass to act as if concentrated\\nat this point. The bob is suspended from the\\npoint of support, 0, by a rigid thread which\\nhas neither weight nor friction. The length\\nof a simple pendulum (I) is the distance,\\nM, from the point of support to the centre\\nof gravity of the bob. (See Fig. 22.)\\nOrdinarily the pendulum will hang in a\\nvertical line, M. If M is displaced through\\nthe angle a to the position M it will tend to return to its\\noriginal position by virtue of its weight. But when it\\nreaches M it has acquired a certain momentum which car-\\n59\\nFift. 21.\u00e2\u0080\u0094 The\\nsimple pen-\\ndulum.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0079.jp2"}, "78": {"fulltext": "60\\nPHYSICS\\nries it to the extreme position on the left, M If it were\\nnot for the resistance of the air (we have assumed the ab-\\nsence of friction) MM would just equal MM and the\\npendulum would go on oscillating forever. As it is, the arc\\nof displacement becomes gradually less, and the pendulum\\nfinally comes to rest again at M.\\n76. The Motion of the Pendulum. When displaced, the\\nreturn of the pendulum to the vertical is due not to the\\nwhole force of gravitation evidently, since the bob is sus-\\nM\\nQr\\nFig. 22.\u00e2\u0080\u0094 Motion of the pendulum. ^H\\na u\\npended from and can only move in an arc of a circle\\nwhose centre is at 0. It must be due to some component\\nof gravitation acting along the arc MM Let us investi-\\ngate the matter. Gravitation can only act vertically down-\\nward, hence we must always represent it by a downward\\nvertical line, as M a. This may be resolved into two com-\\nponents, one (M d) in the direction of the thread produced,\\nand the other (M b) at right angles to this, and consequently", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0080.jp2"}, "79": {"fulltext": "THE PENDULUM 61\\ntangent to M M at 31 The component M d represents the\\npull on the thread, and is therefore to be neglected. The\\ncomponent M b is that part of gravitation which shows itself\\nas motion toward the vertical. As M descends, the com-\\nponent M b decreases, and at M disappears entirely. Here\\nthe entire weight of the bob is exerted as a pull on the\\nthread. But the required momentum carries the bob on to\\nM and the component of motion, corresponding to M b,\\nreappears and increases until it overcomes the momentum\\nand brings the bob to rest at M In passing from M back\\nto M the same course of events repeats itself in inverse order.\\n77. Formula of the Pendulum. The displacement of the\\npendulum on either side of the vertical that is, MM or\\nMM is called the amplitude of the vibration. The motion\\nis periodic, and is found for small displacements to occupy\\npractically the same time. We express this by saying that\\nthe vibrations are isochronous. It is upon this property\\nthat the value of the pendulum as a time-keeper depends.\\nThe time of vibration of a pendulum commonly means\\nthe time that it takes the pendulum to pass from one ex-\\ntreme position M to the other extreme position (M and\\nis represented by t. We find its value by developing the\\nformula of the pendulum. This can only be rigidly carried\\nout by means of higher mathematics, and so we must con-\\ntent ourselves here with a simple statement of the formula\\nt 7T i/~.\\ny 9\\n78. Discussion of Formula. This is a very simple for-\\nmula, but one which involves large consequences. It shows\\nthat the time of vibration depends on two things directly\\non the square root of length, and inversely on the square\\nroot of g. Consequently, to increase the time two, three,\\nfour or five fold, we should have to increase the length four,\\nnine, sixteen, or twenty-five fold. This can readily be veri-\\nfied by experiment. Further, on account of the increase in", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0081.jp2"}, "80": {"fulltext": "62 PHYSICS\\nthe value of a given pendulum vibrates more rapidly if\\ntaken from the equator to the poles.\\n79. Time-keeping and the Seconds Pendulum. In the\\nCathedral of Pisa, and right next door to the celebrated\\nLeaning Tower, there is still to be seen an antique lamp\\nsuspended from the roof by a long cord. It is said that\\naway back in the year 1582 a boy by the name of Galileo\\nnoticed that the oscillations of this venerable lamp were\\nextremely regular, and he was led to believe were isochro-\\nnous. Experiment showed that he was right. By using a\\nball with strings of different length, he also discovered that\\nthe time varied as the square root of length. It was not,\\nhowever, until 1656 that Huygens made use of the pendu-\\nlum to mark time. Each swing of the pendulum is allowed\\nto liberate a single tooth of an escapement wheel, and so\\nregulates the rate at which the clock hand creeps around\\nthe dial.\\nTo find the length of a pendulum which shall beat sec-\\nonds at any given place, we have only to make t 1, sub-\\nstitute the value of g for that place, and solve our time\\nequation for I.\\nl=% (tt 3.14159.)\\n7T\\nIf g 980, we have\\nI s- 99 cm. (appr.).\\nTT\\nThe length of the seconds pendulum is least at the equator\\nand greatest at the poles, but even at the poles it is still a\\nlittle less than a metre.\\n80. Determination of g by the Pendulum. The pendu-\\nlum gives us an indirect but at the same time very simple\\nand accurate method for determining g. Knowing the\\nlength of the pendulum, and observing its time of oscilla-\\ntion, we have only to solve the time equation for g.\\nItt 2\\n9= t", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0082.jp2"}, "81": {"fulltext": "THE PENDULUM 03\\nXearly all determinations of g for practical purposes have\\nbeen made in this way.\\n81. The Compound Pendulum. We can not get a perfect\\nbob and still less a rigid thread without weight or friction.\\nBut the simple pendulum is a capital example of the great\\nusefulness of ideal machines in physical investigations.\\nThe law of the simple pendulum applies equally to the\\nreal or compound pendulum, if we calculate the length (I)\\nof an equivalent simple pendulum. This equivalent length\\nfor the compound pendulum is the distance from the point\\nof suspension to a point called the centre of oscillation.\\nWe have seen that the time of oscillation depends on the\\nsquare root of the length. Hence in a real pendulum all\\nthe particles in the upper part of the rod are retarded, and\\nall the particles in the lower part of the bob are accelerated.\\nBut there must be one point on the axis which is neither\\nretarded nor accelerated, and this is the centre of oscilla-\\ntion. Huygens found that the centre of suspension and\\nthe centre of oscillation are interchangeable that is, the\\ntime of oscillation is not altered by using either centre for\\nthe point of suspension. This gives us a practical method\\nfor finding the centre of oscillation, and so calculating the\\nlength of the indwelling ideal pendulum.\\nProblems. 1. Will a change of temperature affect the time of\\noscillation of a compound pendulum, and why\\n2. How could this variation be avoided\\nReference.\\nFor an approximate derivation of the formula of the pendulum,\\nsee Encyclopaedia Britannica, article Mechanics, paragraphs 51 and\\n134 and for a rigid derivation see any standard work on higher\\nmechanics or advanced physics.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0083.jp2"}, "82": {"fulltext": "CHAPTER XI\\nCOMPOSITION AND RESOLUTION OF MOTIONS\\n82. Composition of Motions. It is evident that a body can\\nonly move in one direction at one and the same moment\\nhence if two or more motions are impressed npon a body at\\nthe same time, these motions mnst be compounded into a\\nsingle motion which represents the actual motion of the\\nbody. This process of substituting one motion for two or\\nmore separate motions we call the Composition of Motions,\\nand the single motion thus substituted is known as the\\nResultant. It is convenient to represent these motions by\\nstraight lines which symbolize by their magnitude and\\ndirection the magnitude and direction of the motions them-\\nselves. In addition we must know where the motion starts,\\nor its point of application.\\nWhen the motions are in the same direction and have\\nthe same point of application, the resultant is evidently\\nequal to their sum.\\nWhen the motions are opposite in direction and have\\nthe same point of application, the resultant is their differ-\\nence and is in the direction of the greater motion.\\nWhen, however, the motions are inclined to each other\\nin direction and have the same point of application, the re-\\nsultant will manifestly take a direction between the two\\nmotions and inclining to the greater motion. We can find\\nits magnitude and direction by representing the two mo-\\ntions in magnitude and direction by straight lines drawn\\nthrough a point and then constructing a parallelogram\\n64", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0084.jp2"}, "83": {"fulltext": "B\\nFig. 23. Parallelogram of motions.\\nCOMPOSITION AND RESOLUTION OF MOTIONS 65\\nupon these lines as adjacent sides. The diagonal will rep-\\nresent the resultant. Thus, let the motions A and B have\\na common point of\\napplication, 0, and O k v\\nconstruct the paral- V\\nlelogram A C B.\\nThen C is the re-\\nsultant.\\nThe figure needs\\nno demonstration. If\\nwe imagine the body\\nto have a motion A, represented in magnitude and direc-\\ntion by A, it is clear that under the action of that mo-\\ntion alone the body would move to A. Similarly, under\\nthe influence of the motion B alone, represented in magni-\\ntude and direction by B, the body would move to B but\\nas these two motions take place at the same time, the body\\nmust respond to both impulses and move along a line C,\\nwhich will take it as far down as B and as far to the right\\nas A. The point C fulfills both conditions.\\n83. Parallelogram of Motions. This method of finding\\nthe resultant of two motions is of the utmost importance in\\nmechanics. It is called the parallelogram of motions and\\nis often stated as follows\\nIf two motions impressed upon a body be represented\\nin magnitude and direction by two straight line^ drawn\\nthrough the center of gravity of the body, and a parallelo-\\ngram be constructed upon these straight lines as adjacent\\nsides, then the resultant motion will be represented in mag-\\nnitude and direction by that diagonal of the parallelogram\\npassing through the center of gravity.\\nIt is clear that the parallelogram of motions can be used\\nto find the resultant of any number of motions by first find-\\ning the resultant of two of the motions, then compounding\\nthis resultant with the third motion, then this second result-\\nant with the fourth motion, and so on until all are considered.\\n6", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0085.jp2"}, "84": {"fulltext": "66 PHYSICS\\n84. Moments. If a pull or a push be exerted upon a\\nbody in a direction passing through the center of the body\\nthat is, center of mass or center of gravity the body if\\nfree will move along in the direction of the. impulse. But\\nsuppose, now, that the direction of the pull or push does\\nnot pass through the center of the body or that one point\\nin the body is fixed, what will happen\\nIn the first case the body will evidently turn until the\\ndirection of motion does pass through the center of gravity,\\nand the body will then move in the given direction.\\nIn the second case the body will turn about the fixed\\npoint as a center, and will only come to rest when the di-\\nrection of motion, the center of gravity, and the fixed point\\nare all in the same straight line.\\nThis tendency to turn about a point has frequently to be\\nconsidered in mechanics, and is measured in a special way\\nby means of the mechanical moment. One can not speak of\\nthe moment of a motion, velocity, or force in the abstract,\\nbut must always speak of the moment with respect to some\\nparticular point. The moment is equal to the magnitude\\nof the motion, velocity, or force multiplied by the perpen-\\ndicular distance from the point to the line of motion, veloci-\\nty, or force. This is illustrated in the following diagram\\nFig. 24. Mechanical moments.\\nIn the first case an irregular stone, whose center of\\ngravity is at c, is given motion in the direction a b. The\\nmoment of the motion a b with respect to c is a b X c d. In\\nthe second case a crank handle is fixed at c\\\\ and a weight,\\nw, is hung from d The moment of w with respect to c is", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0086.jp2"}, "85": {"fulltext": "COMPOSITION AND RESOLUTION OF MOTIONS 67\\na c b\\nA\\nB\\nf\\nFig. 25.\\n-Parallel motions in the same\\ndirection.\\nw X c d This perpendicular distance c d or d cT is known\\nas the arm of the motion, velocity, or force.\\nThe device of arms and moments, or, as we say of such\\nformal agreements, the convention, is of great use in the\\nanalysis of machines.\\n85. Parallel Motions.\\nWhen two motions,\\nnot having the same\\npoint of application,\\nare parallel in direc-\\ntion, they will fall into\\none of the three follow-\\ning classes\\n1. The motions are\\nin the same direction,\\nequal or unequal.\\nThe resultant is their sum, and the only question is as to\\nits point of application. Let A and B be the two parallel mo-\\ntions. The resultant R is evidently equal to A -j- B. The point\\nof application of R must be nearer to the larger motion B,\\nand just in proportion to the relative magnitudes of A and B\\nbe ac A B,\\nor, A X ac B X be.\\nThe moments of A and B with respect to c are equal\\nand opposite, and hence both motions are duly represented\\nA in R. Had A and B been\\nequal, a c and c b would have\\nbeen equal also.\\n2. The motions are oppo-\\nsite in direction and -unequal.\\nThe resultant is their dif-\\nference, and its point of ap-\\nplication must be such that\\nthe motions A and B have\\n26.\u00e2\u0080\u0094 Parallel motions in\\nopposite directions. equal and opposite moments\\n1\\nFig.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0087.jp2"}, "86": {"fulltext": "68\\nPHYSICS\\nB\\nwith respect to the point; consequently it must be some\\npoint c in a b produced, and such that\\nbe ac A B,\\nor, A X ac B X be.\\nIt will seem at first sight as if c should be between a and\\nb, but that is impossible, for then the moments of A and\\nB would re-enforce each other, in-\\nstead of neutralizing each other.\\n3. The motions are opposite and\\nequal.\\nThis gives rise to a curious sys-\\ntem in mechanics, known as a\\ncouple. In this case A and B, by\\nstatement, are equal, and if they\\nhad the same point of application\\ntheir resultant would be zero. But\\nseparated as they are by the dis-\\ntance ab, their effect will be to\\nturn a b around until it, too, comes into the vertical and A\\nand B are in the same straight line. Hence a couple has no\\nresultant. Nor can this rotatory motion be neutralized by\\nany single third motion.\\nThe body can only be\\nkept at rest by opposing\\nto A B an equal and op-\\nposite couple, A B\\n86. Resolution of Mo-\\ntions. In the composition\\nof motions we substitute\\none motion for two. In\\nthe resolution of motion\\ndo the reverse we\\nmotions\\nprocesses\\nFlG. 27. Mechanical couple.\\nwe\\nsubstitute two\\nfor one. Both\\nFjg. 28. Besolution of motion.\\nare of immense importance in\\nphysics, And of frequent application. Any motion R may", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0088.jp2"}, "87": {"fulltext": "COMPOSITION AND RESOLUTION OF MOTIONS 69\\nbe regarded as the diagonal of a parallelogram OA C B,\\nOA C B\\\\ etc., and may thus be resolved into two motions,\\nA and B, A and B\\\\ or into any other pair whatever,\\nwhich may be represented as the adjacent sides of a par-\\nallelogram of which R is the diagonal.\\nThis may seem like a very indefinite process, since the\\nmagnitudes and directions of the components may be\\nalmost anything we like. But in practice the direction\\nof one or both components is generally given, and the res-\\nolution of R takes a more determinate form. We have\\nexamples of this in the pendulum, the inclined plane, and\\nin many other machines and processes.\\nIn the same way we may carry out the resolution of ve-\\nlocities and forces.\\nProblems. 1. Three equal motions imparted to a body leave it\\nat rest. What angles do the motions make with one another\\n2. Four motions are given to a particle E 24 centimetres, S 36\\ncentimetres, W 18 centimetres, and N 30 centimetres. Find the\\nmagnitude and direction of the resultant by means of the polygon\\nof motion.\\nReference.\\nElements of Mechanics Oliver J. Lodge.\\nMatter and Motion J. Clerk Maxwell.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0089.jp2"}, "88": {"fulltext": "CHAPTEE XII\\nWORK, POWER, AND ENERGY\\n87. Work is the overcoming of resistance through space.\\nBoth elements are necessary to our conception of work.\\nMotion through space against no resistance, or a force act-\\ning against a resistance but producing no motion, is doing\\nno work. If we represent work by W, force by F, and space\\nby s, our fundamental formula for work will be\\nW=Fs.\\n88. Measure of Work. In the C.-G.-S. system the unit\\nof work will be a unit of force acting through a unit of\\nspace that is, one dyne (67) acting through one centimetre.\\nSuch a unit is called the erg. It is inconveniently small,\\nhowever, and in practice we commonly use a multiple of\\nthis unit. The joule is 10,000,000 ergs 10 7 ergs and for\\nmost purposes is a more convenient unit. Work is inde-\\npendent of time. An erg or a joule means a definite\\namount of resistance overcome through a definite space,\\nbut implies nothing with respect to the rate at which the\\nwork is done.\\n89. Power. It is often important to express not only\\nthe amount of work done, but also the rate at which it is\\ndone. This is what we mean by power. It is the rate of\\ndoing work. The unit of power is unit work done in unit\\ntime that is, one erg in one second. It is called the erg-\\nsecond. This, like the erg, is inconveniently small, and is\\nalso commonly multiplied by 10 7 The unit so obtained is\\na joule-second, and is called a watt.\\n70", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0090.jp2"}, "89": {"fulltext": "WORK, POWER, AND ENERGY 71\\nThe Horse Poiver. The usual units of work and power\\nin the industrial world are the foot pound and the horse\\npower. The foot pound is the overcoming of one pound re-\\nsistance through one foot. As James Watt supposed that\\nan average horse could lift 33,000 pounds through one foot\\nevery minute, he introduced the unit of power known as\\nthe horse poiver, H. P. It is 33,000 foot pounds per min-\\nute or 550 foot pounds per second. It is equivalent to 746\\nwatts.\\n90. Energy. It seems, then, that the work of the\\nworld is done by bodies in motion. Every moving body\\nhas in it the power of doing work, because by virtue of its\\nown motion it can set other matter into motion. This\\npower of doing work we call Energy. The whole drama of\\nthe world, physically speaking, consists in the transfer and\\ntransformation of energy. Eemembering that energy is rep-\\nresented by matter in motion or matter capable of motion,\\nwe may say that the study of energy is the study of the\\nuniverse. It is for this reason that we have put on the\\ntitle-page of this book, Physics, the Science of Energy.\\nEnergy, like work, is measured in ergs and joules.\\n91. Forms of Energy.\u00e2\u0080\u0094 The ability to do work and the\\neffects produced in matter when work is done upon it show\\nthemselves in various ways and give rise to what are known\\nas the forms of energy. These are all intimately related,\\nand while it may be convenient at times to study the differ-\\nent forms under such separate headings as mechanical mo-\\ntion, sound, heat, light, magnetism, electric current, chemical\\naffinity, and the like, we miss the main thought of modern\\nphysics as we do of modern philosophy if we allow these\\nenergy forms to take separate shape in our minds and get\\nat all far apart. They are but qualities of the one essence\\nenergy. We seldom have one of these qualities mani-\\nfested alone. Any change in one quality, either in its in-\\ntensity or in its continuance, involves similar and compen-\\nsating changes in the other qualities. This is the deep", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0091.jp2"}, "90": {"fulltext": "72 PHYSICS\\ntruth underlying the doctrine of the conservation of energy.\\nYou can not create energy or destroy it. Mechanical mo-\\ntion may stop, sound may cease, heat may disappear, light\\nmay he extinguished, magnetism may vanish, electric im-\\npulse may he lost, chemism may spend itself, hut energy\\nthe one eternal energy, of which these are the qualities or\\nforms energy goes on forever.\\n92. Transfer and Transformation of Energy. We detect\\non all sides a tendency in energy to react with energy that\\nis in a different state of excitement, and to stop reacting\\nonly when the two states are quite alike. This sums up\\nthe possibilities in the physical world. Bodies representing\\ndifferent degrees of energy meet and react. It is incorrect\\nto say that one body acts on another, and to stop there.\\nThe truth is that both bodies are affected, one as much as\\nthe other. The reaction only ceases when the bodies possess\\nthe same degree of energy but when this does occur they\\nare quite indifferent to each other. Were all energy of the\\nsame intensity there would be perfect equilibrium.\\n93. Newton s Laws. When the world of science was\\nstill very young that is to say, about two centuries ago\\nNewton, with an insight that must always appear marvel-\\nous, expressed the main facts about motion and energy in\\nthree laws as following\\nFirst Law Every body perseveres in its state of rest or\\nof moving uniformly in a straight line except in so far as it\\nis made to change that state by external forces (Cause and\\nEffect).\\nSecond Law Change of motion is proportional to im-\\npressed force, and takes place in the direction in which the\\nforce acts.\\nThird Law Eeaction is always equal and opposite to\\naction that is to say, the actions of two bodies upon each\\nother are always equal and in opposite directions.\\n94. Energy Kinetic and Potential. Energy is not only\\nrepresented by matter in actual motion and ready to do", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0092.jp2"}, "91": {"fulltext": "WORK, POWER, AND ENERGY 73\\nwork on the instant, as a hammer descending, but it is also\\nrepresented by matter in such a position that it is capable\\nof motion and ready to do work when the time comes, as a\\nhammer poised. The energy represented by matter in\\nactual motion is called kinetic the energy represented by\\nmatter capable of motion is called potential.\\nReciprocity. When a moving body does work by giving\\nup a part of its motion, it may be said to have negative work\\ndone on it. The body acted upon gains the motion lost by\\nthe body acting, and has positive work done on it. The\\nalgebraic sum of this negative and positive work is zero.\\nIn one sense, therefore, no work is ever done in the world.\\nEnergy is simply transferred.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0093.jp2"}, "92": {"fulltext": "CHAPTEE XIII\\nMACHINES\\n95. A machine is a device. for doing useful work. To\\ndo work is to overcome some sort of resistance through\\nspace. It is very obvious that a machine can not do this\\nwork of itself, but must be energized from without. The\\nability to do work depends upon the motion of the machine,\\nand since this motion is so constantly spent in doing useful\\nwork, the supply must be constantly kept up. The motion\\nis supplied by the expenditure of force chemical, mechan-\\nical, or electrical and since the rate of work is also impor-\\ntant in all practical operations, the element of time comes\\nin, and our force must be expressed in terms of power.\\nHence we may say that a machine is a device for trans-\\nforming power into useful work.\\nIn our analysis of machines we shall speak of the work\\nput into them as Power, p, and the useful work got out of\\nthem simply as Work, w. In this comparison no element\\nof time comes in since they proceed simultaneously. If the\\nmachines were perfect and frictionless, the power put in\\nand the work got out would be just equal in amount. But\\nsome of the power is always lost in doing internal work in\\nthe machine itself that is, in overcoming the resistance or\\nfriction of the several parts. It is not lost in a mechanical\\nsense it reappears as heat and electricity, or is spent in\\nwearing down the bearings. It is only lost in a utilitarian\\nsense. The transformation of power into work is always\\neffected, therefore, at the cost of some loss of power, and the\\n74", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0094.jp2"}, "93": {"fulltext": "MACHINES 75\\nbest we can do is to reduce the loss to the smallest possible\\namount.\\nThe efficiency of a machine is the ratio of work to power\\nthat is, and expresses the exact percentage of power\\nutilized as work.\\n96. Axiom. You can not get more work out of a ma-\\ncltine tlian you put into it.\\nIndeed, as we have just seen, you can not get as much,\\nbut the axiom is worth stating in this emphatic way, for\\nit discredits at once all schemes for perpetual-motion ma-\\nchines. Perpetual motion itself is not only possible, but\\nunavoidable, since motion can never be destroyed. But a\\nperpetual-motion machine is a contradiction, for it im-\\nplies the creation of energy on the part of a mechanism.\\n97. The Principle of Virtual Velocities. But machines,\\nthough they create no energy, do possess advantages beyond\\ntheir mere ability to transform power into work. While\\nthe amount of useful work is always less than the amount\\nof power consumed, we can accomplish tasks greater in\\nmagnitude by the use of machines than we could possibly\\naccomplish without them. If we are willing to spend power\\nover a long period of time and accomplish work at a very\\nslow rate, we can move mountains, and justify the boast of\\nthe old philosopher who said that he could move the world\\nif you would only give him a place to stand on. Let us see\\nhow this is.\\nWork Force X Space, or W Fs.\\nSince work is made up of two factors, force and space,\\nwe may vary these to suit ourselves, making either one large\\nand the other one correspondingly small. Thus, if we make\\ns large, F will be small, and our machine will overcome\\nonly a small resistance, but will do it through a large\\nspace. On the other hand, if we make s small, F may be\\nvery large, and our machine will be a veritable Hercules,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0095.jp2"}, "94": {"fulltext": "76 PHYSICS\\novercoming tremendous resistance, but doing it through a\\nvery small space\u00e2\u0080\u0094 that is, very slowly.\\nMeanwhile the power put into the machine has been a\\nconstant quantity. This is also represented by force acting\\nthrough space. Machines are said to have a mechanical\\nadvantage when the force-element in the work is greater\\nthan the force-element in the power. The difference in the\\nspaces passed over preserves the equality between the two\\namounts of energy. We sum this all up in the principle of\\nvirtual velocities\\nThe force put into a machine, multiplied by the space\\nthrough which it acts, is always equal to the force got out\\nof a machine multiplied by the space through which it acts.\\n98. Simple Machines. The five simple machines, known\\nas the lever, the wheel and axle, the inclined plane, the\\npulley, and the screw, occur in all sorts of mechanisms, and\\nhave many important applications in daily life. They may\\nbe analyzed by means of the principle of virtual velocities,\\nor by applying the principle of moments. We shall use\\neither method and sometimes both. We shall always rep-\\nresent the force put into the machine by p, and the space\\nthrough which it acts by d, and its arm by a. In the same\\nway we shall represent the force got out by w, the space\\npassed over by s, and the arm by o. (See Fig. 32.)\\nThe process of mechanical analysis is very simple. It\\nconsists in finding the relation between^ and iv, and pro-\\nceeds by applying one or both of the fundamental formulae\\nof machines\\n1. (Virtual Velocities), pd ics.\\n2. (Moments), pa tub.\\n99. The Lever consists of a rigid bar supported at one\\npoint, called the fulcrum,/, and capable of turning freely\\nabout this point. There are three possible arrangements in\\nthe disposition of fulcrum, pressure, and weight, and this\\ngives rise to the three classes of levers", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0096.jp2"}, "95": {"fulltext": "MACHINES\\n77\\nVP\\nFig. 29. Lever of the first class.\\n1. The lever of the first class has/ in the midway, and\\nconsequently p and iv at the ends.\\n2. The lever of the second class has w in the midway, and\\nconsequently and p at the ends.\\n3. The lever of the third class has p in the midway, and\\nconsequently and w\\nat the ends.\\nAnalyzing 1 by\\nvirtual velocities, we\\nhave (Figs. 29, 32)\\n7 d\\ntvs pd, or to -p.\\nIf d is greater than\\ns, there is mechanical\\nadvantage if less than\\ns, mechanical disad-\\nvantage. In the first\\ncase the fulcrum will\\nbe nearer w in the\\nlast case, nearer p. In\\nthe figure, d is two\\nthirds of s, since a is\\ntwo thirds of b hence\\nand there is me-\\ns 3\\nchanical disadvantage.\\nAnalyzing 2 by mo-\\nments, we have (Figs.\\n30, 33)\\ntub pa, or w p.\\nFig. 30. Lever of the second class.\\nHimiiiiiimiiiHiiiiiii\\nmum\\nFig. 31. Lever of the third class.\\nThe arm a is the dis-\\ntance of p from the fulcrum, and the arm b is the distance of\\nw from the fulcrum. It is evident that the moments must be\\ntaken with respect to since that is the only fixed point,\\nand consequently any motion must be about as a center.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0097.jp2"}, "96": {"fulltext": "78\\nPHYSICS\\nIn levers of the second class it is evident that there\\nmust always be mechanical advantage, since iv, having the\\nshorter arm, must always be greater than p.\\nAnalyzing 3 by both\\nvirtual velocities and\\nhave\\n(i)\\n32. Analysis of the lever of the\\nfirst class.\\nW\\ndi\\nP\\nFig. 33.\\ni\\ni\\ni\\n\\\\p\\n-Analysis of the lever of the\\nsecond class.\\nFig. 34. Analysis of the lever of the\\nthird class.\\nmome\\nnts,\\nwe\\n(Figs.\\n31,\\n34):\\nws\\npd,\\nor\\nw\\nd\\n~P\\nwl)\\n-pa,\\na\\nor\\nW\\n-TV- (2)\\nIn levers of the\\nthird class there can\\nnever be mechanical\\nadvantage, since p is\\nalways nearer to\\nand must therefore be\\ngreater than w. The\\narms a and b are the ra-\\ndii of the circles over\\nwhich p and iv move\\nwhen displaced, and of\\nwhich d and s are the\\nactual arcs passed over.\\nSince circumferences\\nof circles are to each\\nother as their radii (c\\n2 7ir, and c 2 7tt\\nthe corresponding arcs\\nd and s must be as the\\nradii of their respec-\\ntive circles that is,\\n,a relation which\\ns o", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0098.jp2"}, "97": {"fulltext": "MACHINES\\n79\\nwould have to be true if 1 and 2 are both true. The prin-\\nciple of moments is indeed but a special statement of the\\nprinciple of virtual velocities.\\nApplications. These are almost too numerous to men-\\ntion.\\nFirst class Crowbar, balances, walking beam, steel-\\nyard, seesaw, scissors (double).\\nSecond class Crowbar (when resting against the ground),\\nnut crackers (double), wheelbarrow, oars, canoe paddle,\\nbicycle pedal.\\nThird class Spring shears, pincers, fire tongs, foot\\ntreadle.\\nNote. The analysis of the lever is, after all, but a special applica-\\ntion of the study of parallel forces. Should the forces of either pres-\\nsure or weight be applied obliquely, it would be necessary to resolve\\nthem into two components, one at right angles to the lever and the\\nother in the direction of the lever. We should only consider the com-\\nponent at right angles to the lever, since this would be the only one\\ncapable of producing motion about\\nthe fulcrum. It should also be added\\nthat we have throughout neglected\\nthe weight of the lever itself. In prac-\\ntice this must be taken into consid-\\neration, but the correction may easily\\nbe made.\\n100. The Wheel and Axle.\u00e2\u0080\u0094\\nThis is practically an application\\nof the lever of the second class,\\nthe fulcrum being the common\\naxis of the wheel and the axle.\\nOur analysis can best be made\\nby help of moments. The arm\\nof the weight is the radius of\\nthe axle, b the arm of the pressure is the radius of the\\nwheel, a. As before,\\nFig. 35.\u00e2\u0080\u0094 Wheel and axle.\\nwb\\npa, or w \u00e2\u0080\u0094p.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0099.jp2"}, "98": {"fulltext": "80\\nPHYSICS\\nThe wheel and axle, arranged as shown, will always give\\na\\na mechanical advantage expressed by v-.\\nThe wheel and axle find application in such special ma-\\nchines as the windlass and in many complex mechanisms.\\n101. The Pulley. In its simplest form the pulley is a\\nfixed wheel, which serves to change the direction of motion,\\nbut offers no mechanical advantage. As P and W (Fig. 36)\\nmove through the same distance, they must be equal.\\nW= P.\\nIn this form it is simply a lever of the first class (Fig.\\n32), in which a and b are equal.\\nWhere the pulley is movable (Fig. 37), and one end of\\nthe rope is fixed at C, the force P moves through twice the\\ndistance that the weight, W, is raised, and consequently\\nW=2P.\\nFig. 36.\u00e2\u0080\u0094 Simple\\npulley.\\nFig. 37.\u00e2\u0080\u0094 Movable\\npulley.\\nFig. 38.\u00e2\u0080\u0094 Series of\\nmovable pulleys.\\nIn this form it is simply a lever of the second class\\n(Fig. 33), in which a 2b.\\nBy arranging a suitable system of movable pulleys,\\nalmost any mechanical advantage can be secured. It is,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0100.jp2"}, "99": {"fulltext": "MACHINES\\n81\\nof course, at the expense of speed. Each movable pulley\\ndiminishes the speed one half, and increases the weight that\\nany given force can raise twofold. Such an arrangement\\nis shown in Fig. 38. In this case we\\nhave the force P multiplied by two for\\nevery movable pulley employed. Hence\\nif n be the number of movable pulleys J\\nemployed, we shall have\\nW=2\u00c2\u00bb P.\\nIn the figure n 3, and so W=2 3 P\\n8 P.\\nIt is more convenient in practice to\\narrange one fixed block containing sev-\\neral pulleys on the same axle, and one\\nmovable block also containing several\\npulleys on a common axle. This is\\nshown in Fig. 39. Here there is only\\none rope, whose fixed end is attached to\\nthe fixed block. The rope then passes\\nalternately over the pulleys of the two\\nblocks, and finally emerges from the\\nupper block, passing downward for the\\napplication of the force P. In this case the fixed pulleys\\nin the upper block contribute nothing to the mechanical\\nadvantage. The pulleys in the movable block add each\\na twofold advantage hence, if n be the number of pul-\\nleys, the relation will be\\nW 2 n.P.\\n102. The Inclined Plane in its simplest form is a device\\nfor lifting weights which would otherwise be inconveniently\\nor impossibly great. It may be analyzed in two ways,\\neither by virtual velocities or by resolving the weight into\\ntwo components, one acting along the inclined plane and\\none at right angles to it. In Fig. 40 w is to be lifted\\nthrough the height s, but p may move through d. Hence\\nFig. 39. Compound\\nblock pulley.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0101.jp2"}, "100": {"fulltext": "82\\nPHYSICS\\nthe advantage is greater the longer d is, with respect to s\\nthat is, the smaller the angle of the plane a.\\ni d\\nws pa, or w p.\\ns\\nAs a increases from 0\u00c2\u00b0 to 90\u00c2\u00b0, we can easily see that the\\npressure, p, must be increased, as the plane gets steeper,\\nF;g. 40. Inclined plane.\\nand will finally equal the weight, w, when the plane is ver-\\ntical. Then w p.\\nIn Fig. 41 the weight is represented by a straight line,\\nc g (which, as we have seen, must always be vertical and\\nmust start from the center of gravity, c). This is the only\\nFig. 41. Analysis of inclined plane.\\nforce acting on the body. But the body can not move in\\nthe direction of c g. It can only move down the inclined\\nplane, and this it will soon proceed to do unless we stop it.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0102.jp2"}, "101": {"fulltext": "MACHINES\\n83\\nHence the weight eg must be resolved into a component, c I,\\nparallel to the plane, and a component, I g, at right angles to\\nthe plane. This last component shows itself as pressure\\nagainst the plane and does not concern us here. The com-\\nponent, c represents the motion down the plane, and must\\nbe met by a force, I c, equal and opposite to c I, if the body is\\nto be supported on the plane. I c represents the pressure,\\nor p. Hence,\\nw p eg :lc\\nw x le p X eg\\nWhichever method of analysis we use, we get the same\\nresult.\\nThe Wedge is simply a double inclined plane, in which\\nthe pressure is exerted at right angles to the common back\\nthat is, in the line of the common base. It has applica-\\ntion in all our cutting tools, such as the knife, chisel, and\\naxe. It has also direct use in splitting timber and in sepa-\\nrating layers of rock.\\n103. The Screw. The usual form of the screw, such as\\nis seen in a copying press, may be regarded as a combina-\\ntion of an inclined plane and the wheel and axle. The\\nscrew thread is simply an inclined plane wrapped around a\\ncylindrical support. The pitch of the screw that is, the ver-\\ntical distance be-\\ntween two neigh-\\nboring threads is\\nthe height of the\\nplane. The thread\\ncorresponding to\\none complete turn\\nis the slant length\\nof the plane, and\\nthe circumference\\nof the screw corresponds to the base of the plane. The\\nforce is generally applied to the circumference of a wheel\\nmounted on one end of the screw. We can best analyze the\\nFig. 42. Screw.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0103.jp2"}, "102": {"fulltext": "84 PHYSICS\\nscrew by means of the principle of virtual velocities. Thus\\nthe force, p, moves through the circumference of a circle,\\nwhose radius, r, is the radius of the wheel, while the weight,\\nw y advances a distance equal to the pitch of the screw.\\nws pd.\\niv X pitch p X 2 irr.\\npitch\\nBy making the wheel large and the pitch small, we can\\nget a tremendous mechanical advantage. The screw has\\nmany applications besides the copying press. By means of\\npowerful jack screws, a whole building can be lifted from\\nits foundations. The screw is used in the lathe and other\\nmechanisms, and in many physical instruments, as the mi-\\ncrometer screw, to say nothing of its manifold use as clamp,\\nfastener, and leveler.\\nExperiments. 1. Take a straight bar of strong, sound wood,\\nabout 1 metre long and 2.5 centimetres square, and find its weight\\nby weighing a simple bar, 5 to 10 centimetres long, and of the\\nsame cross-section. By this method one can get an accurate result,\\nand use a delicate balance. Let this weight be x.\\n2. Balance the lever thus obtained on the sharp edge of a trian-\\ngular piece of wood, used as a fulcrum, mark the fulcrum/, and see\\nif it is in the center of the lever.\\n3. Put unequal weights on the ends of the lever balance it\\nafresh measure the two arms, and calculate the moments of the\\ntwo weights. Allowing for the unequal weights of the two arms,\\nare the moments equal\\n4. To weigh the lever by moments. Take the same lever, add a\\nsuitable weight, w, to one extreme end, and balance, marking this\\nfulcrum/ Designate the distance from w to/ as the arm b. The\\nmoment is then wb. The force on the other side of is the weight\\nof the lever, p, and its arm, a, is the distance since the weight\\nof the lever will act as if concentrated at its center of gravity\\nThe moment is pa. wb =pa, or p w. Is this equal to x as\\nobtained in Ex. 1", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0104.jp2"}, "103": {"fulltext": "MACHINES 85\\n5. Mark one end of the lever c, and the other end d. Support d\\non the triangular fulcrum, and c by means of a spring balance. Take\\nthe reading r. Add a known weight, y, to any point of the lever, g,\\nand take a second reading, r\\nDoes (r r) x cd y x gd\\n6. Repeat the experiment, placing the spring balance at g and\\nthe weight y at c. What now is the result\\n7. In the same way, take two boards of equal length, I, and sup-\\nport as above, with a narrow crack between. Support w by a strong,\\nlight thread, passed through the crack, and fastened to the spring\\nbalance. Keeping balance and thread horizontal, determine the re-\\nlation between w and p.\\nProblem. 1. Can the wheel and axle be so arranged that it\\nwill give a mechanical disadvantage If not, or if so, explain the\\nreason.\\n2. Determine the mechanical advantage in the case of the in-\\nclined plane, when the force p is applied parallel to the base, giving\\nyour result in terms of the base and height of the plane.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0105.jp2"}, "104": {"fulltext": "BENJAMIN FRANKLIN (1706-1790)\\nFkanklik was born in Boston, January 17, 1706. At\\nseventeen years of age he hired out as a printer in Phila-\\ndelphia. He became the leading journalist of America.\\nFor twenty-five years he published Poor Eichard s Almanac,\\nwhich attained a marvelous popularity.\\nHe acquired familiarity with French, Spanish, Italian,\\nand Latin. He became America s leading diplomatist and\\nstatesman. He was one of the committee of five which\\nwrote the Declaration of Independence a member of the\\ncommission appointed to negotiate peace with England at\\nthe close of the Revolutionary War a leading member of\\nthe first National Convention elected to frame the Con-\\nstitution and American minister to France for nine years.\\nHis principal scientific researches were upon balloons\\nand atmospheric electricity. He was a member and one of\\nthe managers of the Royal Society, London, and a mem-\\nber of the Royal Academy of Sciences, Paris. Together\\nwith a committee of the French Academy, he investigated\\nmesmerism at the request of the King of France, which re-\\nsulted in the disgrace and flight of Mesmer.\\nMcMaster, in the History of the People of the United\\nStates, vol. i, pp. 233 and 422, says He was renowned\\nthroughout Europe as a philosopher nor has his just\\nfame been cast in the shade by any investigator our coun-\\ntry has since produced. Franklin was in truth the\\ngreatest American then living nor would it be safe to say\\nthat our country has since his day seen his like.\\n86", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0106.jp2"}, "105": {"fulltext": "BENJAMIN FRANKLIN.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0107.jp2"}, "106": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0108.jp2"}, "107": {"fulltext": "MECHANICS OF FLUIDS\\nCHAPTER XIV.\u00e2\u0080\u0094 Pressure in Liquids\\n104. General Definition of Fluids.\\n105. The Mercury Pressure Gauge. Figs. 43 and 44.\\n106. Pressure in Terms of Inches of Mercury.\\n107. Pressure in Terms of Pounds per Square Inch. Fig. 45.\\n108. First Principle. Figs. 46 and 47.\\n109. Pressure is due wholly to Gravity. Figs. 48 and 49.\\n110. Upward Pressure in Liquids. Figs. 50 and 51.\\n111. Liquids seek their own Level. Figs. 52 and 53.\\n112. Buoyancy. Figs. 54 and 55.\\n113. Specific Gravity. Figs. 56, 57, and 58.\\n114. The Specific Gravity of the Human Body.\\n115. How Iron Ships Float.\\n116. Stability of Floating Bodies.\\nCHAPTER XV.\u00e2\u0080\u0094 Pressure in Gases\\n117. General Behavior of Gases.\\n118. Second Principle.\\n119. The Atmosphere.\\n120. Weight of Air.\\n121. The Barometer. Figs. 59, 60, 61, and 62.\\n122. The Aneroid Barometer. Fig. 63.\\n123. Variations in Atmospheric Pressure. Fig. 64.\\n124. Boyle s Law. Figs. 65, 66, and 67.\\n125. Closed Pressure Gauges. Fig. 68.\\n126. Buoyancy of Air. Fig. 69.\\n127. Balloons.\\nCHAPTER XVI. Transmission of Pressure in Fluids\\n128. The Transmission of Pressure.\\n129. Third Principle. Fig. 70.\\n130. Hydrostatic Press. Fig. 71.\\n87", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0109.jp2"}, "108": {"fulltext": "88 PHYSICS\\nCHAPTER. XVII. Applications of Principles of Fluid\\nPressure\\n131. The Density of Milk.\\n132. The Bottle Imp or Cartesian Diver. Figs. 72 and 73.\\n133. Magdeburg Hemispheres. Fig. 74.\\n134. The Relation of Tension and Pressure. Fig. 75.\\n135. Bacchus Illustration. Fig. 76.\\n136. Siphon Bottles, Fire Extinguishers, and Explosions.\\n137. Diving-bells and Caissons.\\n138. The Ear Drum.\\n139. The Physics of Respiration.\\n140. How Atmospheric Pressure upon the Human Body is Sustained.\\n141. The Fountain in Vacuo. Fig. 77.\\n142. Pumps. Fig. 78.\\n143. Force Pumps. Fig. 79.\\n144. Air Pumps. Figs. 80 and 81.\\n145. The Mercury Pump. Fig. 82.\\n146. The Water Exhaust. Fig. 83.\\n147. Air Compressors and Blowing Engines.\\n148. Siphons. Figs. 84, 85, and 86.\\n149. Siphoning Gases. Fig. 87.\\n150. Hero s Fountain. Figs. 88 and 89.\\n151. Tension inside the Barometer Tube.\\n152. The Inverted Tumbler of Water. Fig. 90.\\n153. The Specific Gravity of Liquids measured by balancing them\\nagainst Atmospheric Pressure. Fig. 91.\\n154. Fluids in Motion. Figs. 92 and 93.\\n155. The Hydraulic Ram. Figs. 94 and 95.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0110.jp2"}, "109": {"fulltext": "CHAPTEE XIV\\nPRESSURE IN LIQUIDS\\n104. General Definition of Fluids. We designate both\\nliquids and gases as fluids, because both are characterized\\nby the great mobility of their molecules. But there is a\\ngreat difference between the two in the matter of com-\\npressibility. Liquids are so little compressible that we are\\nalmost justified in speaking of them as Incompressible\\nFluids. Gases, on the other hand, re-\\nspond so perfectly to every change of\\npressure that we may properly speak of\\nthem as Compressible Fluids. This dis-\\ntinction will need to be kept in mind in\\nour study of pressure in liquids and in\\n105. The Mercury Pressure Gauge.\u00e2\u0080\u0094\\nA very convenient instrument for the\\nstudy of pressure in fluids is the mer-\\ncury pressure gauge shown m Figs. 43\\nand 44. In Fig. 43 a column of water,\\na b, is represented as being balanced by\\na column of alcohol, b c, both columns\\nresting upon mercury in the part of the\\ntube below b. In Fig. 44 the column of\\nwater, ab, is balanced by a column of\\nmercury, b c. In both cases it is obvious that the mercury\\nacts as a sort of scales for weighing. In Fig. 44 the col-\\numn of water, a b, has forced the mercury down to b in the\\nc-%\\nT a\\nI 3\\nI s\\nI I\\nS i\\nI 1\\n1 I\\nI\\nFig. 43.\\nU\\nFig. 44.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0111.jp2"}, "110": {"fulltext": "90 PHYSICS\\nleft arm of the pressure gauge and up in the right arm\\nuntil it supports a column of mercury, b c, equal in weight\\nto itself. In Fig. 43 the column of water a b is equal in\\nweight to the column of alcohol b c.\\n106. Pressure in Terms of Inches of Mercury. We may\\nspeak of the pressure in terms of inches of mercury. Thus\\nthe pressure of a column of water 13.6 inches long is about\\nequal to a column of mercury one inch long half an inch\\nof mercury would represent the pressure of a column of\\nalcohol about eight and a half inches long. In inflating\\na football one is likely to exert a pressure of about three\\ninches of mercury. The ordinary pressure upon a steam\\nradiator is likely to be about ten inches of mercury. That\\nis, if we connect one arm of a mercury pressure gauge with\\nthe inflated football or the steam radiator these pressures\\nwould force the mercury up in the other arm of the pres-\\nsure gauge three inches in the first case and ten\\ninches in the second case.\\n107. Pressure in Terms of Pounds per Square\\nInch. We usually speak of pressure in terms of\\npounds per square inch. In Fig. 45 the column of\\nwater ab is represented as having a cross-section\\nof one square inch and a height of 13.6 inches.\\nIt is balanced by a column of mercury b c, which\\nis a cubic inch in volume. Now, a cubic inch of\\nmercury weighs about half a pound the\\nweight of the column of water is, there-\\nfore, about half a pound; the pressure\\nupon the square inch of surface of mer-\\nFig. 45. cury where the water rests upon it is\\nhalf a pound. It is manifest that if the\\ncross-section of the tube were half as large there would\\nbe half the quantity of water, and half the weight i. e.,\\none quarter of a pound upon half a square inch; or if the\\ntube were one quarter or one tenth as large in cross-section\\nthe weight of water would be one quarter or one tenth as", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0112.jp2"}, "111": {"fulltext": "PRESSURE IN LIQUIDS\\n91\\nmuch. The pressure would, however, in all cases be at the\\nrate of one half pound to the square inch, so long as the\\nheight of the column remained 13.6 inches. And let the\\ndiameter of the column a b be never so small or great it will\\nin every case balance the cubic inch of mercury b c, pro-\\nvided its height remains 13.6 inches.\\n108. First Princi-\\nple. (a) Pressure in I r^^\\nliquids is proportional\\nto the depth alone, and\\nis not influenced by\\nthe size or shape of the\\nvessels which contain\\nthem. (b) At any\\ngiven depth the pres-\\nsure is equal in all\\ndirections.\\nThe first part of\\nthis principle may be\\nillustrated by such\\napparatus as is repre-\\nsented in Fig. 46, and\\nthe second part is\\nshown by such\\napparatus as is\\nrepresented in\\nFig. 47; ab is\\nin each case the\\ndepth of the\\nwater measured\\nvertically, and\\nbe is in each\\ncase the mer-\\ncury column\\nsustained by the pressure of the liquid,\\nfound to be 13.6 as long as b c.\\nFig. 46.\\nHI\\nFig. 47.\\nIn all cases a b is", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0113.jp2"}, "112": {"fulltext": "92\\nPHYSICS\\nD\\nm\\nb\\nno S\\n109. Pressure is due wholly to Gravity. A few dia-\\ngrams, such as those represented in Fig. 48, may help one\\nto feel that it is not unnatural that the pressure of gravity\\nupon particles of matter free\\nto move among themselves will\\nresult in pressure sidewise or\\neven upward. Having no sin-\\ngle point or even surface of sup-\\nport, liquids do not, like solids,\\nexert a downward force of mg\\n(mass multiplied hy the accel-\\neration of gravity; sections 65\\nand 69) on the bottom of the\\ncontaining vessel. The pres-\\nsure upon any point of surface\\ndepends not on the amount of\\nliquid, but entirely upon the\\nheight of the liquid above the\\ncenter of the unit surface.\\nIn Fig. 49 the vessels have all the same-sized bases,\\nand the water stands at the same height in all. The\\namount of water in the several vessels is manifestly very\\ndifferent, but the pressure upon the base of each vessel is\\nthe same. This seems at first sight an evident paradox.\\nThe weight of water on the base A is manifestly the whole\\nweight. But this is\\nequal to the volume\\nof the cylinder in\\ncubic centimetres\\n(since one cubic\\ncentimetre weighs\\none gram), and the\\nvolume is equal to\\nthe height multi-\\nplied by the area of the base. By contracting the sides,\\nas in B, the amount of water is greatly reduced, but the\\nFig. 48.\\nFig. 49.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0114.jp2"}, "113": {"fulltext": "PRESSURE IN LIQUIDS 93\\npressure on the base remains the same. The pressure on\\nthe portion of the base a b is equal to a volume of water,\\nh X ab. This has the same intensity per unit surface as\\nin A, since the height, h, is the same. But we could not\\nhave a greater pressure on a b than at c and d, for in that\\ncase there would be a now of water toward c and d accom-\\npanied by depression of the column which stands over a b\\nand a reduced pressure on ab\\\\ but we know from our ex-\\nperience that no such flow does take place. The pressure\\non the base a b is transmitted equally in all directions, and\\nacts downward at c and d with precisely the same force as\\nit does on a b. In the vessel G there is more water than\\nthere is in A, but there is no increase of pressure on the\\nbase.\\n110. Upward Pressure in Liquids. Because liquids trans-\\nmit pressure equally in all directions, it follows that at any\\ndepth the upward pressure due to the weight of the liquid\\nmust be exactly the same as the downward pressure. Con-\\nsider the level a a in the tank of\\nwater shown in Fig. 50. The\\ndownward pressure on a square\\ncentimetre, b c, is the height of a\\ncolumn of water be X h. If this\\npressure were not counterbal- Fig. 50.\\nancecl there would be a downward\\nmovement of the liquid. But no such movement takes\\nplace. Every square centimetre on the level a a has the\\nsame downward pressure of h grams, and that pressure,\\nbeing transmitted equally in all directions, acts upward on\\nb c and just counterbalances the downward pressure.\\nThe upward pressure of liquids is illustrated by a simple\\nexperiment. An open glass cylinder (Fig. 51) with ground\\nedges has one end closed by means of a thin ground-glass\\ncover plate. In the air the plate has to be held up against\\nthe cylinder, but as soon as cylinder and plate are immersed\\nto a depth of about one centimetre in water, the upward pres-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0115.jp2"}, "114": {"fulltext": "94\\nPHYSICS\\nFig. 51.\\nsure of the water holds the plate against the cylinder. The\\ndeeper the cylinder is pushed the greater the upward pres-\\nsure, and the more securely is the plate held against the\\ncylinder. If now water be poured into the\\ncylinder, the cover plate will fall when the\\nwater in the cylinder is nearly at the same\\nlevel as the water outside in the tank. The\\ndifference in level represents the volume of\\nwater whose weight just equals that of the\\ncover plate. Had the cylinder been filled with\\nalcohol, or some liquid lighter than water, the level inside\\nthe cylinder would have to be considerably higher than\\nthe level outside to make the cover plate fall off.\\nThe upward pressure on the plate is equal to the weight\\nof a column of water having the plate for its base, and a\\nheight equal to the distance from the surface to the lower\\nface of the plate. The doivnward pressure is equal to the\\nweight of the liquid inside the cylinder, plus the weight\\nof the plate itself.\\nThis upward pres-\\nsure of liquids is man-\\nifested when you raise\\nthe tubular stopper\\nin a bath tub full of\\nwater. The water\\nrushes up the tube by\\nreason of the pressure\\nof the surrounding\\nwater.\\n111. Liquids\\nseek their own\\nLevel. If we have\\nseveral communicating vessels, as shown in Fig. 52, and\\npour water into one of them, we notice immediately that the\\nwater rises in all of them to the same level. We can not\\nfill one vessel without filling all. On the whole, we should", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0116.jp2"}, "115": {"fulltext": "PRESSURE IN LIQUIDS 95\\nexpect this, for if we imagine for a moment that we have\\nsucceeded in filling one vessel without filling the others,\\nand look at the pressures, we shall find an impossible state\\nof affairs. The liquid in the first vessel will be unsupported\\nat the outlet into the second vessel. With the second ves-\\nsel empty, there will be nothing to balance that pressure\\nand nothing to prevent the liquid from flowing out, which\\nit accordingly does. The pressure is only balanced at each\\noutlet when the liquid stands at the same height in each\\nvessel. This is popularly exjoressed by saying that liquids\\nseek their own level. Every free surface of water, unacted\\nupon by wind or current, is perfectly level, and is perpen-\\ndicular to the direction of gravity. Consider for a moment\\nthe force at work. The only force is gravity, and this al-\\nways acts vertically down-\\nward. If the surface were\\nnot level, but were inclined,\\nas indicated in Fig. 53, we\\nshould have at a a downward\\npressure, represented by the\\narrow. This pressure is trans-\\nmitted equally in all direc-\\ntions, and consequently acts\\nupward at b. In the absence of any corresponding down-\\nward pressure at h the water rises at and must sink at a,\\nonly coming to rest when in all parts of the liquid, the\\ndownward pressure and the upward pressure, are the same.\\nAYe can sum this up by saying that the surface of liquids\\nis always perpendicular to the direction of force acting\\nupon them. Consequently the surface of a still pond or\\nlake is always level, since it is everywhere perpendicular to\\ngravity. In the case of the ocean or of large bodies of\\nwater generally, the direction of gravity changes about 1\u00c2\u00b0\\nevery 69 miles, and consequently the surface, being per-\\npendicular to gravity, is always changing, and is in reality\\nspherical. Of course, the surface of small ponds and lakes", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0117.jp2"}, "116": {"fulltext": "96\\nPHYSICS\\nis also strictly spherical, but in such small distances the\\ndeparture from a strict plane is not noticeable.\\n112. Buoyancy. From what we have learned thus far we\\nknow that any object which sinks beneath the surface of a\\nliquid will have pressure exerted upon it proportional to\\nthe depth which it sinks into the liquid, and due wholly to\\nthe weight of the liquid. Let us consider the forces act-\\ning upon a cubic centimetre of water, a, Fig. 54, in a tank\\nof water. Let us suppose the upper surface of the cube a\\nto be 1 centimetre below the surface of the\\nwater in the vessel. On the upper face of\\nthe cube there will be a downward pressure\\nequal to 1 gram, the weight of the column\\nof water above it. The horizontal pressure\\nupon the four faces may be neglected, since\\nthey come from four directions at right\\nangles and just balance one another. On\\nthe lower face of the cube there will be an\\nupward pressure of 2 grams, equal to the\\nweight of a column of water, whose height is 2 centimetres\\nand whose cross-section is 1 square centimetre. The down-\\nward pressure of water upon the upper face of the cube is\\n1 gram, and the upward pressure of water upon its lower\\nface is 2 grams. But the cube does not move upward, be\\ncause its own weight is 1 gram. All the forces are balanced,\\nand the cube of water stands still. This would of course be\\ntrue also of a cubic centimetre of any other substance which\\nweighed exactly 1 gram. Let us substitute for the cube of\\nwater a cube of wood about half as heavy as water. The\\ndownward forces will be the weight of the wood and the\\nweight of the column of water above it, equal to grams.\\nThe upward force will be equal to 2 grams, as before. Hence\\nthere will be an unbalanced buoyant force of half a gram,\\nand the wood will move upward until it reaches a place\\nwhere the opposing forces are equal. Pursue this method\\nof reasoning, and find out that it must rise until it displaces\\nFig. 54.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0118.jp2"}, "117": {"fulltext": "PRESSURE IN LIQUIDS 97\\njust its own weight of water i. e., until only half of the\\ncube is submerged. Had the cube been of cast iron, density\\n7.2, supposing it to be in its original position, the upward\\npressure upon its lower face would be 2 grams, as before,\\nand the downward pressure would be its own weight 7.2\\ngrams plus the weight of the 1 centimetre of water above\\nit, 1 gram, making a total downward force of 8.2 grams.\\nHence the cube would sink with a force of 8.2 2 6.2\\ngrams. Suppose the bottom of the vessel is 5 centimetres\\nbelow the surface of the w T ater and the iron cube to be rest-\\ning upon it. What would be the buoyant force upon it, and\\nwith how much force would it press upon the bottom of the\\nvessel If this cube of iron were suspended upon a string\\nat various depths within the liquid, but always wholly sub-\\nmerged, would it in every case pull with the same force\\nupon the string Would your answer be the same if liquids\\nwere compressible Balloons may be made to float higher\\nor lower in the air by increasing or decreasing their weight.\\nThis is not possible with objects wholly submerged in\\nliquids. It is a matter of daily experience that as soon as\\na floating object becomes heavy enough to sink beneath the\\nsurface of the water it goes straight to the bottom. The\\nonly way to prevent this would be to have liquids of dif-\\nferent densities, and which do not readily mix, arranged in\\nlayers one above the other. If a vessel is half full of wa-\\nter, density 1.00, and half full of ether, density .71, a block\\nof oak, density .85, dropped into the vessel will sink to the\\nbottom of the ether layer and float on the water under-\\nneath. An egg will sink in fresh water and float in salt\\nwater. Consequently if a jar be half filled with salt water\\nand then fresh water be carefully added, an egg dropped\\ninto the jar will sink halfway, and remain suspended at\\nthe meeting plane of the two liquids. From such investi-\\ngations we may deduce the principle that a body wholly\\nsubmerged in a liquid is buoyed up by a force exactly equal\\nto the weight of its own volume of the liquid.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0119.jp2"}, "118": {"fulltext": "98\\nPHYSICS\\nThis is prettily illustrated by the apparatus represented\\nin Fig. 55. The upper cylinder is hollow, the lower cylin-\\nder solid, and has such a volume as to exactly fit inside of\\nthe upper cylinder. They are suspended as shown in the\\nfigure, and carefully balanced. Then water is poured into\\na vessel so as to submerge the lower cylinder. Its buoyant\\nPig. 55. Principle of Archimedes.\\nforce lifts the left arm of the balance. The upper cylinder\\nis then filled wi^h water, and this is found to restore the\\nbalance, showing that the buoyant force upon the sub-\\nmerged cylinder is exactly equal to the weight of its own\\nvolume of water. The same experiment may be performed\\nless elaborately by weighing any solid of known volume,\\nsay n cubic centimetres, first in air and then in water. The\\nloss of weight will be just n grams.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0120.jp2"}, "119": {"fulltext": "PRESSURE IN LIQUIDS\\n99\\nEvery boy who has lifted a stone under water knows\\nhow heavy it suddenly becomes when he tries to bring it\\nabove the surface. The transporting power of running\\nwater is greatly increased by the buoyancy of the water and\\nthe consequent loss of weight on the part of the material\\ncarried.\\nWe may make use of this principle to find the volume\\nof an object. For example, if an object weighs 3 grams\\nin air and 2 grams when\\nwholly submerged in water,\\nthe buoyant force of the\\nwater is 1 gram i. e., its vol-\\nume is 1 cubic centimetre.\\n113. Specific Gravity.\u00e2\u0080\u0094 It\\nis obvious that the object\\nmentioned in the last para-\\ngraph was three times as\\nheavy as water. We express\\nthis by saying that its spe-\\ncific gravity is 3.\\nThe balance may be used\\nto determine the specific\\ngravity of both solids and\\nliquids.\\na. Solids. A fine silk\\nthread or wire is tied around\\nthe solid and a loop made of\\nthe end several inches away\\nfrom the solid, so that the\\nwhole may be freely suspended from the arm of the bal-\\nance (Fig. 56). The weight is then taken in air. Let\\nthis be represented by x. A glass of water is now brought\\nunder the solid and raised until the entire solid is cov-\\nered by the water. The solid must, of course, swing freely\\nin the water, and not touch the sides of the beaker. The\\nweight is taken in water. Let it be represented by y.\\nFig. 56. Specific-gravity balance.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0121.jp2"}, "120": {"fulltext": "100 PHYSICS\\nThen x y will represent the loss of weight in water, and\\nwe will have -r. x\\nspecific gravity\\ny\\nExample. A piece of limestone rock.\\nWeight in air 17.65\\nWeight in water 10.99\\nLoss of weight in water 6.66\\nSpecific gravity l 2.65.\\nThat is to say, limestone is nearly two and two thirds\\ntimes as heavy as an equal volume of water.\\nb. Liquids. To determine the specific gravity of a\\nliquid we must know the weight of a given volume of it,\\nand also the weight of the same volume of water. The\\nratio of one to the other is the specific gravity. We can\\neasily find these two quantities by taking a suitable glass\\nplunger of known weight (x) and weighing it first in the\\nliquid whose specific gravity is to be tested (y) and then in\\nwater (z). The loss of weight in each case will evidently\\nbe the weight of a volume of liquid equal to the volume of\\nthe plunger, and we shall have specific gravity x\\nExample. Alcohol.\\nWeight of plunger in air 10.21 grams (x)\\nalcohol 8.45 (y)\\nwater 8.02 (z)\\na 10.21-8.45 1.76\\nSpecific gravity 1Q 21 _ 8 Q2 .8\\nWe have two kinds of hydrometers for determining\\nspecific gravity, the hydrometer of constant volume and the\\nhydrometer of constant weight.\\nBy the first we can determine the specific gravity of\\nboth solids and liquids. A form of the instrument, known\\nas Nicholson s hydrometer, is shown in Fig. 57.\\nThe solid whose specific gravity is to be determined is\\nplaced on the upper scale pan and weights added until the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0122.jp2"}, "121": {"fulltext": "PRESSURE IN LIQUIDS\\n101\\nhydrometer sinks to the index point. The solid is then\\nplaced in the lower pan under water and weights added to\\nthe upper scale until the buoyancy of the now submerged\\nsolid is compen-\\nsated. The added\\nweights represent\\nthe weight of the\\nwater displaced by\\nthe solid. This\\ndivided into the\\nweight of the solid\\ngives its specific\\ngravity. In using\\nthe hydrometer for\\nliquids it is simply\\nfloated in the\\nliquid and\\nthen in pure\\nwater, and the\\nweight of the\\nhydrometer it-\\nself, plus the added weights, will give the weights of the\\nliquid and of the water displaced. One divided by the\\nother is the specific gravity.\\nThe hydrometer of constant weight may be used only for\\nliquids. It is made of glass, and consists of a cylinder or\\ntube, terminating below in a bulb loaded with mercury or\\nshot, and above in a long slender tube which carries a scale\\nand projects above the surface when the hydrometer is\\nfloated in water (Fig. 58).\\nXow, in order that any solid may float, it must displace\\nan amount of liquid whose weight is just equal to its own\\nweight. Hence when the hydrometer is put into liquids\\nlighter than water it sinks deeper, and when into liquids\\nheavier than water it rises higher above the surface. If\\nthe point on the scale to which the hydrometer sinks in\\nFig. 57.\\n-Hydrometer of constant weight.\\n(Nicholson s.)", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0123.jp2"}, "122": {"fulltext": "102\\nPHYSICS\\ndistilled water be marked 1, the markings on the scale\\nbelow this point will be greater than 1, and above will be\\nless than 1.\\nBy adjusting the hydrometer so that it will sink about\\nmidway on the scale in water, the one instrument may\\nmeasure specific gravities greater and less than unity but\\nin order to gain\\ngreater sensitive-\\nness it is common\\nto use two instru-\\nments, one for liq-\\nuids denser than\\nwater and the othei\\nfor liquids lighter\\nthan water.\\nThe alcohol-\\nmeter is a hydrom\\neter made especial-\\nly to measure alco\\nhoi. The upper\\nend of the scale,\\nmarked 100, is the\\npoint to which the\\ninstrument sinks\\nin pure alcohol.\\nThe lower part of the scale, marked 0, is the point to which\\nit sinks in distilled water. The intermediate readings give\\ndirectly the percentage of alcohol.\\nThe lactometer is a hydrometer graduated with special\\nreference to milk, and is used by official inspectors. Other\\nhydrometers, such as Baume s, are graduated empirically\\nthat is, without direct reference to specific gravity and\\nare used in industries where it is desired to keep trade\\nsecrets.\\nIn all of the above work it has been assumed that the\\nsolids are heavier than water and will not dissolve. In case\\nHydrometers of constant volume.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0124.jp2"}, "123": {"fulltext": "PRESSURE IN LIQUIDS 103\\nthey are lighter they must be weighted with some solid of\\nknown specific gravity and the calculation made accord-\\ningly. In case they dissolve in water, another liquid in\\nwhich they will not dissolve must be used and the neces-\\nsary correction made.\\nThere is a classic story to the effect that Hiero, Tyrant\\nof Syracuse, having a daintily wrought crown which he\\nsuspected not to be of pure gold, sent it to the philosopher\\nArchimedes to test for him. The philosopher was puzzled,\\nfor the crown was to be tested without any damage to the\\nclever workmanship. But one day, being in the bath and\\nnoticing that his body displaced its own volume of water,\\nit occurred to him that buoyancy would enable him to de-\\ntermine the specific gravity of the crown, and thus he\\nmight compare it with pure gold. He sprang out of the\\nwater shouting, Eureka {I have found it.) He demon-\\nstrated that the crown was not gold, and Hiero had the\\nfraudulent craftsman dreadfully punished. Archimedes\\nis celebrated for his researches in buoyancy and specific\\ngravity.\\n114. The Specific Gravity of the Human Body. There is\\na great difference in the density of the human body. In\\nfat persons it is less and in thin persons more, but the gen-\\neral average may be stated at .89. All persons ought,\\ntherefore, to float; yet many drown each year by taking\\nwater into their lungs until the specific gravity rises above\\n1. It is well known that the bodies of persons who have\\ndrowned float again a few days after death. This is due to\\nthe inflation of the bodies with gases produced by decom-\\nposition.\\nThere are salt lakes where the density of the water is\\nso great that the human body can not sink. The Great\\nSalt Lake in Utah is such a place, and also the Dead Sea in\\nPalestine.\\n115. How Iron Ships Float. Modern ships are some-\\ntimes built of iron or steel, specific gravity 7.75, but being", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0125.jp2"}, "124": {"fulltext": "104 PHYSICS\\nhollow they displace, without sinking to a very great depth,\\nan amount of water that easily equals their own weight.\\nWe sometimes hear that a certain ship is of 10,000 tons\\nburden or displacement. This is the weight of the water\\nwhich it displaces. This must be the buoyant force of the\\nwater and therefore the total weight of ship and cargo.\\nOne cubic foot of water weighs about 62.5 pounds. Ten\\nthousand tons of water would fill a tank 400 feet long, 40\\nfeet wide, and 20 feet deep. These dimensions are not so\\ngreat as some of our largest ocean steamers. By building\\nthe ship in water-tight compartments it is practically un-\\nsinkable. In case of collision one or more compartments\\nmay be broken open and the ship settle considerably, but\\nthe displacement of the other compartments will still keep\\nit afloat.\\n116. Stability of Floating Bodies. There are two points\\nto be considered with reference to the stability of floating\\nbodies. The center of gravity\u00e2\u0080\u0094 that is, the point of appli-\\ncation of the downward force and the point of application\\nof buoyancy the upward force. This latter must be the\\ncenter of mass of the submerged portion. The center of\\ngravity and the center of buoyancy must always be in the\\nsame vertical line, for otherwise, the forces being equal and\\nparallel, we should have a couple (see page 68), and rota-\\ntion would bring the two forces into line. When the cen-\\nter of gravity is below the center of buoyancy and in its\\nlowest possible position the equilibrium is stable. When\\nthe center of gravity is above the center of buoyancy or is\\nnot in its lowest possible position, the equilibrium is un-\\nstable and the floating body will capsize if in doing so the\\ncenter of gravity can assume a lower position. The danger\\nin standing up in a canoe or other light boat is that in\\ndoing so the center of gravity of the system is lifted above\\nthe center of buoyancy. Yachts have keels of lead pro-\\njecting far down into the water so as to carry the center of\\ngravity as far below the center of buoyancy as possible.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0126.jp2"}, "125": {"fulltext": "CHAPTEK XV\\nFRESSURE IN GASES\\n117. General Behavior of Gases. In their general me-\\nchanical behavior, gases differ from liquids only in being\\nsensibly compressible and infinitely expansible. They all\\nexert pressure because they all have weight.\\n118. Second Principle. (a) Pressure in gases increases\\nwith the depth, but is not proportional to it. (b) At any\\ngiven depth the pressure is equal in all directions.\\n119. The Atmosphere. We speak of tumblers, pails, and\\nother hollow vessels as being empty when they contain only\\nair but a very little examination shows us that the air is a\\nvery real substance, and that we must take account of it\\nquite as seriously as of brick and mortar. A tumbler turned\\nupside down and thrust into water is not filled by the water,\\nfor the air is already there and excludes the water.\\nFor us the air is an ever-present reality, for we live at\\nthe bottom of an aerial ocean, which is estimated to be\\nmore than two hundred miles deep. Those of us who live\\nat the sea level are at the bottom of this ocean, where the\\npressure is greatest. Those who live at places like Denver\\n(about five thousand feet high) or Leadville (about ten\\nthousand feet) are less deep in this ocean of air, and are\\nunder considerably less pressure than we are. Men, ani-\\nmals, and plants are no doubt affected to some extent by\\nthe variation in atmospheric pressure at different heights\\nupon the earth s surface. It will not do to forget the\\natmosphere, or leave it out of the count, whether we are\\n105", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0127.jp2"}, "126": {"fulltext": "106 PHYSICS\\ndealing with energy and matter, or with animals and plants.\\nIt is an ever-present and ever-variable fact.\\n120. Weight of Air. Light as air used to mean light\\nas nothing. Aristotle, the encyclopaedia of the ancient\\nworld, had hinted that air might have weight but in gen-\\neral to the early philosophers air and space were about the\\nsame thing. Galileo and Guericke showed that air, like all\\nmatter, has appreciable weight. If a glass globe holding\\n1 litre, 1,000 cubic centimetres, be exhausted of air and\\nweighed, then refilled with air and weighed, the difference\\nin weight, if the experiment be made at the sea level and\\nat the temperature of freezing water, will be found to be\\n1.293 grams. This represents the weight of 1 litre of dry\\nair under normal conditions. Hence 1 centimetre of air\\nweighs .001293 gram, and this number represents the den-\\nsity of air (page 43). The density of water is 773 times as\\ngreat. In the same way we may find the weight of one\\nlitre of hydrogen, .089 gram, or of one litre of oxygen, 1.429\\ngrams, or of one litre of any other gas. These numbers\\ndivided by 1,000 will give the density of the gas. It is\\nmore common to speak of their specific gravity, however.\\nThis is their density divided by the density of air.\\n001 9Q3 69 s P ec c g ravr ty of hydrogen.\\n.001429 K\\n001293 1-1056 specific gravity of oxygen.\\nOr, knowing the weight of one litre of dry air, and the spe-\\ncific gravity of a gas, we can readily calculate the weight of\\none litre of the gas.\\nThus 1.293 gr. X sp. gr. of gas wt. of 1 litre of the gas.\\n1.293 gr. X .069 .089 wt. of 1 litre of hydrogen.\\nA cubic foot of air weighs about 1.28 ounces. Thus, the\\nair in a lecture-room 40 X 50 X 25 feet weighs about two\\ntons. Imagine the air of such a lecture-room moving across\\nthe country at the rate of seventy-five miles an hour, as it", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0128.jp2"}, "127": {"fulltext": "PRESSURE IN GASES\\n107\\nmight in a hurricane. It is easy to conceive that two tons\\nof air moving at such velocity might dislodge some build-\\ning, or uproot some trees, or pile up sand or snow or sea,\\nor drive furiously a heavy sailing vessel and the fact that\\nit moves with such momentum impresses us not only that\\nit has velocity but also weight.\\n121. The Barometer. Over two hundred and fifty years\\nago (1613) Torricelli, a pupil of Galileo, conceived a plan\\nfor measuring the pressure of the\\natmosphere so simple and direct and\\nso altogether excellent that it has\\nbeen used ever since. A straight glass\\ntube (Fig. 59), about one metre long\\nand about five millimetres in diam-\\neter, is closed at one end and com-\\npletely filled with mercury. The open\\nend is then closed by the thumb, and\\nthe tube inverted. It is thrust\\nJ under the surface of a bath of\\nmercury and the thumb with-\\ndrawn, as soon as all com-\\nmunication with the air is\\nclosed off. The mercury in\\nthe tube falls a little,\\nand after a few oscilla-\\ntions comes to rest at a\\npoint many centimetres\\nabove the level of mer-\\ncury in the bath. We Fig. 59.\\nHi represent this height\\nU by h. At the sea level, under usual conditions of\\nFig. 60. weather, and at the freezing point, it is seven\\nhundred and sixty millimetres. The simple form,\\nrepresented in Fig. 60, is much in use. Such an instru-\\nment is known as a barometer (pressure gauge). Let us\\nconsider the forces at work. On the free surface of the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0129.jp2"}, "128": {"fulltext": "108 PHYSICS\\nmercury there is manifestly the downward pressure of the\\natmosphere. This is transmitted, and acts upward in the\\ntube at the same level with undiminished intensity. Here\\nit meets a downward force, the weight of a column of mer-\\ncury of height h. As the mercury in the tube stands still,\\nthe two forces must be equal. As h would be the same,\\nwhatever the cross-section of the tube, let us consider it to\\nbe 1 sq. cm. The weight of a column of mercury 76 cm.\\nhigh and 1 sq. cm. in cross-section is manifestly the weight\\nof 76 cubic cm. of mercury. As the density of mercury is\\n13.596, the weight of 76 cubic cm. must be 76 X 13.596\\n1033.296 grams. This, then, is the pressure exerted by the\\natmosphere on every square centimetre of surface, and is\\ncommonly called one atmosphere.\\nThe pressure of the atmosphere is thus expressed as\\nweight. It may be expressed as force by multiplying the\\nresult by g, since F ma mg. 1033.296 X 980 1,012,630\\ndynes (pages 52 and 55).\\nThe barometer is like a pair of weighing balances where\\nliquid pressure upon one scale-pan counterbalances gaseous\\npressure upon the other scale-pan.\\nIn English units h, under normal conditions, is about\\nthirty inches. If we consider the barometer to have a\\ncross-section of one square inch, the atmospheric pressure\\nper square inch must be the weight of thirty cubic inches\\nof mercury, or 14.7 pounds. Hence, it is common to say\\nthat the atmospheric pressure is fifteen pounds to the\\nsquare inch. In one convenient form of barometer, For-\\ntin s (Fig. 61), the cistern has a flexible bottom, and a little\\nivory pointer establishes the level of the mercury. A\\nscrew in the lower part of the cistern makes it possible to\\nraise and lower the flexible bottom, and so adjust the level\\nof the mercury to the pointer. This forms the zero of the\\npermanent scale. By means of the sliding vernier at the\\ntop of the barometer tube (Fig. 62) the reading may be\\ntaken directly and with great accuracy.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0130.jp2"}, "129": {"fulltext": "PRESSURE IN GASES\\n109\\nOther liquids may be used in a barometer. The special\\nadvantage of mercury is that its great density makes the\\ncolumn conveniently short. Its disadvantage is that the\\nvariations in h are correspondingly\\nsmall. In a water barometer we have\\nthe reverse conditions, an inconvenient-\\nly long column, 76 cm. X 13.596\\n1033.296 cm., and large variations in h.\\n122. The Aneroid Barometer. The\\nmercury barometer is the most accu-\\nrate form that we can have. It is,\\nhowever, not conveniently portable,\\nand where observations are to be made\\non top of a high mountain or other\\nspot of difficult access, the aneroid\\nbarometer is often substi-\\ntuted. In this the atmos-\\nphere acts against the flex-\\nible corrugated metal cover\\nof a sealed box (Fig. 63).\\nThe greater the pressure,\\nthe more the flexible cover\\nwill be forced in. Its mo-\\ntion is transmitted by a\\nsystem of delicate levers\\nto a light pointer, which\\nmoves over the surface of\\na graduated circle. The\\nreading is made directly\\nin millimetres of mercury,\\nthe graduation being effect-\\ned by comparison with a *venderT\\nstandard barometer.\\n123. Variations in Atmospheric Pressure.\u00e2\u0080\u0094 The pressure\\nof the atmosphere is always changing. The barometer\\nrecords this change, and serves us in a double capacity. If\\nFig. 61.\u00e2\u0080\u0094 Fortin s\\nbarometer.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0131.jp2"}, "130": {"fulltext": "110\\nPHYSICS\\nthe barometer be fixed, it records the change at any one\\nspot; if the barometer be taken to different elevations\\nabove the sea, it tells us\\nthe elevation by means\\nof the change.\\nFirst. If the ocean\\nof air covering the earth\\nwere allowed to come\\nto rest we should have\\nfinal equilibrium, when\\nthe pressure was exact-\\nly the same at the same\\naltitude all over the\\nworld. In that case, a\\nfixed barometer would\\nalways give the same\\nreading, and, once\\ntaken, the barometer\\nwould be of no further\\nBut we all know that the air is far from being at\\nrest. It is almost constantly in motion. The rotation of\\nthe earth and the difference of temperature set up cur-\\nrents and counter-currents in this aerial ocean that give us\\nall the phenomena of wind, from gentlest zephyr to fiercest\\nhurricane. But the effort at equilibrium goes on just the\\nsame, and the barometer has much to say about our prob-\\nable weather.\\nA low barometer indicates storm, because it means\\nthat air from surrounding regions will rush in to restore\\nequilibrium, and will probably cause precipitation rain,\\nsnow, hail, sleet according to the season. A high or rising\\nbarometer means fair weather, because it indicates a flowing\\naway of air from that spot, and consequently freedom from\\noutside influence.\\nThe Weather Bureau at Washington receives daily tele-\\ngrams from all the signal stations throughout the country\\nFig. 63.\\nservice.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0132.jp2"}, "131": {"fulltext": "\\\\^**^^^jr^^iL*\\ncS\\nJ\\n10\\n^^c^^^-^p^ \\\\j\\nS\\\\jS\\\\ f \u00c2\u00a3-\\\\l x\\n/sY\\\\i Tv ji\\nA\\nvSs^ *x^x\\\\ i\\nA\\n7\\nr\\n4\\n\\\\V4~~ ^f\\np!s\u00c2\u00bb sii\\nj-^jL\\nf\\nv ^v X^V\\n1\\ny^K\\nci\\nx. i\\\\\\nV x.\\n0*\\ny\\nj T u\\nis? r\\n/w\\n^y\\nJ/A l\\n3\\nW\\ni 1\\n1\\nV\\nS \\\\jr// N.\\nyTy/\\nf i\\nj\\nfl\\\\^^\\\\ I\\nJ\\nwL A\\n1\\nlTx\\ns~\\ni I i^\\n\u00e2\u0096\u00a0^-r ^7 W^\\nI 1\\nv 1 7 xf^\\n1\\n1\\nX. sf s\\nvT~vl\\\\\\nC ^s^.y\\nM\\\\\\nr\\n*^l y\\n4r*", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0133.jp2"}, "132": {"fulltext": "112 PHYSICS\\nstating the barometer and other climatic conditions. These\\ndata are at once put down on the map so that one can see\\nthe conditions over the whole country at a glance. Lines\\njoining places of the same pressure are called isobars.\\nThese lines are found to curve about certain centers. The\\naccompanying weather map (Fig. 64) illustrates the actual\\nconditions of the atmosphere with respect to pressure in all\\nparts of the United States on a certain day and hour.\\nSecondly. The variations in pressure at any one spot\\nare small compared with its variations when taken to differ-\\nent heights. If the atmosphere were of uniform density\\nthroughout, like an ocean of water, it would be about five\\nmiles high and the elevations in it would be directly pro-\\nportional to pressure but on account of its compressibility\\nand variations in the temperature the density of the atmos-\\nphere is very far from uniform, and a somewhat compli-\\ncated formula must be used to get the exact height. The\\natmosphere is naturally much denser near the surface of\\nthe earth, since it is here under greater pressure. Half the\\natmosphere is within three and a half miles of the earth,\\nsince at that elevation, about 5^ kilometres, the barometer\\nstands at 38 centimetres. For moderate altitudes the fall\\nof h is about 1 centimetre for an ascent of 100 metres.\\n124. Boyle s Law. On account of the perfect compressi-\\nbility and elasticity of gases their volume changes with the\\nleast change of pressure. Boyle in England and Mariotte\\non the Continent found that the volume of a gas is in-\\nversely proportional to the pressure it supports, or, in other\\nwords, that the product of pressure and volume, p v, is\\nalways constant.\\np v p v \u00e2\u0080\u0094p v.\\nThis can readily be shown experimentally. For pres-\\nsures greater than one atmosphere, Figs. 65 and 66 represent\\nconvenient forms of apparatus. The latter consists of two\\nshort pieces of glass tubing connected by rubber tubing.\\nThe lower piece of glass tubing is closed at c. Mercury fills", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0134.jp2"}, "133": {"fulltext": "PRESSURE IN GASES\\n113\\nthe tubing from a to b. The arm a is lowered until the\\nmercury stands at the same level in both arms. The length\\nof the column of air b c is then noted while\\nit is under the pressure of the atmosphere\\nalone. The arm a is then raised until the\\nmercury at a is, say, thirty inches higher\\nthan at b. The air b c is then under the\\npressure of two atmospheres, and it will be\\nfound to have contracted to one half its\\noriginal volume. If the difference in level\\nbetween a and b is made fifteen inches, the\\npressure will be three halves of an atmos-\\nphere and air will be compressed to two\\nthirds its original volume. If the pressure\\nis made four thirds of an\\natmosphere, the volume\\nwill be reduced to three\\nfourths, etc.\\nFor pressure less than\\nan atmosphere, Fig. 67 rep-\\nresents the way the appara-\\ntus is used. Suppose a is\\nfifteen inches below b, then\\nthe pressure upon the air\\nb c is one atmosphere minus\\nhalf an atmosphere i. e.,\\nthe pressure is reduced to\\none half and the volume\\nwill be increased to 2. If\\na is made twenty inches be-\\nFig. 66. Fig. 67. low b, the pressure will be\\none third and volume 3, etc.\\nThis is Boyle s law, which may be stated in words as\\nfollows If the temperature be constant, the volume of a\\nbody of gas varies inversely as the pressure. The law is not\\nabsolutely correct, the variation being greatest in case of\\n9\\nFig. 65.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0135.jp2"}, "134": {"fulltext": "114\\nPHYSICS\\nthose gases like ammonia and carbon dioxide that are easily\\nliquefied.\\n125. Closed Pressure Gauges. For many purposes it is\\ndesirable to measure the pressure of a gas, as the pressure of\\nsteam in a boiler, the pressure of illumi-\\nnating gas in a main, the pressure of air\\nin the air blast of a furnace, and the like.\\nIf the pressure is but slightly in excess of\\none atmosphere the pressure gauge may\\nbe open. The reading is generally given\\ndirectly in millimetres of mercury. For\\nlarger pressures the closed pressure gauge\\nis more convenient (Fig. 68). The pres-\\nsure is measured by the decrease in the\\nvolume of the inclosed air. Such an in-\\nstrument is practically a balance\u00e2\u0080\u0094 on one side the elasticity\\nof the air, on the other side the pressure of the gas.\\n126. Buoyancy of Air. It has already been stated that\\nbodies immersed in any fluid, whether liquid or gas, are\\npressed upward with a\\nforce just equal to the\\nweight of the fluid dis-\\nplaced. In the case of\\nair, if the bodies are\\nheavy, the buoyancy is so\\nslight that it is common-\\nly neglected but in very\\naccurate weighing the\\nweight of an equal vol-\\nume of air must always\\nbe added to the apparent\\nweight of a body, since its\\nreal weight is reduced by just that amount. True weight\\nis therefore the equivalent of weighing in a vacuum. This\\nbuoyancy can be shown experimentally by a balanced hol-\\nlow sphere (Fig. 69). When it is placed under the receiver\\nFig", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0136.jp2"}, "135": {"fulltext": "PRESSURE IN GASES 115\\nof an air pump and the air exhausted, the sphere shows\\nitself to be heavier than its counterpoise.\\n127. Balloons. The principle of aerial buoyancy also\\nmakes it possible for us to construct air ships and balloons\\nthat will float and even remain at varying heights at our\\nwill. If we know the dimensions of a balloon and the gas\\nwith which it is filled, we can easily calculate its buoyant\\nforce.\\nExample. What weight will a spherical balloon 20\\nmetres in diameter and filled with hydrogen gas support at\\nsea level Let the conditions be normal.\\nVolume ttD 3 X 3.1416 X (2,000) 3\\n4,188,800,000 cubic centimetres or 4,188,800 litres.\\nWeight of 1 litre of air 1.293 grams.\\nWeight of 1. litre of hydrogen .089 grams.\\nBuoyant force of air upon 1 litre of H 1.204 grams.\\nBuoyant force of the air upon the balloon\\n4,188,800X1.204 5,043,315 grams.\\n5,043.3 kilograms (about 5-J- tons).\\nTo find the available uplift we must, of course, subtract the\\nweight of the silk envelope, cordage, car, and other para-\\nphernalia. Those who know how to make H, and how to\\ncalculate quantities in chemistry by means of atomic\\nweights, can readily calculate how much Zn would have\\nto be dissolved in acid in order to fill such a balloon.\\nVolume of balloon 4,188,800 litres.\\nWeight of 1 litre of H .089 grams.\\nWeight of total H 4,188,800 X .089 252,802.2 grams.\\nXow for the chemical part Zn H 2 S0 4 ZnS0 4 -f 2H.\\nEach atom of Zn dissolved liberates 2 atoms of H, and 65\\ngrams of Zn will yield 2 grams of H, and hence 32| times\\n252,803.2 grams of Zn will be required, or 4,108 kilograms\\n(about 4^ tons). Thus the original question might take\\nthis form How much Zn must be dissolved in acid in\\norder to produce enough H to fill a balloon that is to have\\na buoyant force of 1,000 kilograms", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0137.jp2"}, "136": {"fulltext": "116 PHYSIOS\\nIt follows from the fact that the air is compressible, that\\nthe balloon, if its volume were constant, would displace a\\ngreater weight of air at sea level than at an elevation. If\\nwe desire the balloon to float near the earth s surface we\\nmay load it with bags of sand, and if we desire it to rise to\\ngreater heights we throw out these bags of sand. When\\nwe desire the balloon to descend we open a valve and let\\nout some of the gas with which it is inflated, thus decreas-\\ning its displacement.\\nProblems. 1. What will be the weight of one litre of carbonic-\\nacid gas, the specific gravity being 1.53\\n2. Which is absolutely the heavier, a pound of feathers or a\\npound of gold, and why\\n3. If a body of gas occupy 1.2 litres, when h 760 millimetres,\\nwhat will be its volume when h 748 millimetres\\n4. A steel cylinder 3 feet high and 16 inches in diameter is rilled\\nwith oxygen gas. The pressure gauge shows that the gas has a\\ntension of 240 pounds per square inch. How much space would\\nthis gas occupy if allowed to escape into the atmosphere under nor-\\nmal conditions", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0138.jp2"}, "137": {"fulltext": "CHAPTEE XVI\\nTRANSMISSION OF PRESSURE IN FLUIDS\\n128. The Transmission of Pressure. Chapter XIV dealt\\nwith pressure in liquids, and Chapter XV with pressure in\\ngases. It must not be overlooked that the study of pres-\\nsure in gases was to a large extent a review or reiteration\\nof the first principle stated in section 108. Gases are\\nseparated from liquids in this discussion because they are\\ncompressible, while liquids are not. The third principle,\\nwhich we are about to take up in this chapter, is equally\\napplicable to both liquids and gases, and is merely a more\\nextended discussion of what was first presented in sec-\\ntion 109.\\nWhen pressure is exerted on a rigid solid the pressure\\nis transmitted in a straight line from the point of applica-\\ntion of the pressure to the point of support of the solid.\\nThis is very obvious. When pressure is exerted on a fluid\\nprecisely the same thing takes place, but and this is the\\nimportant matter where is the point of application of the\\npressure on a fluid, and where is the point of support of\\nthe fluid If we can answer these two questions we shall\\nhave the main facts about the mechanics of fluids.\\nFirst, as to the point of application. This can not be a\\npoint at all, since a point would simply penetrate the fluid\\nby pushing its molecules aside, and would exert no pressure\\nwhatever. Xo pressure can be exerted on a fluid except by\\nan extended surface, and only then if the surface be moved\\nagainst the fluid so rapidly that the fluid has no chance to\\n117", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0139.jp2"}, "138": {"fulltext": "118 PHYSICS\\npush by and escape, or by having the surface act against\\nthe fluid in a fluid-tight vessel. The first method is used\\nin the blade of an oar, paddle wheel, propeller screw, or\\nrudder, where pressure is exerted against water. In a\\nwindmill the same method is applied to the air. Observe\\nthat it makes no difference whether the surface is forced\\nagainst the fluid, as in oar and paddle, or the fluid is forced\\nagainst the surface, as in rudder and windmill. The sec-\\nond method of getting hold is well illustrated by the pres-\\nsure of the piston upon the confined air in a bicycle pump.\\n129. Third Principle. Pressure exerted upon a fluid\\n{liquid or gas) inclosed in a vessel is transmitted equally in\\nall directions, the total pressure upon the walls of the vessel\\nbeing proportional to the area.\\nA person applies his mouth to one arm of the mercury\\npressure gauge and finds that he is capable of exerting\\nwith the air from his lungs a pressure sufficient to support\\na column of mercury three inches high a pressure which\\nwe have learned (section 107) to designate as one and a\\nhalf pounds pressure per square inch; if he now applies\\nhis mouth to two pressure gauges at the same time with\\nan effort equal to that used before, he may make each of\\nthem register three inches, or one and a half pounds per\\nsquare inch. In the same manner he may exert pressure\\nupon any number of pressure gauges simultaneously, and\\nfind that it is as easy to hold up a hundred columns of mer-\\ncury as it is to hold up one. There should be no paradoxes\\nin physics. The statement of this third principle has been\\nwithheld until now in order that its truth should appear\\naxiomatic rather than paradoxical. Should any one find\\nthis principle obscure he is advised to review Chapters XIV\\nand XV.\\nIf a certain definite pressure is exerted upon a gas in-\\nclosed in a vessel, one, two, or any number of pressure\\ngauges may be inserted in top, bottom, and sides of that\\nvessel and all will be found to indicate the same pressure.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0140.jp2"}, "139": {"fulltext": "TRANSMISSION OF PRESSUEE IN FLUIDS\\n119\\nFig. 70.\\nIf the fluid had appreciable weight, as would be the case\\nwith a liquid, the pressure gauge would, of course, iudicate\\nthat iu addition to the given external pressure, and they\\nwould vary according to the depth of the liquid.\\nSuppose rubber cloth is tied air-tight over the top of a\\njelly-cake tin (Fig. 70), the diameter of which is ten inches.\\nA tube is inserted air-tight into\\nthe side of the tin a board is\\nlaid on top, and a weight placed\\nupon it. A person who applies\\nhis mouth to the tube and exerts\\na pressure from his lungs of one and a half pounds per\\nsquare inch may have the novel experience of lifting about\\n118 pounds by the breath of his mouth. It is, of course,\\nunderstood that the weight is to be only just started to\\nrise, and not lifted any appreciable distance, in which case\\nthe tension of the rubber cloth may be neglected.\\nThe applications of the principles of fluid pressure in\\npractical life are very numerous and important. They may\\nbe analyzed in the same way as machines (section 98).\\nPower put in, minus friction work got out\\npd w s.\\n130. Hydrostatic Press. This depends upon Pascal s prin-\\nciple that fluids transmit pressure equally in all directions,\\nand was one of the first and most\\nfamous applications of that prin-\\nciple. If a pressure of 100 kilo-\\ngrams be exerted upon a small\\npiston (Fig. 71) having a cross-\\nsection of 1 square centimetre,\\nand if the large piston P have a\\ncross-section of 80 square centi-\\nmetres, it is clear that the up-\\nward pressure exerted on P will\\nbe 80 x 100 8,000 kilograms.\\nFig. 71. The hydrostatic press gives us a", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0141.jp2"}, "140": {"fulltext": "120 PHYSICS\\nmeans of exerting enormous pressures with comparatively\\nsmall forces. It must be remembered, however, that the\\nprinciple of work comes in that is, virtual velocities,\\npd ws, and that what we gain in force we lose in space.\\nIn the present example P exerts a pressure eighty times as\\ngreat as the pressure acting on p, but it only moves through\\none eightieth of the distance that p does. The press is\\nused in some form in nearly every large engineering and\\nindustrial operation. It is also used to compress cotton,\\nhay, and other substances, to extract the oil from seed, and\\nto perform many other useful and Herculean labors.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0142.jp2"}, "141": {"fulltext": "CHAPTER XVII\\nAPPLICATIONS OF PRINCIPLES OF FLUID PRESSURE\\n131. The Density of Milk. Cream is lighter than milk\\nfor this reason it floats npon the top of the milk. Skimmed\\nmilk is therefore heavier than whole milk, and it is evident\\nthat whole milk coming from different\\ncows, and from the same cow at differ-\\nent times, must differ in specific grav-\\nity as the proportion of cream varies.\\nThe lactometer is an instrument for\\ndetermining approximately the amount\\nof cream in the milk by taking its spe-\\ncific gravity, which in fairly good milk\\nought to he about 1.032. It will be\\nnoticed that water is also lighter than\\nmilk, so that it is possible for the milk-\\nman to rob the cream from the milk\\nand then restore it to its proper spe-\\ncific gravity by adding water. This\\nfraud must be detected by the intelli-\\ngence of the customer acting together\\nwith the lactometer.\\n132. The Bottle Imp, or Cartesian\\nDiver. Many historic pieces of appa-\\nratus which were for years the idols\\nof physical museums, but which have\\nrather fallen into disfavor because they served no better\\npurpose than to mystify pupils, may be made interesting\\n121\\nFig. 72.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0143.jp2"}, "142": {"fulltext": "122\\nPHYSICS\\nFig. 73.\\nand properly instructive when used as a means of corre-\\nlating principles which are thoroughly understood. The\\nbottle imp, or Cartesian diver (Fig. 72), always has an air\\nchamber, sometimes concealed, within the body. This cham-\\nber contains just enough air to float the ob-\\nject. The chamber communicates with the\\nwater outside by a very narrow passage. If\\nany extra pressure is exerted upon the water\\nsome of it is forced into the chamber con-\\ndensing the air. The buoyant force is thus\\ndecreased and the object sinks. When the\\npressure is removed the air expands again,\\nand the object rises.\\n133. Magdeburg Hemispheres. The pres-\\nsure of the air is strikingly illustrated by\\nthe apparatus (Fig. 73) invented by Otto\\nvon Guericke, burgomaster of Magdeburg.\\nThe hemispheres should be made to fit to-\\ngether air-tight by smearing vaseline around the edges.\\nOrdinarily they separate with perfect ease, but when the\\nair has been exhausted from within they are held together\\nby a pressure of fifteen pounds per square inch and if\\ntheir diameter is about four inches it will require a pull\\nof nearly two hundred pounds to separate them.\\n134. The Relation of Tension and Pressure. It is helpful\\nto think of the air in a bottle as a coiled spring (Fig. 74).\\nIf a weight of fifteen pounds rests upon the spring its ten-\\nsion is fifteen pounds. By\\nthis we mean the force\\nwith which it tends to ex-\\npand. If now the weight\\nbe reduced to ten pounds\\nthe spring will expand un-\\ntil its tension is ten pounds.\\nIf the weight be reduced\\nto five pounds the spring Fig. 74.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0144.jp2"}, "143": {"fulltext": "PRINCIPLES OF FLUID PRESSURE 123\\nwill expand until its tension is only five pounds, etc. The\\ntension must always equal the pressure in order that there\\nmay be equilibrium. The air acts like this spring, but it dif-\\nfers in that it is indefinitely expansible. We may think of air\\nin a bottle as being condensed in there under a pressure of\\nfifteen pounds per square inch. Its tension or outward push\\nupon the walls of the bottle is thus fifteen pounds per square\\ninch. If the pressure be reduced, one half the air will ex-\\npand until half of it has been pushed out of the bottle.\\n(See Boyle s Law, 124.) Its tension will then be only seven\\nand a half pounds per square inch, etc.\\n135. Bacchus Illustration.\u00e2\u0080\u0094 This relation of tension and\\npressure is nicely illustrated by the apparatus which used\\nto be called Bacchus illustration (Fig. 75). The tension of\\nthe air in the upper part of the bottle is, say, fifteen\\npounds per square inch. This would push the\\nwater out of the curved tube if the atmospheric\\npressure from without did not balance it. If now\\nwe place this bottle under a receiver and reduce j^~7 5\\nthe atmospheric pressure, or if it were carried up\\nin a balloon into reduced atmospheric pressure, the tension\\nof the air within would drive out a stream of water. If by\\nany means the tension of the air within is reduced, or the\\npressure of the air outside is increased, water passes into\\nthe bottle.\\n136. Siphon Bottles, Fire Extinguishers, Compressed-\\nair Motors, and Explosives. It is manifest that the so-\\ncalled siphon bottles depend upon gas compressed\\nwithin so as to have a much greater tension than fifteen\\npounds per square inch to drive out the liquid. This gas\\nis carbon dioxide, and the pressure is frequently 140\\npounds per square inch. Many kinds of fire extinguishers\\nillustrate this same principle. Some depend upon air com-\\npressed within them to throw the liquid upon the fire.\\nAmmonium carbonate dissolved in water makes a very\\ngood liquid for this purpose. Others depend upon carbon-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0145.jp2"}, "144": {"fulltext": "124 PHYSICS\\ndioxide gas generated at the right moment within the\\napparatus to supply the tension which shall throw this\\nstream.\\nAir guns and all the various forms of compressed-air\\nmotors operate by the difference between the tension of the\\nair from within and the pressure of the air from without.\\nFor example, if a cylinder with the capacity of two cubic\\nfeet has forty cubic feet of air compressed within it, its ten-\\nsion, according to Boyle s Law, will be 300 pounds per\\nsquare inch. This operating against an atmospheric pres-\\nsure of fifteen pounds per square inch would give a working\\nforce of 285 pounds per square inch.\\nAll guns operate by the same principle as air guns that\\nis, the force which projects the bullet is the tension of\\ngreatly compressed gases. The explosives used generate a\\nlarge volume of gases in a confined space.\\n137. Diving Bells and Caissons. Diving bells have a ten-\\nsion of air within equal to the pressure of both water and\\natmosphere from without. The same principle is illustrated\\nin the use of caissons for laying foundations under water.\\nTunnels are built through the mud under rivers, the work-\\nmen operating through holes in a huge steel cylinder, the\\ntension of the air within being made sufficiently great to\\nbalance the pressure of mud, water, and atmosphere from\\nwithout. This balance was so nicely adjusted in the work\\non the Hudson Eiver Tunnel that the tension of the air\\nwithin was continually changed to correspond with the\\nvarying water pressure due to the rise and fall of the tide\\nin the river.\\n138. The Eardrum.\u00e2\u0080\u0094 The inner chamber of the ear, like\\nall other cavities of the body, is filled with air, or gases,\\nhaving a tension equal to atmospheric pressure. In order\\nthat the membrane which is stretched across the tube be\\nfree from stress, the volume of the inside air must remain\\nconstant, and this can be done only by having its tension\\nvary according to changes of atmospheric pressure. This", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0146.jp2"}, "145": {"fulltext": "PRINCIPLES OF FLUID PRESSURE 125\\nis accomplished by the Eustachian tube, which communi-\\ncates between the throat and the inner chamber of the ear.\\nWhen atmospheric pressure increases, air is forced in\\nthrough this fleshy tube until the tension within equals\\nthe pressure from without. When atmospheric pressure\\ndecreases, air passes out by the same channel. A cold in\\nthe head sometimes clogs this channel then we experi-\\nence disagreeable sensations about the ears, caused by the\\nsagging in or bulging out of the membrane of the ear, due\\nto inequality between the tension within and atmospheric\\npressure without.\\nPersons who are about to pass into a caisson are advised\\nto try to force air out of their lungs while holding the nose\\nand mouth closed. Why? Try it under ordinary atmos-\\npheric conditions, and explain the physical cause of the\\npeculiar sensation in the ear. Persons about to come out of\\na caisson are advised to close the mouth and hold the nose\\nshut, and perform the act of swallowing. Why Try this\\nalso under ordinary atmospheric conditions, and explain\\nthe physical cause of the peculiar sensation in the ear. It\\nwill be a more striking experiment if you swallow a mouth-\\nful of water or of food. Did you ever have a similar sensa-\\ntion during eating, while suffering from a cold in the\\nhead\\n139. The Physics of Respiration. A similar adjustment\\nof tension to pressure is made in the act of breathing. By\\nthe contraction of certain muscles we are able to force the\\nribs upward and outward, and to depress the diaphragm.\\nThis enlargement of the chest cavity would produce a\\nreduced tension of the gases within, if atmospheric pres-\\nsure did not maintain the balance by pushing more air\\nin, and thus inflating the lungs. By the contraction of\\ncertain other muscles we are able to contract the chest\\ncavity. This would result in increased tension of the gases\\nwithin, if they did not flow out at a rate to maintain the\\nbalance.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0147.jp2"}, "146": {"fulltext": "126\\nPHYSICS\\n140. How Atmospheric Pressure upon the Human Body is\\nsustained. From this discussion it is manifest that the\\nstory is only half told when one speaks of the enormous\\npressure of thousands of pounds which the atmosphere\\nexerts upon the human body. The other half, which\\nshould be coupled with this statement, is that all the tis-\\nsues of the body are permeated by gases which have a ten-\\nsion exactly equal and opposite to the atmospheric pressure;\\nand that while the communica-\\ntion between all bodily cavities\\nis not as free as in the cases of\\nlungs and eardrum, there is a\\nsomewhat slower communica-\\ntion by the process of osmose, by\\nwhich the balance between ten-\\nsion from within and pressure\\nfrom without is always main-\\ntained. As might be expected,\\nsudden and great changes in\\npressure, as one who goes up in\\na balloon experiences, occasion\\npainful sensations before the in-\\nternal tension has had time to\\nadjust itself. The tissues of the\\nbody in ordinary circumstances\\nare under no more stress from\\natmospheric pressure than a very\\nthin glass flask or a delicate tis-\\nsue-paper bag whose mouths are open. Manifestly these\\nare not enduring great stress from atmospheric pressure.\\n141. The Fountain in Vacuo. The apparatus illus-\\ntrated in Fig. 76 shows again the relation of tension and\\npressure. If the tension of the air or any other gas inside\\nthe bottle be reduced by the action of a pump, or the\\ncontraction of the gas by cold, or the absorption of some\\nof the gas by a substance introduced for that purpose, at-\\nFig. 76.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0148.jp2"}, "147": {"fulltext": "PRINCIPLES OP FLUID PRESSURE\\n127\\nmospheric pressure from without will force the water in\\nthe lower vessel to rise until the volume of the gas inside\\nshall be reduced so that its tension may equal the pressure\\nupon it. Manifestly the water which\\nenters the bottle is very nearly a meas-\\nure of the amount of air removed.\\n142. Pumps. It goes without say-\\ning that pumps have to deal with both\\nclasses of fluids liquids and gases.\\nWe may take water pumps and air\\npumps as the two types. Both involve\\nthe same principle, but there are dif-\\nferences in form and construction that\\ndeserve notice. The most common\\nform of water pump is the so-called\\ncucumber pump, in which the pipe\\nleading down into the well is simply a\\nhollow length of cucumber wood. The\\nrod attached to the pump handle has\\na piston at its lower end provided with\\na valve (a) opening upward (Fig. 77).\\nAt a given point somewhat below the\\nlowest possible position of the moving\\npiston, there is a valve (b) also capable\\nof opening in an upward direction\\nonly. The valves are the essential\\npart about such a pump. The action\\nis very simple. hen the pump is at rest, both valves a\\nand b are closed by their own weight. Imagine a down-\\nstroke of the pump rod. The chamber A is filled with air,\\nwhich opens the valve a and escapes. Now picture an up-\\nstroke. The valve a closes, and as the piston rises, increas-\\ning the volume of the space in the chamber between the\\ntwo valves, the tension of the air in this chamber is reduced.\\nAtmospheric pressure, being no longer balanced, presses to\\nenter. The only entrance into the chamber from without\\nFig. 77.\\nCucumber pump.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0149.jp2"}, "148": {"fulltext": "128\\nPHYSICS\\nis by the lower gateway b, and if the lower end of the pump\\ntube dips into water the air will drive the water before it\\nso long as its weight is less than the pressure to be exerted\\nby the air. When enough air from the lower tube has been\\npushed up through b to make the tension in the chamber\\nequal to the atmospheric pressure, minus the pressure of\\nthe column of water which now stands part way up the\\nlower tube, equilibrium is again restored. The next down-\\nand up-strokes repeat the operation until all the air in B is\\nexhausted, and water begins to pass through the valves.\\nThe water that passes a is lifted bodily by the upgoing\\npiston and escapes from the spout. It is plain that B must\\nnot exceed about thirty feet in length, or the pressure of\\nthe atmosphere will not support the column of water, and\\nall our pumping would be in vain.\\nThese cucumber pumps are used in every village and on\\nnearly every farm. The pump has many other forms, but\\nthe principle remains the same. The pump is frequently\\nmade of iron, and in large operations is run by steam.\\n143. Force Pump. The water thrown out by such a\\npump as has been described above falls in intermittent\\nstreams. The more rap-\\nidly the pump is oper-\\nated, the less noticeable\\nthe inequality of the\\nstream. It is possible,\\nhowever, to slightly al-\\nter the construction of\\nthe pump, and make the\\nstream of water reason-\\nably constant. This is\\naccomplished in the so-\\ncalled force pump (Fig.\\n78). As before, there are two valves; one (b) opening up-\\nward into the chamber below the piston, and the other (a)\\nopening out of the chamber into the delivery pipe. This\\nForce pump.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0150.jp2"}, "149": {"fulltext": "PRINCIPLES OF FLUID PRESSURE\\n129\\nlatter pipe does not, however, simply terminate in a spont.\\nIt lias connected with it an air chamber. Picture an up-\\nstroke b opens and water rushes up into the chamber below\\nthe piston. Now, a down-stroke b closes and a opens.\\nDouble-acting pump.\\nWater passes to the air chamber, and thence out of the\\ndelivery tube. The end of the delivery tube is constricted\\nby a nozzle. This offers resistance to the flow of the liquid,\\nand as a result the air in the air chamber is compressed,\\nand continues to force water out of the delivery tube dur-\\ning the next up-stroke of the piston rod. The next down-\\nstroke again opens a and forces water into the air chamber\\nand into the delivery tube beyond. This secures a continu-\\nous and fairly constant stream of water.\\nDouble Pumps. It is usual in the steam pumps to have\\nthe piston double-acting. In this case the piston is com-\\nFig. 79a.\u00e2\u0080\u0094 Typical valves.\\nmonly horizontal, as shown in Fig. 79, and at each stroke\\nof the piston water is drawn into one end of the piston\\n10", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0151.jp2"}, "150": {"fulltext": "130\\nPHYSICS\\nchamber and forced out at the other end. In this way the\\nstream of water is continuous.\\n144. Air Pumps. The air pump serves a double purpose\\nto exhaust the air in a given receiver, and to furnish\\na steady stream of\\nair, just as the force\\npump does of wa-\\nter. The term air\\npump is usually re-\\nserved for instru-\\nments of the first\\nclass, while air com-\\npressor and blow-\\ning engine are used\\nfor the latter. In\\nthe ordinary air\\npump (Figs. 80 and\\n81) the valves are\\njust the same as\\nthose in the water\\npump. The receiver to be pumped out is commonly a glass\\nbell jar resting on a carefully\\nground brass plate, from the\\ncenter of which a tube passes\\nto the cylinder of the pump.\\nThe valve (b) at the end of\\nthis tube opens into the cylin-\\nder. A second valve often\\nfor convenience located in the\\nU piston itself, opens from the\\ncylinder into the atmosphere.\\nAt every up-stroke the air in\\nFig. 8i.-Air pump. the receiver expands into the\\ncylinder at every down-stroke\\nb closes, and the air in the cylinder passes through a into\\nthe outer atmosphere. It is impossible in this way to get a\\nFig. 80.\u00e2\u0080\u0094 Air pump.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0152.jp2"}, "151": {"fulltext": "PRINCIPLES OF FLUID PRESSURE\\n131\\n\u00c2\u00abU^Q\\nperfect vacuum in the receiver, for finally the residual air\\nhas not tension enough to open the valve b. It is also\\nimpossible, theoretically, since any process which removes a\\nfractional part of air then in the receiver must always leave\\na residue of air. A small pressure gauge constructed on\\nthe same principle as the manometer shows exactly the\\namount of residual pressure usually only a few millimetres\\nof mercury. For most purposes the air pump is perfect\\nenough, and allows many interesting experi-\\nments such as removing the air from the\\nMagdeburg hemispheres, from the apparatus\\nknown as the Fountain in Vacuo, etc.\\n145. The Mercury Air Pump (Fig. 82).\u00e2\u0080\u0094\\nThis is constructed on the principle of the\\nbarometer, and what we get is really a Torri-\\ncellian vacuum. As the pellets of mercury\\nfall down the tube they form little air-tight\\npistons but gravity being a constantly accel-\\nerating force tends to make these pellets go\\nfaster and faster. Consequently, they get\\nseparated by small vacuous spaces, and as\\nthese pass the opening a into the receiver,\\nthe air in the receiver expands and fills these\\nspaces. In this way the air in the receiver\\nbecomes more and more rarefied, and as there\\nare no valves to be opened the exhaustion can\\nbe carried to a high degree of perfection.\\nThe residual pressure is shown at any time\\nby subtracting the height of the column of mercury, 1) c,\\nfrom the barometric height. If these columns were equal\\nit would indicate a perfect vacuum.\\n146. The Water Exhaust (Fig. 83).\u00e2\u0080\u0094 In the laboratory it\\noften happens that we want an exhaust at hand without our-\\nselves doing the pumping. Running water permits such an\\nexhaust with the least inconvenience. The principle is simi-\\nlar to that of the mercury pump, but we give the water as\\n1\\nFig. 82.\u00e2\u0080\u0094 Mer-\\ncury pump.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0153.jp2"}, "152": {"fulltext": "132\\nPHYSICS\\ngreat velocity as possible by making it escape through a\\ntapering nozzle. In this way the water carries part of the\\nair away with it, and produces a partial vacuum.\\n147. Air Compressors and Blowing Engines.\u00e2\u0080\u0094 By reversing\\nthe valves in the usual type of air pump, we have a pump for\\ncompressing air (Fig. 84). Each down-stroke of the piston\\ncloses the valve compresses the air in the\\ncylinder, opens the valve and forces the air\\ninto the compressed-air receiver. It is manifest\\nthat this simple instrument may serve at least\\nthree purposes 1. It may be used to exhaust\\nthe receiver A. 2. It ___________\\nmay be used to condense\\ngas in the\\n3. It\\nWater\\nmay\\nreceiver B.\\nbe used for\\nAir\\nI\\nFig. 83.\u00e2\u0080\u0094 Wa-\\nter exhaust.\\ntransferring gas from one receiver to another.\\nThere are many modifications of the pump\\nand many practical applications, such as the\\nbicycle pump, pump for the compressed-air\\nbrake in use on all modern trains, for the com-\\npressed illuminating gas used in many railway\\ncars, for testing the gas pipes in our houses, for\\nproducing sprays in medical treatment, and so\\non. The most important application is in the\\npowerful blowing engines used at all blast fur-\\nnaces.\\n148. Siphons. The siphon is a very simple device for\\ntransferring fluids from one level to a lower level over an in-\\ntervening obstacle. Siphons depend for their action upon\\ntwo principles the pressure of the atmosphere and the\\ntendency of all fluids to seek their own level. They will\\nnot work in a vacuum, and they will not raise fluids to a\\nheight greater than that of a barometer filled with the\\nfluid in question that is, 76 centimetres in the case of\\nmercury, or 1,033 centimetres in the case of water.\\nLet us analyze the simplest form of siphon, a U-shaped", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0154.jp2"}, "153": {"fulltext": "PRINCIPLES OF FLUID PRESSURE\\n133\\ntube of glass with one leg longer than the\\nother. Suppose it to be in operation, trans-\\nferring water from the level bto the level c\\nover the intervening obstacle, represented\\nby the wall of the vessel (Fig. 85). The\\natmosphere acts on the surface of water in\\nboth vessels with an equal pressure, which\\nwe may represent as li. There is also at\\nthe level c in the lower vessel a downward\\npressure of a column of water of height a c,\\nand further, at the level 5, in the upper\\nvessel, a downward pressure\\nof a column of water, a b.\\nThe downward pressure in\\nthe longer leg of the siphon\\ntherefore exceeds the down-\\nward pressure in the shorter leg by the\\nweight of a column of water, b c. Water\\nconsequently flows over the arch of the\\nsiphon and into the lower vessel, and con-\\ntinues to flow either until the upper vessel\\nis emptied or the level of water is the same\\nin both vessels. Ap-\\nparently the atmos-\\nphere has nothing to\\ndo with it, but imagine\\nfor a moment the absence of atmos-\\nphere. The only force being gravity,\\nthe water would flow down in both legs\\nof the siphon, and we should simply\\nhave a vacuum in the tube. Or, imag-\\nine an atmosphere, and make a b 40\\nfeet. Suppose the siphon completely\\nfilled with water and free to act. At\\nonce the water would separate in the arch of the siphon\\nand sink to a height of about 34 feet in each of the legs.\\nFig. 84.\u00e2\u0080\u0094 Com-\\npressor.\\nFig. 85.\u00e2\u0080\u0094 Siphon.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0155.jp2"}, "154": {"fulltext": "134\\nPHYSICS\\nThere would be a barometric vacuum in the arch and no\\nflow of water whatever.\\nA piece of rubber hose completely filled with water and\\ndipping under the surface of water in two vessels at dif-\\nferent levels often serves as a convenient siphon, and is\\nsomewhat easier to fill and start than a rigid glass tube.\\nAspirating Siphon (Fig. 86).\u00e2\u0080\u0094 The difficulty of filling\\nand starting the plain glass siphon is so considerable, and\\nespecially in the case of sulphuric acid and other chem-\\nicals not to be freely handled, that a modification of the\\ninstrument has been de-\\nvised known as the aspi-\\nrating siphon. In this a\\nsecond tube leads upward\\nfrom near the bottom of\\nthe longer leg, and after\\nswelling into a little bulb\\nnear the top is turned at\\nright angles and formed\\ninto a mouthpiece. To\\nstart the siphon the short-\\ner leg is dipped into the\\nliquid in the upper ves-\\nsel and the longer leg\\nis closed either by the\\nthumb, if the liquid be\\nharmless, or by a stop-\\ncock if harmful. The\\nmouth is then applied to\\nthe mouthpiece and the\\nair sucked out of the two\\ntubes. The liquid rushes over and fills both tubes. The\\nbulb is intended to show the operator more plainly when\\nthe liquid is getting dangerously near his mouth. The\\nsuction is stopped and the longer leg of the siphon is\\nopened. The liquid flows over as in the plain siphon, and\\nFig. 86. Aspirating siphon.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0156.jp2"}, "155": {"fulltext": "PRINCIPLES OF FLUID PRESSURE\\n135\\nthe aspirator has no further influence. Great care must\\nbe taken not to get acid or other dangerous chemicals into\\nthe mouth.\\nFountain Siphon (Fig. 87). The siphon may be given\\na multitude of forms, and may be very ingeniously modi-\\nfied. A very pretty form is the\\nfountain siphon. A round-bottom\\nFlorence flask is fitted with a doubly\\nperforated rubber stopper, and is\\nsupported in an inverted position.\\nA straight glass tube passes through\\none of the perforations (preferably\\nin the middle of the stopper) and\\nends inside the flask in a fine jet.\\nA second tube passes through the\\nother perforation, and with the ad-\\ndition of a rubber hose forms the\\nlong leg of the siphon. It is easy\\nto start the fountain by having a\\nlittle water in the flask before it is\\nstoppered. When the flask is in-\\nverted the water runs out the open\\ntube into the hose, and at once the\\nfountain begins to play. If the difference of level in the\\ntwo vessels is considerable the water rises in a single thread\\nand strikes against the walls of the flask with no little\\nforce.\\n149. Siphoning Gases. It is quite as possible to siphon\\ngases as liquids. If the gases are heavier than air we do it\\nright side up if lighter than air we do it upside down. Let\\nus take two large battery jars (Fig. 88) and fill the upper one\\nwith carbon-dioxide gas (C0 2 sp. gr. 1.56. This gas can\\neasily be made by placing fragments of marble (CaC0 3 in a\\ngas-generating flask with a little water, and adding hydro-\\nchloric acid (HC1) through the thistle tube. C0 2 is given\\noff copiously, and by means of a rubber hose may be con-\\nFig. 87.\u00e2\u0080\u0094 Fountain siphon.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0157.jp2"}, "156": {"fulltext": "136\\nPHYSICS\\nFig. 88.\\nducted into the upper jar. The C0 2 is quite\\ninvisible, but it extinguishes a flame at once,\\nand so a burning match will tell us\\nwhen the jar is full. A lighted candle\\nis placed in the lower jar. By\\nmeans of the aspirating siphon,\\nor a bit of rubber tubing,\\na stream of C0 2 is now\\nmade to pass over\\nthe upper jar. The\\ngas stream is, of\\ncourse, invisible,\\nbut it will be no-\\nticed that the can-\\ndle burns less and\\nless brightly, and\\nfinally flickers and\\ngoes quite out.\\nIn the case of light gases like hydrogen (H), sp. gr.\\n.069, both the gas jars and the siphon are inverted, and the\\nH passes from the lower to the higher jar.\\nAt the beginning of the experiment the lower\\njar is filled with H, the upper jar with air.\\nAt the end the H is in the\\nupper jar. It, too, is invisi-\\nble, but its presence can be\\nshown by applying the open\\nend of the jar to a flame.\\nA considerable explosion\\nannounces a mixture of H\\nand air.\\n150. Hero s Fountain\\n(Fig. 90).\u00e2\u0080\u0094 This bit of clas-\\nsical apparatus, invented by\\nHero of Alexandria, 120\\nB. c, deserves notice as an", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0158.jp2"}, "157": {"fulltext": "PRINCIPLES OF FLUID PRESSURE\\n137\\ninteresting case of transmitted pressures. In starting the\\nexperiment M should be nearly full and N nearly empty\\nof water. There must also be some water in the pool D.\\nThe column of water from the pool to the lower globe\\nexerts a pressure upon the air in that globe which is trans-\\nmitted through the tube to the air in the\\nupper globe and forces the water out in a\\njet. It is sometimes used for cologne foun-\\ntains, and the liquid can be\\nused over and over again by\\npouring it back from M to\\nN each time it runs down.\\nA cheaper form is shown in\\nFig. 91. It can be made\\nout of three bottles and a\\nlittle tubing.\\n151. Tension inside the\\nBarometer Tube. If the\\nspace in the upper end of\\nthe barometer is a vacuum\\nthere is no tension there,\\nand it is manifest that the\\nwalls of the tube must sus-\\ntain in that part the whole\\natmospheric pressure of fif-\\nteen pounds per square\\ninch. If this portion of the\\ntube were made of rubber,\\nits sides would collapse un-\\nder the pressure. How is\\nit with other portions of the\\ntube In the lower end of the tube, at the level of the mer-\\ncury in the cistern, the outward pressure of the column of\\nthirty inches of mercury must be equal to the inward pres-\\nsure of the atmosphere. Here the tube might be made of\\nthe thinnest rubber and neither expand outward nor con-\\nFlG. 90.\u00e2\u0080\u0094 Hero s\\nfountain.\\nFig. 91.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0159.jp2"}, "158": {"fulltext": "138\\nPHYSICS\\ntract inward. Halfway up the tube the pressure from with-\\nout is still that of an atmosphere, while the pressure from\\nwithin is that of half an atmosphere\u00e2\u0080\u0094 fif-\\nteen inches of mercury. So it appears\\nthat while the pressure from without is\\nfifteen pounds per square inch throughout\\nthe whole length of the tube, the pres-\\nsure from within varies all the way from\\nfifteen pounds at the lower end to zero\\nat the upper end. A water barometer\\nmay be made of rubber tubing with a\\nclosed glass tube in the upper end, but it needs to be the\\nthick-walled Bunsen pressure tubing. to prevent its sides\\nfrom collapsing. If a pin-prick is made anywhere along\\nthe side of this tube, water does not leak out, but air leaks\\nin. ,A water barometer must not be expected\\nto stand thirteen and six tenths as high as the\\nmercury barometer, although from considera-\\ntion of specific gravity alone we might expect\\nthat. The tension of water vapor in the upper\\nend of the tube depresses the column somewhat.\\n152. The Inverted Tumbler of Water.\u00e2\u0080\u0094 From\\nthe above discussion of tension inside the ba-\\nrometer tube we naturally find an explanation\\nfor the time-honored experiment of the inverted\\ntumbler of water (Fig. 92). The upward pres-\\nsure of the air upon the paper which covers the\\nmouth of the tumbler is fifteen pounds per\\nsquare inch, while the downward pressure is\\nmerely the weight of the water so long as no\\nair gets in to produce an internal tension. The\\nexperiment may even be performed by putting\\nmosquito netting over a wide-mouth bottle full FlG 93\\nof water, and it need not be tied or held in\\nplace atmospheric pressure will do that. Medicine drop-\\npers, students lamps, fountain ink wells, fountain sponge", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0160.jp2"}, "159": {"fulltext": "PRINCIPLES OP FLUID PRESSURE\\n139\\nJ-\\\\\\nH\\ncups, etc., all hold their liquids because atmospheric pres-\\nsure from without is greater than the tension from within.\\n153. The Specific Gravity of Liquids measured by bal-\\nancing them against Atmospheric Pressure. Fig. 93 illus-\\ntrates a simple way of finding the specific gravity of liquids.\\nOne tube dips into a vial of water and the other into a vial\\nof liquid whose specific gravity is to be found. When a\\nperson applies his mouth to the tube e and reduces a little\\nthe tension of the air in the tubes, the atmospheric pressure\\nforces each liquid up its respective tube, and by comparing\\nthe length of the columns it is possible to obtain the rela-\\ntive weights. It is manifest that the col-\\numn of liquid c d must have the same\\nweight as the column of water a since\\nthe weight of each column of liquid must\\nbe equal to the pressure of the air from\\nwithout minus the tension\\nwithin. From this we r K\\nshould find that a column\\nof water eight inches long\\nbalances a column of alco-\\nhol about ten inches long.\\n154. Fluids in Motion.\\nIt is to be noted that in\\nall our stud3 r of fluids thus\\nfar we have considered\\nthem in a state of rest, and\\nthus the elements of fric-\\ntion and momentum have not complicated our problems.\\nIn the apparatus illustrated in Fig. 94 the water in the tube\\nstands at the same level as the water in the reservoir, but\\nFig. 95 illustrates the fact that the water will not flow in\\na fountain to the same level. Friction in the tube, the\\nresistance of the air, and the interference of the falling\\ndrops of water, all act to prevent this. If the water in a\\nsystem of city water works were absolutely at rest it would\\nFig. 94.\\nFig. 95.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0161.jp2"}, "160": {"fulltext": "140\\nPHYSICS\\nrise in a house pipe as high as the level of the water in the\\nreservoir hut the fact that the water is flowing continually\\nthrough the pipes to supply so many faucets during the\\ndaytime prevents its rising to the upper stories of many of\\nthe houses in large cities, although the reservoir may be\\nfar above them. At night when less water is used it may\\nrise even to tanks upon the roofs of these same houses.\\nWater wheels and windmills are run by the momentum\\nof the moving fluids rather than the pressure of those fluids\\nat rest. The word hydrostatic refers\\nto fluids at rest hydraulic refers to\\nfluids in motion.\\n155. The Hydraulic Ram. This\\ninstrument depends upon the momen-\\ntum of running water. The principle\\nof it may be illustrated by a very sim-\\nple piece of apparatus.\\nLet the two reservoirs A and B\\n(Fig. 96) be connected by a rubber\\ntube. The end of the tube in A is\\nsupplied with a valve which prevents\\nthe fluid returning from A. If we\\nseize the rubber tube at b and raise it\\na few inches and then let it fall with\\na sudden jerk, the momentum of the\\nmoving column of water will push a\\nsmall amount of water up through\\nthe valve in A. By repeating this\\nmovement several times B may be\\nemptied of its water and carried above\\nits level in A. This is the idea which\\nunderlies the hydraulic ram, whereby water is made to. flow\\nfrom a source upon a hillside, first down into a valley, and\\nthen to a house farther up the hillside than the source.\\nIn order to accomplish this a portion of the water must\\nrun to waste. It is the energy of this portion of the water\\nFig. 96.\u00e2\u0080\u0094 Principle of\\nhydraulic ram.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0162.jp2"}, "161": {"fulltext": "PRINCIPLES OF FLUID PRESSURE\\n141\\nthat does the work of lifting the other portions of the\\nwater to the house. A diagram will make the mechanism\\nplain.\\nD (Fig. 97) is the spring from which water is to be car-\\nried through a pipe C to a house which is higher than the\\nspring. If the valve A should remain closed, water would\\nFig. 97. Diagram of hydraulic ram.\\nstand at the same level in C as at D but the valve A is\\nmade heavy enough to sink in quiet water. As soon as it\\nsinks, however, the water ceases to be quiet, and rushes out\\nthrough the orifice above with such a rush as to toss the\\nvalve shut again with a smart thump. When the flow of\\nthe water is thus suddenly stopped at A its momentum\\nforces open the valve b, and some of it passes in to com-\\npress the air in the chamber B. At the rebound of this air\\nthe valve b closes and some water is forced higher up the\\ntube C leading to the house. As soon as the water in the\\napparatus becomes quiet the valve A sinks again, and the\\nevents just described are repeated.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0163.jp2"}, "162": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0164.jp2"}, "163": {"fulltext": "HEAT\\nCHAPTER, XVIII.\u00e2\u0080\u0094 How Heat is produced\\n156. General Definition of Heat.\\n157. Heat produced by Friction.\\n158. Heat produced by Percussion.\\n159. Heat produced by Pressure. Figs. 98, 99, and 100.\\n160. Heat produced by Chemical Action.\\n161. Other Sources of Heat.\\nCHAPTER XIX.\u00e2\u0080\u0094 Some Effects of Heat\\n162. General Statement.\\n163. Expansion of Solids. Fig. 101.\\n164. Applications.\\n165. Irregularities.\\n166. Expansion of Liquids.\\n167. Measurement of Temperature by the Expansion of Mercury in the\\nThermometer. Figs. 102 and 103.\\n168. Centigrade, Reaumur, and Fahrenheit Scales. Fig. 104.\\n169. Conversion of one Scale into another.\\n170. Self-recording Thermometers. Fig. 105.\\n171. Expansion of Gases. Correction of Volume for Temperature.\\n172. The Air Thermometer. Fig. 106.\\n173. Pyrometers.\\n174. Range of Temperatures.\\n175. Relation of Temperature to Animal and Vegetable Life.\\n176. Heat determines the State of a Substance.\\n177. Fusion.\\n178. Change of Volume due to Fusion.\\n179. Change of Fusing Point under Pressure.\\n180. Effect of Alloys upon Fusing Point.\\n181. Vaporization.\\n182. Five Factors of Evaporation.\\n183. The Evaporation of Solids.\\n184. Vapors.\\n185. Critical Temperature.\\n186. Boiling. Fig. 107.\\n187. Laws of Boiling and Table of Boiling Points.\\n188. Changes in the Boiling Point.\\n189. Determination of Altitude by Thermometers.\\n190. Saturation.\\n143", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0165.jp2"}, "164": {"fulltext": "144 PHYSICS\\n191. Vapor in the Air. Dew Point.\\n192. Humidity. Fig. 108.\\n193. Rainfall.\\n194. Moisture and Health.\\n195. Illustrations.\\n196. Condensation, Solidification, and Crystallization.\\nCHAPTER XX.\u00e2\u0080\u0094 How Heat is transferred\\n197. General Statement.\\n198. Conduction. Fig. 109.\\n199. Applications.\\n200. Convection. Figs. 110 and 111.\\n201. Radiation.\\n202. Absorption, Radiation, and Reflection.\\n203. Relation of Heat and Light.\\n204. Radiometer. Fig. 112.\\nCHAPTER XXI. Calorimetry and Specific Heat\\n205. Measurement of Heat.\\n206. Temperature.\\n207. Quantity of Heat.\\n208. Specific Heat.\\n209. Determination of Specific Heat.\\n210. Applications.\\nCHAPTER XXII.\u00e2\u0080\u0094 Latent Heat\\nA. Heat disappears when Solids liquefy\\n211. Heat Latent in Solutions.\\n212. Freezing Mixtures.\\nB. Heat disappears when Liquids vaporize\\n213. Heat Latent in Vapors.\\n214. Absolute Temperature.\\n215. The Production of Cold.\\n216. Expansion of Gases.\\n217. Cold by Evaporation. Fig. 113.\\nC. Heat reappears ivhen Vapors liquefy\\n218. Heat recovered from Vapors.\\nD. Heat reappears when Liquids solidify\\n219. Heat recovered from Solutions.\\n220. Recapitulation.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0168.jp2"}, "165": {"fulltext": "CHAPTEE XVIII\\nHOW HEAT IS PRODUCED\\n156. General Definition of Heat. In studying heat, we\\nstudy only a particular form of energy molecular motion\\nand all that we have learned about motion in general is\\napplicable to the motion of molecules. Like all forms of\\nenergy, heat represents two elements matter and motion.\\nIt is a measurable quantity, and the measurement may be\\nmade with respect to the two aspects of energy studied in\\nmechanics\u00e2\u0080\u0094 that is, to the degree or intensity of motion\\nand to the total amount of motion or momentum. By the\\ndegree or rate of motion we mean speed or velocity, meas-\\nured in centimetres per second. This measurement is inde-\\npendent of the amount of matter. In the case of heat we\\ncan not measure the velocity directly in centimetres. The\\nmotion, being molecular, is quite invisible. It consists of a\\nto-and-fro motion, a vibration, and not of a plain and sim-\\nple change of position. We can only measure the intensity\\nof the molecular motion by means of its effects, and this\\nwe do with a thermometer (section 167).\\nThe total amount of motion, or momentum, is the prod-\\nuct of mass and velocity, or m v.\\nIn heat the amount is measured in the same way. It is\\nthe degree of heat motion multiplied by the mass of the\\nmatter in motion. But here, again, the measurement must\\nbe conventional, since the degree of heat motion can not\\nbe measured in absolute units. The measurement of heat\\n11 145", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0169.jp2"}, "166": {"fulltext": "146 PHYSICS\\nquantities is treated under the head of Calorimetry (Chap-\\nter XXI).\\nThe term heat is used in two very different senses.\\nFirst, the physical sense, the molecular motion of a body\\nand, second, the physiological sense, the sensation produced\\nin us by contact with a hot body. We shall use it always\\nin the physical sense, to represent the thermal condition of\\na body. We can not judge of this accurately by means of\\nour own sensations, for hot and cold are merely relative\\nterms. When we come in from the cold a moderately warm\\nroom seems hot to us, and when we pass from an overheated\\nroom into a moderately warm one it feels cold to us.\\nNeither can we judge of the relative heat of two bodies\\nby simply touching them, for the sensation produced does\\nnot depend alone upon the degree of heat in the bodies\\ntouched, but also upon the relative speed with which they\\ngive up or absorb heat when brought in contact with the\\nhand. Thus, pieces of iron and of wood may be equally\\nhot, but to the hand the iron will seem much the hotter,\\nbecause it gives up its heat more readily than the wood.\\nThe two may be equally cold, but not to the touch the\\niron will seem much the colder, because it takes away heat\\nmore rapidly from the hand. On a cold morning we instinc-\\ntively avoid handling all metal objects, but we pick up wood\\nor cloth without hesitation, although they are all of the\\nsame, or nearly the same, temperature.\\nUntil the end of the eighteenth century it had been\\nbelieved by many eminent philosophers, among whom was\\nSir Isaac Newton, that heat was a very subtle fluid that\\nmore or less completely filled the pores of all substances,\\nand could be transferred from one to another, much as\\nwater flows from one vessel to a communicating one, and\\nonly comes to rest when the level is the same in both. In\\nthe closing years of that century two celebrated experi-\\nments were made, that showed once for all that heat is not\\na substance, but is simply a motion of the molecules.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0170.jp2"}, "167": {"fulltext": "HOW HEAT IS PRODUCED 147\\nAn American, Benjamin Thompson, afterward Count\\nEumford, had charge of the boring of cannon in the arse-\\nnal at Munich, and, observing that great heat was produced,\\nhe became interested to investigate the matter. He found\\nthat by immersing the cannon in water and by purposely\\nusing a very blunt boring tool he could easily produce\\nenough heat to make the water boil. He rightly reasoned\\nthat what could be produced in such unlimited quantity by\\nthe expenditure of mechanical energy must itself be a form\\nof energy. He even established a rough relation between\\nthe amount of mechanical energy that disappeared and the\\namount of heat that took its place. This was in 1798. The\\nyear following, Sir Humphry Davy showed that two pieces\\nof ice rubbed together below the freezing point could be\\nmelted by the heat of friction.\\nAt the present time no one seriously doubts that heat is\\na mode of motion that is, a form of energy but it took\\nthe first third or even the first half of the nineteenth cen-\\ntury to establish the doctrine on firm scientific grounds.\\nThe final victory was gained by the experiments establish-\\ning the exact quantitative relation between heat and me-\\nchanical energy that is, the mechanical equivalent of heat\\nwork that will always be associated with the name of the\\nEnglish scientist Joule. The doctrine has been theoretic-\\nally worked out by such men as Clausius, Helmholtz, Tait,\\nand Maxwell, and made popular by Tyndall and other able\\nexperimenters.\\nHeat, from the standpoint of physics, is a vibration of\\nmolecules\u00e2\u0080\u0094 the greater the amplitude of vibration the more\\nintense the heat. From the standpoint of physiology it is\\nan irritation of certain nerve endings b;y appropriate means\\nas, for example, the pelting of these vibrating molecules\\nof matter against the skin.\\nSince heat is a form of energy one variety of molecu-\\nlar motion it can only be produced by the transformation\\nof some other form of energy into heat. This is accom-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0171.jp2"}, "168": {"fulltext": "148 PHYSICS\\nplished so readily that heat has been called the currency,\\nor medium of exchange, in the realm of energy. We may\\ntherefore expect to find that there are a great variety of\\nways of producing heat.\\n157. Heat produced by Friction. When mechanical mo-\\ntion is interrupted in any way, as in friction, we have the\\nmovement of the whole transformed into a movement of\\nthe parts that is, into heat. We do this when we rub our\\nhands together on a cold morning. A coin or other bit of\\nmetal rubbed against a flannel blanket or against our coat\\nsleeve becomes uncomfortably warm. It is quite possible to\\nmeasure the relation between mechanical motion and heat\\nthe quantity of heat that corresponds to a given amount\\nof mechanical energy. In this way we may get the thermal\\nequivalent of motion, or the mechanical equivalent of heat.\\nIt is a familiar fact that machinery warms up while\\nrunning. It has already been said that the work done by\\nany machine is never fully equivalent to the power applied\\nto it. The loss is due to friction, and the heat which warms\\nup the machine while in motion is the equivalent of this\\napparently lost energy. Anything which will reduce fric-\\ntion should therefore diminish this loss. Hence we oil the\\nmachine when we desire it to perform work rather than\\nproduce heat.\\nThe relation between heat and work constitutes a dis-\\ntinct branch of physical science called thermodynamics. It\\nexpresses the quantitative relation between two important\\nforms of energy, and is an application of the doctrine of\\nthe conservation of energy.\\n158. Heat produced by Percussion.\u00e2\u0080\u0094 When a bullet strikes\\na target its mass motion is converted into molecular motion,\\nor heat. When we hammer a nail, both the hammer and\\nthe nail become hot the pile driver and the pile become\\nhot in the same manner. The earth is moving through\\nspace, around the sun, at the rate of about nineteen miles\\nper second. Could it be stopped, its motion would be", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0172.jp2"}, "169": {"fulltext": "HOW HEAT IS PRODUCED\\n149\\ntransformed into heat, and this would be sufficient to\\nvaporize the entire earth. Indeed, that is precisely what\\nis happening to hundreds of meteors which daily fall into\\nthe earth s atmosphere. In 1854 Sir William Thomson\\nconcluded that the heat of the sun was chiefly due to the\\npercussion of meteors which fall upon it.\\n159. Heat produced by Pressure. When gases are con-\\ndensed by a pump, temperature rises (Fig. 98). When they\\nare allowed to expand again they return\\nto their original temperature. If, while a\\ngas is under pressure, the heat is conducted\\noff and the pressure is then removed, the\\nexpansion will cause the temperature to\\nfall as far below the original temperature\\nas it was raised above\\nthat by pressure. This is\\nwell illustrated in cer-\\ntain ice machines, where\\nthe heat produced, by\\npressure is removed by\\nrunning water, and the\\ncold which is produced\\nby the sudden expansion\\nof the gases is sufficient\\nto freeze water. (See\\nalso 216.)\\nIt is pretty generally\\nknown that water boils at\\n212\u00c2\u00b0 Fahrenheit. With-\\nout extra pressure its temperature can not be raised above\\nthat point. We may, however, raise it to any desired tem-\\nperature by putting its steam under sufficiently great pres-\\nsure (Fig. 99). Because of great -pressure, steam in a loco-\\nmotive boiler is much hotter than 212\u00c2\u00b0. When this steam\\nissues in a jet, however, the sudden expansion reduces its\\ntemperature, so that it is only lukewarm (Fig. 100).\\nFig\\nFig. 98.\u00e2\u0080\u0094 Heat by\\npressure.\\n-Tempera-\\nture of steam un-\\nder pressure.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0173.jp2"}, "170": {"fulltext": "150\\nPHYSICS\\nThe internal heat of the earth may be due to the pres-\\nsure of its mass. The rise in temperature is about one\\ndegree Fahrenheit for every fifty or sixty feet of descent\\nvarying much in different localities. It must be understood\\nthat motion must result from pres-\\nsure in order to produce heat\u00e2\u0080\u0094 that\\nis, the earth must be still contracting\\nunder its own weight if heat is being\\nnow produced. But the internal heat\\nwhich was produced in former cen-\\nturies by this contraction has very\\ngreat difficulty in getting away from\\nthe, earth. It has been estimated that\\nso little of it reaches the surface as\\nto effect a rise in temperature of only\\nFlG 100 one thirty-sixth of a degree. So like-\\nwise the heat of the sun may be pro-\\nduced chiefly by the action of gravitation in pulling its par-\\nticles of matter nearer together. Von Helmholtz calcu-\\nlated that all the sun s heat for a year would be produced\\nby the contraction of thirty-eight metres in its radius. If\\nit continues to give out heat at the present rate for four\\nmillion years, it will then be contracted to half its present\\ndiameter.\\nThe total heat sent to the earth annually from the sun\\nwould be capable of melting a sheet of ice fifty-four metres\\nthick, extending over the whole surface of the globe. The\\nearth, being distant about ninety-two million miles from the\\nsun, receives only the one-twenty-one-hundred-millionth part\\nof the entire amount of heat which the sun sends forth on-\\nall sides. How the sun s heat is transmitted through space\\nfrom the sun to the earth, and what transformations it\\npasses through after it reaches the earth, will be discussed\\nin other chapters.\\n160. Heat produced by Chemical Action.^The process\\nof ordinary burning, or combustion, is the union of a sub-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0174.jp2"}, "171": {"fulltext": "HOW HEAT IS PRODUCED 151\\nstance with oxygen. Burning, combustion, and oxidation are\\nnearly synonymous terms. The process, however rapid, as\\nin the case of combustion, or slow, as in the case of the rust-\\ning of a metal, is always accompanied by the production of\\na definite amount of heat, which bears a fixed ratio to the\\namount of chemical action.\\nThe familiar instance of the slaking of lime with water\\nis an illustration of the production of heat by chemical\\naction. Both the lime and the water may be very cold, but\\nwhen they are mixed their atoms clash together in forming\\na new compound, and the molecules of the new substance\\nare left in a state of vibration so intense as to cause the\\nwater to boil, or even to set wood on fire. Storehouses of\\nlime frequently take fire by rain leaking in upon the lime.\\nShips loaded with lime are in similar danger. Compost\\nheaps get very warm by reason of the slow chemical decom-\\nposition that is going on in them. Piles of green grass,\\nnew grain, new hay, new flour, cotton with seed in it, or\\noily cotton waste, all produce heat for the same reason.\\nAnimal heat is produced in like manner. Most of our\\nfoods are particularly liable to chemical change indeed,\\ntheir value as foods depends upon this characteristic. Ani-\\nmal heat is due chiefly to the breaking down of these com-\\npounds in the body.\\n161. Other Sources of Heat. Electricity is one of the\\nlatest sources of heat to be utilized by man. We shall see,\\nwhen we come to this subject, that whenever a current of\\nelectricity meets resistance in its passage, heat is produced.\\nThis is sufficient to cook with in the electric stove. Our\\nelectric cars are warmed in winter by turning electric\\nenergy into heat. Heat is produced from the electric cur-\\nrent for welding metals and for fusing the most refrac-\\ntory substances. AYe shall study this matter more in detail\\nunder Electricity.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0175.jp2"}, "172": {"fulltext": "CHAPTEK XIX\\nSOME EFFECTS OF HEAT\\n162. General Statement. A body at a given tempera-\\nture possesses a definite kinetic or molecular energy, and\\ntherefore displays definite qualities. If the temperature is\\nthat ordinarily experienced, and remains fairly constant, we\\nare not apt to think of the qualities as the effect of heat.\\nIn looking at a sheet of water or at a bowl of mercury we\\nare not apt to think of the liquid state of either as an effect\\nof heat. We are more apt to consider it as an essential\\nquality of the water or the mercury. But a scientific con-\\nception of the world about us requires that we shall regard\\neverything not as fixed and permanent in itself, but simply\\nas the effects of given conditions, and therefore only per-\\nmanent so long as these conditions are permanent. Changes\\nof temperature, pressure, light, and electrical conditions\\nproduce corresponding changes in the qualities of things,\\nand, if these changes are sufficiently great, produce a very\\ndifferent world.\\nSolids, liquids, and gases are not such by necessity, but\\nonly so under the particular conditions which happen now\\nto prevail. We can imagine a cold so intense that all things\\nwould be solid, and a heat so intense that all things would\\nbe gaseous. For example, many things which are in the\\nliquid or gaseous state upon the earth, perhaps exist on\\nthe moon in a solid state and many things which are in\\nthe solid state on the earth exist on the sun in a gaseous\\nstate.\\n152", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0176.jp2"}, "173": {"fulltext": "SOME EFFECTS OF HEAT 153\\nThe direct effects of heat become very evident when we\\nkeep all the other conditions constant and change only the\\nheat conditions. We can do this by giving heat or by taking\\naway heat. The most important effects are change of vol-\\nume and change of state. It is a common piece of every-\\nday knowledge that heat expands and cold contracts. This\\nmay be observed on all sides and these observed facts help\\nto establish our theory of the nature of heat. If heat be\\nmolecular motion, an increase of heat must mean an increase\\nof molecular motion, and this very naturally would cause\\nexpansion, since the greater motion would require the\\ngreater space. In the same way a diminution of motion\\nwould mean contraction, since smaller space would natu-\\nrally suffice for the smaller motion. Water is in the solid,\\nliquid, or gaseous state, according to the amount of heat or\\nmolecular motion which it has. So it is with other sub-\\nstances.\\n163. Expansion of Solids. Fig. 101 represents a ball\\nwhich, when cold, will pass through the ring, but when it\\nefficient of expan- FlG 101 _ Expansion by heat\\nsion. This may\\nbe of the volume or of the length. The coefficient of vol-\\nume expansion is the increase of volume due to a rise of\\n1\u00c2\u00b0 in temperature but for solids the coefficient of linear\\nexpansion is of greater importance practically. It is the\\nincrease of length due to a rise of 1\u00c2\u00b0 in temperature. It", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0177.jp2"}, "174": {"fulltext": "154 PHYSICS\\nis determined by taking a bar of the material of unit cross-\\nsection, one square centimetre, making two marks on the\\nbar, one near each end, measuring the distance between\\nthem very accurately, and noting the temperature. The\\nbar is then brought to a higher temperature by surround-\\ning it with steam. The distance between the two marks\\nis now measured. From this is calculated the increase of\\nlength for 1\u00c2\u00b0 rise in temperature. For example, wrought\\niron is found to expand by a twelve-millionth part of its\\nlength for 1\u00c2\u00b0 rise in temperature. That is, a wire of this\\nmaterial one mile in length, or 63,360 inches, would expand\\nTooVo oo \u00c2\u00b0f 63,360 inches, or about three quarters of an inch\\nfor 1\u00c2\u00b0 rise in temperature; for 10\u00c2\u00b0 it would expand 7.5\\ninches, and for 100\u00c2\u00b0 it would expand about 75 inches, or\\n6 feet.\\nTABLE OF LIKEAB COEFFICIENTS.\\nFlint glass 000008\\nPlatinum 000009\\nWrought iron 000012\\nGold 000015\\nCopper 000017\\nBrass 000019\\nSilver 000019\\nTin 000022\\nZinc 000029\\nLead 000028\\n164. Applications. Iron tires are clasped around wheels\\nwhile still quite hot, so that their contraction may press\\nthe rims more firmly on the spokes, and the spokes more\\nfirmly into the hub. For the same reason sheet-iron plates\\nare fastened together, as in boilers, by red-hot rivets. When\\nthe rivets cool they contract, and bind the plates together\\nwith tremendous force. Bulging walls are sometimes brought\\nto place by passing hot iron rods through them. The con-\\ntraction of the rods brings the wall back into place. Dial\\nthermometers operate through the expansion and contrac-\\ntion of metal spirals whose motion is communicated by a\\nsystem of levers to the pointer over the dial.\\nBut not only do we utilize the tremendous force of con-\\ntraction and expansion, but we are also obliged in many", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0178.jp2"}, "175": {"fulltext": "SOME EFFECTS OF HEAT 155\\ninstances to provide against it in order to avoid disaster.\\nThus, the ends of steel rails must have a little free space\\nbetween them, or in hot weather they would force each\\nother out of line. In the same way, sections of an iron\\nbridge must have sufficient play to prevent harmful tension\\nor pressure. Some of our most appalling railroad accidents\\nhave been caused by the contraction and consequent break-\\ning of iron rods. The Brooklyn Bridge is not far from a\\nyard longer in summer than in winter, owing to the expan-\\nsion of the suspending cables.\\nGlass lamp chimneys, tumblers, bottles, etc., crack when\\nheated in one part only, because of the stress produced by a\\ngreater expansion in one part than another. Such things\\nmay be heated safely if put in an oven or immersed in\\nwater and heated gradually, so that all parts may expand\\nalike. Thin glassware, used for test tubes, beakers, flasks,\\nand the like in the chemical laboratory, may safely be\\nheated in one part more than another because of its flexi-\\nbility. The most common cause of disaster to this glass-\\nware in the laboratory is a drop of liquid coming in contact\\nwith dry, hot glass. The contraction due to sudden cooling\\nin one spot shatters the glass. We may heat it wet or heat\\nit dry, but we may not wet it while hot.\\nThe expansion and contraction due to changes in tem-\\nperature causes cracks to start in the more brittle rocks,\\nsuch as the trap rocks of the Palisades and other highlands.\\nWater gets into these small cracks, and in winter freezes.\\nThis, as we shall learn in section 178, causes expansion.\\nThus, the summer s sun and the winter s frost conspire to\\ntear down the mountains.\\nIce expands and contracts with changes of temperature.\\nThis may account for the snapping and cracking of the ice\\non a still pond in very cold weather.\\n165. Irregularities. In general, solids expand equally\\nin all directions, but there are certain crystals that are an\\nexception to this rule. On being heated, they expand most", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0179.jp2"}, "176": {"fulltext": "156 PHYSICS\\nalong one principal axis, and may even contract at right\\nangles to this direction. This is the case with Iceland spar.\\nThere are variations in the coefficients of expansion at\\ndifferent positions on the thermometer scale, the coefficient\\nincreasing slowly with the temperature. The values given\\nin the table are, however, sufficiently accurate for all prac-\\ntical uses.\\n166. Expansion of Liquids. Since liquids have no defi-\\nnite shape, but assume the form, of the containing vessel,\\nwe can only measure the increase of temperature that is,\\ntheir coefficient of volume expansion. Since the contain-\\ning vessel also changes its volume with change of tempera-\\nture, all determinations of the expansion of liquids must\\ntake this into account. In general, the change of volume\\nis very small. The coefficient rises with the temperature.\\nWater and mercury are the two liquids whose coefficients\\nof volume expansion are of the largest importance. Water\\npresents the curious case of a liquid which does not expand\\nuniformly with the application of heat. A body of water\\nat the freezing point 32\u00c2\u00b0 on our ordinary thermometers\\non being heated, contracts in volume until it reaches 39\u00c2\u00b0.\\nIt then begins to expand, and at 46\u00c2\u00b0 has the same volume\\nas at 32\u00c2\u00b0. Beyond this point the expansion proceeds con-\\ntinuously until the boiling point, 212\u00c2\u00b0, is reached, and the\\nwatei passes into steam. Thirty-nine degrees is therefore\\nknown as the point of maximum density of water.\\nThis irregularity in the behavior of water has the utmost\\nsignificance in the economy of Nature. Bodies of water,\\nsuch as ponds and lakes, cool at the surface. The upper\\nlayers in growing cold also grow heavy, and sink to the\\nbottom. This process continues until the whole body of\\nwater has a temperature of 39\u00c2\u00b0. When this point is reached\\na further loss of heat makes the surface layers lighter as\\nwell as colder, and they consequently remain on top. When\\nthey reach 32\u00c2\u00b0 ice forms and shuts off the under water from\\nany further large loss of heat. As both ice and water are", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0180.jp2"}, "177": {"fulltext": "SOME EFFECTS OF HEAT\\n157\\npoor conductors, the lower strata of water remain at 39\u00c2\u00b0,\\nand the water life is preserved. If water continued to grow\\nheavier down to 32\u00c2\u00b0, the ice would form at the bottom of\\nall bodies of water, and the hottest of summer suns would\\nhardly suffice to melt it.\\nThe ordinary thermometer is an illustration of the ex-\\npansion of liquids by heat. Mercury and alcohol expand\\nby heat with sufficient regularity so that we use them to\\nmeasure rise and fall in temperature.\\n167. Measurement of Temperature by the Expansion of\\nMercury in the Thermometer. All ordinary temperatures\\nare measured by means of a well-known instrument the\\nthermometer. This depends for its\\naction upon the effect\\nof heat in making\\nfluids expand. Alco-\\nhol was formerly used,\\nand for low tempera-\\ntures is still used, but\\nmercury has been sub-\\nstituted for the al-\\ncohol in nearly all\\ninstruments for every-\\nday use. As the tem-\\nperature rises, mer-\\ncury expands, but the\\nincrease of volume is\\nso slight that, unless\\n-r-srl ^HF we em ploy some spe-\\n1 cial device for render-\\ning the expansion vis-\\nible, we should hardly\\nbe the wiser. This special device is very simple. We have\\na glass bulb capable of holding an appreciable amount of\\nmercury, and provided with a fine capillary tube as its only\\noutlet. In this way we have a considerable body of mer-\\nFig. 102.\\nFig. 103.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0181.jp2"}, "178": {"fulltext": "158\\nPHYSICS\\ncury to expand and contract, but any change in its volume,\\nhowever slight, makes a very noticeable change in the length\\nof the column of mercury in the capillary tube. Heat also\\nexpands the glass bulb, giving it greater capacity, so that\\nthe first effect of heating a thermometer is to make the\\ncolumn of mercury sink but as soon as the mercury also\\nbecomes heated, the column of mercury rises, and quite\\nenough for our purpose, since the increased volume of mer-\\ncury is greater than the increased capacity of the bulb.\\nWhat we really measure is their difference.\\nThe coefficient of volume expansion for mer-\\ncury is .0001817, and for glass .0000254.\\nThe difference between these coefficients,\\n.0001563, represents the apparent expansion\\nof mercury in glass.\\nPure water, under a pressure of 760 milli-\\nmetres of mercury, always freezes and boils\\nat the same temperatures, and so we take\\nthese as fixed points of temperature. Figs.\\n102 and 103 show how these points are found\\nwhen the thermometer is made.\\n168. Centigrade, R6aumur, and Fahrenheit\\nScales. There are unfortunately three differ-\\nent scales of temperature used in civilized\\ncountries.\\nCentigrade Scale. In this the freezing\\npoint of water is called 0\u00c2\u00b0, and the boiling\\npoint 100\u00c2\u00b0. The varying temperature of\\nliquid water is thus expressed in one hundred\\nsteps, hence the name. This scale was sug-\\ngested by Celsius, a Swedish scientist, and is\\nused in all scientific work, because of all the\\nscales it is the most rational and convenient. It is also in pop-\\nular use in France and in the Eomance countries generally.\\nReaumur Scale. The freezing point of water in this\\nscale is also called 0\u00c2\u00b0, but the boiling point is marked 80\u00c2\u00b0,\\n2\\no\\nFig. 104.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0182.jp2"}, "179": {"fulltext": "SOME EFFECTS OF HEAT 159\\nand the degrees are therefore larger than in the centigrade\\nscale. It was devised by Reaumur, of France, and has\\nnothing to commend it. Curiously, it is in popular use in\\nGermany and Switzerland.\\nFahrenheit Scale. This is the least admirable of the\\nthree. The freezing point is marked 32\u00c2\u00b0, and the boiling\\npoint 212\u00c2\u00b0, thus making 180\u00c2\u00b0 between the two points. The\\nzero of the scale is therefore 32\u00c2\u00b0 below freezing, and is the\\npoint that was erroneously supposed to mark the greatest\\nartificial cold producible. This scale is unfortunately the\\none in common use in the United States, in Great Britain,\\nand in all English-speaking countries. It was devised by\\nFahrenheit, a German philosopher.\\nNot one of these scales is used in the country where it\\noriginated.\\n169. Conversion of One Scale into Another.\\n1. Fahrenheit into Centigrade. To change any Fahren-\\nheit reading into centigrade, we must first subtract 32\u00c2\u00b0, in\\norder that both readings may count from the same starting\\npoint, the freezing point of water. The remainder is then\\nmultiplied by f since 180\u00c2\u00b0 F. 100\u00c2\u00b0 0. Putting this into\\na compact formula, we have\\n0.=f(P.-32) (1)\\nIllustrations Suppose the Fahrenheit reading was 212\u00c2\u00b0\\n(boiling point in F.), then 0. (212 32) f (180) 100\u00c2\u00b0\\n(boiling point in C).\\n2. Centigrade into Fahrenheit. In this case we multiply\\nthe C, reading by f, since 100\u00c2\u00b0 C. 180\u00c2\u00b0 F., and then add 32,\\nor F. |C. 32 (2)\\nSuppose C. 100\u00c2\u00b0, then F. f 100 3.2 180 32 212\u00c2\u00b0.\\nBy making C. F. in either (1) or (2) we can find the point\\nwhere both scales have the same reading. Thus\\nF. =f F. 32\\n5 F. 9 F. 160\u00c2\u00b0\\n4 F. 160\u00c2\u00b0\\nF. 40\u00c2\u00b0 C.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0183.jp2"}, "180": {"fulltext": "160 PHYSICS\\n3. Reaumur and Fahrenheit. In the same way by using\\nf and since 180\u00c2\u00b0 F. 80\u00c2\u00b0 E., we may turn E. and F. about\\nE. i (F. 32) (3)\\nF. |E. 32 (4)\\n4. Centigrade and Reaumur. Since 100\u00c2\u00b0 C. 80\u00c2\u00b0 E., we\\nhave C. E., and E. 0. (5)\\nIn nearly all German towns there is a public bathing\\nplace, where university professors and college students and\\nschoolboys go in warm weather for a daily swim. In some of\\nthe places the temperature of the water in degrees Eeaumur\\nis posted up each day, so that one may decide for or against\\na plunge. In the same way the regulations in German art\\ngalleries state in terms of Eeaumur the allowable variation\\nin temperature.\\n170. Self-recording Thermometers. It is sometimes desir-\\nable to have an instrument which will record either its own\\nFig. 105. Maximum and minimum thermometers.\\nextremes or its whole variation. The maximum and mini-\\nmum thermometer does the former, and Draper s the latter.\\nIn the first, two thermometer tubes are mounted horizon-\\ntally on the same scale board. The maximum thermometer\\nhas a small indicator, usually a bit of glass, inside the tube,\\nwhich the expanding mercury pushes in front of it, but\\nfails to pull back when it retreats itself. In this way we\\nhave a record of the highest temperature reached. The\\nminimum thermometer is filled with colored alcohol, and car-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0184.jp2"}, "181": {"fulltext": "SOME EFFECTS OF HEAT 161\\nries a little rider inside the fluid, which is so arranged that\\nit will retreat with the alcohol, but offers too much friction\\nwhen going in the other direction to advance with the alco-\\nhol. In this way we have a record of the lowest tempera-\\nture reached. Such instruments are often used in green-\\nhouses and other places where a narrow range of tempera-\\nture is necessary for success.\\nIn meteorological stations a more complete record is\\nwanted. In Draper s self-recording thermometer a pointer,\\nmoved by the expansion and contraction of metallic bars,\\ntraces its own movements on cards prepared for the pur-\\npose and made to rotate back of the pointer by means of\\nclockwork. Or the fluctuations of a column of mercury\\nmay directly photograph themselves on a roll of slowly\\nmoving sensitive paper passing back of them.\\n171. Expansion of Gases Correction of Volume for Tem-\\nperature. We have in gases the most perfect example of\\nexpansion and contraction. A cubic foot of any gas meas-\\nured in winter may expand in summer so as to occupy 170\\ncubic inches more than a foot. We have already found,\\nfrom a study of Boyle s law (124), that the measured\\nvolume of a gas must be corrected for pressure. It is evi-\\ndent, from what we have learned of the effects of heat, that\\nthe measured volume of gas must also be corrected for tem-\\nperature. It was a French physicist, Charles, who in 1787\\nfirst pointed out the law for the relation of volume of a gas\\nto changes of temperature. The volume coefficients for\\ndifferent gases vary slightly, but in general may be stated\\nto be .003663, or of their volume at zero centigrade.\\nThat is, gas which would measure a cubic foot at 0\u00c2\u00b0 0. would\\nmeasure at 27\u00c2\u00b0 C, the temperature of a rather warm summer\\nday (what would it be on Fahrenheit scale 1 cubic foot -f-\\n27 X .003663 cubic feet, or 170 cubic inches more than a\\ncubic foot. If the volume V is given of any gas at 0\u00c2\u00b0 C,\\nand we are required to calculate what its volume would be\\nat a given temperature t higher than zero, we multiply V\\n12", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0185.jp2"}, "182": {"fulltext": "162\\nPHYSICS\\nby 1 .003663 t. If we are required to calculate what its\\nvolume would be at a given temperature below zero we\\nmultiply V by 1 .003663 t. If the volume is given at a\\ntemperature above zero, and we are required to calculate\\nwhat it would be at zero, we divide V by 1 +.003663 t. If\\nthe volume is given at a temperature below zero, and we are\\nrequired to calculate what it would be at zero, we divide\\nFby 1 .003663 t.\\n172. The Air Thermometer.\u00e2\u0080\u0094 The coefficient of volume\\nexpansion for air was found by Gay-Lussac by means of a\\nthermometer with a very large bulb. This was\\nfilled with dry air, which was separated from\\nthe outside atmosphere by a little pellet of\\nmercury in the tube. Knowing the capacity\\nof the bulb and the diameter of the tube, the\\npercentage increase of volume on heating the\\nair through any given range of temperature\\ncould readily be calculated. The same instru-\\nment may be used as a thermometer.\\nIf the tube be made of some difficultly fusi-\\nble material, such as hard porcelain, the air\\nthermometer serves as an excellent instrument\\nfor measuring very high temperatures.\\n173. Pyrometers. As mercury boils at 350\u00c2\u00b0\\nC, and glass speedily softens, the ordinary\\nmercury thermometer can not be used to deter-\\nmine high temperatures. We use here a spe-\\ncial class of instruments known as pyrometers\\n(fire measures), which depend for their action\\nupon the expansion of air; the expansion of\\nmetal bars the melting of alloys of known melting points\\nthe softening of fire clays or the variable electric resistance\\nin a platinum conductor, due to change in the temperature.\\nIn general the resistance of the metals increases with heat,\\nand consequently the current passing through the con-\\nductor becomes weaker the higher the temperature. By\\nFig. 106.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0186.jp2"}, "183": {"fulltext": "SOME EFFECTS OF HEAT 163\\nmeasuring the current with a galvanometer we can measure\\nthe heat.\\n174. Range of Temperature. The lowest temperature so\\nfar reached is probably \u00e2\u0080\u0094225\u00c2\u00b0 C. (what would this be on\\nFahrenheit scale?), obtained by the evaporation of solid\\nnitrogen. The highest is probably that of the electric arc,\\nwhich is estimated to be about 3,500\u00c2\u00b0 C. Higher and lower\\ntemperatures than these are entirely conceivable, and un-\\ndoubtedly exist in other parts of the universe, but they are\\nquite outside the range of human experience.\\n175. Relation of Temperature to Animal and Vegetable\\nLife. Human life exists within rather narrow ranges of\\ntemperature, about 60\u00c2\u00b0 F. and 120\u00c2\u00b0 F., and none of us\\ncare to endure either of these extremes for any great length\\nof time.\\nWarm-blooded animals keep a constant bodily tempera-\\nture, however much the temperature may vary about them.\\nFor example, the temperature of the internal organs of a\\nhuman body must be kept at about 98\u00c2\u00b0 F., summer and win-\\nter, without change. How this is accomplished will be\\nlearned later. Some birds keep a constant temperature of\\n110\u00c2\u00b0 F. The temperature constant varies among different\\ntypes of warm-blooded animals. Birds and mammals (ani-\\nmals whose young are fed by the mother s milk) are warm-\\nblooded. All other animals are variable in temperature,\\nand their temperature varies as that of their surroundings.\\nThey are sluggish as the temperature falls, and more or less\\nactive as it rises.\\nThe distribution of plants and animals over the globe\\nappears to be controlled by temperature, so that we have\\ncertain kinds of plants and animals peculiar \\\\o the tropics,\\ncertain other kinds peculiar to the temperate zone, and still\\nother kinds peculiar to the frigid zones. All three kinds\\nof temperature zones may be found upon the slope of a\\nsingle mountain, each to a limited degree supplied with its\\nappropriate plants and animals.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0187.jp2"}, "184": {"fulltext": "164 PHYSICS\\n176. Heat determines the State of a Substance. A gas\\nmay apparently be expanded indefinitely, and so may take\\nany increase of temperature without changing its state.\\nNot so with solids and liquids. The heat may be increased\\nto a given point, called respectively the fusing and the boil-\\ning point, but beyond this any further increase of heat\\nshows itself by liquefaction and vaporization.\\n177. Fusion. All solids heated to a sufficient tempera-\\nture will melt. We can prove this by direct experiment\\nfor most solids and for others, such as carbon, we believe\\nit to be true. Some solids pass directly from a solid to a\\nliquid state, as ice, while others pass through an interme-\\ndiate pasty condition. The latter appears to be the result\\nof a change in the molecular structure, and has not yet\\nbeen clearly explained. This pasty condition is important\\npractically, since it allows the process of welding. Two\\npieces of wrought iron heated to a white heat may be\\njoined together into practically one piece by appropriate\\nhammering.\\nSulphur behaves very oddly. Heated at 114.5\u00c2\u00b0, it melts\\nto a thin, straw-colored liquid. At from 200\u00c2\u00b0 to 250\u00c2\u00b0 the\\nliquid takes on a rich reddish-brown color and becomes so\\npasty that the test-tube may be turned upside down with-\\nout loss. Heated still further, the pasty mass again be-\\ncomes perfectly liquid, grows darker in color, and finally\\nboils at 448.4\u00c2\u00b0 and may be distilled. Or if poured into\\ncold water and suddenly cooled, it for a time has the appear-\\nance of crude rubber.\\nThe following laws of fusion apply only to substances\\nwhich show a sharp, distinct melting point\\n1. The fusing temperature, under constant pressure, is\\nalways the same for the same substance.\\n2. The temperature during fusion remains constant\\nuntil the whole substance is melted.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0188.jp2"}, "185": {"fulltext": "SOME EFFECTS OF HEAT\\n165\\nTABLE OF MELTING POINTS.\\nMercury 39\u00c2\u00b0\\nIce 0\u00c2\u00b0\\nButter and lard 33\u00c2\u00b0\\nPhosphorus 44\u00c2\u00b0\\nPotassium 63\u00c2\u00b0\\nWax 65\u00c2\u00b0\\nSodium 95\u00c2\u00b0\\nSulphur 110\u00c2\u00b0\\nTin 230\u00c2\u00b0\\nBismuth 262\u00c2\u00b0\\nLead 326\u00c2\u00b0\\nZinc 412\u00c2\u00b0\\nAntimony 432\u00c2\u00b0\\nAluminium 600\u00c2\u00b0\\nBronze 900\u00c2\u00b0\\nSilver 954\u00c2\u00b0\\nGold 1045\u00c2\u00b0\\nCopper 1054\u00c2\u00b0\\nCast iron 1150\u00c2\u00b0\\nSteel 1350\u00c2\u00b0\\nWrought iron 1550\u00c2\u00b0\\nPlatinum 1775\u00c2\u00b0\\n178. Change of Volume due to Fusion. Nearly all solids\\nincrease in volume when they melt, so that as liquids they\\nare less dense, and consequently any unfused portions sink\\nto the bottom. With cast iron, water, and bismuth the\\nvery opposite is the case. They expand at the point of\\nsolidifying to make room for the crystals which form.\\nThis force of crystallization is immeasurably great, and, as\\nwe saw in section 164, is leveling mountains. As a result\\nof expansion, these solids are less dense and float on their\\ncorresponding liquids. Bismuth is added to lead in type\\nmetal so as to make it expand on solidifying, and fill out all\\nthe fine lines of the mold. For the same reason iron makes\\nfine castings and may be fashioned into delicate patterns in\\nstove castings and the like. Metals which do not thus ex-\\npand are made to receive impressions by stamping them with\\ndies. Ice, as we all know, floats on water. It has a density\\nof only .92, and consequently floats with .08 of its bulk out\\nof water. The giant icebergs seen in northern waters have\\n11^ times as much ice under water as above.\\n179. Change of Fusing Point under Pressure. The change\\nof volume that takes place on fusion makes it easy to\\nunderstand why pressure should change the fusing temper-\\nature. Where a solid expands on fusing, pressure increases\\nthe amount of work to be done, and hences raises the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0189.jp2"}, "186": {"fulltext": "166 PHYSICS\\nfusing point; but where the solid contracts on melting,\\npressure diminishes the amount of work to be done, and\\nso lowers the fusing point.\\n180. Effect of Alloys upon Fusing Point. In general,\\nmixtures of two or more solids melt at a temperature lower\\nthan their average fusing point, and sometimes less than\\nthe fusing point of any one of them. Thus an alloy con-\\ntaining two parts bismuth and one part each of lead and\\ntin melts at from 95\u00c2\u00b0 to 98\u00c2\u00b0 C. A bar of this alloy held in\\na jet of steam melts and drops off like butter.\\n181. Vaporization. Liquids pass to the state of vapor\\nby evaporation and boiling. Evaporation takes place at the\\nsurface only, and proceeds at all temperatures. In boiling,\\nthe formation of vapor takes place throughout the mass of\\nthe liquid, and only occurs at a definite temperature, which\\nvaries with the pressure and the nature of the liquid, but is\\nconstant for any given liquid under the same pressure.\\n182. Five Factors of Evaporation. The evaporation of\\nliquids depends upon five factors\\n1. Temperature of liquid.\\n2. Surface exposed.\\n3. Pressure.\\n4. Amount of vapor already in the atmosphere.\\n5. Eenewal of fresh atmosphere.\\nA moment s reflection will show this to be the case.\\nThe hotter the liquid, the more motion will its little par-\\nticles have, and the more able will they be to detach them-\\nselves from their neighbors and go off into space. Evapora-\\ntion, being a surface phenomenon, takes place in larger\\nmeasure the larger the surface exposed.\\nIn the chemical laboratory, where we often have occa-\\nsion to evaporate solutions, we satisfy these two conditions\\nof temperature and surface by using evaporating dishes\\nshallow little porcelain dishes which may be heated over a.\\nBunsen burner. Where we wish the temperature not to\\nexceed 100\u00c2\u00b0 C, we put the dish on a water bath. The same", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0190.jp2"}, "187": {"fulltext": "SOME EFFECTS OF HEAT 167\\nprinciples are utilized in drying fruit and other products by\\nspreading them out in the sun.\\nWhen a liquid evaporates, its vapor has to make way\\nagainst the overlying atmosphere. Consequently, the\\nsmaller the pressure, the less work to be done. Where a\\nhigh temperature is undesirable, evaporation is now gen-\\nerally carried on in vacuum pans. Our best dried fruits,\\ncondensed milk, sugar sirups, etc., are evaporated in this\\nway.\\nThe amount of vapor already in the atmosphere deter-\\nmines the rate of evaporation, because, as we shall see in\\nthe next paragraph, a given space can only take up a given\\namount of vapor. For the same reason a renewal of atmos-\\nphere furthers evaporation. The weekly wash is hung out\\nin the open air to dry, utilizing the heat of the sun, the sur-\\nface of the garments, and the renewal of air by the wind.\\nIn dry climates, as in Colorado, one s collar never wilts\\nhowever hot the weather, since the skin always remains dry,\\nthe perspiration evaporating as soon as formed.\\n183. The Evaporation of Solids. By the term evapora-\\ntion we mean, in general, the passage of a liquid to a gase-\\nous condition. But we have also apparently the changing\\nof solids to gases without passing through the liquid state.\\nThus snow and ice pass directly into a vapor without the\\nvisible formation of moisture when the weather is very dry,\\neven though the temperature may be below the freezing\\npoint. Wet clothes hung out upon the line in such weather\\nfreeze stiff, but the ice will nevertheless disappear from\\nthem in a few hours. Often after a little rain in winter it\\nclears off cold and windy. The moisture upon the sidewalk\\nfreezes to a thin glade of ice. A dry wind is blowing, and\\nthe temperature is falling all the time, but in a few hours\\nall the ice disappears. In the same way certain volatile\\nsolids, such as camphor and ammonium-carbonate, are\\ngreedily taken up by the atmosphere. Under the influence\\nof heat other solids, such as iodine and arsenic, pass directly", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0191.jp2"}, "188": {"fulltext": "168 PHYSICS\\ninto the condition of vapor, and condense as solids again\\nwhen sufficiently cooled, a process which we distinguish as\\nsublimation, the condensed products being called subli-\\nmates. But in all these cases we are forced to imagine\\nthat the solids passed, if only momentarily, through the\\ncondition of liquid before it reaches the gaseous state,\\nsince our experience obliges us to conceive of these states\\nas continuous.\\n184. Vapors. The amount of evaporation that may take\\nplace when a liquid is exposed to a given space is almost\\nindependent of the amount of other gases and vapors pres-\\nent in that space a condition which is commonly summed\\nup by saying that to vapors all space is empty. Under given\\nconditions of temperature and pressure, a given space can\\nonly contain a certain amount of a vapor. When this maxi-\\nmum amount is present, the vapor is said to be saturated.\\nBelow this point the vapor is said to be unsaturated.\\nThere is no hard-and-fast line between gases and vapors.\\nThe term gas is usually applied to those bodies, like oxygen,\\nhydrogen, and nitrogen, that may be liquefied only under\\nvery high pressure and at very low temperature, while\\nthe term vapor is reserved for the gaseous state of those\\nbodies, such as water, ether, and alcohol, which under ordi-\\nnary conditions exist as liquids.\\n185. Critical Temperature. The greater instrumental\\nfacilities that have been brought about by the mechanical\\nprogress of recent years have made many remarkable ex-\\nperiments possible. Especially has it enabled us to study\\nthe behavior of gases under great pressure. The old dis-\\ntinction of the permanent gases has been broken down\\ncompletely, since every one of them\u00e2\u0080\u0094 oxygen, hydrogen,\\nnitrogen, the atmosphere itself has been reduced to the\\nliquid and even to the solid state. But the temperature\\nmust always be taken into account. These experiments\\nhave all been conducted at very low temperatures, under\\nconditions therefore which rob the gases of a large part of", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0192.jp2"}, "189": {"fulltext": "SOME EFFECTS OF HEAT\\n169\\ntheir molecular energy. It has been found, for example,\\nthat carbonic-acid gas (C0 2 which can readily be liquefied\\nunder a pressure of a few atmospheres, can not be liquefied\\nat all if the temperature be above 31\u00c2\u00b0 C. Below this tem-\\nperature, under pressure, the substance becomes a liquid\\n31\u00c2\u00b0 C. is therefore spoken of as the critical temperature for\\ncarbon dioxide. It is probable that all gases have such\\na critical temperature, above which they can not by any\\namount of pressure be liquefied.\\n186. Boiling. With increasing temperature, vapors exert\\nan increasing pressure. As soon as this pressure becomes\\nequal to the surrounding atmospheric pressure, the process\\nof boiling takes place, which, as we have seen, is simply the\\nformation of vapor throughout the liquid. If water be\\nheated in a glass flask, the heat being applied, of course, to\\nthe bottom of the flask, it will be noticed that the first\\nbubbles produced at the bottom of the water collapse before\\nthey reach the surface. This produces the well-known\\nsinging which is familiar to every watcher of the tea-\\nkettle. In spite of the rapid cur-\\nrents, the upper layers of water are\\ncolder than those below, and so\\ncondense the rising bubbles. When\\nall the water is boiling hot, the bub-\\nbles reach the surface, and the wa-\\nter boils freely.\\nAfter the water has been boiling\\nfor some time we shall have all the\\nair driven out of the flask, and only\\nvapor of water occupying the space\\nabove the water. If, now, the flask\\nbe tightly corked and inverted in a\\nstand over a suitable trough, we\\nmay make the water boil again, and quite tempestuously,\\nby pouring cold water over the outside of the flask. This\\nresult is ordinarily so unexpected that it was early named\\nFig", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0193.jp2"}, "190": {"fulltext": "170 PHYSICS\\nthe culinary paradox, but in reality it is very easily ex-\\nplained. The cold water chills the flask, and so condenses\\nthe vapor of water inside. This greatly reduces the pres-\\nsure, and consequently the boiling point. Though now\\nbelow 100\u00c2\u00b0, the water in the flask is still highly heated.\\nThe cold water can not, of course, heat the water in the\\nflask up to the ordinary boiling point, but it can and does\\nbring the boiling point down to the temperature of the\\nwater.\\n187. Laws of Boiling and Table of Boiling Points.\\n1. Under a given pressure, every liquid has a definite\\nboiling point.\\n2. When the boiling point is reached, the temperature\\nremains constant, until the liquid is completely vaporized.\\n3. The pressure of the vapor given off during boiling is\\nequal to the atmospheric pressure.\\nTABLE OF BOILING POINTS.\\nWater 100 c\\nAlcohol 79 c\\nEther 37\u00c2\u00b0\\nSpirits of turpentine 130\u00c2\u00b0\\nSulphuric acid 325\u00c2\u00b0\\nMercury 353\u00c2\u00b0\\nSulphur 440\u00c2\u00b0\\nPhosphorus 290\u00c2\u00b0\\n188. Changes in the Boiling Point. The boiling point is\\nso characteristic that it is often used, particularly in organic\\nchemistry, to determine whether we have to deal with a\\nsingle liquid or a mixture. The same principle is made use\\nof in fractional distillation. By keeping the temperature\\nconstant, the liquids which distill over will be mainly those\\nboiling at or under that temperature. Or we may allow the\\ntemperature to rise at will, and collect the vapors given off\\nwithin certain limits, such as 80\u00c2\u00b0 to 85\u00c2\u00b0, 85\u00c2\u00b0 to 90\u00c2\u00b0, etc.\\nThis process is used in separating the lighter constituents\\nbenzine, naphtha, etc. from the heavier oils in crude petro-\\nleum. Any change in the composition of a liquid at once\\nchanges its boiling point. Pure water alone boils at 100\u00c2\u00b0 C.\\nIf mixed with alcohol, the boiling point is lowered. If there", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0194.jp2"}, "191": {"fulltext": "SOME EFFECTS OF HEAT 171\\nare any salts in solution, the boiling point is raised. Com-\\nmon salt may be dissolved in water so as to raise the boiling\\npoint to 102\u00c2\u00b0, saltpeter to 116\u00c2\u00b0, potassium carbonate to\\n135\u00c2\u00b0, and calcium chloride to 179\u00c2\u00b0.\\nThe range in boiling points is very great. Liquefied\\ngases boil at many degrees, even hundreds of degrees below\\nzero, as liquid oxygen, at 1 80\u00c2\u00b0 C. Light liquids boil below\\n100\u00c2\u00b0, as alcohol at 78\u00c2\u00b0, and benzine at 80\u00c2\u00b0. Heavy liquids\\nboil at higher temperatures, as mercury at 350\u00c2\u00b0.\\nBut the greatest change in the boiling point comes from\\nvariations in the pressure. This is but natural, since boil-\\ning takes place when the vapor pressure equals the atmos-\\npheric pressure. Water boils at 0\u00c2\u00b0, when the pressure is\\nreduced to almost nothing. At places much above the sea,\\nwater boils at so low a temperature as to introduce incon-\\nveniences into the kitchen. Eggs and vegetables boiled in\\nsuch water are not sufficiently cooked. Devices are used\\nto increase the boiling point by either adding some salt to\\nthe water or by increasing the pressure artificially. On\\nthe other hand, where the pressure is greatly increased, as\\nin the boiler of a locomotive, the boiling point may even be\\ndoubled. Under a pressure of 30 pounds the boiling point\\nrises to 120\u00c2\u00b0 C. under 45 pounds, to 134\u00c2\u00b0 under 60 pounds,\\nto 144\u00c2\u00b0 under 75 pounds, to 152\u00c2\u00b0 under 90 pounds, to 156\u00c2\u00b0\\nand under 150 pounds, to 180\u00c2\u00b0. If the pressure upon such\\na body of superheated water be suddenly removed, as by a\\nleak, the water bursts into steam, and we have an explosion\\ncomparable to that of gunpowder.\\nThe nature of the containing vessel also influences the\\nboiling point. Water may be made to boil several degrees\\nhigher in a glass vessel than in a metal one. Under favor-\\nable conditions, we have found this difference as great as\\n3\u00c2\u00b0 C, and other experimenters have even reported a differ-\\nence of 6\u00c2\u00b0. For this reason, thermometers are standardized\\nfor 100\u00c2\u00b0 by immersion in steam rather than in water. (See\\nFig. 103.)", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0195.jp2"}, "192": {"fulltext": "172 PHYSICS\\n189. Determination of Altitude by Thermometer. The\\nlowering of the boiling point of water by decrease of pres-\\nsure furnishes a means of measuring height by the ther-\\nmometer. At sea level the boiling point is 100\u00c2\u00b0 0. The\\ndecrease is not uniform, but in general it may be said that\\na lowering of the boiling point 1\u00c2\u00b0 C. indicates an ascent\\nof 295 metres, or 538 feet for 1\u00c2\u00b0 F.\\nAltitude 295 (100 t) metres.\\n190. Saturation. A certain volume of air, or the same\\nempty space, can hold only a given quantity of vapor. It\\nis then said to be saturated. It is found, however, that\\nthis quantity increases with the temperature, and that the\\nmaximum quantity is constant only for a given tempera-\\nture. We may express the quantity of vapor present in\\nthe atmosphere, or in empty space, in three ways\\n1. By stating in grams the absolute weight of the vapor\\npresent in, say, one cubic metre.\\n2. By expressing the relative saturation or humidity\\nthat is, the actual vapor present as a percentage of the\\nmaximum vapor that might be present at that temperature.\\n3. By giving the vapor tension.\\n191. Vapor in the Air\u00e2\u0080\u0094 Dew Point. The most impor-\\ntant application of these principles is found in the measure-\\nment of the water vapor present in the atmosphere, for\\nupon this depends so many climatic and hygienic con-\\nditions. So long as the atmosphere is not saturated, and\\nis not chilled at any one point, we are only indirectly con-\\nscious that there is any moisture present. But if a body\\nof moist air suffers a decrease of temperature, the actual\\namount of water vapor remains the same, but the relative\\nhumidity increases, since the cool air is nearer to its point\\nof saturation. If the cooling proceed far enough, the point\\nof saturation is reached, and moisture thus formed is known\\nas deiv, if it deposit as a liquid film on solid objects as\\nfrost, if it deposit as a solid film of ice as cloud, or mist, or\\nfog, if it deposit as liquid particles in the air or, finally,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0196.jp2"}, "193": {"fulltext": "SOME EFFECTS OF HEAT\\n173\\nas snow, or sleet, or hail, if it deposit as a solid precipitate in\\nthe air. The temperature at which such precipitation of\\nmoisture takes place is called the dew point. In dry air,\\nthe dew point is very low, since the air must be greatly\\ncooled before it will deposit any moisture.\\nIn damp air, on the contrary, the dew point\\nis very high, because a slight cooling causes\\na precipitation of moisture.\\n192. Humidity. A variety of instruments\\nare used for measuring the amount of mois-\\nture in the air among others are the wet-\\nand dry-bulb thermometers.\\nTwo thermometers are mounted on arms\\nfrom the same stand. The bulb of one of\\nthem is covered with muslin, kept moist by\\na cotton wick leading from a glass of water.\\nThe constant evaporation from the muslin\\nreduces the temperature and makes the read-\\ning of this thermometer lower than that of\\nthe free one (217). But the rate of evapo-\\nration depends, among other things, upon\\nthe amount of moisture already present in\\nthe atmosphere, and the fall in the wet-bulb\\nthermometer will therefore be an indication\\nof the hygroscopic condition of the atmos-\\nphere. The relative humidity is obtained from specially\\nprepared tables.\\n193. Rainfall. The amount of precipitation, or the\\nrainfall, is measured in English-speaking countries in\\ninches. The annual rainfall is the depth at which the\\ntotal rain would stand had it fallen on a perfectly level sur-\\nface and none been lost. It is measured by means of a\\nrain gauge, an instrument which collects the precipitation\\nover a given area. The water collected is poured into a\\ntall measuring glass of small diameter, so that the rainfall\\ncan be measured to the hundredths of an inch.\\nFig. 108.\u00e2\u0080\u0094 Wet-\\nand dry-bulb\\nthermometers.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0197.jp2"}, "194": {"fulltext": "1?4\\nPHYSICS\\nThere are places in the interior of the continent, in\\nDeath Valley, in the Sahara, and elsewhere, which have no\\nrain the year round. The greatest rainfall is supposed to\\nbe in northern India, at the foot of the Himalaya Moun-\\ntains, where it amounts to over 600 inches. In the English\\nlake district the rainfall amounts to over 150 inches. It is\\nonly 24 at London and Edinburgh, yet the prevalence of\\nfog makes these cities seem much damper than our own.\\nIn the United States it varies over a wide range. It is about\\n45 inches in our Eastern seaport cities. The following table\\nshows the annual rainfall in a number of localities\\nBoston, Mass 44.96\\nNew York, N. Y 44.80\\nPhiladelphia, Pa 39.84\\nBaltimore, Md 43.95\\nWashington, D. C 43.46\\nCharleston, S. C 56.74\\nNew Orleans, La 60.52\\nSt. Louis, Mo 41.08\\nChicago, 111 34.76\\nSt. Paul, Minn 27.47\\nDenver, Col.. 14.49\\nSanta Fe., New Mexico 14.25\\nPhoenix, Ariz 7.21\\nSan Diego, Cal..... 10.51\\nLos Angeles, Cal 18.30\\nSan Francisco, Cal 13.71\\nSeattle, Wash 37.44\\nPortland, Ore 46.83\\n194. Moisture and Health. The humidity of the air has\\na marked influence on comfort and health. Moisture makes\\nthe sensations of both heat and cold particularly painful.\\nIn the dry interior in Minnesota and Dakota, for example\\na temperature of \u00e2\u0080\u009440\u00c2\u00b0 F. is not uncomfortable if the wind\\nbe very light, while in damper Eastern climates a tempera-\\nture of 0\u00c2\u00b0 E. chills us through.\\nOn the other hand, our methods of heating buildings in\\nwinter make the air too dry for health and comfort. It is\\nnot the absolute amount of moisture, but the relative amount\\nwith reference to temperature\u00e2\u0080\u0094 the approximation to the\\ndew point\u00e2\u0080\u0094 that is to be considered for health and comfort.\\nWe are most comfortable when the moisture in the air is\\nfrom fifty to seventy-five per cent of the amount required\\nfor complete saturation. Prof. E. De 0. Ward, of Harvard\\nUniversity, says our houses in winter have a desert climate.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0198.jp2"}, "195": {"fulltext": "SOME EFFECTS OF HEAT 175\\nThe mean annual humidity at Santa Fe is 44.8 per cent.\\nThe humidity in our houses in winter time is frequently\\n30 per cent, while, at the same time, the humidity out-\\ndoors may be 71 per cent.\\n195. Illustrations. The air exhaled from the lungs, or\\nthe breath, as we call it, is warm and moist warm from\\nthe bodily heat and moist from the evaporation that takes\\nplace from the internal pores. If the surrounding air be\\ncold, the moisture in the breath precipitates as a mist, and\\nwe have the phenomenon known as seeing our breath.\\nIn summer time, the air being more moist then, a glass of\\ncold water, or an ice pitcher, becomes covered with dew, and\\nsome people wonder how the water ever got through the\\nglass or the pitcher, but we soon learn that the water did\\nnot come through at all. It deposited from the surround-\\ning air. This was cooled to the dew point by contact with\\nthe cold glass or pitcher, and so had to deposit some of its\\nmoisture.\\nOn a cool morning in spring or fall, or on a damp morn-\\ning in summer, we find a fine deposit of dew on the grass,\\non cobwebs, stones, boards, and other objects. These cool\\nmore rapidly than the surrounding air, and so have a lower\\ntemperature hence the deposit of dew. Again, on a damp\\nday, a few strokes of the air pump will so far expand and\\ncool the air in the receiver that a noticeable mist will be\\nproduced.\\nTyndall mentions that on one occasion, when a ball was\\nin progress at the Winter Palace in St. Petersburg, the\\nrooms became overheated, and the outside doors were\\nthrown open. The very cold air that rushed in chilled the\\nwarm, moist air to such an extent that the precipitated\\nmoisture froze and fell as snow. The same phenomenon\\nhas been known to take place in large train sheds. The\\nhot, moist air from the locomotives, rising into the cold\\nair in the upper regions of the sheds, produces a slight\\nsnowfall.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0199.jp2"}, "196": {"fulltext": "176 PHYSICS\\nIn Nature, the precipitation of moisture is seen on all\\nsides. The air directly over a river or lake is moist. When\\nthis air is chilled by other air currents, the moisture pre-\\ncipitates, and often, in the early morning, if one is on top\\nof a mountain, the course of a neighboring river can be dis-\\ntinctly traced by the serpentine line of fog. A very hot\\nday gives rise to generous evaporation on all sides, and the\\nafternoon of such a day is apt to see heavy thunder clouds\\nand showers. The phenomenon of regular fog precipitation\\nis perhaps nowhere better seen than in southern California.\\nThe air presses eastward across California, to replace the\\nhot air of the arid regions in the southeastern part of the\\nState and in western Arizona. This air comes off the\\nPacific, and is therefore moist. As it chills, the moisture\\nfalls out as a heavy fog, which may trail eastward from the\\ncoast for several miles.\\nThe same thing is seen in the cloud banners that attach\\nto some of the slender mountain peaks in the Alps, such as\\nthe Matterhorn. The moist air blowing against these cold,\\nneedle-like summits is sufficiently chilled to deposit its\\nmoisture. The cloud thus formed trails off from the moun-\\ntain as a long, graceful banner, and takes, of course, the\\ndirection of the wind. Such a cloud may appear constant\\nfor several hours, although it is continually making and\\nunmaking making at the mountain, and unmaking at the\\nend, by dissolving into the air again.\\nThe formation of dew and frost depends largely upon\\nthe clearness of the atmosphere. (This will be explained in\\nsection 203.) On a cloudless, quiet night, the deposit will\\nbe comparatively heavy. Plants and other objects part with\\ntheir heat more freely on such a night. A very thin covering,\\nsuch as a piece of paper, by preventing the escape of heat,\\nwill present dew from collecting upon an object. .Note\\nthat it is not that the paper collects the dew which would\\nfall upon the object, but that the paper prevents the object\\nfrom cooling so as to collect dew from the air which touches", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0200.jp2"}, "197": {"fulltext": "SOME EFFECTS OF HEAT 177\\nit. Compare this with the way an ice pitcher collects dew.\\nOn a cloudy night there is much less deposit, because the\\nclouds act as the paper screen. If a wind is blowing, there\\nis also less chance for deposit, since the air does not remain\\nlong enough in contact with the earth to become chilled.\\nOn cloudy, windy nights, there is rarely either dew or frost.\\n196. Condensation, Solidification, and Crystallization.\\nThese processes are the opposite of vaporization and melt-\\ning, and are always accompanied by the giving out of heat.\\nAny change in matter which makes it more mobile, as\\nmelting, solution, vaporization, takes in heat while any\\nchange which makes it less mobile gives out heat. (Sec-\\ntions 218 and 219.)\\n13", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0201.jp2"}, "198": {"fulltext": "CHAPTEE XX\\nHOW HEAT IS TRANSFERRED\\n197. General Statement. The transference of heat means\\nsimply the transference of molecular motion from one body\\nvibrating with a given intensity to another body vibrating\\nwith a less intensity. It is a transfer of energy in precisely\\nthe same way that mechanical reactions are transfers of\\nmass energy. There are many ways by which mass energy\\nmay be transferred from one body to another, as we saw in\\nstudying machines. There are three ways by which heat\\nmay be transferred from one body to another conduction,\\nconvection, and radiation.\\n198. Conduction. This, although the least effective, is a\\nvery common way by which heat is diffused. If a stout\\niron wire have one end placed in a fire or other source of\\nheat until it become red hot, we notice that the heat ap-\\npears to travel along the wire, and, if the wire is not too\\nlong, affects the distant end perceptibly. Since the mole-\\ncules are not free to move along the length of the wire, but\\nare only free to vibrate within very narrow limits, it must\\nbe that the motion is passed along the wire from molecule\\nto molecule, just as a blow may be passed along a line of\\nboys, each boy receiving a blow from one neighbor and\\npassing it on somewhat diminished (we will say) to the\\nneighbor on the other side. We thus have at one end of\\nour wire molecules so excited that they are red hot, and at\\nthe other end molecules that are comparatively cool. But\\ntwo molecules in different states of motion can not exist\\n178", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0202.jp2"}, "199": {"fulltext": "HOW HEAT IS TRANSFERRED\\n179\\nside by side without an interchange taking place, and some\\nmovement toward equilibrium. So the tendency is for the\\nwire to become equally hot throughout its length, and for\\nthe stream of heat-motion to continue flowing from the hot\\nto the cold end until this equilibrium is brought about.\\nIf there were no loss of heat, the wire would in reality\\nbecome red hot throughout its entire length* whatever that\\nmight be. But meanwhile the wire is in contact with the\\ncooler air, and must give up its heat to that as well as to\\nthe colder portions of its own length. Consequently, if the\\nwire be long enough, there will be a point where the loss\\nand gain just equal each other. Heat will consequently\\nflow from the source to this point, and the wire will show\\ndiminishing heat intensity. Beyond this point the wire\\nwill have the same degree of heat as the surrounding air.\\nWe might define conduction, then, as a transference of\\nheat from molecule to molecule, and limited mainly to solid\\nbodies. There is slight conduction among the molecules of\\nfluids, but the mobility of the molecules makes it possible\\nfor them to be the direct carriers of heat without passing it\\nalong molecule to molecule, as in the case of the more rigid\\nsolids.\\nSolids and fluids differ much in their conducting power.\\nIn genera], the more compact the structure, the greater the\\nconductivity. Hence the metals are the best conductors\\nwood and stone are poor conductors, and fibrous materials,\\nsuch as fur, felt, and cloth, which contain many air spaces,\\nare bad conductors. The best conductor we have is silver\\nthe worst conductor, air. The following table arranges the\\nmetals in order of diminishing conductivity relative to\\nsilver\\nSilver 1.000\\nCopper 736\\nGold 532\\nBrass 231\\nZinc 190\\nIron 119\\nSteel 116\\nLead 085\\nPlatinum 084\\nBismuth 018", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0203.jp2"}, "200": {"fulltext": "180 PHYSICS\\nThere are many practical ways of showing the different\\nconducting power of the metals. Thus wires of different\\nmetals are fastened in-\\nFig. i09.-Conduction. the projecting ends.\\nWhen boiling water is\\npoured into the box, the unequal melting of the wax shows\\nthe unequal conductivity of the metals.\\nLiquids are very poor conductors. A test tube full of\\nwater may be made to boil in the upper portions, while the\\nlower portions are quite cool.\\n199. Applications. There are hundreds of daily applica-\\ntions of these principles. The non-conductors are used either\\nto keep heat out or to keep it in. In the former case, as in\\nice-houses, the walls are made of brick, straw, sawdust,\\nashes, etc., and serve to keep out heat. But more frequently\\nnon-conductors are used to keep the heat in. In buildings,\\nboth of brick and of wood, a hollow air chamber is allowed\\nbetween the outer and the inner walls, since, as we have\\nseen, air is the poorest conductor. For the same reason,\\ndouble windows keep out the cold, not so much by guarding\\nus from currents of air as by interposing an air chamber.\\nThe same principles obtain in our clothing. Loose, fibrous\\nmaterials and loose garments are warmer than close, tight-\\nfitting goods. Flannel blankets are warmer when new, and\\nbefore the fibers have been closely matted together. The\\nNorwegian cooking box is another application. It is made\\nof wood and lined with felt. A covered metal pail, con-\\ntaining water and the joint of meat boiling hot, is placed\\ninside the cooking box, and the whole carefully closed.\\nThe loss of heat is very slow, and the cooking process goes\\non for several hours without the application of any addi-\\ntional outside heat.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0204.jp2"}, "201": {"fulltext": "HOW HEAT IS TRANSFERRED 181\\nThe furnace in the basement for heating houses is mere-\\nly a large iron stove, around which a wall of brick is built to\\nprevent the heat from passing out into the cellar. If it is\\na hot-air furnace or a hot-water heater, its heat is\\ncarried to all parts of the building by a process to be dis-\\ncussed in the next section. If it is a steam-heater, its\\nheat is stored, distributed about the building, and recovered\\nby processes to be discussed in sections 213 and 218. The\\nducts which carry the hot air, hot water, or steam about the\\nbuilding are incased in brick walls, where that is possible,\\nto prevent the loss of their heat in transmission. Where\\nthese ducts pass through the open basement, they are some-\\ntimes covered with non-conducting material of loosely\\nwoven hair or felt. Wrapped with this covering, steam\\npipes are frequently carried long distances underground\\nto heat remote buildings. In comparison with other mate-\\nrials, the earth is not a very bad conductor, and yet con-\\nduction is such a poor method of diffusing heat that, as\\nhas already been said, although heat so intense exists be-\\nneath the surface as to fuse the rocks, yet that heat does\\nnot penetrate to the surface sufficiently to effect a rise in\\ntemperature of one thirty-sixth of a degree.\\nWater pipes are laid a few feet underground to prevent\\nthem from freezing in winter\u00e2\u0080\u0094 that is, the earth is a suffi-\\nciently poor conductor to prevent the heat from passing out\\nof the water to such an extent that it may freeze. (It is\\nbetter to state it thus, than to speak of cold passing in\\nthrough the earth to the pipes just as we speak of light\\ncoming into a room through a window, but do not speak\\nof darkness doing the same.) We should remind ourselves\\nthat all things have some heat, and that when things grow\\ncold they are simply losing some of their heat.\\nWe sometimes ride in an open carriage in the coldest\\nweather and are quite comfortable, because we wrap our-\\nselves in what we call warm clothing and blankets. We\\nsleep in cold rooms comfortably, or may be even too hot,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0205.jp2"}, "202": {"fulltext": "182 PHYSICS\\nunder our warm blankets. Now, they are not warm at\\nall indeed they are just the temperature of all other\\nthings around them, so that if we wrap a thermometer up\\nin warm clothes or blankets it will not show the least\\nbit of rise in temperature. In order that our ideas may\\nbe clear we should use some other word than warm to\\ndescribe these coverings. What we need is some word like\\nnon-conducting, which would imply that they keep the\\nheat of our bodies from passing off. Our bodies generate\\nat all times a great deal more heat than we need. It is\\nonly necessary that we regulate the outflow of this heat so\\nthat the temperature of our vital organs may be always\\nabout 98\u00c2\u00b0 F., night and day, summer and winter, at work\\nor at rest.\\nThe chemical action, which, as was said in section 160,\\nproduces heat in piles of green grass, new hay, piles of oily\\ncotton waste, etc., is very slow and produces very little\\nheat per hour, but these substances are such poor conduc-\\ntors that the heat is not allowed to pass off, and it is pos-\\nsible for it to accumulate until it reaches the kindling tem-\\nperature of the substance, when spontaneous combustion\\nwill take place.\\nSnow protects vegetation in winter from killing frosts.\\nIt must be remembered that solutions do not freeze as\\nreadily as pure water, and therefore the juices of plants\\nwill not freeze at 32\u00c2\u00b0 F. While the snow can not enable\\nthe plants to rise above that temperature, it does prevent\\nthem from falling much below it among other reasons,\\nbecause being filled with air spaces it is a very poor con-\\nductor.\\n200. Convection. This practically means the transfer of\\nheat by the transfer of the heated body itself. Fluids are\\nheated almost entirely by this process. If we consider the\\nheating of water in a teakettle, or, better still, in a glass\\nbeaker, where we can see what is going on, we shall notice\\nthat the whole fluid is in a state of constant motion. A", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0206.jp2"}, "203": {"fulltext": "HOW HEAT IS TRANSFERRED\\n183\\nFia. 110.\u00e2\u0080\u0094 Convection.\\nlittle sawdust in the water will make the action plainer.\\nThe source of heat is under the beaker (Fig. 110), and the\\nbottom is naturally the hot-\\ntest part. The water di-\\nrectly in contact with this\\nbecomes heated, expands,\\nand in so doing grows light-\\ner. The colder, heavier wa-\\nter, therefore, presses down\\nunder this and buoys it up\\ntoward the surface. As soon\\nas this becomes cooled and the other hot, another overturn-\\ning occurs, and so the process goes on until the whole mass\\nof water is heated to the boiling point, if the source of heat\\nbe intense enough, or to the point where loss and gain of\\nheat just balance. In the same way a stove or a steam radi-\\nator warms the air of a room. The air is such a poor con-\\nductor that we should be badly off if we had to depend\\nupon its passing along the heat to us by conduction. In\\nreality, the air in contact with the stove or radiator becomes\\nheated and is buoyed\\nup by colder, heavier\\nair.\\nThis is illustrated\\nby Fig. 111. We may\\nthink of the air in\\nthe pasteboard box as\\na pair of scales with\\ncolumns of air of\\nequal weight stand-\\ning upon either scale\\npan. A candle is\\nlighted at the bottom\\nof column a, which expands it and drives a portion of the\\nair out. What remains is no longer heavy enough to bal-\\nance the weight of the column b, and it pushes down and\\nV\\nX mJh\\nf\\ni\\na\\n\u00e2\u0096\u00a0S\\nb\\nJi\\n1\\nz^m\\nFig. 111. Convection.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0207.jp2"}, "204": {"fulltext": "18J: PHYSICS\\nforces a movement of air through the box and up which\\ncontinues as long as the heat is supplied by the c.andle.\\nThe upper part of a room is warmest and may be many\\ndegrees above the air near the floor. We notice it very\\nplainly if we have occasion to climb up on a stepladder to\\nhang a picture. If we set the door of a room ajar, we may,\\nby means of a candle flame, show that currents of air (cold\\nair) are coming in at the bottom and currents of air (warm\\nair) are going out at the top of the door.\\nIf a room is to be ventilated by the windows, the best\\nway is to make a small opening at both top and bottom,\\nsince this promotes convection currents.\\nThis principle of convection is of the utmost impor-\\ntance in Nature. It is the great source of movement in the\\natmosphere. The unequal heating of the air above land\\nand sea creates our so-called land and sea breezes. The\\ngreater heat at the tropics causes the air there to expand,\\nand in consequence the colder air from polar latitudes\\npushes in and takes its place. This action, combined with\\nthe earth s daily rotation, is the source of those permanent\\nair movements known as the trade winds.\\nThe heating of water by convection, and the resulting\\nconvection currents in oceans and lakes, are great equal-\\nizers of temperature the world over. By convection we\\nheat the water in the kitchen boiler from the stove. By a\\nsimilar process houses are heated by hot water. The hot-\\nair furnace is dependent upon convection to convey its\\nheat over the house and many methods of ventilation\\ndepend upon this way of promoting air currents.\\n201. Radiation. This third process of transferring heat\\nis different from either conduction or convection. It is so\\nclosely allied to the propagation of light that we shall con-\\nsider it at length when we come to take up the mechanics\\nof the ether. We shall discuss it here rather briefly.\\nConsider how we get heat from a fire on the hearth.\\nEvidently it is not brought to us by conduction, for air", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0208.jp2"}, "205": {"fulltext": "HOW HEAT IS TRANSFERRED 185\\nis almost an absolute non-conductor. Neither can it reach\\nus by convection, for all the air currents move from us\\ntoward the fireplace, and up the chimney. Indeed, it is\\nfound that the heat would reach us quite as well, and even\\nbetter, if there were no air or any other substance between\\nus and the fire. The sun, and every other heated body,\\nappears to give off heat in all directions throughout space.\\nYet we believe that heat, being molecular motion, can not\\nexist apart from matter, and consequently we think it can\\nnot be transmitted as heat through space. Space reacts as\\nif it were filled with some medium, neither gaseous nor\\nliquid, but having some properties of a solid. The more\\nwe study the phenomena of space, the more we seem com-\\npelled to assume that all space is filled with a very tenuous\\nmedium called the ether, which is capable of transmitting\\na variety of wave motions, some of which beget heat, some\\nlight, and some electrical phenomena, upon reaching the\\nearth. Hot bodies are supposed to be able, by means of\\nmolecular motions, to set up vibrations in the ether, and the\\nether is capable of setting up molecular motions in bodies of\\nmatter. Heat transferred by radiation is supposed, there-\\nfore, to be transferred by a wave motion of the ether. It is\\ncalled radiant heat, because it goes out in all directions\\nthrough space in straight lines or radii, which have their\\ncenter in the heated body. This wav e motion has a velocity\\nof about 186,000 miles per second, and for such distances as\\nwe have to deal with on the earth, may be considered in-\\nstantaneous.\\nAll matter with which we are acquainted radiates ether\\nwaves, because all substances have some heat that is, mo-\\nlecular motion so that every portion of matter is radiating\\nheat to every other portion of matter. The hotter ones\\nradiate more abundantly than the cooler ones, and thus\\ntend to bring about a state of equilibrium. Moisture in\\nthe air converts ether waves into heat. If we go up into\\nthe upper regions of our atmosphere, either upon a moun-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0209.jp2"}, "206": {"fulltext": "186 PHYSICS\\ntain top or in a balloon, where there is scarcely any moist-\\nure, we find that the sun s rays produce intense heat in us,\\nbut the air about us is, nevertheless, extremely cold. Tyn-\\ndall says A joint of meat might be roasted before a fire\\nwith the air around the joint as cold as ice. The air on\\nhigh mountains may be intensely cold, while a burning sun\\nis overhead the solar rays which, striking on the human\\nskin, are almost intolerable, are incompetent to heat the\\nair sensibly, and we have only to withdraw into perfect\\nshade to feel the chill of the atmosphere. I never, on any\\noccasion, suffered so much from solar heat as in descend-\\ning from the Corridor to the Grand Plateau of Mont\\nBlanc, on August 13, 1857. Though Mr. Hirst and myself\\nwere at the time hip-deep in snow, the sun blazed against\\nus with unendurable power. Immersion in the shadows of\\nthe Dome du Goute at once changed our feelings, for here\\nthe air was at freezing temperature. It is not, however,\\nsensibly colder than the air through which the sunbeams\\npassed and we suffered, not from the contact of hot air,\\nbut from radiant heat, which had reached us through an\\nicy cold medium.\\nA hot body, by .its molecular motion, sets up ether\\nwaves. These ether waves may be sent through a lens cut\\nout of ice and focused upon paper, there to set up those\\nmolecular motions which we call heat and set fire to the\\npaper. It was heat in the radiating body, and it became\\nheat again in the body or bodies which received it, but it\\nwas not heat in passing.\\n202. Absorption, Radiation, and Reflection. When ether\\nwaves impinge upon matter, one or more of three things\\nmust happen 1. They may be transmitted without pro-\\nducing any effect upon the substance. This not only hap-\\npens with dry air, but it may also happen with certain\\nliquids, and even* solids. 2. They may be reflected wholly\\nor in part. 3. They may set up molecular motions (heat)\\nin the substance, wholly or in part. This is called absorp-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0210.jp2"}, "207": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0211.jp2"}, "208": {"fulltext": "JOHN TYNDALL (1820-1893).\\nSucceeded Faraday as professor in the Royal Institution of Great Britain. No\\nman has done more hy his lectures and writings than he to disseminate science.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0212.jp2"}, "209": {"fulltext": "HOW HEAT IS TRANSFERRED 187\\ntion. The law of the conservation of energy obtains here.\\nSuppose we put a glass screen between us and the fire, and\\nthat ninety per cent of the radiant energy which falls upon\\nthe glass is converted into heat, then the remaining ten per\\ncent must be accounted for as transmitted or reflected. It\\nmust also be remembered that all of the ninety per cent\\nwhich was converted into heat will, by molecular motions\\nin the body, set up again an exactly equivalent amount of\\nether vibration and then radiate off again. The power to\\narrest ether waves and convert them into heat varies much\\nwith different substances. A piece of zinc will protect\\nwoodwork from the heat of a stove better than a sheet of\\nasbestos can do it, because the zinc reflects back most\\nof the ether waves which strike it, while the asbestos con-\\nverts a very large portion of them into heat and will scorch\\nthe paint or the wood underneath it. Indeed, the thinnest\\ncoating of metal, like gilt lettering, will protect wood from\\nthe heat of the stove, while ordinary paint, no matter what\\ncolor, so far from protecting it, converts the ether waves\\ninto heat and scorches the wood. For this reason water in\\na clean metal dish before the fire will not heat as rapidly\\nas water in a metal dish that has been smoked or coated\\nwith varnish, enamel, etc. In the first case the waves\\nwhich come to the dish are reflected, and in the second\\ncase they are converted into heat and raise the tempera-\\nture of the water. If hot water is poured into these two\\nkinds of vessels, its heat will radiate out from the coated\\nmetal vessel faster than from the other, and a thermometer\\nwill show a more rapid loss of temperature. In general,\\nthose forms of matter whose molecules are most readily set\\nin motion by the ether waves (good absorbers) are best\\ncapable of setting up ether waves by their molecular\\nmotions (good radiators).\\n203. Relation of Heat and Light.\u00e2\u0080\u0094 When we watch an\\niron ball slowly heated until it gives out light first a dull\\nred and afterward a bright light we very naturally are led", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0213.jp2"}, "210": {"fulltext": "188 PHYSICS\\nto suspect that heat and light are closely akin to one\\nanother. This we shall find to be true when we study\\nlight, and we shall then learn in what their kinship consists.\\nIt is sufficient at present to say that it is analogous to the\\nrelation which exists between sounds of low pitch and\\nthose of high pitch. The sun sends us both kinds of ether\\nwaves those which give us the sensation of light and\\nthose which give us the sensation of heat. One is readily\\nconverted into the other. Dry air is perfectly transparent\\nto both kinds of rays, but the moisture of our atmosphere\\nabsorbs most of the heat-producing rays. The moisture\\nradiates this heat in all directions, and thus a large portion\\nof it passes off into space again without ever reaching the\\nearth. Waves which give us the sensation of light pass,\\nwithout much loss, through the air to the earth, where they\\nare partly reflected again into space, but for the most part\\nare absorbed and converted into heat. This heat sets up\\nether waves of the heat-producing kind which would pass\\noff into space if the moisture of the air did not arrest them,\\nabsorb them, and radiate a portion of them back again.\\nThus it will be seen that the moisture of our atmosphere\\nacts as a sort of valve to entrap sunlight and warm the\\nearth. What the moisture of the air is to the earth, the\\nglass is to the hot bed in the garden, or the glass roof\\nto the greenhouse. Indeed, the same thing is true in a\\nmeasure of a shingle roof, or any kind of cover, as for\\nexample an umbrella for, however opaque these coverings\\nmay appear to the eye to be, they are in reality transparent\\nto a large number of the rays which come from the sun\\nand produce heat in objects upon the earth but these same\\ncoverings are opaque to the rays which these warm objects\\nupon the earth send out, and they prevent them from pass-\\ning off again into space. A covering of snow protects the\\ncrops in the same manner that a hot bed protects young\\nplants although it can not raise the temperature above\\n32\u00c2\u00b0 F., it does prevent it from falling below that degree,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0214.jp2"}, "211": {"fulltext": "HOW HEAT IS TRANSFERRED 189\\nand there are many plants to which this temperature is not\\ninjurious.\\nBecause different substances differ in their power of\\nradiating, no two things are likely to be of the same tem-\\nperature. This is why dew and frost collect more upon\\nsome things than upon others, and they thus tell us which\\nthings are the best radiators. It should be noted that dew\\nand frost collect more upon the grass than upon the bare\\nground. Which of these spots is, therefore, the best ab-\\nsorber of the sun s rays From which will a thin layer of\\nsnow disappear sooner? Why does earth sprinkled upon\\nsnow melt away the snow from underneath it\\nIn Sahara the cold at night and the heat by day are\\nequally painful to bear. Whenever the climate is dry the\\ndaily range of temperature is great. This is the marked\\ndifference between mountainous or interior climate, and\\nthat by the sea or other bodies of water.\\nA piece of paper will prevent the loss of heat from a\\nplant during the night, so that a thermometer may stand\\n10\u00c2\u00b0 higher under the paper than outside.\\nThe clouds act like this paper screen, and hence we\\nhave more dew or frost at night when the sky is clear than\\nwhen it is overcast. Indeed, a thermometer will rise and\\nfall at night as a cloud is passing over.\\nA thermometer resting on the grass at night has been\\nfound to be 14\u00c2\u00b0 lower than one suspended four feet above it.\\nPainted metals will collect more dew than bright metals.\\nThis is merely a question of temperature, as the thermom-\\neter will show.\\n204. Radiometer. This consists of a glass globe from\\nwhich nearly all the air has been removed. A light vane,\\nmade of tiny mica plates mounted on an aluminium frame,\\nis so arranged that it is free to rotate on the steel pivot in\\nthe center of the globe. One face of each mica plate is\\ndarkened with lampblack. When the radiometer is exposed\\nto radiant energy coming from the sun, or from a cup of", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0215.jp2"}, "212": {"fulltext": "190\\nPHYSICS\\nhot water, or the warm hands of a person, the little vane\\nbegins to rotate, spinning the more rapidly as the radia-\\ntion is greater. The darkened\\nfaces absorb more heat, and\\nJ the straggling air particles\\nti A coming in contact with these\\nfaces are themselves heated\\n-7; and fly off. The reaction\\nsends the vane in the opposite\\ndirection, and so it spins on\\nits pivot, the darkened face\\nin the rear. If a tin cup be\\nsmoked on one side, filled\\nwith hot water and held near\\nthe radiometer, we may show,\\nby turning the cup about, that\\nthe blackened side radiates\\nmore heat than the bright\\nmetal side. We may now\\ncover the bright metal side\\nwith white paint and show\\nthat it radiates as well as\\nlampblack. The power to\\nabsorb is always equal to the power to radiate, and the\\nwhite paint absorbs heat-radiation as readily as lampblack\\ndoes, but this is not true for light-radiation, of which, as\\nwe know, the white reflects more.\\nFig. 112.\u00e2\u0080\u0094 Eadiometer.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0216.jp2"}, "213": {"fulltext": "CHAPTEE XXI\\nCALORIMETRY AND SPECIFIC HEAT\\n205. Measurement of Heat. Heat, like all forms of en-\\nergy, is a measurable quantity. The process of measuring\\nheat is one of great scientific and practical importance.\\nWe may measure either of the two aspects of heat that we\\nhave mentioned, either its degree or its amount. We call\\nthe first measure Temperature, and the second Quantity.\\n206. Temperature. This, as we have seen, corresponds\\nin mass-mechanics to velocity or rate of motion, and is\\nquite independent of the amount of matter in motion. In\\nheat-mechanics temperature is the degree of molecular\\nmotion, and is also quite independent of mass.\\nAs temperature can not be directly measured in C.-G-.-S.\\nunits, we are forced to devise some conventional and quite\\nempirical unit, and to make our measurement consist\\nmerely of a statement of relative intensity. This we do\\nwith a thermometer (167).\\n207. Quantity of Heat, as we have seen, corresponds in\\nmass-mechanics to momentum. It is not only the degree\\nof heat, the temperature, but it is also the amount of mat-\\nter heated. It is evident that although a cup of boiling\\nwater is hotter than a ten-gallon tank of lukewarm water,\\nthe tank has a greater quantity of heat and will do more\\ntoward warming a cold room. So it is evident that a great\\nlake at a temperature of 40\u00c2\u00b0 F., although it is not hotter,\\nyet it contains more heat than a cup of boiling water, and\\nwill do more to modify the winter climate of that region\\n191", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0217.jp2"}, "214": {"fulltext": "192 PHYSICS\\nthan many thousand cups of boiling water could. The\\nrelation of temperature to quantity of heat is analogous to\\nthe relation of water pressure to volume of water. The\\nmountain stream may exhibit high pressure of water the\\nquantity may, however, be too small to be useful. We can\\nnot measure quantity of heat in C.-G.-S. units, and so must\\ndevise an empirical unit. The Calorie is our name for\\nsuch a unit. It is the quantity of heat needed to raise the\\ntemperature of 1 gram of pure water 1\u00c2\u00b0 C. It is a mere\\nconvention. We might use 1 kilogram, or 1 pound, or 1\u00c2\u00b0 F.,\\nand often do, but this unit is, on the whole, the most\\nconvenient.\\n208. Specific Heat. As soon as we come to measure\\ntemperature and quantity of heat, we come upon a very\\ncharacteristic and important difference in the behavior of\\nbodies toward heat. If we take a kilogram of water and a\\nkilogram of some metal such as lead or mercury, and raise\\nthe temperature of water and metal the same number of\\ndegrees, we find that it takes a different and much larger\\namount of heat to increase the temperature of the water\\nthan that of the metal. We express this by saying that\\ndifferent bodies have different capacity for heat. As water\\nabsorbs a great amount of heat in changing its temperature\\nby a given number of degrees, we say that water has a great\\ncapacity for heat. We measure the heat capacity of any\\nbody by comparing it with the capacity of water. We call\\nthe ratio Specific Heat, which we may define as the heat\\ncapacity of a given mass of a substance compared with the\\nheat capacity of the same mass of water.\\n209. Determination of Specific Heat.\u00e2\u0080\u0094 There are several\\nmethods in use for the determination of specific heat.\\nThe method of mixtures is the one generally used, and\\nis the only one suitable for elementary work. In this\\nmethod we heat a known mass of the body to a definite\\ntemperature, say 100\u00c2\u00b0 C, and then plunge it into a known\\nmass of water whose temperature is also known. The tern-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0218.jp2"}, "215": {"fulltext": "CALORIMETRY AND SPECIFIC HEAT 193\\nperature of the water is generally taken at that of the room,\\nand consequently rises when brought into contact with the\\nhotter body. The water is well stirred, and when the tem-\\nperature ceases to rise, the hot body and the water must\\nhave reached the same temperature. The increase in the\\ntemperature of the water multiplied by its weight in grams\\ngives the quantity of heat imparted to the water by the cool-\\ning body. The heat gained by the water and the heat lost\\nby the body are manifestly equal. The total number of\\nheat units given out by the cooling body, divided by the\\nnumber of degrees of fall in temperature, gives the amount\\nof heat for each degree, and this amount divided by the\\nnumber of grams of weight in the body gives the amount\\nof heat yielded by each gram as it falls one degree. Since\\nthe temperature of the vessel containing the water, as well\\nas that of the water itself was raised, its heat capacity must\\nalso be taken into account.\\nThe case will be made clear by an example. Suppose\\nwe take 100 grams of water in a copper cup weighing 12\\ngrams, both at the temperature of the room, which is 17.5\u00c2\u00b0\\ndegrees. From a vessel of boiling water we lift a piece of\\nlead weighing 100 grams and put it into the copper cup of\\nwater. We stir the lead about, so that it and the water\\nmay become of the same temperature, and when the tem-\\nperature becomes stationary we find it is 20\u00c2\u00b0. The lead\\nhas given out heat enough to raise\\n100 grams of water 2.5 degrees 250 heat units, and\\n12 grams of copper 2.5 degrees 12 X 2.5 X.0933* =2.8\\nheat units.\\nTotal number of heat units given out by the lead 252.8\\nin falling 80 degrees.\\nAmount given out for each degree ^M _ 3 16 heat\\nunits. 80\\nSee table on the following page for specific heat of copper.\\n14", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0219.jp2"}, "216": {"fulltext": "194 PHYSICS\\nAmount given out by each gram for each degree of fall\\nin temperature .0316. If one gram of lead gives\\nout .0316 heat units in falling one degree, it would require\\n.0316 heat units to raise one gram of lead one degree. This\\nis called the specific heat of lead. In accurate work, allow-\\nance must also be made for the heat capacity of the ther-\\nmometer, and for the loss of heat by radiation but we\\nneglect these, and still get fair results.\\nTABLE OF SPECIFIC HEATS.\\nWater 1.000\\nAluminium 212\\nIron 114\\nCopper 093\\nTin 056\\nSilver 057\\nMercury 033\\nGold 032\\nPlatinum 032\\nLead 032\\nGlass .019\\nSulphur 203\\nGraphite 218\\nCharcoal .241\\nIce 504\\nAlcohol 610\\n210. Applications. Among liquids, water has the largest\\nspecific heat, and this is of immense importance in the\\neconomy of Nature. Water acts everywhere as an equalizer\\nof temperature. It has such great capacity for heat that it\\nwarms up slowly and cools down slowly. Hence the cli-\\nmate near large bodies of water is much less subject to\\nextremes of temperature than places surrounded by land.\\nThe movement of large bodies of hot water from the\\ntropics to the poles, and of cold water from the poles to the\\ntropics, make habitable large areas of land that would\\notherwise be lost to human uses. The Gulf current\\ngreatly moderates the climate of the British Islands and of\\nthe northwest coast of Europe, while the Japan current\\nperforms the same service for the northwest coast of\\nAmerica.\\nThe kitchen range may be much hotter than the water\\nin the hot-water tank which is connected with it, but if the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0220.jp2"}, "217": {"fulltext": "CALORIMETRY AND SPECIFIC HEAT 195\\nfire goes out on a cold winter night the warm water in the\\ntank will give out its heat all night long and perceptibly\\nwarm the room, while the stove will have parted with its\\ncomparatively small amount of heat in a very short time.\\nThe summer sun beats alike upon the seashore and the\\nadjacent waters of the sea, but the specific heat of sand\\nbeing much less than that of water, its temperature rises\\nmuch higher than the water. The air over the water will,\\ntherefore, be cooler than that over the land, and will press\\ntoward the land, giving a sea breeze. At night the land,\\nlike the kitchen range, will lose its heat sooner than the\\nwater does, and the air over the land will become cooler\\nthan that over the sea, and will press toward the sea, giv-\\ning a land breeze.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0221.jp2"}, "218": {"fulltext": "CHAPTER XXII\\nLATENT HEAT\\nA. Heat disappeaks when Solids liquefy\\n211. Heat latent in Solutions. If we apply heat to some\\nfragments of ice, the temperature rises until the whole\\nstands 0\u00c2\u00b0 C. The ice then begins to melt, but though the\\napplication of heat be continued, no rise of temperature\\ntakes place until all the ice has melted and passes into wa-\\nter at 0\u00c2\u00b0. The heat applied during this interval has accom-\\nplished no change in the temperature, but has been solely\\nspent in changing the ice at zero into water at zero. Evi-\\ndently a large quantity of heat has disappeared in the pro-\\ncess. We say that it has become latent. It has been em-\\nployed to do internal work among the molecules, and is in\\nthe form of potential energy. All this heat may be recov-\\nered again, as we shall see in section 219.\\nCommon salt put into water will cause its temperature\\nto fall several degrees. It abstracts heat from the water, as\\nit dissolves or passes into the liquid state. This heat does\\nnot raise the temperature of the salt, but becomes latent.\\nThis is true of all solids when they dissolve.\\nEach solid has its own peculiar power of rendering heat\\nlatent. Ice, for example, absorbs 80 heat units for each\\ngram liquefied. And it is a physical impossibility for ice\\nor snow any form of water in the solid state to pass into\\nthe liquid state without its absorbing this amount of heat\\nbut ice and snow do not take heat very readily by either\\n196", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0222.jp2"}, "219": {"fulltext": "LATENT HEAT 197\\nconduction or radiation, and this explains why they linger\\nso long even under a hot sun. Every one must have some-\\ntimes wondered that a cake of ice will endure for so long a\\ntime the broiling summer s sun, and that snow will some-\\ntimes last until late in spring.\\n212. Freezing Mixtures. When we want only a moder-\\nate cold, as in the case of drinking water, the ice is simply\\ndissolved in water. When the ice melts, we have, of course,\\nwater at 0\u00c2\u00b0 C. as the immediate result, but we also have the\\noriginal drinking water greatly cooled, since the ice, to melt,\\nmust take its heat of liquefaction, 80 calories per gram,\\nfrom the surrounding water. So it is possible, by using\\nlittle water and much ice, to keep the contents of a water\\npitcher at 0\u00c2\u00b0 C. for a considerable time, since the ice can\\nmelt only as it can absorb the requisite heat from the sur-\\nrounding water.\\nWhen a greater cold is wanted, as in freezing creams and\\nfruits and ices, it is gained by mixing salt with the cracked\\nice. The action is double the melting of the ice and the\\nsolution of the salt and both processes require heat that\\nis, are cold-producing. The salt (sodium chloride, NaCl)\\nhas a great affinity for water. We express this by saying\\nthat it is deliquescent. We all know how damp table salt\\nbecomes if exposed to the air on a moist day. So strong is\\nthis affinity that the salt melts the ice in order to dissolve in\\nthe water formed. But, in order to dissolve, the salt must\\nitself absorb its own heat of liquefaction, and so contribute\\nits share to the production of cold. It is possible in this\\nway to obtain a temperature as low as 22\u00c2\u00b0 C.\\nThe act of solution is always accompanied by a lowering\\nof the temperature. If we take a mixture of solid ammo-\\nnium chloride (XH 4 C1) and ammonium nitrate (NH 4 N0 3\\nand place them in a beaker, and then add just enough cold\\nwater to dissolve them, we shall have a temperature consid-\\nerably below zero. This can be shown by stirring the mix-\\nture with a chemical thermometer and noting the reading,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0223.jp2"}, "220": {"fulltext": "198 PHYSICS\\nor, better still, by using a small test-tube with a little water\\nin the bottom, as a stirrer. The water will be frozen\\nsolid, and may be turned out on the table as a transparent\\nlump.\\nThe faculty of salt to liquefy ice is made use of to re-\\nmove ice from the pavements in cold winter weather. It\\nliquefies the ice, although it makes it colder than it was be-\\nfore. We should, therefore, avoid saying it melts the ice.\\nThe salt solution which is formed flows off and clears the\\npavement. It does not freeze until a very low temperature\\nis reached.\\nB. Heat disappeaes when Liquids yapoeize\\n213. Heat latent in Vapors. When we supply heat to\\nwater its temperature rises constantly until it reaches 100\u00c2\u00b0\\nC, and here a halt takes place until all the water at 100\u00c2\u00b0\\nhas been converted into steam at 100\u00c2\u00b0. The heat mean-\\nwhile has been spent in changing the water into water\\nvapor. Evidently a large quantity of heat has disappeared\\nin the process, and yet all this heat may be recovered again,\\nas we shall learn in section 218. We therefore say that it\\nhas become latent. When water or any other liquid changes\\nits state, passing from liquid to gas, heat is apparently used\\nup in producing this change of state. Each liquid has its\\nown peculiar power of rendering heat latent. Water, for\\nexample, absorbs 537 heat units for each gram vaporized.\\nIt is not possible for water or any other liquid at any tem-\\nperature to pass into the vapor state unless it is supplied\\nwith the number of heat units required to bring about that\\nchange. That is, 1,000 grams of water (about 1 quart)\\nmust absorb 537,000 heat units before it can vaporize.\\nThis shows why a little shower on a summer day, whose\\nwater quickly evaporates, cools the earth so much.\\nThose who have seen experiments with liquid air must\\nhave marveled that the liquid does not fly away into the\\ngaseous state more readily than it does. This is because it", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0224.jp2"}, "221": {"fulltext": "LATENT HEAT 199\\nis unable to appropriate to itself the necessary amount of\\nheat to change its state.\\nIn general, we may say that when substances pass to a\\nmore fluid state solids to liquids, liquids to gases, gases in\\nexpanding heat is absorbed, and that when substances\\npass to a less fluid state gases in condensing, gases to\\nliquids, liquids to solids heat is given out. For the same\\nsubstance, the amount of heat absorbed in any given change\\nis precisely the same as the amount given out when the\\nchange is in the opposite direction.\\n214. Absolute Temperature. We have called attention\\nto the fact that temperature is analogous to velocity in\\nmass-mechanics. But velocity may diminish until it finally\\nceases altogether, and the body comes to rest. If the anal-\\nogy were complete, there would be a corresponding point\\nin the thermal scale where molecular activity would cease,\\nand the body be devoid of all heat. Such a condition would\\nbe absolute cold, or the absolute zero of temperature. It has\\nnever been attained experimentally, but we can estimate it.\\nIf a body of air at 0\u00c2\u00b0 C. be chilled to \u00e2\u0080\u00941\u00c2\u00b0, or heated to\\n1\u00c2\u00b0, its volume will change by of its original volume\\nat 0\u00c2\u00b0. If, therefore, we should heat it to +273\u00c2\u00b0, its vol-\\n273\\nume would increase by rrr of its original volume. That is,\\nits volume would just double. If, now, we should cool this\\n273\\nbody of air to \u00e2\u0080\u0094273\u00c2\u00b0, it ought to shrink of its original\\nvolume, and therefore cease to have any volume whatever.\\nBefore reaching that temperature, however, every gas would\\nbecome liquid, and cease to follow Boyle s law. This point,\\n273\u00c2\u00b0 C, we call the absolute zero.\\nWe may construct a scale of absolute temperature by\\nreferring all readings to the absolute zero. We can readily\\ndo this in the centigrade scale by simply adding 273\u00c2\u00b0 to\\nall ordinary readings. Thus all readings in absolute tern-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0225.jp2"}, "222": {"fulltext": "200 PHYSICS\\nperature must be positive. Water freezes at 273\u00c2\u00b0 and boils\\nat 373\u00c2\u00b0.\\n215. The Production of Cold.\u00e2\u0080\u0094 Cold is the absence of\\nheat, and is simply relative. It means a lower degree of\\nmolecular energy. Cold is produced, therefore, by the\\nreversal of all those processes which are the sources of heat.\\nHowever, it is not practically possible to reverse all of them,\\nsuch as solar radiation, mechanical motion, and electricity.\\nNor can we, except in rare cases, make chemical reaction a\\nsource of cold. The reverse of chemical combination that\\nis, chemical decomposition requires the taking in of heat,\\nbut the process is not self-promoted and can not, therefore,\\nbe used as a source of cold. Practically we are thrown back\\nupon three sources for the production of all artificial cold\\nexpansion of gases, evaporation of liquids, and the dis-\\nsolving of solids.\\n216. Expansion of Gases. This is a very effective source\\nof cold, but it is rarely used in the arts, because there are\\nmore convenient methods. It usually appears, indeed, as\\nan inconvenience. Motors driven by compressed air be-\\ncome very cold, and consequently brittle, by the expansion\\nof the air in the cylinder. It is sometimes the custom to\\nsurround parts with running water in order to equalize\\ntemperatures. The cold produced by expanding air may\\nbe beautifully seen in the receiver of an air pump. On a\\ndamp day a few strokes of the pump suffice to fill the\\nreceiver with fog, a precipitation of moisture due entirely\\nto the chilling effect of expansion.\\nIn Nature, the expansion of air in the upper regions of\\nthe atmosphere is a source of considerable cold, and is\\nprobably one reason why the higher clouds are made up of\\ntiny ice crystals instead of globules of condensed water\\nvapor. Whatever be the cause of this fall in temperature,\\nit amounts to about 1\u00c2\u00b0 for each 300 feet of elevation.\\n217. Cold by Evaporation. This is the great source of\\nartificial cold, and also one of the most convenient in way", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0226.jp2"}, "223": {"fulltext": "LATENT HEAT 201\\nof application. It has already been incidentally referred\\nto (192).\\nWhenever a liquid evaporates, it must take in its own\\nheat of evaporation, and so make surrounding objects cold.\\nIn ordinary evaporation, the heat is supplied from some-\\nwhat wide territory as rapidly as it is needed, but by\\nincreasing the rate of evaporation and shutting out exter-\\nnal sources of heat, we may produce very intense arti-\\nficial cold.\\nEemembering the five factors upon which evaporation\\ndepends, it will readily be seen that we can not well use the\\nfirst, temperature, since that would be fatal to our purpose,\\nbut we can use the other four conditions. We can increase\\nthe surface, we can diminish the pressure, we can remove\\nthe vapor as fast as it is formed by pumping or by con-\\nstantly renewing the atmosphere.\\nThe porous water jars of the East depend for their\\ncooling action upon the large surface exposed, and the\\nrenewal of atmosphere which comes when the jars are hung\\nin a good draught of air. They are made of unglazed\\nearthenware, and consequently the water makes its way\\nthrough the pores to the surface, and by evaporation cools\\nthe water still in the jar several degrees below that of the\\nsurrounding air. The experiment may be made by using\\nthe porous cup of a battery, and either placing it in a good\\ndraught of air, or directing a jet of air against it from a\\nbellows or pump.\\nThe Carre Ice Machine, one of the oldest, depends on\\nthe evaporation of liquefied ammonia gas, KH 3 Under\\nordinary conditions NH 3 is a gas, but under a pressure of\\nseven atmospheres it becomes a colorless liquid which boils\\nat \u00e2\u0080\u009433.7 C. The liquefied gas is passed through coils sur-\\nrounding the body of water to be frozen. By simply remov-\\ning the pressure the XH 3 passes back to the gaseous state,\\nand in doing so absorbs enough heat to reduce the temper-\\nature of surrounding objects to something below zero.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0227.jp2"}, "224": {"fulltext": "202 PHYSICS\\nThe ammonia gas may be again liquefied, and so used over\\nand over again with little loss. The ice is thus made at\\nthe cost of the mechanical energy used in liquefying the\\nammonia.\\nThe most intense cold is produced by the evaporation of\\nmuch more difficultly liquefiable gases, such as carbon diox-\\nide, C0 2 and even the elementary gases N and 0. By the\\nevaporation of N, a cold of 225 0. has been attained.\\nThe value of bathing the forehead with cologne or bay\\nrum, in case of headache or fever, comes from the cooling\\neffected by the evaporation of the alcohol.\\nA simple application of evaporation, in freezing water,\\nis an ice machine, consisting merely of an air pump pro-\\nvided with a chamber containing strong sulphuric acid,\\nH 2 S0 4 A flask, half filled with water, is connected by\\nmeans of a rubber stopper and tube with the acid chamber\\nand the pump. A few strokes of the pump remove most of\\nthe air from the flask, and under the reduced pressure the\\nwater begins to evaporate very rapidly. But the H 2 S0 4 has\\nstrong affinity for water vapor, and absorbs it so rapidly\\nthat it re-enforces the air pump in maintaining a vacuum,\\nand so hastening the evaporation of the water in the flask.\\nUnder this greatly diminished pressure, bubbles of vapor\\nform throughout the mass of the liquid, so that it boils at\\na very low temperature. But, meanwhile, the rapid evap-\\noration of the water has been carrying off so much heat\\nthat a film of ice begins to form on the surface, while the\\nwater below continues to boil. We have thus the spectacle\\nof water boiling and freezing in the same vessel and at the\\nsame temperature. When the flask is brought on the table,\\nthose not in the secret naturally wonder how such a large\\nsheet of ice got into such a small-necked bottle.\\nThis experiment may be made with the ordinary air\\npump by introducing into the receiver a vessel containing\\nstrong H 2 S0 4 and another containing water. It was in this\\nform that the experiment was originally made by Leslie.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0228.jp2"}, "225": {"fulltext": "LATENT HEAT\\n203\\nFig. 113.\u00e2\u0080\u0094 Wollaston s\\nCryophorus.\\nWollaston s Cryophorus (Fig. 113) illustrates the same\\nprinciple. It consists of a U-tube with a bulb at each end.\\nOne bulb is half filled with water, and\\nthe other bulb and the tube itself with\\nvapor of water. When this second bulb\\nis surrounded by cracked ice, the water\\ncondenses, and thus reduces the pres-\\nsure inside the tube. The water in the\\nother bulb rapidly evaporates, and crys-\\ntals of ice are seen to form on the sur-\\nface.\\nIf two large watch crystals be moist-\\nened on their convex sides and placed\\non top of each other, with some highly\\nvolatile liquid, such as ether, placed in the upper crystal, it\\nwill be easily possible to freeze the two crystals together by\\nthe rapid evaporation of the ether. This may be brought\\nabout by simply blowing on its surface, or by directing an\\nair jet against it from a bellows.\\nStill another instance. The cold produced by evapora-\\ntion may be readily observed by dipping the bulb of a\\nchemical thermometer into ether or chloroform, or even\\ninto alcohol or water, and rapidly swinging it in the air\\nor by wetting a cloth with one of these liquids, wrap-\\nping the cloth around the bulb, and then swinging the\\nthermometer as before, or directing a blast of air against\\nthe cloth.\\nBesides these applications, there are numerous other cir-\\ncumstances where we wish an intense cold. In engineering\\nwork it is now the custom to freeze quicksands by\\nmeans of liquefied ammonia gas, XH 3 A tunnel or shaft\\ncan be driven through this solid mass of sand and water,\\nwhen it would be quite impossible to deal with the semi-\\nfluid, shifting quicksand.\\nA freezing cold is also used in microscopic work in\\nstudying delicate organic structure that must be cut into", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0229.jp2"}, "226": {"fulltext": "204 PHYSICS\\nsections thin enough to allow the light to pass through. It\\nis so used in the Department of Agriculture at Washington\\nin investigating diseases of domestic animals. The heart,\\nliver, or kidney, or whatever organ is under examination,\\nis first frozen stiff, and then, by means of a sharp razor, a\\nwonderfully thin section is sliced off and mounted between\\nlittle glass slides before it has a chance to melt and become\\nunmanageable.\\nAll volatile liquids, such as alcohol, ether, benzine, etc.,\\nfeel cold to us. Yet the liquids are not cold, except when\\nthey are allowed to evaporate.\\nThe water bath in the laboratory and the double boiler\\nin the kitchen are used because the evaporation of the wa-\\nter will absorb all heat above a certain temperature, and\\nprevent the burning of the food, etc. Upon the moun-\\ntain top, where the pressure of the air is reduced, evapora-\\ntion proceeds more rapidly, and it may abstract heat to such\\nan extent as to prevent cooking, by boiling water, of certain\\nthings which require a temperature of at least 100\u00c2\u00b0 C.\\nAll animals produce more heat than they need. Their\\nlife processes depend upon the elimination of superfluous\\nheat. This is absorbed chiefly by the evaporation of moist-\\nure produced from countless pores in the skin. Cold con-\\ntracts the surface blood vessels and sends the blood to the\\ninterior of the body where it will not lose so much heat,\\nbut it also contracts the mouth of these pores as evidenced\\nby the so-called goose pimples \u00e2\u0080\u0094checks the flow of per-\\nspiration, and thus evaporation and the consequent loss of\\nheat are reduced. Heat causes the surface blood vessels\\nto relax and the warm blood to flush the skin where it\\ncools. Heat also opens the pores, causes the perspiration\\nto flow, and if the conditions of evaporation are favorable,\\nwe do not suffer with the heat. If, however, there is great\\nhumidity in the atmosphere, so that evaporation does not\\nproceed readily from our bodies, we suffer greatly from the\\nheat, and we callit a muggy day.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0230.jp2"}, "227": {"fulltext": "LATENT HEAT 205\\nC. Heat reappears when Vapors liquefy\\n218. Heat recovered from Vapors. When any gas passes\\nto the state of a liquid, its latent heat is given out. If the\\ngas be steam, then the liquid must be water, and each gram\\nof condensed water at 100 represents the liberation of 537\\ncalories. This method of heat production is illustrated in\\nour steam radiators. The condensing steam yields its heat\\nto the^ iron radiator, and this in turn to the apartment.\\nIn ^Nature, the liquefaction of vapor is a most important\\nsource of heat. Whenever the moisture in the atmosphere\\ncoudenses into rain or snow, heat is liberatedo Conse-\\nquently, precipitation is always accompanied by rise of tem-\\nperature. We notice a moderation of the weather during a\\nrain. It has been calculated that the moist air accompany-\\ning the Gulf Stream yields as much heat to Great Britain,\\nby the precipitation of the moisture, as is brought by the\\nGulf Stream itself.\\nD. Heat reappears when Liquids solidify\\n219. Heat recovered from Solutions. The freezing of\\nwater requires the giving up of the exact amount of heat\\nrequired to liquefy the ice, 80 calories for each gram, and is\\na most important natural source of heat. Farmers under-\\nstand this, and put tubs of water in their vegetable cellars\\non a cold night, so that if the temperature falls below 32\u00c2\u00b0\\nF. the freezing of the water will give out such quantities of\\nheat as shall prevent the temperature from falling far below\\n32\u00c2\u00b0, and the vegetables will not freeze until a temperature\\nconsiderably below 32\u00c2\u00b0 is reached. Ponds and lakes, by the\\nfreezing of their waters, do much toward preventing the\\ntemperature of the immediate neighborhood from falling\\nfar below 32\u00c2\u00b0 F. For the same reason the atmosphere is\\ngenial and agreeable during a quiet snowstorm.\\n220. Recapitulation.\u00e2\u0080\u0094 Suppose 1,000 grams of ice at \u00e2\u0080\u009410\u00c2\u00b0\\nC. rises to 0\u00c2\u00b0. The specific heat of ice being .5 (209), this", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0231.jp2"}, "228": {"fulltext": "206 PHYSICS\\nwould require the absorption of 5,000 heat units. Next let\\nus suppose this ice to melt. This would require 80 X\\n1,000 80,000 heat units. If now we heat this quart of\\nwater to the boiling point, 100 x 1,000 100,000 heat units\\nwill be absorbed, and if we vaporize this water, 537 X 1,000\\n537,000 heat units will be required. Thus a total of 722,000\\nheat units have been absorbed, and will all surely be restored\\nto the atmosphere before that water can again become ice at\\n\u00e2\u0080\u009410\u00c2\u00b0 C. So it appears that water is the great equalizer of\\ntemperatures, carrying the summer heat far into the winter\\nto modify its climate, and storing the winter cold (if we\\nmay use the expression) with which to refresh the summer\\nseason.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0232.jp2"}, "229": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0233.jp2"}, "230": {"fulltext": "MICHAEL FAEADAY (1791-1867).\\nProfessor thirty-four years in the Royal Institution of Great Britain. Induction\\nof electric currents. Effect of magnetism upon polarized light. The greatest\\nexperimental philosopher the world has ever seen. A superior lecturer.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0234.jp2"}, "231": {"fulltext": "MAGNETISM AND ELECTRICITY\\nCHAPTER XXIII.\u00e2\u0080\u0094 Magnets\\n221. Magnetite. Fig. 114.\\n222. Steel Magnets.\\n223. The Poles of a Magnet. Fig. 115.\\n224. Magnetic Substances.\\n225. Influence of Magnets upon Magnetic Substances. Fig. 116.\\n226. Each Molecule a Magnet. Figs. 117 and 118.\\n227. The Earth a Magnet. Figs. 119, 120, 121, and 122.\\n228. The Mariner s Compass. Fig. 123.\\n229. The Law of Inverse Squares. Fig. 124.\\n230. Lines of Magnetic Force. Figs. 125, 126, 127, 128, and 129.\\nCHAPTER XXIV.\u00e2\u0080\u0094 Static Electricity\\n231. Electrification.\\n232. Two States of Electrification.\\n233. Static Electricity and Electric Currents.\\n234. Conductors. Fig. 130.\\n235. Induction, the Influence of Electrified Bodies upon Neighboring\\nObjects. Figs. 131 and 132.\\n236. By Induction a Polarized Body may receive a Charge from a\\nNeutral Body. Fig. 133.\\n237. The Electrophorus. Figs. 134, 135, 136, and 137.\\n238. Condensers. Figs. 138 and 139.\\n239. Lightning.\\n240. Electrical Distribution\u00e2\u0080\u0094 Effect of Points. Figs. 140, 141, 142,\\nand 143.\\nCHAPTER XXV.\u00e2\u0080\u0094 Electric Currents\\nI. Generators of Electric Currents\\n241. Sources of Electric Currents. Fig. 144.\\n242. Electric Potential.\\n243. The Voltaic Cell. Fig. 145.\\n207", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0235.jp2"}, "232": {"fulltext": "208 PHYSICS\\n244. The Electro-Chemical Series.\\n245. Local Action and Polarization.\\n246. Some Typical Cells. Figs. 146, 147, 148, and 149.\\n247. The Battery of Cells. Figs. 150, 151, 152, and 153.\\nII. Some Effects of Electric Currents\\n248. Electric Currents recognized by their Effects.\\n249. Physiological Effects.\\n250. Thermal Effects.\\n251. Chemical Effects. Figs. 154, 155, and 156.\\n252. Magnetic Effects. Figs. 157, 158, 159, 160, 161, 162, 163, 164, 165,\\n166, 167, 168, and 169.\\nIII. Electrical Measurements\\n253. The Problem of Measurement.\\n254. Ohm s Law.\\n255. The Tangent Galvanometer. Figs. 170, 171, 172, and 173.\\n256. Resistance. Figs. 174, 175, 176, 177, and 178.\\n257. Arrangement of Battery Cells. Figs. 179, 180, 181, and 182.\\n258. Divided Circuits. Fig. 183.\\nIV. Induction\\n259. Methods of Induction.\\n260. Induction by a Magnet. Fig. 184.\\n261. Induction by Varying Currents. Fig. 185.\\n262. Direction of Induced Currents.\\n263. Strength of Induced Currents.\\n264. The Induction Coil. Fig. 186.\\n265. Spark Coil and Electric Gas Lighting. Fig. 187.\\n266. The Telephone. Fig. 188.\\n267. Transformers.\\nV. Electric Currents by Mechanical Means\\n268. The Magneto-Electric Machine. Fig. 189.\\n269. The Dynamo. Figs. 190 and 191.\\nVI. Electric Currents produced by Heat\\n270. Thermo-Electric Currents. Figs. 192 and 193.\\n271. The Thermopile.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0236.jp2"}, "233": {"fulltext": "CHAPTER XXIII\\nMAGNETS\\n221. Magnetite. There is found in various parts of the\\nearth an iron ore composed of oxygen and iron (Fe 3 4 which\\nwill attract small bits of iron. This is called magnetite\\nto indicate that it is a magnet. It has also been called\\nloadstone for reasons which will appear later. The small\\npieces of iron do not cling to all parts of it alike. If a\\npiece of the ore is rolled\\nabout among filings of\\niron, most of them will\\nfall away from the piece of\\nore when it is lifted, but\\nmany will be found cling-\\ning to two spots (Fig. 114)\\nsituated upon opposite\\nsides or opposite ends from\\none another. A straight line connecting these two parts is\\ncalled the axis, and the ends of this line are called the\\npoles of the magnet. It is not necessary that the poles be\\nthe ends of the lump. They may be anywhere along the\\nsides, but it is true that they are always opposite to one\\nanother. If we suspend the piece of magnetite by a slen-\\nder thread, it will come to rest with the same one of these\\npoles always north. Let us mark this pole with the letter\\nX and call it the north pole, and the opposite portion we\\nwill call the south pole. Because of this property of point-\\ning north, it was originally called loadstone, or the leading\\n15 209\\nFig. 114.\u00e2\u0080\u0094 Majmets.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0237.jp2"}, "234": {"fulltext": "210\\nPHYSICS\\nstone. The reason for its pointing north and south will\\nbe given in section 227.\\n222. Steel Magnets. If either pole of the magnetite is\\nrubbed several times upon a steel sewing needle, always\\nin the same direction, from one end to the other, the sew-\\ning needle will be found to have acquired the property of\\nattracting iron filings at its two extremities. It has become\\na magnet. Its two ends are the poles, and they will point\\nnorth and south if free to move.\\n223. The Poles of a Magnet. If the needle is suspended\\nby a thread, so that it may swing freely in a horizontal\\nplane (Fig. 115), it will be found\\nthat the pole of the magnetite\\nwhich was used to magnetize this\\nneedle will attract the pole of the\\nneedle which it touched last, but\\nwill repel the other. It will also\\nbe found that the opposite pole\\nof the magnetite will repel this\\npole of the needle but attract the\\nother. If a second sewing needle\\nbe magnetized in the same way as\\nthe first (let us suppose that the\\nnorth pole of the magnetite is\\nused in each case, and that it is\\ndrawn from the eye toward the\\npoint of each needle), it will be\\nfound that the points of these needles repel each other,\\nand that the ends containing the eyes repel each other, but\\nthat the point of each will attract the eye of the other.\\nThe law is unlike poles attract, and like poles repel. It\\nwill be found that if these needles are allowed to swing\\nfreely, without being influenced by any magnet, they will\\narrange themselves so that their eyes will point north. It\\nwill also be found that their eyes will attract the south\\npole of the magnetite but repel the north pole of the same\\nFig. 115. Magnetized needle.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0238.jp2"}, "235": {"fulltext": "MAGNETS 211\\nalso that their points will attract the north pole of the mag-\\nnetite, but repel its south pole. The poles of these needles\\nmay be reversed by rubbing them in the opposite direction\\nwith the same pole of the magnetite as was used before, or\\nby rubbing them in the same direction with the opposite\\npole of the magnetite. These sewing needles are small\\nbar magnets.\\nThe bar magnets which are on sale have the letter N\\nstamped upon one end of them. If a bar magnet is free to\\nmove, this end will point north. If it is brought to the\\nnorth pole of the magnetite, or the north pole of the sew-\\ning needles mentioned above, it will repel, while it will\\nattract the south pole of the same. The reverse is true of\\nthe south pole of the bar magnet. Steel magnets are often\\ngiven the shape of a horseshoe, so that the force of both\\npoles may be applied to the same object.\\n224. Magnetic Substances. While a large number of\\nsubstances are affected to a slight degree by very power-\\nful magnets, only steel and iron are visibly affected by mag-\\nnets of ordinary strength. Soft iron may be magnetized,\\nbut will not retain magnetism. The harder the iron, the\\nlonger it will retain its magnetism. This is why steel,\\nwhich is iron hardened by carbon, makes the most perma-\\nnent magnets. Since both poles of a magnet attract mag-\\nnetic substances, the way to determine whether a magnetic\\nsubstance has become a magnet is to find whether there is a\\nrepulsion between any part of it and either pole of a magnet.\\n225. Influence of Magnets upon Magnetic Substances. A\\nmagnetic substance when brought near to a magnet is itself\\nalways polarized that is, converted into a magnet. The\\nharder the substance the less this action takes place but,\\non the other hand, the more permanent is the result. Soft\\niron is readily magnetized and as readily loses its magnetism.\\nIf a horseshoe magnet (Fig. 116) is brought near to a\\nbar of soft iron, even though they do not touch, the iron\\nwill become a magnet, as will be shown by the way bits of", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0239.jp2"}, "236": {"fulltext": "212\\nPHYSICS\\nFig. 116.\u00e2\u0080\u0094 Horse\\nshoe magnet po\\nlarizing soft iron\\niron, as carpet tacks, will cling to it. With a magnetic\\nneedle we may learn that the bar of soft iron is polarized so\\nthat its north pole is opposite the south\\npole of the horseshoe magnet, and its south\\npole opposite the north pole of the mag-\\nnet. As soon as the horseshoe magnet is\\nremoved the bar of soft iron loses its mag-\\nnetism, or, at least, retains too little to be\\nrecognized by ordinary means. A power-\\nful magnet will reverse the poles of a weak\\nmagnet if like poles are presented to each\\nother for this reason students should be\\ncareful about bringing magnets near to\\ncompass needles which are not free to\\nmove.\\n226. Each Molecule a Magnet. To enable us to appre-\\nciate what may take place in the needles when we magnet-\\nize them, let us arrange some coarse steel filings in a row\\nupon a sheet of paper and draw the north pole of a magnet\\nunderneath the paper from left to right. The magnet po-\\nlarizes each small sliver of steel as it passes by, so that the\\nend of the sliver nearest to the north pole of the magnet\\nbecomes a south pole and\\nthe more remote end of\\nthe sliver becomes a north\\npole. The repulsion be-\\ntween like poles and the\\nattraction between unlike\\npoles causes each sliver in\\nturn to rise up on end\\nand turn a somersault the\\nsouth pole of the sliver al-\\nways turning toward the\\nnorth pole of the magnet (see Fig. 117). The result is that\\nafter the magnet has passed, the slivers are all arranged in\\nline along its pathway with each north pole pointing toward\\nFig. 117. A magnet polarizing\\nsteel filings.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0240.jp2"}, "237": {"fulltext": "MAGNETS 213\\nthe left, and inasmuch as they are steel they retain their\\nmagnetism, the whole mass of filings acting as a solid har\\nof steel would as the sewing needles referred to in section\\n223 having the pole which is like the one used for indu-\\ncing magnetism at the end first approached, and the unlike\\npole at the end last approached hy the inducing magnet.\\nThis we think may be analogous to what happens when a\\nbar of steel is magnetized by rubbing it with a magnet,\\neach molecule behaving as these slivers of steel do. By\\ntapping the paper upon which the steel filings are arranged\\n(Fig. 117), after the influence of the magnet has been re-\\nmoved, they will again become disarranged, so that the\\nmass will no longer exhibit north and south poles. So, by\\nhammering a steel magnet, its magnetism is made to disap-\\npear. Heating, twisting, bending anything which might\\nFig. 118. New poles formed by breaking a magnet.\\ntend to disarrange the molecule weakens a magnet. If\\none of the magnetized needles mentioned in section 223 be\\nbroken into little pieces never so small each piece will\\nhave a north and south pole, just as the steel slivers men-\\ntioned in the early part of this section and if the eye of\\nthe needle is north pole, the end of each small piece of\\nneedle which pointed toward the eye will be its north pole.\\nIf the needles could be broken up into molecules, we sup-\\npose that each molecule would exhibit the same kind of\\npolarity. Fig. 118 helps us to imagine how the small par-\\nticles may be arranged with reference to each other. This\\nexplains why the iron filings do not cling to the middle\\nportion of the magnet. There the north and south poles\\nneutralize each other, while at the ends they are free to\\nact. The molecules of iron and steel are assumed to be\\nmagnets at all times. When they fail to exhibit it they are\\nmerely disarranged, and when we magnetize iron or steel\\nwe simply cause its molecules to take the proper arrange-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0241.jp2"}, "238": {"fulltext": "214 PHYSICS\\nment. The molecules of iron appear to move more freely\\nthan those of steel, hence it is more readily magnetized\\nand more easily loses its magnetism. If a piece of steel is\\nhammered or heated while under the influence of a magnet,\\ngreater magnetism will be induced in it, as though some\\nsuch assistance were needed to help move the molecules.\\nWhen iron is strongly magnetized its length is slightly\\nincreased. A faint crackling noise is heard when iron or\\nsteel are very powerfully magnetized or demagnetized. If\\nit is magnetized and demagnetized in rapid succession, the\\nmetal grows hot, which indicates molecular motion.\\n227. The Earth a Magnet. If we lay a bar magnet upon\\nthe table under a magnetic needle (Fig. 119), the needle\\nwill arrange itself so that its south pole will be over the\\nnorth pole of the bar magnet, and its north pole over\\nthe south pole of the bar magnet. The axis of the needle\\nwill always be parallel with that of the bar magnet, what-\\never direction that may take, showing that the force of the\\nbar magnet is greater than\\nthat which tends to cause the\\nneedle to point north. We\\nhave reason to believe that\\nthe earth is a great magnet,\\nalthough not a powerful one.\\nIts magnetic axis is in the\\nsame general direction with\\nits geographical axis, and its\\nmagnetic poles are in the arc-\\ntic and antarctic zones. The\\nnorth magnetic pole of the\\nearth must be unlike the north pole of our needle, because\\nthey attract. For this reason it has been proposed to call\\nthe end of the needle which points north the north-seeking\\npole, but the custom of calling it the north pole persists.\\nIf we suspend a magnetic needle so that it is free to\\nswing in a vertical plane (Fig. 120), and move it about\\nFig. 119. Magnetic needle.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0242.jp2"}, "239": {"fulltext": "MAGNETS\\n215\\nover a bar magnet, its north pole will point downward\\nwhen it approaches the south pole of the bar magnet, and\\nits south pole will dip when it approaches the north pole\\nof the bar magnet. The dipping\\nneedle is affected by the earth as\\nby a bar magnet. In the vicinity\\nof the equator it hangs horizontally.\\nAs it is moved north, its so-called\\nnorth pole dips until finally it\\nstands vertical over a point north\\nof North America, but some dis-\\ntance from the geographical north\\npole, as will be seen by reference to\\nFig. 121. Likewise, the magnetic\\nsouth pole does not coincide with\\nthe geographical south pole, as may\\nbe seen by reference to Fig. 122.\\nFrom this it is evident that the\\nmagnetic needle mounted so as to\\nswing horizontally does not point\\nexactly north and south. Its deviation from that direction\\nis called its declination.\\nFigs. 121 and 122 show the lines of equal declination,\\nand the lines of equal dip, or inclination, as it is called, for\\nthe whole earth. These figures also show how much the\\nmagnetic equator differs from the geographical equator.\\nThe magnetic poles of the earth are gradually shifting their\\nposition, so that these figures are not correct for all time.\\nThe table below gives the declination and the inclina-\\ntion of the needle at various places for the present year,\\n1900. The table also gives the intensity of the magnetic\\nforce at these various places relative to New York. The\\nabsolute force of the earth s magnetism at New York, as\\nexpressed in the C.-G.-S. system, is .61 dynes\u00e2\u0080\u0094 that is, a force\\nsufficient to move .61 grams 1 centimetre in a second, or 1\\ngram .61 centimetres in a second.\\nFig. 120.\u00e2\u0080\u0094 Dipping needle.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0243.jp2"}, "240": {"fulltext": "216\\nPHYSICS\\nFig. 121. Northern Hemisphere.\\nTABLE OF MAGNETIC DECLINATION, INCLINATION, AND\\nINTENSITY FOE 1900-\\nDeclination.\\nDip.\\nIntensity relative to\\nthat of New York.\\nNew York\\n9\u00c2\u00b0 12 W.\\n4\u00c2\u00b0 35 W.\\n16\u00c2\u00b0 42 E.\\n29\u00c2\u00b0 24 W.\\n16\u00c2\u00b0 16 W.\\n14\u00c2\u00b0 30 W.\\n9\u00c2\u00b0 30 W.\\n10\u00c2\u00b0 0 W.\\n0\u00c2\u00b0 30 E.\\n70\u00c2\u00b0 6 N.\\n70\u00c2\u00b0 18 N.\\n62\u00c2\u00b0 20 N.\\n58\u00c2\u00b0 2 S.\\n67\u00c2\u00b0 9 N.\\n64\u00c2\u00b0 55 N.\\n66\u00c2\u00b0 43 N.\\n58\u00c2\u00b0 0 N.\\n70\u00c2\u00b0 46 N.\\n1.00\\nWashington\\nSan Francisco\\nCape Town\\n.98\\n.89\\n.59\\nLondon\\n.77\\nParis\\n.77\\nBerlin\\n.79\\nRome\\n.74\\nSt. Petersburg\\n.79", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0244.jp2"}, "241": {"fulltext": "MAGNETS\\n217\\nFig. 122.\u00e2\u0080\u0094 Southern Hemisphere.\\nThe declination, dip, and intensity are all gradually\\nchanging. The following table exhibits the change in\\ndeclination at London for three hundred years\\nd. 1580\\nII 3 17 E.\\nA. D. 1816\\n24\u00c2\u00b0 30 W.\\n1622\\n6\u00c2\u00b0 12 E.\\n1868\\n20\u00c2\u00b0 33 W.\\n1657\\n0\u00c2\u00b0 0\\n1880\\n18\u00c2\u00b0 40 W.\\n1705\\n9\u00c2\u00b0 0 W.\\n1890\\n1900\\n17\u00c2\u00b0 26 W.\\n1760\\n19\u00c2\u00b0 30 W.\\n16\u00c2\u00b0 16 W.\\n228. The Mariner s Compass. This is merely a magnetic\\nneedle free to move in a horizontal plane. It is attached\\nto the underside of a card (Fig. 123). This is inclosed in\\na box called the binnacle. A fixed line shows the direction\\nof the keel of the ship, while the card, being carried about", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0245.jp2"}, "242": {"fulltext": "218\\nPHYSICS\\nby the compass needle, shows always the deviation of the\\nship s course from a north-and-south direction. TJiis devia-\\ntion is measured in points, each point being 11^ degrees.\\nOf course it is necessary for the mariner to correct his\\nFig. 123.\\nreading for the declination of the needle, which he must\\ndetermine from tables and charts.\\nThe mariner s compass appears to have been used by\\nthe Chinese in very crude form long before it was known\\nto the Western world. It was discovered independently in\\nEurope, perhaps in the twelfth century, but it took several\\ncenturies for it to reach its perfection. It is difficult to\\nestimate the great value it became in the fifteenth century\\nin enabling mariners to extend the boundaries of the known\\nworld.\\nFrom the fact that the earth is a magnet, we might\\nexpect to find that it would induce magnetism in magnetic\\nsubstances, and this we find to be true. This accounts for\\nthe magnetism of the ore called magnetite. A compass\\nneedle brought near to the base of an iron pillar will have", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0246.jp2"}, "243": {"fulltext": "MAGNETS\\n219\\nits south pole attracted if it is carried to the top of the\\npillar, its north pole will be attracted. From the fact that\\nthe inclination of the dipping needle is over 70\u00c2\u00b0 in New\\nYork, we might expect to find that the bottoms of iron\\npillars would become south poles by the induction of the\\nearth, and such is the fact. Thus it happens that no mag-\\nnetic substance is ever entirely free from magnetism.\\n229. The Law of Inverse Squares. The magnetic force,\\nlike gravitation, heat, light, and electric attractions and\\nrepulsions, varies inversely as the square of the distance.\\nFig. 124 explains this. The force proceeding from F in\\nall directions as the radii of a circle, would produce a cer-\\ntain effect at and only one quarter of that effect at c,\\nwhich is twice the distance of a and one ninth the effect\\nat c\\\\ which is three times the distance of a and one six-\\nteenth the effect at c which is four times the distance of\\na. The areas at c, c\\\\ and c being respectively 4, 9, and\\n16 times as great as that of a (see Geometry), the force\\nmust distribute itself accordingly but these numbers are\\nthe squares of 2, 3, and 4 respectively hence if we square\\nthe distances to be compared, we shall get the rate at which\\nFig. 124. Law of inverse squares.\\nthese forces diminish at those distances. The usual form of\\nstatement is: Hie force varies inversely as the square of the\\ndistance.\\nThis helps us to answer the question, Why should a sliver\\nof iron move toward a magnet The magnet polarizes the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0247.jp2"}, "244": {"fulltext": "220\\nPHYSICS\\nFig. 125.\\nsliver of iron, so that the pole of the sliver nearest to the\\npole of the magnet is unlike it, and therefore they attract\\neach other the farther pole of the\\nsliver is like the pole of the magnet,\\nand therefore they repel each other.\\nBut the attraction is greater than the\\nrepulsion, because the pole which at-\\ntracts is nearer than the pole which\\nrepels, hence the object, if light, and\\nif very near, is moved toward the\\nmagnet.\\nNote that magnets in order to exert any large force\\nmust be very near to the magnetic substance.\\n230. Lines of Magnetic Force. Fig. 125 shows how lines\\nof force go out from the pole of a magnet. Figs. 126,\\n127, 128, and 129 show how these lines are affected by the\\nproximity of other poles. These lines of force may be\\nmapped out upon paper by placing the magnet underneath\\nand distributing slivers of iron over the surface. Each\\nsliver will become polarized and act like a small magnetic\\nneedle. A fuller illustration,\\nhowever, will be obtained by\\nV:. h\\nFig.. 126.\\nFig. 127.\\nmoving a small compass around in the vicinity of magnets\\nplaced as in the figures. By means of the compass needle", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0248.jp2"}, "245": {"fulltext": "MAGNETS 221\\nwe get the lines in three dimensions of space, rather than\\nin the one plane alone of the paper.\\nWe shall learn in the chapter upon Current Electricity\\nthat these lines of magnetic force may exist without a mag-\\nnet. We speak of the region penetrated by these lines of\\nforce as a magnetic field, and we are able to produce, by\\nmeans of electricity, a magnetic field without the presence\\nof any magnetic substance. If soft iron be brought into\\nthis field, produced by an electric current, it becomes a\\nmagnet, as when brought near a steel magnet. We speak\\nFig. 128. Fig. 129.\\nof it then as an electro-magnet. This subject will be\\ntreated more fully under Electricity (Chapter XXV). The\\nreasons for the earth being a magnet will also be found\\nthere.\\nLines of magnetic force penetrate with perfect ease\\nthrough any substance except iron. The experiments rep-\\nresented by Figs. 117 and 125-129 would not be success-\\nful if sheet iron were used instead of paper. Glass, wood,\\nor anything else may be used, provided it is thin, so as to\\nallow the magnet to come very near to the iron filings.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0249.jp2"}, "246": {"fulltext": "CHAPTER XXIV\\nSTATIC ELECTRICITY\\n231. Electrification. Experience teaches ns that in cold\\nweather many things are easily electrified one s hair, when\\nit is brushed a cat s fur, when it is rubbed a rubber pen-\\nholder or comb, when dropped upon the floor; our own\\nbodies, when we rub our feet upon the carpet. The elec-\\ntrification is shown by attraction and repulsion of light ob-\\njects, crackling sounds, and sparks. All bodies are capable\\nof being electrified, under proper conditions, and any ob-\\nject which is electrified exhibits attraction and repulsion\\nfor all other forms of matter. In this respect electricity\\nappears to be very unlike magnetism, which affects iron\\nalone. The objects which we choose as suiting best our\\npurpose for experiment are sealing wax and glass. We get\\nthe best results when we rub the sealing wax with flannel\\nand the glass with silk. Pith balls are chosen for the ex-\\nperiments, simply because they are very light, and there-\\nfore move more readily under the influence of the slight\\nforces with which we deal. It is well to gild the pith balls\\nfor reasons which will appear in section 234.\\n232. Two States of Electrification. Pith balls which have\\nbeen electrified by contact with the electrified sealing wax\\nrepel each other, likewise pith balls which have been- elec-\\ntrified by contact with the electrified glass repel each other\\nbut pith balls which have been electrified, one by contact\\nwith the sealing wax, and the other by contact with the\\nglass, attract each other. The law is Bodies with like\\n222", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0250.jp2"}, "247": {"fulltext": "STATIC ELECTRICITY 223\\nkind of electrification repel, those with unlike kinds attract.\\nWe prefer to speak of kinds of electrification rather than\\nkinds of electricity, because we do not believe there are two\\nkinds of electricity. We shall speak of glass as being posi-\\ntively electrified, and sealing wax as negatively electrified.\\nThe flannel which is rubbed upon the sealing wax becomes\\npositively electrified, and the silk which is rubbed upon the\\nglass becomes negatively electrified. Pith balls, when they\\ncome in contact with an electrified body, acquire the same\\nkind of electrification as that body. The way to determine\\nwhether a body is electrified, or which kind of electrifica-\\ntion it may have, is to present it to pith balls electrified\\nwith each kind repulsion, not attraction, determines the\\nmatter. One s hair flies when brushed in cold weather,\\nbecause bodies having like kind of electrification repel each\\nother.\\n233. Static Electricity and Electric Currents. The titles\\nof Chapters XXIV and XXV, Static Electricity F and Elec-\\ntric Currents, are not intended to convey the impression\\nthat there is more than one kind of electricity, but that\\nelectricity may manifest itself in different conditions. The\\npresent chapter treats of electricity in a state of tension.\\nThe analogous term in water pressure is hydrostatic, which\\nrefers to the pressure of water at rest. But electricity may\\nflow, and we have conductors for it. Whether the flow of\\nelectricity through a conductor is like that of water, or like\\nthat of heat, we may not, at this point, discuss intelligently.\\nChapter XXV treats of Electric Currents, but their con-\\nsideration must also enter, to a slight extent, into this\\nchapter.\\n234. Conductors. In Fig. 130 b c represents a copper\\nwire attached at either end to silk threads a b and c d.\\nAt e two pith balls are suspended upon silk threads, and\\nat two pith balls are suspended by very fine copper wire.\\nBefore the experiment begins, the pith balls at hang in\\ncontact with one another, as those at e. If now we touch", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0251.jp2"}, "248": {"fulltext": "224 PHYSICS\\nan electrified body to any part of the copper wire b c, the\\nelectricity flows through the copper wire to the pith balls\\nat and, each having the same kind of electrification, they\\nrepel, as represented in the figure. Copper is a conductor\\nof electricity. Dry silk is\\nd not a conductor or, as we\\nsay, it is a wow-conductor.\\nHence the pith balls at e\\ndo not separate, because\\nthey are hung upon silk\\nthreads. The silk threads,\\na b and c d, are used to pre-\\nFlG 130 vent the electricity from\\nflowing away from the pith\\nballs at They are called insulators another word for\\nnon-conductors. If we moisten either a b or c d, the pith\\nballs at f will fall together again, showing that the elec-\\ntricity flows away through moist silk. If the silk threads\\nwhich suspend the pith balls at e are moistened, while a b\\nand c d are dry, an electrified body touching b c will cause\\nthe pith balls at e to separate, as well as those at There\\nare no perfect conductors, and there are no perfect insu-\\nlators hence electricity leaks away from all electrified\\nbodies, and it is difficult to keep them charged long. Dry\\nair is a very good insulator, but the moisture in the air is\\na good conductor. Hence these electrical experiments work\\nbest in cold weather when there is less moisture in the air.\\nIt is well to remember that the moisture of the breath may\\ninterfere with our experiments.\\nA telegraph wire is a conductor of electricity, and the\\nglass knobs upon telegraph poles are insulators.\\nIn the table which follows, the best conductors are at\\nthe head of the list. Electricity produced by friction will\\nforce its way quite readily through all those in the first\\nhalf of the list. They may, therefore, all be called con-\\nductors, although they differ very widely among themselves", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0252.jp2"}, "249": {"fulltext": "STATIC ELECTRICITY 225\\nin this respect. Copper conducts more than a million\\ntimes as well as water. Those in the last half of the\\nlist may be called insulators, the poorest conductors being\\nat the end of the list\\nCopper.\\nPaper.\\nIron.\\nAir.\\nCarbon.\\nSilk.\\nDilute sulphuric acid.\\nSealing wax.\\nWater.\\nGlass.\\nHuman body.\\nIlard rubber.\\nLinen.\\nPorcelain.\\nCotton.\\nShellac.\\nWood.\\nThe chief difference between electricity produced by\\nfriction, as in this chapter, and that produced by chem-\\nical action, as in the next chapter, is that although fric-\\ntion produces exceedingly small quantities of electricity, it\\nis vastly more capable of pushing its way through resist-\\nance and hence some things which are called conductors\\nin this chapter will be considered insulators in the next.\\nOnly the first four substances mentioned in the above list\\nwill be considered good conductors in the next chapter,\\nand only the last six are to be considered really good in-\\nsulators in this chapter.\\nWe may now see why we chose sealing wax and glass.\\nIt is because, being good insulators, they retain their elec-\\ntrification, while metals and other conductors lose their\\nelectrification as fast as it is produced. This, however,\\nmay be obviated by putting glass handles upon metals.\\nOf course, the electricity spreads all over the metal sub-\\nstance, while with a non-conductor it remains in those parts\\nwhere it is produced. This may be shown by rubbing seal-\\ning wax or hard rubber, in spots, with flannel, and then lay-\\ning it upon some granulated sugar. It will pick up the\\nsugar on those spots only which have been rubbed. It will\\nnow appear why we proposed to gild the pith balls in sec-\\n16", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0253.jp2"}, "250": {"fulltext": "226 PHYSICS\\ntion 231. The electricity will thus flow all over the sur-\\nface, and they will carry a much larger charge. Dry pith\\nis a poor conductor.\\n235. Induction, the Influence of Electrified Bodies upon\\nNeighboring Objects. Electrified bodies, like magnetized\\nbodies, exert an influence upon objects near them. One\\ndifference, however, is that an electrified body exerts its\\ninfluence upon all kinds of matter alike whereas magnets\\neffect iron only. In the case of both magnetism and elec-\\ntricity, we believe that the power to influence objects with-\\nout contact is due to the ether, which, by its waves, may\\nproduce heat, light, electric and magnetic\\nphenomena. Indeed, many think that\\nelectricity is the ether.\\nWhen an electrified body is brought\\nnear any neutral substance, wdthout touch-\\ning it, that substance is, as we might say,\\npolarized. The part nearest to the elec-\\ntrified body exhibits the opposite kind of\\nelectrification, and the more remote part\\nexhibits the same kind of electrification\\nas that of the inducing body. This ap-\\nparent action at a distance is known as induction. It is\\nnot, however, action at a distance, but action through the\\nmedium of the ether.\\nWe may now see why there is an attraction between\\nneutral bodies and electrified bodies, and why, if either of\\nthem is very light and free to move, they will come to-\\ngether. Fig. 131 represents an electrified stick of sealing\\nwax held near to a pith ball, which it has not yet touched.\\nIts influence polarizes the pith ball. The side nearest the\\nsealing w T ax becomes positively charged, and the farther side\\nbecomes negatively charged.\\nSince bodies with unlike kinds of electrification attract,\\nand those with like kinds repel, the pith ball is both at-\\ntracted and repelled but the law of inverse squares, as", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0254.jp2"}, "251": {"fulltext": "STATIC ELECTRICITY 227\\nstated in section 229, holds for electricity as well as mag-\\nnetism. Because of the difference in distance, the attrac-\\ntion is greater than the repulsion, and the pith ball moves\\ntoward the sealing wax. As the distance between them grows\\nless, the difference between attraction and repulsion grows\\nrapidly greater. When the space between the sealing wax\\nand the pith ball is about equal to the diameter of the ball,\\nthe attraction will be four times as great as the repulsion.\\nWhen the distance becomes one quarter as great, the attrac-\\ntion will be sixteen times as great as the\\nrepulsion, etc. Thus the pith ball moves\\nfaster and faster as it approaches the elec-\\ntrified body. When it touches, there is a\\nflow of electricity from the neutral body\\nto the other, until they are in the same\\nstate. Then repulsion begins and the pith\\nball flies off from the sealing wax. It\\nis now negatively charged, and will act\\ntoward a neutral object as the sealing wax acted toward it.\\nIf it is brought near to a neutral body it polarizes it, so\\nthat attraction is greater than repulsion between them. If\\nthe neutral body is heavier, or is not free to move, the pith\\nball will move to it. If the neutral object should be a\\nsecond pith ball, of equal weight with itself (Fig. 132), they\\nwill move equal distances toward one another. When they\\ntouch there will be a flow of electricity from one to the\\nother, and they will then be exactly alike, and repel. The\\nsecond ball will produce exactly the same effect toward\\nneutralizing the first ball as the first does toward electrify-\\ning the second. Hence, every time an electrified conductor\\ncharges another body, it tends to neutralize itself. This is\\ndifferent from magnetism. A magnet is not at all weak-\\nened by magnetizing other pieces of iron. In the next two\\nsections we shall see how an electrified body may enable us\\nto electrify any number of other bodies, without itself be-\\ncoming discharged at all.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0255.jp2"}, "252": {"fulltext": "228 PHYSICS\\n236. By Induction a Polarized Body may receive a Charge\\nfrom a Neutral Body. Fig. 133 represents an electrified stick\\nof sealing wax held near to a neutral pith ball, so as to influ-\\nence it without contact. The pith ball is polarized and\\ndrawn toward the sealing wax, as explained in section 235.\\nIf now the sealing wax shquld be removed, the pith ball\\nwould return to its former neutral state but if, while it is\\npolarized under the influence of the sealing wax, a neutral\\nobject, as for example one s finger, is allowed to touch the\\npith ball and after that the sealing wax is removed, the pith\\nball will be found to be positively charged. While we must\\nguard against thinking that we know\\njust what happens, it is interesting to\\nlearn what those who have thought much\\nabout these things have conjectured.\\nBenjamin Franklin conjectured that it\\nmight be something like this The elec-\\ntricity of the pith ball may have accumu-\\nlated, under the influence of the sealing\\nwax, in the under part of the ball, leav-\\nFiG. 133. r\\ning the upper part rather destitute. This\\nfact he indicated by the -j- an( i signs. When another\\nobject touches the pith ball, electricity flows in to fill the\\nvacancy, and now when the sealing wax is removed the ball\\nhas more than the normal charge.\\n237. The Electrophorus. This is a further illustration of\\nthe subject presented in the last section. A jelly-cake tin\\nwith sealing wax melted in it, and hardened into a layer\\nfrom an eighth to a quarter of an inch in thickness, makes\\na satisfactory form of electrophorus. It serves as a con-\\nvenient means for electrifying other objects, without losing\\nits own charge. The sealing wax is rubbed with flannel.\\nThis, by induction, enables us to electrify a neutral disk,\\nfrom neutral objects, an indefinite number of times. An-\\nother jelly-cake tin, a little smaller in size,- serves well for\\nthe neutral disk. This disk when charged is handled by", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0256.jp2"}, "253": {"fulltext": "STATIC ELECTRICITY 229\\nmeans of silk threads for insulation (see Fig. 134). The\\nsealing wax, being a non-conductor, does not impart elec-\\ntricity to the neutral disk in sufficient quantities to charge\\nit, as a stick of sealing wax may charge a pith ball. In-\\ndeed, the points of contact between the sheet of wax and\\nthe neutral disk are extremely\\nslight. The result is that the\\nmetal disk is polarized while\\nFig. 134. Fig. 135.\\nresting upon the wax, as shown in Fig. 135, where a b rep-\\nresents the metal disk and c d the sealing wax. If now one\\ntouches the disk with his finger, while in this condition,\\nthe disk becomes positively charged in the same manner\\nas the pith ball described in section 236. If the disk is\\nlifted by the silk threads, it will carry away a positive\\ncharge as many times greater than that which a pith ball\\nwould carry as its area is greater than that of the pith\\nball. The process may be repeated an indefinite number\\nof times without again rubbing the wax with the flannel.\\nThe disk is charged each time by electricity from the earth\\nflowing through the body of the operator and off the finger\\nwith which he touches the disk. If this charged disk is\\nbrought near to any neutral object, the discharge is marked\\nby a spark of considerable length. This spark will light\\nthe gas if the disk is presented to a gas jet. It will ex-\\nplode the mixture of oxygen and hydrogen in the eudi-\\nometer (see Fig. 1, page 9). If one brings a finger to this\\ncharged disk after it is removed from the influence of the\\nsealing wax, which, as we say, holds the charge bound,\\nhe will experience, when the spark passes, a slight prick-\\ning sensation. We may, however, store, so to speak, several", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0257.jp2"}, "254": {"fulltext": "230\\nPHYSICS\\nFig. 136.\u00e2\u0080\u0094 Electrophorus.\\nof its charges in a condenser, described in the next section,\\nso that one will feel a larger shock, when the charge is\\ntaken all at once, through the\\nbody.\\nA very common form of\\nelectrophorus is shown in Fig.\\n136, which consists of a cake\\nof hard rubber and a metal\\ndisk with a glass or hard-rub-\\nber handle.\\nThe electrical machines in\\ncommon use (see Fig. 137)\\nwork upon the same principle\\nas the electrophorus. Kotat-\\ning the glass disk accomplishes precisely the same thing as\\ncarrying a charge by means of the metal disk of the elec-\\ntrophorus and delivering it to some object. The machine\\ndelivers a continuous flow of charge through a conductor.\\nThese machines also have\\nattached to them con-\\ndensers, described in the\\nnext section.\\n238. Condensers. A\\nlarge beaker of chemical\\nglassware makes a good\\ncondenser. The inside\\nand outside are gilded, or\\ncovered with tinfoil, to\\nabout two inches from\\nthe top. Suppose this is\\nheld upon the hand, as\\nshown in Fig. 138, and the electrified cover of the electro-\\nphorus is brought to the outer coating. The outer coating\\nbecomes positively electrified, and this polarizes the inner\\ncoating by induction. The positive electrification is dis-\\ncharged through the hand, leaving the inner coating nega-\\nFig. 137. Electrical machine.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0258.jp2"}, "255": {"fulltext": "STATIC ELECTRICITY\\n231\\nill\\nill!\\nFig. 138.\\ntively electrified. If now the other hand is brought to the\\nouter coating, the coatings of the beaker neutralize each\\nother by discharging through the body. If\\nthe cover of the electrophorus is discharged\\ninto the outer coating of the beaker several\\ntimes, we find the shock produced by the\\ndischarge proportionally increased. Twenty\\nsparks from the electrophorus will charge\\nthe condenser sufficiently to send a consid-\\nerable shock through a class of thirty or\\nforty pupils with hands joined. Condensers\\nhave a variety of shapes. The most con-\\nvenient form is that of the Ley den jar, illus-\\ntrated in Fig. 139. The name is derived\\nfrom the city of Leyden in Holland, where it was invented\\nin the year 1746.\\n239. Lightning. The earth, the air, and the clouds con-\\nstitute a natural condenser like a huge Leyden jar. The\\nclouds constitute\\none coating, the\\nearth the other, and\\nthe atmosphere rep-\\nresents the glass in-\\nsulator between the\\ntwo. This natural\\ncondenser becomes\\ncharged in various\\nways. Evaporation\\nis perhaps one cause\\nof electrification.\\nIf the vapor is posi-\\ntively charged, as it\\naccumulates in the\\nclouds, it induces a\\nnegative charge in objects upon the earth s surface, im-\\nmediately underneath the clouds. Lightning is the spark\\nFig. 139.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0259.jp2"}, "256": {"fulltext": "232\\nPHYSICS\\nwhich attends the discharge of this natural condenser. It\\nfrequently happens that the vapor of one cloud is positively\\ncharged with reference to that of another, and it is prob-\\nable that the lightning discharge between two clouds is of\\nmuch more frequent occurrence than that between cloud\\nand earth.\\n240. Electrical Distribution\u00e2\u0080\u0094 Effect of Points.\u00e2\u0080\u0094 If the\\nelectrified body is a non-conductor, the electrification ap-\\npears only in those spots where it was produced but if the\\nbody is a conductor, the charge spreads itself over all the\\nsurface. The opposite extremities are not poles, as in the\\ncase of a magnet, nor is the intervening part neutral. The\\ncharge, however, whether positive or negative, affects the\\nouter surface only, and this gives us trouble with Franklin s\\nconjecture, men-\\ntioned in section\\n236. The fact is,\\nthat if the gild-\\ning of an electri-\\nfied pith ball should fall\\noff, it would remove all\\nsigns of electrification,\\nwhether -f- or from the\\npith ball. This is shown\\nby an experiment with the\\napparatus illustrated in\\nFig. 140. A neutral ball\\nupon an insulated sup-\\nport is covered with two\\nmetal hemispheres. It is\\nelectrified either before or after the hemispheres are put\\non; but when the hemispheres are removed by the glass\\nhandles they alone are found to be electrified. The sphere\\nitself is left in a neutral state. If an insulated tin cup is\\nelectrified, no sign of a charge will be found inside the cup,\\nbut only upon the outer surface. The charge is also found", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0260.jp2"}, "257": {"fulltext": "STATIC ELECTRICITY\\n233\\nFig. 141.\\nto be most intense upon projecting portions, as the handle\\nof the cup. If an egg is insulated and electrified the\\ngreatest in-\\ntensity of\\ncharge will be\\nfound upon\\nthe small end\\nof the egg.\\nIf we con-\\nstruct an object egg-shaped,\\nbut with the small end very\\nmuch drawn out, as in Fig.\\n141, the difference between\\nthe intensity of the charge\\nupon this prolongation and\\nthe rest of the surface will\\nbe very marked. If the small end is made into a sharp\\npoint, the tension of the charge will be increased at this\\npoint to such an ex-\\ntent that the elec-\\ntricity which, as\\nwas said in section\\n234, always leaks\\naway to some ex-\\ntent, will disappear\\nrapidly. Hence,\\nobjects like the\\npith ball, which\\nshould retain a\\ncharge, are made as\\nround and smooth\\nas possible. This\\naccounts for the\\nmany knobs upon\\nelectrical apparatus. When points are used, as, for example,\\nthe combs on the electrical machine (see Fig. 137), they\\nFig. 142.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0261.jp2"}, "258": {"fulltext": "234\\nPHYSICS\\nare to facilitate the discharge from one portion to another\\nof the apparatus. If a portion of the electrical machine\\nhas a point projecting from it, as shown in Fig. 142, it\\nwill create a sufficient breeze to blow out a candle. This\\nmay be accounted for by supposing that the particles of\\nair are electrified and thrown off at this point, like pith\\nballs, in a stream. If the points are\\narranged at the extremities of the\\nspokes of a wheel, as shown in Fig.\\n143, the wheel will rotate as a lawn\\nsprinkler, which throws off streams\\nof water from its arms. As has been\\nalready stated, an electrified cloud\\ninduces the opposite state of electri-\\nfication in that portion of the earth\\nwhich is immediately underneath it.\\nMountain peaks, spires of buildings,\\nlightning rods, masts of ships, etc.,\\nlike points upon electrical appara-\\ntus, facilitate the discharge between\\nthe earth and the clouds. If an electrical machine is oper-\\nated in a dark room, a pale light is seen to stream from\\nsharp points upon the machine. This phenomenon occurs\\nin Nature on a grand scale. Sailors notice pale flames\\nstreaming from the tips of the masts when a strongly elec-\\ntrified cloud is passing over. This is called by them St.\\nElmo s Fire.\\nFig. 143.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0262.jp2"}, "259": {"fulltext": "CHAPTEE XXV\\nELECTRIC CURRENTS\\nI. GENERATORS OF ELECTRIC CURRENTS\\n241. Sources of Electric Currents. Observe that we do\\nnot say sources of electricity. That would be inconsistent.\\nAssuming electricity to be identical with the ether, we can\\nneither create nor destroy it. But electricity may be set in\\nmotion this flow of electricity from one point to another\\nis the subject of this chapter, and we may properly begin\\nwith the sources of the\\ncurrent. The discharge\\nof a Ley den jar, or other\\nelectrified body, through\\na conductor, is a current\\nof electricity. If we con-\\nnect the two knobs of the\\nelectrical machine repre-\\nsented in Fig. 144 by a\\ncopper wire, a constant\\ncurrent of electricity\\nflows through the wire\\nwhile the machine is\\noperated. The current produced by this machine is, how-\\never, extremely slight in quantity, and is therefore of little\\nuse, although, as was stated in section 234, it has exceed-\\ningly high tension and can push its way through poor con-\\nductors. A few analogies will help to make clear the dis-\\ntinction between high-tension and large-quantity currents.\\n235\\nFig. 144. Electrical machine.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0263.jp2"}, "260": {"fulltext": "236 PHYSICS\\nThe current which we get from the electrical machine men-\\ntioned above may be compared with a stream of water com-\\ning through a pin hole in the bottom of a very deep tank\\nwhich is full of water. Although the head of water may\\nbe very great, the quantity is too small to turn a mill\\nwheel. Or it may be compared with a pile driver weighing\\nonly one ounce, but raised to a great height. It falls with\\ngreat velocity, but with too little momentum to move the\\npile. Or it may be compared with a cup of water heated to\\nthe boiling point. Its temperature is very high, but the\\nquantity of heat is too small to modify the climate, or to\\nheat a house or to cook a dinner. In these analogies water\\npressure, velocity, and temperature represent electric tension.\\nIn the present chapter we shall discover means for produ-\\ncing electric currents in larger quantities, although the\\ntension will be quite low and they will not flow through\\nmuch resistance. By way of analogy they may be compared\\nwith the flow of a large stream of water, having only a few\\nfeet of fall but capable of operating a water wheel. Or\\nthey may be compared with a pile driver of considerable\\nsize, capable of driving a pile by falling only a few feet.\\nOr they may be compared with a large body of water\\nslightly warm, but able to modify the temperature of sur-\\nrounding objects for a long time by reason of its large\\nquantity of heat.\\nWe shall present in this chapter three sources of cur-\\nrent chemical action, mechanical motion, and heat and\\nthese forms of energy are transformed into current by\\nmeans of the battery, the dynamo, and the thermopile re-\\nspectively. Turning back for a moment to the general\\nconception of work, it will be recalled that work is the\\novercoming of resistance through space, and involves both\\nmotion and something to be moved. Energy, or the power\\nto do work, is only possible, therefore, when we have mat-\\nter in such a position that it is capable of motion. This\\nmeans inequality of condition, and therefore possible ex-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0264.jp2"}, "261": {"fulltext": "ELECTRIC CURRENTS 237\\nchange. The weight on top of the pile .driver represents\\nstored-up work simply because there is a lower level to\\nwhich the weight may fall. The steam in the boiler repre-\\nsents stored-up work simply because there is a lower tem-\\nperature to which the steam may fall. All matter at the\\nsame level, all bodies at the same temperature, represent no\\npossible interchange, and therefore no available energy.\\nLift some of the matter above the general level, and at\\nonce we have potential energy. Heat some of the bodies\\nabove the general temperature, and we have available en-\\nergy. The water upstream turns the mill because of the\\nlower level downstream. Applying this thought to elec-\\ntricity, we see that so long as the electric level is undis-\\nturbed, there is no electric current. The universe is as\\nfull of electricity as the ocean is of water, but just as the\\nocean must be lifted up by evaporation and precipitated in\\nrain upon the hills before it is available as a water power,\\nso to make electricity available as a source of energy we\\nmust disturb its level, and we must provide a suitable chan-\\nnel through which the equilibrium may be brought about.\\nAll devices for producing electric currents may be regarded\\nas devices for changing the electric level, and all conduct-\\nors as channels for bringing about equalization of level.\\nIf the difference of level is temporary, the current will be\\ntemporary but if the difference of level is constantly\\nmaintained, and the channel remains the same, the current\\nwill also be constant.\\n242. Electric Potential is the term applied to electric\\nlevel. Currents flow from a place of high potential to a\\nplace of low potential. In case the potential is equal,\\nthere is no flow of current. The production of current is\\npractically the process of maintaining a difference of po-\\ntential. This is also called electro-motive force, abbreviated\\nto E. M. F., or simply E the unit for the measurement of\\nwhich is called the volt (254), a name derived from Volta,\\nthe inventor of the voltaic cell.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0265.jp2"}, "262": {"fulltext": "238 PHYSICS\\n243. The Voltaic Cell (Fig. 145) is a machine for main-\\ntaining a constant difference of potential through constant\\nchemical action. In its simplest form it consists of two\\nmetals joined by a conductor and moistened by some liquid\\nthat will dissolve one of them. A jar of water acidulated\\nwith sulphuric acid, H 2 S0 4\\nand containing a strip of cop-\\nper and a strip of zinc, con-\\nstitutes a simple voltaic cell.\\nOn joining the copper and the\\nzinc by a wire, a current flows\\nfrom the one to the other.\\nMeanwhile the zinc is being\\nacted upon by the acid, and is\\npassing into solution as zinc\\nsulphate, ZnS0 4 while bubbles\\nFig. 145.-The voltaic cell. of hydrogen, H, appear on the\\ncopper plate. The chemical\\naction is as follows Zn H 2 S0 4 ZnS0 4 2H. The\\nsource of current here is the chemical action between the\\nzinc and the acid. The copper remains unchanged, but\\nin its absence we should have no current we should have\\nthe same chemical reaction, but the physical product would\\nbe heat. The solution would become very hot. The cop-\\nper largely prevents this production of heat, and causes the\\nenergy to appear as electric current. The zinc, being the\\nmetal acted upon, and the apparent source of the differ-\\nence of potential, is termed the electro-positive metal, while\\nthe copper is the electro-negative metal.\\nThe galvanic cell consists, then, of\\n1. The electro-positive metal.\\n2. The electrolyte, or substance which will produce a\\nchemical reaction with the positive metal.\\n3. The electro-negative element.\\nWe may substitute for zinc any other metal that will be\\nacted upon by the electrolyte chosen. Instead of the sul-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0266.jp2"}, "263": {"fulltext": "ELECTRIC CURRENTS 239\\nphuric acid, we may use any other substance that will\\nproduce a chemical change with the electro-positive metal.\\nAnd, finally, the electro-negative element may be any con-\\nductor, such as platinum or carbon that is, insoluble or\\nless soluble than the electro-positive metal. It need not\\nitself be a metal.\\nBy means of a condensing electroscope, the upper end\\nof the carbon can be shown to be positively but very feebly\\ncharged, and the upper end of the zinc to be likewise nega-\\ntively charged by a conductor, wire or other. In order that\\nthere may be a current of electricity, there must be a com-\\nplete circuit that is, the upper ends of the carbon and the\\nzinc mast be connected. We think that the current flows\\nthrough the wire from the carbon to the zinc, and through\\nthe solution from the zinc to the carbon.\\nFor convenience in introducing various pieces of appa-\\nratus into the electric circuit we have two wires, one con-\\nnected with the carbon and the other connected with the\\nzinc. The free ends of these wires are called poles. The\\nfree end of that connected with the carbon is called the\\npositive pole, and the free end of the other wire is called\\nthe negative pole. In short, any point in the circuit is\\npositive with reference to any other point in the circuit\\ntoward which the current flows, and negative with refer-\\nence to any other point in the circuit from which the cur-\\nrent flows. So that in the solution the zinc is positive\\nwith reference to the copper or carbon but outside of the\\ncell the wire connected with the copper or carbon is called\\nthe positive pole or the anode, while that connected with\\nthe zinc is called the negative pole or kathode.\\n244. The Electro-Chemical Series. Since we need only\\nchemical action and a suitable conductor, the choice of ma-\\nterials for a galvanic cell covers a wide range. But what we\\nare working for is a strong, constant current of electricity,\\nand so our choice of material must practically be limited to\\ncombinations that will give this result. If we arrange the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0267.jp2"}, "264": {"fulltext": "240 PHYSICS\\navailable chemical elements in a list according to their\\nproperties, putting those first which are the most readily\\noxidized, we shall find that the strongest current results\\nwhen two widely separated elements are chosen. Such a\\nlist would stand as follows\\nSodium. Copper.\\nMagnesium. Silver.\\nZin c. Gold.\\nLead Platinum.\\nTin -Carbon.\\nIron.\\nThe alkali metals, such as sodium, and the alkaline-earth\\nmetals, such as magnesium, are practically ruled out on\\naccount of the too great energy of their chemical affinity\\nand their expense. Zinc, therefore, is the electro-positive\\nmetal usually chosen. At the other end of the series cop-\\nper and carbon are the electro-negative elements most\\nfrequently used. But any element in the list is electro-\\npositive with respect to the element following it, and elec-\\ntro-negative to the one before it. The order of the list\\nalso represents the heat-producing power of the elements.\\nThis is very significant when we remember that the chem-\\nical action yields heat when the conditions are such that it\\nmay not yield a current, as when the copper or carbon is\\nwanting.\\n245. Local Action and Polarization. The zinc-carbon-\\nsulphuric acid cell just described is not a very practical\\nmachine, for two reasons the zinc wastes away when the\\ncell is not in operation, and the current is far from con-\\nstant. The waste is due to local action, and the uncon-\\nstancy to polarization.\\nLocal Action. If chemically pure zinc be used, it will\\nonly dissolve when it is in connection with the carbon and\\nthe current is flowing. But the zinc of commerce is far\\nfrom pure. It contains appreciable quantities of iron and\\ncarbon, and dissolves in the acid even when not connected", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0268.jp2"}, "265": {"fulltext": "ELECTRIC CURRENTS 241\\nwith the copper. This is due to local action between the\\nzinc and the iron or other impurity by which we have\\ninternal currents set up, and, as a result, constant waste.\\nIt may be avoided by amalgamating the zinc. A few drops\\nof mercury are rubbed over the clean and acid-moistened\\nplate of zinc, forming a surface amalgam. The impurities\\ndo not dissolve in the mercury. Hence the plate acts like\\npure zinc, and the amalgam goes on forming during the\\naction of the cell, just as rapidly as the zinc is dissolved\\nout by the acid.\\nPolarization is a more serious evil. The hydrogen lib-\\nerated by the chemical action of the zinc and sulphuric\\nacid is electro-positive, and hence gathers upon the carbon\\nor electro-negative plate. This not only acts as an insu-\\nlator of the negative plate from the current the gas not\\nbeing so good a conductor as the solution but it lessens\\nthe difference of potential between the two plates. Indeed,\\nthe hydrogen, if it should completely cover the carbon\\nplate, would change it from an electro-negative to an elec-\\ntro-positive plate. The current in consequence grows\\nweaker and weaker, the carbon plate is said to be polar-\\nized, and can only be restored to full action by the removal\\nof the hydrogen. Different methods have been suggested\\nfor the prevention of polarization, and have given rise to\\nour present large number of kinds of voltaic cells, some of\\nwhich are mentioned in the following list\\n246. Some Typical Cells.\\nE. M. F.\\nVolts.\\nBichromate cell 2.1\\nBunsen cell 1.9\\nLeclanche cell 1.4\\nDaniell cell 1.05\\nGravity cell 1.05\\nIn the bichromate cell (Fig. 146) the zinc plate is sus-\\npended between two plates of carbon, and, being attached\\nto an adjustable rod, may be drawn up into the neck of the\\n17", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0269.jp2"}, "266": {"fulltext": "242\\nPHYSICS\\nbottle and quite out of the solution when the cell is not in\\nuse. Chemical depolarization depends in all cases upon\\nthe action of an oxidizing agent.\\nThe hydrogen is thus changed\\ninto water, H 2 0. In the bichro-\\nmate cell the oxidizing agent is\\nbichromate of sodium, Na 2 Cr 2 7\\nAbout one pound is added to a\\ngallon of water and a pint of sul-\\nphuric acid. When the solu-\\ntion is fresh it is bright red, but\\ngradually turns dark and green\\nfrom the reduction of the bi-\\nchromate. The capacity of the\\njars varies from half a pint up to\\na gallon. The bichromate cell\\nhas long been a favorite one for\\nlecture use, as it gives a powerful\\ncurrent and is always ready.\\nThe Bunsen cell (Fig. 147) is a double-fluid cell. The\\nelectro-negative element is carbon, immersed in the oxidiz-\\ning agent, strong nitric acid, HX0 3 contained in an inner\\nporous cup. The zinc is\\namalgamated, and is in the\\nform of a cylinder open at\\nboth ends. It surrounds the\\nporous cup, and stands itself\\nin dilute sulphuric acid. The\\nhydrogen liberated by the solu-\\ntion of the zinc passes through\\nthe porous cup, but fails to\\nreach the carbon, because it\\nmeets the nitric acid and is\\noxidized to II 2 with the lib-\\neration of red fumes of nitro-\\ngen peroxide, N0 2 The cell Fig. 147.\u00e2\u0080\u0094 The Bunsen cell.\\nFig. 146.\u00e2\u0080\u0094 The bichromate cell.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0270.jp2"}, "267": {"fulltext": "ELECTRIC CURRENTS\\n243\\nis strong and constant, but the peroxide fumes are corro-\\nsive and poisonous.\\nThe Leclanche cell (Fig. 148) is a single-fluid combina-\\ntion in which zinc and carbon are immersed in a solution\\nof ammonium chloride, NH 4 C1, and polarization is pre-\\nvented by surrounding the carbon with a packing of mixed\\ncarbon and black oxide of manganese, Mn0 2 The zinc\\nmay be in the form of a pencil, or a cylinder surrounding\\nthe carbon. The action is very simple. The zinc forms a\\nsoluble double chloride of zinc and ammonia, while free\\nhydrogen and ammonia gas, NH 3 pass toward the carbon.\\nBut the oxide interposes, tak-\\ning care of the hydrogen, and\\nthe ammonia gas escapes in-\\nto the air. The oxide of man-\\nganese is itself reduced to a\\nlower oxide, and must in time\\nbe removed. These cells are\\nused in almost every house\\nfor ringing electric bells.\\nTheir great virtue is that no\\nchemical action takes place\\nin them except when the\\nelectric current is flowing.\\nHence they are known as\\nopen circuit batteries.\\nFor ordinary household pur-\\nposes they may last a year or\\ntwo without any replenishing\\nof parts.\\nTlie Daniell cell introduces an entirely new method of\\npreventing polarization. A copper plate is immersed in a\\nsolution of copper sulphate, CuS0 4 in the outer glass jar,\\nand zinc is immersed in sulphuric acid in an inner porous\\njar. The hydrogen which is set free by the action of the\\nsulphuric acid upon the zinc passes through the porous cup,\\nFig. 148.\u00e2\u0080\u0094 The Leclanche cell.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0271.jp2"}, "268": {"fulltext": "244 PHYSICS\\nbut instead of collecting upon the copper plate it decom-\\nposes the copper sulphate, forming H 2 S0 4 and setting the\\ncopper free which is deposited upon the copper plate. The\\ncopper, being electro-negatiye, does not change the char-\\nacter of the negative element, and the current therefore is\\nalmost constant. The outer liquid is maintained a satu-\\nrated solution of copper sulphate by crystals of the salt.\\nThe gravity cell (Fig. 149) is a modification of Daniell s,\\nand dispenses with the porous cup. The copper rests on\\nthe bottom of the jar. A saturated solution of copper sul-\\nphate completely covers the copper, extra crystals of the\\nsulphate being placed in the bottom. The zinc is sus-\\npended from the top of the jar, about four inches above the\\nz copper. It is surrounded by a solu-\\nA j tion of zinc sulphate, which, being\\n|iK||^Hi|yH l ess dense, floats on top of the heavy\\nJSPiHifH copper sulphate solution. The cell\\nZnS 4 K gets its name fr m the fact that\\n|j jliL _ 2 i gravity replaces the porous cup in\\nCwS04 |\u00c2\u00a3J~_ 111 keeping the two solutions apart.\\nj,U ;r?.f ,J| _^m The zinc sulphate increases as the\\n^|8||~ $00^~ z i llc wastes away, and must be re-\\nFig. 149.-The gravity cell. m0ved fr0m time to time Tne\\ncopper sulphate is used up, and\\nmust be renewed by dropping fresh crystals into the bot-\\ntom of the jar. As the copper sulphate forms a deep-blue\\nsolution, one can always tell when more crystals are needed.\\nThe blue color should extend above the copper, but never\\nquite reach the zinc.\\nOn account of its convenience, economy, and constancy,\\nthe gravity cell is used almost entirely for telegraphic\\nwork. One may see them at nearly every railway station.\\nThe number of actual and possible cells is legion. We\\nhave described only those which are to-day most important\\nand most frequently met. They are all simple machines\\nfor maintaining a more or less constant difference of poten-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0272.jp2"}, "269": {"fulltext": "ELECTRIC CURRENTS\\n245\\ntial between two points, and consequently setting up an\\nelectric current.\\n247. The Battery of Cells. When several cells are joined\\ntogether, they form a voltaic battery. If the positive\\nmetal of one cell is joined to the negative element of the\\nnext cell, and so on throughout the series,\\nthe current passes through one cell after an-\\nother, and the battery is said to be arranged\\nin series (Fig. 150). Thus the difference in\\nthe potential of carbon and zinc\\nof each cell is multiplied by the\\nFig. 150.\u00e2\u0080\u0094 Cells in series.\\nFig. 151. Pumps in series.\\nnumber of cells, and a battery of three cells so arranged\\nwill push its current through three times as much resist-\\nance as one cell would be able to do. The analogy of\\nthree water pumps, arranged as represented in Fig. 151,\\nwill help to make this clear. All the water which traverses\\nthe circuit must go through each pump. Each pump\\nraises the water level by a certain amount, and it is mani-\\nfest that the water pressure in the return pipe is three\\ntimes as great as it would be if it returned from the outlet\\nof the first pump.\\nIf all the positive metals are joined together and all the\\nnegative elements, the current passing through all the cells\\nat the same moment, the battery is said to be arranged in\\nparallel (Fig. 152). This is analogous to the arrangement\\nof pumps represented in Fig. 153, where only one third of\\nthe water goes through each pump. Three pumps raise", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0273.jp2"}, "270": {"fulltext": "246\\nPHYSICS\\nthe level of the water no higher than one pump would, and\\nthe water pressure in the return pipe is no greater than it\\nwould be if one pump acted alone, but three times as great\\nz c z c z c\\nFig. 152.\u00e2\u0080\u0094 Cells in parallel.\\nFig. 153. Pumps in parallel.\\na quantity of water may be supplied to the return pipe as\\nin the former case. The arrangement chosen must depend\\nupon the work to be done, and this will be discussed in\\nsection 257.\\nII. Some Effects of Electric Currents\\n248. Electric Currents recognized by their Effects. To a\\ncasual observer there is no evidence that the cell produces\\nan electric current, and we must therefore learn to recog-\\nnize the current from some effect which it may produce.\\nWe will stop to study some of the effects of the current\\nbefore we go on to consider its further production by the\\ndynamo and thermopile. These effects cover a very wide\\nrange, and the immense variety of the phenomena growing\\nout of electricity constitutes its chief fascination. Those\\nwhich we shall consider are physiological, thermal, chemical,\\nand magnetic.\\n249. Physiological Effects.\u00e2\u0080\u0094 It is difficult to get any evi-\\ndence from our sense of feeling that the cell produces any\\nelectric current, because our bodies are not sufficiently\\ngood conductors (see 234) for the cell, with its slight poten-\\ntial, to send any of the current through our flesh. Of\\ncourse, a sufficiently large number of cells arranged in series", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0274.jp2"}, "271": {"fulltext": "ELECTRIC CURRENTS 247\\nwould send a current that might be felt, but the batteries\\nof such number of cells as we are likely to use in the lab-\\noratory are not capable of sending through the human body\\nany appreciable current. If the poles of two or three cells\\nconnected in series are touched to the tip of the tongue a\\nfew millimetres apart, a slight sensation is felt, but the\\namount of current that passes is exceedingly small. We\\nmay therefore handle our battery wires without insulation\\nand lose no current. For more interesting physiological\\neffects we must have high-tension currents, such as will be\\nconsidered in future sections upon induction.\\n250. Thermal Effects. Whenever a current meets resist-\\nance, heat is produced in much the same way as when me-\\nchanical motion encounters friction. In both cases there\\nis waste of energy. Even the best conductors offer some\\nresistance, and consequently the temperature of every con-\\nductor rises a little while an electric current is passing\\nthrough it. In the case of all forms of electric light we\\npurposely introduce resistance to the current, so as to get\\nheat and light from it. In the arc lamp the tremendous\\nresistance of the air produces the voltaic arc, one of our\\nmost intense sources of heat. In the incandescent lamp\\nthe high resistance of the filament of carbon develops\\nenough heat to make the carbon white hot.\\nElectric stoves are simply resistance boxes. The elec-\\ntric stove used in the trolley cars consists of several coils of\\nwire. They offer so much resistance to the passage of the\\ncurrent that they become much heated, and then act simply\\nas radiators. In the stoves used for cooking the wires are\\ngenerally of platinum or German silver, buried in fire clay\\nor in asbestos.\\nThe electric furnaces used to reduce ores of aluminium\\nand other metals consist of a fire-clay box provided at each\\nend with a carbon terminal, and packed with a mixture of\\ncarbon and ore. When the current passes it meets such\\ntremendous resistance that a corresponding .amount of", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0275.jp2"}, "272": {"fulltext": "248 PHYSICS\\nheat is developed, and the refractory ore is reduced to\\nmetal.\\nThe current is applied with great success to the welding\\nof metals. The pieces to be welded are pressed together\\nwith much force, and a large current is passed through the\\njuncture. Great heat is developed and the welding is very\\nperfect.\\nThe solutions in the battery cells rise in temperature\\nwhen the current passes, because of the resistance which\\nthey offer to the current.\\nIf the wires from a battery of two cells connected in\\nseries be rubbed upon a file, a brilliant shower of sparks\\nwill be produced. Minute particles of metal are made in-\\ncandescent by the resistance offered to the current as the\\nwires dance along over the file.\\n251. Chemical Effects. The chemical action in the cell\\nproduces an electric current, and this electric current is in\\nturn able to produce chemical action. In the cell zinc de-\\ncomposes the sulphuric acid, forming zinc sulphate, which\\nremains dissolved in the water used in the cell. If, when\\nthe cell is run down, we dip the poles of a sufficiently\\nstrong battery into this solution of zinc sulphate, the elec-\\ntric current will decompose this zinc sulphate again, the\\nzinc gathering about the negative pole and the sulphuric\\nacid gathering about the positive pole. This process of\\ndecomposing compounds by electricity is called electrolysis.\\nWhen we have decomposed this zinc sulphate into zinc and\\nsulphuric acid it will act as a battery cell and produce\\nagain an electric current. This is one form of a storage\\nbattery, and the act of decomposing its zinc sulphate into\\nzinc and sulphuric acid by means of an electric current is\\ncalled storing the battery cell, or storing electricity an\\nexpression which is misleading.\\nStorage batteries, or accumulators, were first announced\\nin practical form by Gaston Plant e in 1860. In its com-\\nmonest form the storage-battery cell consists of two plates", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0276.jp2"}, "273": {"fulltext": "ELECTRIC CURRENTS 249\\nof lead, each having holes filled with a paste of lead sul-\\nphate, in dilute sulphuric acid. When an electric current\\nis passed through this cell the anode (the plate of lead\\nwhich is the positive pole that is, which is connected with\\nthe wire from the negative plate in the battery) becomes\\ncovered with a coating of peroxide of lead, Pb0 2 while the\\nkathode is covered with particles of lead in a spongy form.\\nIn this condition the accumulator is said to be charged.\\nFor this reason it is sometimes called a storage battery, but\\nin reality electricity is not stored in it any more than heat\\nis stored in coal, or houses and farms are stored in a bank.\\nThe electric current sent through the accumulator does\\nchemical work in breaking chemical compounds, which,\\nwhen they reform again, will generate a current. It is a\\ncurious fact that these chemical compounds do not reform\\nagain in the cell until the circuit is closed and the electric\\ncurrent produced thereby flows. Yet this is the case with\\nevery battery cell to a certain extent, and particularly so\\nwith those, such as the Leclanche type, which are called\\nopen-circuit cells. Storage batteries are much used for\\nrunning electric launches and automobiles, and to supple-\\nment a dynamo, from which it may store energy to be\\nexpended at intervals when the dynamo is insufficient or\\nat rest.\\nElectrolysis of Water. This is conveniently carried out\\nin the Hoffmann apparatus, shown in Fig. 154, or some\\nother simple form like that represented in Fig. 155. The\\nwater has a little sulphuric acid added to it, in order to\\nmake it a conductor of electricity. The current from a\\nbattery of several cells is allowed to pass through the appa-\\nratus until enough gas has been collected in each tube to\\nbe examined satisfactorily. Twice as much gas collects at\\nthe negative electrode (the kathode) as at the positive elec-\\ntrode (the anode). The first-mentioned gas is found to\\nburn with a pale-blue flame it is hydrogen. The gas at\\nthe anode, when tested by a glowing splinter, is shown to", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0277.jp2"}, "274": {"fulltext": "250\\nPHYSICS\\nbe oxygen. The decomposition is expressed by the chem-\\nical reaction\\nH 2 H 2 0.\\nElectrolysis of Salts. The current may be used to de-\\ncompose water solutions of any of the salts of the more\\nelectro-negative metals, such as copper, nickel, silver, and\\ngold. This is the basis\\nof our electroplating and\\nelectrotyping. The object\\nto be plated is made the\\nkathode, the anode being\\neither a plate of the metal,\\nin which case the solution\\nor bath keeps a con-\\nstant strength, or else a\\nstrip of platinum (Fig.\\n156). The cyanides of gold\\nand silver are generally\\n\\\\o\\\\\\nH\\n1 i\\njj\u00c2\u00a7\\nwiiiijllliyp\\n1b\\niiiiiiiiiliillllllllllllllllilill\\nFig. 154. Hoffmann apparatus.\\nFig. 155.\u00e2\u0080\u0094 Electrolysis of water.\\nemployed, and a double sulphate of nickel and ammonia.\\nCopper succeeds best from a slightly acid solution of the\\nsulphate. In electrotyping, an impression of the type or\\ncut is first made in wax or gutta-percha, and this is then\\nrubbed over with graphite, in order to make it a conductor.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0278.jp2"}, "275": {"fulltext": "ELECTRIC QUERENTS 251\\nThe mold is then suspended in a bath of copper sulphate\\nas a kathode, the anode being a copper plate. In this way\\na very thin film or skin of copper is obtained, which is\\nFig. 156. Electroplating.\\nafterward backed with type metal and mounted on a\\nwooden block, so as to make its face height equal to that\\nof ordinary type.\\nMost of the copper ore of the world is bought and sold\\non the basis of the electrolytic assay. About a gram of\\nore is digested with acid. The insoluble gang is filtered\\noff. The dissolved copper is placed in a weighed platinum\\ndish, which is then made the kathode, a little spiral of\\nplatinum dipping into the solution being the anode. The\\ncurrent is allowed to pass overnight. In the morning all\\nthe copper is found deposited on the platinum dish, and,\\nafter drying, may be directly weighed.\\n252. Magnetic Effects. If the copper wire which con-\\nnects the carbon and zinc terminals of a cell is made into\\na coil as shown in Fig. 157 which coil is called a helix\\nthe electric current will develop a magnetic field. The\\nregion around this helix behaves exactly as that around\\nall magnets.\\nWe regard a magnetic field as an ether vortex, and to\\nproduce this we cause the electric or ether current to move\\nin whirls. The successive turns of the wire must not touch", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0279.jp2"}, "276": {"fulltext": "252\\nPHYSICS\\none another, for if they did the current would take the\\nshortest path from the carbon to the zinc. The best way\\nto make the helix is to nse wire which has a thin insulating\\ncovering. No. 24 single, cotton-covered copper wire is\\nFig. 157.\u00e2\u0080\u0094 Helix.\\nFig. 158.\\nbest. This may be coiled around a wire nail, making a\\nhelix about an inch long, with the wires, say, three layers\\ndeep. The nail may then be withdrawn, and the helix,\\nwhen an electric current is passing around it, will be found\\nto be the center of a rather strong magnetic field. The\\nFig. 159.\u00e2\u0080\u0094 The floating helix.\\nend of this helix, around which the current is passing in\\nthe direction in which the hands of a watch move, will be\\nfound to attract the north pole of a compass needle that\\nis, it is a south pole, and the other end of the helix is its", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0280.jp2"}, "277": {"fulltext": "ELECTRIC CURRENTS 253\\nnorth pole (see Fig. 158). Such a helix may be floated\\nupon a battery solution, and will itself behave as a compass\\nneedle (see Fig. 159). If the wire nail is inserted in this\\nhelix it will be strongly magnetized when the current\\npasses, and the field will be found to be much more strongly\\nm\\nFig. 160.\\nmagnetic than before the iron core was used. A helix with\\nan iron core is called an electro-magnet. We shall meet\\nwith it many times in future sections. If the iron is very\\nsoft, it will lose its magnetism as soon as the current ceases\\nto flow. If, however, it is steel or hardened iron, it will\\nretain its magnetism after it is removed from the helix.\\nIn this way we may make permanent magnets of steel\\n(Fig. 160).\\nWe are now prepared to state what we believe to be the\\nconnection between magnetism, static electricity, and elec-\\ntric currents. Magnetism we regard as an ether vortex,\\nstatic electricity is an ether stress, and an electric current is\\nether flowing in a stream. The ether vortex is not confined\\nto the magnet, although that is its center the vortex ex-\\ntends some distance around the magnet, and is called the\\nmagnetic field. Ether stress is not confined to an elec-\\ntrified body, although that is the center of it. By bring-\\ning a pith ball near to an electrified body, we discover\\nthat the ether stress extends to some distance around the\\nbody.\\nAn ether current is not confined to the conducting\\nwire, although that is the center of the stream. We shall\\nlearn more about this in future sections.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0281.jp2"}, "278": {"fulltext": "254\\nPHYSICS\\nIf we bring a magnetic needle near to a straight wire\\nthrough which a current is passing (Fig. 161), we have evi-\\ndence that the field about the wire is affected by the elec-\\n^MM\\ntrie current. The needle will be deflected toward a direc-\\ntion at right angles to the wire. The accompanying\\ndiagrams (Fig. 162) show the direction which the needle\\nwill take, and at the same time suggest the explanation.\\nSuppose the current to be flowing from left to right, as\\nrepresented by the large straight arrow in the upper dia-\\ngram, and the needle to be brought over it, the north pole\\nis turned toward the observer if under it, the south pole\\na\\nH\\nFig. 162.\\nFig. 163.\\nis turned toward the observer. This permits the ether\\nwhirl to move with the ether flow. If the current flows\\nfrom right to left, as represented by the large straight arrow", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0282.jp2"}, "279": {"fulltext": "ELECTRIC CURRENTS\\n255\\nin the lower diagram, the needle will be deflected as there\\nrepresented.\\nThe galvanometer, for which we shall have much use in\\nfuture sections, is presented here as an illustration of\\nmagnetism in a helix, a b (Fig. 163) is a coil of wire about\\nsix inches in diameter. Suspended in the center of this\\ncoil or helix is a small magnetic needle. If the electric\\ncurrent is sent around the coil in the direction of the\\narrow, a magnetic field will be created, the south pole of\\nwhich is on the side of the helix toward the observer, and\\nthe magnetic needle will be deflected so that its north pole\\nwill point toward the observer.\\nThe telegraph-sounder is a simple device for making use\\nof the magnetic effect of the current. The diagram (Fig.\\n164) will make plain the principle of telegraphing.\\nLine\\nT\\na\\nEarth Connection Earth Connection\\nFig. 164.\u00e2\u0080\u0094 The telegraph.\\nSuppose the electric current to flow from the battery\\nthrough the apparatus at station X, and through the line wire\\nconnecting this with station Y, and through the apparatus\\nat Y and back from a! to a through the earth. The electro-\\nmagnets c and c will attract and hold down the springs e\\nand e If, now, an operator at either station wishes to\\nsignal to one at the other station, he may separate the\\nwires at b or b when the magnets will cease to attract and\\nthe springs e and e will fly up and click against the stops\\nat d and d When the operator brings together again the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0283.jp2"}, "280": {"fulltext": "256\\nPHYSICS\\nwires at b or V, the magnets will again pull down the\\nsprings e and e upon themselves with a click. These clicks\\nare made to represent letters, and thus the operators spell\\nout words. The earth connections are made by gas or water\\npipes, or by metal plates buried in moist earth. The ex-\\npense of a second wire is thus spared and also its resist-\\nance, since the earth offers practically no resistance. In\\nconsequence, the required battery power is reduced just\\none half. In reality, the earth does not act as a return\\nwire in completing the circuit, but simply serves to keep\\nthe earth terminals at the same potential. When this is\\nthe case, the effect on the circuit is the same as if the earth\\nterminals were in direct contact with each other.\\nThe telegraph wires are usually strung through the air\\non poles, and must be supported on glass or porcelain insu-\\nlators. In very large cities, however, there are ordinances\\nagainst overhead wires, and the city circuits must conse-\\nquently be underground.\\nIn this case the wires are insulated, usually with gutta-\\npercha, and are laid in pipes, opening at regular intervals\\ninto more sizable manholes. The air lines were formerly\\nb\\ne\\nC\\n1 Rnttpry\\nBattery\\nFig. 165.\u00e2\u0080\u0094 Single-stroke bell.\\nFig. 166.\u00e2\u0080\u0094 Clatter bell.\\nmade of galvanized iron wire, but modern installations,\\nboth in Europe and America, are increasingly making use\\nof copper wire, on account of its greater conductivity.\\nThe electric bell is a further application of the electro-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0284.jp2"}, "281": {"fulltext": "ELECTRIC CURRENTS\\n257\\nmagnet. In Fig. 165, suppose we close the circuit by\\nbringing the wires together at b. This may be what is\\ncalled a push button or a switch. The current will cause\\nthe electro-magnet to attract the spring e, which is fre-\\nquently called an armature. As it descends it will strike\\nthe bell d. This arrangement is called the single-stroke\\nbell. The clatter bell is arranged as shown in Fig. 166.\\nWhen b is closed the spring\\ne is drawn down by the mag-\\nnet, but the moment it leaves\\nthe stop at the current\\nceases to flow, the magnet\\nceases to act, and the spring e\\nflies upward against the stop\\nonly to be pulled away again.\\nThus it vibrates rapidly, and\\ncauses the bell d to clatter.\\nThe electric motor is another application of the electro-\\nmagnet. Fig. 167 shows how this electric current might\\nBattery\\nFig. 167. Electric motor.\\nFig\\nBattery\\n168. Electric motor.\\nbe used to make a wheel go around. This device is used\\nfor many purposes, and might be called a motor but Fig.\\n18", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0285.jp2"}, "282": {"fulltext": "258 PHYSICS\\n168 will explain in a very general way the principle usually\\nemployed in electric motors. Suppose an electric current\\npasses around the magnet a, so as to make its right-hand\\nend a north pole. Suppose, then, the current is led by the\\nspring to the semicircular plate of metal e, borne upon a\\nwooden disk, where it divides, half of it going about the\\ncoil c, so as to make it an electro-magnet with its upper\\nend a north pole, and the other half of the current going\\nabout the coil d, so as to make its lower end a south pole.\\nThe current then returns to the semicircular metal plate/,\\nand from that by the spring h to the coil b, the left-hand\\nend of which it makes a south pole. It is manifest that c\\nwill be repelled from a and attracted toward b, and that d\\nwill be repelled from b and attracted toward a. As c passes\\nby b the springs h and g will change to the opposite metal\\nplates e and This will reverse the current in c and d,\\nso that while the farther end of c is passing through the\\nFig. 169. Electric motor\\nlower half of its circular path it will be a south pole, and\\nwhile the farther end of d is passing through the upper\\nhalf of its circular path it will be a north pole. In other", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0286.jp2"}, "283": {"fulltext": "ELECTRIC CURRENTS 259\\nwords, the pole which is above will always be a north pole,\\nand that below will always be a south pole.\\nThe arrangement by which the current is reversed at e\\nand/ is called the commutator. These rotating magnets\\nbeing fixed to an axis may cause other wheels to revolve,\\nand thus set in motion a variety of machinery. The ac-\\ncompanying figure (169) is more nearly the form of motors\\nin use. It will appear again under the head of Dynamos.\\nIII. Electrical Measurements\\n253. The Problem of Measurement is easy only when one\\nhas very definite ideas about what is to be measured. In\\nthe case of the electric current there are several measur-\\nable aspects. We must begin with a very definite idea of\\nthese several aspects themselves.\\nThe thing we want to measure is manifestly motion, but\\nthe difficulty is that it is associated with something so alto-\\ngether intangible and beyond our experience, that we are\\nnot able to call it matter, much less lay hold of it and\\ndetermine its amount. Yet the best we can do is to con-\\nsider the current as electricity in motion, and we must get\\nsome quantitative hold on it in order to study it at all\\nscientifically. We must answer the question, How much\\nThe first thing that strikes us about electric motion is\\nthat it is quite independent of direction goes up or down,\\nright or left, north or south, wherever the conductor leads\\nit, and apparently with equal facility. Matter does not\\nbehave in this free way, because it has weight. We can\\nnot ascribe weight, therefore, to electricity. Yet the two\\nare alike in one respect. Matter falls to the earth, because,\\nfor it, that is the line of least resistance, and it is being\\nurged on by gravitation. However little we know about\\nelectricity, we must believe that these same general prin-\\nciples hold, that electricity follows its own line of least\\nresistance, and is urged on by some force quite as irresist-\\nible as gravitation.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0287.jp2"}, "284": {"fulltext": "260 PHYSICS\\nSo much happens in the neighborhood of an electric\\nconductor, that we are coming to believe that the real cur-\\nrent is outside the conductor, and that the conductor sim-\\nply determines the direction of the current, pierces the\\nether in some way, and opens up a line of least resistance\\nfor the current to follow. In the same way we account for\\nthe force driving the electricity by assuming different elec-\\ntrical levels, or potential, and ascribing the driving force to\\ndifference of potential, or E. M. F. This clearly is one\\nmeasurable aspect of electricity, and corresponds very closely\\nto difference of level in the action of gravitation as, for\\nexample, water pressure. A second measurable aspect is\\nthe resistance to the flow of the current. This may be\\ncompared to constrictions in the water pipe. The motor\\nman when he turns on more or less current in his car does\\nit by putting into the circuit less or more resistance, just\\nas one may do in the case of the flow of water from a pipe\\nopening more or less the stopcock at the faucet. A third\\nmeasurable aspect of the electric current is the quantity\\nthat will flow through a conductor in a given time. This\\nwe measure by the work which it will perform.\\n254. Ohm s Law. There are two ways of affecting the\\nquantity of water that may flow from a water pipe one is\\nto change the water pressure, the other is to change the\\nsize of opening in the faucet. Just so with the measure-\\nment of electric currents. Make the pressure or potential\\ntwice as great, and we make twice as much current flow\\nmake the resistance twice as great, and we reduce the flow\\nof current one half. Three times as much potential, three\\ntimes as much current three times as much resistance, one\\nthird as much current, etc. This is known as Ohm s Law,\\nwhich may be stated as follows The current varies directly\\nas the potential and inversely as the resistance. If we\\nrepresent current by C, potential or electro-motive force by\\nE, and resistance by 7\u00c2\u00a3, the formula which states this law\\nw\\nin brief form is, C\\nR", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0288.jp2"}, "285": {"fulltext": "ELECTRIC CURRENTS 261\\nAs was stated in section 242, the unit for electro-motive\\nforce is called a volt. (Named in honor of Alessandro Volta,\\n1745-1872, born at Como, Italy.) It is very nearly the\\namount of pressure which is exerted by a Daniell cell (246).\\nThe unit of resistance is called the ohm. (Earned in honor\\nof Georg Simon Ohm, 1781-1854, born at Erlangen, a town\\nof Bavaria.) It is about the resistance offered by 39 feet\\nof No. 24 copper wire. The unit of current is called an\\nampere. (Named in honor of Andre Marie Ampere, 1775-\\n1836, born at Lyons, France.) It is about that current\\nwhich a Daniell cell will send through 39 feet of No. 24\\ncopper wire. That is, it is the rate of flow which one volt\\ncan push through one ohm of resistance. (These units\\nappear in the formula of Ohm s law thus Amperes of\\nYolts of potential T\\ncurrent =7^ r It is measurable by its\\nOhms of resistance J\\nchemical effects, magnetic effects, or heating effects. Let\\nus take, for example, the chemical work which it may per-\\nform. Any current which will decompose water and liber-\\nate 0.036 grams of hydrogen in an hour is a one-ampere\\ncurrent. The ampere will deposit 1.18 grams of copper\\nfrom copper-sulphate solution in an hour. If the solution\\noffers ten ohms of resistance, it will require an electro-\\nmotive force of ten volts to maintain a one-ampere current.\\nIf the electro-motive force is five volts, while the resistance\\nis ten ohms, only a one-half-ampere current will flow, and it\\nwill require two hours for it to deposit 1.18 grams of the\\ncopper. If we have a ten-volt current and the resistance is\\nfive ohms, it will furnish a two-ampere current, and this\\nwill deposit 1.18 grams of copper in half an hour.\\nOr we may take the heating effects as a measure of the\\ncurrent. If an incandescent electric lamp offers a resist-\\nance of 220 ohms, a potential of 110 volts will send through\\nk x HO volts\\nit one halt an ampere 01 current 0.5 ampere j-\\nSuppose this heats the filament sufficiently to make it give", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0289.jp2"}, "286": {"fulltext": "262\\nPHYSICS\\na light equal to that of sixteen candles this we call a six-\\nteen-candle-power lamp. A thirty-two-candle-power lamp\\nwill require twice the amount of current, or one ampere,\\nand we may produce it in one of two ways First, we may\\nA W 4.1. 14- 1 220 VOltS A\\ndouble the voltage, 1 ampere r or we may reduce\\nthe resistance one half, 1 ampere j\u00e2\u0080\u0094^ r But in any\\ncase the heat and light will be proportional to the amount\\nof current which passes.\\n255. The Tangent Galvanometer. It is our custom, how-\\never, to measure the current by its magnetic effects. It\\nwill be remembered that the galvanome-\\nter, Fig. 170, creates a magnetic field when\\nthe electric current passes around it (page\\n255). We have a very simple means of\\nmeasuring the amount of magnetic force\\ndeveloped in this field, and the magnetic\\nforce is a measure of the amount of elec-\\ntric current which passes through the coil\\nof the galvanometer; the needle is de-\\nflected by the magnetic force of this helix through a cer-\\ntain angle, and it is found that the tangent of this angle\\nIn Fig. 171, let a e be a tangent to the circle\\na is called the tangent of the angle aob, ac,\\na d, and a e are respectively the tangents of the\\nangles a o c, a o d, and a o e. The length of these\\ntangents is given in terms of the radius of the\\ncircle. In the figure a b is equal to the radius\\nac, ad, and a e are respectively two, three, and\\nfour times as great as the radius. By referring\\nto the table of tangents, page 263. we may see\\nthat if the tangent of a o b is 1, the angle must\\nbe 45\u00c2\u00b0 the tangent of a o c being two, the angle\\nmust be about 64\u00c2\u00b0 likewise the angle a o d must\\nbe about 72\u00c2\u00b0, and ao e about 76\u00c2\u00b0. The law is that\\nif a certain amount of current will deflect the\\nneedle from o a to the direction of o b, it will re-\\nFig. 170.\u00e2\u0080\u0094 Tangent\\ngalvanometer.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0290.jp2"}, "287": {"fulltext": "ELECTRIC CURRENTS\\n263\\nTABLE OF TANGENTS.\\nDeg.\\nTan.\\nDeg.\\nTan.\\nDeg.\\nTan.\\n1\\n02\\n31\\n60\\n61\\n1.80\\n2\\n04\\n05\\n32\\n63\\n62\\n63\\n1.88\\n3\\n33\\n65\\n1.96\\n4\\n07\\n34\\n68\\n64\\n2.05\\n5\\n09\\n35\\n70\\n65\\n2.15\\n6\\n11\\n12\\n36\\n73\\n66\\n67\\n2.25\\n7\\n37\\n75\\n2.36\\n8\\n14\\n38\\n78\\n68\\n2.48\\n9\\n16\\n18\\n39\\n81\\n69\\n70\\n2.61\\n10\\n40\\n84\\n2.75\\n11\\n19\\n41\\n87\\n71\\n2.90\\n12\\n.21\\n42\\n90\\n72\\n3.08\\n13\\n23\\n43\\n93\\n73\\n3.27\\n14\\n25\\n44\\n45\\n46\\n97\\n1.00\\n1.03\\n74\\n75\\n3.49\\n15\\n27\\n29\\n3.73\\n16\\n76\\n4.01\\n17\\n31\\n47\\n1.07\\n77\\n4.33\\n18\\n33\\n48\\n1.11\\n78\\n4.71\\n19\\n34\\n49\\n1.15\\n79\\n5.15\\n20\\n36\\n50\\n1.19\\n80\\n5.67\\n21\\n38\\n51\\n1.24\\n81\\n6.31\\n22\\n40\\n52\\n1.28\\n82\\n7.12\\n23\\n42\\n45\\n53\\n1 33\\n83...\\n8.14\\n24\\n54\\n1.38\\n84\\n9.51\\n25\\n47\\n55\\n1.43\\n85\\n11.43\\n26\\n49\\n56\\n1.48\\n86\\n14.30\\n27\\n51\\n57\\n1.54\\n87\\n19.08\\n28\\n.53\\n58\\n58\\n59\\n60\\n1.60\\n1.66\\n1.73\\n88\\n28.64\\n29\\n89\\n57.29\\n30\\n90\\nInf.\\nvaries as the current. For example, suppose we introduce\\ninto a battery circuit a galvanometer and a cell contain-\\ning copper-sulphate solution (Fig. 172) suppose also we\\nfind that copper is being deposited at the rate of 1.18\\ngrams per hour, and that the needle of the galvanometer\\nis deflected to 83\u00c2\u00b0. As has already been said, the amount\\nof current which will deposit copper at that rate is called an\\nampere. Xow, it will be found that every time an ampere\\nof current is passed through this particular galvanometer\\nquire twice that current to deflect it to the direction of o c, and three\\ntimes that current to deflect it to the direction of o d, and four times\\nthat current to deflect it to the direction of o e.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0291.jp2"}, "288": {"fulltext": "264 PHYSICS\\nits needle will be deflected to 83\u00c2\u00b0. The tangent of 83\u00c2\u00b0 is\\n8.14 (see table, page 263). If now we send through this\\ncircuit such a current as will deposit copper at one half\\nthe above rate, we shall find that the needle of the galva-\\nCopper sulphate Galvanometer.\\nBattery\\nFig. 172.\\nnometer is deflected not to 41.5\u00c2\u00b0, which would be half the\\nangle, but to 76\u00c2\u00b0, whose tangent is about half that of 83\u00c2\u00b0.\\nA current which would deposit one quarter as much cop-\\nper would deflect the needle to 64\u00c2\u00b0, whose tangent is one\\nquarter that of 83\u00c2\u00b0, etc. Thus a galvanometer which has\\nbeen tested for some one known quantity of current may\\nbe very readily used, by aid of the table of tangents, to\\ndetermine any amount of current which passes through it.\\nA galvanometer used for measuring the quantity of cur-\\nrent, or the amperes, is frequently called an ammeter, but\\ngalvanometers may also be arranged for measuring the\\nelectro-motive force, in which case they are called volt-\\nmeters. Since it follows from Ohm s law that G and E\\ndepend directly upon each other, whatever measures one\\npractically measures the other also.\\nGalvanometers used for voltmeters are usually con-\\nstructed with a coil of very large resistance that is, the\\nwire is long and very fine. The resistance is sometimes\\nas much as several thousand ohms. The amount of cur-\\nrent flowing through such an instrument is proportional\\nto the E. M. F., and by observing the deflections produced\\nby known currents, we may either standardize the galva-\\nnometer by making the voltage directly on the graduated\\ncircle, or by preparing a reference table. As strong cur-\\nrents would destroy such a fine coil, only tiny currents are", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0292.jp2"}, "289": {"fulltext": "ELECTRIC CURRENTS 265\\never sent through it. This is managed by providing two\\npaths for the current (Fig. 173) one of low resistance, R,\\nwhich will carry the major\\npart, and the other of high\\nresistance, r that is, the gal-\\nvanometer to carry a very\\nminor part. But since R and\\nr are constant, the current FlG 173\\nthrough the galvanometer,\\nthough very small, will always bear a direct relation to\\nthe whole current, and serve to measure it.\\nIt is manifest that if we know any two of the quantities\\nE\\nin the formula, 0= we may calculate the third. It is\\nmanifest also that we must know the resistance through-\\nout the entire circuit that is, the internal resistance of\\nthe cell as well as the external resistance of the wires and\\ngalvanometer, and various pieces of apparatus used. We\\nfrequently designate the internal resistance by r and the\\nexternal resistance by R. In which case, of course, the\\nE\\nformula becomes C\\nr R\\n256. Resistance is a factor coming in at all times to re-\\nduce current strength. One method of measuring it is by\\nmeans of the AVheatstone bridge. This depends upon the\\nprinciple that no current will flow between two points at the\\nsame potential, and that in any given uniform conductor,\\nthe fall of potential is also uniform. Suppose A B, Fig.\\n174, to be a uniform conductor. In the first place, no cur-\\nrent will flow at all if A and B are at the same potential,\\nand a galvanometer introduced into such a circuit would\\nFig. 174.\\nshow no deflection. But if A is at higher potential than B,\\nthe fall of potential in passing from A to B will be uni-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0293.jp2"}, "290": {"fulltext": "%66 PHYSICS\\nform. If the difference is three volts, any point C mid-\\nway between A and B will differ from either by one and a\\nhalf volt.\\nThe Wheatstone bridge is a uniform wire stretched\\nbetween two fixed binding posts, and over a graduated scale\\nwhich is provided with a sliding contact, dividing the wire\\ninto two determined portions. The action can best be\\nunderstood by means of a diagram, Fig. 175. The current\\ncoming from the battery E divides at A into two portions,\\none taking the path AD B and the other the path A C B.\\nIf a galvanometer, G, is introduced between C and D, there\\nwill be no deflection if there is no current, and there will\\nE\\nFig. 175. Wheatstone bridge.\\nbe no current if C and D have the same potential. They\\nwill have the same potential if the resistance of A D bears\\nthe same relation to that of D B as the resistance of A\\nbears to that of GB, or when\\nAB:DB AG:GB.\\nIf we substitute for A D the resistance to be measured, i\u00c2\u00a3,\\nand for D B some known resistance, W, we shall evidently\\nbe able to find some position for G such that no current\\nwill pass through the galvanometer. When this is the case,\\nwe have\\nR W A G G B, or R X W.\\nResistance Coils. The known resistance W is usually\\nsupplied by means of a standard set of coils. They are", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0294.jp2"}, "291": {"fulltext": "ELECTRIC CURRENTS\\n267\\nmade of German silver, with their ends soldered to solid\\npieces of brass on the top of the box. When all the plugs\\nare in place, the current passes through the solid brass, and\\nmeets comparatively no resist-\\nance. When a plug is re-\\nmoved, the current must pass\\nthrough the wire beneath, and\\nFig. 176.\\nFig. 177.\\nso meet the corresponding resistance (Figs. 176, 177, and\\n178). A very common way to measure resistance is to\\nplace the battery, galvanometer, and object whose resistance\\nis to be found in circuit. Note the deflection of the gal-\\nvanometer needle, then put the standard resistance coils in\\nthe place of the object whose resistance is to be determined,\\nand throw into circuit enough resistance to bring the gal-\\nvanometer needle to the\\nsame point as before.\\nThe resistance, which\\nmay now be read from\\nthe standard coils, is the\\nresistance which was\\nsought.\\nEesistance increases\\nwith the length of the\\nconductor, and in the\\ncase of wires is greater\\nthe smaller the wire. Sil-\\nver, copper, and brass, being good conductors, offer the\\nleast resistance. In general the resistance increases with\\nFig. 178.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0295.jp2"}, "292": {"fulltext": "268\\nPHYSICS\\nthe temperature in the case of metals, but decreases in the\\ncase of carbon.\\nThe following list shows the resistance of certain metals\\ncompared with copper, the length, thickness, and temper-\\nature being the same for all\\nCopper 100\\nAluminium 246\\nZinc 446\\nPlatinum 630\\nIron 662\\nTin 738\\nGerman silver 1228\\nLead 1462\\n257. Arrangement of Battery Cells. If a battery consist\\nof n cells, and we connect them in series (247), we shall\\nhave\\nbecause the potential differences E and the\\ninternal resistances r are propor-\\ntional to the number of cells.\\nFigs. 179 and 180.\u00e2\u0080\u0094 Arrangement in series.\\nThe same battery joined in parallel (247) would give\\nE\\nC\\n(2)\\nR\\nsince we really form one giant cell, whose E. M. F. is the\\nsame as a single cell, but whose internal resistance is reduced\\nin proportion.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0296.jp2"}, "293": {"fulltext": "ELECTRIC CURRENTS 269\\nWe reduce this last formula to the expression\\n0=-^ (3)\\nr nR v\\nTo give this fraction the greatest possible value, and\\ntherefore make (7 a maximum current, we may either in-\\ncrease the numerator or diminish the denominator. Com-\\nFigs. 181 and 182.\u00e2\u0080\u0094 Arrangement in parallel.\\nparing (1) and (3) we see that they have the same numer-\\nator, n E. The whole question turns then upon the value\\nof the denominators. One is nr B, and the other\\nr-\\\\-nR. If r is less than B, we can better afford to mul-\\ntiply r by n, and so we choose the first arrangement in\\nseries. But if r is greater than B, we can better multiply\\ni?, and we choose the arrangement in parallel.\\n258. Divided Circuits. It often happens that a conductor\\ndivides and offers two paths to the current. This happens,\\nindeed, every time a battery is joined in parallel. The con-\\nductor divides into as many separate paths as there are\\ncells. In all such cases the current also divides and trav-\\nerses all the paths offered. If they have equal resistance,\\neach path gets the same amount of current, but if they\\nhave unequal resistance, each path gets an amount inversely\\nproportional to its resistance.\\nThe inverse of resistance, is conductance. The total\\nr\\nconductance of the system must evidently be the sum of\\nthe separate conductances.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0297.jp2"}, "294": {"fulltext": "270\\nPHYSICS\\nThe circuit branching off from a main circuit is called\\na shunt.\\nIf a current divides into two or more paths, it may be\\nshown that the sum of the separate currents equals the\\nmain current. If, for example, in Fig. 183, the current C\\nCuSo.\\nFig. 183.\\nCuSo+\\nDivided circuit.\\nis divided into two currents, c and c and copper-sulphate\\ncells be introduced into the main circuit and into each of\\nthe branches, the weight of copper deposited by C will just\\nequal the sum of the weight deposited by c x and c 2 The\\nsame result would have been shown by galvanometers, or\\nany other form of ammeter or voltmeter.\\nIV. INDUCTION\\n259. Methods of Induction. Induction is applied in elec-\\ntricity, as well as in magnetism, to cover all action at a\\ndistance. But this means, in reality, all action confined to\\nthe surrounding medium, to the ether. Induction were\\nbetter defined, therefore, as action between bodies without\\ncontact, and solely through the mechanism of the ether.\\nDefined in this broad way, induction covers all ether stress\\nmagnetic, electric, or gravitational.\\nOne can not move through an ordinary apartment with-\\nout more or less disturbing every particle of air in the\\napartment. The more rapid the movement, the greater\\nthe disturbance. A circuit of copper wire is equally sensi-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0298.jp2"}, "295": {"fulltext": "ELECTRIC CURRENTS\\n271\\ntive to changes in the snrronnding field. No matter\\nhow brought about, the conductor responds to every change,\\nand the induced current, like the air disturbed, is propor-\\ntional to the rapidity of the change.\\nThese changes in the electric field may be brought\\nabout by the motion of a magnet by a field of varying\\nstrength by the movement of a conductor through which\\na variable current is flowing by the motion of the con-\\nductor itself in which the current is to be induced or,\\nfinally, by any combination of these five variables. They\\ncan best be studied experimentally.\\n260. Induction by a Magnet. If we take a coil of wire\\nwrapped on a hollow spool, and connect the ends of the\\ncoil with a sensitive galvanometer, no current flows so long\\nas the surrounding field remains the same. If, however, a\\nFig. 184.\u00e2\u0080\u0094 Current induced by magnet.\\nbar magnet be thrust into the center of the coil, the galva-\\nnometer will show an immediate deflection. The magnet\\nhas no power except when in motion, for if allowed to\\nremain quietly inside the coil the galvanometer needle comes\\nto rest again and indicates no current. When the magnet", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0299.jp2"}, "296": {"fulltext": "272 PHYSICS\\nis withdrawn, the needle swings in the opposite direction,\\nshowing a second induced current. We find that the more\\nrapid the motion of the magnet, the greater the deflection\\nof the needle.\\nInstead of moving the magnet bodily, we may alter its\\nintensity, and so produce the same series of induced cur-\\nrents. This is conveniently done by introducing an elec-\\ntro-magnet into the center of the coil. On making or\\nbreaking the current we get induced currents in opposite\\ndirections, surging through the coil and galvanometer but\\nso long as a uniform current circulates through the electro-\\nmagnet, the field remains constant and no induced current\\npasses through the galvanometer.\\n-We might combine these conditions and have a movable\\nmagnet of variable strength. Or we might make the con-\\nductor itself approach or recede from a fixed magnet,\\neither constant or variable, and so induce a current in the\\nconductor.\\nWhatever combination we use, the induced current de-\\npends upon the amount and rate of change in the magnetic\\nfield. Practically the current depends upon the number of\\nlines of magnetic force cut in one second. Hence the mag-\\nnet may move or the conductor may move, or both may move\\nor both may remain fixed bodily, and the lines themselves\\nmay move. The relative motion is the essential thing, and\\nthe greater the motion the stronger the induced current.\\n261. Induction by Varying Currents. Since all currents\\nare surrounded by magnetic whirls, we may substitute a\\ncurrent for the magnet in any or all of the above experi-\\nments.\\nEemoving the iron core from the electro-magnet, the\\ncorresponding coil which for convenience may be distin-\\nguished as the primary coil may be thrust into the sec-\\nondary coil and withdrawn, producing induced currents in\\nopposite directions, just as in the case of the magnet (Fig.\\n185). If the primary coil remains within the secondary", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0300.jp2"}, "297": {"fulltext": "ELECTRIC CURRENTS\\n273\\ncoil, and the primary current be made and broken, we shall\\nhave corresponding induced currents in the secondary coil.\\nSimilarly, if the primary coil remain fixed and the current\\nconstant, induced currents may be produced by the motion\\nFig. 185. Currents induced by varying currents.\\nof the secondary coil. Furthermore, the parallelism be-\\ntween induction by currents and induction by magnets is\\ncompleted by the fact that here again the strength of the\\ninduced current depends upon the amount and rate of\\nchange in the primary field.\\n262. Direction of Induced Currents. The currents in the\\nsecondary coil vary in direction according to the conditions\\nunder which they are produced. We distinguish them as\\ndirect and inverse currents. Those are direct which so\\nflow that they would give to the magnet, were it a core of\\nsoft iron, a magnetism of the same polarity that it now\\npossesses. Those currents are inverse which flow in an\\nopposite direction. When the field is increasing in strength,\\nthe induced currents are all inverse. When the field is\\ndiminishing, the induced currents are direct.\\n263. Strength of Induced Currents. Just as the direc-\\ntion of the induced current depends upon the conditions\\nunder which they have been generated, so, then, strength\\n19", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0301.jp2"}, "298": {"fulltext": "274\\nPHYSICS\\ndepends upon the conditions. In a circuit of given resist-\\nance, the strength of the induced current depends solely\\non the electro-motive force, and this in turn depends solely\\nupon the number of lines of magnetic force cut in one sec-\\nond. The voltage of an induced current is therefore in-\\ncreased (1) by increasing the magnetic field that is, the\\nnumber of lines (2) by increasing the rate at which these\\nlines are cut\u00e2\u0080\u0094 that is, the speed and (3) by increasing\\nthe length of the conductor\u00e2\u0080\u0094 that is, the number of turns\\nof wire.\\n264. The Induction Coil is a simple and effective device\\nfor producing induced currents of very high electro-motive\\nforce, by increasing the number of turns of wire in the sec-\\nondary circuit. It consists of a central primary coil of\\nshort thick wire with a soft iron core, surrounded by a\\nsecondary coil of long, fine wire (Fig. 186). The primary\\nFig. 186. Induction coil.\\ncircuit contains a current-interrupter, for rapidly mak-\\ning and breaking the current, and so inducing a rapid\\nsuccession of inverse and direct currents. It acts upon\\nthe same principle as the interrupter used with the elec-\\ntric bell. (See Fig. 166,/.) The coil is generally mounted\\non a hollow wooden base, which contains a condenser\\nmade of alternate layers of tin foil and paper saturated\\nwith paraffin, and connected with the primary circuit.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0302.jp2"}, "299": {"fulltext": "ELECTRIC CURRENTS 275\\nThe action of the condenser is to dispose of the currents\\nwhich are self-induced in the primary coil on breaking the\\ncurrent (see next paragraph), and so avoid the spark at the\\ninterrupter. The object of having the primary coil made\\nof stout, short wire is to reduce resistance and so increase\\nthe quantity of the primary current. The secondary coil\\nis made tremendously long. In the case of Mr. Spottis-\\nwoode s famous coil, it is 280 miles long, and gave a spark\\n-42 cm. long. The very large voltage of the induced cur-\\nrent enables it to overcome the great resistance of the air,\\nand so give us these flashes of miniature lightning.\\nWhen provided with a condenser the induction coil is\\nknown as Ruhmkorff s coil.\\n265. Spark Coil and Electric Gas Lighting. When a\\ncurrent passes through a single coil of wire we have mani-\\nfestly a series of parallel circuits made by the successive\\nturns of the wire, and all the phenomena of induced currents\\ntake place in and about the single wire whenever the cur-\\nrent itself is made or broken. On making the current, the\\ninduced current is inverse, and consequently the only effect\\nis to retard the establishment of maximum current in the\\ncircuit. But, on breaking the current, the induced current\\nis direct and has the effect of prolonging the flow. While\\nthis extra current, as it is called, is most noticeable in\\nthe case of circuits containing coils, it is a self-induction,\\nwhich shows itself in all circuits, and produces the spark\\nwhenever the current is broken. This principle provided\\nagainst by the condenser in the Ruhmkorff coil is made\\nserviceable in the spark coil, used in electric gas lighting.\\nThe core is made of a bundle of iron wires, and the coil, in\\nthis case single, consists of many turns of moderately thick\\nwire. The introduction of such a coil into a circuit provides\\na good strong spark, which conveniently takes the place of\\na match, at any point where the circuit may be alternately\\nmade and broken. The spark which appears in a clatter\\nbell (Fig. 187) at the point/ where the current is alternately", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0303.jp2"}, "300": {"fulltext": "276\\nPHYSICS\\nmade and broken is due to the induced current. The spark\\nis evidence that the induced current has high voltage.\\nThis spark will light the gas.\\nIf one touches the conductor\\non both sides of this point,\\nthus making it possible for\\nthis induced current to pass\\nthrough his body rather than\\nthe air, he will feel a slight\\nshock, particularly if he\\nmoistens his hands and uses\\nmetal handles to make better\\ncontact. The dry outer skin\\nbeing a poor conductor, the tongue or inner surface of the\\nmouth may be used to furnish a place for contact.\\n266. The Telephone.\u00e2\u0080\u0094 Fig. 188 will serve to illustrate\\nthe essential features of the telephone. The transmitter,\\nI 7 is a box filled with granules of carbon, into which the\\nbattery wires enter. P is the primary circuit of an induc-\\ntion coil. Tapping upon the box, T, or speaking into its\\ncauses the battery current to vary in strength. These\\nvariations in the primary circuit cause a secondary current\\nof high intensity to surge to and flow through the secondary\\ncoils, S and 8\\\\ and around the permanent steel magnets,\\nFig. 188.\u00e2\u0080\u0094 The telephone.\\nm and m When these induced currents go in one direc-\\ntion they strengthen the magnet, and when they go in the\\nopposite direction they weaken the power of the magnet.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0304.jp2"}, "301": {"fulltext": "ELECTRIC CURRENTS 277\\nThis causes the disks of soft iron, R and R to vibrate\\nexactly as they would if one spoke directly against them,\\nand, strange to say, if one of these receivers, R or R\\\\ is held\\nnear to a person s ear, this vibration will reproduce the\\nsounds which are made by a voice speaking into the box of\\nthe transmitter, T or T\\n267. Transformers. If the electric current is to be con-\\nducted far, as, for example, to light dwellings several miles\\naway from the central station where the electricity is pro-\\nduced, it must have high voltage to push its way through\\nthe long conductors. The voltage will probably need to be\\nso high as to be a deadly current. Before receiving this\\ninto our houses, we would prefer to have its voltage reduced.\\nThis is done by transformers which are simply induction\\ncoils. What we lose in voltage in this way we gain in\\nquantity, as might be expected from what we know of the\\nconservation of energy. Transformers of the induction\\ncoil type require alternating currents. They consist of an\\niron core, a primary coil, and a secondary coil. The ratio\\nof the electro-motive force in the primary coil to that in\\nthe secondary coil is known as the ratio of transformation.\\nThis may be either up or down that is, the voltage may\\nbe either raised or lowered. As this depends upon the\\nnumber of turns of wire in the two coils, the ratio of trans-\\nformation is practically the ratio of the number of turns of\\nwire in the primary coil to the number of turns in the sec-\\nondary coil. If, for example, an external circuit has a pres-\\nsure of 3,000 volts, and we wish a house current for incan-\\ndescent lamps under a pressure of but 100 volts, the ratio\\nwill clearly be 30 and the coils will be wound accordingly.\\nIn a closely peopled district the transformer may be at the\\nentrance to the town, while in a more scattered district the\\ntransformer may be in each house.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0305.jp2"}, "302": {"fulltext": "278\\nPHYSICS\\nV. Electric Currents by Mechanical Means\\n268. The Magneto-Electric Machine. Faraday followed\\nup his discovery of current induction in 1831 by the inven-\\ntion of a magneto-electric machine. It consisted of a cop-\\nper disk mounted to rotate between the poles of a per-\\nmanent horseshoe magnet. The current generated in the\\ndisk was collected by strips of copper pressing respectively\\nagainst the axle and the circum-\\nference of the disk. This little\\nmachine is the honorable ancestor\\nof all the company of machines,\\ngreat and small, magnetos and dy-\\nnamos, that have since been invent-\\ned for the purpose of turning me-\\nchanical motion into electric energy.\\nIt is the simplest combination pos-\\nsible of the two essential elements,\\na magnetic field and a movable con-\\nductor.\\nLater machines substitute a coil\\nof wire, an armature for the disk.\\nA simple form of this is presented in\\nFig. 189. It is manifest that the\\ncurrent is produced in this machine\\nby causing a helix of wire to alter-\\n-Magneto-eiectric na t e l y approach and recede from a\\nmachine. J rr\\nsteel magnet. The current thus\\ninduced has high potential. It is used by physicians in\\ntreating patients by electricity. Its more common use is\\nfor telephone calls.\\n269. The Dynamo. It was early realized that no field\\nmagnet, of steel could be so powerful as an electro-magnet.\\nIn the dynamo this field electro-magnet is energized by\\nmeans of the current generated by the machine itself.\\nThis is possible by reason of the residual magnetism which\\nFig. 189.-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0306.jp2"}, "303": {"fulltext": "ELECTRIC CURRENTS\\n279\\nis found to inhere in the iron core of the field magnet.\\nThe field thus produced is very weak, but it is not without\\neffect. When the armature rotates in this field, very feeble\\ncurrents are set up. These pass into the external circuit\\nand through the coils of the electro-magnets, thus strength-\\nGalvanometer\\nFig. 190.\u00e2\u0080\u0094 The dynamo.\\nening the magnetic field, which in turn induces stronger\\ncurrents in the armature. By this cumulative process the\\nfield soon mounts to its maximum strength, and the\\nmachine generates a powerful current.\\nThe principle of the dynamo may be illustrated by Fig.\\n190, which will be recognized as very closely resembling\\nFig. 168, used to illustrate an electric motor. A galva-\\nnometer has been substituted for the battery, to indicate\\nthe current which this will produce. The electro-magnets\\na and b are the field magnets, and the electro-magnets c\\nand d are the armatures. The iron cores of these electro-\\nmagnets are never entirely without magnetism, hence if we\\ncause c and d to rotate, when they approach b and a they\\nwill induce reverse currents in the wires which encircle\\nthese cores, and when they recede from b and a they will\\ninduce direct currents in these wires. This would result in", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0307.jp2"}, "304": {"fulltext": "280\\nPHYSICS\\nan alternating current if it were not for the commutator\\n(see pp. 259 and 281).\\nAll dynamos consist essentially of three elements\\n1. The magnetic field.\\n2. The armature.\\n3. The collecting apparatus.\\na. Commutator in the direct-current machines.\\nb. Collecting brushes in the alternating-current ma-\\nchines.\\nThe Magnetic Field. The smaller dynamos have a\\nsimple field produced by two pole pieces of opposite polar-\\nity, facing each other. Each pole piece is hollowed out\\ninto a semi-cylinder, and as the two pieces almost touch\\neach other, the armature rotates in a nearly closed cylinder\\nof highly magnetized iron (Fig. 191).\\nFig. 191.\u00e2\u0080\u0094 The dynamo.\\nThe powerful modern dynamos are frequently multi-\\npolar, having four, six, or even eight pole pieces.\\nThe armature in all modern machines is made up of\\nmany circuits. The single-coil armature can not give a", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0308.jp2"}, "305": {"fulltext": "ELECTRIC CURRENTS 281\\nsteady current, because at each reversal of current that is,\\ntwice every rotation the current must be reduced to zero,\\nand consequently the current in the external circuit is in\\nreality a series of momentary currents, all in the same\\ndirection but not continuous. By having several separate\\ncircuits moving in different parts of the field, we shall\\nalways have one or more of them current-producing, and\\nconsequently in the external circuit, though the current\\nis still subject to pulsations, it never entirely dies away.\\nIt is also possible to cut out the separate circuits when\\nthey are not active, and so reduce the resistance of the\\narmature.\\nThe Collecting Apparatus The Commutator. When\\nthe current desired must be direct, the collecting brushes\\nhave the added function of changing the alternate currents\\ninto a direct and continuous one. The simple commutator\\nhas already been described in connection with the electric\\nmotor (page 259).\\nBy referring to Fig. 190, we may see how these brushes\\nserve to change an alternating current into a direct one.\\nSuppose c and d to be approaching o and a respectively.\\nCurrents will be induced in the wire encircling these cores\\nwhich will take the direction of the arrows that is, a cur-\\nrent will be induced which will pass around c from f to e\\nand around d from f to e. These currents will combine\\nand pass out by the spring or brush, g, around the core\\na so as to intensify its magnetism, through the galvanom-\\neter, whose needle it will deflect, showing at the same time\\nthe direction and the strength of the current, then around\\nb so as to increase its magnetism, and finally back to by\\nthe spring or brush, h. When c and d pass b and a and\\nbegin to recede from them, the current which encircles\\nthem will be induced in the opposite direction, but at the\\nsame instant the brushes shift to the opposite plates, e com-\\ning under h and /coming under g. So that the moment\\nthe magnets c and d require the current to pass from e to/,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0309.jp2"}, "306": {"fulltext": "282 PHYSICS\\ne comes in contact with li and with g, and thns the current\\ncontinues to flow from h to g as before. Of course, it is\\nunderstood that e and are semicircles of metal upon a\\nwooden disk, so that the only way the current may pass\\nfrom to e is through the wires which encircle the cores\\nc and d.\\nIn the case of alternate-current machines, the brushes\\nhave only to collect the current and send it over the main\\ncircuit. Alternators are very much used in electric light-\\ning. The current surges back and forth so rapidly through\\nthe lamp as to produce a steady light. They have the\\nadvantage of requiring no commutator. The Westinghouse\\nmachine is the one best known in America.\\nThe total output of electric energy in any machine is\\nequal to the product of C and E or C E Watts, and this\\ndivided by 746 will give the equivalence in horse power.\\nThe mechanical efficiency is the ratio of the total output\\nof energy to the energy put into the dynamo in the form\\nof mechanical work. It must be remembered that we never\\nget out of any machine as much as we put into it. We use\\na steam engine or water power to cause the dynamos to go\\na 60-horse-power steam engine can not produce electrical\\nenergy through the dynamos which will do the work of 60\\nhorse power. Electricity is not to be regarded as a source\\nof power. It can not be called a rival of steam, since we\\nare dependent upon steam to produce it. Its use is to\\ntransmit the power of the steam engine, and hence, if it is\\nthe rival of anything, it is the rival of the engine belt. A\\nshort time ago most of the street cars in New York city\\nwere cable cars that is, they ran by grappling a cable, or\\nhuge engine belt, which ran from a central steam engine\\nfor many miles in a conduit under the street. This cable\\nwas not the source of power it only transmitted the\\npower. But more recently electricity has been adopted as\\na successful rival to this cable as a means of transmitting\\nthe power of the central steam engine. The engine is still", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0310.jp2"}, "307": {"fulltext": "ELECTRIC CURRENTS 283\\nthe power which moves the cars, but instead of pulling\\nthem along now by means of a very long cable passing\\naround the driving wheel of the engine and for miles under\\nthe street, the engine now operates dynamos, and the dyna-\\nmos send the current through conductors running in con-\\nduits under the street where the cable used to run. The\\ncars receive the electric current from these conductors\\nthrough motors underneath each car, which are geared to\\nthe car axle. Whenever the motorman turns the electric\\ncurrent upon a car to make it go, it throws a load upon the\\ncentral steam engine just as much as the cable did and\\nwhen the electric car goes up hill it throws an extra load\\nupon the engine, just as the cable did and when the elec-\\ntric lights or the electric radiators in the cars are turned\\non, the central engine does a definite additional amount of\\nwork, which requires a definite additional amount of coal\\nto be burned just as truly as though the cars were heated\\nby steam or lighted by coal gas. If the dynamo current is\\nused to ring an electric bell, or decompose water, or do\\nwork of any kind, the dynamo goes harder and the steam\\nengine goes harder. More steam must be produced and\\nmore coal burned to just the extent of the work per-\\nformed.\\nElectricity is the most convenient method of transmit-\\nting power. It will go over hill, through dale, up and down,\\nright and left, and may be tapped wherever you will. It\\nhas now become the most economical method as well. The\\nmore carefully the current is studied, the more wisely are\\nwe able to make use of it. In any circuit the loss of energy\\nappears as heat. By sending currents of excessively high\\nvoltage, as much as 10,000 volts or more, with current\\nstrength of only a few amperes, this loss is made compara-\\ntively trifling. When the current has reached the place\\nwhere it is to be used, its character may be changed, as\\ndesired, from alternating to direct, and from high voltage\\nto low voltage, with proportionally increased quantity.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0311.jp2"}, "308": {"fulltext": "284 PHYSICS\\nAs time passes, the water powers of the country are\\nbeing increasingly harnessed to the work of current genera-\\ntion, and the current is being transmitted over long dis-\\ntances. At the Frankford Electrical Exhibition a current\\nof 140 horse power was brought 117 miles from the Falls of\\nthe Necker with a loss of only 26 per cent. It is also quite\\npossible that we may speedily find it more economical to\\nburn our coal at the mines themselves, and send the energy\\nto town over copper wires instead of in railroad cars.\\nThe usefulness of the current depends very largely upon\\nthe fact that it may readily be transformed into mechan-\\nical motion again by means of the electric motor. In the\\ndynamo we put in mechanical energy and get out electric\\ncurrent in the motor we put in current and get out me-\\nchanical motion. Dynamo and motor are thus the converse\\nof each other. They are, indeed, entirely interchangeable.\\nA dynamo fed with current becomes a motor a motor fed\\nwith mechanical motion becomes a dynamo.\\nVI. Electkic Currents produced by Heat\\n270. Thermo-electric Currents. When the junction of\\ntwo dissimilar metals, such as antimony and bismuth, is\\nheated and their colder ends are connected by a copper\\nwire, a current is found to flow in the wire from the anti-\\nmony to the bismuth. When several such pairs are united\\nr 1 1 1 i 1 1 r. i i-\\nFigs. 192 and 193.\\nin series, and the alternate junctions heated, the resulting\\nthermo-electric current is proportional to the number of\\npairs (Figs. 192 and 193).", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0312.jp2"}, "309": {"fulltext": "ELECTRIC CURRENTS 285\\n271. The Thermopile is a compact bundle of such anti-\\nmony-bismuth pairs, sometimes as many as thirty-six, and\\nwhen connected with a sensitive galvanometer forms a\\nwonderfully delicate means of detecting and measuring the\\nslightest differences of temperature. It is with this instru-\\nment that we explore the spectrum and measure the com-\\nparative temperature of the various rays. Thermopiles are\\nnow manufactured and sold, which are a very practical\\nmeans of furnishing electric currents for laboratory and\\nlecture-room work.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0313.jp2"}, "310": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0314.jp2"}, "311": {"fulltext": "LIGHT\\nCHAPTER XXVI. Rays of Light in Straight Lines\\n272. What is Light?\\n273. How the Velocity of Light was determined. Fig. 194.\\n274. Some Results of the Fact that it takes Light Time to Travel.\\n275. The Sources of Light.\\n276. Photometry Law of Inverse Squares. Figs. 195 and 196.\\n277. The Relative Illumination of a Page of Reading Matter when\\nheld near to or far from the Source of Light.\\n278. Relation between Temperature and Intensity of Light.\\n279. The Visual Angle. How we use it for estimating Distances.\\n280. Shadows. Figs. 197 and 198.\\n281. The Moon s Shadow. Eclipses of Sun and Moon. Figs. 199, 200,\\nand 201.\\n282. Light through Small Apertures. Fig. 202.\\nCHAPTER XXVII.\u00e2\u0080\u0094 Reflection of Light\\n283. Laws of Reflection. Fig. 203.\\n284. Images in Plain Mirrors. Figs. 204 and 205.\\n285. Concave Mirrors. Principal Focus and Conjugate Foci. Figs.\\n206 and 207.\\n286. Enlarged Images formed in Concave Mirrors. Fig. 208.\\n287. How an Inverted Image is formed in a Concave Mirror. Fig. 209.\\n288. Diminished Images formed in a Convex Mirror. Fig. 210.\\n289. A Silver Spoon as a Concave and a Convex Mirror.\\n290. A Curved Image from a Straight Object.\\nCHAPTER XXVIII. Miscellaneous Observations on Reflection\\n291. How Daylight is diffused.\\n292. Halos about Street Lights and the Circle around the Moon.\\n293. The Sun drawing Water.\\n294. Illumination of Clouds at Sunset.\\n295. Moonlight and the Phases of the Moon. Fig. 211.\\n296. How the Dark Part of the New Moon is made Visible.\\n297. Why are Transparent Objects and very good Reflectors so nearly\\nInvisible Themselves f Figs. 212 and 213.\\n287", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0315.jp2"}, "312": {"fulltext": "288 PHYSICS\\n298. Visibility of Print upon Glazed and Unglazed Paper; Drawings\\nupon Rough and upon Highly Polished Surfaces.\\n299. Twilight. Fig. 214.\\nCHAPTER XXIX.\u00e2\u0080\u0094 Refraction of Light\\n300. Refraction of Light denned and illustrated. Fig. 215.\\n301. Index of Refraction.\\n302. Cause of Refraction. Fig. 216.\\n303. Value of the Index.\\n304. The Critical Angle. Fig. 217.\\n305. Total Reflection.\\n306. Applications. Figs. 218, 219, 220, and 221.\\n307. Refractions in Prisms. Fig. 222.\\n308. Enlarged Images produced by Refraction. Fig. 223.\\n309. Different Kinds of Lenses and the way they refract Light. Fig.\\n224.\\n310. Inverted Images produced by Refraction. Fig. 225.\\n311. The Path of Rays of Light exhibited by Crayon Dust. Measuring\\nthe Focal Distance of a Lens. Fig. 226.\\n312. Pictures formed at the Focus of a Lens.\\n313. How a Lens forms a Picture. Fig. 227.\\n314. Material of Lenses.\\n315. Familiar Illustrations of Lenses.\\n316. The Simple Microscope. Fig. 228.\\n317. Compound Microscope. Fig. 229.\\n318. The Telescope.\\n319. The Human Eye. Figs. 230, 231, and 232.\\n320. The Spectrum. Figs. 233, 234, and 235.\\n321. The Invisible Spectrum.\\n322. Complimentary Colors. Fig. 236.\\n323. Fluorescence and Phosphorescence.\\n324. Temperature and Color.\\n325. Rontgen Rays. Figs. 237 and 238.\\n326. Hertz Rays.\\nCHAPTER XXX.\u00e2\u0080\u0094 Polarization of Light\\n327. Transverse Vibrations. Fig. 239.\\n328. Polarization of Light. Figs. 240 and 241.\\n329. Applications of Polarized Light.\\n330. Rotation of the Plane of Polarization.\\n331. The Identitv of the Various Forms of Radiation.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0316.jp2"}, "313": {"fulltext": "CHAPTER XXVI*\\nRAYS OF LIGHT IN STRAIGHT LINES\\n272. What is Light We know that sunlight tans the\\nskin and fades the colors in our clothes, while at the same\\ntime it causes the brilliant colors of the flowers. It makes\\nthe green color in plants, for potatoes sprout and grow\\nwhite vines in a dark cellar, but green ones in the open\\nsunlight. It assists the healthy growth of most plants\\nand animals, but hinders the growth of molds and many\\nobnoxious germs. Milk pans, butter pots, bread jars, bed-\\nding, etc., are put out to sun in order that they may\\nbecome sweet. Sunlight is the most efficient disinfect-\\nant for our apartments. Yet, what is this light? We\\nspeak of its coming from an object and going to an object,\\nand we know that it requires about eight minutes for light\\nto travel from the sun to the earth, about forty minutes\\nfor it to come from the planet Jupiter, about four hours\\nfor it to come from the planet Neptune, and about forty\\nyears for.it to come from the North Star. Thus the\\nvelocity of light is 186,000 miles per second. This is also\\nthe velocity of electricity and of heat radiation. What- do\\nwe mean when we speak of light streaming into a room\\nIs it a substance Has it weight Can it fill a space and\\nexclude other things from the same space We naturally\\nthink of light as closely connected with heat. We are\\nConsiderable portions of these chapters on Light have been taken\\nfrom WoodhulPs First Course in Science, with the permission of the\\npublishers, Messrs. Henry Holt Co., New York.\\n20 289", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0317.jp2"}, "314": {"fulltext": "290 PHYSICS\\nfamiliar with the heating of substances until they give out\\nlight, first dull red, and afterward brilliant white light.\\nWe naturally think of both light and heat as being the\\nessential characteristics of the sun s rays. In succeeding\\npages we shall learn how to concentrate the sun s rays by\\nmeans of concave mirrors or convex lenses, so as to set fire\\nto wood or paper. We shall also learn how, by means of\\nprisms, to separate the light rays from the heat rays.\\nThey may be separated also by filtration or absorption, as\\nhas already been stated in sections 202 and 203. From\\nthis we may learn that while heat rays and light rays are\\nvery closely associated, they are not the same. Our pres-\\nent conception is that light rays, heat rays, and electric\\ncurrents are all forms of ether vibrations, differing only in\\nwave lengths. Those which are capable of exciting the\\noptic nerve we call light rays they have the shortest wave\\nlengths. Those which excite the nerves of temperature\\nsensation we call heat rays they have medium wave\\nlengths. Those which produce electric phenomena we call\\nelectric waves they are the longest of the three kinds\\nmentioned here. These waves may readily be transformed,\\nthe one into the other, and all may set up those molecular\\nmotions in matter which we call heat. The distinction\\nbetween these various kinds of ether vibrations will be\\nmade more clear in section 331.\\n273. How the Velocity of Light was determined.\u00e2\u0080\u0094 It was\\nnoticed by a Danish astronomer, Olaf Eoemer, in 1675, that\\nthe observed and computed times of the eclipse of Jupiter s\\nsatellites differed by an amount too great and too constant\\nto be assigned to observational error. The eclipse of a\\nsatellite occurs, as we all know, when it passes into the\\nshadow of its planet, and the precise time and duration of\\nan eclipse may therefore be calculated with great accuracy.\\nEoemer noticed that when the eclipse was seen while the\\nearth (Fig. 194, A) and Jupiter were on the same side of\\nthe sun as the astronomers say, in conjunction the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0318.jp2"}, "315": {"fulltext": "RAYS OF LIGHT IN STRAIGHT LINES\\n291\\ntime was 1(3 36 earlier than when the earth (Fig. 194, B)\\nand Jupiter were on opposite sides of the sun that is, in\\nopposition. In the latter case it is very plain that the light\\nreflected from the satellite has to\\ntravel farther through space by just\\nthe diameter of the earth s orbit\\nabout 184,000,000 miles. Dividing\\nthe distance by the time in seconds,\\nwe have a speed of about 186,000\\nmiles per second. Several more re-\\nfined methods of determining the\\nvelocity of light have been employed,\\nbut all give about the same result.\\n274. Some Results of the Fact that\\nit takes Light Time to travel. As a\\nresult of the appreciable time re-\\nquired by light to pass over space, we\\nsee the celestial universe never as it\\nis, but always as it ivas. Even the\\nmoon, our nearest neighbor in space,\\nis over a second behindhand in all\\nher reports, and the* sun is 8 18 be-\\nhind time. He is mathematically\\nabove our horizon by that amount of\\ntime before we see him at all, and he\\nremains visible to us for the same\\nlength of time after he has really\\npassed below the western horizon.\\nXow in eight minutes of time the\\nearth will cover an angle of 2\u00c2\u00b0 in\\nrotation. But the sun, as seen from\\nthe earth, only covers an angle of\\nabout half a degree. Consequently\\nthe sun is really four times his own\\ndiameter above the horizon before we know that he is up\\nat all. (These calculations neglect refraction, Chapter\\nFig. 194.\u00e2\u0080\u0094 The velocity\\nof light.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0319.jp2"}, "316": {"fulltext": "292 PHYSICS\\nXXIX, section 306.) The reports from the distant planets\\nare correspondingly retarded, but the delay is the most\\nnoticeable in the case of the fixed stars. The nearest one,\\na Oentauri, is so far off that it takes about three and a\\nhalf years for its light to reach us. Sirius, the brightest\\nstar in our heavens, requires 16.7 years to send its light\\nto us Arcturus 25.4 years Polaris, the North Star, 42.4\\nyears and o- Draconis 129.1 years that is, if the last-men-\\ntioned star should cease to send forth light to-day, it would\\nbe 129.1 years before its last light wave would reach us,\\nalthough during each second in all that time it would have\\ntraveled toward us at the inconceivable speed of 186,000\\nmiles.\\n275. The Sources of Light are practically the same as the\\nsources of heat the sun, chemical energy, mechanical power,\\nand electricity. These agents all have the power of setting\\nup ether vibrations of such rapidity that they are sensible to\\nus as light. The one principle in all our artificial lights is\\nthe heating of matter to incandescence that is, to such a\\ntemperature as will set the ether into vibration within the\\nprescribed limits of light. In the case of candle, kerosene\\nlamp, or gas flame, by far the largest product of the chem-\\nical action is heat. This heat raises a small portion of\\nthe more refractory particles of carbon to incandescence,\\nand these are responsible for all the light. This is well\\nillustrated by holding a small wire in the flame of a Bun-\\nsen burner until it gets white hot. To gain the incan-\\ndescence needed a high degree of heat is required. We\\nare obliged to spend much of our energy in producing\\nthe long vibrations in the ether that are of no direct use\\nin illumination. It is very natural, therefore, that physi-\\ncists should look to the possibility of producing the\\nshorter ether waves, which affect our eyes as light with-\\nout passing through the heat stage at all. Tesla especially\\nhas worked over this problem with much patience and\\ningenuity.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0320.jp2"}, "317": {"fulltext": "RAYS OF LIGHT IN STRAIGHT LINES 293\\n276. Photometry Law of Inverse Squares. The farther\\nwe get away from a light the less intense it becomes. Let\\na candle flame (Fig. 195) be the source of light. We can\\npicture rays goiug out in all directions. Suppose we trace\\n2\\no\\nFig. 195. Law of inverse squares.\\nthe four rays which at any given distance, say one metre,\\nbound a one-inch-square screen. As the rays come from a\\ncommon center they are divergent, and the farther away we\\ngo, the wider apart do they become. At a distance of two\\nmetres let us place a second screen. By similar triangles\\neach side of this second square must be twice as long as\\nthose of the first, and consequently the area must be four\\ntimes as great as that of the first. If we remove the first\\nscreen, the amount of light that formerly fell on it is now\\ndistributed over four times the area, and consequently can\\nbe only one fourth as intense. If we place a third screen\\nthree metres away from the flame, each side of the square\\nwill evidently be three times as long as those of the first,\\nand the area consequently nine times that of the first. If\\nthe second screen be now removed the original illumina-\\ntion is spread over nine times the area, and consequently\\ncan be only one ninth as intense. The distances are,\\n1:2:3; the areas, 1:4:9; the intensities, 1 J J. Hence\\nthe law of inverse squares The intensity of light varies\\ninversely as the square of the distance from the source.\\nThe law holds for gravitation, heat, and the attractions\\nand repulsions of magnets and electrified bodies. In every\\ncase the force varies inversely as the square of the distance.\\nThe standard in America and Great Britain is the candle\\npower. A standard sperm candle, weighing six to the\\npound, seven eighths inch in diameter, and burning 120\\ngrains an hour, gives 1 candle power an average gas jet", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0321.jp2"}, "318": {"fulltext": "294\\nPHYSICS\\nyields 10 candle power an incandescent lamp usually 16\\ncandle power the more powerful oil lamps as high as 60\\ncandle power and the usual arc lamps about 120 candle\\npower.\\nPhotometry is a science of light measurement. It has\\nboth scientific and practical importance. Since light, like\\nother commodities, is now bought and sold, people want to\\nknow how much they are getting or giving. An instru-\\nment for measuring the intensity of light is known as a\\nphotometer. We will consider only one. All methods of\\nmeasuring light depend on the law of inverse squares.\\nRumford s Photometer. If a vertical rod or other opaque\\nobject be placed in front of a screen (Fig. 196), and light\\nfrom two sources fall upon the rod, it will cast two shadows\\nPhotometer.\\non the screen. Each shadow, however, will be illuminated\\nby light coming from the other source. By having the\\nshadows not too far apart, we may compare their intensities\\nby the eye with fair accuracy. If the lights are placed at\\nsuitable distances, the shadows may be made equally intense.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0322.jp2"}, "319": {"fulltext": "RAYS OF LIGHT IN STRAIGHT LINES 295\\nAs the illumination from both sources is now equal, their\\ncandle powers will be as the square of their distances from\\nthe screen.\\n277. The Relative Illumination of a Page of Reading\\nMatter when held near to or far from the Source of Light.\\nA kerosene lamp or a gas name may give a light of six-\\nteen candle power, and when we reflect that not many years\\nago people used fewer candles than we now use of lamps or\\ngas jets, it appears that we are more than sixteen times as\\nwell provided with light as our ancestors. They, however,\\nusually held a candle very near to the page while reading,\\nand people in these days often employ a poor lamp and sit\\nfar from it. One should frequently remind himself that\\nwhen he is twice as far from the light he receives one quar-\\nter as much of it, and when he is three times as far away\\nhe receives only one ninth as much of it, etc.\\n278. Relation between Temperature and Intensity of\\nLight. It is found that the intensity of the light proceed-\\ning from any given source increases remarkably with an in-\\ncrease in the temperature of the source. Authorities differ\\nas to the temperature at which light waves begin to be\\ngiven off, Weber placing it at 390\u00c2\u00b0 C. and Draper at 500\u00c2\u00b0\\nC. It depends, of course, upon the sensitiveness of the\\nobserver, and we can never know absolutely. Ordinary\\nsolids must be heated from 800\u00c2\u00b0 C. to 1,000\u00c2\u00b0 C. in order to\\nemit rays of white light that is, to become white hot.\\nBut all observers agree as to the remarkable increase at the\\nhigher temperatures. It is estimated that platinum gives\\nthirty-six times as much light at 1,400\u00c2\u00b0 C. as it does at\\n1,000\u00c2\u00b0. This fact is utilized in the incandescent electric\\nlamp. The carbon filaments are heated just as hot as they\\nmay be without suffering too rapid disintegration. Econ-\\nomy is found in the nice balance between these two con-\\nsiderations. The temperature of the crater of an arc\\nlamp is about 3,500\u00c2\u00b0 C. Hence its large illuminating power\\nand its economy.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0323.jp2"}, "320": {"fulltext": "296 PHYSICS\\n279. The Visual Angle How we use it for estimating\\nDistances. The angle which the lines of light from the\\nopposite extremities of an object make at the eye is called\\nthe visual angle. Our estimates of the size of things seem\\nto be founded to a certain extent upon their supposed dis-\\ntance and the visual angle which they subtend. This mar-\\nvelous faculty which we have of judging distance is un-\\ndoubtedly acquired by a slow process of education. The\\nstory is familiar of the person born blind who, having in\\nlater years obtained his sight through a surgical operation,\\nreached out his hand to lay it upon a distant church steeple\\nwhich he supposed to be near enough to touch. Subtend-\\ning so small a visual angle as it did, if he conceived its dis-\\ntance so little, he must have thought it a miniature toy.\\nOne appreciates that this faculty can be trained when he\\nsees how efficient sailors become in the use of it. The\\nlandsman finds himself greatly at loss to estimate distances\\nupon the sea.\\nIf we can form no conception of the distance of an\\nobject, we are at a loss to make any estimate as to its size.\\nPeople sometimes amuse themselves making comparisons\\nbetween the apparent size of the moon and that of familiar\\nobjects. One says it looks about the size of a silver dime,\\nanother compares it to a silver dollar, and still a third finds\\na carriage wheel represents it. How completely without\\nfoundation these estimates are will be seen when one con-\\nsiders that if the eye were placed at one end of a metre\\nstick, and an object one centimetre in diameter were placed\\nat the other end, it would subtend about the same, visual\\nangle as the moon.\\nSome curious errors of judgment as to size occur when\\nwe have formed a wrong estimate of the distance of an\\nobject. In the dim twilight, one evening, a cat shot across\\nthe field of vision and ran up a little tree not more than\\nfour rods distant from the observer, who had not noticed\\nthe little tree because a very large tree about twice as far", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0324.jp2"}, "321": {"fulltext": "RAYS OF LIGHT IN STRAIGHT LINES 297\\ndistant stood directly in line with it. Supposing, therefore,\\nthat the cat was twice her actual distance away, he was at\\nthe moment rather appalled at the apparition of a cat\\nthree feet long instead of eighteen inches, as she probably\\nwas. Such hallucinations are apt to fade from the mind as\\nsuddenly as they come.\\nThe sun and moon each subtend a visual angle of about\\nhalf a degree. The sun is about four hundred times as far\\naway as the moon, and is about four hundred times as broad.\\nYet they appear to us to be about the same size, because\\nwe conceive of them as being at the same distance. If by\\nany means we could make the sun appear to be farther\\nfrom us than the moon, it would appear larger. To most\\npersons the sky appears like a flattened dome, with the\\nzenith much nearer than either horizon. Hence the sun\\nand moon appear to us larger when in the horizon than in\\nthe zenith.\\nThe sun is so far away that the rays of its light which\\nreach us are very nearly parallel. The greatest possible\\nvariation from parallel would obviously exist between those\\nrays which start from opposite extremities of the sun s disk\\nand meet at the eye of the observer. Such rays would vary\\nhalf a degree from parallel.\\nAn object becomes invisible when it subtends a smaller\\nangle than J, 7 of a degree. If it is one of the largest bodies\\nin the universe, but far enough distant to subtend\\nof a degree, it is invisible without the aid of a telescope\\nor if it is ever so near at hand but subtends so small an\\nangle, it is invisible without the aid of a microscope. These\\ninstruments increase the visual angle by means of lenses,\\nas will be explained in Chapter XXIX.\\nWe are deceived with reference to the size of an object\\nif it gives a very brilliant light. The filament in an incan-\\ndescent electric lamp, which is so small as to be seen with\\ndifficulty when it is not giving light, appears very much\\nlarger when it is giving light. The sun, although it sub-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0325.jp2"}, "322": {"fulltext": "298 PHYSICS\\ntends the same visual angle as the moon, appears larger\\nbecause it is more brilliant. When the sun is seen through\\na thin cloud which shuts off some of its light, persons are\\noften surprised to find that it appears smaller than they\\nhad imagined.\\n280. Shadows. In Fig. 197 let L represent a point of\\nlight, cd an opaque object, and ef a screen. It is manifest\\nthat no light from L will pass into the region c d ef. This\\nis the shadow. Its length may extend indefinitely as the\\nscreen is moved away from c d. We more often think of\\nthe shadow as being mere- p\\nly that portion of the screen y\\nwhich receives no light.\\nFig. 197. Umbra. Fig. 198.\u00e2\u0080\u0094 Umbra and penumbra.\\nUmbra and Penumbra. In Fig. 198 let F represent a\\nflame, and let a and b represent its extremities c d is an\\nopaque object, and ef a screen as before. The region into\\nwhich no light may pass is cd g li. Around this there is\\na region ceg and dfh into which a more or less limited\\nportion of the light from F may pass. To distinguish\\nbetween these regions, we call the portion which receives\\nno light the umbra, and the other the penumbra. The\\npenumbra grows gradually denser as we pass from its outer\\nlimits inward toward the umbra, and there is no distinct\\ndividing line, as eg or dh.\\n281. The Moon s Shadow\u00e2\u0080\u0094 Eclipses of the Sun and\\nMoon. In Fig. 199 the angle a o b is made just half a de-\\ngree. If an observer were stationed at o, and the lines oa\\nand o b were extended 240,000 miles (the distance of the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0326.jp2"}, "323": {"fulltext": "RAYS OF LIGHT IN STRAIGHT LINES\\nmoon), they would then be just far enough apart to\\nspan the moon that is, 2,000 miles apart. If then\\nthey should be extended 92,500,000 miles (the dis-\\ntance of the sun), they would be far enough apart to\\nspan the sun that is, 860,000 miles apart.\\nIf it were strictly true that both the sun and\\nmoon subtend an angle of half a degree, it would\\nfollow that the moon s shadow as cast by the sun\\nwould be just long enough to reach the earth. The\\ntruth is that the moon s umbra is sometimes a little\\nlonger than its distance from the earth, and it cov-\\ners a small portion of the earth s surface when it\\nchances to sweep across it. Usually, however, we\\npass through nothing but the penumbra on an occa-\\nsion of an eclipse of the sun.\\nThe umbra has the shape of a cone, whose length\\nis about 240,000 miles and whose base is about 2,000\\nmiles. The penumbra is also an exceedingly slim\\ncone, whose base is removed to an indefinite dis-\\ntance, and whose apex is cut by the umbra, which\\nextends into it like the crater of a volcano. Fig.\\n200 gives a suggestion of their appearance.\\nThe earth s shadow is similar in appearance to\\nthe moon s. The umbra is a cone whose base is\\nabout 8,000 miles in diameter, and whose length is\\nabout 868,000 miles.\\nIt is convenient to remember that the length of\\nthe earth s umbra is about equal to the diameter of\\nthe sun, but it is more to our present purpose to\\nnotice that it is nearly four times as long as the\\nmoon s umbra, and herein lies the reason for its\\ndarkening the face of the moon more often than the\\nmoon s shadow eclipses the earth. In Fig. 200 sun-\\nlight is supposed to come from the left-hand mar-\\ngin of the page in lines deviating from parallel, as\\nFig. 199 represents, and lighting half of the earth", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0327.jp2"}, "324": {"fulltext": "300\\nPHYSICS\\nand moon. The umbra cast by each, with its proportional\\nlength, is shown*. The penumbra in each case may be im-\\nagined. The moon is represented as approaching the part\\nof its orbit where it will cast its shadow upon the earth.\\nPersons upon the earth s surface will, where the shadow\\npasses, notice a dark body apparently passing across the\\nface of the sun. This phenomenon is called an eclipse of\\nthe sun. It requires about a month for the moon to re-\\nvolve around the earth hence in about half a month it\\nwill be approaching the earth s shadow, and when it passes\\nthrough it, persons upon that part of the earth s surface\\nturned toward the moon will notice a dark body apparently\\npassing across the face of the moon. This phenomenon is\\ncalled an eclipse of the moon. From this it would appear\\nthat there should be an eclipse of both sun and moon each\\nmonth, but this is certainly not the case, an eclipse of the\\nsun being very rare, and one of the moon occurring far\\nfrom once a month. This is explained by the fact that the\\nmoon does not revolve in the same plane as that in which\\nthe earth s shadow lies, as will be seen by referring to Fig.\\n201, which represents what we might suppose we would see\\nMoon /Umbra 340,000 ^liles\\nJ\\nFig. 200.\\nif we were to look down upon Fig. 200 from the direction\\nof the top of the page. From this it would appear that an\\neclipse of neither sun nor moon might ever occur.\\nBut it", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0328.jp2"}, "325": {"fulltext": "RAYS OF LIGHT IN STRAIGHT LINES 301\\nmust be remembered that the earth accompanied by the\\nmoon is revolving around the sun in the plane in which\\nar, y, and z lie in Figs. 200 and 201, and there will be places\\nin its orbit where eclipses may occur eclipses of the moon\\nfar more frequently than eclipses of the sun, because the\\nearth s shadow is so much larger than the moon s. It\\nFig. 201.\\nmust be true that whenever any place comes within the\\numbra, a total eclipse occurs for that place hence we see\\nwhy partial eclipses are tolerably frequent, while total\\neclipses are very rare. It should be mentioned that the\\norbit of the earth is slightly elliptical, and therefore the\\nsun is a little nearer at one time than another, and the\\numbra of both the earth and the moon must therefore be a\\nlittle shorter at one time than another. For this cause the\\numbra of the moon is not long enough to reach the earth\\nduring a portion of each year.\\nIt may be interesting to note that two rays of light\\nstarting from opposite edges of the sun, and meeting at a\\npoint on the earth s surface, converge at the rate of 1 mile\\nin 114; but if they extend from opposite edges of the sun\\nto opposite edges of the earth, they converge at the rate of\\n1 mile in 108. Of so little importance is the earth s diam-\\neter when considering the vast distances between the heav-\\nenly bodies, that the earth may be looked upon as a mere\\npoint in space. A young child looking at the moon over\\nhis head thinks he may walk out from under it, and it is\\nmany years before he really appreciates that on account of\\nthe moon s great distance from the earth, it may appear to\\nbe overhead at the same moment to two persons situated\\nmany miles apart.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0329.jp2"}, "326": {"fulltext": "302 PHYSICS\\n282. Light through Small Apertures. In Fig. 202, cd\\nrepresents a very small hole, about one tenth of an inch, in\\na piece of cardboard an inch or two in front of a candle\\nflame, and a screen is held a few inches behind it. An\\ninverted image of the flame will appear upon the screen.\\nThe reason for the image being inverted and for its be-\\ning more or less indistinct will be seen from a study of\\nthe figure. Light from the tip of the flame a will fall\\nupon the screen at a and will cover an area somewhat\\nlarger than the hole c d. Likewise a point, b, at the base\\nof the flame, will illuminate that portion of the screen\\nmarked V The light which comes from the single point\\nb not only spreads over an area considerably larger than\\nthe hole c d, but it is also overlapped by the light from\\nFig. 202. Light through small apertures.\\nneighboring points in the flame. Hence the image is\\nmore or less indistinct. When a pencil, or similar object,\\nis passed downward between the flame and c d, the shadow\\nof the pencil moves upward upon the screen, and vice versa\\nalso when the pencil is moved horizontally in a direction\\nparallel to the screen its shadow makes the reverse move-\\nment.\\nA Camera made from a Small Pasteboard Box. A hole\\nscarcely one tenth of an inch broad is made in the cover of\\na small pasteboard box and a window about two inches\\nsquare is cut in the bottom of the box over this the thin-\\nnest tissue paper is pasted. A candle flame is placed before\\nthe small hole about an inch and a half distant. An in-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0330.jp2"}, "327": {"fulltext": "RAYS OF LIGHT IN STRAIGHT LINES 303\\nverted image of the flame appears upon the tissue-paper\\nscreen. This is seen much more plainly when a dark\\ncloth, such as photographers use, is thrown over the head\\nto shut the outside light from the eyes and from the\\nscreeu.\\nThis box represents a camera, and although it has no\\nlens it takes a very fair picture of a landscape when a\\nsensitive plate, such as photographers use, is placed in the\\nbottom of the box. This must be done in a dark room,\\nand a cloth must be wrapped around the box to prevent\\nlight from getting in and spoiling the plate before one is\\nready to take the picture. In taking the picture the cloth\\nis removed from the small hole not from the rest of the\\nbox for a brief interval and then replaced, and the plate\\nis taken out of the box in a dark room and put into the\\ndeveloping solution which photographers use. Such a\\npasteboard box as the sensitive plates come in serves well\\nfor this kind of a camera.\\nA Picture received through a Keyhole. In the evening\\none may get an inverted picture through a keyhole by going\\ninto a dark room and holding a thin piece of paper a foot\\nor two from the keyhole of the door, while some one holds\\na lighted lamp about the same distance from the other side\\nof the keyhole.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0331.jp2"}, "328": {"fulltext": "CHAPTEK XXVII\\nREFLECTION OF LIGHT\\n283. Laws of Reflection. The angle which a ray of light\\nmakes with the perpendicular to a reflecting surface at the\\npoint where the ray strikes is known as the angle of inci-\\n(i, Fig. 203). After reflection the ray makes a second\\n[_\\nFig.\\n203\\nMirror\\nLaw of reflection.\\nangle with the perpendicular, known as the angle of reflec-\\ntion, r. Two simple laws are found to hold in all cases of\\nreflection\\n1. The angle of reflection is equal to the angle of inci-\\ndence.\\n2. The incident ray, the perpendicular, and the reflected\\nray are in the same plane.\\nHeat rays are reflected in the same way. A billiard ball\\nsent against the cushion tends to return according to the\\nsame law; other causes, however, operate to change the\\ndirection in this case.\\n284. Images in Plane Mirrors. If such a reflected ray\\nenter the eye, it produces there an image of the point from\\nwhich it has come, but the image will not seem to be in the\\n304", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0332.jp2"}, "329": {"fulltext": "REFLECTION OF LIGHT\\n305\\nFig. 204. Location of image.\\ndirection of the incident ray, but will appear lack of the\\nreflecting surface as far as the real object is in front of it,\\nand in the direction of the reflected ray produced. Such\\nan image has, of course, no real existence. All the images\\nproduced by plane mirrors\\nare of this character. They\\nare constructed as follows\\nLet MR (Fig. 204) be the\\nsurface of a plane mirror, and\\nlet a represent an object in\\nfront of it. We may locate\\nthe point where we imagine\\nthe image to be as follows\\nConsider any two rays pass-\\ning from a to the mirror as\\na c and a d. They will be\\nreflected in obedience to the first law, the angle of reflec-\\ntion, in both cases equaling the corresponding angle of in-\\ncidence. Producing the reflected rays, they are found to\\nmeet at a as far back of the mirror as a is in front of it.\\nHowever complicated the object may be, its image is\\nfound in precisely the same way, practically by dropping\\nperpendiculars from various points in an object to the mir-\\nror, and extending\\nthem to the rear as\\nfar as the actual\\npoints are to the\\nfront. Fig. 205\\nshows how rays of\\nlight will pass from\\na and b, the two ex-\\ntremities of an ob-\\nject, to a mirror,\\nMR, and be reflect-\\ned from the mirror to the eye of the observer at e, the\\nimage of the object appearing at a V. The image, while\\n21\\nFig. 205. Location of image.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0333.jp2"}, "330": {"fulltext": "300\\nPHYSICS\\nresembling the object in every other particular, is re-\\nversed.\\n285. Concave Mirrors Principal Focus and Conjugate\\nFoci. Let aob (Fig. 206) represent a concave mirror, and\\nlet rays of light, 8 a and Sb,\\nfall on its surface parallel to\\nthe principal axis, do. If d be\\nthe center of curvature of the\\ni\u00e2\u0080\u0094 d mirror, lines drawn from d to\\nany point on the surface of the\\nmirror will be perpendicular at\\nthat point. Hence any ray,\\n8 a, will be reflected to a point\\nFig. 206.-Eeflecto by a con- g() located that 8ad e q ualg\\nFad. All parallel rays will be\\napproximately reflected to F, which is called the Principal\\nFocus of the mirror. Conversely, all rays originating at F\\nwill be reflected parallel to the principal axis d o.\\nEays of sunlight may be considered parallel. They may\\nbe collected at F, which would thus be a center of great\\nheat. This may be shown experimentally by turning a\\nconcave mirror toward the sun and finding F.\\nConjugate Foci. A source of light must be infinitely\\ndistant to send parallel\\nrays to the mirror. Let us\\nconsider a nearer source of\\nlight, such as a candle at a\\n(Fig. 207). The rays are J^^C;::^ ;^u\\ndivergent, and after reflec-\\ntion will be gathered to\\nsome point, farther from\\nthe mirror than the prin-\\ncipal focus is. Conversely, Fig. 207.\u00e2\u0080\u0094 Conjugate foci,\\nrays originating at /would,\\nafter reflection, be gathered at a. Points so related as a and\\nare called Conjugate Foci, since they are interchangeable.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0334.jp2"}, "331": {"fulltext": "REFLECTION OF LIGHT\\n30\\n286. Enlarged Images formed in Concave Mirrors. In\\nFig. 208, a b represents the curved mirror, d is the center\\nof its curve, the eye is supposed to be at e, and m n is an\\nobject. A ray of light from m reaches the eye by being\\nreflected at c so as to make the angle of incidence, m c d,\\nequal to the angle of reflection, dee. And it appears that,\\nof all the rays of light which pass out from m and fall upon\\nthe mirror, this is the\\nonly one which may\\nreach the eye. One\\nshould convince him-\\nself of this fact by\\ndrawing a series of dia-\\ngrams showing the\\ncourse which various\\nrays from m to the mir-\\nror will take upon being\\nreflected according to\\nthe law. The image of\\nthe point m appears to\\nbe behind the mirror\\nin the direction e c, but\\nthe distance of m from\\ne is determined by the\\nimagination, which dif-\\nfers with different peo-\\nple. In this book m!\\nhas been located so that\\nt ig. 208. Enlarged images.\\nm c shall be equal to\\nm c, because this seemed to be as reasonable as any other\\nconclusion, and it is a convenient measurement. In like\\nmanner the image of each of the points n, o, and p will\\nappear behind the mirror at n\\\\ o\\\\ p the extremities of\\nlines e c and e e and e c extended so that c n e o\\nand c p shall be equal to e n, c o, and e p respectively.\\nThe angles of incidence and reflection are in every case", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0335.jp2"}, "332": {"fulltext": "308\\nPHYSICS\\nequal to each other. The image appears curved and en-\\nlarged. It appears enlarged both because it seems to sub-\\ntend a greater visual angle, and because it seems- to be\\nfarther distant than the object it appears curved for rea-\\nsons which are given in section 290.\\n287. How an Inverted Image is formed in a Concave\\nMirror. In Fig. 209, m n represents a vertical line across\\nthe face, e the position of the eye, a b the mirror, d the\\ncenter of the curve, c and c the places upon the mirror\\nwhere the rays of light from the points m and n respect-\\nively are reflected to the eye. Of all the rays of light\\nwhich pass out from w, the one which meets the mirror at\\nc is the only one which can be reflected to e, because it is\\nthe only one which can make the angle of incidence, m cd,\\nequal to the angle of reflection, e c d. Hence the image of\\nthe point m will appear in the direction e c, and that of n\\nin the direction e c The image m n will therefore repre-\\nsent the object turned end for end or inverted, and the\\nimage appears to be located about as\\nfar behind the mirror as the object is\\nin front of the mirror. It does not\\nappear curved in this case. For a dis-\\ncussion on this point see section 290.\\nWhen the mirror is near the face\\nan upright image is seen, which grows\\nrapidly larger as the mirror is moved\\nfarther away. The image soon be-\\ncomes very indistinct, some parts ap-\\npearing double, and then an inverted\\nimage of large size appears, which\\ngrows smaller as the mirror continues\\nto move farther away.\\nThe reason for this will appear to\\nany one who will take the trouble to\\ndraw a series of diagrams after the plan of Fig. 209, in\\nwhich the object m n shall be represented in various posi-\\nm\\nFig. 209.\u00e2\u0080\u0094 Inverted\\nimages.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0336.jp2"}, "333": {"fulltext": "REFLECTION OF LIGHT\\n309\\ntions, some of which shall be between the center d and the\\nmirror. It will be found that direct images will be pro-\\nduced in all cases where e is between d and the mirror,\\nand that inverted images are produced when e is farther\\nfrom the mirror than d is, and that the nearer e is to d the\\nlarger is the image.\\n288. Diminished Images formed in a Convex Mirror.\\nFig. 210 represents a case where the convex side of the\\nmirror is turned toward the face.\\nThe image always appears direct,\\nalways smaller than the object,\\nand grows smaller as it recedes\\nfrom the mirror. The figure\\nrepresents the relation of the\\nimage to the object for one sin-\\ngle position. It will be found\\nto be instructive to make a\\nseries of diagrams for various\\npositions which the object may\\noccupy.\\n289. A Silver Spoon as a Concave and a Convex Mirror.\\nThe bowl of a bright silver spoon gives images that are\\nenlarged or diminished in some directions more than others\\ni. e., the image is not a symmetrical representation of the\\nobject, as it always is when a true spherical mirror is used.\\nThis is due to the fact that the bowl of the spoon has a\\ncurve of a smaller circle from side to side than from end to\\nend. A little experimenting with a piece of bright tin by\\nbending it more or less while observing one s face in it will\\nreveal the fact that in the case of convex mirrors the image\\nalways grows smaller as the mirror becomes more convex\\nbut, in the case of concave mirrors, as long as the object is\\nfarther from the mirror than the center of the curve, the\\nimage grows smaller as the mirror becomes more concave;\\nif, however, the object is situated between the mirror and\\nthe center of the curve, the image enlarges as the mirror\\nDiminished images.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0337.jp2"}, "334": {"fulltext": "310 PHYSICS\\nbecomes more concave. This latter condition is never real-\\nized when one observes his face in the bowl of a spoon. A\\nseries of drawings like those represented in Figs. 209 and\\n210, in which the curve of the arc a b shall vary, will fur-\\nnish an explanation of these phenomena.\\n290. A Curved Image from a Straight Object. The\\nimage of a straight object appears curved in either convex\\nor concave mirrors only when the object is very near to the\\nmirror. It would appear, referring to Fig. 208, that, under\\nthese conditions, the mind instinctively conceives m o, o c\\np c and n c to be respectively equal to m c, o c\\\\p c\\nand n c and that it is unable to recognize that relation-\\nship when the object is more remote from the mirror.\\nThis may be due to the fact that when the object is far\\nfrom the mirror its image must be looked at very nearly in\\nthe plane of its curve, if it has one, and the eye fails to\\nrecognize the curve, just as it can not see the curve of a\\ncircle when looked at edgewise.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0338.jp2"}, "335": {"fulltext": "CHAPTER XXVIII\\nMISCELLANEOUS OBSERVATIONS ON REFLECTION\\n291. How Daylight is diffused. Every one knows that\\nmirrors reflect light, but few, if any, appreciate what a\\ntangled lot of reflected and re-reflected rays we are using\\ncontinually. All things reflect light to a greater or less\\ndegree.\\nIt is easy to see that, although the direct sunlight is\\nparallel and travels in straight lines, it scarcely travels far\\nafter it reaches the earth without meeting various objects\\nwhich reflect it in all possible directions and into every\\nnook and corner.\\n292. Halos about Street Lights and the Circle around\\nthe Moon. A beam of sunlight passing into a dark room\\nis made apparent by particles of dust which reflect the light\\nto the eye. If one takes a piece of glass and breathes upon\\nit to bedew it with moisture, and holds it* very near to the\\neye while looking through it at a candle flame, the flame\\nwill have the same appearance as the street lights do upon\\nfoggy nights. The small particles of moisture reflect light\\nas the particles of dust do. These, distributed everywhere\\nin the atmosphere, reflect the light of the moon at night,\\nbut only those occupying certain positions with reference\\nto the observer can reflect light to his eye. This phenome-\\nnon may indicate the presence of much moisture in the air,\\nbut that does not always presage a storm.\\n293. The Sun drawing Water. The phenomenon\\nwhich some people call the sun drawing water is pro-\\n311", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0339.jp2"}, "336": {"fulltext": "312 PHYSICS\\nduced by particles of dust or moisture in the atmosphere\\nreflecting sunlight and marking the path of sunbeams\\nwhich pass out from behind a cloud. These sunbeams are\\nfrequently seen in the latter part of the afternoon shooting\\nupward toward the zenith as well as downward toward the\\nhorizon. People who suppose they are streams of water\\ncan not take the trouble to consider the difficulties which\\nmight appear to be counter to such a supposition.\\n294. Illumination of Clouds at Sunset. Clouds, like the\\nmoon, catch the sunlight and reflect it to us after sunset.\\nWe see them best when the direct sunlight is shut off from\\nour eyes by the horizon, but is still shining upon the clouds,\\njust as we see the moon after the sun has gone out of our\\nsight, but is still shining upon it.\\n295. Moonlight and the Phases of the Moon. We are\\nwholly unable to see an object unless light comes from that\\nparticular object to the eye. The moon is visible only when\\nthe sun shines upon it, and only that portion of it is visible\\nupon which the sun shines, excepting that the dark part\\nof the new moon is slightly illuminated by light reflected\\neo\\nFIRST\\nQUARTER\\nMOON\\nFig. 211. Phases of the moon.\\nupon it from the earth, and is somewhat visible by this\\nlight being reflected back again from the moon to our eyes.\\nFig. 211 is intended to explain the phases of the moon.\\nSunlight is supposed to come from the right-hand margin\\nof the page in parallel lines and illuminate the right half", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0340.jp2"}, "337": {"fulltext": "MISCELLANEOUS OBSERVATIONS ON REFLECTION 313\\nof m m and m which represent the moon in three posi-\\ntions in the western horizon, in the zenith, and in the\\neastern horizon. E represents the earth, the right half of\\nwhich is also illuminated by sunlight a represents the posi-\\ntion of an observer upon the earth.\\nSuppose the observer looks at the moon when it is in\\nthe position m the earth meanwhile is turning over in\\nthe direction indicated by the arrow, carrying the observer\\ninto the darkened portion where he no longer sees the\\ndirect sunlight. The sun appears to sink below the west-\\nern horizon, but the moon is still a little above the horizon,\\nand he sees a little of the side of it which the sun is shining\\nupon, and it appears crescent-shaped and is called the new\\nmoon. About a week later, at the same time in the day,\\nwhen he looks for the moon he will find it overhead in a\\ndirection ninety degrees from that of the sun, and it will\\nappear like a semicircle. It is then said to be in first\\nquarter. In another week at sunset he will find the moon\\nupon the eastern horizon showing a complete circle, when\\nit is called full moon. These appearances of the moon are\\ncalled phases of the moon.\\n296. How the Dark Part of the New Moon is made Visi-\\nble. If we could transfer ourselves from the earth to the\\nnew moon, we should be able to look back upon the earth\\nas upon a full moon four times as broad as the moon itself\\never appeared to us from the earth, and reflecting sixteen\\ntimes as much light, because its apparent area would be\\nsixteen times as great as that of a full moon. The earth,\\nthen, shines so brightly upon the darkened side of a new\\nmoon that it illuminates it sufficiently to make it visible\\nfrom the earth when the atmosphere is very clear. Clouds\\nin our atmosphere might interfere with the earth s giving\\nso much light to the moon as stated above, and they inter-\\nfere with our receiving the light reflected back again from\\nthe moon. Whenever, therefore, we see the dark portion\\nof the moon we may remember that we are receiving into", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0341.jp2"}, "338": {"fulltext": "314 PHYSICS\\nour eyes sunlight which has been first reflected from the\\nearth to the moon and then back again from the moon to\\nus. If we could visit the moon in first quarter, the earth\\nwould appear to us as a larger moon in the first quarter\\nand if we could visit the full moon, the earth would appear\\nas a very large new moon. In neither of these cases does\\nthe earth reflect light enough to the moon to make its dark\\npart visible to the earth.\\nVenus at all times, as seen through a telescope, appears\\nlike a new moon.\\n297. Why are Transparent Objects and Very Good Reflect-\\nors so nearly Invisible Themselves It seems probable that\\nif an object could be either perfectly transparent or a per-\\nfect reflector it would be wholly invisible. When a bottle\\nis entirely filled with very clear water it often appears\\nempty. Window panes may be so clear that it is difficult\\nto tell whether they are present or wanting. Air is invisi-\\nble because of its transparency. Moreover, a mirror is often\\nwell-nigh invisible itself because it is so perfect a reflector\\nof light. Most substances reflect a part only of the light\\nwhich falls upon them, and transmit or absorb the rest. A\\nglass put over a picture often transmits too little light and\\nreflects too much to serve well its purpose. The same is\\nfrequently true of a show window. It is particularly so the\\nmore obliquely one attempts to look through them. It is\\nalso a matter of familiar experience that, when one attempts\\nto look through a window from the outside, the farther he\\nis from the window the greater is the proportion of reflected\\nlight, and the nearer he is to the window the greater is the\\nproportion of transmitted light.\\nObjects which are nearly invisible, either because they\\nare good reflectors or because they transmit light well,\\nbecome readily visible if covered with dust or moisture or\\nare scratched, or if in any way the surface is made rough,\\nA bright tin reflector may be scoured with sand or scratched\\nwith a file so that it will no longer reflect an image. A", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0342.jp2"}, "339": {"fulltext": "MISCELLANEOUS OBSERVATIONS ON REFLECTION 315\\nglass mirror might be treated in the same way. Trans-\\nparent glass, if treated in this way, loses its transparency\\nand becomes ground glass. A quiet body of water which\\nacts like a mirror ceases to do so when ruffled by a -breeze.\\nFig. 212. Fig. 213.\\nThe accompanying figures (212 and 213) present an\\nexplanation for this fact.\\n298. Visibility of Print upon Glazed andUnglazed Paper\\nDrawings upon Rough and upon Highly Polished Surfaces.\\nAH objects have a somewhat ruffled surface, and it seems\\nprobable that they are themselves made visible, not by the\\nlight which they transmit or reflect from a smooth surface,\\nbut by the rays which they scatter. Thus, in Fig. 212, the\\nrays of light which meet the eye at e from the various\\npoints of the arrow abed, being reflected in regular order,\\nmake the observer conscious of the arrow, but not of the\\nmirror on the other hand, in the case represented in Fig.\\n213, a jumble of rays from a great variety of objects is\\nreflected to the eye, and the mind, not being able to form\\nan image of any object beyond the mirror, traces the light\\nonly so far as the mirror itself, and is conscious of that\\nalone.\\nIt is much easier to read from a rough page than a\\nglossy one. Drawings and paintings show much better\\nfrom rough than from highly polished surfaces. Polished\\nblackboards would be of little use. Shading a picture with\\ncrayon is only a matter of diffusing the light which it will\\nreflect.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0343.jp2"}, "340": {"fulltext": "316\\nPHYSICS\\n299. Twilight. Every one who is at all thoughtful\\nconcerning natural phenomena must sometimes ask the\\nquestion, Why, after the sun has set, does light linger\\nso long and darkness come so slowly? This period be-\\ntween day and night we call tivttight. It occurs in the\\nmorning as well as in the evening. It lasts much longer\\nin summer than in winter. We may properly consider\\none of the causes of twilight in this chapter it is reflec-\\ntion. In Eig. 214, E represents the earth. Sunlight comes\\nfrom the right-hand side. U U is the umbra, a a a is the\\natmosphere. The ratio of its depth to the diameter of the\\nearth is greatly exaggerated, however. The arrow shows\\nthe direction in which the earth rotates. is the position\\nFig. 214.\u00e2\u0080\u0094 Twilight.\\nof an observer for whom the sun has set, and he is now in\\nthe region of twilight. Clouds and innumerable particles\\nof moisture and dust floating in the atmosphere above still\\ncatch the sunlight and reflect it down upon him. In the\\nmorning he will enter another such region of twilight, rep-\\nresented at the lower margin of the figure, before he receives\\nthe full light of the sun.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0344.jp2"}, "341": {"fulltext": "CHAPTER XXIX\\nREFRACTION OF LIGHT\\n300. Refraction of Light defined and illustrated. The\\nfact that rays of light are bent in passing through various\\ntransparent substances is illustrated on every hand. This\\nbending of rays of light is called refraction. It only requires\\nthat one should be fairly attentive to what he sees about\\nhim to become familiar with most of the phenomena of\\nrefraction. At the dinner- table one may see objects through\\nhis tumbler of water, not only apparently displaced, but\\nalso enlarged, distorted, and even inverted horizontally.\\nThe handle of a teaspoon in the tumbler of water may\\nappear to be broken. A bubble or a crack in a window\\npane may make an object outside appear to be broken, dis-\\nplaced, or distorted. An inkstand, a paper-weight, a bev-\\neled mirror, or other household articles may give prismatic\\ncolors.\\nWhen a beam of light passes obliquely from one medium\\nto another of different density, as from air into water, or\\nair into glass, it suffers refraction. The entire beam does\\nnot enter the second medium. A part of it is thrown off\\nas a reflection. The part that enters the second medium is\\nnot all refracted. A portion of it is absorbed and appears\\nas heat. The portion that is refracted is subject to definite\\nlaws, just as the reflected part is.\\nRefraction may be conveniently studied by means of a\\nglass vessel with parallel sides, on which a circle is painted\\n(Fig. 215). The vessel is filled with liquid, say water, up to\\n317", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0345.jp2"}, "342": {"fulltext": "318\\nPHYSICS\\n1.33.\\nthe horizontal diameter of the circle. A lamp is placed at\\nL, so that its light will strike the water at the center of the\\ncircle. If the experiment is performed in a dark room, it\\nwill be plainly seen that where the light strikes the water\\nits rays are bent toward the perpendicular.\\n301. Index of Refraction.\u00e2\u0080\u0094 The amount of refraction is\\nmeasured in this way a o and d o being made equal, the\\ndistance of each of these points\\nfrom the perpendicular is meas-\\nured and compared\\nab_ 4\\ndc~ 3\\nThis value is called the index of\\nrefraction. It is found to be\\nconstant for any two given me-\\ndia, however much the obliquity\\nof the ray of light may change\\ni. e., so long as the two media\\nremain air and water, we may\\nchange the direction of the ray\\nao, and consequently the value of a b, never so much, dc\\nwill likewise change so as to be three fourths of a b.\\nThe index of refraction varies with different media.\\nFor light passing from air into ether it is 1.36 into alco-\\nhol, 1.37 into turpentine, 1.47 into crown glass, 1.53\\ninto flint glass, 1.63 into carbon bisulphide, 1.67 into\\ndiamond, 2.75.\\nIt is manifest from this that optical density is not the\\nsame as ordinary density for, although ether, alcohol, and\\nturpentine are all lighter than water, they have a larger\\nindex of refraction. This is illustrated in Fig. 219. The\\nfollowing laws are found to hold\\n1. The incident ray, the perpendicular, and the refracted\\nray are in the same plane.\\n2. When light passes from an optically rarer into a\\ndenser medium obliquely to the surface, which is between\\nFig. 215.\u00e2\u0080\u0094 Eefraction.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0346.jp2"}, "343": {"fulltext": "REFRACTION OF LIGHT 319\\nthe two media, it is bent toward the perpendicular to that\\nsurface or, conversely, if it passes from a denser into a\\nrarer medium, it is bent away from the perpendicular.\\n3. The index of refraction is always a constant value for\\nany two given media, however much the obliquity of the\\nray may change.\\n302. Cause of Refraction. These facts are purely experi-\\nmental, and therefore quite independent of any theory.\\nBut we have now to inquire why the ray is bent a definite\\namount if oblique, and is not bent if perpendicular. Sup-\\npose a beam of light with a wave front, IV (Fig. 216), to\\nstrike obliquely against the surface of water, s s. It has\\nbeen found by experiment that light travels one third again\\nas fast in air as in water. Consequently the whole wave is\\nretarded in the water. But all portions of the wave front\\ndo not enter the water at the same time. When I reaches\\nss, V is still some distance away. If, now, I traveled as fast\\nas V, the beam would pass into the second medium without\\nany bending, as indicated in the dotted lines. But this is\\nnot the case while V passes\\nto ss, I can only go three\\nfourths as far that is, to h\\nand hence the wave front\\nswings around to It h\\\\ and\\nthe beam itself, which must\\nalways be perpendicular to the\\nwave front, takes the new\\ndirection shown, bent toward M\u00c2\u00a5\u00c2\u00a7i\\nthe common perpendicular, /r f\\nhli When the beam is per-\\npendicular to s s, the wave fig. 216.\u00e2\u0080\u0094 Refraction.\\nfront IV, is equally retarded\\nalong its entire length, and consequently there is no change\\nof direction.\\n303. Value of the Index. The numerical value of the\\nIndex of Refraction is always the ratio of the velocity of", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0347.jp2"}, "344": {"fulltext": "320\\nPHYSICS\\nlight in the first medium to the velocity in the second.\\nWhen, therefore, light passes into a medium of greater\\ndensity, the index is always greater than one, and the ray\\nis bent toward the common perpendicular. When light\\npasses into a medium of less density, the index is always\\nless than one, and the ray is bent away from the common\\nperpendicular.\\nWhen the direction of a beam is reversed, the second\\nbecomes the reciprocal of the first. Thus, the index, when\\nlight passes from air into water, is f but when light passes\\nfrom water into air, the index is f\\n304. The Critical Angle. It follows from all this that a\\nray of light can always pass from a rare into a dense medium,\\nFig. 217.\u00e2\u0080\u0094 Critical angle.\\nbecause it is bent toward the common perpendicular but\\nthe ray can not always pass from a dense into a rare\\nmedium, for if the ray should be bent away from the com-\\nmon perpendicular more than 90\u00c2\u00b0 it would fail altogether\\nto emerge from the denser medium. No ray of light can\\npass from water into air if it makes a greater angle with\\nthe perpendicular than 48\u00c2\u00b0 35", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0348.jp2"}, "345": {"fulltext": "REFRACTION OP LIGHT 321\\nReferring to Fig. 217, let A B represent the surface of\\nwater. A ray of light starting from a will be bent so as to\\nreach a likewise those which start from b and c will reach\\nV and d respectively, but one which starts from d would be\\nbent so as to pass along the surface through B, and one\\nwhich starts from i would be bent so as to return beneath\\nthe surface of the water to i\\n305. Total Reflection. We may well be interested to\\ninquire what becomes of rays which make greater incident\\nangles than the critical angle, and which consequently can\\nnot emerge.\\nThey are reflected, and since the reflection is complete,\\nit is called total reflection. Could we stand at the bottom of\\na pool of clear water and look upward, we should see objects\\non the surface of the water within a cone which had our\\neye for its apex, and whose elements made an angle of 48\u00c2\u00b0\\n35 with its axis. Beyond the circular base of this cone we\\nshould see a perfect mirror, which would reflect objects\\nlying on the bottom of the pool. The same effect on a\\nsmall scale may be seen when we look at the underside of\\nthe surface of water in a clear tumbler, provided the angle\\nof vision be greater than the critical angle. The surface\\nappears like a burnished mirror. A silver spoon or a bright\\ncoin will give a brilliant image. For the same reason, water\\nin a test-tube seems covered with a film of silver when\\nlooked at from below.\\n306. Applications. Eefraction is the source of many illu-\\nsions. Bent rays of light make objects appear where they\\nare not. The sun, moon, and stars, when near the horizon,\\nare elevated about half a degree by the refraction of the\\nearth s atmosphere. This is equal to the apparent diam-\\neters of the sun and moon. Sticks and other objects partly\\nimmersed in water appear bent at the surface (see Fig. 218).\\nClear water appears less deep than it really is. The hot air\\nover the surface of a desert bends the rays of light and\\nproduces the mirage, the appearance of reflection in water.\\n22", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0349.jp2"}, "346": {"fulltext": "322\\nPHYSICS\\nPrecious stones owe their brilliancy to high refractive\\npower, and consequently to total reflections from the facets\\non the other side. The critical angle for the diamond is\\n23\u00c2\u00b0 53 All the light that passes into the diamond, and\\nstrikes any of the facets at angles greater than this, suffers\\n5^\\nINDEX OF\\nTURPENTINE\\n-\u00e2\u0080\u00941.47\\nCARBON BISULPHIDE\\n1.67\\nFig\\n219\\nFig. 218.\u00e2\u0080\u0094 Eefraction.\\ntotal reflection within the stone, and finally emerges in pen-\\ncils of light, which produce the magnificent fire and sparkle\\nof the gem. Many of the rays of light are so refracted as\\nto produce prismatic colors. The diamond owes all its\\nbrilliancy to the cutting, for in its natural state it is dull.\\nOur heaviest flint glass has a critical angle of 35\u00c2\u00b0 37\\nArtificial diamonds made of this material must, therefore,\\nhave much less brilliancy than the real stone. If we could\\nmake a glass as transparent as the diamond, and having an\\nequally high refractive index, we should have an equally\\nbrilliant gem.\\nRefraction of light enables us to see colorless and trans-\\nparent fluids. Fig. 219 represents a bottle which contains\\nthree colorless and transparent liquids. They remain sepa-\\nrate from one another as oil and water do. Carbon bisul-\\nphide is at the bottom, upon this floats the water, and upon\\nthe water floats the turpentine. A straight line is drawn\\nvertically upon the back face of the bottle, and this, as seen\\nthrough the liquid obliquely, appears as a broken line, by\\nreason of the differing powers of refraction of the liquids.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0350.jp2"}, "347": {"fulltext": "REFRACTION OF LIGHT\\n323\\nThe fact that we may distinguish between these various\\nliquids is due to the variation in their refracting power.\\nAir refracts light, and cold air more than warm air. This\\nis the reason why we can see hot air rising above a stove.\\nSmall currents of warm air pass up. through the cold air,\\nand rays of light coming from objects seen through these\\ncurrents of air are made to quiver by reason of rapid\\nchanges in their refraction. Something similar appears\\nwhen one of the liquids mentioned above is poured in a\\nsmall stream into another in the bottle. It is well shown\\nby pouring glycerin into water.\\nRefraction enables us to see the sun two minutes after\\nit has set and two minutes before it rises, hence it has the\\neffect of lengthening the day four minutes. Reflection, by\\nproducing twilight, lengthens the day several hours. We\\nmay see the sun ten minutes after it has set, on account of\\nboth refraction and the velocity of light, but on the same\\naccount we do not see it until six minutes after it has risen.\\nFig. 220.\\nFig. 221.\\nA body of clear water, which when calm may reveal\\nobjects at great depths, will not do so when the surface is", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0351.jp2"}, "348": {"fulltext": "324\\nPHYSICS\\nFig. 222. Refraction by a prism.\\ndisturbed by a breeze. This is due to refraction, as will be\\nseen from Figs. 220 and 221. In Fig. 220 each point in\\nthe object abed under water sends its light in regular\\norder to the eye, e, held above the water, but in Fig. 221\\nthese rays are so bent as to give a confused image.\\n307. Refraction in Prisms. The path of a ray of light in\\npassing through a prism is illustrated in Fig. 222. Suppose\\nBE to be an incident ray\\nupon the face of a glass\\nprism. After refraction the\\nray will take the direction\\nEI, being bent toward the\\nperpendicular at E, and will\\nsuffer a second refraction\\nat Here the ray is pass-\\ning into a less dense me-\\ndium, and must consequent-\\nly be bent away from the perpendicular, and must take\\nsome such direction as IS. From the nature of the case,\\nthe ray is always bent toward the base of the prism that\\nis, toward the thicker part.\\n308. Enlarged Images produced by Refraction. A cross-\\nsection of a prism is represented in Fig. 223 m n repre-\\nsents an object, and e the\\nposition of the eye. The\\nobject appears to be en-\\nlarged to the size of m n\\\\\\nwhich may be measured\\nand perhaps found to be\\nhalf as large again. The\\nratio of the size of the image to the size of the object\\nis expressed thus\\nm! n 15 mm.\\nzr^ 1.5.\\nm n 10 mm.\\n309. Different Kinds of Lenses and the Way they refract\\nLight. If the prism mentioned above were slightly modi-\\nFig. 223", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0352.jp2"}, "349": {"fulltext": "REFRACTION OF LIGHT\\n325\\nfied in shape so that its cross-section would look like Fig.\\n224, b, we should call it a lens, and, since one of its surfaces\\nb c d e\\nFig. 224.\u00e2\u0080\u0094 Typical lenses.\\nis plane, while the other is convex, it would be called a\\nplano-convex lens if the plane surface were made convex\\nalso, it would be called a double-convex lens (a) if one sur-\\nface were plane while the other were concave, as repre-\\nsented at e, it would be a plano-concave lens and if both\\nsurfaces were concave, it would be called a double-concave\\nlens (d).\\nAfter what has been said, it is a simple matter to under-\\nstand how rays of light will be bent in passing through\\nthese lenses. The principle to be borne in mind is that\\nwhen a ray passes from air into glass it is bent toward the\\nperpendicular, and when it passes from glass into air it is\\nbent away from the perpendicular. It is evident that the\\nlens represented at e, for example, makes the image appear\\nsmaller than the object, and that the lens at a has the\\ngreatest magnifying power.\\n310. Inverted Images produced by Refraction. In Fig.\\n225, a b represents a lens, m n represents an object, and\\nn a e and m b e are lines of light which pass from the ex-\\ntremities of the object through the lens to the eye, which\\nis supposed to be situated at e. The image m n appears\\nto be inverted. The reason for this is not hard to find.\\nRays of light pass out from the point m in all directions.\\nOne ray takes the direction of the line m b e. The mind", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0353.jp2"}, "350": {"fulltext": "326\\nPHYSICS\\nconceives that it sees m in the straight line e h at m For\\nthe same reason the image of n appears at n! i. e., the image\\nof the arrow appears to point in the opposite direction from\\nthe way the arrow itself points. JSTone of the rays of light\\nwhich start from the points m and n and fall upon the lens\\n.n\\nn\\nhn\\nFig. 225. Enlarged and inverted image.\\ncan reach the eye except those which pass through i and\\nas represented all others will be bent, according to the law\\nof refraction, so as to pass one side or the other of the eye.\\n311. The Path of Rays of Light exhibited by Crayon-\\ndust Measuring the Focal Distance of a Lens. When the\\nlens is held in sunlight and plenty of dust is made to\\nfloat in the air around it, by beating blackboard erasers or\\ndusty clothing near it, the rays of light are easily traced\\nby means of these reflecting particles, and they are seen to\\nmeet and cross, forming two cones of light as represented\\nin Fig. 226. The points where the apices of the cones\\nmeet is the principal focus, and its distance from the lens\\nmay be measured.\\nThese cones of light may be traced by using a screen.\\nWhen the screen is brought against the face of the lens, the\\ncircle of light upon it is about the size of the lens. If the\\nFig. 226.\u00e2\u0080\u0094 Principal focus.\\nscreen is placed halfway between the lens and the focus,\\nthe circle of light has about half the diameter of the lens", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0354.jp2"}, "351": {"fulltext": "REFRACTION OF LIGHT 327\\nits area is therefore one quarter as great as in the first posi-\\ntion, and the intensity of its light four times as great.\\nWhen it is placed one quarter of the distance from the\\nfocus to the lens its circle of light is one quarter as broad\\nand its area one sixteenth as great and the intensity of its\\nlight sixteen times as great as at the first position. At the\\nfocus it is a point of light of dazzling brightness, the heat\\nof which is sufficient to burn a hole in paper when the\\nexperiment is tried in the brightest sunlight. The focal\\ndistance can be readily measured by placing the screen\\nwhere the cross-section of the cone of light is nearest to a\\npoint and measuring the distance from the lens to the\\nscreen.\\n312. Pictures formed at the Focus of a Lens. When a\\nlens is held before a screen at its focal distance, an inverted\\npicture of distant objects is formed upon the screen. The\\nobjects in this case are so far away that rays of light from\\nthem are nearly parallel. When objects are brought nearer\\nto the lens the screen must be moved farther away from\\nthe lens in order to receive the picture. A candle flame\\nis a good object to experiment with, because it furnishes\\nbrighter rays of light than are reflected from objects in\\ngeneral. When the screen is placed so that a picture of\\nthe candle is formed upon it by the lens, the candle and\\nscreen occupy the positions of one pair of conjugate foci.\\nIf either one of these is brought nearer to the lens, it is\\nfound necessary to remove the other farther away, and\\nvice versa. When a photographer takes a picture of a\\nperson sitting very near his instrument, he draws out the\\ncamera so as to move the plate which is to receive the\\npicture farther away from the lens and when the person\\nsits farther from the instrument, the operator moves the\\nplate nearer to the lens by contracting his camera.\\n313. To illustrate how a Lens forms a Picture. It may\\nbe easy to see how a lens magnifies and inverts, but why\\nshould it form a picture at all", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0355.jp2"}, "352": {"fulltext": "328 PHYSICS\\nIf an object were placed before a screen without a lens\\nbetween them, light would be reflected from every point\\non the object to every point on the screen, so that each\\npoint on the screen would receive an equal amount of\\nlight from each and all points of the object. In order to\\nhave a picture formed, each point of the object must send\\nits light to one, and only one, point on the screen. This is\\nbrought about by the lens, as will be seen by reference to\\nFig. 227. All the rays of light which pass out from the\\nFig. 227.\u00e2\u0080\u0094 Conjugate foci.\\npoint m and fall upon the lens are collected at the point\\nm This is one pair of conjugate foci. In the same way\\nall the rays which pass from n. to the lens are collected at\\nn\\\\ and these form another pair of conjugate foci. But\\nwhen the screen is placed in focus for the light from m\\nand n it is found to be out of focus for light from the\\npoints o and p, whose conjugate foci are found to be\\nfarther away from the lens than m and n are, because\\nthe points o and p are nearer the lens than m and n are.\\nThis consideration is important only when the object is\\nnear to the lens, for only then would the difference be-\\ntween the distance of m and o from the lens be appreci-\\nable. If, however, a photographer should attempt to take\\na picture of a group of persons formed in a straight line\\nhaving his camera near the group, the individuals at the\\nextremities of the group could not be in focus at the same\\ntime with those in the center.\\n314. Material of Lenses.\u00e2\u0080\u0094 The lenses used for optical\\npurposes are made of flint glass. This is a double silicate\\nof potash and lead. The lead makes the glass much more", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0356.jp2"}, "353": {"fulltext": "REFRACTION OF LIGHT 329\\ndense, and gives it, consequently, a greater refractive index.\\nFor the same reason flint glass is used for the cut glass of\\ntableware and toilet articles. Their cut facets have a very\\nbrilliant effect on account of refraction.\\n315. Familiar Illustrations of Lenses. Very many objects\\nact as lenses. When the eye is held near to a drop of\\nwater upon a window pane, an inverted picture of the out-\\nside world is seen. If the sun is shining through it, a\\npiece of paper held near it will show that the rays are made\\nto converge to a point. Fish globes, and the globes used in\\ndrug-store windows, give magnified and inverted pictures.\\nThe neck of a small bottle magnifies so that if the bottle is\\nfilled to the neck with water containing microscopic objects,\\nmany of them may be seen. The animals which are usu-\\nally found in vinegar may be easily seen if the vinegar\\ncruse is filled to the neck.\\n316. The Simple Microscope. A microscope is an instru-\\nment for enabling us to see very small objects by producing\\nmagnified images of them. The simple microscope is usu-\\nally a double-convex lens, and in use is so placed that the\\nobject to be viewed is back of the lens at a distance less\\nthan the focal length. Under these conditions we have a\\nmagnified and erect image. The construction of the image\\nis of course purely imaginary. It has no real existence.\\nBut the imagination has the power of constructing such an\\nFro. 228. Simple microscope.\\nimage, just as it has the power of constructing images back\\nof a looking-glass. The rays that come from the object\\nare bent by the lens, as shown in Fig. 228, and enter the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0357.jp2"}, "354": {"fulltext": "330 PHYSICS\\neye at a wider angle than the direct rays would. This\\nangle, known as the visual angle, determines the apparent\\nsize of objects. The simple microscope increases this angle,\\nand consequently makes the object seem larger.\\n317. Compound Microscope. In its simplest form .the\\ncompound microscope consists of two lenses, the objective\\ncd, and the eyepieces ab (Fig. 229). The two are mounted\\nFig. 229.\u00e2\u0080\u0094 Compound microscope.\\nin a tube on a suitable stand. In this way we have a\\ndouble magnification, and the power of a compound micro-\\nscope is equal to the product of the magnifying powers\\nof the objective and the eyepiece. The image is inverted.\\nIn practice the compound microscope is very compli-\\ncated in its construction. Both eyepiece and objective are\\nthemselves compound. In addition there are various ac-\\ncessories for biological, mineralogical, and technical work\\nthat make the instrument quite an elaborate piece of mech-\\nanism.\\n318. The Telescope is an instrument for viewing objects\\nfrom afar. There are two classes the reflecting and the\\nrefracting. The latter are of the greater importance, but\\nthe former have played a historic part in astronomy, and\\nare still doing good service in both England and France.\\nThe refracting telescope is, in its elements, very similar to\\nthe compound microscope. It consists of an objective and\\neyepiece.\\nIn astronomical telescopes it is desirable that the objec-\\ntive should be as large as possible in order to include much\\nlight. The mechanical difficulties in the way of producing", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0358.jp2"}, "355": {"fulltext": "REFRACTION OF LIGHT 331\\nlarge refractors are very great, but they have been success-\\nfully overcome. The construction of such an instrument\\ninvolves the combined skill of several nations. The glass\\nis usually cast in France. The largest lenses, so far, have\\nbeen ground by the Clark Brothers, in Cambridge, Mass.\\nThe mountings and requisite machinery are made where\\nmost convenient. The largest lens yet made is the giant\\nobjective of the University of Chicago, and is located at\\nLake Geneva, Wis. It is 40 inches in diameter. Next to\\nthis comes that of the Lick Observatory, in California 91\\ncentimetres, or 35.82 inches, in diameter. The objective at\\nthe Imperial Eussian Observatory at Pulkowa, also made by\\nthe Clarks, is 76 centimetres, or 29.92 inches, in diameter.\\n319. The Human Eye. Most wonderful of all optical\\ninstruments is the human eye, and also the most imper-\\nfect. Looking at the eye, what we see first is the trans-\\nparent, bulging cornea, which is a modification of the outer\\ncoat of the whole eyeball,\\nthe white of the eye, or\\nthe sclerotic coat (Fig.\\n230).\\nImmediately back of\\nthe cornea there is a cav-\\nity filled with a liquid\\nknown as the aqueous hu-\\nmor. Back of this cavity\\nthere is a muscular screen,\\nthe iris, Which is annular FlG 230 ._SectioB of the human eye.\\nin form, and gives color to\\nthe eye. The opening in the iris is known as the pupil.\\nUnder the influence of strong light the iris contracts, and\\nthe pupil becomes very small, so as to shut out as much\\nlight as necessary. In the dark, or in subdued light, the\\nmuscles relax and the pupils become larger. Directly back\\nof the iris is the crystalline lens. It is transparent, and\\ntough and elastic. The interior of the eyeball is filled with", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0359.jp2"}, "356": {"fulltext": "332 PHYSICS\\na jellylike substance, the vitreous humor. The innermost\\nlining of the eyeball is the retina, formed by an extension\\nof the optic nerve leading directly to the brain. Between\\nthe retina and the sclerotic coat is a black pigment, the\\nchoroid coat.\\nIn its operation the eye is quite similar to a photo-\\ngraphic camera. The crystalline lens is double convex,\\nand forms an inverted image on the retina. The retina\\nmay be compared to the sensitive plate of the photographic\\ncamera, and the pupil, or opening in the iris, which serves\\nto admit more or less light, may be compared to the dia-\\nphragms, or stops, used for the same purpose in the cam-\\nera. So far it is very simple and well understood. But\\nour explanation ends here. As a physical fact, the image\\non the retina means simply light-waves of varying wave\\nlength and intensity, and these have varying effects upon\\nthe nerves of the retina. All these complex impulses pass by\\nmeans of the optic nerve to the brain, and it is in the brain\\nthat we see. But how these nerve impulses get translated\\ninto a mental impression we are quite at a loss to explain.\\nWe have said that the human eye is one of the most\\nimperfect of optical instruments. Few persons have per-\\nfect eyes.\\nCataract is caused by the crystalline lens becoming\\nopaque, and therefore ceasing to transmit distinct rays.\\nOperations are sometimes successfully carried out by\\nwhich the lens is removed altogether and sight restored,\\nthe humors in this case acting as the sole refracting me-\\ndium.\\nThe common defects of vision, such as short- and long-\\nsightedness and astigmatism, result from structural de-\\nfects. Clear vision requires that a distinct image shall be\\nformed on the retina. As the object, the crystalline lens,\\nand the retina are fixed in position, the focusing can only\\nbe brought about by a change in the curvature of the lens.\\nThis is a matter of muscular contraction, and in normal", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0360.jp2"}, "357": {"fulltext": "REFRACTION OF LIGHT\\n333\\neyes is done so quickly and unconsciously that we pass\\nfrom the contemplation of distant to near objects, and vice\\nversa, without the least difficulty. Xear-sightedness results\\nfrom too great curvature of the lens, so that it forms\\nDouble-concave glass for near-sightedness.\\nimages in front of the retina. It is remedied by the use\\nof glasses which cause rays of light to diverge (Fig. 231).\\nFar-sightedness, on the contrary, results from too little\\ncurvature of the lens, so that images form back of the ret-\\nina. It must be remedied by glasses which cause rays of\\nlight to converge (Fig. 232). It is a universal defect of old\\nage. Astigmatism means an irregular curvature of the\\ncornea, by which the eye is never in focus for all objects\\nin the field of vision, even at the same distance. It is\\nremedied by special lenses combining spherical and cylindri-\\nFig. 232. Double-convex glass for far-sightedness.\\ncal surfaces. Few people have eyes that are perfectly adapt-\\ned for parallel vision. The muscular eifect necessary to\\nbring them to parallel is a most frequent cause of headaches.\\n320. The Spectrum. We have seen that the index of\\nrefraction is in reality the ratio of the velocity of light in\\nthe first medium to the velocity in the second medium, and\\nwe have assumed that we had to deal with homogeneous", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0361.jp2"}, "358": {"fulltext": "334\\nPHYSICS\\nrays that is, rays of uniform wave length. But white light\\nis heterogeneous, consisting of wave lengths varying from\\n.0004 millimetres in the violet, to .0007 millimetres in the\\nred. These different rays are found to have different in-\\ndices of refraction, and to suffer unequal bending on pass-\\ning into a second medium. In consequence, the various\\ncolored rays which, taken together, make a beam of white\\nlight, on passing through a prism are separated, so that the\\nviolet rays are on one side and the red rays on the other.\\nIf they be allowed to fall on a screen, we have the fine suc-\\ncession of rainbow c61ors known as the spectrum (Fig. 233).\\nFig. 233.\u00e2\u0080\u0094 The spectrum.\\nNewton, in 1676, was the first to explain the matter. He\\ndistinguished seven primary colors, and named them violet,\\nindigo, blue, green, yellow, orange, and red. It will be\\nnoticed, in looking at the spectrum on the screen, that the\\nviolet has been turned out of its path the most, and the\\nred the least. The shorter violet waves are more retarded\\nthan the longer red waves in passing through the glass.\\nA single prism will give a spectrum, but the effect will\\nbe magnified by combining a succession of prisms, and so\\nincreasing the total dispersive power. The train of prisms\\nmay be arranged in a circle, so that the beam of light con-\\nstantly changes its direction and constantly widens (Fig.\\n234). On the other hand, prisms may be combined in pairs,\\nso as to neutralize one another (Fig. 235).", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0362.jp2"}, "359": {"fulltext": "REFRACTION OF LIGHT\\n335\\nThere seems to be no limit to the possible length of\\nether waves. To produce any effect upon us, however,\\nthey must fall within\\nvery well-defined limits.\\nThe longest ether waves\\napparently have no ef-\\nfect. As they shorten\\nthey manifest them-\\nselves as heat; as they\\ngrow still shorter they\\nbecome visible as light,\\nthen as a source of chem-\\nical activity, and finally\\nthey again pass beyond\\nthe range of our sensa-\\ntions. We perceive only\\na small part of the possi-\\nble waves.\\nColor. We should ex-\\npect these varying lengths of wave to affect us differently,\\njust as the different pitch in musical notes, which is due\\nto difference in length of air waves, and such, indeed, is\\nthe case. Color is the name given to this difference of\\nFig. 234. A train of prisms.\\nFig. 235. A pair of prisms.\\nsensation, and depends wholly upon wave length. Ordi-\\nnary sunlight contains waves of all lengths within the range", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0363.jp2"}, "360": {"fulltext": "330 PHYSICS\\nof vision and is distinguished as white light. The range\\nof vision lies between .0007 millimetres in the red and .0004\\nmillimetres in the violet. The following table shows the\\nwave length corresponding to the different colors\\nWave Length. Wave Length.\\nRed 0007 ram.\\nOrange 0006 mm.\\nYellow 00058 mm.\\nGreen 00053 mm.\\nBlue 00047 mm.\\nViolet .0004 mm.\\n321. The Invisible Spectrum. At both ends of the spec-\\ntrum we have a dark region, quite invisible to the eye, but\\nmanifesting itself by its effects. Beyond the visible red\\nwe have a region of dark heat rays, which manifest them-\\nselves if a delicate thermometer, such as a thermopile (see\\n271), be placed in their path. We call this the heat end\\nof the spectrum, and the colors at that end are sometimes\\nreferred to as warm colors. Beyond the visible violet we\\nhave another dark region, that of the so-called actinic rays,\\nwhich have the power of bringing about chemical reactions,\\nsuch as decomposing the sensitive silver salts used on photo-\\ngraphic paper, and of making certain fluorescent substances\\nsuch as fluor spar, quinine, and platino-cyanide of barium\\nvisible in the dark.\\nThe invisible spectrum has a far greater range than the\\nvisible. In musical terms we might say that the visible\\nspectrum covers about one octave. The heat spectrum\\nextends for five octaves below the red, and the actinic or\\nchemical spectrum for two octaves above the violet.\\nWe can easily imagine that the world would appear very\\ndifferent if our eyes were different in their power to per-\\nceive ether waves.\\n322. Complementary Colors. To produce white light it\\nis not necessary to have waves of all lengths present. It\\nis found, indeed, that two colors, if properly chosen, will\\nsuffice. As these extinguish each other, they are called\\ncomplementary colors. Thus, red and greenish-blue, orange", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0364.jp2"}, "361": {"fulltext": "KEFRACTIOX OF LIGHT 337\\nand Prussian blue, yellow and ultramarine, green-yelloAV\\nand purple produce white light when taken in pairs.\\nThere appear to be three primary color sensations\u00e2\u0080\u0094 red,\\ngreen (slightly yellowish), and violet (bluish) and when\\nthese are all excited at the same moment, the result is the\\nsensation of white. Xo two of these primary colors can be\\ncomplementary, for the third sensation would be lacking.\\nBut any one of the three is the complementary color of the\\nresult of the other two. Taking the pairs of colors men-\\ntioned above, this principle will be found to apply. Thus,\\ngreenish-blue contains both green and violet, and is there-\\nfore complementary to red purple, containing both red\\nand violet, is complementary to green-yellow, etc.\\nThe phenomena of color are very fascinating and almost\\nunending. In reality no objects are, properly speaking,\\ncolored. The sky is not blue, the grass is not green, the\\nrose is not red. They appear so to us because of their\\neffect on white light. The color ascribed to them is the\\ncolor they reject. A bit of red glass is one that absorbs\\nthe complementary color, greenish-blue, and allows the red\\nlight to pass through, or else reflect it to us. If such a\\npiece of glass be put into the fire, the red color remains\\nso long as the glass is cooler than the fire that is, so\\nlong as it is absorbing green. The color disappears when\\nthe glass has the same temperature as the source of heat\\nback of it, for then the radiation emitted and absorbed just\\nbalance each other. If the glass be the hotter, it appears\\nblue-green, for it is emitting more radiation than it is ab-\\nsorbing. In general, we may say that substances emit radia-\\ntions of the same wave length that they absorb.\\nThe Color Wheel The blending of several colors into\\none impression may be capitally shown by means of a rotat-\\ning wheel or color-whirler (Fig. 236). Disks of colored\\ncardboard may be attached and made to rotate with the\\nwheel. Thus a disk having alternate sectors of black and\\nwhite, when rotating appear a uniform gray. If the white\\n23", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0365.jp2"}, "362": {"fulltext": "338\\nPHYSICS\\nsectors are larger, it will be a light gray if smaller, a dark\\ngray. So red and blue produce purple. Complementary\\ncolors produce white. A disk having all the colors of the\\nspectrum, properly proportioned, will produce white. The\\nvarious pairs of colors opposite to one another in the circle\\n(Fig. 236) are complementary and will produce white when\\nconfused together by rapid motion.\\nSunlight, according to Professor Rood, contains in 1,000\\nparts the following ingredients\\nGreen and blue-green. 134 parts.\\nPrussian blue 32\\nBlue 40\\nRed 54 parts.\\nOrange-red 140\\nOrange 80\\nOrange-yellow 114\\nYellow 54\\nGreen-yellow 206\\nYellow-green 121\\nUltramarine and\\nviolet\\nViolet\\nblue-\\n20\\n5\\nAs the pigments used in coloring the pasteboard upon\\nthe color wheel are impure colors, one must not be disap-\\npointed if the impressions are somewhat muddy. They\\nare, however, enough to the point to\\nillustrate the truth of what has been\\nsaid. The art of color mixing in\\npainting is far from being the sim-\\nple matter it might at first seem,\\nchiefly because of the tendency to\\nchemical change which most pig-\\nments have.\\nIn modern picture windows,\\nwhich in the hands of Tiffany and\\nLa Farge have become genuine\\nworks of art, the effects are often produced by doubling\\nor even tripling the glass. Eobes of royal purple are thus\\nobtained by separate thicknesses of blue and ruby glass.\\n323. Fluorescence and Phosphorescence. It is very plain\\nthat if by any operation we could change wave length of\\nradiations, we should change their character. Retarding\\nFig.\\nGreen\\n236. Complementary-\\ncolors.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0366.jp2"}, "363": {"fulltext": "REFRACTION OF LIGHT 339\\nrapidity of vibrations and increasing the wave lengths\\nmight change chemical rays to light rays and light rays\\nto heat rays, or change light rays of one kind into those\\nof another kind. Quite a number of substances possess\\nthis power. Sulphate or quinine solution in the ultra-\\nviolet emits a pale-blue light; uranium glass gives a\\nbrilliant green fluorescein gives a beautiful green. The\\ncommon mineral fluorite, CaF 2 has the same power, and\\nhence the name fluorescence has been given to the phe-\\nnomenon. The platino-cyanide of barium is even more\\npowerful. Its ordinary color is a dull yellow, but in the\\nultraviolet it gives a magnificent yellowish-green light.\\nPhosphorescence, the power which certain substances\\nhave of emitting light in the dark after due exposure to\\nstrong light, is a similar property, but more persistent in\\ncharacter. The so-called luminous paints, made usually\\nof sulphide of barium, BaS, have this property, and serve\\nto call our attention to the house number, the match box,\\nand other articles usually sought for in the dark.\\nBut of far greater importance than even these beautiful\\nphenomena is the change of wave length which takes place\\nby the absorption and radiation again which occur in all\\nforms of matter, since upon these depend very largely the\\nhabitability of the globe itself. The light radiations from\\nthe sun are thus changed by the earth into waves perhaps\\ntwenty times as long as the longest waves that are visible.\\nOur hot-beds are constructed upon this principle. The\\nlight-waves pass through the glass freely, but when they\\nappear as heat waves they are imprisoned.\\n324. Temperature and Color.\u00e2\u0080\u0094 The radiations given off\\nfrom a slightly heated body are invisible. As the tempera-\\nture rises, the vibration frequency of the radiations appears\\nto rise with it. If a platinum wire be gradually heated, by\\npassing an electric current through it, a spectral gray color\\nis emitted at about 400\u00c2\u00b0 C, and the wire appears as a dark-\\nred line at 525\u00c2\u00b0. As the temperature continues to rise,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0367.jp2"}, "364": {"fulltext": "3i0\\nPHYSICS\\nwaves of shorter and shorter lengths are constantly added,\\nand the wire appears orange, then yellow, and finally in-\\ntensely white. We are unable to perceive the colors toward\\nthe violet end of the spectrum because they are masked by\\nthe longer wave lengths already present. But the colors\\ngreen, blue, and violet become visible if the longer wave\\nlengths are filtered off by suitable glass.\\n325. Ro ntgen Rays. In the year 1895, Professor W. C.\\nEontgen, of the University of Wiirzburg, announced his\\ndiscovery of a new kind of radiation, which he modestly\\ncalled X-rays, but which are more frequently designated by\\nthe name of their discoverer. The rays themselves are in-\\nvisible, but when allowed\\nto fall upon certain phos-\\nphorescent material, such\\nas barium platino-cyanide\\nor calcium tungstate, they\\ncause it to emit rays of\\nsuch length as to affect the\\neye. They also have the\\npower to effect chemical\\nchanges in a photographic\\nplate. All bodies are trans-\\nparent to these rays, but\\nin varying degrees. If, for\\nexample, we lay a hand\\nupon the holder contain-\\ning a photographic plate,\\nand let the Eontgen rays\\nfall upon the hand, and\\nthen develop the plate, we\\nfind that the rays passed\\nthrough the flesh of the\\nhand more readily than through the bones, and through\\nthe bones more readily than through the metal finger ring,\\nas shown by the varying degree to which chemical change\\nFig. 237.-\\n-Photograph by Eontgen\\nrays.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0368.jp2"}, "365": {"fulltext": "REFRACTION OF LIGHT\\n341\\nwas effected in the plate underneath these different parts\\nof the hand (Fig. 237). Thus surgeons may locate a for-\\neign body, such as a bullet, in the flesh without probing\\nfor it and thus, too, they may locate abnormal growths,\\nsuch as internal tumors, etc.\\nFig. 238. Apparatus for Eontgen rays.\\nThe Eontgen rays are produced at the point where\\nkathode rays, which have been discharged into a high\\nvacuum, strike upon a platinum screen or the walls of the\\nvessel in which the discharge takes place. In order to\\nobtain the necessary voltage to drive the electric current\\nthrough the high vacuum, an induction coil may be used.\\nFig. 238 shows the vacuum tube, the induction coil, and\\nthe fluoroscope, into which the observer looks while hold-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0369.jp2"}, "366": {"fulltext": "342 PHYSICS\\ning it turned toward the vacuum tube. The larger end of\\nthe fluoroscope has a screen coated with calcium tungstate or\\nbarium platino-cyanide, which fluoresces when the Ront-\\ngen rays fall upon it.\\n326. Herz Waves. When a discharge takes place be-\\ntween the knobs of an electrical machine (Fig. 137), or an\\ninduction coil (Fig. 186), in addition to the light rays\\nwhich emanate from the spark, invisible rays pass out in\\nevery direction which have wave lengths of several metres.\\nThese are sometimes called Herz waves, because of the re-\\nsearches in that field made by a German physicist, Heinrich\\nHerz (1857-1894). Although brick walls are transparent\\nto these waves, they are reflected and refracted by certain\\nother substances. It is with these rays that wireless teleg-\\nraphy is carried on. By means of suitable receiving instru-\\nments, signals have thus been transmitted as far as fifty\\nmiles.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0370.jp2"}, "367": {"fulltext": "CHAPTEE XXX\\nPOLARIZATION OF LIGHT\\n327. Transverse Vibrations. To understand polarization\\nwe must go back a moment to the nature of the light waves\\nthemselves. While we represent light rays as going out\\nfrom a luminous body in all directions in perfectly straight\\nlines, the real motion is in a plane at right angles to these\\nrays, and in all possible directions. If we fasten a cord at\\none end, and, holding the other end in our hand, make the\\ncord ripple in all possible planes, we shall have a rough rep-\\nresentation of a real light ray. If the\\nmotion of the cord is projected upon the\\nsurface to which the end is fastened, we\\nwill have a series of radial lines, as\\nshown in Fig. 239, which represents\\nsome of the planes in which the ether\\nvibrates. To represent every possible\\nplane of vibration, we should have to\\nturn this circle of radiant lines into a\\nsolid black circle. In thinking, then, of a ray of light, we\\nmust think of it as vibrating in all possible directions, in\\na plane at right angles to its line of propagation. When\\nsuch a ray passes through a homogeneous medium, like the\\nether, no particular result follows but when it passes\\nthrough certain media to be described, we have the inter-\\nesting phenomena of polarization.\\n328. Polarization of Light. A cord with one end fas-\\ntened and the other end held in the hand may be rippled in\\nFig. 239.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0371.jp2"}, "368": {"fulltext": "344\\nPHYSIOS\\nany and every plane so long as it passes freely through the\\nair. If now it passes through a couple of vertical gratings,\\nthe ripples must all be in a vertical plane. Had the grat-\\nings been horizontal, only horizontal ripples would have\\nbeen possible. If one grating be vertical and the other\\nhorizontal, no ripples can pass to the end of the cord, for\\nonly vertical ripples can pass the second grating conse-\\nquently everything stops at the second grating, and beyond\\nthat there is no motion (Fig. 240). Something like this\\nappears to happen in certain cases with light, and we call it\\npolarization of light.\\nFig. 240. Apparatus to illustrate polarization of light.\\nTo illustrate this we may cut two thin slices of tourma-\\nline parallel to the axis of the crystal. These appear to act\\nupon a ray of light as the gratings, represented in Fig. 240,\\nact upon the vibrating cord. When these slices are arranged\\nso that their axes are parallel, as in Fig. 241, a b, the ray of\\nlight passes through. If they are crossed obliquely, as in\\na b\\\\ we have partial extinction of the ray. If they are\\ncrossed at right angles, as in A B, we have complete extinc-\\ntion of the light. We believe that when the ray of light", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0372.jp2"}, "369": {"fulltext": "POLARIZATION OF LIGHT 345\\npasses through the first of these slices of tourmaline, all its\\ntransverse vibrations are cut off except those parallel to the\\naxis of the crystal. A ray of light which has thus been\\nrobbed of all its vibra- a\\ntions except those in 0%. B A.\\none plane is said to be\\npolarized, and the first\\ncrystal of tourmaline\\nthrough which the ray Fig. 241.\u00e2\u0080\u0094 Tourmaline polarizers and\\nanalyzers.\\npasses is called a polar-\\nizer. The second crystal of tourmaline is called an analy-\\nzer, because it is by turning this at right angles to the\\nother, and thus extinguishing the light, that we may deter-\\nmine whether or not a ray has been polarized.\\nLight may be polarized by reflection from a plane mir-\\nror. It is also polarized by refraction, and various sub-\\nstances, such as Iceland spar or tourmaline, if cut in the\\nproper manner, may serve as analyzers. If a ray of light\\nmake with the perpendicular to a mirror an incident angle\\nof about fifty-seven degrees, the reflected ray will be\\npolarized.\\n329. Applications of Polarized Light. If we arrange a\\nprojecting lantern so that we may introduce a polarizer and\\nan analyzer (somewhat separated) between the condensing\\nand converging lenses, we shall be able to exhibit the most\\ninteresting and beautiful phenomena of polarized light.\\nBy simply turning the analyzer, we may show the vary-\\ning degrees of light, from full illumination when polarizer\\nand analyzer are parallel, to complete extinction when they\\nare crossed.\\nGeologists now study the rocks by making very thin\\nsections, mounting them on glass, and then examining them\\nby means of polarized light. By turning the analyzer we get\\na beautiful display of changing color. We may, by means\\nof polarized light, test the genuineness of certain gems.\\nWonderfully beautiful experiments may be made by dis-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0373.jp2"}, "370": {"fulltext": "346 PHYSICS\\nsolving any crystallizable compound, such as salicin or\\nurea, in alcohol, spreading a film of the solution on glass,\\nand introducing the glass, while still wet, between the\\npolarizer and the analyzer. As the solution evaporates,\\ntiny crystals appear on the plate, and with the turning of\\nthe analyzer we have the screen covered with a display of\\nrare beauty and variety.\\n330. Rotation of the Plane of Polarization\u00e2\u0080\u0094 It is found\\nthat certain substances, such as quartz cut perpendicular\\nto its axis, and certain solutions, such as sugar, when intro-\\nduced between the polarizer and analyzer, rotate the plane\\nof polarization. The amount the plane of polarization has\\nbeen rotated is found by turning the analyzer.\\nIn the case of sugar, the angle depends upon the strength\\nof the solution, and this gives us a convenient and accurate\\nmethod of determining the strength of such solutions.\\nIt was Faraday s great discovery that a wave of polar-\\nized light may be rotated by means of a magnet.\\n331. The Identity of the Various Forms of Radiation.\\nAll forms of radiation may be polarized, may be refracted,\\nmay be reflected, and may be transformed, the one into the\\nother. We believe that they differ from one another only\\nin wave length, and consequently in the rapidity of vibra-\\ntion. We believe that they are all rays of ether, having\\ntransverse vibrations. Those with longest wave lengths\\nand slowest vibrations produce electrical phenomena, those\\nwith the next shortest wave length and next fastest vibra-\\ntions produce heat phenomena, those with the next shortest\\nwave length and next fastest vibrations affect the optic\\nnerve with what we call light, and those with the shortest\\nwave length and fastest vibrations are called chemical or\\nactinic rays, because of their power to effect chemical\\nchanges. As might be expected, all ether vibrations tend\\nto effect chemical changes that is, dissociate the atoms\\nin the molecule and all ether vibrations tend to effect\\nmolecular motion, which is heat.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0374.jp2"}, "371": {"fulltext": "SOUND\\nCHAPTER XXXI.\u00e2\u0080\u0094 General Principles\\n332. Sources.\\n333. Transmission. Figs. 242 and 243.\\n334. Loudness Re-enforcement.\\n335. Pitch. Figs. 244, 245, 246, and 247.\\n336 Quality. Fig. 248.\\n337. Reflection\u00e2\u0080\u0094 Echoes. Fig. 249.\\n338. Velocity.\\n339. Vibrations of Strings. Fig. 250.\\n340. Sympathetic Vibrations.\\nCHAPTER XXXII.\u00e2\u0080\u0094 Music\\n341. Music and Noise.\\n342. The Scale.\\n343. The Octave. Fig. 251.\\n344. Vibration Ratio of the Musical Scale. Fig. 252.\\n345. Musical Score Fig. 253.\\n346. Melody. Fig. 254.\\n347. Chords. Fig. 255.\\n348. Harmony. Fig. 256.\\n349. Counterpoint, Fig. 257.\\n350. Reading Music.\\nCHAPTER XXXIII.\u00e2\u0080\u0094 Miscellaneous Application\\n351. Speaking. Fig. 258.\\n352. Hearing.\\n353. Limits of Sound.\\n354. The Phonograph.\\n355. The Telephone. Fig. 259.\\n347", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0375.jp2"}, "372": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0376.jp2"}, "373": {"fulltext": "CHAPTER XXXI\\nGENERAL PRINCIPLES\\n332. Sources. All sound-producing instruments must\\nbe in a state of rapid vibration. A tuning fork while pro-\\nducing a sound may be shown to be in vibration by touch-\\ning it to a pith ball suspended by a thread. The ball will\\nbound away as if it had been struck and truly it has, but\\nso quickly that our eyes can not see the blow. Or, if the\\nprongs of a sounding fork be dipped into water it will\\nthrow a spray, and the fork will soon be brought to rest.\\nA sounding bell, if touched with the finger, will instantly\\ncease to produce sound. The long strings of the piano\\nmay be seen to vibrate while sounding. A pin or other\\nlight object will dance upon the sounding board while the\\npiano is played, and a heavy organ pipe can be felt to be in\\nvibration while producing a sound.\\n333. Transmission. In order that a sounding body may\\nproduce in our ears the sensation of sound, some medium\\nsolid, liquid, or gas must intervene. If we take the medium\\naway, our sensation of sound ceases, no matter how vigor-\\nously the sounding body may keep up its vibrations. If,\\nfor example, we put a bell run by clockwork under the\\nreceiver of an air pump, and either suspend it by threads,\\nor let it rest on thick wads of cotton or wool, the sound\\nwill grow fainter and fainter as the exhaustion proceeds,\\nand will finally cease altogether when a vacuum has been\\nattained. We are justified in believing that the medium is\\nnecessary for the transmission of sound, because when we\\n349", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0377.jp2"}, "374": {"fulltext": "350\\nPHYSICS\\n6 o\\n6 o\\nFig. 242.\\ntake the medium away the sound ceases to reach our ears.\\nExperience teaches us that sounds are even more readily\\ntransmitted through solids than through gases. If one\\nputs his ear against a\\nlong wire or a stick of\\ntimber, the scratching\\nof a pin at the other end\\nmay be readily heard\\nthrough the solid when\\nit can not be heard at\\nall through the air. So\\nalso liquids transmit\\nsound more readily than\\ngases. The denser the medium the more readily it trans-\\nmits sound. Also the more elasticity a substance has the\\nmore readily does it transmit sound. Fig. 242, representing\\na number of billiard balls suspended in a row, each an inch\\nor two from its neighbor, may serve to illustrate how sound\\nis transmitted through the air or any other medium. Sup-\\npose the ball at one end of the line to be pulled one side\\nand allowed to swing against its neighbor, the second ball\\nwill swing over and transmit the blow to the third ball,\\nwhich will in turn pass on the blow to the next, and so on\\nthrough the line. If these balls are of ivory or glass, or\\nany elastic substance, the wave will quickly run through\\nthe line without much loss but if the balls are of some\\ninelastic substance, as lead or putty, the impulse rapidly\\nloses force. Thus it is that sound appears to be transmitted\\nthrough any medium. The sound must be produced by a\\nbody in vibration a column of air, as in the organ pipe\\nand all wind instruments or a stretched string, as in the\\npiano, violin, harp, and all stringed instruments or a\\nmembrane, as in the drum or a metallic plate, as in the\\ncymbal, or in fact anything capable of vibration and these\\nvibrations are transmitted through the air to our ears,\\nwhich are constructed so as to receive the impression and", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0378.jp2"}, "375": {"fulltext": "GENERAL PRINCIPLES 351\\ntranslate it into our sensation sound, which is conveyed to\\nthe brain by the auditory nerve.\\nSounds differ so much that it is hard to realize that\\nthey all are the result of the vibration of the air. The air,\\nbeing a perfectly elastic fluid, and transmitting pressure\\nequally in all directions vibrates from a center outwardly\\nin all directions. Suppose a disturbance to be set up at\\nany one point, as, for instance, by the vibration of a bell\\n(Fig. 213), the sides of the bell in vibration move first in\\none direction and then in the other, and the air receives\\nthe blows of the quivering metal in just the way that the\\npith ball did from the tuning fork (section 332) and not\\none blow, but many, up to two or three hundred in a second.\\nEach time then the air receives a blow, it is compressed,\\nand a spherical wave of compression is set up. But between\\nFig. 243.\u00e2\u0080\u0094 Sound waves.\\neach blow the metal draws back, and consequently sets up\\na similar spherical wave of rarefaction. A sound wave is\\nspherical in shape, and consists of alternate spherical shells\\nof compressed and rarefied air. There are three respects\\nin which sounds differ loudness, pitch, and quality.\\n334. Loudness. The harder we strike the tuning fork\\nthe louder its sound. If we examine its amplitude of vibra-\\ntion, by dipping it into water, or touching it to a pith ball,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0379.jp2"}, "376": {"fulltext": "352 PHYSICS\\nwe shall get a correspondingly vigorous fountain or lively\\nblow. It must be that the vibrations of the loud-sounding\\nbody are more ample than those of the quieter body. If\\nwhen the tuning fork is sounding very feebly it is dipped\\ninto water, the resulting splash will be found to be corre-\\nspondingly feeble. Our entire experience leads us to believe\\nthat the loudness of a sound depends upon the amplitude\\nof the wave that makes it that is, upon the degree in\\nwhich the air is compressed and rarefied.\\nRe-enforcement. The tuning fork set vibrating and\\nsimply held in the hand produces a very feeble note. To\\nmake it audible in a classroom or lecture hall, the fork\\nmust be held against some elastic body of larger surface,\\nsuch as a wooden table top, a door, or an ordinary sound-\\ning-board. In this case the larger body is also set into\\nvibration, and the surrounding air is more deeply affected.\\nIn most musical instruments we have such an arrangement\\nfor re-enforcing the sound, and to give it the volume needed.\\nLoudness is seldom measured in any strict way. In\\nmusic it is indicated by some word usually borrowed from\\nthe Italian, such as forte, loud fortissimo, very loud piano,\\nsoft pianissimo, very soft, etc. In physics it is represented,\\nrather than measured, by the amplitude of the wave. The\\nintensity of two sounds may be compared by observing the\\ndistance at which they may be heard. The sound wave,\\nbeing spherical in form, is represented at any instant by\\nthe surface of a sphere whose radius is the distance from\\nthe sounding body. We know from geometry that the sur-\\nface of a sphere is equal to 4 w r 2 Hence the surface de-\\npends on r 2 or the square of the distance. By the prin-\\nciple of virtual velocity, the original energy spread over this\\nlarger space must be less intense in exact proportion so\\nwe say that the intensity of any given sound varies inversely\\nas the square of the distance. There is a slight variation\\nfrom this, due to the fact that some of the energy of sound\\nis changed to heat.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0380.jp2"}, "377": {"fulltext": "GENERAL PRINCIPLES\\n353\\nOAA/VWVWWV\\nFig. 244.\\n335. Pitch. The term pitch is used in music and in\\nordinary speech to indicate the position of a sound in the\\nmusical scale. The pitch is high if the note is up toward\\nthe treble the pitch is low\\nif the note is down toward Vl/l/WWW\\\\AAAAA/\\\\AAAAAAy\\nthe bass. And this is quite\\nindependent of loudness. We\\nall know that women s voices\\nhave higher pitch than men s,\\nand children s voices than older people s. However un-\\nmusical one may be, one is pretty sure to be aware of the\\nfact that the notes on the right-hand side of the keyboard\\nof a piano or organ are much higher in pitch than the\\nnotes on the left-hand side of the keyboard. The idea of\\npitch in sound is a perfectly definite one. Pitch trans-\\nlated into vibration is equally definite. If two tuning forks\\nof different pitch have a bristle attached to each, and if\\nduring vibration each bristle be allowed to trace a line by\\ndrawing the fork over smoked glass, it will be found that\\nthe tuning fork of higher pitch, the shorter fork, will trace\\nFig. 245.\u00e2\u0080\u0094 Savart s wheel.\\na greater number of waves, giving evidence of being in\\nmore rapid vibration than the tuning fork of lower pitch,\\nthe longer fork (Fig. 244). We say then that pitch depends\\nupon the number of vibrations per second.\\nWe may determine the number of vibrations which cor-\\n24", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0381.jp2"}, "378": {"fulltext": "354 PHYSICS\\nrespond to any given pitch by various devices. One is\\nSavart s wheel (Fig. 245), which consists of a large-toothed\\nwheel capable of rotation, and provided with\\na flexible tongue against which the teeth\\nmay strike. The number of teeth, multi-\\nplied by the number of turns per second,\\nwill give the number of blows the flexible\\ntongue receives, and so the pitch of the\\nFig. 246. resultant note. The faster the wheel turns\\nthe higher the note. If, for example, we\\nwish to measure the vibration frequency of a given tuning\\nfork, we have only to set it into vibration, and then rotate\\nthe toothed wheel until it gives out the same note. An-\\nother simple device is illustrated in Fig. 246. The disk is\\nmade to rotate in front of a tube through which a stream\\nof air is passing. Each time a hole in the disk passes the\\nend of the tube a puff of air passes through it. When the\\ndisk moves slowly we hear each separate puff; but when\\nthe disk moves so rapidly that we may not distinguish the\\nseparate puffs, we begin to recognize a tone which rises in\\npitch as the speed of the disk increases. By attaching to\\nthe disk a mechanism similar to that used in the cyclometer\\nof a bicycle, we may, with watch in hand, count the num-\\nber of revolutions, and from that the number of puffs per\\nsecond which correspond to a certain pitch of tone. When\\nthe tone compares in pitch to the middle C on the piano\\nit is found to have two hundred and fifty-six vibrations per\\nsecond. Fig. 247 represents an instrument for determin-\\ning pitch. It works upon the principle just stated, with\\nsome modifications in its mechanism. It is known as a\\nsiren.\\n336. Quality or Timbre. The Germans call this tone-\\ncolor. If a note of given pitch be sung by two voices, or\\nsounded by two instruments, say the piano and violin, it\\nwill be noticed that there is something distinctive about\\neach note, and we can generally recognize the source of the", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0382.jp2"}, "379": {"fulltext": "GENERAL PRINCIPLES\\n355\\nnote. It can not be a difference in the fundamental tone,\\nas the pitch is the same in all four notes. Yet so real and\\nsubtle is it, that it makes one voice or instrument agreeable\\nto our ear, and another voice or instrument disagreeable.\\nVon Helmholtz, the great German physicist, investigated\\nthe matter very carefully, and found that this difference\\nFig. 247.\u00e2\u0080\u0094 Siren.\\nin the quality of sound is due to overtones or secondary\\nsound waves that accompany the fundamental or major\\nsound, and give it so characteristic a coloring that no two\\nhuman voices, and no two instruments, even of the same\\nclass and make, ever sound precisely the same note. From\\na human and aesthetic point of view the quality of a sound\\nis its most valuable character. The tuning fork gives an", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0383.jp2"}, "380": {"fulltext": "356\\nPHYSICS\\nFig. 248\u00e2\u0080\u0094 Helmholtz\\nresonator.\\nalmost pure note, which, on account of its lack of shading,\\nfails to be acceptable to the ear. Helmholtz was the first\\nto measure the quality of a musical note by measuring the\\naccompanying overtones. For this\\npurpose he devised his resonators\\n(Fig. 248), hollow globes of thin brass\\nwith openings on opposite sides, the\\nsmaller one for insertion in the ear,\\nand the larger one for the reception\\nof the sound impulse. The inclosed\\nbody of air will vibrate in sympathy\\nwith one special note only, and hence\\nserves to detect that note in the midst\\nof many others. By having a series\\nof these resonators it is possible to\\ndetect the overtones accompanying any fundamental. This\\nmethod gives, however, only a partial measure, since the\\ntotal musical effect depends not alone upon the overtones\\nthemselves, but also upon their relative intensity.\\n337. Reflection, Echoes. If we place the chain of ivory\\nballs represented in Fig. 249 so that the last one shall be\\nnear to a wall, and then send an impulse along the line by\\nswinging the first ball against the second, this impulse\\nwill be reflected back\\nby the last ball strik-\\ning against the wall and\\nbounding back against\\nits neighbor. In like\\nmanner sound waves in\\nthe air are reflected by\\nwalls of buildings, moun-\\ntain peaks, etc. This is\\nwhat we call the echo.\\n338. Velocity.\u00e2\u0080\u0094 The velocity of sound in air may be de-\\ntermined as follows Two stations are selected at a known\\ndistance apart, and sharp noises, such as the report of a\\nFig. 249.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0384.jp2"}, "381": {"fulltext": "GENERAL PRINCIPLES 357\\ncannon or gun, are made at either or both stations, and the\\ntime that it takes for the sound to reach the other station\\nis carefully noted. The time at which the discharge took\\nplace is known to the observer at the second station either\\nby the flash or by an electric signal. Such experiments\\nhave been repeated very often and in different parts of the\\nworld, and while the results differ slightly, they all give\\nnearly the same result, viz., about eleven hundred feet per\\nsecond. We may count the seconds between the lightning\\nflash and the sound of the thunder and calculate our dis-\\ntance from the thunder cloud. We may see the steam\\npouring from the whistle of a distant steamship, and by\\nFig. 250.\u00e2\u0080\u0094 Sonometer.\\ncounting the seconds before the sound is heard calculate\\nits distance.\\nIt is evident that loudness, pitch, or quality have no\\neffect upon velocity for when we hear a band of musicians\\nplaying at a distance the loud tones and the soft tones, the\\ntones of high pitch and low pitch, and the tones of vari-\\nous quality, if played simultaneously, all reach the ear\\ntogether.\\n339. Vibration of Strings. A useful and standard in-\\nstrument for examining the vibrations of strings is the\\nsonometer, or monocliord (Fig. 250). A stretched string,\\ncapable of vibrating under varying tensions and lengths,", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0385.jp2"}, "382": {"fulltext": "358 PHYSICS\\nand capable of being replaced by other strings, is re-en-\\nforced by a sounding box made of dry, elastic wood. By\\nmeans of this instrument the following laws may be illus-\\ntrated and verified\\n1. Pitch varies with the material of the string.\\n2. Pitch varies inversely with the length.\\n3. Pitch varies inversely with the diameter.\\n4. Pitch varies with the square root of the tension.\\nWe may sum this up by saying that strings which are\\nheavy, long, thick, and slack, give a low note, while strings\\nwhich are light, short, thin, and tense, give a high note.\\nIn the piano the strings are tightly stretched steel wire\\nfor the treble, and steel wire wrapped around with copper for\\nthe bass. The keyboard is fixed, and when a key is struck\\nthe blow is transmitted by means of levers and hammers to\\nthe corresponding string. The wires are stretched between\\niron pins fastened to the frame of the instrument. The\\nlength of the wire is determined by the position of the\\nagraffe, or bridge, which rests directly upon the large spruce\\nsounding-board that forms the bottom of the piano box.\\nThe instrument is tuned by turning the pins and so chang-\\ning the tension of the strings. The position of the ham-\\nmers is a matter of great importance, since the blow on\\nthe strings determines the overtones. In most pianos the\\nstrings are struck at a distance of one seventh, one eighth,\\nor one ninth from the end, so as to bring out the desirable\\novertones. Different pianos differ in sweetness and tone\\nlargely because of their overtones and the greater or less\\nefficiency of their sounding-boards.\\nA modern grand piano, such as the Steinway, contains\\nforty thousand separate pieces of material. The piano, in\\nspite of many musical defects, is a singularly rich- instru-\\nment, since it offers such large opportunities for the play\\nof harmony. Not only may several notes be struck at once\\nin a given chord, but the combination of two parts the\\nbass and treble allows added richness and variety.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0386.jp2"}, "383": {"fulltext": "GENERAL PRINCIPLES 359\\nIn other stringed instruments, such as the violin and vio-\\nloncello, the vibrations are induced by means of a rosined\\nbow, and the sound is re-enforced by a box beneath the\\nstrings, a box which is of all forms for acoustical re-en-\\nforcement the most perfect in design. The much-prized\\ninstruments of Stradivarius, Amati, and Guarnerius, owe\\ntheir value to their perfect form, to the elasticity of their\\nwell-seasoned wood and marvelous varnish, and, some per-\\nsons think, to the fact that several subsequent generations\\nof master violinists have induced in them the habit of\\nharmonic vibration. Musically, the violin is much superior\\nto the piano the single notes are far richer by reason of\\nthe full set of harmonics present, and particularly of the\\nhigher harmonics.\\n340. Sympathetic Vibrations. The richness of the organ,\\npiano, and other musical instruments is due not only to\\nthe overtones accompanying the fundamental note, but also\\nto a second group of accompanying notes due to what is\\ncalled sympathetic vibration. If two tuning forks of the\\nsame pitch, and mounted on suitable resonator boxes be\\nplaced near each other and one of them set in vibration,\\nit can readily be shown that the second untouched fork is\\nalso vibrating. A pith ball brought in contact with the\\nfork will be thrown aside or, if the original fork be\\nsilenced, the second fork will be found emitting an unmis-\\ntakable note. Had the forks been of different pitch, no\\nsuch sympathetic reaction would have taken place. Simi-\\nlarly, if the loud pedal be pressed down, and a strong, pure\\nnote be sung into a piano, the string corresponding to that\\nnote will be set into vibration.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0387.jp2"}, "384": {"fulltext": "CHAPTEE XXXII\\nMUSIC\\n341. Music and Noise. We know the sensation differ-\\nences between music and noise. The one pleases by its\\nregularity and rhythm and by a certain anticipatory quality\\nwhich leads us to expect a given effect, and then gratifies\\nour sense of anticipation by giving us the effect. The other\\ndispleases us, and the more so the more sensitive our organi-\\nzation. It displeases by its irregularity. It must be said,\\nhowever, that the line between music and noise is not a\\nhard-and-fast one, even to musicians. There are certain\\npassages in the compositions of Wagner and of the more\\nstormy Eussian artists which are music to one school of\\nmusicians and noise to another school. However, we all of\\nus know in general the sensation differences between music\\nand noise. A vibrating tuning fork gives an undoubted\\nmusical note of very pure quality, while a door slammed\\ngives a decided noise. The tuning fork vibrates regularly,\\ngiving so many perfect waves per second, and, as we have\\nseen, traces an even, symmetrical line on smoked glass. If\\na visiting card is drawn slowly over the teeth of a saw we\\nhear the successive taps or noises of the card striking\\nagainst the teeth of the saw but if the card is moved very\\nrapidly, so that we may no longer recognize the distinct\\ntaps, the noise begins to assume the character of a tone.\\nSo it is with the puffs of the siren (335) so it is also with\\nthe sound of a buzz saw.\\n342. The Musical Scale. All nations have made such a\\nselection of musical notes, and have framed them into a\\n360", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0388.jp2"}, "385": {"fulltext": "MUSIC\\n361\\nseries known as the musical scale. This has varied greatly\\nin historic times, and even now we may not regard it as\\nquite fixed. The Greeks had what seems to us now a very\\nmeager and almost unmusical scale. It was, however, care-\\nfully thought out, and has practically formed the basis of\\nall modern music. The scale was greatly enriched during\\nthe middle ages, and particularly when music came into\\nsuch large service in the Church. The sacred music of\\nmediaeval times, especially in Italy and Germany, made great\\nand rapid advance toward modern perfection. All this\\nwork, however, was purely art work, and not as yet science.\\nThe musical scale that has thus come down to us is a\\nproduct of the rich, emotional, and aesthetic life of the\\nworld, and not of its thought. The older musicians knew\\nnothing of acoustics, knew nothing of vibration numbers,\\nand sound waves. They knew only what pleased the heart\\nand expressed its reverence and delight.\\n343. The Octave. Pitch depends solely upon the num-\\nber of vibrations per second but as soon as we begin to\\ncompare notes of definite pitch with one another we are\\nHIWIWWIWWillWWIW MlWIiff\\nA 4 B 4 C 3\\nC 2\\nc x\\nc\\nc\\nC\\nc 1\\nC ,V\\n.6 \u00c2\u00a730 32\\n64\\n128\\n256\\n512\\n1024\\n2048\\n4096\\nFig. 251.\u00e2\u0080\u0094 The piano keyboard.\\nstruck with the fact that when we have gone a certain dis-\\ntance in either direction the notes appear to be repeating\\nthemselves. They are higher or lower, it is true, but they\\nhave the same musical character. A corresponding rela-\\ntion is found to exist between their vibration frequencies.\\nTaking the note C, making 256 vibrations per second, it is\\nfound that the next note above it, C 1 that has the same\\nmusical character, makes 512 vibrations, or just twice as\\nmany as C. Above that the next similar note is C n with\\n1,024 vibrations. Then comes G m with 2,048 and C IV with", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0389.jp2"}, "386": {"fulltext": "362 PHYSICS\\n4,096 vibrations, and we reach the upper limit of the piano.\\nHad we gone down instead of up, we should have found the\\nfirst lower note similar to to be C l5 making just half the\\nnumber of vibrations, or 128. Below that comes C 2 with\\n64 vibrations, and still below that C 3 very far down among\\nthe thunderous notes of the bass, and making only 32 vibra-\\ntions per second. This is very near the lower limit of\\nmusical sound. C 3 to C IV covers about the range of an\\nordinary piano keyboard (Fig. 251). Between C and C 1\\ncustom has introduced six notes, and we designate them by\\nthe letters of the alphabet\u00e2\u0080\u0094 D, E, F, G, A, B. The scale\\nthus repeats itself every seven notes. This group of eight\\nnotes is called the octave. C n is two octaves above C C IV\\nis four octaves. Similarly, C 3 is three octaves below C.\\nThe scale may begin on any note of the octave, but it will\\nbe best to regard the scale beginning with C as a type.\\n344. Vibration Ratios of the Musical Scale. If we take\\nthe number of vibrations of the fundamental note of the\\nscale as unity, then its octave will be 2, and the interven-\\ning notes as follows\\nC D E F G A B C (1)\\ndo re mi fa sol la si do (2)\\n1 I I I I I V- 2 (3)\\n256 288 320 341 384 426| 480 512 (4)\\n(1) is the usual musical notation (2) is the notation com-\\nmonly used in singing (3) is the vibration ratios which hold\\nfor the scale whatever its position on the keyboard and\\n(4) is the working out of these ratios for the octave, begin-\\nning with the middle C.\\nIntervals. When we look closely at such a scale we see\\nthat the intervals are not all equal. The intervals between\\nmi and fa and between si and do are called half tones, and\\nthe other intervals are called whole tones, although the\\nwhole tones are not equal to each other, nor are the so-\\ncalled half tones half of any one of them. On the piano", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0390.jp2"}, "387": {"fulltext": "MUSIC\\n363\\nkeyboard each of the so-called whole tones are divided into\\nhalves by the black keys (see Fig. 252). This enables one to\\nI II III II III Hill II III il III II III II III\\nI I ii ITi i ii Mini ill in 1 mill 1 imili i iTTh 1 1 111\\n.B.C. c c, c c 1 c c m\\nA 4 B,C 3\\nC 3\\nC! C C\\nC\\n26 f30 32\\n64\\n128 256 512\\nFig. 252. Piano keyboard.\\n1024\\nbegin with do on any letter and bring in the half step\\nbetween m i and fa.\\n345. Musical Score. It is the custom to represent mu-\\nsical notes by conventional signs\\nI I s fc fc\\ns S\\nwhich are read whole note, half note, quarter note, eighth,\\nsixteenth, thirty-second, and sixty-fourth. These terms\\napply, not to the tone intervals, but solely to the time to\\nbe given to each tone. Five parallel lines constitute the\\nstaff on which the\\nnotes are to be --^-f-\\nplaced, and the po-\\nsition of the notes\\non the staff indi-\\ncates their pitch.\\nWhen the staff will\\nnot accommodate\\nall the score, addi-\\ntional lines, called\\nledger lines, are em-\\nployed. In music written for two hands, as the score for\\npiano and organ, separate conventions are used for the\\nright hand the treble clef, 3\u00c2\u00a3 and for the left hand the\\nbase clef, 2z Fig. 253 represents the position of the\\nletters upon the score.\\n346. Melody. The art of musical composition is per-\\nhaps the supreme act of which the human mind is capable.\\nFig. 253.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0391.jp2"}, "388": {"fulltext": "364\\nPHYSICS\\nThe earliest composition was naturally the simple arrange-\\nment of sounds in pleasing succession, and for this sequence\\nof sound the term melody has long been used. The arrange-\\nment and the effect are both simple one sound is followed\\nby another according to no perceived physical law, but\\nsolely, perhaps, in accordance with some aesthetic law by\\nwhich the succession gives us pleasure. Some of our most\\nLar ghetto. -J--J-. 3 1 -3-\\nnrt j,i 3 1 1\\n1\u00c2\u00bb\\n3 LH U I 3 i^\\nH\\n-=i\u00e2\u0080\u0094 =i-\\n=i-\\n-i 9 =1 -Hl\u00c2\u00bb\\ni\\nFig. 254.\u00e2\u0080\u0094 Theme from Beethoven s Fifth Symphony.\\ntouching music, our folk songs, ballads, and the like, are\\npure melody. So, in more complicated music, melody is\\nsometimes introduced by way of contrast or relief, or to\\nemphasize, by its very simplicity, a leading thought in\\nthe composition. Wagner nearly always introduces the\\ncharacters in his operas by such a melody, or Leit-motif.\\nA simple melody is often used as the theme or text out of\\nwhich more elaborate music is to be developed. The above\\nexample of very beautiful melody is the theme of the slow\\nmovement of Beethoven s Fifth Symphony (Fig 254).\\n347. Chords. Melody is simplicity itself, for, while it\\nmay please in greater or less degree, it can never absolutely\\ndisplease, because it can never be other than musical. But\\nthe possibilities of music would be ill explored if we con-\\nfined ourselves to a mere succession of musical sounds,\\nhowever agreeable they might be. There are tremendously\\ngreater possibilities when we come to sound several notes\\nat the same time. Two or more notes sounded simultane-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0392.jp2"}, "389": {"fulltext": "MUSIC 365\\nously constitute a chord. If the effect is agreeable, we call\\nit concord if disagreeable, discord.\\nThe simplest chords contain but two notes, as the\\noctave, C C the perfect fifth, G the fourth, C F the\\nmajor third, C E the major sixth, C A, and the less agree-\\nable minor third, minor sixth, etc. These binary combina-\\ntions form the basis of our musical analysis, since chords of\\nthree or more notes may be resolved into their binary chords.\\nThe most important chord in music is the major triad,\\nC E G, or common cliord, which may be considered as made\\nup of a major third, C E a minor third, E G and a per-\\nfect fifth, C G. By substituting C for C, we get the cliord\\nof the sixth, EGC; and by the further substitution of E\\nfor E, we get the chord of the sixth and fourth, G 0 E\\\\\\nThese three chords are all agreeable, but produce somewhat\\ndifferent musical sensations.\\nHarmonics. The quality of a musical note depends, as\\nwe have seen, upon the overtones. The upper harmonics\\nare too faint to be appreciable, but the lower ones are very\\nimportant. When we strike C, we have the following suc-\\ncession of notes\\nC C G C E Gt etc.\\n12 3 4 5 6, etc. (vibration ratios).\\nWe may discard all above G and represent it thus\\n(Eig. 255) In the harmonics of this one note we have\\nalready present the principal chord of _ i9m\\nmusic, the octave, C C the perfect fifth,\\nC G the fourth, G C the major third, ih Z\\nC E the minor third, E G This may Sp===z\\naccount for the fact that these chords are FlG 255\\nagreeable, since they merely emphasize\\nnotes already present in the fundamental. In general, notes\\nto be harmonious must have vibration frequencies that\\nstand to each other in a simple ratio. There is, however,\\nconflict between the two series of harmonics.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0393.jp2"}, "390": {"fulltext": "366\\nPHYSICS\\n348. Harmony. The highest expression of musical art\\nis in harmony, which is the combining of many sounds into\\none agreeable composition. It is practically a progression\\nof chords, groups of notes sounded in such orderly succes-\\nBT-4-kd\u00e2\u0080\u0094\\nif\\n!S\\nf \u00c2\u00abf ~ta\\n\u00c2\u00a34\\nV\\nq u\\nis it\\n^Mb=\\n9vf\\nN-\\n-=j fs-\\nST*\\n^\u00e2\u0080\u0094\u00c2\u00a3-4\u00e2\u0080\u0094\\np_\\n4.\\nT\\n\u00e2\u0080\u0094A -A\u00e2\u0080\u0094\\nN\\n1\\n=t\\n=t\\n2\\nIS\u00e2\u0080\u0094Jt-ft\\n-1 w-\\nill\\n-=u\\nfe\u00c2\u00a3\\n3=fcz\\nIV\\nP-3-\\nP*r\\nA=3==\u00c2\u00a3\\n=t\\n=t\\n=t\\n4=5=8\\n\u00c2\u00a3i\\n-=4- -M-\\n--=1=\\n=t\\nFig. 256. Illustration of harmony from Schumann s Nachtstuck, No. 4.\\nsion as to produce the impression of unity and purpose.\\nThe laws of harmony are very intricate, and presuppose an\\nacquaintance with elementary music. The above bars from\\nSchumann s Nachtstiick is a beautiful illustration of har-\\nmony (Fig. 256).\\n349. Counterpoint. As harmony is the highest expres-\\nsion of music, so counterpoint is the highest expression of\\nharmony. In counterpoint we have harmony brought about\\nby the combination of two or more me]odies, a combination\\nwhich yields the fullness and satisfaction of harmony with\\nthe movement and life of melody. The great master of\\ncounterpoint was Sebastian Bach (1685-1750). The accom-\\npanying excerpt from Palestrina illustrates counterpoint", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0394.jp2"}, "391": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0395.jp2"}, "392": {"fulltext": "WOLFGANG AMADEUS MOZART (1756-1791).\\nOne of the greatest musicians the world has produced. While a\\nmere lad he played before nearly all the sovereigns of Europe.\\nHis music from the first to the last has been most highly appre-\\nciated.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0396.jp2"}, "393": {"fulltext": "MUSIC\\n367\\n(Fig. 257). Handel, in England, and other masters of the\\nseventeenth and eighteenth centuries brought counterpoint\\nto a perfection that it has never since reattained. It occu-\\npies, indeed, a very subordinate part in the compositions of\\nthe nineteenth century, which are mainly engaged in ex-\\nploiting the possibilities of harmony. But as harmony\\n4\\nErom Palestrixa.\\nI. hi I\\n5-\\nm\\nQ\\nI I\\nf -m -P- V\\nIm^s\\nr.jT\\ns\\nF=F\\nii\\n:p*t\\n-m (2\\n1^S=W-\\nJ i I ,i J: m i\\netc.\\n-3-\u00c2\u00ab\\nw {g\\nv-i\\nFig. 257. Illustration of counterpoint.\\ngrew out of counterpoint, so it now seems probable that a\\nmore magnificent counterpoint will grow out of our enlarged\\nknowledge of harmony. The tendency to return to coun-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0397.jp2"}, "394": {"fulltext": "368 PHYSICS\\nterpoint is shown in the work of such modern composers as\\nMozart and Mendelssohn.\\nIt has been well said that melody gives one the idea of\\nmotion, and harmony the feeling of rest. Melody must\\nprogress, or it ceases to be melody, but a simple harmonious\\nchord is complete and perfect in itself. In modern counter-\\npoint we have the strength of both, the movement of the\\ncontrasted melodies and the restful background of their\\nunderlying harmony.\\nOur ideas of musical beauty are so variable that it seems\\nimpossible to reduce them to strict physical statement.\\nTaste changes, and each new master gives greater flexibility\\nto the material of music. To the complaint that one of\\nhis works contained a certain passage that was not allowed,\\nBeethoven replied Then I allow it j let that be its justi-\\nfication.\\n350. Reading Music. It might well be a part of every\\nliberal education to learn to read music intelligently. There\\nare people who read music so easily, and construct it in\\ntheir minds so vividly, that they get as great pleasure in\\nsimply turning over the leaves of a musical composition as\\nwe do in glancing over a favorite poet.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0398.jp2"}, "395": {"fulltext": "CHAPTEE XXXIII\\nMISCELLANEOUS APPLICATIONS\\n351. Speaking. The opening between the vocal cords is\\ncalled the glottis, and is practically a slit, somewhat like\\nthe lip of an organ pipe. When no sound is produced, the\\nvocal cords are far apart, and\\nthe glottis takes the shape of\\na V, with the wide part behind.\\nWhen voice is produced, the\\nvocal cords are drawn together\\nunder some tension, their edges\\nare parallel, and the glottis be-\\ncomes a mere narrow slit (Fig.\\n258). The pitch of the emitted\\nsound depends on the tension\\nof the vocal cords. As this is\\ncontrolled by the muscles of the larynx, we can alter the\\npitch of our voice at will, but only, of course, within some-\\nwhat narrow range.\\nThe character of the voice depends on small structural\\ndifferences in the larynx. In women and in boys the voice\\nis higher, simply because the vocal cords are shorter, and\\nhence vibrate a greater number of times per second. In\\nthe same way, soprano and alto voices in women, and tenor\\nand bass voices in men, result from the size and tension of\\nthe vocal cords. A trained singer, by altering the tension\\nof the cords, can cultivate great flexibility. This control,\\nlike the control of nearly all our faculties, is best acquired\\nwhen we are young.\\n25 369", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0399.jp2"}, "396": {"fulltext": "370 PHYSICS\\nThis accounts, however, only for the voice itself, and\\nnot at all for speech. The animals have a very similar\\napparatus for producing sound, and, in the case of the birds,\\nthey use it very skillfully.\\nIn speech the voice has to have a very definite charac-\\nter, and many modifications, in order to express all our\\nvarying shades of meaning. The primary speech sounds,\\nvowels and consonants, are brought about by changing the\\nshape of the cavity of the mouth, an operation depending\\nmainly on the tongue and lips. This change in the quality\\nof the tone is due, physically speaking, to the overtones\\nwhich are produced by the varying form of the mouth.\\nThe character of the sounds, as elements of speech, is quite\\nindependent of the tension of the vocal cords.\\nThe human voice only covers a range of about two oc-\\ntaves. Few people in ordinary speech cover one octave.\\nThe rising inflection at the end of a question sometimes\\namounts to a fourth the falling inflection at the end of a\\nsimple sentence to a fifth, and even emphasis, where pro-\\nduced by a change of pitch, seldom exceeds a fifth. The\\ncultivation of a greater range would add much to our power\\nof expression.\\nIn singing, the sound itself is the great thing, and the\\nwords quite secondary. The great operas are sung in\\nItalian, because of the greater wealth of vowel sounds in\\nthat language. In some modern music no words are used\\nat all. A simple vowel sound is selected, and the musical\\neffect gained by variations of pitch and time. In this case,\\nthe voice is treated as a simple musical instrument, and\\nnot at all as an organ of speech. The physical process of\\nsinging depends for its success mainly on the flexibility\\nand control of the vocal cords, and upon the ability to pro-\\nduce a sustained and uniform blast of air through the glottis.\\nIn the best systems of modern voice culture, this flexibility\\nis the main thing sought for, and the singing voice, as\\nit is well called, is cultivated both for speech and song.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0400.jp2"}, "397": {"fulltext": "MISCELLANEOUS APPLICATIONS 371\\nIn compass, the human voice ranges from about F 2 in\\nthe base (86 vibrations) to about F 1 in the treble (768 vibra-\\ntions). Exceptional soprano voices have gone as high as\\nE 11 (1,280 vibrations). One voice is seldom able to cover\\nmore than two octaves.\\n352. Hearing is physiologically the reverse process of\\nspeaking. Speech begins in the brain as a thought, passes\\nto the muscles of the larynx, tongue, and lips as a nerve\\nimpulse, and emerges into space as an air vibration. Hear-\\ning, on the contrary, depends for its stimulus upon an air\\nvibration, which is transmitted by the ear as a sensory im-\\npulse, and ends in the brain with thought. Hearing, there-\\nfore, consists of three distinct processes excitation, trans-\\nmission, and interpretation. The excitation consists in a\\nsound wave impinging on the drum of the ear. The sound\\nwave is usually of the air, but it may also be of the water,\\nif we put our ear beneath the surface. The excitation may\\nalso be produced by direct contact with a vibrating solid\\nbody, as when a sounding fork is held against the bridge of\\nthe nose, or against the teeth. But in general the excita-\\ntion is aerial, and strikes the ear drum. Here a whole series\\nof wonderful things happen. The ear drum is a stretched\\nmembrane, very thin and very strong. It will bear the\\npressure of a column of mercury fifteen inches high that\\nis, an extra pressure of half an atmosphere. This ear drum\\nor membrane separates the outer ear from the drum cavity.\\nIn this there are three small and delicately poised bones\\nwhich receive the vibrations of the ear drum, and pass them\\non to the inner ear, and so, by means of the auditory nerve,\\nto the brain itself.\\nThe act of transmission is a very complicated one, in-\\nvolving as it does so many distinct physiological parts the\\nexternal ear, the external auditory canal, the drum mem-\\nbrane, the middle ear with its three tiny bones, and the\\nventilating canal that leads to the back of the mouth the\\nEustachian tube the internal ear with its wonderful canals", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0401.jp2"}, "398": {"fulltext": "372 PHYSICS\\nand processes and finally the auditory nerve going directly\\nto the temporal lobes of the brain.\\nBut even more wonderful than this process of transmis-\\nsion is the interpretation of the nerve impulse into signifi-\\ncant sound, when it reaches the brain, and about this we\\nknow absolutely nothing at all.\\n353. Limits of Sound. As a sensation, sound is limited.\\nThe human ear will not respond to those which have more\\nthan 40,000 vibrations per second. Many persons can hear\\nnothing above about 12,000 vibrations, and consequently\\ndo not detect the squeal of a mouse or the cry of a bat.\\nWe are all deaf to many of the shrill sounds of the insect\\nworld. Some animals are believed to be able to hear sounds\\nthat quite escape our own ears.\\nMusic employs only the lower notes, from about A 4 (27-J\\nvibrations) to C IV (4,224 vibrations) on the piano, and up\\nto D IV (4,752 vibrations) on the piccolo. The middle is\\ncounted at 256.\\n354. The Phonograph. No scientific instrument in its\\nday has excited greater interest than Mr. Thomas A. Edi-\\nson s phonograph, or sound-recording apparatus, invented in\\n1878, and first apprehended as a scientific toy, but since\\nbrought forward as a serious servant in the affairs of every-\\nday life. The phonograph consists in a horizontal axle\\ncapable both of rotation and of longitudinal advance. On\\nthis is mounted a cylinder, covered in the early days with\\ntin foil, but now made with some plastic composition for\\nits surface. A fixed mouthpiece is mounted over one end\\nof the cylinder, when the axle is at its extreme position.\\nThe mouthpiece has a flexible diaphragm, provided at the\\ncenter of its rear face with a small, sharp stylus, which\\npresses against the plastic surface of the cylinder.\\nWhen talking into the machine the cylinder rotates,\\nand also slowly advances, so that a fresh portion of its sur-\\nface is constantly passing under the stylus. Imagine the\\nmouthpiece in position, and the cylinder slowly rotating.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0402.jp2"}, "399": {"fulltext": "SIR WILLIAM THOMSON (1824-\\n(Lord Kelvin.)", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0403.jp2"}, "400": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0404.jp2"}, "401": {"fulltext": "MISCELLANEOUS APPLICATIONS 373\\nAny sound waves striking against the diaphragm set it into\\nvibration, and the little stylus no longer traces an even\\ngroove on the surface of the cylinder, but a groove which\\nis now of varying and constantly changing depth. Every\\nsound is thus recorded in these minute characters on the\\nsurface of the cylinder, and may be reproduced by throwing\\nback the mouthpiece, bringing the cylinder back to its\\noriginal position, adding a suitable speaking trumpet to the\\nmouthpiece, and then repeating the motion of the cylinder.\\nThe little stylus, passing over its own tracing, moves in and\\nout with the varying depth of the groove, and so produces\\nin the diaphragm vibrations similar to those originally in-\\nduced in it. The trumpet strengthens these sound waves,\\nand we have a reproduction of the speech or music curiously\\nlike and curiously unlike the original.\\nUses of the Phonograph. It was hoped that the phono-\\ngraph might be used in place of dictation, both by editors\\nand busy letter writers, the cylinder being sent at once to\\nthe printing office, or mailed to the correspondent at the\\nother end, but this practical use of the phonograph has not\\nyet been realized. It remains chiefly as an amusement for\\nthe curious in our big cities and popular resorts.\\nA much more important use than this would be the\\napplication of the phonograph to the reproduction of books,\\nso that the blind could be read to, and all of us, tired per-\\nhaps with the day s work, and willing to save our eyes of\\nan evening, could hear our favorite author read. When\\nwe went to buy such books, the shopkeepers would ask us,\\nnot whether we preferred the Avon edition, or the Eiver-\\nside, or the half calf or morocco, but simply whether we\\npreferred Mrs. Scott Siddons s rendition, or Mr. Horace\\nHoward Furness s, or Mr. Eobertson s, or some other good\\nreader s.\\n355. The Telephone means sound at a distance, and is\\none of the most important of modern sound instruments.\\nThe acoustic telephone is only a box, but its principle is", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0405.jp2"}, "402": {"fulltext": "374\\nPHYSICS\\nworth considering. The transmitter and receiver are alike\\nsimply a little cylinder of wood or metal having one end\\nopen and the other end closed by parchment or other flex-\\nible diaphragm. A fine wire or string leads from the center\\nof the diaphragm of one instrument to the center of the\\ndiaphragm of the other. The wire or string must pass\\nfreely from one instrument to the other, and must be mod-\\nerately taut. When you speak into one cylinder, the trans-\\nmitter, the diaphragm is set into vibration, and these vibra-\\ntions produce corresponding longitudinal vibrations in the\\nwire or string, and so in turn are transmitted to the dia-\\nphragm of the receiver. Here they produce vibrations of\\nFig. 259. Telephone receiver.\\nthe air similar to the original sound waves. If the receiver\\nbe held to the ear, the message is distinctly heard over a\\ndistance of several hundred feet.\\nThe magneto-telephone depends upon both acoustical\\nand electrical principles, but with a little care may be read-\\nily understood. Kemove the top of a regular telephone\\nreceiver and examine its construction, or else consult the\\naccompanying figure (259). There is a flexible diaphragm\\nor disk, D, made of thin iron, and directly back of this disk\\na steel bar magnet, running the length of the instrument.\\nThe end of the magnet nearest to the disk is surrounded\\nby a coil of fine insulated copper wire, i?, whose ends are con-", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0406.jp2"}, "403": {"fulltext": "MISCELLANEOUS APPLICATIONS 375\\nnected with the binding posts, C, on the far end of the tele-\\nphone receiver, and through those with the line wire. This\\ninstrument may serve either as transmitter or receiver,\\nthough it is now only used in practice as a receiver. When\\nyou speak into the telephone, the iron diaphragm is set into\\nvibration, and currents of electricity are induced in the coil\\nof copper wire (Fig. 259). The direction of these currents\\nvaries with the approach and recession of the diaphragm,\\nand produces variations in the strength of the magnets at\\neach end of the lines. These variations set up correspond-\\ning vibrations in the diaphragm of the receiver at the farther\\nend of the line the air is thrown into corresponding vibra-\\ntions, and so brings the sound to the ear. The acoustic\\nprinciple of the Bell telephone is very similar to that of\\nthe acoustic telephone, except that the vibrations are trans-\\nmitted not directly as a pulsation of the string, but indi-\\nrectly as a varying current in the wire. The electricity\\nsimply acts as the carrier of the energy. In the transmitter\\nthe sound energy is transformed into electric energy, and\\nthis, in the receiver, is retransformed into sound energy.\\nSuch a telephone is in reality a magneto-electric machine.\\nFor this and the modern form of the telephone see sec-\\ntions 266 and 268.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0407.jp2"}, "404": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0408.jp2"}, "405": {"fulltext": "INDEX\\nAbsolute cold, 199.\\nAbsolute temperature, 199.\\nAbsolute zero, 199.\\nAbsorption, 186.\\nAcceleration, 49.\\nAccumulation of electricity, 248.\\nAdhesion. 18.\\nAir, buoyancy of, 114.\\ncompressor, 132.\\ngun, 124.\\npump, 130.\\nthermometer, 162.\\nweight of, 106.\\nAlcoholometer, 102.\\nAlloys affecting fusing point, 166.\\nAlternators, 282.\\nAltitude determined by ther-\\nmometer, 172.\\nAmati. 359.\\nAmmeter. 264.\\nAmmonia, 201, 203.\\nAmorphous, 17.\\nAmpere, 261.\\nAmpere, Andre Marie, 261.\\nAnalyzers, 345.\\nAngles of incidence and reflection,\\n304.\\nAnimal heat, 151, 204.\\nAnimals, cold-blooded, 163.\\nwarm-blooded, 163.\\nAnode, 239.\\nAntimony, 284.\\nArchimedes, 103.\\nprinciple of, 98.\\nArc lamp, temperature of, 295.\\nAristotle, 106.\\nArmature. 280.\\nArrangement of battery cells, 268.\\nAspirating siphon. 134.\\nAstigmatism, 332.\\nAtmosphere, 9, 105.\\ndensity at different heights, 112.\\npressure of, 108.\\npressure on human body. 126.\\nvariations in pressure, 109.\\nAtoms, 8.\\nAxioms, 75.\\nBacchus illustration, 123.\\nBach, Sebastian, 366.\\nBalance, 40.\\nBalloons, 115.\\nBarium, platino-cyanide of, 339,\\n340.\\nBarium sulphide, 339.\\nBarometer, aneroid, 109.\\nFortin s, 109.\\nmercury. 107.\\ntension inside, 137.\\nBattery cells. 245.\\nin parallel, 269.\\nin series, 268.\\n377", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0409.jp2"}, "406": {"fulltext": "378\\nPHYSICS\\nBeethoven, 364, 308.\\nBichromate cell, 242.\\nBismuth, 284.\\nBlack keys of piano, 3(53.\\nBlowing engines, 132.\\nBlushing, 204.\\nBodies, simple and compound, 7.\\nBoiler rivets, 154.\\nBoiling, 169.\\nlaws of, 170.\\non mountain top, 204.\\nBoiling point affected by altitude,\\n172.\\naffected by nature of containing\\nvessel, 171.\\naffected by pressure, 171.\\nchanges of, 170.\\nof water, 149.\\ntable of, 170.\\nBottle imp, 121.\\nBoyle s law, 112.\\nBrittleness, 19.\\nBrooklyn Bridge, 155.\\nBrush, 281.\\nBulging walls, 154.\\nBunsen cell, 242.\\nBuoyancy, 96.\\nCaissons, 124.\\nCalcium tungstate, 340.\\nCalipers, 31.\\nCaloric, 192.\\nCandle power of various lights,\\n294.\\nCandle, standard, 293.\\nCapillarity, 22.\\nCarbon dioxide, 135, 202.\\nliquefying, 169.\\nCarre ice machine, 201.\\nCartesian diver, 121.\\nCasting metals, 165.\\nCataract, 332.\\nCathetometer, 32.\\nCells in parallel, 246.\\nin series, 245.\\nCelsius, 158.\\nCenter of oscillation, 63.\\nCentigrade scale, 158.\\nCentimeter, 25.\\nC.-G.-S. system, 26, 52.\\nChange of state by heat, 152, 153,\\n164.\\nChange of volume by fusion, 165.\\nChange of volume by heat, 153.\\nChanges, physical and chemical,\\n10.\\nCharles, law of, 161.\\nChemical effects of electricity, 248.\\nChemical rays, 339, 346.\\nChemistry, 4.\\nChords, musical, 364.\\nClark Brothers, 331.\\nClatter bell, 257.\\nClausius, 147.\\nClef, 363.\\nClothing, 180.\\nCloud banners, 176.\\nClouds, 172.\\nClouds at sunset, 312.\\nCoefficient of expansion, 153.\\nof gases, 161.\\nirregularities, 156.\\ntable of, 154.\\nCohesion, 17.\\nCoil, telephone, 276.\\nCold by evaporation, 200.\\nCold by expansion of gases, 200.\\nCollecting apparatus, 281.\\nColor, 335.\\nColor and temperature, 339.\\nColors, complementary, 336.\\nin sunlight, 338.\\nColor wheel, 337.\\nCombustion, 150.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0410.jp2"}, "407": {"fulltext": "INDEX\\n379\\nCommutator, 259. 281.\\nCompass, spring, 31.\\nComplementary colors, 336.\\nCompost heaps, 151.\\nCompound microscope, 330.\\nCompounds. 8.\\nCompressed-air motors. 123.\\nConcave mirrors, 306.\\nCondensation, 177.\\nCondensers of electricity, 230.\\nConduction of heat, applications\\nof, 180.\\nConductivity of heat, table. 179.\\nConductors of electricity, 223, 260.\\nConjugate foci. 306.\\nConvection, 182.\\nConvex mirrors, 309.\\nCooking by electricity, 151.\\nCounterpoint, 366.\\nCouple, 68.\\nCritical angle, 320.\\nCritical temperature, 168.\\nCrystals. 155.\\nCrystalline form. 16.\\nCrystallization. 177.\\nCurved image from straight ob-\\nject, 310.\\nCurvilinear motion, 50.\\nDalton, 15.\\nDaniell cell, 243.\\nDavy. Sir Humphry, 147.\\nDaylight, how diffused, 311.\\nDecimeter. 25.\\nDeclination of magnetic needle.\\n215.\\nDeliquescence, 197.\\nDensities, table of, 42.\\nDensity. 42.\\nDew on grass, 175.\\non ice pitcher, 175.\\nDew Point. 172.\\nDial thermometers, 154.\\nDialysis, 21.\\nDialyzer, 21.\\nDiffusibility, 20.\\nDiffusion, 20.\\nDiminished images in convex mir-\\nror, 309.\\nDipping needle, 214.\\nDistances, how estimated from\\nvisual angle, 296.\\nDistribution of plants and animals,\\n163.\\nDivided circuits, 269.\\nDiving bell, 124.\\nDouble boiler, 204.\\npump, 129.\\nwindows, 180.\\nDraper, 295.\\nDrawings upon highly polished\\nsurfaces, 315.\\nDuctility, 19.\\nDynamo. 278, 284.\\nDyne, 52, 70.\\nEar, 371.\\nEardrum, 124.\\nEarth a magnet. 214.\\nEarth as seen from the moon, 313.\\nEarth s shadow, 299.\\nEchoes, 356.\\nEclipses, 298, 301.\\nEdison, Thomas A., 372.\\nEffect of an electric current upon\\na magnetic needle, 254.\\nof heat and cold on rocks, 155.\\nEffects of electric currents, 246.\\nElasticity, 18.\\nElectrical distribution, 232.\\neffects of points, 232.\\nmachines. 230.\\nElectric and cable cars, 282.\\nElectric bell. 256.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0411.jp2"}, "408": {"fulltext": "380\\nPHYSICS\\nElectric conductors, 260.\\ncurrents by mechanical means,\\n278.\\nby heat, 284.\\nsources of, 235.\\nfurnaces, 247.\\ngas lighting, 275.\\nlight, 247.\\nmeasurements, 259.\\nmotor, 257, 259, 284.\\npotential, 237, 260.\\nstove, 247.\\nwaves, 290, 346.\\nwelding, 248.\\nwhirl, 234.\\nElectricity and steam, 282.\\nElectricity for transmitting power,\\n283.\\nElectrification, two states of, 222.\\nElectro-chemical series, 239.\\nElectrolysis of salts, 250.\\nof water, 249.\\nElectrolytic assay, 251.\\nElectro-magnet, 253.\\nElectro-motive force, 237.\\nElectrophorus, 228.\\nElectroplating, 251.\\nElements, 7.\\ntable of, 12.\\nEllipse, 51.\\nEnergy, 32, 71.\\nkinetic and potential, 72.\\ntransformation of, 72.\\nEnlarged images by refraction, 324.\\nin concave mirrors, 307.\\nErg, 70.\\nEther, 3, 54, 184, 185, 211, 220, 226,\\n280, 295, 339, 340, 342, 346.\\nflow, 253.\\nstress, 253.\\nvibrations, 290, 292.\\nvortex, 251, 253.\\nEudiometer, 10.\\nEustachian tube, 125.\\nEvaporation, five factors of, 166.\\nof snow and ice, 167.\\nof solids, 167.\\nproduces cold, 200.\\nExpansion by heat, applications of,\\n154.\\nof crystals, 155.\\nof gases, correction of volume\\nfor temperature, 161.\\nof glass, 158.\\nof ice, 155.\\nof liquids, 156.\\nof rocks, 155.\\nof solids, 153.\\ntable of, 154.\\nExplosion by superheated steam,\\n171.\\nExplosives, 123.\\nExtension in one direction, 30.\\nin two directions, 33.\\nin three directions, 34.\\nExtra currents, 275.\\nEye, 331.\\nFahrenheit scale, 159.\\nFalling bodies, 56.\\nFaraday, 278, 346.\\nFaraday, Michael, portrait of, 207.\\nFar-sightedness, 333.\\nFiltering colors, 340.\\nFire extinguishers, 123.\\nFireplace, i85.\\nFloating bodies, stability of, 104.\\nFluids, 89.\\nin motion, 139.\\nFluorescence, 338.\\nFocal distance of a lens, 326.\\nFog, 172, 176.\\nFoot pound, 71.\\nForce, 32.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0412.jp2"}, "409": {"fulltext": "INDEX\\n381\\nForce of crystallization, 165.\\npump, 128.\\nFountain ink wells, 138.\\nin vacuo, 126.\\nsiphon, 135.\\nsponge cup, 138.\\nFractional distillation, 170.\\nFrankford Exhibition, 284.\\nFranklin, 86. 228.\\nBenjamin, portrait of, 86.\\nFreezing mixtures, 197.\\nFrost, 172. 176.\\nFurnace, 181, 184.\\nFurness. Horace Howard, 373.\\nFusing by electricity, 151.\\nFusing point, affected by alloys,\\n166.\\naffected by pressure, 165.\\nFusion, 164.\\nlaws of, 164.\\nof sulphur, 164.\\nGalileo, 106.\\nGalvanometer, 255.\\nGang, 251.\\nGases, 3, 152.\\nbehavior of, 105\\nexpansion of. 200.\\nrelation of volume to pressure,\\n112.\\nand vapors, 168.\\nGay-Lussac, 162.\\nG, determination of, by the pendu-\\nlum, 62.\\nvalue of, 55.\\nGlottis, 369.\\nGood reflectors invisible, 314.\\nGoose pimples, 204.\\nGrain. 25.\\nGravitation. 37, 54.\\nGravity cell, 244.\\nGreat Britain, 205.\\nGuarnerius, 359.\\nGuericke, 106, 122.\\nGulf Stream, 205.\\nHail, 173.\\nHalf tones of sound, 362.\\nHalos, 311.\\nHandel, 367.\\nHardness, 16.\\nHarmonics, 365.\\nHarmony, 366.\\nHearing, 371.\\nHeat, 145.\\na mode of motion, 147.\\nby liquefaction of vapors, 205.\\nconduction of, 178.\\nconvection of, 182.\\neffects of, 152.\\nfrom electricity, 247.\\nfrom light rays, 339.\\nfrom rain or snow, 205.\\nfrom solutions, 205.\\nfrom the sun, 185.\\nin battery cell, 248.\\nmeasurement of, 191.\\nmedium of exchange, 148.\\nNewton s ideas of, 146.\\nof combustion, 151.\\nof earth, 150.\\nof foods, 151.\\nof rusting, 151.\\nof the sun, 149, 150.\\nproduced by chemical action,\\n150.\\nproduced by electricity, 151.\\nproduced by friction, 148.\\nproduced by percussion, 148.\\nproduced by pressure, 149.\\nproducing electric current, 284.\\nquantity of, 191.\\nrays, 339.\\nrelation to light, 187.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0413.jp2"}, "410": {"fulltext": "382\\nPHYSICS\\nHeat, theory of, 153.\\ntransference of, 178.\\nwaves, 290, 346.\\nHeating chemical glassware, 155.\\nelectric cars, 151.\\nof hay, grain, etc., 151.\\nHelix, 251.\\nHelmholtz, 147, 150.\\nHelmholtz s resonators, 356.\\nHero s fountain, 136.\\nHerz, Heinrich, 342.\\nHerz waves, 342.\\nHiero, 103.\\nHoffman apparatus, 10.\\nHorse power, 71, 282.\\nPlot-bed, 188, 339.\\nHudson River Tunnel, 124.\\nHuman eye, 331.\\nHuman voice, range of, 370.\\nHumidity, 173.\\nHuxley, 12.\\nHuygens, 63.\\nHydraulic, 140.\\nHydraulic ram, 140.\\nHydrochloric acid, 135.\\nHydrogen, 7, 10, 20, 21, 136.\\nspecific gravity of, 106.\\nHydrometer, 102.\\nNicholson s, 101.\\nBaume s, 102.\\nHydrostatic, 140.\\npress, 119.\\nIcebergs, 165.\\nIceland spar, 345.\\nIllumination of clouds at sunset,\\n312.\\nIllumination of page of reading\\nmatter, 295.\\nImage curved from straight ob-\\nject, 310.\\nImages by refraction, 324-327.\\nImages in concave mirrors, 307,\\n308.\\nin convex mirrors, 309.\\nin plane. mirrors, 304.\\nhow constructed, 305.\\nInclination of magnetic needle,\\n215.\\nInclined plane, 81.\\nIndex of refraction, 318.\\nvalue of, 319.\\nInduced currents, direction of, 273.\\nstrength of, 273.\\nInduction, by a magnet, 271.\\nby static electricity, 226, 228.\\nby varying currents, 272.\\ncoil, 274.\\nmagnetic and electric, 253.\\nof electric current, 270.\\nInsulators, 224.\\nIntervals of sound, 362.\\nInverse squares, law of, 219, 227,\\n293, 352.\\nInverted images by refraction, 325.\\nin concave mirrors, 308.\\nInverted tumbler of water, 138.\\nIron bridges, 155.\\nIron oxide, 209.\\nIron ships, 103.\\nIsobars, 112.\\nJoule, 70, 147.\\nJupiter s satellites, 291.\\nKathode, 239.\\nKelvin, 8.\\nKelvin, Lord, portrait of, 372.\\nKeyboard of piano, 361.\\nKilogram, 25.\\nKilometer, 25.\\nLactometer, 102.\\nLa Parge, 338.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0414.jp2"}, "411": {"fulltext": "INDEX\\n383\\nLand and sea breezes, 184, 195.\\nLatent heat, 205.\\nof solution, 196.\\nof vapors, 198.\\nLaws of boiling, 170.\\nof Boyle, 112.\\nof Charles, 161.\\nof fusion, 164.\\nof inverse squares, 219, 227, 293,\\n352.\\nOhm s, 260.\\nof reflection, 304.\\nof refraction, 318.\\nof vibrating strings, 358.\\nNewton s, 72.\\nLeclanche cell, 243.\\nLeit-motif, 364.\\nLength, 25.\\nLenses, 324.\\nmaterial of, 328.\\nfamiliar illustration, 329.\\nLeslie, 202.\\nLever, 76.\\nLeyden jar, 231.\\nLight, its effects, 289.\\nmeasurement of, 293.\\npolarization of, 343.\\nradiations change to heat, 339.\\nrays, 339.\\nreflection of, 304.\\nrefraction of, 317.\\nrelation to heat, 292.\\nrelation to temperature, 295.\\nsources of, 292.\\nthrough small apertures, 302.\\nvelocity of, 290.\\nwaves, 290, 295, 346.\\nLightning, 231.\\nLights, artificial, 292.\\nLimits of sound, 372.\\nLines of magnetic force, 220.\\nLiquid air, 198.\\nLiquids, 2, 152.\\nLiquids seek their own level, 94.\\nLiter, 25.\\nLoadstone, 209.\\nLocal action in voltaic cell, 240.\\nLoudness of sound, 351.\\nLuminous paints, 339.\\nMachines, 74.\\nMagdeburg Hemispheres, 122.\\nMagnet, effect on polarized light,\\n346.\\ninfluence upon magnetic sub-\\nstances, 211.\\nMagnetic effects of electricity, 251.\\nfield, 280.\\nforce, lines of, 220.\\ninduction, 211.\\npoles, 214.\\nsubstances, 211.\\nMagnetism and electricity, rela-\\ntion of, 253.\\nMagnetism of the earth, 214.\\nMagnetite, 209, 218.\\nMagneto-electric machine, 278.\\nMagneto telephone, 374.\\nMagnets, 209.\\nMalleability, 18.\\nMariner s compass, 217.\\nMariotte, 112.\\nMass, 25, 36.\\nand weight, 36.\\nmeasurement of, 39.\\nMatter, 1.\\nconservation of, 28, 71.\\nmeasurement of, 30.\\nproperties of, 15.\\nradiant, 3.\\nthree states of, 2.\\nMatterhorn, 176.\\nMaxwell, 7, 9, 147.\\nMeasurements, 24, 27.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0415.jp2"}, "412": {"fulltext": "384\\nPHYSICS\\nMedicine dropper, 138.\\nMelody, 363.\\nMendelssohn, 308.\\nMercury, 10.\\nMercury pumps, 131.\\nMetaphysics, 5.\\nMeteors. 149.\\nMeter, 25.\\nMetric system, 25.\\nMicrometer screw, 31.\\nMicroscope, 329.\\nMicroscopic sections, 203.\\nMilk, density of, 121.\\nMillimeter, 25.\\nMist, 172.\\nMirrors, plane, 304.\\nconcave, 306.\\nconvex, 309.\\nMixtures and compounds, 9.\\nMoisture absorbs heat radiation,\\n188.\\nMoisture and health, 174.\\nMolecular theory of magnets, 212.\\nMolecule, 2, 8.\\nMolecule size of, 8.\\nMoments, 66.\\nMomentum, 48.\\nMonochord, 357.\\nMont Blanc, 186.\\nMoon, 152.\\ndistance of, 291, 299.\\nphases of, 312.\\nMoonlight, 312.\\nMoon s shadow, 298.\\numbra, 298.\\nMotion, 3, 4, 47, 49.\\nunits of, 52.\\nMotions, composition of, 64.\\nparallel, 67.\\nparallelogram of, 65.\\nresolution of, 68.\\nMotor, electric, 257, 259, 284.\\nMoving body, path of, 49.\\nMozart, 368.\\nportrait of, 367.\\nMuggy day, 204.\\nMusic, 360.\\nMusical notation, 362.\\nscale, 360, 362.\\nscore, 363.\\nNear-sightedness, 333.\\nNew moon, how dark part is made\\nvisible, 313.\\nNewton, 37, 54, 146.\\nNewton, Sir Isaac, portrait of,\\nFrontispiece.\\nNewton s laws, 72.\\nNicholson s hydrometer, 101.\\nNitrogen, 9, 10, 202.\\nNon-conductors of heat, 180.\\nNorwegian cooking box, 180.\\nOcean currents, 184.\\nOctave, 361.\\nOhm, 261.\\nOhm, Oeorg Simon, 261.\\nOhm s law, 260.\\nOpen-circuit batteries, 243.\\nOsmose, 21.\\nOvertones, 355, 365.\\nOxygen, 9, 10, 20.\\nspecific gravity of, 106.\\nPalestrina, 367.\\nPalisades, 155.\\nPascal, 119.\\nPendulum, compound, 63.\\nsimple, 59.\\nmotion of, 61.\\nseconds, 62.\\nPenumbra, 298.\\nPermanent gases, 168.\\nPhases of the moon, 312.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0416.jp2"}, "413": {"fulltext": "INDEX\\n385\\nPhonograph, 372.\\nPhosphorescence, 338.\\nPhotometer, Ruinford s, 294.\\nPhotometry, 293.\\nPhysical science, 1.\\nPhysics, 4, 5, 7, 12, 27.\\nPhysiological effects of electricity,\\n246.\\nPiano, 358.\\nPictures at focus of lens, 327.\\nthrough a keyhole, 303.\\nPiston, 128.\\nPlane mirrors, 304.\\nPlante, Gaston, 248.\\nPolarization, in voltaic cell, 240.\\nof light, 343.\\nof light, applications of, 345.\\nof light, affected by magnet, 346.\\nrotation of plane of, 346.\\nPolarized pith ball, 226.\\nPolarizers, 345.\\nPoles of a magnet, 210.\\nof voltaic cell, 239.\\nPower, 70, 74.\\nPressure, affecting fusing point,\\n165.\\ndue to gravity, 92.\\ngauge, 89.\\ngauge closed, 114.\\nin gases, second principle, 105.\\nin liquids, first principle, 91.\\nin fluids, third principle, 118.\\nupward, 93.\\nPrincipal focus. 306.\\nPrint upon glazed paper, 315.\\nPrism, 324.\\nProjectiles, patn of, 57.\\nProtyle, 11.\\nPulley, 80.\\nPump, double acting, 129.\\nforce, 128.\\nmercury, 131.\\n26\\nPump, air, 130.\\nPumps, 127.\\nPyrometers, 162.\\nQuality of sound, 354.\\nQuicksands, 203.\\nRadiant matter, 3.\\nRadiation, 184.\\nidentity of various forms, 346.\\nRadiations, 339.\\nRadiometer, 189.\\nRainfall, 173.\\ntable of, 174.\\nRationality, 29.\\nReaction equal action, 73.\\nReading, music, 368.\\nReaumur scale, 158.\\nReceiver, telephone, 277.\\nReciprocity, 73.\\nReflection, heat, 186.\\nlight, 304.\\nmiscellaneous observations on,\\n311.\\nsound, 356.\\ntotal, 321.\\nRefraction, affects apparent posi-\\ntion of heavenly bodies, 321.\\napplications of, 321.\\ncause of, 319.\\nenables us to see transparent and\\ncolorless substances, 322.\\nindex of, 317.\\nin prisms, 324.\\nlaws of, 318.\\nof light, 317.\\nRe-enforcement of sound, 352.\\nResistance, coils, 266.\\nelectric, 265.\\nof metals, 268.\\nResonators, Helmholtz, 356.\\nRespiration, physics of, 125.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0417.jp2"}, "414": {"fulltext": "386\\nPHYSICS\\nResultant, 64.\\nRobertson, 373.\\nRoemer, Olaf, 290.\\nRontgen, Prof. W. C., 340.\\nRontgen rays, 340.\\nRood, Prof. Ogden, 338.\\nRotating bodies, 51.\\nRotation of plane of polarization,\\n346.\\nRuhmkorff s coil, 275.\\nRuraford, Count, 147.\\nSahara, 189.\\nSalt lakes, 103.\\nSaturation of vapors, 172.\\nSavart s wheel, 353.\\nSchumann, 366.\\nScience, first course in, 289.\\nScrew, 83.\\nScrew gauge, 31.\\nShadows, 298.\\nShunt, 276.\\nSiddons, Mrs. Scott, 373.\\nSilver spoon as curved mirror, 309.\\nSimple microscope, 329.\\nSingle-stroke bell, 257.\\nSiphon, 132.\\naspirating, 134.\\nbottles, 123.\\nfountain, 135.\\nSiphoning gases, 135.\\nSiren, 354.\\nSlaking lime, 151.\\nSleet, 173.\\nSnow, 173, 175.\\nprotects vegetation, 182, 188.\\nSolidification, 177.\\nSolids, 2, 152.\\nevaporation of, 167.\\nSonometer, 357.\\nSound, 347.\\nby sympathetic vibrations, 352.\\nSound, half tones and whole tones,\\n362.\\nintervals of, 362.\\nlimits of, 372.\\nloudness of, 351.\\nmiscellaneous applications, 369.\\nreflection of, 356.\\nre-enforcement of, 352.\\nsources of, 349.\\ntransmission of, 349.\\nvelocity of, 356.\\nvibration ratio of, 362.\\nwaves, 351.\\nSpark coil, 275.\\nSpeaking, 369.\\nSpecific gravity, 43, 99.\\nbalance, 99.\\nbottle, 45.\\nof gases, 44.\\nof human body, 103.\\nof liquids, 100.\\nof liquids by balancing against\\natmospheric pressure, 139.\\nof solids, 45, 99.\\nSpecific heat, 192.\\napplications, 194.\\ntable of, 194.\\nSpectrum, 333.\\ninvisible, 336.\\nSpherometer, 32.\\nSpottiswoode, 275.\\nStaff, musical, 363.\\nStamping metals. 165.\\nStars, distance of, 292.\\nStatic electricity, 222.\\nSteam radiators, 205.\\nSteinway, 358.\\nSt. Elmo s fire, 234.\\nStorage batteries, 248.\\nStradivarius, 359.\\nStrength of induced currents, 273.\\nSublimation, 168.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0418.jp2"}, "415": {"fulltext": "INDEX\\n387\\nSulphate of quinine. 339.\\nSulphur, fusion of, 164.\\nplastic, 164.\\nSun, 152.\\nSun and moon, relative size and\\ndistance, 297, 299.\\nSun, distance of, 150, 291, 299.\\nSun drawing water, 311.\\nSunset clouds, 312.\\nSurveying, 33.\\nSympathetic vibrations, 359.\\nTable of boiling points, 170.\\nconductivity, 179.\\nconductors and insulators of\\nelectricity, 225.\\ndensities, 42.\\nelectro-chemical series, 240.\\nelements, 12.\\nlineal coefficient of expansion,\\n154.\\nmagnetic declination, inclina-\\ntion, and intensity, 216.\\nmelting points, 165.\\nrainfall, 174.\\nresistance of metals, 268.\\nspecific heats, 194.\\ntangents, 263.\\nTait. 12, 147.\\nTangent, 262.\\ngalvanometer, 262.\\nTelegraph sounder, 255.\\nTelegraph wires, 256.\\nTelegraphy, wireless, 342.\\nTelephone. 276. 373.\\nTelescope, 330.\\nTemperature, 161.\\nand color, 3o9.\\nat various elevations, 200.\\nof birds. 163.\\nof the human body, 163.\\nrange of, 163.\\nTemperature, relation to animal\\nand vegetable life, 163.\\nrelation to light, 295.\\nTension and pressure, relation of,\\n122.\\nTesla, 292.\\nThermal effects of electricity, 247.\\nThermodynamics, 148.\\nThermo-electric currents, 284.\\nThermometer, air, 162.\\nDraper s, 160.\\nfor high temperature, 162.\\nmaximum and minimum, 160.\\nmercury, 157.\\nalcohol, 157.\\nmetal, 154.\\nself-recording, 160.\\nstandardized in steam rather\\nthan water, 171.\\nused to determine altitude, 172.\\nwet and dry bulb, 173.\\nThermopile, 285.\\nThird principle of fluid pressure,\\n118.\\nThompson, Benjamin, 147.\\nThomson, Sir William, 149.\\nportrait of, 372.\\nTiffany, 338.\\nTimbre of sound, 354.\\nTime, 25.\\nTime-keeping, 62.\\nTone color, 354.\\nTorricelli, 107.\\nTotal reflection, 321.\\nTourmaline crystals, 345.\\nTrade winds, 184.\\nTransformers, 277.\\nTransmission of pressure in fluids,\\n117.\\nTransmitter, telephone, 276.\\nTransparent objects invisible, 314.\\nTransverse vibrations, 343.", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0419.jp2"}, "416": {"fulltext": "388\\nPHYSICS\\nTrap rock, 155.\\nTwilight, 316.\\nTyndall, 147, 175, 186.\\nTyndall, John, portrait of, 187.\\nType metal, 165.\\nTypical cells, 241.\\nUmbra, 298.\\nUnits, 2, 24.\\nVacuum pans, 167.\\nVapor in atmosphere, 172.\\nVaporization, 166.\\nVapors, 168.\\nsaturated, 168.\\nVapor tension, 172.\\nVariations in earth s magnetism,\\n217.\\nVelocity, 48.\\nof sound, 356.\\nVentilation, 183, 184.\\nVenus, crescent-shaped, 314.\\nVernier, 32.\\nVibration ratios of sound, 362.\\nVibrations of strings, 357.\\nVibrations, transverse, 343.\\nViolin, 359.\\nVioloncello, 359.\\nVirtual velocities, 75.\\nViscosity, 19.\\nVisual angle, 296.\\nof sun and moon, 297, 299.\\nVocal cords, 369.\\nVolt, 237, 261.\\nVolta, 237, 261.\\nVoltaic cell, 238.\\nVoltmeter, 264.\\nVolume of stone, 34.\\nVon Helmholtz, 355.\\nWagner, 364.\\nWard, Prof. R. De C, 174.\\nWater as a reflector, 315.\\nWater barometer, 138.\\nbath, 166, 204.\\nexhaust, 131.\\njars of the East, 201.\\nlife preserved by ice, 157.\\nmaximum density of, 156.\\nwheels, 140.\\nWatt, 70, 71, 282.\\nWave lengths, 339, 340, 346.\\nWeather Bureau\\nmap, 111.\\nreport, 112.\\nWeber, 295.\\nWedge, 83.\\nWeighing, 39.\\nWeight, 38.\\nWeight of mercury, 35.\\nWelding metals by electricity,\\n151.\\nWheatstone bridge, 265.\\nWheel and axle, 79.\\nWindmills, 140.\\nWireless telegraphy, 342.\\nWollaston s cryophorus, 203.\\nWork, 70, 74.\\nX-rays, 340.\\nTHE END", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0420.jp2"}, "417": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0421.jp2"}, "418": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0422.jp2"}, "419": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0423.jp2"}, "420": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0424.jp2"}, "421": {"fulltext": "", "height": "3383", "width": "2081", "jp2-path": "elementsofphysic00hend_0425.jp2"}, "422": {"fulltext": "", "height": "3713", "width": "2367", "jp2-path": "elementsofphysic00hend_0426.jp2"}}