{"1": {"fulltext": "", "height": "3773", "width": "2137", "jp2-path": "compendiumofas00olms_0001.jp2"}, "2": {"fulltext": "LI BRARY OF CONGRESS. V\\nI *Lf. QB45\\nUNITED STATES OF AMKHICA.!\\nm", "height": "3368", "width": "2124", "jp2-path": "compendiumofas00olms_0002.jp2"}, "3": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0003.jp2"}, "4": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0004.jp2"}, "5": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0005.jp2"}, "6": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0006.jp2"}, "7": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0007.jp2"}, "8": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0008.jp2"}, "9": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0009.jp2"}, "10": {"fulltext": "1. Great Cluster of Stars in Hercules.\\n2. Whirlpool Nebula of Lord Rosse.", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0010.jp2"}, "11": {"fulltext": "SHELL S OLMSTED S SCHOOL ASTRONOMY.\\nCOMPENDIUM\\nOF\\nASTEONOMT:\\ngJbajjfeb to $se of\\nSCHOOLS AND ACADEMIES.\\nBY\\nDENISON* OLMSTED, LL.D.,\\nLATE PROFESSOR OF NATURAL PHILOSOPHY AND ASTRONOMY IN YALE COLLEGE.\\nKEVISED BY\\nE, S. SNELL, LL.D.,\\nPROFESSOR OF MATHEMATICS AND NATURAL PHILOSOPHY IN AMHERST COLLEGE.\\nC NEW YOEK\\nCOLLINS BBOTHEB,\\nNo. 106 LEONARD STREET.\\n1868.\\nV", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0013.jp2"}, "12": {"fulltext": "Entered, according to Act of Congress, in the year 1S67, by\\nJULIA M. OLMSTED,\\nFOE THE CHILDREN OF DENISON OLMSTED, DECEASED,\\nIn the Clerk s Office of the District Court of the United States for the District of\\nConnecticut.\\nElectrotyped by Smith McDougal, 82 and 84 Beekman St., N. Y.\\nO", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0014.jp2"}, "13": {"fulltext": "PEEFACB\\nI have endeavored, in the present volume, to per-\\nform a work for Professor Olmsted s School Astron-\\nomy, similar to that which I performed a few years\\nsince for his School Philosophy. Besides bringing\\nthe science more fully down to the present time, I\\nhave made it my special aim to present the facts and\\nprinciples of the subject in clear language, and in\\nfew words, believing such a style most profitable to\\nthe pupil and most satisfactory to the teacher. It\\nis believed that a decided improvement will be\\nfound in the engravings. Those which in former\\neditions were erroneous have given place to more\\ncorrect ones, taken from the revised College As-\\ntronomy, and a large proportion of the remain-\\nder have been changed in their style, and newly\\ndrawn and engraved expressly for this edition.\\nE. S. SNELL.\\nAmherst College, October, 1867.", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0015.jp2"}, "14": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0016.jp2"}, "15": {"fulltext": "CONTENTS\\nCHAPTER I.\\nGENERAL FORM AND DIMENSION S OF THE EARTH THE\\nDIURNAL MOTION ARTIFICIAL GLOBES.\\nPAGE\\nAstronomy 13\\nForm of the earth 14\\nProofs that it is globular 14\\nThe words up and down 15\\nSize of the earth 16\\nInequalities of surface 16\\nThe diurnal rotation IT\\nThe equator of the earth 17\\nMeridians ._ 17\\nLatitude and longitude 17\\nThe terrestrial sphere 18\\nThe celestial sphere 18\\nThe horizon 18\\nThe vertical circles 19\\nAltitude and azimuth 19\\nCelestial equator 19\\nPAGE\\nThe ecliptic 21\\nEquinoxes 21\\nSolstices 21\\nThe colures 21\\nSigns of the ecliptic 22\\nRight ascension and declination 22\\nCelestial longitude and latitude 22\\nApparent daily motion of the heavens 23\\nRising, setting, culmination 23\\nDiurnal circles and horizon 24\\nThe right sphere 25\\nThe parallel sphere 26\\nThe oblique sphere 26\\nArtificial globes 27\\nProblems on the terrestrial globe 29\\nProblems on the celestial globe 30\\nCHAPTER II.\\nPARALLAX ATMOSPHERIC REFRACTION TWILIGHT.\\nParallax 38\\nDiurnal parallax 33\\nGreatest at the horizon 35\\nDiminishes as distance increases 35\\nHorizontal parallax 35\\nParallax of the moon 35\\nAtmospheric refraction 35\\nIts effect on rising and setting 36\\nDistortion of the sun s disk 37\\nIllumination of the sky 37\\nTwilight 38\\nDuration of twilight 39\\nCHAPTER IH.\\nASTRONOMICAL INSTRUMENTS THE EARTH S MOTION ABOUT\\nTHE SUN THE SEASONS FORM OF THE EARTH S ORBIT.\\nThe equatorial telescope 40\\nThe transit instrument 40\\nThe astronomical clock 42\\nSidereal time 42\\nTo find right ascension 42\\nTo find declination 42\\nThe mural circle 43\\nThe altitude and azimuth instru-\\nment 43\\nThe sextant 44\\nObservations of the sun s place 45\\nThe ecliptic and zodiac 46", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0017.jp2"}, "16": {"fulltext": "Vlll\\nCONTENTS\\nPAGE\\nThe tropics and polar circles 46\\nTerrestrial zones 47\\nThe annual motion observed without\\ninstruments 4S\\nA motion of the earth, not the sun.. 48\\nCause of the change of seasons 49\\nCauses of heat in summer and of cold\\nin winter 51\\nPAGE\\nTime of greatest heat and greatest cold 52\\nEffect of no obliquity on seasons 52\\nObliquity of 90\u00c2\u00b0 53\\nTo find the form of the earth s orbit. 53\\nPerihelion, aphelion, etc 54\\nLine of apsides 55\\nEffect of sun s distance on the sea-\\nsons 55\\nCHAPTER IV.\\nSIDEREAL TIME MEAN AND APPARENT SOLAR TIME THE\\nCALENDAR.\\nThe sidereal day 57\\nThe mean solar day 57\\nThe apparent solar day 53\\nCauses of unequal solar days 58\\nThe equation of time 59\\nCivil and astronomical timer 59\\nThe Julian calendar 60\\nThe Gregorian calendar 60\\nDays of the month and of the week... 61\\nCHAPTER V.\\nOBLATE FORM OF THE EARTH ITS MASS AND DENSITY\\nPROOFS OF ITS ROTATION ON AN AXIS.\\nCentral forces 63\\nIllustrations 63\\nLoss of weight on the earth 64\\nLoss from a second cause 64\\nOblate form of the earth 64\\nEquatorial belt 65\\nWeight and density of the earth. 67\\nProofs of the earth s rotation 67\\nCHAPTER VI.\\nTHE SUN SOLAR SPOTS CONDITION OF THE SUN S SUR-\\nFACE THE ZODIACAL LIGHT.\\nThe form of the sun 69\\nThe sun s distance and size 69\\nThe sun s mass and strength of gravity 70\\nDiurnal rotation of the sun 70\\nIts apparent time 71\\nIts real time 71\\nAppearance of solar spots 71\\nTheir motions and changes 72\\nTheir nature 73\\nHerschel s theory 73\\nThe zodiacal light 73\\nCHAPTER VII.\\nGRAVITATION KEPLER S LAWS MOTION IN AN ELLIPTICAL\\nORBIT PRECESSION OF THE EQUINOXES.\\nGravitation 75\\nFirst law of gravitation 75\\nSecond law 76\\nKepler s laws 76\\nThe first law 76\\nThe second law 77\\nThe third law 78\\nPaths of projectiles 7S\\nEffect of increased velocity 78\\nWhy a planet returns from aphelion 79\\nWhy a planet departs from aphelion.. 80\\nPrecession of equinoxes 81\\nSigns of ecliptic displaced 81\\nMotion of the poles 82\\nCause of precession 82\\nThe tropical year 83\\nThe sidereal year 83", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0018.jp2"}, "17": {"fulltext": "C ONTENTS.\\nIX\\nCHAPTER VIII.\\nTHE MOON ITS EEVOLUTIONS ITS PHASES THE CONDITION\\nOF ITS SUEFACE.\\nPAGE\\nDistance and size of the moon 84\\nEevolution about the earth 84\\nMonths 85\\nNodes t 85\\nConj unction and opposition 85\\nQuadratures 86\\nOctants 86\\nForm of orbit 86\\nDiurnal motion 86\\nLibration of longitude 87\\nLibration of latitude 87\\nDiurnal libration 87\\nEevolution round the sun 88\\nPhases of the moon 88\\nPAGE\\nMoon running high or low 90\\nThe harvest moon 90\\nInequalities of moon s surface 91\\nForm of valleys 92\\nVolcanic appearance 92\\nHeight of its mountains 93\\nNo atmosphere or vapor 93\\nChanges of temperature on the moon. 94\\nView of the earth from the moon 94\\nAs to magnitude 94\\nAs to phase 94\\nAs to position in the sky 95\\nAs to surface 95\\nCHAPTER IX.\\nECLIPSES OF THE MOON AND SUN.\\nGeneral relations in eclipses 97\\nEclipse months 98\\nEclipse of the moon 99\\nForms of shadows 99\\nDuration of eclipse 100\\nAppearance of moon 100\\nEclipse of the sun 100\\nTotal shadow and penumbra of the\\nmoon 101\\nTotal and partial eclipses of the sun 101\\nAnnular eclipse 103\\nVelocity of the shadow 103\\nEelative number of solar and lunar\\neclipses 103\\nEclipses at the moon 104\\nTrue form of shadows 104\\nCHAPTER X.\\nLONGITUDE TIDES.\\nLocal time 105\\nConnection between longitude and\\nlocal time 105\\nLongitude by the chronometer 106\\nLongitude by a lunar eclipse 106\\nBy eclipses of Jupiter s satellites 106\\nBy a solar eclipse 107\\nBy occupations of stars 107\\nBy the lunar method 107\\nBy the magnetic telegraph 108\\nChange of days in going round the\\nearth 109\\nAmbiguity as to days among the\\nislands of the Pacific 109\\nTides, high and low water 110\\nSpring and neap tides Ill\\nOpposite tides Ill\\nForm of the water acted on by the\\nmoon Ill\\nDirect and opposite tides 112\\nTides by the sun 112\\nJoint action of sun and moon 113\\nEffect of inertia of water 113\\nDiurnal inequality 114\\nEffects of coasts 115\\nCotidal lines 116\\nTides in lakes 118", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0019.jp2"}, "18": {"fulltext": "CONTENTS.\\nCHAPTER XL\\nTHE PLANETS TABULAR STATEMENTS MERCURY VENUS\\nMARS.\\nPAGE\\nPlanetary bodies classified 119\\nThree groups 119\\nInferior planets 120\\nSuperior planets 120\\nSatellites 120\\nTable of distances 121\\nTable of revolutions 121\\nTable of magnitudes 122\\nTable of masses 122\\nSun and planets compared 123\\nDiameters and distances compared. 123\\nDirection of motions 123\\nMercury apparent motions 124\\nModified by the earth s motions 125\\nStationary points 127\\nPAGE\\nForm and position of Mercury s orbit 127\\nPhases of Mercury 127\\nPoint of greatest brightness 128\\nTransits of Mercury 12S\\nVenus\u00e2\u0080\u0094 its apparent motions 129\\nThe phases and brightness of Venus. 129\\nTransits of Venus 129\\nUse made of them 130\\nMars\u00e2\u0080\u0094 its situation in the System... 130\\nApparent motions 130\\nPhases and changes of apparent size. 132\\nAppearance of disk 132\\nOrbit and equator of Mars 133\\nDays on the small planets 133\\nCHAPTER XII.\\nTHE PLANETOIDS JUPITER SATURN URANUS NEPTUNE\\nDISTURBANCES OF THE PLANETS.\\nSpace between Mars and Jupiter 134\\nThe planetoids 134\\nWhen discovered number 134\\nCharacteristics 134\\nJupiter its magnitude 136\\nIts place in the System 136\\nIts form and orbit 136\\nBelts of Jupiter 137\\nSatellites of Jupiter 138\\nEclipses of Jupiter and its satellites. 138\\nSaturn\u00e2\u0080\u0094 its disk 140\\nRings of Saturn 140\\nDisappearance of rings 140\\nPhenomena of rings at the planet. 142\\nSatellites of Saturn 143\\nUranus discovery 143\\nPlace in the System 143\\nSatellites of Uranus 144\\nNeptune its discovery 144\\nMotions of the planets disturbed 145\\nNodes retrograde 146\\nApsides advance 146\\nEccentricity changes 146\\nStability preserved 146\\nCHAPTER XIII.\\nCOMETS SHOOTING STARS.\\nNucleus, coma, and envelope of a\\ncomet 148\\nNumber of comets 148\\nEccentricity of orbit 149\\nForm and direction of tail 149\\nDimensions of comets 150\\nLight of comets 151\\nMass of the comets 151\\nDirections of their motions 152\\nTo find a comet s orbit 152\\nComets of known period 153\\nHalley s comet 153\\nRemarkable comets 15*3\\nComet of 1680 153\\nOf 1744 153\\nOf 1770 154\\nOf 1843 154\\nOf 1858 154\\nOf 1861 154\\nShooting stars 155\\nGaseous meteors 155\\nSolid meteors 156\\nAerolites 156", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0020.jp2"}, "19": {"fulltext": "CONTENTS\\nXI\\nCHAPTER XIV.\\nTHE FIXED STARS\u00e2\u0080\u0094 CONSTELLATIONS.\\nPAGE\\nThe stellar universe 158\\nThe fixed stars and their magnitudes 158\\nNumber included in the several mag-\\nnitudes 159\\nCause of unequal brightness 159\\nConstellations 160\\nStar catalogues 161\\nDescriptions of constellations 161\\nConstellations of the Zodiac described 161\\nAries Taurus Gemini Cancer\\nLeo\u00e2\u0080\u0094 Virgo\u00e2\u0080\u0094 Libra 161-165\\nScorpio Sagittarius 165\\nCapricorn us\u00e2\u0080\u0094 Aquarius\u00e2\u0080\u0094 Pisces 166\\nConstellations north of the Zodiac. 168\\nUrsa Minor Ursa Major 168\\nDraco Cepheus Cassiopeia Cam-\\nelopardalus 168-171\\nPAGE\\nAndromeda Perseus 1T2\\nAuriga Leo Minor Canes Venatici\\nComa Berenices\u00e2\u0080\u0094 Bootes 173\\nCorona Borealis Hercules Lyra. 174\\nCygnus Vulpecula 175\\nAquila Antinous 176\\nDelphinus\u00e2\u0080\u0094 Pegasus 176, 177\\nOphiuchus 177\\nConstellations south of the Zodiac. 177\\nCetus Orion 177\\nLepus Canis Major Canis Minor. 178\\nMonoceros\u00e2\u0080\u0094 Hydra 180\\nEvening constellations of autumn.. 181\\nOf winter 182\\nOf spring 183\\nOf summer 183\\nCHAPTER XV.\\nEffect of telescopic power on fixed\\nstars 185\\nAnnual parallax 185\\nDistances of the stars 186\\nNature of the fixed stars 187\\nDouble stars 188\\nTwo ways of appearing double 188\\nBinary stars 189\\nTheir periods 190\\nDimensions of their orbits 190\\nTriple and quadruple stars 191\\nPeriodic and temporary stars 191\\nClusters of stars 192\\nNebulae 192\\nSeveral forms 193\\nThe galaxy. 193", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0021.jp2"}, "20": {"fulltext": "", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0022.jp2"}, "21": {"fulltext": "COMPENDIUM OF ASTRONOMY,\\nCHAPTEE I.\\nGENEEAL FOEM AND DIMENSIONS OF THE EAETH THE\\nDIUENAL MOTION AETTFICIAL GLOBES.\\n1, General Definitions. Astronomy is the science\\nwhich treats of the heavenly bodies that is, of the\\nsun, the planets and their satellites, the comets, and\\nthe fixed stars.\\nThe sun, planets, satellites and comets constitute\\nthe Solar System, which is so called because the sun\\nis the principal body belonging to it, and controls the\\nmovements of all the others.\\nThe Fixed Stars are at an immense distance out-\\nside of the solar system and each fixed star is sup-\\nposed to be the sun of a separate system. Nearly\\nall the bright points seen in the sky in a clear night\\nare fixed stars, the whole number of which has never\\nyet been counted.\\n1. Define astronomy. What is the solar system What bodies\\nare outside of the solar system?", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0023.jp2"}, "22": {"fulltext": "14 THE EARTH.\\n2. The Globular Form of the Earth, The earth\\non which we live is one of the planets of the solar\\nsystem. Its form, like that of all the other planets,\\nis almost perfectly spherical. This is learned in sev-\\neral ways.\\n1. When the sun casts the shadow of the earth on\\nthe moon in a lunar eclipse, the edge of the shadow\\nis always circular.\\n2. The earth shows its globular form by concealing\\nthe lower parts of objects when seen at a distance.\\nFig. 1.\\nThus, a person at A (Fig. 1) can see only the top of\\nthe mast of a ship, because the earth conceals all\\ntne lower parts. If the surface of the ocean were\\nperfectly flat, as in Fig. 2, then the whole ship could\\nbe seen, the lower part as well the upper, at any\\ndistance.\\n2. To what class of bodies does the earth belong Mention the\\nfirst proof that it is spherical\u00e2\u0080\u0094 the second the third.", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0024.jp2"}, "23": {"fulltext": "WORDS up and down. 15\\nFig. 2.\\n3. The measurements made on various parts of the\\nearth lead to the conclusion that the distance from\\nthe surface to the center is everywhere about the\\nsame.\\n3, Use of the words up and dotvn. Wher-\\never a person stands, up means from the earth,\\ntoward the highest point of the sky, and down means\\ntoward the center of the earth. Now, as the earth is\\na globe, the word up must express different directions\\nin different places, though to us it always seems to be\\nthe same and so of the word dotvn, For example,\\nthe person at A (Fig. 3), sees the point E directly over\\nhis head, and calls that direction up; while at B, up\\nis toward F, although directed 90\u00c2\u00b0 from AE. At 0,\\nwp is toward G, precisely opposite to what it is at A.\\n3. Explain the meaning of up, and of dovm. How can up be in\\ndifferent directions", "height": "3368", "width": "2000", "jp2-path": "compendiumofas00olms_0025.jp2"}, "24": {"fulltext": "16\\nTHE EAETH\\nFig. 3.\\nIn like manner, down, which is everywhere toward the\\ncenter, is in all possible directions from the different\\nplaces on the earth.\\n4, Size of the Earth. If a person sails away from\\nland till the ocean just conceals the whole height\\nof a certain mountain, then, by means of its height\\nand his distance from it, the Size of the earth can be\\neasily calculated. For it is plain that the larger a\\nglobe is, the more nearly flat is its surface, and the\\nfarther off can the mountain be seen. In this and in\\nother ways it is found that the diameter of the earth\\nis 7,912 miles. Therefore the distance from the sur-\\nface of the earth to its center is 3,956 miles, and the\\ncircumference is 24,857 miles.\\nInequalities of Surface. As the surface of the\\nearth is very uneven, and there are high mountains\\n4. How can the size of the earth be found\\nter its radius its circumference\\nWhat is its diame-", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0026.jp2"}, "25": {"fulltext": "EQUATOR AND ITS SECONDARIES. 17\\nand deep valleys on many parts of it, it seems, at\\nfirst, as though it could not have the regular form of\\na sphere. But we call an orange round, though it is\\ncovered with roughnesses and the mountains of the\\nearth are comparatively a great deal smaller than the\\nroughnesses on the outside of an orange.\\n6. The Diurnal notation. The earth revolves\\ncontinually from west to east on an imaginary line\\ndrawn through its center. This line is called the\\nEarth s Axis. The ends of the axis are called the\\nNorth and South Poles of the earth. The time occu-\\npied by the earth in revolving once round is called\\na Day and this is divided into 24 hours.\\n7\u00c2\u00bb Tlie Earth s Equator and its Secondaries, A\\ngreat circle drawn round the earth, midway between\\nits poles, is called the Equator. Meridians are great\\ncircles of the earth drawn through the poles, and\\ntherefore perpendicular to the equator. Since all\\ngreat circles of a sphere which are perpendicular to\\na given great circle are called its Secondaries, there-\\nfore the meridians are secondaries of the equator.\\nThe Latitude of a place is its distance north or south\\nfrom the equator, measured on the meridian of that\\nplace, in degrees, minutes, and seconds. Parallels of\\nlatitude are small circles of the earth, parallel to the\\nequator.\\n5. How can the earth be spherical, when there are high moun-\\ntains and deep valleys upon it\\n6. Describe the earth s rotation. Define its axis poles a day.\\n7. Define the equator and the meridians. What are the secon-\\ndaries of a great circle Meridians are secondaries of what De-\\nfine latitude longitude. How is a place on the earth determined", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0027.jp2"}, "26": {"fulltext": "18 THE EARTH.\\nThe Longitude of a place is the distance of its me-\\nridian, in degrees, minutes, and seconds, east or west\\nfrom some standard meridian, as that of Greenwich,\\nnear London, or that of Washington. The situation\\nof any place on the earth is determined by giving its\\nlatitude and longitude.\\n8. The earth is called the Terrestrial Sphere. The\\nCelestial Sphere is that apparent vault, called the\\nSky, which surrounds the earth on every side and to\\nwhich the heavenly bodies seem to be attached. The\\n-celestial sphere is often called The Heavens. For most\\npurposes of astronomy, the eye of an observer may\\nbe considered as the center of the celestial sphere.\\n0* TJie Horizon and Ms Secondaries. If the\\nplumb-line (usually called the vertical), at any place\\non the earth, is supposed to be extended till it\\nreaches the celestial sphere, it marks the Zenith above,\\nand the Nadir below. And a plane passed through\\nthe center of the earth, perpendicular to the vertical,\\nis called the Rational Horizon of that place. This is\\na great circle of the celestial sphere, and divides it\\ninto upper and lower hemispheres. The Sensible Hori-\\nzon is parallel to the rational horizon, and passes\\nthrough the place on the earth s surface. The planes\\nof these two horizons are, therefore, nearly 4,000\\nmiles apart but so great is the distance of the heav-\\n8. Describe the two spheres. What may be taken for the center\\nof the celestial sphere\\n9. Define zenith nadir. Define the rational horizon the sensi-\\nble horizon. Why are they one in the sky What are the secon-", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0028.jp2"}, "27": {"fulltext": "THE CELESTIAL EQUATOR. 19\\nenly bodies, that the two planes seem to unite in the\\nsame great circle of the celestial sphere.\\nThe secondaries of the horizon intersect each other\\nin the vertical line, and are called Vertical Circles.\\nOne of them is the meridian of the place. This cuts\\nthe horizon in the North and South Points of compass.\\nThe vertical circle, at right angles to the meridian, is\\ncalled the Prime Vertical This cuts the horizon in\\nthe points called East and West\\nThe Altitude of a heavenly body is its elevation\\nabove the horizon, measured on the vertical circle\\npassing through the body. The Zenith Distance of a\\nbody is the distance between it and the zenith, and\\nis, therefore, the complement of its altitude.\\nThe Azimuth of a heavenly body is an arc of the\\nhorizon, measured from the meridian to the vertical\\ncircle, which passes through the body. The Ampli-\\ntude is measured from the vertical circle passing\\nthrough the body to the prime vertical, and is, there-\\nfore, the complement of the azimuth. The altitude,\\nor zenith distance of a heavenly body, along with its\\nazimuth or amplitude, determines its place in the vis-\\nible heavens.\\n10, The Celestial Equator and its Secondaries,\\nIf the axis on which the earth revolves is produced\\nto the heavens, it becomes the Axis of the Celestial\\nSphere, and marks the North and South Poles of that\\nsphere. The north pole is at present in the constel-\\nlation of Ursa Minor. If the plane of the equator\\nbe extended in like manner, it becomes the Celestial\\ndaries of the horizon How are the points of compass fixed\\nDefine altitude zenith distance azimuth amplitude.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0029.jp2"}, "28": {"fulltext": "20\\nTHE EAETH\\nEquator. The secondaries to this circle are called\\nmeridians, as on the earth. They are also called\\nHour-circles, because the arcs of the equator inter-\\ncepted between them are used as measures of time.\\nTii\\nLet n (Fig. 4) represent the north pole of the earth,\\ns its south pole, eq the equator (projected in a straight\\nline), o a given place whose north latitude is eo.\\nThen N, S, are the poles of the celestial sphere, EQ\\nis the celestial equator, Z is the zenith of the place o,\\nE is its nadir, and HO its rational horizon oesqn\\nis the terrestrial meridian of the same place, and\\nZESQN is its celestial meridian, or hour-circle.\\n10. How are the celestial poles fixed? the celestial equator?\\nWhat are the hour-circles Describe by the figure.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0030.jp2"}, "29": {"fulltext": "THE ECLIPTIC. 21\\n11. The Ecliptic. Besides tlie equator, there is\\nan important circle of the celestial sphere, called the\\nEcliptic. It is that in which the sun appears to make\\nits annual circuit around the heavens. It is inclined\\nto the equator at an angle of nearly 23J\u00c2\u00b0, crossing it\\nin two opposite points, called the Equinoctial Points,\\nor Equinoxes. The word equinoxes is used, also, to\\nexpress the times at which the sun crosses the equa-\\ntor, because at those times the nights are equal to the\\ndays. The vernal equinox is the time when the sun\\npasses the equator from south to north, as it occurs\\nin the spring, about March 21st. The autumnal equi-\\nnox occurs on or near September 22d, when the sun\\nreturns to the south of the equator.\\nThe Solstitial Points, or Solstices, are those points of\\nthe ecliptic which are furthest north or south from\\nthe equator, situated, therefore, midway between the\\nequinoxes. They are so named because there the\\nsun stops in his advance northward or southward, and\\nbegins to return. The summer solstice is the point\\nivhere, and also the time w hen, the sun is furthest\\nnorth, about the 22d of June. He passes the winter\\nsolstice on or near the 22d of December.\\nThe Equinoctial Colure is that secondary to the\\nequator which passes through the equinoxes. The\\nSolstitial Colure is that which passes through the sol-\\nstices. They are, therefore, at right angles to each\\nother, and the latter is a secondary to the ecliptic, as\\nwell as to the equator.\\n11. Define the ecliptic the equinoxes and give their names.\\nDefine the solstices. When does the sun pass each of these four\\npoints Define the two colures.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0031.jp2"}, "30": {"fulltext": "22\\nTHE EARTH.\\n12. Signs of the Ecliptic. The ecliptic is divided\\ninto 12 equal parts of 30\u00c2\u00b0 each, called Signs, which\\nbeginning at the vernal equinox, succeed each other\\neastward in the following order\\nNORTHERN\\nSOUTHERN.\\n1. Aries,\\nT\\n7. Libra,\\n2. Taurus,\\n8. Scorpio,\\n*l\\n3. Gemini,\\nH\\n9. Sagittarius,\\nt\\n4. Cancer,\\n23\\n10. Capricornus,\\nV?\\n5. Leo,\\na\\n11. Aquarius,\\n6. Virgo,\\nw\\n12. Pisces,\\nX\\nThe vernal equinox being at the first point of Aries,\\nthe summer solstice is at the first of Cancer, the\\nautumnal equinox at the first of Libra, and the\\nwinter solstice at the first of Capricorn.\\n13. Right Ascer ion and Declination, The right\\nascension of a heavenly body is the angular distance\\nof its meridian from the vernal equinox, measured\\neastward on the equator. The declination of a body\\nis its angular distance north or south from the equa-\\ntor, measured on the meridian of the body.\\n14L. Celestial Longitude and Latitude* On the\\ncelestial sphere, longitude and latitude are referred to\\nthe ecliptic, not to the equator. Suppose a second-\\nary to the ecliptic to pass through a heavenly body\\nthe distance of the body from the ecliptic, measured\\non the secondary, is its latitude and the distance of\\n12. What are signs of the ecliptic Name them in order.\\n13. What is the right ascension of a body its declination\\n14. Define celestial longitude and latitude. Which way is longi-\\ntude reckoned right ascension", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0032.jp2"}, "31": {"fulltext": "BISING AND SETTING. 23\\nthis secondary, measured eastward on the ecliptic, is\\nits longitude.\\nBight ascension and longitude are reckoned only\\neastward, from 0\u00c2\u00b0 to 360\u00c2\u00b0, the first on the equator,\\nthe other on the ecliptic.\\n15\u00c2\u00bb Apparent Diurnal Motion of the Heavens.\\nAs the earth revolves from west to east on the axis ns,\\nan observer, not being conscious of this motion, sees\\nthe heavenly bodies apparently revolving in the oppo-\\nsite direction that is, from east to west, about the axis\\nNS. The sun, moon, and every planet, comet and\\nstar is observed to pass over from the eastern part of\\nthe sky toward the western, with a regular motion,\\nreappearing again in the east, after the lapse of about\\none day, in the same, or nearly the same place. The\\nfixed stars describe the circles, which are exactly\\nparallel to the equator, and in precisely the same\\nlength of time. But the other bodies vary somewhat\\nin their paths, and the periods of describing them,\\nthus showing that they are affected by other motions\\nbesides the diurnal rotation.\\n16* Kising, Setting, and Culmination* In Fig. 4,\\nAB, DO, FG, c, drawn parallel to EQ, represent the\\ndiurnal circles of stars, viewed edgewise, and, there-\\nfore, appearing as straight lines. Some of these\\ncircles intersect the horizon PIO. These intersections\\nare the points of rising or setting. Thus, a star de-\\n15. Explain the diurnal motion.\\n16. What are the points of a body s rising and setting What\\nare the points of its culmination Are both culminations ever in\\nsight Are both ever out of sight", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0033.jp2"}, "32": {"fulltext": "24: THE EAETH.\\nscribing the circle GF, rises in the northeast quarter,\\nand sets in the northwest, at points which are both\\nrepresented bj r. The star whose diurnal circle is\\nIK, rises in the southeast, and sets in the southwest,\\nat t. A star on the equator rises exactly in the east,\\nand sets in the west, at the point 0.\\nThe points in which these circles cut the meridian\\nare called the points of culmination. Thus, the star\\non FG makes its upper culmination at F, and its\\nlower one at G. On AB, both the upper and lower\\nculminations are above the horizon; on MP, they\\nare both below. If both culminations of a star are\\nabove the horizon, it is always in view if both\\nbelow, it never comes in sight. The number of stars\\nwhich do not rise and set depends on the position of\\nthe celestial poles in relation to the horizon that is,\\non the latitude of the place.\\nBy the culmination of a body, in the ordinary use\\nof the word, is meant its upper culmination.\\n17 Relations of the Horizon to the Diurnal Circles.\\nEvery change of position on the earth changes the\\nhorizon. If an observer moves eastward, all the\\nheavenly bodies which rise and set rise earlier, and\\nalso culminate and set earlier. If he moves west-\\nward, they rise, culminate and set later. If he moves\\ntoward the nearer pole of the earth, the correspond-\\ning pole of the celestial sphere becomes more ele-\\n17. Describe the effect of a person s moving east west toward\\nthe pole toward the equator. Show what the elevation of one\\npole is equal to. Which pole is elevated How much is the other", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0034.jp2"}, "33": {"fulltext": "THE EIGHT SPHERE. 25\\nvated, and the other more depressed and the con-\\ntrary, if he moves from the nearer pole that is,\\ntoward the equator. In all north latitudes, the north\\npole is elevated, and the south pole depressed and\\nthe reverse in south latitudes. And the elevation\\nof one pole, and the depression of the other, equals\\nthe latitude. For (Fig. 4) NO, the elevation of one\\npole HS, the depression of the other), equals EZ,\\nsince each is the complement of ZN. But EZ eo,\\nthe latitude, because they subtend the same angle\\natC.\\nThe elevation of the celestial equator equals the\\ncomplement of latitude. For EH is the complement\\nof EZ, which equals eo, the latitude. Hence, the\\nangle by which all the circles of diurnal motion are\\ninclined to the plane of the horizon, equals the com-\\nplement of latitude, since they are parallel to the\\nequator.\\nOn account of this change of inclination between\\nthe horizon and the diurnal circles, the aspect of the\\ndiurnal rotation is very different in different parts of\\nthe earth.\\n18* The Might Sphere, This name is given to\\nthose positions in which the diurnal circles cut the\\nhorizon at right angles. All points of the equator are\\nso situated. As the latitude is zero, the poles, hav-\\ning no elevation or depression (Art. 17), are both in\\nthe horizon the celestial equator passes through the\\nzenith, thus coinciding with the prime vertical and\\nall the paths of daily motion, being parallel to the\\n18/ Describe tlie right sphere.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0035.jp2"}, "34": {"fulltext": "26 THE EAETH.\\nequator, are perpendicular to the horizon. Every\\nheavenly body, unless situated exactly at one of the\\npoles, rises and sets during each revolution, and con-\\ntinues above the horizon just as long as it remains\\nbelow it, If a star rises in the east, it sets in the\\nwest, and culminates in the zenith and nadir.\\n19. TJie Parallel Sphere, This term expresses\\nthe appearance of the heavens at those points of the\\nearth where the circles of daily rotation are par-\\nallel to the horizon. This aspect can be presented\\nonly at the poles. For, at those points the latitude\\nbeing 90\u00c2\u00b0, one pole must be elevated 90\u00c2\u00b0; that is, to\\nthe zenith, and the other depressed 90\u00c2\u00b0, or to the\\nnadir. Hence, the diurnal circles, being perpendicu-\\nlar to the axis, must be horizontal, and the equator\\nmust coincide with the horizon. Every star in view\\npasses around the sky, maintaining the same eleva-\\ntion at every point of its path, and, therefore, never\\nrises or sets.\\nAt the north pole, that half the year in which the\\nsun is north of the equator, is uninterrupted day.\\nDuring the other half, the sun being south of the\\nequator, it is constant night.\\n20. The Oblique Sphere. At all latitudes, except\\n0\u00c2\u00b0 and 90\u00c2\u00b0, the circles of daily motion are oblique to\\nthe horizon, since they incline at an angle equal to\\nthe complement of the latitude. Thus, at 42\u00c2\u00b0 north\\nlatitude, the celestial equator is elevated 48\u00c2\u00b0 above\\n19. Describe the parallel sphere.\\n20. Describe the oblique sphere. What bodies are more than\\nhalf the time above the horizon below", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0036.jp2"}, "35": {"fulltext": "ARTIFICIAL GLOBES. 27\\nthe southern horizon, as represented in Fig. 4 and\\nall the diurnal circles, being parallel to the equator,\\nmake the same angle (48\u00c2\u00b0) with the horizon. The\\ncircle OX), whose distance from the elevated pole\\nequals its elevation, just touches the horizon at the\\nlower culmination, and is the limit of that part of the\\nsky which is always in view. This is called the circle\\nof Perpetual Apparition. The circle HL, at the same\\ndistance from the depressed pole, also touches the\\nhorizon, and is called the circle of Perpetual Occulta-\\nHon, since it limits that part of the sky which is\\nalways concealed.\\nThe horizon HO bisects the equator EQ. Hence,\\na body on the equator is as long above the horizon as\\nbelow it, in every part of the earth. But all bodies\\nbetween the equator and the elevated pole are longer\\nabove the horizon than below, while on the opposite\\nside they are longer below than above.\\n21c Artificial Globes. They are of two kinds, ter-\\nrestrial and celestial. The terrestial globe is a minia-\\nture representation of the earth, having, also, the\\nequator and several meridians and parallels of lati-\\ntude traced upon it. The celestial globe exhibits the\\nprincipal fixed stars in their relations to each other,\\nand to the equator and ecliptic.\\nThe artificial globe is suspended in a strong brass\\nring by an axis passing through the north and south\\npoles, on which it is free to revolve. This ring repre-\\nsents the meridian of any place, and is supported\\n21. Describe the artificial globes. What is the quadrant of alti-\\ntude? State the mode of adjusting the globe for the latitude.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0037.jp2"}, "36": {"fulltext": "28 THE EAETH.\\nvertically within a horizontal wooden ring which\\nstands upon a tripod. The wooden ring represents\\nthe horizon. The brass ring may be slid around in\\nits own plane, so as to elevate or depress either pole\\nto any angle with the horizon. It is graduated from\\nthe equator each way to the poles, for measuring lati-\\ntude and declination while the horizon ring has near\\nits inner edge two graduated circles, one for azimuth,\\nand the other for amplitude. On this ring, also, for\\nconvenient reference, are delineated the signs of the\\necliptic, and the sun s place in it for every day of the\\nyear.\\nAround the north pole is a small circle, marked\\nwith the hours of the day and at the same pole a\\nbrass index is attached to the meridian, which can be\\nset at any hour of the circle.\\nThe Quadrant of Altitude is a flexible strip of brass,\\ngraduated into 90 parts, each equal to a degree of the\\nglobe. This can be used for measuring angular dis-\\ntances in any direction on the sphere and when\\napplied to a vertical circle of the celestial globe, it\\ndetermines the altitude, or zenith distance of a heav-\\nenly body.\\nTo adjust either globe for any place on the earth,\\nelevate the corresponding pole to a height equal to\\nthe latitude. By moving the tripod, the axis can then\\nbe made parallel to that of the earth or the heavens.\\nAnd if the globe is turned (the celestial westward, or\\nthe terrestrial eastward), the diurnal motion will be\\ntruly represented.\\n22. Tell how to find the latitude and longitude of a place. The\\nlatitude and longitude of a place being given, how is it found?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0038.jp2"}, "37": {"fulltext": "PROBLEMS. 29\\n22* Problems on the Terrestrial Globe*\\n1. To find tJie Latitude and Longitude of a Place.\\nTurn the globe so as to bring the place to the brass\\nmeridian then the degree and minute on the merid-\\nian over the place shows its latitude, and the point of\\nthe equator, under the meridian, shows its longitude.\\nExample. What are the latitude and longitude of\\nNew York\\n2. To find a Place by its given Latitude and Longitude.\\nEind the given longitude on the equator, and bring\\nit to the meridian then under the meridian, at the\\ngiven latitude, will be found the required place.\\nEx. What place is in latitude 39\u00c2\u00b0 N., and longitude\\n77\u00c2\u00b0 W.\\n3. To find tlie Bearing and Distance of one Place from\\nanother\\nAdjust the globe for one of the places, and bring\\nit to the meridian screw the quadrant of altitude\\ndirectly over the place, and bring its edge to the\\nother place. Then the azimuth will be the bearing of\\nthe second place from the first, and the number of\\ndegrees beween them, multiplied by 69J, will give\\ntheir distance apart in miles.\\nEx. Find the bearing of New Orleans from New\\nYork, and the distance between them.\\nHow is the bearing of one place from another found? Find the\\ndifference of time at different places. When it is 2 P. M. in Paris,\\nwhat time is it in Boston", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0039.jp2"}, "38": {"fulltext": "30 THE EAETH.\\n4. To find the Difference of Time at Different Places.\\nBring to the meridian the place which lies west of\\nthe other, and set the hour-index at XII. Turn the\\nglobe westward, until the other place comes to the\\nmeridian, and the index will show the hour at the\\nsecond place when it is noon at the first. The hour\\nthus found is the difference required.\\nEx. When it is noon at New York, what time is it\\nat London\\n5. The Hour being given at any Place, to find ivhat Hour\\nit is at any other Place.\\nFind the difference of time between the two places,\\nas in (4) then, if the place whose time is required is\\neast of the other, add this difference to the given\\ntime but if west, subtract it.\\nEx. What time is it in Boston, when it is 2 P. M. in\\nParis\\n23, Problems on the Celestial Globe.\\n1. To find the Right Ascension and Declination of a\\nHeavenly Body.\\nBring the place of the body to the meridian then\\nthe point directly over it shows its declination, and\\nthe point of the equator under the meridian, its right\\nascension.\\nEx. Find the right ascension and declination of\\nAlpha Lyrse. Also, of the sun on the 3d of May.\\n23. How are the riglit ascension and declination of a star found\\nDescribe the manner of adjusting tho globe to represent the heav-", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0040.jp2"}, "39": {"fulltext": "PROBLEMS. 31\\n2. To Represent the Appearance of the Heavens at any\\nTime.\\nAdjust the globe for the place (Art. 21). On the\\nwooden horizon find the day of the month, and\\nagainst it is given the sun s place in the ecliptic. On\\nthe ecliptic find the same sign and degree, and bring\\nthe point to the meridian. The globe then presents\\nthe positions of the stars at noon. Set the hour-\\nindex at XII, and turn the globe till the index points\\nto the required hour. The aspect of the heavens at\\nthat hour is then represented.\\nEx. Kequired the aspect of the stars at Lat. 51\u00c2\u00b0,\\nDecember 5th, at 10 P. M.\\n3. To find the Time of the Rising and Setting of any\\nHeavenly Body at a given Blace.\\nHaving adjusted for the latitude, bring the sun s\\nplace in the ecliptic to the meridian, and set the\\nindex at XII. Turn the globe eastward, and then\\nwestward, till the given body meets the horizon, and\\nthe index will show the times of rising and setting.\\nThe times of the sun s rising and setting may be\\nfound in the same manner on the terrestrial globe,\\nsince the ecliptic is usually represented on it.\\nEx. At what time does the sun rise and set on the\\n4th of July?\\nEind the time of the rising and setting of Arcturus\\non the 10th of November.\\nens at a given time. How are the times of rising and setting of a\\nbody found How are the altitude and azimuth of a body found\\nThe distance between two stars Find the height of the sun at\\nnoon, August 1st, Lat. 28\u00c2\u00b0 30 N.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0041.jp2"}, "40": {"fulltext": "32 THE EARTH.\\n4. To find the Altitude and Azimuth of a Star for a given\\nLatitude and Time.\\nAdjust the globe for the aspect of the heavens (2)\\nscrew the quadrant of altitude to the zenith, and\\ndirect it through the place of the star then, the arc\\nbetween the star and the horizon is the altitude, and\\nthe arc of the horizon between the quadrant of alti-\\ntude and the meridian is the azimuth.\\nEx. Find the altitude and azimuth of Sirius, De-\\ncember 25th, at 9 p. m. Lat. 43\u00c2\u00b0.\\n5. To find the Angular Distance between two Stars.\\nLay the quadrant of altitude across the two stars,\\nso that the zero shall fall on one of them then, the\\ndegree at the other will show their distance from each\\nother.\\nEx. Find the distance between Arcturus and Alpha\\nLyrae.\\n6. To find the Suns Meridian Altitude for a given Lati-\\ntude and Day.\\nFind the sun s place, and bring it to the meridian.\\nThe degree over it will show its declination. If the\\ndeclination and latitude are both north or south, add\\nthe declination to the co-latitude if not, subtract it.\\nEx. Find the sun s meridian altitude at noon, Aug.\\n1st, Lat. 38\u00c2\u00b0 30 K", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0042.jp2"}, "41": {"fulltext": "CHAPTEE II.\\nPARALLAX ATMOSPHERIC REFRACTION TWILIGHT.\\n24. Parallax Defined. When a person changes\\nhis place, objects about him in general appear in dif-\\nferent directions from him. This change of direction\\nis called Parallax. If, for example, he moves north,\\nan object which was directly ivest of him is moved by\\nparallax towards the soidhivest and an object which\\nwas east now appears in the southeast quarter. The\\ndirection of every thing is more or less altered,\\nexcept those objects which are directly before, or\\ndirectly behind him.\\nIt is easily perceived, also, that objects which are\\nnear change their direction very rapidly while distant\\nthings change slowly, or even appear to remain at\\nrest, unless the person moves a great way. The par-\\nallax of a body may, therefore, be used to enable us\\nto find out how far off it is.\\n25. Diurnal Parallax. While a person travels\\nover the earth, or is carried about it by the diurnal\\nrotation, the heavenly bodies must in the same way\\nsuffer some change of direction.\\n24. Define parallax. Illustrate it. Compare near and distant\\nobjects.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0043.jp2"}, "42": {"fulltext": "34\\nTHE EARTH.\\nBy the true place of a heavenly body is meant that\\nwhich it would seem to occupy if viewed from the\\ncenter of the earth. At the surface, therefore, it ap-\\npears generally displaced from its true position and\\nthis displacement is called the Diurnal Parallax,\\nThus, the true place of the body M (Fig. 5) is in the\\ndirection CK but at A it appears in the line AH\\nand the parallax is the angle AMO. So, the true\\nplace of M is Q, its apparent place is P, and the par-\\nallax is AM C. But the body M appears at Z,\\nwhether viewed from A or C, and the parallax in\\nthis case is zero. Since the earth s radius, in each\\ninstance, subtends the angle of parallax, we have the\\nfollowing definition\\nThe diurnal parallax of a body is the angle at that\\nbody subtended by the semi-diameter of the earth.\\n25. What is diurnal parallax What is the true place of a body\\nShow the effect of parallax by the figure.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0044.jp2"}, "43": {"fulltext": "ATMOSPHEEIC EEFKACTION. 35\\n2G* On what Diurnal Parallax Depends. At the\\nhorizon, the angle M, being subtended perpendicu-\\nlarly by the earth s radius AC, is larger than M or\\nM which are subtended obliquely. And it is plain,\\nthat the higher the body in the sky, the less is its\\nparallax, till at M m when seen in the zenith, it has\\nno parallax at all.\\nAgain, if the body were further removed from the\\nearth, it is obvious that the angle M, subtended by\\nthe same line AC, would be smaller. Hence, the par-\\nallax of a body is greatest at the horizon, and varies in-\\nversely as the distance of the body from the earth s center.\\nThe parallax of a body at the horizon is called its\\nHorizontal Parallax.\\n7. TJie Parallax of the 3Ioon. There is no one\\nof the heavenly bodies which has so great a parallax\\nas the moon. It is, therefore, the nearest of them all.\\nBut even the moon s parallax is less than one degree;\\nthat is, if a person were to travel over the line AC,\\nwhich is about 4,000 miles long, the direction of the\\nmoon would not be changed so much as one degree.\\nThis shows that the moon, though nearer than any\\nother body, is yet at a very great distance from us.\\n28* Atmospheric Hefraction. The atmosphere of\\nthe earth refracts or bends the rays of light as they\\ncome through it from the heavenly bodies. Let DD\\n(Fig. 6) be a part of the surface of the earth, and AA\\n20. On what does parallax depend? Where is it nothing?\\nWhere is it greatest What i3 it called\\n\u00c2\u00a37. What heavenly body has the greatest parallax How much", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0045.jp2"}, "44": {"fulltext": "36\\nTHE EAKTH\\nthe top of the atmosphere. If a person is at O, the\\nlight of the star S does not come to hLn in a straight\\nline, but first strikes at a, and is bent downward to b,\\nthen to c, and finally to O. Therefore it does not\\nseem to come from S, but from S in the line Oc pro-\\nduced. Thus, the star appears elevated above its\\nABCD DOBA\\ntrue place. In this figure, the effect of refraction is\\nvery much exaggerated. The greatest refraction\\ntakes place at the horizon but even there it elevates\\nan object only about 34 or a little more than the\\nbreadth of the sun. As the height above the horizon\\nincreases, the refraction becomes less, and is nothing\\nat the zenith.\\n29* Time of Rising and Setting Affected by Re-\\nfraction. Since a body at the horizon appears raised\\n28. Show by the figure how light from a star comes to a person.\\nWhat effect is produced? Where is refraction greatest? How\\nmuch is it", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0046.jp2"}, "45": {"fulltext": "ILLUMINATION OF THE SKY. 37\\nabove its true place about the breadth of the sun or\\nmoon, it must appear to rise earlier and to set later\\nthan it really does. This circumstance causes the\\nsun and all the bodies which rise and set to be seen\\nabove the horizon at least four minutes longer than\\nthey would do if there were no atmosphere.\\n30, Distortion of the Sun s and Bloon s Disk by\\nRefraction. The change in the amount of refraction\\nis so rapid near the horizon, that when the sun has\\njust risen, or is just about to set, the lower limb is\\nelevated more than the upper by a very perceptible\\nquantity. Its form, therefore, does not appear circu-\\nlar, but nearly elliptical, the vertical diameter being\\nshortened about 5 or 6 The lower half, however,\\nappears more flattened than the upper half, because\\nthe difference of refraction between the lower limb\\nand the center is greater than that between the center\\nand the upper limb.\\nSI, Illumination of the Sky. During the day the\\natmosphere is illuminated by the light of the sun,\\nwhich penetrates every part of it, and is reflected in\\nall directions. If there were no air, the sky, instead\\nof appearing luminous by day, would exhibit the\\nsame blackness as by night, and the stars would be\\nvisible alike at all times. We should, in that case,\\nlose a great part of that generally diffused light\\nwhich illuminates the interior of buildings and other\\n29. Its effect on the time of rising and setting\\n30. Describe and explain the effect on the disk of the sun.\\n31. How would the sky appear if there were no air Why", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0047.jp2"}, "46": {"fulltext": "38 THE EAETH.\\nplaces screened from the direct rays of the sun. The\\nearth s surface, and all terrestrial objects on which\\nthe sunlight falls directly, would indeed, by radiant\\nreflection, cause a degree of illumination, but it would\\nbe far less than we now enjoy. It has been observed,\\nin ascending to great heights, either on mountains or\\nin balloons, where, of course, the air which is most\\ndense and reflects most abundantly is left below, that\\nthe sky assumes a very dark hue, and the general\\nillumination is greatly diminished.\\n32, Twilight. The illumination of the sky begins\\nbefore the sun rises, and continues after it sets. It is\\nthen called twilight. More or less of it is visible as\\nlong as the sun is not more than 18\u00c2\u00b0 vertically below\\nthe horizon. Those parts of the atmosphere are\\nmost luminous which lie nearest to the direction of\\nthe sun. Thus, in Fig. 7, let A be a place on the earth\\nwhere the sun is just setting. The whole sky, IEFH,\\nis illuminated. But, to a place further east, as B, the\\ntwilight extends from E to H, the part of the sky\\nHK, remote from the sun being in the* shadow of the\\n32. Explain twilight by Fig. 7.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0048.jp2"}, "47": {"fulltext": "DUBATION OF TWILIGHT. 39\\nearth. At C, only FH is illuminated, and HL is\\ndark. At D, the twilight is entirely gone.\\nThough the twilight terminates at H, there is no\\nabrupt transition from light to shade at that point,\\nsince the reflection from those high and rare parts of\\nthe air is exceedingly feeble and, also, because the\\nthickness of the illuminated segment, through which\\nwe look, diminishes gradually to that limit, as is obvi-\\nous from an inspection of the figure.\\nS3. Duration of Twilight. To an observer at the\\nequator, at those times of the year when the sun is\\non the celestial equator, the twilight continues Ih.\\n12m. For, in the diurnal motion, 15\u00c2\u00b0 are described\\nin an hour, and, therefore, 18\u00c2\u00b0 in l^h. lh. 12m.\\nThis is the shortest duration possible. For, if the\\nsun were north or south of the equator, the degrees\\nof diurnal motion would be shorter than those on a\\ngreat circle. And, if the observer were on some par-\\nallel of latitude, the circles of daily motion would be\\noblique to his horizon, and the sun must, therefore,\\npass over more than 18\u00c2\u00b0 in order to move 18\u00c2\u00b0 verti-\\ncally. An extreme case occurs at the poles, where\\ntwilight lasts several months.\\n33. How long does it last in different cases.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0049.jp2"}, "48": {"fulltext": "CHAPTEE III.\\nASTRONOMICAL INSTRUMENTS-\\nTHE SUN THE SEASONS FOKM OF THE EARTH S ORBIT.\\n34, The Equatorial Telescope. In order that the\\ntelescope may be used to the best advantage for\\nastronomical purposes, it is often mounted equator-\\nidtty that is, it can be turned on tivo axes, one par-\\nallel to the earth s axis, and the other perpendicular\\nto it. And, besides this, a clock is connected with\\nthe first axis in such a way as to revolve the telescope\\njust as fast as the earth revolves, and in the opposite\\ndirection. Thus, any heavenly body to which the\\ntelescope is directed remains steadily in the field of\\nview, and can be examined leisurely and with care.\\n35. The Transit Instrument. This is a telescope\\nso mounted as to observe a heavenly body at the\\ninstant when it crosses the meridian. AD (Fig. 8)\\nrepresents the telescope supported by a horizontal\\naxis, which consists of two hollow cones placed base\\nto base, so as to combine lightness and strength.\\nThe ends of the axis rest in sockets, attached to two\\nstone piers, E and W. That the instrument may re-\\nceive no tremors from the building, the piers stand\\n34. Describe the equatorial telescope. Why so mounted", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0050.jp2"}, "49": {"fulltext": "ASTEONOMICAL INSTKUMENTS\\n41\\non a firm foundation in the ground, passing through\\nthe floor without contact. The axis being placed east\\nand west horizontally, the telescope, which is perpen-\\ndicular to it, will, when turned, revolve in the plane of\\nFig. 8.\\nthe meridian. A graduated circle, N, is attached to\\none end of the axis, for marking altitudes or zenith\\ndistances. The whole instrument can be raised from\\nthe sockets, and the axis inverted, so that the east\\nend shall rest on the pier W, and the west end on the\\n35. Describe the transit instrument.. Why so called", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0051.jp2"}, "50": {"fulltext": "42 THE SAETH.\\npier E. In the focus of the eye-glass there is a fine\\nhorizontal wire, and several vertical wires, of which\\nthe middle one is on the meridian. When a star\\nwhich is crossing the field of view is seen on the\\nmiddle wire, it is at that moment making a transit of\\nthe meridian.\\nSO. TJie Astronomical Clock. A clock must be\\nnear the transit instrument, to show the exact time of\\nthe transit. The clock of the observatory is made to\\nkeep sidereal time that is, star time instead of sun\\ntime. One sidereal day is the length of time from\\nthe moment a star passes the meridian till it passes\\nit again and it is about four minutes shorter than a\\nday as measured by the sun. The sidereal day be-\\ngins and ends at the moment when the vernal equinox\\nis on the meridian.\\n37* To find the Might Ascension and Declination\\nof a Heavenly Body. Observe the exact sidereal\\ntime when the body makes its transit. That time ex-\\npresses its right ascension, or its distance east of the\\nvernal equinox, in hours, minutes, and seconds. This\\nmay be changed into degrees, minutes, and seconds.\\nFor, since a star makes an apparent revolution of\\n360\u00c2\u00b0 in 24 sidereal hours, it describes 15\u00c2\u00b0 in one hour,\\n15 in one minute, and 15 in one second. Bight\\nascension is measured either in time or in arc.\\nThe declination of the body is found by observing\\n36. What accompanies it Wliat kind of time is kept\\n37. State how to find the right ascension of a body. In what\\ndenominations is it measured? How is its declination found?\\nWhat other instrument is sometimes used for this?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0052.jp2"}, "51": {"fulltext": "ASTRONOMICAL INSTRUMENTS\\n43\\nits height above the horizon, as indicated on the\\ncircle N, and then finding the difference between this\\nheight and the height of the equator, which is known\\nby the latitude of the place. A separate instrument,\\ncalled the Mural Circle, is sometimes employed in the\\nobservatory for finding the declination.\\n38* The Altitude and Azimuth Instrument. The\\nessential parts of this instrument are a telescope and\\ntwo graduated circles, one vertical, the other horizon-\\nFra. 9.\\ntal. Fig. 9 presents one of its more simple forms.\\nThe telescope AB is movable on a horizontal axis,\\n88. Describe the altitude and azimuth instrument, and its use.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0053.jp2"}, "52": {"fulltext": "44 THE EARTH.\\nat the center of the vertical circle abc, and also on a\\nvertical axis, passing through the center of the hori-\\nzontal circle EFG. The levels g and h, placed at\\nright angles to each other, show when the circle EFG\\nis brought to a horizontal position by the tripod\\nscrews. The tangent screws, d and e, give slow mo-\\ntions, one in a vertical, the other in a horizontal plane.\\nIf the reading of the vertical circle is taken when the\\ntelescope is horizontal, and again when it is directed\\nto a star, the difference of the readings is equal to the\\naltitude of the star. In a similar manner, if the hori-\\nzontal circle is read when the telescope is directed to\\nthe north, and read again when it is directed to a\\nstar, the difference is its azimuth.\\n39o The Sextant. This is an instrument for meas-\\nuring the angular distance between two points situ-\\nated in any plane whatever. It is represented in Fig.\\n10. I and H are two small mirrors, and T a small\\ntelescope. ID is a movable radius or index, carrying\\nthe index mirror at the center of motion, I, and a\\nvernier at the extremity, D. The horizon glass, H, is\\nsilvered only on one-half of its surface. When the\\nzero of the vernier coincides with that of the arc at\\nF, the mirrors are precisely parallel. If now we\\ndirect the telescope to a star, it may be seen in the\\ntransparent part of the horizon glass, and its image\\nin close contact with it, in the silvered part.\\nIn order to measure an angle, as, for example, that\\nbetween the moon M and the star S, direct the tele-\\n39. Describe the sextant, and how to measure the distance be-\\ntween the mocn and a star.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0054.jp2"}, "53": {"fulltext": "THE SUN S PLAGE,\\nFig. 10.\\n45\\nscope to S, and turn the index from F toward E, till\\nthe moon is seen to touch the star. The vernier will\\nthen show on the graduated arc the size of the angle\\nbetween the star and the moon s limb.\\n40, Observations of the Sun s Place. If we em-\\nploy the instruments of the observatory in measuring\\nfrom day to day the right ascension and declination\\nof the sun, at the moment of its crossing the merid-\\nian, it will be discovered that these quantities are\\nconstantly changing or, in other words, that the sun\\nis constantly shifting its place in relation to the stars.\\n40. What motion has the sun in right ascension What in de-\\nclination? When is It furthest north? When furthest south?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0055.jp2"}, "54": {"fulltext": "46 THE EAETH.\\nIn right ascension, the sun gains nearly a degree\\nevery day that is, it moves eastivard nearly a degree\\neach day so that, in 365 or 366 days, it comes round\\nagain to the same place among the stars.\\nBut in declination, it moves alternately north and\\nsouth, crossing the equator on the 21st of March, as\\nit moves northward, and again on the 22d of Septem-\\nber, as it returns southward. On the 22d of June it\\nis furthest north, and on the 22d of December it is\\nfurthest south. Its greatest distance north and south\\nof the equator is about 23 J\u00c2\u00b0.\\n41. The Ecliptic and Zodiac* The apparent an-\\nnual path of the sun is found, by the foregoing ob-\\nservations, to lie in a ptarw, cutting the celestial sphere\\nin a circle called the Ecliptic (Art. 11), and inclined to\\nthe plane of the equator at an angle of about 23\u00c2\u00b0 27\\nThe Zjdiac is the name given to a zone of the\\nheavens, 16\u00c2\u00b0 wide, extending along the circle of the\\necliptic, 8\u00c2\u00b0 on each side of it. The paths of the prin-\\ncipal planets lie within this zone. Its length is\\ndivided into 12 signs of 30\u00c2\u00b0 each, having the same\\nnames and arranged in the same order as those of\\nthe ecliptic (Art. 12), though not coincident with\\nthem. The signs of the zodiac are distinguished\\nfrom each other by the stars which occupy them.\\n42. The Tropics and Polar Circles. Through the\\ntwo points of the ecliptic most distant from the equa-\\nWlien does it cross the equator How far north, and how far south\\ndoes it go\\n41. How does the sun s path lie? What is the zodiac? How\\ndivided", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0056.jp2"}, "55": {"fulltext": "THE ANNUAL MOTION. 47\\ntor, called the solstices, (Art. 11), we imagine circles\\nto be drawn parallel to the equator, called the Tropics.\\nThe northern circle, passing through the first of Can-\\ncer on the ecliptic, is called the tropic of Cancer the\\nsouthern one, for a like reason, is called the tropic of\\nCapricorn. Two other parallels to the equator, pass-\\ning through the poles of the ecliptic, and therefore\\n23\u00c2\u00b0 27 from the poles of the equator, are called the\\nPolar Circles.\\n43. Terrestrial Zones. On the terrestrial sphere,\\na similar system of circles divides the earth s surface\\ninto the well-known zones of geography, called the\\ntorrid, temperate, and frigid zones. The tropics are\\nthe limits of vertical sunshine in mid-summer. The\\npolar circles are the limits within which the sun\\nmakes a diurnal revolution in mid-summer and mid-\\nwinter without rising or setting.\\n44:, The Annual Motion Observed without Instru-\\nmentsm If the stars were visible in the daytime, we\\nshould perceive the sun making progress among them\\ntoward the east, by a distance equal to nearly twice\\nits own breadth every day, since the apparent diame-\\nter of the sun is a little more than half a degree.\\nBut, as they are invisible by day, we detect the same\\nfact, when we notice that at a given hour of the night\\nall the stars are further west than on a previous night.\\nFor example, at 9 o clock p. m. that is, 9 hours after\\n42. Define the tropics the polar circles.\\n43. The zones of the earth.\\n44. How is the annual motion of the sun perceived without in-\\nstruments? How far each day does it move", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0057.jp2"}, "56": {"fulltext": "48\\nTHE EAETH.\\nnoon it is easily observed that there is, from one\\nevening to another, a regular progress of all the stars\\nwestward, as long as we choose to watch them. In\\nother words, the sun is at the same rate advancing\\neastward relatively to the stars.\\n43. The Annual 3Iotion is a Motion of the Earth,\\nnot of the Sun. There is abundant evidence that the\\nmotion of the sun around the earth, above described,\\nis only apparent, and results from a real motion of the\\nearth about the sun. Thus, suppose the earth to pass\\nFig. 11.\\naround the sun S (Fig. 11) in the orbit ABPC, in the\\norder of the signs. If we were unconscious of this\\nmotion, the sun would appear to us to move about\\n45. Is this really the sun s motion Use Fig. 11.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0058.jp2"}, "57": {"fulltext": "CHANGE OF SEASONS. 49\\nthe earth in the same order of the signs, though,\\nat any given moment, in a contrary direction. When\\nthe earth is at B (in the sign T, as seen from the\\nsun), we could see the sun in the sign when we\\nreach b the sun is seen in fit and so on.\\n46. Catise of the Change of Seasons. The phe-\\nnomena of the seasons are due to the fact that the\\ntwo revolutions of the earth, one on its axis, and the\\nother around the sun, are in different planes in other\\nwords, that the equator and the ecliptic make an\\nangle with each other. In Fig. 12, let the ecliptic be\\nrepresented by the large circle in the plane of the\\npaper. And suppose the earth to pass round the sun\\nin the order of the signs, \u00c2\u00b0P, s n, etc., occupying the\\nposition A on the 21st of March, B on June 22d, C on\\nSeptember 22d, and D on December 22d.\\nNext, suppose the plane of the equator (represented\\nby the straight line eq) to be inclined to the plane of\\nthe paper by an angle of 23J\u00c2\u00b0, and always in the\\nsame direction. The axis ns, which is perpendicular\\nto eq, will, therefore, be parallel to itself in all posi-\\ntions of the earth. In the figure, it is represented as\\neverywhere leaning to the right. At A, the earth s\\nposition, March 21st, the rays of the sun just reach to\\nn and s so that, if the earth revolves on ns at that\\nplace, every spot on its surface will be one-half the\\ntime in the light, and the other half in darkness.\\nThe days and nights are, therefore, equal. In this\\nposition, the plane eq, if extended, passes through\\n46. By Fig. 12, show how the seasons are caused. Position A\\nposition B, C, D.\\n3", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0059.jp2"}, "58": {"fulltext": "50\\nTHE BAETH.\\nthe sun; that is, the sun is in the equator of the\\nheavens, and it is the time of the vernal equinox.\\nFig. 12.\\nIn the position B, the circle of illumination, as\\nrepresented, reaches beyond n to the polar circle, and\\nfalls short of s by the same distance, the sun being\\nseen north of the equator eq. As the earth revolves\\non ns, it is evident that all places north of eq are\\nlonger in light than in darkness and the reverse is\\ntrue of all places south of eq. It is now summer in\\nthe northern hemisphere, and winter in the southern.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0060.jp2"}, "59": {"fulltext": "HEATANDCOLD. 51\\nAt C, the earth has reached the autumnal equinox\\nthe circle of illumination passes through n and s, and\\nthe phenomena are the same as at A.\\nAt D, the north pole is turned as far as possible\\ninto the shade, and the south pole into the sunlight.\\nThe sun is at the tropic of Capricorn and as the\\nearth rotates on ns 9 all places north of the equator\\nexperience the short days and the long nights of\\nwinter, and the reverse at all places south of the\\nequator.\\n47 Causes of Seat in Summer and Cold in Win-\\nter. These are two.\\n1st. The length of the day compared with the\\nnight. The heat of the earth is passing off by radi-\\nation during the whole time, whether the sun shines\\nor not. But the earth receives heat from the sun\\nonly while the sun is above the horizon. Hence, the\\nlonger the period of sunshine, compared with the\\ntime of a diurnal revolution, the greater the heat.\\nFor this reason, therefore, the summer is warmer\\nthan the winter.\\n2d. The greater altitude of the sun in summer than\\nin winter. The greater the sun s height is, the more\\nnumerous are the rays which fall on a given area.\\nBetween March and September the northern hemi-\\nsphere has its summer, both because the days are\\nlongest and the sun is highest. And for a similar\\nreason the southern hemisphere has its summer be-\\ntween September and March. Of course the winter\\n47. Give the first reason for heat in summer, and cold in winter,\\nthe second.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0061.jp2"}, "60": {"fulltext": "52 THEEAETH.\\nof each hemisphere occurs at the same time as the\\nsummer of the other.\\n48. Wliy the Greatest Heat is Later than the Sum-\\nmer Solstice, and the Greatest Cold Later than the\\nWhiter Solstice. If the sun sheds on a given surface\\nmore heat each day than the surface loses by radi-\\nation, then the heat accumulates from day to day.\\nThis is the case during the long days of summer; and\\nmore heat is gained than lost till a month or more\\nafter the summer solstice. For a like reason, during\\nthe middle hours of the day, heat is received from\\nthe sun more rapidly than it is lost by radiation, so\\nthat the hottest hour is 2 or 3 o clock p. M.\\nIn the winter, on the contrary, the loss by radiation\\nexceeds the quantity received from the sun during all\\nthe shortest days, so that the temperature descends\\ntill many weeks after the winter solstice.\\n49\u00c2\u00bb iVo Change of Seasons if there were no Obli-\\nquity. The angle between the planes of the two mo-\\ntions of the earth being the cause of the change of\\nseasons, it follows that there would be no such change\\nif those motions were in the same plane. If, while\\nthe earth advances in its orbit about the sun, it should\\nrotate in the same direction on its axis, then the sun\\nwould always be in the plane of the equator, and\\nwould, every day of the year, describe the equator as\\nits diurnal circle, rising exactly in the east, culmi-\\n48. Why is it hottest after the longest days Why coldest after\\nthe shortest days\\n49. If the ecliptic coincided with the equator, what would be the\\nseasons", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0062.jp2"}, "61": {"fulltext": "FORM OF THE EARTH S ORBIT. 53\\nnating at a zenith distance equal to the latitude of\\nthe place, and setting exactly in the west. At the\\nequator, the sun would always follow the prime verti-\\ncal, and at either pole it would always be passing\\nround in the horizon.\\noO\u00c2\u00bb The Greatest Changes of Season if the Obli-\\nquity were 90\\\\ If, while the earth revolves on its\\naxis from west to east, it should pass around the sun\\nin a plane lying north and south, then the ecliptic\\nwould pas\u00c2\u00a7 through the north and south poles, and\\nthe solstices would be at the poles. Hence, at a\\nstation on the equator, the sun would, during the\\nyear, describe the prime vertical and various small\\ncircles parallel to it, down to the north and south\\npoints of the horizon, where it would be stationary\\nalternately at the times of the solstices. At the\\nequator, therefore, there would be an alternation from\\nsummer to winter, or the reverse, every three months.\\nSI Mode of Determining the Form of the JEqrth s\\nOrbit. The earth s orbit is an ellipse described\\nabout the sun, which is situated in one of its foci.\\nThis is ascertained by observing the changes in the\\nsun s apparent diameter throughout the year. When\\nthe sun appears smallest, it is most distant; and\\nwhen largest, it is nearest. And its distance, in all\\ncases, varies inversely as its apparent diameter.\\nTherefore, if the sun s apparent diameter be accu-\\nrately measured as frequently as possible, we can\\nfrom these measurements find the relative distances\\nand these distances determine the form of the orbit.\\n50. What if the obliquity were 90\u00c2\u00b0?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0063.jp2"}, "62": {"fulltext": "54\\nTHE EAETH.\\nThus, suppose the earth to be at E (Fig. 13), and\\nthat the sun s apparent diameter is measured when in\\nthe direction Ea. After it has advanced eastward\\nsome days, so as to be seen in the direction E6, let it\\nbe measured again and so on, at every opportunity\\nthrough the year. Then the proportion of the lines\\nFig. 13.\\nEa, W), Ec, etc., will be known and if they are laid\\ndown of the proper length, and in the proper direc-\\ntions, the dotted line abmv, passing through their\\nextremities, will be the true form of the sun s ap-\\nparent orbit about the earth, and, therefore, of the\\nearth s orbit about the sun. This form is found to\\nbe an ellipse, having the sun in one of its foci.\\n52. Definitions Relating to a Planetary Orbit,\\nLet E be the focus occupied by the sun, and am the\\n51. What observations are made to find the form of the earth s\\norbit Describe by the figure. What is the form", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0064.jp2"}, "63": {"fulltext": "LINE OE APSIDES. 55\\nthe major axis of an elliptical orbit described about\\nit the nearest point, a, is called the perihelion, and the\\nmost distant point, m, the aphelion. The two points\\na and m are also called the apsides. The varying dis-\\ntance, Ea, E Wi, etc., is called the radius vector. If\\nthe major axis, am,, is bisected in C, the ratio of EG\\nto the semi-major axis, aC, is called the eccentricity of\\nthe orbit. The less EC is, compared with aC, the\\nless is the eccentricity, and the nearer does the ellipse\\napproach to a circle. If E coincides with C, the\\neccentricity is nothing, and the orbit is a circle.\\nThe eccentricity of the earth s orbit is only g 1\\nthat is, EC is of aC. If the figure were drawn in\\nthat proportion, it could not be distinguished from a\\ncircle.\\n53, Position of the Line of Apsides. The direc-\\ntion of the major axis of the earth s orbit, or the line\\nof apsides, is slowly changing but at present it\\npasses through the 10th degree of Cancer and Capri-\\ncorn, as represented in Eig. 11. The earth is at peri-\\nhelion on the 1st of January, and at aphelion on the\\n1st of July. We are, therefore, nearest to the sun in\\nthe winter of the northern hemisphere, and furthest\\nfrom it in the summer.\\n54. Distance from the Sun, as Affecting the Sea-\\nsons. The intensity of the sun s heat at the earth, as\\nwell as that of its light, varies inversely as the square\\n52. Define the several parts of an orbit. How much is the eccen-\\ntricity of the earth s orbit It is nearly of what shape\\n53. When does the earth pass the perihelion and the aphelion", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0065.jp2"}, "64": {"fulltext": "56 THE EAETH.\\nof our distance from it. On this account, the inten-\\nsity of heat at perihelion is to that at aphelion as\\n6V 59 3 which is nearly as 31 29. Therefore, so\\nfar as distance is concerned, the earth receives s\\nmore heat on the 1st of January than on the 1st of\\nJuly. This produces a slight effect to mitigate the\\nseverity of cold in winter and of heat in summer,\\nin the northern hemisphere, and to aggravate the\\nsame in the southern hemisphere.\\n54. Why is it not colder when we are furthest from the sun", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0066.jp2"}, "65": {"fulltext": "CHAPTEE IY.\\nSIDEEEAL TIME MEAN AND APPAEENT SOLAE TIME\\nTHE CALENDAE.\\nHie Sidereal Day. This is the interval of\\ntime which elapses between two successive culmina-\\ntions of a star (Art. 36). The length of this interval\\nappears to be invariable, whatever star is observed,\\nor in whatever season or year the observation is\\nmade. On this account, the sidereal day is regarded\\nas the true period of the earth s rotation on its axis.\\nIn order to reckon by sidereal time, the moment\\nchosen for the beginning of each sidereal day is the\\nmoment when the vernal equinox culminates. The\\nsidereal clock, if correct, then points to 0/?. 0m. 0s.\\nEach sidereal day is divided into 24 sidereal hours,\\neach hour into 60 sidereal minutes, and each minute\\ninto 60 sidereal seconds.\\n\u00c2\u00a38. Hie Mean Solar Bay. This is the mean in-\\nterval between two successive culminations of the\\nSun. It will be shown, presently, that these inter-\\nvals vary throughout the year. As the sun, by the\\nannual motion, is advancing eastward continually\\n55. What is a sidereal day When does it begin\\n56. What is the mean solar day How does it differ from the\\nsidereal day?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0067.jp2"}, "66": {"fulltext": "58 THE EAETH.\\namong the stars, the solar day must always be longer\\nthan the sidereal day. For, if the sun and a star\\nwere on the meridian of a place together, then, while\\nthat place passes around eastward till its meridian\\nmeets the star again, the sun has advanced eastward\\nnearly a degree, and the place must revolve nearly a\\ndegree more than one revolution before its meridian\\nwill reach the sun. This will require nearly 4 minutes\\nof time for, in the diurnal motion, 15\u00c2\u00b0 correspond\\nto one hour, and, therefore, 1\u00c2\u00b0 to of an hour that\\nis, 4 minutes.\\n\u00c2\u00ab57. The Apparent Solar Day. This is the actual\\ninterval between two successive culminations of the\\nsun. And this interval changes its length from day\\nto day through the entire year, being sometimes\\ngreater and sometimes less than the mean solar day.\\nIn keeping solar time by clocks and watches, it is\\ncustomary, for convenience, to aim to keep the mean\\nrather than the apparent time, and to regard the sun\\nas going alternately too fast and too slow.\\n$8, Causes of Unequal Solar Daus. After the\\nearth has completed a sidereal day, it must always\\nrevolve a little further to bring the meridian of a\\nplace to the sun, which has advanced nearly one\\ndegree eastward. Now, if the sun advanced east-\\nward exactly the same distance every day, then the\\nsolar days, as well as the sidereal days, would all\\n57. What is the apparent solar day Which is used in keeping\\ntime?\\n58. What makes the solar days unequal", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0068.jp2"}, "67": {"fulltext": "CIVIL AND ASTRONOMICAL TIME. 59\\nbe equal. But it does not for sometimes the annual\\nmotion is faster, and sometimes slower; and some-\\ntimes it is parallel to the daily motion, and again it is\\noblique. Hence, the arc of right ascension, to be\\nadded to the sidereal day in order to complete the\\nsolar day, varies in its length and, therefore, the\\nsolar days themselves must be of different lengths.\\nS9. The Equation of Time. The difference be-\\ntween mean time and apparent time, on any given\\nday, is the equation of time for that day. If the sun\\nis slow, the equation must be added to the apparerst\\ntime if fast, it must be subtracted, in order to give\\nmean time. The mean and apparent time agree four\\ntimes in a year April 15th, June 15th, September\\n1st, and December 24th. The two largest equations\\nare, +14 minutes, February 11th, and \u00e2\u0080\u009416 minutes,\\nNovember 2d.\\nS0\u00c2\u00bb Civil and Astronomical Time* -The mean\\nsolar day, when employed for civil purposes, is sup-\\nposed to begin and end at midnight, and is divided\\ninto hours, numbering from 1 to 12 A. M., and then\\nfrom 1 to 12 P. M. But the astronomical day (which is\\nalso the mean solar day) begins and ends at noon, 12\\nhours later than the corresponding civil day, and its\\nhours are counted from 1 to 24. Thus, the astronom-\\nical date, April 12c/, 207*., is the same as the civil date,\\nApril 13th, 8 o clock A. m.\\n59. What is tlie equation of time How large does it ever be-\\ncome\\n60. State the diffsrencs between civil and astronomical time.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0069.jp2"}, "68": {"fulltext": "60 THE EARTH.\\nGl, Tlie Julian Calendar. The period in which\\nthe sun passes from the vernal equinox to the same\\npoint again, is called the Tropical Year. In that\\nperiod the round of the seasons is exactly completed.\\nThe length of the tropical year is 365c?. 5h. 4.8m.\\n46.155. This is so near 3 65 J days, that in the adjust-\\nment of the calendar made by Julius Caesar (hence\\ncalled the Julian calendar), three successive years\\nwere made to contain 365 days each, and the fourth\\n366 days. The additional day is called the intercalary\\nday. In this calendar it was introduced by reckoning\\ntwice the 6th day before the Kalends of March and\\nhence the year containing this additional day was\\ncalled the Bissextile. The intercalary day is now the\\n29fch of February, and the year containing such a day\\nis called Leap Year.\\n62. The Gregorian Calendar. By calling the\\ntropical year 365 days, the Julian calendar makes it\\nmore than 11 minutes too long, and the intercalation\\nof one day in four years is, therefore, too great.\\nThis excess amounts to more than 18 hours in a cen-\\ntury. Hence, by dropping the intercalary day three\\ntimes in four centuries, the adjustment is nearly com-\\nplete. The Julian calendar, thus amended, is called\\nthe Gregorian calendar, because adopted under Pope\\nGregory XIII. At that time, 1582, the vernal equi-\\nnox, by the error of the Julian calendar, had fallen\\n61. What is the tropical year? Describe the Julian calendar.\\nWhat is meant by leap year\\n62. What was the defect in the Julian calendar Describe the\\nGregorian calendar. Will it always be correct? What is old\\nstyle?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0070.jp2"}, "69": {"fulltext": "HOW TO COMPAEE DAYS. 61\\nback to March, 11th. To bring the equinox to its\\nproper date, 10 days were first dropped (the 5th being\\ncalled the 15th), and then the following system was\\nadopted\\nEvery year not exactly divisible by 4, has 365\\ndays.\\nEvery year divisible by 4, and not by 100, has 366\\ndays.\\nEvery year divisible by 100, and not by 400, has\\n365 days.\\nEvery year divisible by 400, has 366 days.\\nThe Gregorian calendar will not be correct perpet-\\nually, but the error will not amount to a day in 4,000\\nyears.\\nThe nation of Russia has not yet adopted the Gre-\\ngorian calendar, so that there is now a discrepancy of\\n12 days between their dates and those of other na-\\ntions. The reckoning still used by them is known as\\nOld Style, and is distinguished by appending the let-\\nters O. S. to every date.\\nOS. JEEoiv to Compare Days of the Month and of\\nthe Week in Passing from one Year to Another, A\\ncommon year of 365 days contains 52 weeks and one\\nday a leap-year contains 52 weeks and two days.\\nHence, a year usually begins a day later in the week\\nthan the year previous. And, generally, any day of\\nany month is one day later in the week than the same\\nday of the preceding year. Thus, July 4th, 1365,\\n63. What is tlie change in a given day of the month, in passing\\nfrom one year to another? Why does it fall a day later in the\\nweek When does it fall two days later, and why", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0071.jp2"}, "70": {"fulltext": "62 THE EAETH.\\nfalls on Tuesday; 1866, on Wednesday; 1867, on\\nThursday. But, in leap-year, this rule applies only\\ntill the end of February. From that time to the\\nsame date in the year following, every day of a\\nmonth falls two days later in the week than in the\\nprevious year. Thus, July 14th, 1871, is Tuesday\\n1872, Thursday and February 22d, 1872, is Thurs-\\nday 1873, it is Saturday.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0072.jp2"}, "71": {"fulltext": "CHAPTEE V.\\nOBLATE FORM OF THE EAETH ITS MASS AND DENSITY\\nPKOOFS OF ITS ROTATION ON AN AXIS.\\n64. Central Forces. When a body is revolving on\\nan axis, the parts, on account of their inertia, tend to\\nmove in straight lines, tangent to their respective cir-\\ncles, and thus leave the rest of the body and they\\nwould do so, unless restrained by some force. The\\nforce which tends to carry the particles off in a tan-\\ngent is called the projectile force that which holds\\nthem in is called the centripetal force and that com-\\nponent of the projectile force which acts directly\\naway from the center is called the centrifugal force.\\nAll these are frequently called central forces.\\n65. Illustrations. We see an illustration of the\\nprojectile force when a wheel is revolved, having\\nwater on its edge. The drops are thrown off in tan-\\ngent lines.\\nIf a ball is whirled by a string, the projectile force\\nis prevented from carrying the body away by the\\n64. What is the projectile force? the centripetal? the centrifiii\\ngal What common name is given to them all\\n65. Illustrate by wheel by ball and string by the curve of a\\nrailroad.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0073.jp2"}, "72": {"fulltext": "64 THE EAETH.\\nstrength of tlie string, which is the centripetal force.\\nBut the string is strained, and may possibly be\\nbroken by the centrifugal force, which is a part of\\nthe projectile force.\\nWhen a train of cars turns a curve, there is a cen-\\ntrifugal force tending to throw it off from the track\\non the convex side. Hence, the outside rail is laid\\nhighest, so that the cars may lean in the opposite\\ndirection.\\n66, Loss of Weight on the Earth. As the earth\\nrevolves on its axis, all objects upon it are affected\\nby the centrifugal force, and lose a little of their\\nweight. The loss is greatest at the equator, where\\nthe motion is swiftest but even there it is very\\nsmall, only 2 -|-g of the whole. At all other places the\\nloss of weight is less than this, according as the dis-\\ntance from the equator is greater. At the poles there\\nis no loss at all.\\nThere is an additional loss of weight at the equa-\\ntor, arising from the oblate form mentioned in the\\nnext article. The whole loss amounts to T of the\\nweight. Therefore, a body on the equator, which\\nwould weigh 194 pounds if the earth were a sphere\\nand at rest, actually weighs only 193 pounds.\\n67, Oblate Form of the Earth. The centrifugal\\nforce on the earth produces another effect upon\\nall the yielding parts, such as the water of the oceans.\\n66. How are bodies on the earth affected by its rotation Where\\nis loss of weight greatest How much is the loss by centrifugal\\nforce In what other way is there a loss How great is the whole\\nloss?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0074.jp2"}, "73": {"fulltext": "OBLATE FORM OE THE EAETH\\n65\\nThey tend to flow away from the poles, and all places\\nnear the poles, towards the equator, until the water at\\nthe equator is about 13 miles further from the center\\nthan the poles are. Thus, the earth, as a whole, is\\nnot an exact sphere, but is flattened in the polar re-\\ngions, and has the form which is called an Oblate\\nFig.\\n14.\\nWW\\n/UrP\\n\\\\\\\\\\\\Y\\\\\\nn i\\nJiiv\\ni\\n1\\nG 1\\nEll\\nv\\\\\\nI 1\\nI i\\nvaVA\\nrrn\\n\\\\w\\\\\\nn^z/y\\n\u00e2\u0096\u00a0r\u00c2\u00a3z?y\\nD\\nSpheroid. Fig. 14 will give an idea of the earth s\\nform, C and D being the poles, and AEGFB the\\nequator. The diameter AB of the equator is about\\n26 miles longer than CD, the axis on which the earth\\nrevolves. If we imagine a sphere constructed on the\\npolar diameter of the earth, the difference between\\nthe sphere and spheroid will be a sort of shell or\\nling, 13 miles thick at the equator, and growing thin-\\nner on every side to the poles. This is sometimes\\ncalled the Equatorial Ring or Belt of the earth, and it\\n67. What is the earth s form?\\nequatorial belt\\nWhy What is meant by the", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0075.jp2"}, "74": {"fulltext": "66\\nTHE EARTH\\nproduces sensible effects on the earth s relations to\\nthe moon and sun.\\n08* Weight and Density of the Earth. The weight\\nof the whole earth has been found, by comparing its\\nattraction with the attraction of a mountain of given\\nFig. 15.\\nsize. Thus, if the mountain M exerted no attraction,\\nthe plumb-lines AB and CD would hang towards the\\ncenter of the earth. But if the mountain alone\\nattracted them, they would be drawn directly towards\\nthe center of gravity of the mountain. But since the\\nearth and the mountain both attract, they hang a\\nlittle sideways towards the mountain, as in the dotted\\nlines. By carefully measuring the deviation of the\\nplumb-lines, it may be learned how much greater the\\n68. Describe the mode of finding the weight of the whole earth.\\nHow great is it What is its density, or specific gravity", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0076.jp2"}, "75": {"fulltext": "ROTATION OF THE EARTH. 67\\nearth s attraction is than that of the mountain. The\\nweight of the earth is about 6,000,000,000,000,000,-\\n000,000 tons.\\nThe size and weight of the earth being both known,\\nits density, or specific gravity, is easily found. It is\\nexpressed by the number 5.67 that is, it weighs 5.67\\ntimes as much as the same bulk of water.\\n09* Proofs that the Earth Revolves on its Axis,\\nThe early belief of all people is that the earth is im-\\nmovable, and that the heavenly bodies revolve about\\nit. It is only a few centuries since the wisest philos-\\nophers began to teach that the earth itself revolves.\\nBut there are several independent proofs that the\\nearth really revolves once round every day.\\n1. This is the only reasonable way of explaining\\nthe fact that all the millions of fixed stars, at various\\nand immense distances from us, in large and in small\\ncircles of the sphere, perform their apparent revolu-\\ntions about us in precisely the same length of time, viz.,\\none sidereal day.\\n2. Without supposing the earth to rotate on its\\naxis, we cannot account for the oblate form of the\\nwaters of the ocean. Whatever form the solid parts\\nmight have, the movable portion would be spherical,\\nif the earth were at rest. Moreover, the degree of\\noblateness is exactly that which is required on a\\nsphere having the diameter and mass of the earth, if\\nit be supposed to rotate once in 24 hours.\\n69. Did ancient philosophers believe that the earth revolves?\\nWhat is the first proof that it does the second the third the\\nfourth the fifth the sixth 1", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0077.jp2"}, "76": {"fulltext": "68 THE EARTH.\\n3. The weight of a body at the equator, compared\\nwith that at the poles, is too small to be wholly ac-\\ncounted for by increased distance. Centrifugal force,\\narising from rotation, can alone explain the remain-\\ning difference.\\n4. A body dropped from a great height strikes/wr-\\ntlier east than the vertical line in which it began to\\nfall. If the earth rotates, the top of a tower moves\\nfaster than the base and, therefore, a body let fall\\nfrom the top, retaining the eastward motion of that\\npoint, will strike further east -than the base. At the\\nequator, this distance would be near 2 inches for a\\nfall of 500 feet. Numerous experiments on the fall of\\nbodies through great distances have been very care-\\nfully made by different individuals, and in different\\nlatitudes and they all concur in proving that a body\\nin falling deviates from a vertical line toward the\\neast.\\n5. It is also proved by FoucauWs pendulum experi-\\nment If a very long pendulum be set vibrating north\\nand south, it will slowly change to the northeast and\\nsouthwest, thus showing its tendency to preserve, as\\nnearly as possible, the original direction of its vibra-\\ntion in space.\\n6. The precession of the equinoxes can be explained\\nonly on the supposition that the earth rotates on an\\naxis.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0078.jp2"}, "77": {"fulltext": "CHAPTEE VI.\\nTHE SUN SOLAE SPOTS\u00e2\u0080\u0094 CONDITION OF THE SUN S\\nSUEEACE THE ZODIACAL LIGHT.\\n70* The Form of the Sun. As the sun revolves\\non an axis, the centrifugal force must produce some\\noblateness. It is, however, too slight to be perceived,\\nbecause the velocity of rotation is small, and the\\nforce of attraction very great. Hence, the appear-\\nance of the sun is that of a perfect sphere.\\n71\u00c2\u00bb Tlie Sun s Distance and Size.\u00e2\u0080\u0094 The horizontal\\nparallax of the son is so small that there is much dif-\\nficulty in measuring it accurately. According to the\\nbest determinations, it is about 8.6 from which it is\\ncalculated that the earth s distance from the sun is a\\nlittle more than 95,000,000 miles.\\nThe distance of the sun being found, and its appa-\\nrent breadth being measured, it is easy to compute its\\ndiameter. This is found to be 887,000 miles, which is\\n112 times as great as the diameter of the earth. In\\n70. What appears to be tiie form of the sun What is its real\\nform Why does it not appear so\\n71 What is the sun s horizontal parallax Is it easily found\\nWhat is our distance from the sun What is the sun s diameter\\nCompare it with the earth. Compare the sun s and the earth s bulk.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0079.jp2"}, "78": {"fulltext": "70 THE SUN.\\nbulk, therefore, the sun is 1,400,000 times as large as\\nthe earth.\\n72o The Sun s Mass, and Strength of Gravity, In\\nrespect to quantity of matter, the sun does not ex-\\nceed the earth nearly as much as in size for while its\\nvolume is 1,400,000 times as great as that of the earth,\\nits mass is only 355,000 times as great as the mass of\\nthe earth. It follows that its density is only one-fourth\\nas great as the earth s density.\\nThe strength of gravity on the sun is 28 times\\nas great as it is on the earth so that, what weighs\\n100 pounds here, if transported to the sun, would\\nweigh 2,800 pounds; and a body there would fall\\nthrough 450 feet in the first second of its descent,\\nwhile on the earth it falls only 16 feet.\\n73. Diurnal notation of the Sun. By means of\\nspots on the sun, it is found that it revolves on its\\naxis in about 25 days, from west to east, nearly in the\\nsame plane in which the earth revolves about the sun.\\nAfter a spot has presented itself on the edge of the\\nsun s disk, it occupies almost two weeks in going\\nacross, and then is out of sight as much longer, re-\\nappearing in the same place as at first, in 27J- days.\\nIf the earth were at rest, then 27 J- days would be the\\nperiod of the sun s rotation on its axis but since the\\nearth revolves about the sun in the same direction, it\\nrequires more than one revolution of the sun to bring\\n72. Compare them in respect to mass. Which is the most dense\\nHow many times What is the strength of gravity at the sun\\n73. How is it found that the sun revolves on its axis In what\\ntime, and in what direction, does it revolve? What is the appa-", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0080.jp2"}, "79": {"fulltext": "SOLAE SPOTS,\\n71\\nthe spot again to the edge. Suppose the earth at rest\\nat the point E (Fig. 16). Then a spot coming into\\nFig. 16.\\nview at A would go round through B, D, and H, to A\\nagain, when it would reappear. But while it goes\\nround, the earth in fact advances in its orbit from E\\nto F. The edge of the sun s disk is changed to B,\\nand the spot mast move so much further before it\\ncomes in sight again. As it requires about tivo days\\nto go over AB, the time of one revolution of the sun\\non its axis is a little more than 25 days.\\n74. Appearance of the Solar Spots. Nearly every\\nspot on the sun consists of two parts a black center\\nof irregular form, called the nucleus, and a surround-\\ning part of lighter shade, called the umbra (Fig. 17).\\nThese parts are distinct, and do not shade into each\\nother. The spots not only move across the disk, but\\nrent time of revolution Describe the cause of the difference, by\\nFig. 16.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0081.jp2"}, "80": {"fulltext": "72\\nTHE SUN.\\nFig. 17.\\nJuly 9\\nW\\n1844.\\nJuly 11\\nchange their form and appearance from day to day.\\nSometimes a large spot divides into two or more,\\nsmaller ones and, again, a group unites into one or\\ntwo larger spots. A spot sometimes diminishes and\\ndisappears, first the nucleus, then the umbra. The\\nreverse also happens; a spot is seen in the midst\\nof the disk, where there was none the day before.\\nThough only a few are commonly in sight at once, yet\\nin some instances they have been counted by tens,\\nand even hundreds. Yery rarely a spot is so large\\nas to be seen by the naked eye. They do not cross\\nall parts of the disk, but appear chiefly in two zones,\\none on each side of the equator, from 10\u00c2\u00b0 to 35\u00c2\u00b0 of\\nlatitude, as shown by the dotted lines in Fig. 17.\\n74. Describe a solar spot. What is the nucleus the umbra\\nState what changes the spots undergo. What parts of the disk do\\nthey pass across", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0082.jp2"}, "81": {"fulltext": "THE ZODIACAL LIGHT. 73\\nThe same figure exhibits the change which took place\\nin a group of spots in the course of two days.\\n7 The Nature of the Spots. From the changes\\nwhich the spots undergo in passing near the edge of\\nthe disc, it is found that they are cavities in the lumi-\\nnous atmosphere of the sun, the nucleus being deeper\\nthan the umbra which surrounds it. Sir William\\nHerschel proposed the theory that an atmosphere of\\nflaming gas forms the outer surface of the sun, having\\na less luminous stratum beneath, while lower down is\\nthe liquid or solid surface of the sun, which is still\\ndarker. When an opening is rent in the outer\\nstratum, we look in upon the second stratum, and this\\nforms the umbra of a spot\u00c2\u00bb And, supposing a smaller\\nrent to exist in that, we are able to see the more\\ndense portion below, as the nucleus of the spot. Sir\\nJohn Herschel has suggested that these openings,\\none below the other, may be occasioned by rotating\\nstorms in the solar atmosphere, resembling some\\nwhich take place on the earth.\\n76* The Zodiacal Light* This name is given to a\\nfaint, ill-defined light, extending along the zodiac,\\neither in the west, after sunset, or in the east, before\\nsunrise. It so much resembles the twilight that it is\\nnot ordinarily noticed, because it appears as a mere\\nupward extension of it. It is projected on the sky as\\na triangle, inclined to the horizon at the same angle\\nas the ecliptic (Fig. 18). In the evening, it is best seen\\n75. What is the nature of the spots What is Sir William Her-\\nBchel s theory\\n4", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0083.jp2"}, "82": {"fulltext": "74\\nTHE SUN.\\nat the season when the ecliptic is most nearly perpen-\\ndicular to the horizon, after twilight has ceased. It\\nis, therefore, most conspicuous, at evening, in the\\nmonth of February. When the air is clear, and there\\nFig. 18\\nis no moon, it is visible till after 9 o clock. For a like\\nreason, the best time for seeing it before morning twi-\\nlight is the month of October. The apparent extent\\nof it, both in breadth and height, is much increased\\nby indirect vision.\\n76. Describe the zodiacal light. When does it appear in the\\nmorning? When in the evening?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0084.jp2"}, "83": {"fulltext": "CHAPTEE VII.\\nGEAVTTATTON KEPLEE S LAWS MOTION LN AN ELLIPTICAL\\nOEBIT PEECESSION OE THE EQUINOXES.\\n77 o Gravitation. AH portions oi matter in the\\nuniverse show a tendency towards each other. This\\ntendency is called gravity or gravitation. It is by this\\nforce that bodies fall to the earth, when left at rest in\\nthe air, or when thrown in any direction. And it is\\ndiscovered that the same force causes the moon to go\\nround the earth, and the planets to go round the sun,\\ninstead of moving off in straight lines, as they would\\ndo if there were no such force as gravitation.\\n78. First Laiv of Gravitation. When the distance\\nis the same, gravity varies as the quantity of matter.\\nBodies fall as swiftly as they do, because the earth\\ncontains so great a quantity of matter and if it con-\\ntained more or less, bodies would fall faster or slower\\nin the same proportion. So, also, bodies fall toward\\nthe earth, instead of falling toward a mountain, be-\\ncause the earth contains vastly more matter than the\\nmountain.\\nAgain, we see that gravity varies as the quantity of\\n77. What is gravitation Where do we observe its operations\\n78. What is the first, law of gravitation Give the proofs.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0085.jp2"}, "84": {"fulltext": "76 GKAVITATION.\\nmatter, in the fact that the weight of a body increases\\nas the quantity of matter in it for weight is only\\nanother name for strength of gravity.\\n79. Second Law of Gravitation. When the quan-\\ntity of matter is the same, gravity varies inversely as\\nthe square of the distance. Hence, if the distance is\\ntwice as great, gravity is four times less if three times\\nas great, it is nine times less, and so on. It can be\\ndemonstrated that this must be the law of gravitation\\nin regard to distance, in order that a planet may de-\\nscribe an ellipse about the sun, or a satellite about a\\nplanet, while the central body is situated in the focus.\\n80. Kepler s Laws. From the observed motions\\nof the planets about the sun, Kepler deduced the\\nthree following laws, which are applicable to all\\nbodies revolving about a central body. Though Kep-\\nler discovered them as facts in the solar system, they\\nwere afterwards proved by Newton to be necessarily\\ninvolved in the laws of inertia and gravitation\\n81. (1.) The Areas Described about the Sun by the\\nMadias Vector vary as the Times of Describing Them.\\nOf course, if equal times are spent, the areas passed\\nover are also equal. This is illustrated by a reference\\nto Fig. 13. If the sun is at E, and a planet describes\\nthe orbit aemt, and passes over ah, be, cd, c, in equal\\ntimes, then the areas dEb, bEc, cEd, c, are equal.\\n79. The second law Illustrate by numbers.\\n80. Who proved the truth of Kepler s laws mathematically?\\nWhy are the following laws called Kepler s laws?\\n81. State the first law of Kepler. Illustrate by Fig. 13.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0086.jp2"}, "85": {"fulltext": "OEBITS OF THE PLANETS.\\n77\\nThis implies that the planet moves fastest when it\\nis nearest the central body for there the areas are\\nshortest, and need to be widest. The velocity is,\\ntherefore, greatest at a, the perihelion, and least at\\nm, the aphelion.\\n82, (2,) TJie Orbit of each Planet is an Ellipse, the\\nSun being in one Focus. Thus, ACBD may represent\\nthe orbit of a planet, the sun being at E or F, which\\nare the two foci. If the foci are nearer the center, the\\nellipse approaches more nearly to the form of a cir-\\ncle, in which case it is said to be less eccentric. But\\na more eccentric ellipse is one whose foci are further\\nfrom the center. The figure is then narrower, and\\ndiffers more from a circle. The orbits of the comets\\nare generally very eccentric, while those of the planets\\n82. State the second law. Where is the sun in a planet s orbit\\nWhat is the eccentricity of an orbit? Are the orbits of the planets\\nvery eccentric", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0087.jp2"}, "86": {"fulltext": "78 GEAVXTATION.\\nhave very little eccentricity, and, if correctly repre-\\nsented, could not be distinguished from circles.\\n83. (3.) Tlie Squares of the Periodic Times vary\\nas the Cubes of the Mean Distances. The periodic\\ntime is the time occupied by a planet in making a\\ncomplete revolution. And, according to this third\\nlaw, the times increase faster than the distances for\\nthe distances must be raised to the third power, in\\norder to vary as fast as the second power of the times.\\nHence, the further off a planet is from the sun, the\\nslower it moves.\\n84. Paths of Projectiles. When a stone is thrown,\\nor a ball is fired, its path (if undisturbed by the air)\\nis part of an elliptic orbit, one of whose foci is at the\\ncenter of the earth. This ellipse, however, is one of\\nextreme eccentricity, and is, therefore, usually called\\na parabola. Making use of the time and distance of\\nthe moon s revolution, it is calculated, by Kepler s\\nthird law, that if there were nothing to- obstruct the\\nmotion of the projectile, it would complete its orbit,\\nand return to the place from which it was thrown, in\\nabout 31 minutes. The perihelion of this orbit would\\nbe only a few feet beyond the center of the earth.\\n85. Effect of Increased Velocity of Projection.\\nSuppose that P (Fig. 20) is a point near the earth,\\n83. State Kepler s third law. What planets have the swiftest\\nmotion\\n84. When a stone is thrown, what is the form of its path What\\nis it usually called Why When would it return if uninter-\\nrupted Which focus is at the earth s center", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0088.jp2"}, "87": {"fulltext": "WHY PLANETS RETURN AND DEPART. 79\\nADE, and that the velocity of projection, in the direc-\\ntion PB, is so greatly increased that the projectile\\nstrikes the earth at D. By a still greater increase of\\nvelocity it might meet the earth at E. In these cases\\nthe earth s center would be in the most remote focus\\nof the orbit. But if we suppose the velocity so much\\nincreased that the centrifugal force just equals the\\nforce of gravity, then the body would describe the\\ncircular orbit PFG. Any increase of the velocity of\\nprojection beyond this will again produce an ellipse,\\nas PK, whose nearer focus is at the earth s center.\\nAnd we can imagine the velocity increased till the\\nellipse becomes one of extreme eccentricity.\\nSG\u00c2\u00bb Why a Planet at Aphelion begins to Return, or\\nat Perihelion begins to Depart, It might be thought\\n85. What is the effect of increasing the velocity of projection?\\nWhen will the orbit become a circle What if the velocity is still\\nmore increased", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0089.jp2"}, "88": {"fulltext": "80\\nGRAVITATION\\nthat a planet at its aphelion, C (Fig. 21), being less\\nattracted toward the sun than at any other point,\\nwould continue to withdraw, instead of commencing\\nto return and that when at its perihelion, G, being\\nmore attracted than elsewhere, it would continue to\\napproach till it falls to the sun. The reason why a\\nplanet begins to return after reaching the aphelion is\\nto be found in its diminished velocity. As the planet\\nrecedes through H, K, and A, the centripetal force\\ntoward S draws it back, and causes continual retard-\\nation, till at C the velocity is so much diminished that\\nthe attraction of S, though less than elsewhere, is\\nstill sufficient to curve the path so that it falls within\\na circle about the centre S, and the planet begins to\\napproach the sun.\\nAgain, as the planet passes through D, E, and F,\\n86. Explain by Fig. 21 why a planet returns from aphelion, or\\ndeparts from perihelion.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0090.jp2"}, "89": {"fulltext": "PEECESSION OF EQUINOXES. 81\\nthe attraction toward S partly conspires with its iner-\\ntia, and it is continually accelerated, till, at Gr, its\\nvelocity has become so great that its path strikes\\noutside of a circle about the center S, and it begins\\nagain to depart as before.\\n87* Precession of Equinoxes Described, The points\\nin which the equator intersects the ecliptic on the\\ncelestial sphere are not stationary, but have a slow\\nretrograde movement that is, they revolve from east\\nto west. The sun, therefore, in its annual progress\\neastward, crosses the equator each year a little fur-\\nther west than it did the year previous. This motion\\nis called the Precession of the Equinoxes. These points\\nmove about 50 J in a year. At this rate, it will re-\\nquire 25,800 years to make a complete circuit of the\\nheavens.\\n88* Signs of the Ecliptic Displaced from the Signs\\nof the Zodiac. The want of coincidence between the\\nsigns of the ecliptic and the signs of the zodiac was\\nnoticed (Art. 41). They coincided at the time the\\ndivision was made, about 2,000 years ago and the\\nprecession, during this period, has moved the equi-\\nnoxes backward 2,000 x 50J 28\u00c2\u00b0, nearly. Hence,\\nAries, of the zodiac, almost coincides with Taurus, of\\nthe ecliptic Taurus, of the zodiac, with Gemini, of\\nthe ecliptic, c.\\n87. What is meant by the precession of equinoxes? How fast\\ndo they recede\\n88. What effect has precession produced on the position of the\\nsigns of the ecliptic How much are they now displaced?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0091.jp2"}, "90": {"fulltext": "82 GBAVITATION.\\n89* Motion of the North and South Poles. Con-\\nsidering the plane of the ecliptic as fixed, its poles, of\\ncourse, occupy fixed positions among the stars. But\\nthis is not true of the poles of the equator. Their\\ndistance from the poles of the ecliptic is equal to the\\nobliquity of the two circles that is, 23\u00c2\u00b0 27 As this\\nangle remains nearly constant, and the points of in-\\ntersection move around westward, the poles of the\\nequator must likewise move round those of the eclip-\\ntic in the same direction, and occupy the same period,\\n25,800 years, in completing their revolution. The\\nnorth pole of the equator is now near the star in Ursa\\nMinor known as the pole-star. According to the ear-\\nliest catalogues, the pole was 12\u00c2\u00b0 distant from the\\npole-star. It is now somewhat more than 1\u00c2\u00b0 distant,\\nand will, at the nearest, pass within J\u00c2\u00b0 of it. In\\nabout 13,000 years the pole will be on the opposite\\nside of the pole of the ecliptic, near the bright star\\nAlpha Lyrse, which will then be the pole-star.\\n90o Cause of Precession. The precession of the\\nequinoxes is a disturbance produced by the sun s and\\nmoon s attraction upon the equatorial ring of the\\nearth. The sun being always in the plane of the\\necliptic, and the moon always near it, both bodies act\\nupon the equatorial ring to tip it into the same plane.\\nThis action, in connection with the inertia of the earth\\nas it revolves on its axis, causes the equinoxes to\\nmove backward.\\n89. What is the effect on the poles of the equator What is\\nsaid respecting the pole-star\\n90. Explain how precession i3 caused.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0092.jp2"}, "91": {"fulltext": "TROPICAL AND SIDEREAL YEAR. 83\\n91 The Tropical and Sidereal Year, Tlie fact\\nof precession shows that the year has two different\\nvalues, according as we reckon from a star or from an\\nequinox. Hence, the Sidereal Year is defined to be\\nthe period occupied by the sun in passing eastward\\naround the heavens from a star to the same star\\nagain and the Tropical Tear, the time of passing\\naround from one equinox to the same equinox again\\n(Art. 61). vAs the equinox moves westward, the sun\\nreaches it sooner than if it were stationary, and thus\\nmakes the tropical year shorter than the sidereal,\\nby the time required to pass over 50J which is 20m.\\n22.9s. As the tropical year is 365c?. 5k 4.8m. 46.155.\\n(Art. 61), the sidereal year, therefore, is 365d. 6h.\\n9771. 9s.\\nThough the sidereal year is the true period of the\\nearth s revolution about the sun, yet the tropical year\\npossesses by far the greatest interest, because it is\\nthe period in which the seasons are completed.\\n91. What two kinds of year are described Why are there two?\\nWhich is the true period of the earth s revolution", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0093.jp2"}, "92": {"fulltext": "CHAPTEE VIII.\\nTHE MOON\u00e2\u0080\u0094 ITS INVOLUTIONS\u00e2\u0080\u0094 ITS PHASES THE\\nCONDITION OF ITS SUKFACE.\\n02, Distance and Dimensions of the Moon* The\\nmoon is a satellite of the earth, revolving about it\\nwithin a comparatively small distance, and accom-\\npanying it in its orbit around the sun. The mean\\nhorizontal parallax of the moon at the earth s equator\\nbeing 57 5 its mean distance is found to be 238,650\\nmiles. As its apparent diameter is 31 6 its real\\ndiameter must be 2,161 miles. Therefore, the surface\\nof the moon is 13 times less, and its volume 49 times\\nless, than the surface and volume of the earth. But\\nin respect to mass, the moon is 80 times less than the\\nearth.\\n93. Revolution about the Earth. The slightest\\nattention to the position of the moon, from night to\\nnight, shows that it moves eastward, among the stars,\\nseveral degrees every day. If the instruments of the\\nobservatory be employed to measure its right ascen-\\n92. What is the moon s parallax? its distance from the earth?\\nits diameter Compare its surface and volume with the earth s\\nalso its mass.\\n93. How does the moon move in relation to the earth", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0094.jp2"}, "93": {"fulltext": "Telescopic view of the Moon.\\nTelescopic view of the Moon when five days old.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0095.jp2"}, "94": {"fulltext": "", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0096.jp2"}, "95": {"fulltext": "THE NODES. 85\\nsion and declination, it is ascertained that the moon\\ndescribes nearly a great circle, inclined about 5\u00c2\u00b0 to\\nthe ecliptic, and occupies 27.32 days in returning to\\nthe same place among the stars.\\n94. Months. The period just mentioned, in which\\nthe moon makes a revolution from a star to the same\\nstar again, is called the Sidereal Month. The time\\noccupied in making a revolution relatively to the sun,\\ninstead of a star, is called a Synodical Month. This\\nis more than two days longer than the sidereal\\nmonth for the moon s daily progress is about 13\u00c2\u00b0;\\nand during the 27 days of its revolution, the sun, at\\nthe rate of 1\u00c2\u00b0 per day, will advance 27\u00c2\u00b0, requiring\\nmore than two additional days for the moon to over-\\ntake it.\\nThe mean length of the synodical month is 29.53\\ndays.\\n95. Nodes. The points where the moon s path\\ncuts the circle of the ecliptic are called the moon s\\nnodes. The ascending node is the one through which\\nthe moon passes from the south to the north side of\\nthe ecliptic the other, 180\u00c2\u00b0 from it, is called the de-\\nscending node.\\n96. The Moon s Positions in Relation to the Sun.\\nThe moon is said to be in Conjunction with the sun,\\nwhen both bodies have the same longitude in Oppo-\\nsition, when their longitudes differ by 180\u00c2\u00b0. The con-\\n94. What kinds of month are described Explain them.\\n95. Name and describe the nodes.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0097.jp2"}, "96": {"fulltext": "86 THE MOON.\\njunction and opposition are called by the common\\nname of Syzygies.\\nWhen the longitude of the moon is 90\u00c2\u00b0, or 270\u00c2\u00b0\\ngreater than that of the sun, it is said to be in Quad-\\nrature.\\nThe points midway between syzygies and quadra-\\ntures are called Octants.\\nThe period in which the moon passes from any one\\nof these points to the same point again (that is, a\\nsynodical month), is also called a Lunation.\\n07* Form of the Moon s Orbit. It is ascertained\\nby the same method as was described (Art. 51), that\\nthe moon s orbit is an ellipse, one of whose foci is at\\nthe earth. But its eccentricity is 4J times greater\\nthan that of the earth s orbit.\\nThe point of the moon s orbit nearest the earth is\\ncalled the Perigee; the most distant point, the Apogee.\\n08* T7ie Moon s Diurnal Motion. The moon not\\nonly revolves about the earth, but also on its own\\naxis, in the same length of time that is, once in 27.32\\ndays and its axis is nearly perpendicular to the\\nplane of its orbit. This rotation is indicated by the\\nfact that the same side of the moon is always pre-\\nsented toward the earth. If it should pass around\\nthe earth, and not turn upon an axis, it would obvi-\\n96. Name and describe the several positions of the moon in rela-\\ntion to the sun.\\n97. What is the shape of the moon s orbit What is apogee\\nWhat is perigee\\n98. What other motion has the moon 1 Do we see all sides of the\\nmoon?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0098.jp2"}, "97": {"fulltext": "THE MOON S LIBEATIONS. 87\\nously present all sides to us in the course of each\\nrevolution.\\nBut though it keeps the same side toward the\\nearth, it presents all sides to the sun once in each\\nsynodical month. Therefore, the days and nights on\\nthe moon are nearly 30 (29.53) times the length of\\nthose on the earth.\\n99* The Moon s Librations. Though the same\\nside of the moon is turned to us on the whole, yet\\nthere are slight apparent oscillations, by which nar-\\nrow portions of the other hemisphere alternately\\ncome into view. These are called Librations. They\\nare of three kinds the libration in longitude, the\\nlibration in latitude, and the diurnal libration.\\nBy the libration in longitude, we see a little way\\nround upon the back side, first on the eastern edge,\\nand then on the western. This arises from the un-\\nequal velocity of the moon in its elliptical orbit.\\nBy the libration in latitude, we at one time see a\\nlittle beyond the moon s north pole, then beyond its\\nsouth pole. This is because the moon s axis is not\\nexactly perpendicular to the plane of its orbit.\\nBoth these librations are completed in one sidereal\\nmonth.\\nBy the diurnal libration, we see a little beyond the\\nmoon s western limb at its rising, and a little beyond\\nits eastern limb at setting; on account of our being\\nelevated 4,000 miles above the earth s center.\\n99. Do we see any of the back side In how many ways De-\\nscribe the libration of longitude the libration of latitude the\\ndiurnal libration.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0099.jp2"}, "98": {"fulltext": "88 THE MOON.\\n100. TJie 3Ioon s Revolution about the Sun. While\\nthe moon revolves about the earth, the earth revolves\\nabout the sun, at a distance 400 times as great.\\nTherefore the moon really has a third revolution;\\nnamely, that in company with the earth around the\\nsun. And this is far greater than its other revolu-\\ntions, which have been described. Since the moon\\ngoes round the earth, its path jnust lie outside of the\\nearth s orbit one-half of the time, and the other half\\nwithin it. The path is, therefore, a waving line, which\\ncrosses the earth s path 25 times in a year. But the\\nmoon s orbit is so small, and the earth s motion so\\nswift, that the waves are very long and narrow, and\\neverywhere concave toward the sun.\\n101. Phases of the Moon. The moon is not self-\\nluminous, and is seen only as it reflects to us the light\\nwhich falls upon it. The several forms which the\\npart illuminated by the sun presents to our view, are\\ncalled Phases.\\nThe Circle of Illumination, or the Terminator, is the\\ncircle which separates the hemisphere enlightened by\\nthe sun from the dark hemisphere, and is perpendicu-\\nlar to the sun s rays which fall on the moon. The\\nCircle of tlie Disk is that which separates the hemi-\\nsphere turned toward the earth from the opposite\\none, and is perpendicular to our line of vision. The\\nphase depends on the size of the angle formed at the\\nmoon, between the solar ray and our visual line.\\nLet the earth be at E (Fig. 22), and the moon in\\n100. What third revolution lias the moon What kind of a path\\nis it How can it be everywhere concave toward the sun", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0100.jp2"}, "99": {"fulltext": "PHASES OF THE MOON.\\n89\\nseveral positions, A, B, c., and let the lines AS, BS,\\nc, be directed toward the sun. At A, the moon is\\nin conjunction, and wholly invisible this is called\\nNeiv Moon; and the angle SAE, between the solar ray\\nand visual ray, is 180\u00c2\u00b0. From A to C (as at B), the\\nphase is called Crescent; and the angle SBE is obtuse.\\nThe First Quarter occurs at C, the quadrature, where\\nSCE is a right angle. From to F (as at D), the\\nFig. 22.\\nO\\nphase is called Gibbous. In this phase, the angle SDE\\nis always acute. At F, the moon is in opposition,\\nand wholly illuminated. This is called Full Moon.\\nThe angle SFE is 0\u00c2\u00b0. From F to A, the phases are\\nrepeated in reverse order, the Last Quarter being at\\nH. The outer figures at B, C, c, show the corres-\\nponding phase.\\n101. What is meant by phases\\nusing Fig. 22.\\nExplain the several phases,", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0101.jp2"}, "100": {"fulltext": "90 THEMOON.\\n102. Moon Munning High or JLoiv. It is gener-\\nally observed that, at a given age of the moon, for\\ninstance, at the full, its meridian altitude is very dif-\\nferent at different seasons of the year that is, that\\nthe full moon runs high at some seasons, and low\\nat others. This is readily explained by noticing the\\nmoon s relations to the sun. As the moon s path is\\neverywhere near the ecliptic, the new moon will cul-\\nminate at a high point when the sun does that is, in\\nthe summer. But, in the same season, the full moon,\\nbeing opposite to the sun, will culminate low. On the\\ncontrary, when the sun is in the most southern part of\\nthe ecliptic, and culminates low, as is the case in win-\\nter, the new moon will do so likewise but the full\\nmoon will culminate at a high point. In the polar\\nwinter, therefore, when the sun is absent for months,\\nthe moon, whenever near the full, circulates round\\nthe sky without setting.\\n103. The Harvest Moon, This name is given to\\nthe full moon which occurs nearest to the autumnal\\nequinox, September 22d, and which rises from evening\\nto evening with a less interval of time than the full\\nmoon of any other season.\\nThe sun being at the autumnal equinox, the moon\\nis near the vernal equinox, and at sunset the southern\\nhalf of the ecliptic is above the horizon, and makes\\nthe smallest possible angle with it. It is this small\\nIf 2. When does the full moon run high when low Show why.\\nWhere does the full moon shine all the time for many days with-\\nout setting?\\n103. Which moon is called harvest moon Explain the small\\ndifference in the time of rising. Why not noticed every month", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0102.jp2"}, "101": {"fulltext": "THE MOON S SUE3TACE. 91\\nangle, made by the ecliptic, and, therefore, by the\\nmoon s orbit with the horizon, which causes the small\\ninterval in the time of the moon s rising from one\\nevening to another for, as the moon advances 13\u00c2\u00b0\\neach day in its orbit, this arc is so^oblique to the\\nhorizon, that its two extremities rise with only a few\\nminutes difference of time but the place of rising\\nmoves rapidly northward.\\nThe harvest moon attracts most attention in high\\nlatitudes, where the angle between the ecliptic and\\nhorizon is smaller, and, therefore, the intervals of time\\nare less.\\nThe moon passes the vernal equinox every month,\\nand, therefore, rises with the same small intervals.\\nBut when the moon is not full at the same time, the\\ncircumstance is unnoticed.\\n104. Inequalities of the Moon s Surface. These\\nare clearly revealed by the changing direction of the\\nsun s rays. As the terminator advances over the disc,\\nthe light strikes the highest peaks, which appear as\\nbright points a little way upon the dark part of the\\nmoon. After the terminator has passed over them,\\nthey project shadows away from the sun, which cor-\\nrespond to the apparent shape of the elevations, and\\ngrow shorter as the rays fall more nearly vertical.\\nAnd again, in the waning of the moon, the shadows\\nare cast in the opposite direction, lengthening until\\nthe dark part of the disc reaches them, and the sum-\\nmits once more become isolated bright points, and\\nthen disappear.\\n104. How do we know the moon is mountainous", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0103.jp2"}, "102": {"fulltext": "92 THE MOON.\\n105. Forms of Valleys. The most striking char-\\nacteristic of the moon s surface is its numerous circu-\\nlar valleys. The smaller and more regular ones are\\nof all sizes, from one or two miles in diameter up to\\nsixty miles. These are numbered by hundreds. The\\nmountain ridge which surrounds one of these cavities\\nis a ring, very steep and precipitous on the inner\\nside but externally it falls off by a rugged but grad-\\nual slope. These ridges are called Ring Mountains.\\nIn the central part of the cavity are generally one or\\nmore steep, conical mountains.\\nThere is another class of larger but less regular\\ncavities, sometimes called Bulwark Plains. Their\\ndiameters are often more than one hundred miles.\\nThese are also surrounded by rough mountain masses\\narranged in a circle. Over these plains are sparsely\\nscattered small conical and ring mountains.\\nThere are still larger tracts, more level than the\\ngeneral lunar surface, and of a darkish hue, which\\nstill retain the name of seas, formerly given them,\\nthough they are covered with permanent inequalities,\\nand show no signs of being fluid.\\nAt the time of full moon, there are seen around\\na few of the principal ring mountains a great many\\nluminous stripes, radiating in straight lines, and ex-\\ntending, in some cases, hundreds of miles. These are\\nsometimes called Lava Lines.\\n10G\u00c2\u00bb Volcanic Appearance of the Moon, Every\\npart of the moon s surface has the appearance of\\n105. Describe the valleys. What is meant by the seas What\\nappearance at full moon", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0104.jp2"}, "103": {"fulltext": "NO ATMOSPHERE OE VAPOR. 93\\nrocky hardness. The interior slopes of the ring\\nmountains are steep, rough, and angular. The coni-\\ncal peaks within them appear like isolated rocks,\\nresembling the needles of the Alps. The surface\\nnowhere gives indication of having been softened\\ndown by the action of water. The circular cavities,\\nwith steep and rugged sides, appear like vast craters,\\nand the mountains within them like volcanic cones,\\nmore recently thrown up. Nearly every part of the\\nhemisphere presented to our view exhibits these indi-\\ncations of former volcanic action, on a scale far be-\\nyond anything on the earth. But there is no evidence\\nof volcanic action at present.\\n107 Height of the Lunar Mountains. The height\\nof a mountain on the moon can be determined either\\nby observing how far from the terminator it is when\\nthe sunlight just touches its summit, or by measuring\\nthe length of its shadow. The highest of the lunar\\nmountains are from three to four and a half miles\\nhigh. While the diameter of the moon is not much\\nmore than one-fourth as great as the earth s diame-\\nter, its mountains are nearly equal in height to the\\nmountains of the earth.\\n10S\u00c2\u00bb Wo Atmosphere or Vapor. If any kind of\\natmosphere were spread over the disk of the moon, it\\nwould reflect the sun s light so strongly as to dim the\\nfeatures of the solid surface. Nothing of the kind is\\never perceived. No terrestrial objects, however near,\\n106. What are tlie proofs of past volcanic action\\n107. How is the height of lunar mountains found How high\\nare they", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0105.jp2"}, "104": {"fulltext": "94 THE MOON.\\never exhibit greater sharpness of outline than the in-\\nequalities of the moon and they never vary in this\\nrespect, except in a manner which is obviously occa-\\nsioned by our own atmosphere.\\nA still better proof that there is no atmosphere on\\nthe moon is the fact that when its edge passes be-\\ntween us and the stars, they are not dimmed, nor\\ntheir position disturbed in the least.\\n100. Changes of Temperature on the Moon. The\\nmoon s equator makes an angle of only 1J\u00c2\u00b0 with the\\necliptic, and, therefore, experiences no perceptible\\nchange of seasons but its diurnal rotation is so slow\\nthat the extremes of heat and cold during each day\\nare excessive. A place on the moon is exposed to the\\nfull power of the sun s rays for about two weeks, and\\nthen is for as long a time turned away from the sun,\\nwithout clouds, or even air, to prevent the free radia-\\ntion of heat.\\n110. View of the Earth from the Moon,\\n1. As to Magnitude. The apparent dimensions of\\nthe two bodies, as seen one from the other, are pro-\\nportional to their real dimensions. Hence, in diame-\\nter, the earth, as seen from the moon, is 3f times as\\nlarge as the moon, viewed from the earth, and in area\\nis about 13 times as large.\\n2. As to Phase. It is obvious, from Fig. 22, that\\nwhen the full moon is presented to the earth, the\\nearth s dark side is toward the moon, and the reverse.\\n108. Has the moon an atmosphere How proved\\n109. What is said of changes of temperature on the moon", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0106.jp2"}, "105": {"fulltext": "VIEW OF THE EAETH. 95\\nAlso, that when we see the gibbous phases of the\\nmoon, a spectator on the moon would see crescent\\nphases of the earth for the angle SED or SEG\\nwould then be obtuse. In like manner, the relative\\nphases are in every case supplementary to each\\nother. This relation explains the well-known fact\\nthat near the time of new moon, the part of the moon\\nnot directly enlightened by the sun is distinctly visi-\\nble. It is then illuminated indirectly by the earth,\\nwhich is nearly full, as seen from the moon, and re-\\nflects a strong light upon it.\\nFor the same reason, the moon can be faintly seen\\nin a total solar eclipse.\\n3. As to Position in the SJcy.\u00e2\u0080\u0094The earth, seen from\\nthe moon, has no apparent diurnal rotation, as all\\nother heavenly bodies have, but. remains nearly fixed\\nin the same part of the sky. This is owing to the\\nfact that the moon s monthly motion and its diurnal\\nmotion are at the same rate in the same direction, so\\nthat one apparent motion of the earth neutralizes the\\nother. Hence, a spectator occupying the middle of\\nthe moon s disk sees the earth perpetually near his\\nzenith. Another, at the edge of the disk, sees it\\nalways near the same point of the horizon.\\nThe first and second librations of the moon, since\\nthey vary the spectator s position a little in relation\\nto the disk, merely cause small oscillations of the\\nearth s place in the sky.\\n4 As to Surface. The earth, by its rotation, pre-\\nsents all its parts to the view of the nearer hemi-\\n110. State how the earth appears, seen from the moon as to\\nmagnitude as to phase as to position in the sky as to surface.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0107.jp2"}, "106": {"fulltext": "96 THE MOON.\\nsphere of the moon once in 25 hours. To the other\\nhemisphere it never appears at all.\\nOn account of its nearness, and its great size, we\\nmight suppose that the geographical features of the\\nearth would be very conspicuous to a spectator on\\nthe moon, and that the nature of its surface in nearly\\nall respects could be thoroughly observed. But the\\ndeep and dense atmosphere of the earth would reflect\\nan intense light, so as probably to render the inequal-\\nities of the terrestrial surface nearly invisible and\\nwhenever clouds prevail over a country, that portion\\nof the earth s surface would, of course, be entirely\\nhidden from view.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0108.jp2"}, "107": {"fulltext": "CHAPTEE IX.\\nECLIPSES OF THE MOON AND SUN.\\n1 11, General Relations in Eclipses. The moon is\\neclipsed when it is obscured wholly or in part by the\\nearth s shadow. It can occur, therefore, only at op-\\nposition, or full moon. The sun is eclipsed when it is\\neither wholly or partially concealed from view by the\\nmoon coming between it and the earth. This can\\nhappen only at conjunction, or new moon.\\nIf the moon s orbit and the ecliptic were coincident\\nplanes, there must be an eclipse of the moon at every\\nfull moon, and an eclipse of the sun at every new\\nmoon for at those times the three bodies would be\\nin a straight line. But as the moon s orbit and the\\necliptic make an angle of 5\u00c2\u00b0 with each other, the\\nmoon generally passes opposition and conjunction so\\nfar north or south of the sun, that there is no eclipse.\\nThat an eclipse may occur, the syzygies must happen\\nnear the line of nodes, so that, as the moon comes\\ninto conjunction or opposition, some parts of the\\nthree bodies may be in a straight line. Fig. 23 will\\nillustrate this. Let NA be a small portion of the\\necliptic, and KB, of the moon s orbit. N is the\\n111. When is the moon eclipsed the sun Why are there not\\neclipses every month Show by Fig. 23.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0109.jp2"}, "108": {"fulltext": "98 ECLIPSES.\\nascending node. If the sun is at N, when the moon\\nis in conjunction, the latter will come exactly between\\nthe sun and the center of the earth, and cause a cen-\\ntral eclipse. But if the sun has passed by the node\\nFig. 23.\\nto E, when the moon comes to conjunction at F, then\\nit will conceal only the north limb of the sun. If the\\nsun is still further from the node, as at C or A, then\\nthe moon will pass by at D or B, without appearing\\nto overlap the sun, and no eclipse will occur.\\n112. Eclipse Months. As there are two nodes on\\nopposite sides of the heavens, the sun, in its annual\\nprogress, must pass through both of them every year,\\nat intervals of about six months. And as the moon\\ncomes into the line of syzygies every two weeks, the\\nsun will certainly be near enough to a node for one or\\ntwo eclipses, and possibly for three, every six months.\\nThus, the eclipses of any year always occur in clus-\\nters, at opposite seasons. If two or three are in Jan-\\nuary, the others are in July. These are called the\\n112. How are the eclipses of any year arranged Why", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0110.jp2"}, "109": {"fulltext": "ECLIPSE OF THE MOON\\n99\\nNode Months of that year. In 1866, for example, the\\nnode months are parts of March and April, and parts\\nof September and October. On account of the retro-\\ngrade motion of the nodes, the sun passes from a\\nnode to the same one again in less than a year, so\\nthat the node months occur earlier each successive\\nyear perpetually.\\n113. Eclipse of the Moon. When the moon is\\neclipsed, there is nothing interposed to hide it from\\nour view but it merely falls into the shadow of the\\nearth, and is obscured. This obscuration may possi-\\nbly continue for several hours.\\nFig. 24.\\nThe sun being vastly larger than the earth, the\\ntotal shadow of the latter is a cone, as represented in\\nFig. 24, where the cone of the earth s shadow extends\\nto the extreme right hand. It is found by calculation\\n113. What is the shape of the earth s total phadow? How long\\nis it Where does the nioon pass it What is the penumbra?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0111.jp2"}, "110": {"fulltext": "100 ECLIPSES.\\nto be nearly 900,000 miles long and the moon is so\\nnear the earth as to go through the broader part of\\nthe shadow.\\nBut besides the total shadow, there is a partial\\nshadow, called the Penumbra, surrounding the other.\\nIt has the form of an increasing cone. When the\\nmoon is eclipsed, it must pass through the penumbra\\nbefore it reaches the total shadow, and again after\\nleaving it. In Fig. 24, the moon enters the penumbra\\nat a, and finally leaves it at b.\\n114. Length of Lunar Eclipses, and Appearance\\nof the Moon. The breadth of the total shadow,\\nwhere the moon passes it, is nearly three times, and\\nthat of the penumbra nearly five times, the breadth of\\nthe moon. Now the moon moves over its own breadth\\nin about an hour. Hence, when the eclipse is central,\\nit continues between five and six hours. The penum-\\nbra, however, is so faint that its effect is scarcely no-\\nticeable so that the whole apparent duration of a\\ncentral eclipse is only about four hours.\\nBut even when buried in the total shadow, the\\nmoon is not invisible, but shines very dimly, appear-\\ning of a dull red color. This is owing to the sun s\\nfight which the earth s atmosphere refracts into the\\nshadow. Some of the sunlight thus falls on the face\\nof the moon all the while it is in eclipse, and renders\\nit visible.\\n115. Eclipse of the Sun, An eclipse of the sun is\\nof a different character from an eclipse of the moon.\\n114. How long can a lunar eclipse last How does the moon ap-\\npear in eclipse Why", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0112.jp2"}, "111": {"fulltext": "ECLIPSE OE THE SUN. 101\\nWhen the moon is eclipsed, it is obscured by the\\nearth s shadow falling on it. The moon itself is\\naffected. But the sun is said to be eclipsed when the\\nmoon intervenes between it and the earth, and hides\\nit from our view. The sun itself suffers no change,\\nbut we are placed in circumstances which prevent our\\nseeing it. The phenomenon would more properly be\\ncalled an Occultation of the sun.\\n110. Total Shadow and Penumbra of the Moon.\\nThe moon s total shadow is a cone of tne same form\\nas the earth s but its mean length is only about\\n232,000 miles, and does not generally quite reach the\\nearth. The moon s total shadow is also surrounded\\nby a penumbra. These are both represented in Fig.\\n24, where the moon at m stretches its total shadow\\nnearly to the earth s surface, while the penumbra\\nspreads over a large portion of it. When the moon\\nis nearest, and its shadow longest, it reaches so far as\\nto be cut off by the earth s surface, and form a dark\\ncircle, 170 miles in diameter. The penumbra gener-\\nally covers a circle 4,000 miles in diameter, repre-\\nsented by cd in the figure. The circle of the penum-\\nbra is faintly shaded at the edges, and grows darker\\ntowards the center, where the dark circle is situated.\\n117. Total and Partial Eclipses of the Sun.\u00e2\u0080\u0094 When\\nthe moon s total shadow reaches the earth, and forms\\na dark circle on it, a person within that circle wit-\\n115. How does a solar eclipse differ in character from a lunar\\neclipse What is the appropriate name\\n116. State the form and length of the moon s total shadow. How\\nmuch of the earth s surface can it possibly cover How much can\\nthe penumbra cover", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0113.jp2"}, "112": {"fulltext": "102\\nECLIPSES\\nnesses a total eclipse of the sun. This is one of the\\nmost sublime and impressive phenomena of nature.\\nThe sun is completely hidden from view, though the\\nsky may be perfectly clear. The whole heavens have\\nsomething of the appearance of night, and the bright-\\nest stars are visible. The chill of evening is also felt,\\nand animals retire to their resting places.\\nBut those who are situated outside of the total\\nshadow, and within the penumbra, perceive the sun\\npartially hidden, one side of it being covered up by\\nthe circular edge of the moon. A partial eclipse of\\nthe sun usually attracts no great attention, because,\\nunless nearly the whole of it is covered, its light is\\nnot so much diminished as it often is by clouds.\\nFig. 25.\\n117. Describe a total eclipse of the sun. What persons see it\\nAnd what persons see a partial eclipse", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0114.jp2"}, "113": {"fulltext": "NUMBEE OE ECLIPSES. 103\\n118* Annular Eclipse. When the moon s shadow\\ndoes not reach the earth, those who are in the direc-\\ntion of it see a partial eclipse of a very peculiar form.\\nThe sun is all covered by the moon, except a narrow\\nring around its edge. As the visible part of the sun\\nhas the form of a ring, this kind of eclipse is called\\nAnnular. (See Fig. 25.)\\n119* Velocity of the Shadow, and Duration of an\\nEclipse. The moon moves in its orbit at the rate of\\nabout 2,000 miles in an hour. Therefore its shadow\\ncrosses the whole breadth of the earth in a little less\\nthan 4 hours. But since the earth revolves on its\\naxis in nearly the same direction, and with one-half\\nthe same velocity at the equator, the shadow passes\\nby a place at the rate of a little more than 1,000 miles\\nper hour. Of course, all total and annular eclipses\\nare short, the former not more than 8 minutes, and\\nthe latter not more than 13 minutes but the whole\\nduration of an eclipse, at a place where it is central,\\nmay be about 2 hours.\\n120, Relative Number of Solar and Lunar Eclipses.\\nOn the whole earth there are only about two- thirds\\nas many eclipses of the moon as of the sun but,\\nbecause one is really an eclipse, and the other an\\noccultation, eclipses of the moon at a given place are\\nmore frequent than those of the sun. An eclipse of\\n118. What is an annular eclipse In what circumstances does it\\noccur\\n119. How swiftly does the shadow move over the earth How\\nlong can a total eclipse continue an annular a partial\\n120. Which kind of eclipses occurs most frequently on the whole\\nearth at any given place Explain the reason.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0115.jp2"}, "114": {"fulltext": "104 ECLIPSES.\\nthe moon is visible to all on the hemisphere nearest\\nto it, without regard to locality. But an eclipse of\\nthe sun is not seen at a place, unless the moon s\\nshadow falls at that place.\\n121. Eclipses at the 3Ioon. When we witness a\\nsolar eclipse, a spectator at the moon would notice\\nonly a small, dimly-defined circular shadow passing\\nover the earth s disk. It would be a partial eclipse\\nof the earth.\\nBut when we see a total lunar eclipse, the phenom-\\nenon at the moon would be one of great interest, and\\nof very strange appearance. A dim red light from\\nall parts of the sun s disk is spread over the moon,\\nbeing refracted thither by the earth s atmosphere.\\nHence, a spectator there would see the sun expanded\\nout into a thin dull red ring, surrounding the earth,\\nand, therefore, having nearly four times the usual\\ndiameter of the sun s disk.\\n122, True Form of SJiadoivs. It is impossible,\\nin ordinary diagrams, to present the shadows of the\\nearth and moon in their true proportions. The dis-\\ntance of the sun is so very great, compared with its\\ndiameter, that the shadows are exceedingly slender,\\nhaving a length about 110 times the diameter of the\\nbase. The earth being represented as in Fig. 24, the\\nlength of its shadow, if rightly proportioned, ought\\nto be more than five feet long.\\n121. When we see a solar eclipse, what can be seen at the moon\\nAnd what, when we see a total lunar eclipse\\n122. What is the true form of the shadows of earth and moon\\nWhy not exhibited in diagrams", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0116.jp2"}, "115": {"fulltext": "CHAPTEE X.\\nLONGITUDE TIDES.\\n123. Local Time,\u00e2\u0080\u0094 Time is reckoned at every place\\nfrom the moment when the sun crosses the meridian\\nat either the upper or the lower culmination. This is\\ncalled local time for at the same absolute instant,\\nthe time thus reckoned at any place differs from that\\non every other meridian.\\n124:* Connection between Longitude and Local\\nTime. The earth turns uniformly on its axis toward\\nthe east through 15\u00c2\u00b0 every hour. Therefore, a place\\nlying eastward of another will have the sun earlier\\non its meridian, and, consequently, in respect to the\\nhour of the day, will be in advance of the other at\\nthe rate of one hour for every 15\u00c2\u00b0. Thus, to a place\\n15\u00c2\u00b0 east of Greenwich observatory, it is 1 o clock\\nP. M. when it is noon at Greenwich and to a place\\n15\u00c2\u00b0 west of that meridian, it is 11 o clock A. m. at\\nthe same instant. Hence, the difference of local\\ntime at any two places indicates their difference of\\nlongitude.\\n123. What is local time\\n124. How is it connected with longitude Illustrate.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0117.jp2"}, "116": {"fulltext": "106 LONGITUDE TIDES.\\n12o, Longitude by the Chronometer. If a person\\nleaves London with a chronometer accurately ad-\\njusted to Greenwich time, and travels eastward till he\\nfinds his own time slower than the local time of the\\nplace by Hi. 30???., then he knows the place to be\\n22\u00c2\u00b0 30 east longitude. For 15\u00c2\u00b0 x 1J 22J On\\nthe contrary, if he travels westward, and at length\\nfinds his time-piece at Qh. 44m., when the local time is\\n4/?. 32m. (in other words, that his Greenwich time is\\n2/?. 12??2. too fast), then the longitude of the place is\\n33\u00c2\u00b0 W. In the same manner, the longitudes of any\\ntwo places may be compared with each other.\\nFor the use of navigators, chronometers are made\\nwhich run with very great accuracy, and may be\\nrelied on during long voyages. There is always a\\nprobability, however, that a chronometer may change\\nits rate somewhat, when it comes to be transported\\nfrom place to place. It is, therefore, safer, on long\\nvoyages, to use several chronometers, and employ the\\nmean of all their indications.\\n126o Longitude by Eclipses of the Moon, and of\\nJupiter s Satellites. In one respect, these eclipses\\nare very favorable for the comparison of longitudes.\\nThey are distant phenomena, seen at the same abso-\\nlute instant by all. Hence, any difference of time in\\nthe observations at different places is entirely due to\\ndifference of longitude.\\nBut in another respect, they are quite unfitted for\\n125. How is longitude found by a chronometer\\n126. How found by eclipses of moon and Jupiter s satellites\\nWhat is the advantage, and what the disadvantage of this method", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0118.jp2"}, "117": {"fulltext": "THE LUNAR METHOD. 107\\nthe purpose. On account of the penumbra, there is\\nno definite edge to the shadow which passes over the\\ndisk, and, consequently, there is great uncertainty as\\nto the time of beginning or end of the eclipse. This\\nmethod is but little depended on for accurate results.\\n127 Longitude by a Solar Eclipse, In both the\\nabove particulars, a solar eclipse differs from a lunar.\\nIt is not an event at a distance, seen at once by all,\\nbut on the earth s surface, happening to one place at\\none instant, and to another place at another. The\\ntime of beginning or end of a solar eclipse depends\\non the position of the observer.\\nOn the other hand, the phenomenon is very defi-\\nnite, and the moments of immersion and emersion\\nof the sun s limb can be quite accurately fixed by\\nobservation*\\nOccultations of stars by the moon are much more\\nfrequent than the occultation of the sun; and these\\nare phenomena of the same general character, and\\nmay be used in the same way for finding the longi-\\ntude of a place.\\n128* Longitude by the Lunar Method. This is a\\nmethod particularly useful to navigators, because the\\nobservations are made by the sextant. It consists in\\nmeasuring the angular distance between the moon\\nand some conspicuous heavenly body, as the sun, or\\na large planet or star, and then correcting the ob-\\n127. How is a solar eclipse favorable, and how -unfavorable, for\\nfinding longitude\\n128. What is the lunar method", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0119.jp2"}, "118": {"fulltext": "108 LONGITUDE TIDES.\\nservation for parallax or refraction, so as to have the\\ntrue distance between the bodies, as seen from the\\ncenter of the earth. The observer must also note the\\nlocal time when this measurement is made.\\nHaving with him the Nautical Almanac, in which\\nthe distances, as seen from the earth s center, are pre-\\ndicted for every day and hour of Greenwich time, he\\nlooks for the Greenwich time at which the distance\\nagrees with the distance as he has obtained it. The\\nabsolute time is the same hence, the difference of\\ntime shows his longitude from Greenwich.\\nThe bodies whose angular distances from the moon\\nthe Nautical Almanac gives for every three hours,\\nwith proportional numbers for interpolation, are the\\nSun, Venus, Mars, Jupiter, Saturn, and nine bright\\nfixed stars.\\n129. Longitude by the Telegraph. Since the in-\\nvention of the magnetic telegraph, it has been em-\\nployed to determine the differences of longitude\\nbetween fixed stations on land with a precision which\\nwas before altogether unattainable. Suppose two\\nstations to be connected by the telegraphic line, and\\nthat there is at each a clock keeping the local time.\\nThe observers make signals at certain times agreed\\non and each notes on his own clock the times of the\\nsignals given by the other. Electricity moves so\\nswiftly, that a signal may be considered as received\\nat the same absolute instant in which it is given.\\nHence, the difference of the clocks is merely a dif-\\nference of longitude.\\n129. State how the telegraph is used for this purpose.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0120.jp2"}, "119": {"fulltext": "AMBIGUITY AS TO DAYS. 109\\n130* Change of Days in Circumnavigating the\\nEarth* While a person travels westward, he length-\\nens his days by one hour for every 15\u00c2\u00b0, or 4 minutes\\nfor every degree, since he moves along with the ap-\\nparent diurnal motion of the sun. In traveling east-\\nward, on the contrary, he shortens the days at the\\nsame rate, by moving in opposition to the sun s daily\\nprogress. If we suppose him to go westward entirely\\nround the earth to the same meridian again, whether\\nhe takes a longer or a shorter time for the journey,\\nhe will lengthen the individual days sufficiently to\\nmake the whole number just one day less than if he\\nhad remained where he was. The 5th of a month is\\nto him the 4th and Tuesday, according to his reck-\\noning, is Monday. The reason is obvious for during\\nhis journey, the earth has made a certain number of\\ndiurnal revolutions from west to east; but he, by\\ngoing round from east to west, has, in respect to him-\\nself, diminished that number by one.\\nAll this is exactly reversed when one goes round\\nthe globe from west to east. He gains just a day by\\nmaking all the days of his travel a little shorter. It\\nis plain that he makes one more diurnal revolution\\nfrom west to east than the earth does.\\nOf course, if these two individuals meet at their\\nplace of starting, they differ from each other just two\\ndays in their reckoning.\\n~L31., Ambiguity as to Days among the Islands of\\nthe Pacific Ocean, If an island in the Pacific were\\n130. What change of day is there to a person who goes round\\nthe earth to the east to the west How will they differ from\\neach other", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0121.jp2"}, "120": {"fulltext": "110 LONGITUDE TIDES.\\nsettled by navigators, who had gone westward, and\\nalso by others, who had sailed eastward, the reckoning\\nof these two parties would differ by one day. To the\\nformer, a day will be the first of a month when it is\\nthe 2d to the latter. It is, in fact, true that there are\\nislands lying contiguous to each other which have\\nthis difference of reckoning.\\nIf inhabited land extended entirely round the earth,\\nit would be necessary to fix arbitrarily on some me-\\nridian on which the change of day should be made.\\nFor it is impossible that the reckoning of days should\\ngo on unbroken around the earth. The arbitrary\\nmeridian would separate between places which differ\\na day from each other so that, on the west side of it,\\nthe time is one day later, both in the month and the\\nweek, than on the east side.\\n132. Definitions Melating to Tides. The Tides are\\nthe daily rising and falling of the waters of the ocean.\\nWhen the water, in this dailv oscillation, has reached\\nits highest point, it is called High Water; at its lowest\\npoint, it is called Low Water. Y/hile the water is\\nrising, it is called Flood; and while falling, El)b.\\nA Lunar Bay is the time between two successive\\nculminations of the moon. Its length is about 24 7\\n52m., being nearly an hour longer than a solar day on\\naccount of the rapid eastward motion of the moon.\\nThe tides make their revolutions within the lunar\\nday.\\n131. What difference of days occurs among the islands of the\\nPacific ocean\\n132. Define the terms in this article. How long is the lunar day", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0122.jp2"}, "121": {"fulltext": "OPPOSITE TIDES. Ill\\nTwice in a lunation high water is at a maximum,\\nand twice it is at a minimum. The former are called\\nSpring Tides the latter, Neap Tides. The spring\\ntides occur near the time of syzygies the neap tides\\nnear the time of quadratures.\\n133* Opposite Tides. There are two tide-waves\\non opposite sides of the globe, moving around it from\\neast to west, and arriving at any place at intervals,\\nwhose mean value is 12h. 26m., or half a lunar day.\\nSince the mean diurnal motion of each of the two\\nopposite tides is the same as that of the moon, the\\naction of the moon must be regarded as the principal\\ncause of the tides.\\n134. Form of the Water acted on by the 3Ioon,\\nIf the earth were covered with water, and no force\\nwere exerted except gravitation toward the earth\\nitself, its form would be exactly spherical, as repre-\\nsented in Fig. 26. But if a distant body, as the\\nmoon, should also attract it, the sphere would be\\nchanged into a Prolate Spheroid that is, into a form\\nproduced by revolving an ellipse about its major axis.\\nLet the moon be in the direction of CE produced, and\\nsuppose the center of gravity of the nearer half of\\nthe water, DEF, to be at A, and that of the remote\\nhalf at B, while the center of the earth, as a whole,\\nis at 0. Since A is more attracted than C, and C\\nmore than B, the form of equilibrium must be dis-\\nturbed, and some of the water will flow toward E, and\\n133. What is meant by opposite tides\\n134. How would tho moon change the form of the globe if cov-\\nered with water Explain by Fig. 26.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0123.jp2"}, "122": {"fulltext": "112\\nLONGITUDE TIDES\\noilier parts toward G, till the particles are in equi-\\nlibrio between their unequal tendencies to the moon\\nand their gravity on the inclined surface of the\\nspheroid. E and G are the highest points of the\\nspheroid, and all points on the circle DF (perpen-\\ndicular to EG) are the lowest. Every section through\\nEG is an ellipse, whose major axis is EG, and whose\\nminor axis is equal to DF. The ellipticity of the\\nsection will obviously depend not only on the strength\\nof the moon s attraction, but also on the difference\\nbetween the attractions on the nearer and remoter\\nparts.\\nIn the case of the earth and moon, it is computed\\nthat the major axis would exceed the minor by 5 feet\\nthat is, the tides would be only 2J feet high, and on\\nopposite sides of the earth, one directed toward the\\nmoon, the other from it. The tide on the side nearest\\nthe moon is sometimes called the direct tide the one\\non the remote side, the opposite tide.\\n135, Tides by the Sun. The same kind of effect\\nis produced by the sun as by the moon. But the dis-", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0124.jp2"}, "123": {"fulltext": "INERTIA OF WATER. 113\\ntance of the sun is so great, that though it attracts\\nthe earth more than the moon does, yet the difference\\nof its attractions on the several parts is less. The\\npower of the moon to raise a tide is to that of the\\nsun about as 5 to 2.\\nISO. Joint Action of the Sun and 31oon. At the\\ntime of conjunction, the moon and sun attract in the\\nsame direction, and, therefore, the tides are equal to\\nthe sum of the lunar and solar tides. The same is\\ntrue at opposition, because each body produces two\\ntides at once and the direct lunar tide coincides with\\nthe opposite solar tide, and vice versa. These are the\\nspring tides which occur at the syzygies.\\nAt quadratures, each body raises a tide at the ex-\\npense of that raised by the other. For if the moon\\nis in the direction of EG produced (Fig. 26), it causes\\nhigh water at E and G, and low water at D and F.\\nAnd if the sun is in the direction of DF produced, it\\ncauses high water at D and F, and Ioy/ water at E\\nand G. As the lunar tides are the highest, E and G\\nare the neap tides, made less by this action of the\\nsun than if the moon had acted alone.\\n137. Effect of the Inertia of Water. If the moon\\nand earth were at rest, the tides would be directed\\nexactly to and from the moon. But while the waters\\nare flowing toward these points, the moon, by the\\ndiurnal motion, passes westward, and causes them to\\n135. Compare the sun s action with the moon s.\\n186. When will the sun and moon conspire in their action?\\nWhen will they counteract each other\\n137. What is the effect of the inertia of the water", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0125.jp2"}, "124": {"fulltext": "114\\nLONGITUDE TIDES,\\nchange the places at which they tend to accumulate.\\nThus, even if the waves were unchecked by the shores\\nof continents and islands, the summit would be two\\nor three hours behind the moon in passing a given\\nmeridian.\\n138. Diurnal inequality. At a given place, the\\ntwo tides which follow the culmination of the moon\\nwill vary in height, according to the relation between\\nthe latitude of the place and the mioon s declination.\\nFig. 27.\\nIf the moon, M (Fig. 27), is on the equator, it is clear\\nthat the tides on the equator, EQ,~are greatest, and\\nthat in other places they are less, as the latitude is\\ngreater. But the two successive tides at any place\\nare equal for, by the rotation on NS, the tide at B\\nin 12 -J hours will come round to A, and be equal to\\nthe tide now there. The same is true of the tides C\\nand D, or F and G. Hence, when the moon has no\\ndeclination, there is no diurnal inequality.\\n138. Describe the diurnal inequality. When will the direct tide\\nbe greater than the opposite tide? When will the opposite tide be\\nthe greatest", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0126.jp2"}, "125": {"fulltext": "EFFECT OF COAST;\\n115\\nBut suppose the moon has a northern declination,\\nas in Fig. 28. Then the highest points of the tide\\nare at A in north latitude, and D in south. At A,\\nwhere the direct tide is large, the opposite tide, now\\nat B, will arrive in 12J hours, and will be small. But\\nafc 0, this is reversed the direct tide is small, and\\nFig. 28.\\nthe opposite one (now at D, and arriving at C 12J\\nhours later), is large. Therefore, when the declina-\\ntion and the latitude are both north, or both south,\\nthe direct tide (that is, the tide which first succeeds\\nthe upper culmination of the moon) is larger than the\\nopposite tide but if one is north, and the other\\nsouth, the direct tide is smaller than the opposite\\ntide. This difference in the height of the two suc-\\ncessive tides is called the diurnal inequality.\\n130o Change of Direction and Velocity caused by\\nCoasts. The tide-wave, which would move regularly\\nwestward around the earth, if it were wholly covered\\nby deep water, is exceedingly broken up and changed,\\n139. Explain how coasts affect the direction and velocity of tides.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0127.jp2"}, "126": {"fulltext": "116\\nLONGITUDE TIDES\\nboth in direction and velocity, by coasts and shoals.\\nIts general direction is westward but as it can pass\\nthe continents only at their southern extremities, it\\nbears to the northwest, and then to the north, in the\\nAtlantic and Pacific oceans and when it enters seas\\nor channels, it usually bends its course in the direc-\\ntion of their length.\\n140. Cotidal Lines. These are lines drawn on a\\nchart of the oceans, showing the position of the sum-\\nmit of the tide-wave for each hour of a day. Such a\\nsystem of lines expresses to the eye the direction and\\nvelocity of the tide at all places. Thus, on the open\\nFig.\\nocean, the figures 1, 2, 3, 4 (Fig. 29), show the situa-\\ntion of one and the same tide-wave at those hours,\\n140. Describe the cotidal lines. Why is the tide-wave convex\\nforward in channels How can there be four tides in a day at any-\\nplace", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0128.jp2"}, "127": {"fulltext": "EFFECT OF COASTS. 117\\nrespectively. And in the channel which extends\\nnorthward, the wave, having separated from the ocean\\ntide, advances northward, and occupies the places\\nmarked at the hours indicated. The wave advances\\nmost rapidly in the deepest water. Hence, the front\\nis generally convex, as in Eig. 29, since it moves fast-\\nest in the central part, where the water is deepest.\\nFor this reason, also, the tide may occupy as long a\\ntime in running through a long channel of shallow\\nwater as in advancing half round the earth. The\\ngreatest velocity of tide in the deep open ocean is\\nnear 1,000 miles per hour. Some channels are\\naffected by tides entering at both extremities. For\\nexample, the German Ocean and English Channel\\nreceive the Atlantic tide both at the north and at\\nthe south end. As a consequence, the tide system is\\ndoubled, causing, at some points, four tides per day.\\n141. Modification in the Height of the Tide caused\\nby Coasts. The relation of coast lines to each other\\nalso very much affects the height of the tide at partic-\\nular places. When the tide directly enters a broad-\\nmouthed bay, it grows higher as the bay contracts in\\nbreadth and at the head of the bay there is usually\\nfound the greatest height of all. One of the most\\nremarkable examples is the Bay of Eundy. The\\nwestern extremity of the Atlantic tide-wave, after en-\\ntering this bay, is gradually contracted by the shores\\nas it advances, till, at the head of the bay, it some-\\ntimes rises to 70 feet.\\n141. How is the height of the tide affected by the coasts Where\\nis the tide likely to he highest in a hay", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0129.jp2"}, "128": {"fulltext": "118 LONGITUDE TIDES.\\nThe height of the tide on the coast is generally\\ngreater than in the open ocean, owing to the effect of\\nshoal water. The most advanced part of the wave\\nmoves slower than the hinder portion so that the\\ncross-section of the ridge becomes shorter, and, there-\\nfore, higher, as the depth of water diminishes.\\nThe mean height of the spring tides at any place\\nis called the Unit of Altitude for that place.\\n142. Tides of Lalces and Inland Seas. In general,\\nthe tides of lakes and inland seas are scarcely per-\\nceptible. The reason is, their extent is so small that\\nall parts are to be considered as almost equi-distant\\nfrom the moon. There is little opportunity for water\\nto be attracted from the more distant to the nearer\\npart. The largest North American lakes have tides\\nbut an inch or two in height. In the Mediterranean,\\nhowever, which derives no tide from the ocean, the\\ntide-wave reaches 1^ or 2 feet.\\n142. Why is there so little tide in inland seas", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0130.jp2"}, "129": {"fulltext": "CHAPTER XI.\\nTHE PLANETS TABULAR STATEMENTS\u00e2\u0080\u0094 MERCURY\u00e2\u0080\u0094\\nVENUS MARS.\\n143, Names and Classification of the Planets.\u00e2\u0080\u0094 The\\nPlanets are solid spherical bodies revolving about the\\nsun in orbits which are nearly circular. The name\\nplanet signifies a wanderer, and was given to these\\nbodies because they continually change their places\\namong the fixed stars, generally moving from west to\\neast, but sometimes from east to west. These appar-\\nently irregular motions are fully explained by our\\nown annual motion, the earth on which we live being\\none of the planets.\\nThe planets are naturally arranged in three classes.\\n1. Four small planets near the sun, of which the\\nearth is the largest, namely Mercury, Venus, Earth,\\nMars.\\n2. The Planetoids, an indefinite number of bodies,\\ntoo small to be measured with certainty, and occupy-\\ning a ring outside of the first class. They are also\\ncalled Asteroids and Minor Planets.\\n143. What are planets State and describe the three groups.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0131.jp2"}, "130": {"fulltext": "120 THE PLANETS.\\n3. Four large planets, moving outside of the ring of\\nplanetoids, widely separated from each other, and at\\nvast distances from the sun. These are Jupiter,\\nSaturn, Uranus, Neptune,\\nTwo planets of the first class, Mercury and Yenus,\\nrevolve in orbits within the earth s orbit. These are\\ncalled inferior planets, being loiver down in the solar\\nsystem than the earth is. All the others, including\\nthe planetoids, are called superior planets because,\\nin relation to the sun, the great center of attraction,\\nthey are higher than the earth, and revolve in orbits\\nexterior to the earth s orbit.\\n144. Satellites.\u00e2\u0080\u0094 There is another class of spheri-\\ncal bodies, holding a subordinate place in the solar\\nsystem, since they revolve around the planets as cen-\\nters. These are called Satellites. The moon, already\\ndescribed in Chapter VIII, is a satellite of the earth.\\nThey are distributed as follows The earth has 1\\nJupiter, 4 Saturn, 8 Uranus, 4 Neptune, 1. Mer-\\ncury, Yenus, and Mars, have no satellites.\\nThe satellites are also called secondary planets;\\nand the planets, in distinction from them, primary\\nplanets.\\n145. Distances of the Planets from the Sun. The\\nfollowing table presents the mean distances of the\\nplanets from the sun in millions of miles, and also\\ntheir relative distances, the earth s being called 1\\n144. V\\\\That are satellites j What planets do they attend\\n145. Give the distances of the planets from the sun.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0132.jp2"}, "131": {"fulltext": "PEEIODIC TIMES. 121\\nI. Mean Relative\\nDistances. Distances.\\nMercury 37,000,000 0.39\\nVenus 69,000,000 0.72\\nEarth 95,000,000 1.00\\nMars 145,000,000 1.52\\nPlanetoids 254,000 000 2.67\\nJupiter 496,000,000 5.20\\nSaturn 909,000,000 9.54\\nUranus 1,828,000,000 19.18\\nNeptune 2,862,000,000 30.04\\nIt appears, by this table, that the remotest planet\\nis 77 times as far from the sun as the nearest. Hence\\nit is that orreries, unless of inconvenient size, always\\nfail of truly representing the planetary distances.\\nThe same is generally true of diagrams.\\n146* Periodic Times of the Planets. The follow-\\ning table contains the length of the sidereal revolu-\\ntions in months and years, which is the most con-\\nvenient form for the memory their length in days\\nand decimals, for calculations and their mean daily\\nmotion\\nIL\\nSidereal Sidereal Revolu- Mean Daily\\nRevolution. tion in Days. Motion.\\nMercury 3 months. 87.969 4\u00c2\u00b0 5 22.6\\nVenus 7\u00c2\u00b1 224.701 1\u00c2\u00b0 36 7.7\\nEarth 1 year. 365.256 0\u00c2\u00b0 59 8.3\\nMars 2 686.980 0\u00c2\u00b0 31 26.5\\nPlanetoids 4-|-\\nJupiter 12 4,332.585 0\u00c2\u00b0 4 59.1\\nSaturn 29 10,759.220 0\u00c2\u00b0 2 0.5\\nUranus 84 30,686.821 0\u00c2\u00b0 0 42.2\\nNeptune 164 60,126.720 0\u00c2\u00b0 0 21.6\\n146. State the periods of revolution.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0133.jp2"}, "132": {"fulltext": "Diameters.\\nVolumes.\\n82 2\\n1,405,000\\n0 8\\n0 17\\nft\\n1\\n0 6\\nt\\n0 37\\n1,521\\n0 16\\n921\\n0 4\\n87\\n0 2\\n79\\n122 THE PLANETS.\\n147* Magnitudes of the Planets, Table III gives\\nthe diameters of trie sun and planets in miles, with\\ntheir mean apparent diameters, and their volumes\\ncompared with the earth\\nIII.\\nDiameters.\\nSun 886,000\\nMercury 3,100\\nVenus 7,800\\nEarth 7,912\\nMars 4,500\\nJupiter 91,000\\nSaturn 77,000\\nUranus 35,000\\nNeptune 34,000\\n148* Masses and Densities of the Planets. Table\\nIV exhibits the masses and densities of the sun and\\nplanets, the earth being called I. It appears, from\\nthis table, that the small planets are much more\\ndense than the large planets and the sun\\niv.\\nMasses. Density.\\nSun 355,000.00 0.25\\nMercury 0.12 1.97\\nVenus 0.88 0.92\\nEarth 1.00 1.00\\nMars 0.13 0.72\\nJupiter 338.03 0.22\\nSaturn 101.06 0.11\\nUranus 14.79 0.15\\nNeptune 24.65 0.31\\n147. Give their diameters and volumes.\\n148. Also their inasses. Which aie the most dense", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0134.jp2"}, "133": {"fulltext": "PLANETARY MOTIONS. 123\\n149. The Sun and Planets Compared. By Table\\nIII, we see that the sun has 10 times the diameter,\\nand 1,000 times the volume, of Jupiter, the largest\\nplanet in the system. Table IY shows that the mass\\nof the sun is also more than 1,000 times as great as\\nthat of Jupiter, and 700 times greater than the united\\nmasses of all the planets. Its attraction mainly con-\\ntrols the movements of all the planets, satellites, and\\ncomets. Hence, these bodies describe their various\\npaths about it, scarcely disturbing it from a state of\\nrest. For this reason, this system of bodies is called\\nthe Solar System.\\nISO* Diameters of Planets, and their Distances\\nfrom the Sun. One of the most remarkable facts\\nrelating to the planets is brought to view in com-\\nparing the distances in Table I with the diameters in\\nTable III. While the diameters of the planets are\\nonly a few thousands of miles, their distances from\\nthe sun are many millions. The diameter of Nep-\\ntune s orbit is more than 20,000 times the diameters\\nof all the planets added together. To attempt to\\nrepresent both the distances a*ad magnitudes of the\\nplanets in their proportions, by an orrery or diagram,\\nis out of the question.\\n151. Directions of the Planetary Motions, It has\\nbeen stated in preceding chapters that all the mo-\\ntions of the sun, earth and moon are from west to\\n149. Compare the sun with the planets in diameter, in volume,\\nand in mass. Why is the system called the solar system\\n150. Compare the diameters of the planets and their distances\\nfrom the sun.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0135.jp2"}, "134": {"fulltext": "124\\nTHE PLANETS.\\neast. The same thing is true, in general, of all the\\nplanets and satellites and in nearly every case the\\ninclination to the ecliptic is very small. Since the\\nmotions in the solar system are so generally from\\nwest to east, this is regarded as direct motion and\\nany motions, real or apparent, which are from east to\\nwest, are called retrograde.\\nMERCURY.\\n152. Apparent 3Iotions. Mercury is an inferior\\nplanet, whose orbit is far within the earth s for it is\\nseen alternately east and west of the sun, and never\\nFig\\nmore than 29\u00c2\u00b0 from it. Let E (Fig. 30), be the earth,\\nsupposed, for the present, to be at rest the circle\\n151. What is the general direction of the planetary motions", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0136.jp2"}, "135": {"fulltext": "MEKCUKY. 125\\nABD, the orbit of Mercury S, the sun and BA/,\\nthe sky, on which the bodies are seen projected.\\nWhen Mercury is at B, it is seen at B as it passes\\nthrough D to A, it appears to advance to A as it is\\nnow coming toward the earth, it seems to be station-\\nary at A then from A through C to B, it appears to\\nretrograde from A to B where it is again stationary,\\nas it moves away from us. Since the sun appears at\\nS f the planet passes by it, both when advancing and\\nwhen retrograding.\\nWhen the planet is at D and C, it is in conjunction\\nwith the sun at C, between the earth and sun, it is\\nsaid to be in the inferior conjunction at D, in supe-\\nrior conjunction. B and A are called the points of\\ngreatest elongation. At superior conjunction, the mo-\\ntion of Mercury appears to be forward at the infe-\\nrior conjunction, backward and if the earth were at\\nrest, as we are now supposing, the planet would ap-\\npear stationary at the points of greatest elongation,\\n153. The Motions of Mercury as Modified by the\\nEarth s Motion. To simplify the case, it was sup-\\nposed, in the preceding article, that the earth is at\\nrest. But the earth moves in nearly the same direc-\\ntion as Mercury, making about one revolution while\\nMercury makes four (Table II). The effect is to\\nlengthen the arc of apparent advance, and shorten\\nthat of retrogradation. Thus, let the earth be at A\\n(Fig. 31), when Mercury is at F then it will appear\\nin the sky at L. While the earth is advancing to B,\\n152. Describe the apparent motions of Mercury, the earth being\\nat rest. Define superior and inferior conjunctions, and greatest\\nelongations.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0137.jp2"}, "136": {"fulltext": "126\\nTHE PLANETS.\\nMercury passes the inferior conjunction, and arrives\\nat G, and appears at M, having moved apparently\\nbackward from L to M. As the earth moves to C,\\nMercury describes GKE, and is at superior conjunc-\\ntion N. Again, while the earth moves to D, Mercury\\nFig. 31.\\npasses round to G, still advancing in the sky to O.\\nBut while the earth describes DE, Mercury again\\npasses the inferior conjunction from G to K, and ap-\\nparently retrogrades from O to P; after which, it\\nbegins once more to advance. Thus, by the earth s\\nmotion, the planet is made to retrograde through a\\nshorter arc, and to advance through a longer one,\\nthan if the earth were at rest.\\n153. Show how the earth s motion modifies the apparent motions\\nof Mercury.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0138.jp2"}, "137": {"fulltext": "MEECUEY. 127\\n154. Stationary Points. If the earth were at\\nrest, as supposed in Fig. 30, the points where the\\nplanet would appear to be stationary, in relation to\\nthe stars, would be A and B, at which tangents drawn\\nfrom the earth would meet the orbit. But the earth s\\nmotion removes the apparently stationary points a\\nlittle way toward the inferior conjunction. For, in\\norder to appear stationary, the advance which the\\nearth s motion causes must be just neutralized by the\\nretrogradation of Mercury. This planet appears sta-\\ntionary when its elongation from the sun is 15\u00c2\u00b0 or\\n20\u00c2\u00b0, according as it is nearer the perihelion or the\\naphelion.\\n155. Form and Position of Mercury s Orbit. The\\norbit of Mercury is more eccentric, and more inclined\\nto the ecliptic than that of any other of the eight\\nplanets. While the eccentricity of the earth s orbit\\nis only that of Mercury is nearly Yet this ren-\\nders the minor only shorter than the major axis\\nso that the form of the most eccentric of the plane-\\ntary orbits, if correctly drawn, would appear to the\\neye to be a circle.\\nThe inclination of Mercury s orbit to the plane of\\nthe ecliptic is 7\u00c2\u00b0.\\n156. Phases of Mercury. At the inferior con-\\njunction, C (Fig. 30), the unilluminated side of Mer-\\ncury is turned toward the earth, so that, like the new\\nmoon, it is invisible. At the superior conjunction, D,\\n154. Where would Mercury appear stationary, if the earth were\\nat rest Where, if the earth is in motion\\n155. State the form and position of Mercury s orbit.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0139.jp2"}, "138": {"fulltext": "128 THE PLANETS.\\nits illuminated side is toward us, and it is full. At A\\nor B, where the ray AS, and our line of vision, AE,\\nare at right angles, the phase is a semicircle. On the\\narc ACB occur the crescent phases on BDA, the\\ngibbous phases.\\n157. Point of Greatest Brightness. Mercury is\\nnot brightest when full, because it is then too far dis-\\ntant. It is not brightest when nearest, because its\\ndark side is toward us. Nor is it brightest at the\\nplace of greatest elongation but beyond it, toward\\nthe superior conjunction, when about 22\u00c2\u00b0 from the\\nsun. Its apparent diameter, when nearest the earth,\\nand when most distant from it, is as 2J to 1.\\n158. Transits of 3Iercury. As Mercury, at the\\ninferior conjunction, passes nearly between the earth\\nand sun, it may possibly come exactly in a line with\\nthem, and thus be seen as a black round spot going\\nacross the sun s disk. This phenomenon is called a\\ntransit of Mercury. If the plane of its orbit were\\ncoincident with that of the ecliptic, a transit would\\nobviously occur at every inferior conjunction. Since\\nthe angle between the two planes is 7\u00c2\u00b0, the planet\\ncannot be seen on the disk unless near the node.\\nThe nodes of Mercury s orbit lie in those parts of the\\nheavens which the sun passes through in May and\\n156. Describe the phases of Mercury, and when they respectively\\noccur.\\n157. Where is Mercury when brightest Why not at the point\\nnearest to us\\n158. What is a transit of Mercury Why does not a transit oc-\\ncur at every inferior conjunction In what months do they occur", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0140.jp2"}, "139": {"fulltext": "VENUS. 129\\nNovember. Therefore, a transit of that planet can\\noccur only in those months. The shortest interval\\nbetween two transits of Mercury is 3J years.\\nVENUS.\\n159* Apparent Motions. Like Mercury, Venus\\nappears to pass back and forth by the sun, reaching\\na distance of 47\u00c2\u00b0 at its greatest elongation. This\\nproves it to be an inferior planet, between Mercury\\nand the earth. Its sidereal period approaches so\\nnear to that of the earth that its synodic period is\\nlengthened to nearly If years. Hence, after making\\nan apparent retrograde motion, as LM (Fig. 31), it\\nadvances once and two-thirds round the heavens be-\\nfore it commences the next retrograde arc, OP.\\n160* Phases and Brightness of Venus, Venus\\npasses through the same changes of phase as Mer-\\ncury. But its apparent diameter, when the crescent\\nphase is narrowest, is more than 6 times as great as\\nwhen at full, because it is more than 6 times as near.\\nVenus is the brightest of the planets, and has been\\nknown from ancient times as the morning and evening\\nstar, according as it west of the sun, or east of it.\\nThe place of greatest brightness for Venus is when\\nabout 40\u00c2\u00b0 from the sun, between the point of great-\\nest elongation and the inferior conjunction. In this\\nsituation, it is frequently visible all day.\\n161. Transits of Venus. The orbit of Venus is\\ninclined to the ecliptic about 3J degrees. The sun\\n159. Describe the apparent motions of Venus.\\n160. State respecting its phases and its greatest brightness.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0141.jp2"}, "140": {"fulltext": "130 THE PLANETS.\\npasses its nodes in June and December. Therefore,\\nthe transits of that planet always occur in those\\nmonths.\\nThe shortest interval between two transits of\\nVenus is 8 years but after the occurrence of two\\nsuch, there cannot be another for more than a cen-\\ntury. Between 1800 and 1900 there are two transits\\nof Yenus, viz. December 8th, 1878, and December\\n6fch, 1882.\\nA transit of Venus is an occurrence of great inter-\\nest to astronomers, because it furnishes the best\\nmethod known for determining the sun s horizontal\\nparallax, and, therefore, the earth s distance from the\\nsun.\\nMAES.\\n102. Situation of Mars in the Solar System.\u00e2\u0080\u0094 This\\nis the most remote planet of the first group described\\nin Art. 258, namely Mercury, Venus, Earth, Mars.\\nIt is also the nearest to the earth of those planets\\nwhich are called superior.\\nAs Mars revolves in an orbit outside of the earth s,\\nit can come into Opposition to the sun, as well as into\\nconjunction with it, appearing at every degree of\\nelongation from 0\u00c2\u00b0 to 180\u00c2\u00b0.\\n163. Apparent Motions.\u00e2\u0080\u0094 The real motion of Mars\\nis from west to east and during most of the year, its\\napparent motion is in the same direction, sometimes\\n161. What is the shortest interval between two transits of Venus?\\nAfter two such transits, how long before another Why is a tran-\\nsit of Venus important\\n162. Where is Mars in the solar system What is the opposition\\nof Mars", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0142.jp2"}, "141": {"fulltext": "MAES.\\n131\\naccelerated, and sometimes retarded, by the earth s\\nmotion. Near opposition, however, when the earth\\novertakes and passes by Mars, its motion appears re-\\ntrograde. Thus, let the earth make one revolution\\nFm. 32.\\nfrom F to F again (Fig. 32), while Mars describes\\nnearly a half revolution from G to N. When the\\nearth is at F, Mars appears in the direction FG;\\nwhen at A, Mars, at H, appears in the sky at O when\\nthe earth is at B, Mars, at I, appears at P. Thus far\\nthe motion has been in advance, though becoming re-\\ntarded near P. But as the earth passes from B,\\nthrough C, to D, Mars, passing over the shorter arc\\nIKL, appears to retrograde from P to Q after which\\nit again advances, appearing at B, when the earth is\\nat E, and in the direction FN when the earth is at F.\\nFor the same reason, all the superior planets have\\na retrograde motion at the time of opposition.\\n163. By Fig. 32, describe tlie apparent motions of Mars, When\\nwill it appear to go backwards", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0143.jp2"}, "142": {"fulltext": "132\\nTHE PLANET\\n164. Phases, and Changes of Apparent Size, At\\nopposition, M (Fig. 33), and at conjunction, M it is\\nobvious that Mars appears full, since we look in the\\nsame direction in which the sun shines upon it. In\\nother positions, the angle between the sun s rays and\\nour visual line is acute, and the phase is gibbous (Art.\\n101). The planet is so near us that the phase differs\\nperceptibly from the full, when about half-way from\\nconjunction to opposition, as at Q, Q\\nThe least possible distance of Mars from the earth,\\nat opposition, is 35,000,000 miles and the greatest\\npossible distance, at conjunction, is 255,000,000 miles.\\n165. Appearance of Disk. Mars is remarkable\\namong the planets for its redness. The telescope\\n164. What changes of phase has Mars? How near the earth,\\nand how far from it, can Mars be", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0144.jp2"}, "143": {"fulltext": "MARS. 133\\nreveals some permanent inequalities of surface, by\\nwhich its diurnal rotation has been determined more\\nsatisfactorily than in the cases of Mercury and Ye-\\nnus. And there are other appearances, which change\\nas the relation of the equator to the sun changes.\\nThe polar regions, when turned away from the sun,\\nexhibit a whiteness which is supposed to be the effect\\nof ice and snow and this whiteness disappears grad-\\nually when the pole is turned again toward the sun.\\n166. Orbit and Equator of Mars. The orbit of\\nMars is inclined to the ecliptic nearly 2\u00c2\u00b0, and has an\\neccentricity equal to T\\nIn its diurnal rotation, it considerably resembles\\nthe earth, having about the same length of day, and\\nits equator being inclined nearly 29\u00c2\u00b0 to its orbit.\\nHence, the seasons vary somewhat more than those\\non the earth.\\nThe four small planets are all nearly alike as to the\\nlength of their day. Mercury revolves in 24Ji. 5rn.\\nYenus in 23h. 21m., the earth in 23k 56m., and Mars\\nin 24Ji. 37m.\\n165. Describe its telescopic appearance.\\n166. What are the form and position of its orbit What is the\\nlength of day on the four planets nearest the sun", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0145.jp2"}, "144": {"fulltext": "CHAPTER XII.\\nTHE PLANETOIDS JUPITER\u00e2\u0080\u0094 SATURN URANUS NEP-\\nTUNE DISTURBANCES OF THE PLANETS.\\n107 Hie Space between the Four Small Planets\\nand the Four Large Ones. There is a wide space\\nbetween Mars and Jupiter, within which the astrono-\\nmers of the last century conjectured there might re-\\nvolve another planet. The search for such a planet\\nat length led to the discovery of those bodies called\\nthe Planetoids, known, also, by the name of Asteroids.\\nTHE PLANETOIDS.\\n108* Their Number, and the Time of their Dis-\\ncovery. Four of these bodies were discovered within\\nthe first seven years of the present century, namely\\nCeres, Pallas, Juno, and Yesta. Since 1845, others\\nhave been found nearly every year, till their number\\nat the present time (1867) is between 90 and 100. The\\nwhole number of planetoids may be regarded as in-\\ndefinitely great.\\n169. Characteristics.\u00e2\u0080\u0094 -They are distinguished from\\nthe eight planets in the following particulars\\n167. What is said of the space between Mars and Jupiter? What\\nwas discovered in it\\n168. Give an account of the discovery.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0146.jp2"}, "145": {"fulltext": "THE PLANETOIDS, 135\\n1. By their Diminutive Size. They are invisible to\\nthe naked eye, and by the telescope cannot be distin-\\nguished from faint fixed stars, except by their motion.\\nThey are generally too small to show a sensible disk,\\nand hence cannot be measured with any certainty.\\nThe largest of them is believed to be only about 200\\nmiles in diameter. And it is estimated, by the slight\\ndisturbing influence which they exert, that their entire\\nmass is equal only to a small fraction of the earth.\\n2. By the Large Eccentricity and Obliquity of their\\nOrbits. The eccentricity of most of them is much\\ngreater than that of any of the eight planets.\\nThe obliquity of the orbit of Hebe is 14\u00c2\u00b0, and that\\nof Pallas is 34\u00c2\u00b0, which is the greatest yet discovered.\\n3. By their being Clustered in a Ring. The orbits\\nvary considerably in size, and, therefore, the periodic\\ntimes are various. But as they are generally quite\\neccentric, every planetoid is nearer the sun at perihe-\\nlion than any other one is at aphelion. The orbits are,\\ntherefore, all linked together, and pass through each\\nother. Thus, the planetoids are to be regarded as\\nmoving among each other about the sun, within the\\nlimits of a ring, whose breadth, in the direction of\\nthe radius vector, is more than 100,000,000 miles.\\nFlora, which moves in the smallest orbit yet discov-\\nered, performs its revolution in 3 J years Cybele, the\\nmost remote, in 6J years. Their mean periodic time\\nis 4J years and their mean distance from the sun is\\n254,000,000 miles.\\n169. What is the first particular which distinguishes the planet-\\noids from the planets? the second? the third? What are the\\nlongest and shortest periods of the planetoids", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0147.jp2"}, "146": {"fulltext": "136 THE PLANETS.\\nJUPITER.\\n17 Oo Jupiter s Magnitude and Place in the Solar\\nSystem. Jupiter is the nearest of the large planets\\noutside of the planetoids, and its orbit is not far from\\n200,000,000 miles beyond the ring which includes\\nthem. On account of its great distance from the sun,\\ncompared with the earth s, Jupiter presents to us no\\nvisible change of phase, appearing always full. Its\\ndisk, as presented to us, is almost the same as if we\\nwere at the sun. The same is, of course, true of all\\nthe planets still more remote.\\nJupiter greatly surpasses all the other planets in\\nmagnitude. In volume, it is about 1| times the sum\\nof all the others, and in mass, more than 2-J times\\ntheir united mass.\\n171. Its Form and Orbit. Though the diameter\\nof Jupiter is 11 times that of the earth, yet it rotates\\non its axis in less than 10 hours so that the equa-\\ntorial velocity is about 27 times as great as the\\nearth s. This rapidity of rotation produces a sensi-\\nble oblateness of the planet. Its ellipticity is T\\nand so considerable a deviation from the spherical\\nform is perceptible to the eye without measurement.\\nThe orbit of Jupiter is nearly in the plane of the\\necliptic, and has an eccentricity of J-q, which is three\\ntimes that of the earth s orbit. The equator of the\\n170. Where is Jupiter in the solar system? Does it present\\nchanges of phase Why Compare its size and mass with those\\nof the other planets.\\n1 71 How swiftly does it rotate on its axis What is the effect\\nIs there a change of seasons on Jupiter Why", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0148.jp2"}, "147": {"fulltext": "JUPITER.\\n137\\nplanet is inclined only about 3\u00c2\u00b0 to the plane of its\\norbit, so that there is no perceptible change of\\nseasons.\\n172. The Belts of Jtipiter. This name is given to\\nbands or stripes of darker shade than the rest of the\\ndisk, stretching across it in the direction of its rota-\\nFig. 34.\\ntion (Fig. 34). xhey vary, from time to time, in num-\\nber and in breadth, often covering a large part of the\\nsurface. A belt usually appears of uniform breadth\\nentirely across, but not always its edge is occasion-\\nally broken, and sometimes it is much wider on one\\npart of the disk than on the other, the change of\\nbreadth being commonly quite abrupt, and thereby\\nrevealing the rotation of the planet. There are, ordi-\\nnarily, two conspicuous belts, lying near the equator,\\none north, and the other south of it.\\nJupiter is supposed to have an atmosphere, in\\nwhich there are always many clouds floating. These,\\n172. Describe tlio belts. Explain their formation.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0149.jp2"}, "148": {"fulltext": "138 THE PLANETS.\\nby the swift rotation of the planet, are thrown into\\nstripes parallel with the equator and the dark belts\\nare considered to be the spaces between the clouds,\\nthrough which we look upon the planet itself.\\n173. Satellites of Jupiter. These are four in num-\\nber, revolving in orbits very nearly circular, and in\\nplanes which make small angles, both with the orbit\\nand the ecliptic. They are called the first, second,\\nthird, and fourth, reckoning outward from the planet.\\nTheir orbits being presented edgewise to us, they\\nseem to move back and forth across the place of Ju-\\npiter, one way in front of the planet, and the other\\nw^ay behind it, and always appear nearly in a straight\\nline. (See Tig. 34.)\\nJupiter s satellites are all somewhat larger than the\\nmoon, but on account of their great distance from us,\\nthey are too small to be seen except by a telescope.\\nBecause of the great attraction of Jupiter, exerted\\nupon them, they revolve a great deal quicker than\\nthe moon about the earth, as shown in the following\\ntable\\nSatellites. Diameters. Distances. Sidereal Revolutions.\\n1 2,440 275,000 Id. lSd. 28m\\n2 2,190 438,000 M. ISh. 15m\\n8 3,580 698,000 7d. Sh. 43m.\\n4 3,060 1,229,000 16d. 16A. 32m.\\n174:. Eclipses of Jupiter and its Satellites, On\\naccount of the great size of Jupiter and its shadow,\\n173. How many satellites lias Jupiter How do they appear to\\nmove Give their sises and times of revolution. Why do they re-\\nvolve so swiftlv", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0150.jp2"}, "149": {"fulltext": "JUPITEK. 139\\nand the small inclination between its own orbit and\\nthose of its satellites, most of them are eclipsed at\\nevery revolution, when on the opposite side of the\\nplanet from the sun and they generally eclipse Jupi-\\nter itself in passing between it and the sun. And\\nsince they revolve very rapidly, these eclipses are oc-\\ncurring every day. When Jupiter is eclipsed by one\\nof its moons, there is seen only a small dark spot\\ngoing across its disk. Both kinds of eclipses will be\\nFig. 35.\\nunderstood by reference to Fig. 35, where J repre-\\nsents Jupiter, 1, 2, 3, 4, the orbits of the satellites,\\nand A, B, C, D, different positions of the earth in its\\nown orbit. At a, the first satellite is just entering the\\nshadow at b, it has just emerged and when any\\nsatellite comes between J and the sun, its shadow will\\nfall on the planet.\\nBy means of the eclipses of Jupiter s satellites it\\nhas been discovered how swiftly light moves. For,\\nwhen the earth is at A, it is observed that an eclipse\\n174. What phenomena do they present Describe and explain\\nthe eclipses of the satellites and of the planet. What discovery\\nwas made by these means", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0151.jp2"}, "150": {"fulltext": "140\\nTHE PLANETS.\\nis seen about 16 minutes earlier than if it were at C.\\nAnd this must be because it requires 16 minutes for\\nthe light to cross the earth s orbit.\\nSATURN.\\n.175, Saturn s Disk. Saturn is the second planet\\nin size and being the second in order beyond the\\nplanetoids, is not too far from the earth to present a\\nlarge disk. Its form is seen to be elliptical, and it is\\nfaintly striped with belts in the direction of the major\\naxis. Both these appearances are explained by the\\nrapid rotation of the planet on its axis, as in the case\\nof Jupiter. It\\nellipticity is\\nrevolves in about 10J hours, and its\\n176, Saturn s Mings. The distinguishing feature\\nof this planet is the system of broad thin rings which\\nFig. 36\\nsurround it. They lie in a plane inclined about 28\u00c2\u00b0\\nto the ecliptic, and, therefore, generally present an\\n175. Where is Saturn s place in respect to distance from the sun\\nIn respect to size What is the appearance of its disk", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0152.jp2"}, "151": {"fulltext": "SATURN.\\n141\\nelliptical appearance to the earth (Fig. 36). The\\nring, as usually seen, consists of two rings, the inner\\nof which is the widest. The inner edge is 20,000\\nmiles from the surface of the planet and the diame-\\nter from outside to outside is 176,000 miles. The line\\nin which the plane of the ring intersects the plane of\\nSaturn s orbit is called the line of the nodes.\\nThe rings revolve in the same time as the planet\\nthat is, in about 10 J hours.\\n177. Disappearance of the Mings. Saturn re-\\nvolves about the sun once in 29 years, and its rings\\nalways remain parallel to themselves, as represented\\nFig. 37.\\nin Fig. 37, where GO is Saturn s orbit, and db the\\nearth s. As Saturn moves from A, through C, to E,\\nwe look upon the northern side of the rings and\\n176. What distinguishes Saturn? Describe the rings and their\\nmotions.\\n177. What is Saturn s period What are the changes in the as-\\npect of the rings Can the rings disappear more than once during\\nthe year of disappearance Why", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0153.jp2"}, "152": {"fulltext": "142 THE PLANETS.\\nfrom E to A, upon the southern side. At A and E,\\nthe rings present their edge toward us, and can\\nscarcely be seen at all. Thus, the rings disappear\\nonce in about 15 years.\\nBut it requires about a year for the plane of the\\nrings to pass by the whole breadth of the earth s\\norbit. It, therefore, happens that, during the year of\\nthe edge-view, the plane will pass once through the\\nsun, and perhaps two or three times through the\\nearth and, during a portion of the year, the plane\\nwill He between the sun and the earth, so that the\\ndark side of the rings will be presented toward us.\\n1 78, Phenomena of the Mings at the Planet. On\\nthat hemisphere of the planet to which the luminous\\nside of the rings is presented, there is the appearance\\nof splendid arches spanning the sky, having a breadth\\nand elevation according to the latitude of the place.\\nAt latitude 30\u00c2\u00b0 the breadth is about 18\u00c2\u00b0, and the ele-\\nvation of the lower edge on the meridian about 22\u00c2\u00b0.\\nNear the poles, however, it is below the horizon. The\\nluminous side is presented to the northern hemisphere\\nnear 15 years, and then the same length of time to the\\nsouthern hemisphere, in regular alternation.\\nA part of the rings is generally eclipsed by the\\nshadow of the planet falling on it.\\nAlso, during the 15 years in which the dark side of\\nthe rings is turned toward a hemisphere, its shadow\\nis cast across a zone of it, which causes an eclipse of\\nthe sun. And at a given place, a total solar eclipse\\nmay continue from day to day, without interruption,\\nfor several years.\\n178. How do tlie rings appear on the planet itself?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0154.jp2"}, "153": {"fulltext": "UEANUS. 143\\n179, Satellites of Saturn, Saturn is attended by\\neight satellites. Their periods of revolution vary\\nfrom less than one day to 79 days. Their diameters\\nvary from 500 to 3,000 miles but on account of their\\nimmense distance from the earth, they are seen only\\nwith the best instruments. They are all external to\\nthe rings, at distances from the planet varying from\\n129,000 to 2,478,000 miles. Their orbits are nearly\\nin the plane of the rings, and make an angle of about\\n28\u00c2\u00b0 with the orbit of the planet. Hence, they are\\nnot very liable to be eclipsed. The principal time for\\neclipses is that at which the rings disappear for\\nthen the sun is nearly in the plane of their orbits, as\\nwell as of the rings.\\nURANUS.\\n180* Discovery, and Place in the System. Uranus\\nwas unknown to the ancient astronomers and to\\nthem, therefore, Saturn s orbit was the boundary of\\nthe solar system. Uranus was discovered by Sir\\nWilliam Herschel, in 1781, and has made but little\\nmore than one revolution since that time for its\\nperiodic time is 84 years. It was, however, repeat-\\nedly seen by earlier astronomers, and recorded in\\ntheir catalogues as a fixed star. By this discovery,\\nthe diameter of the known solar system was doubled.\\nUranus is the third of the four great planets, both\\nin size and in order of distance. But its distance\\nfrom us is so immense that it appears only as a faint\\n179. Describe the satellites of Saturn.\\n180. When, and by whom, was Uranus discovered How dees\\nit appear", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0155.jp2"}, "154": {"fulltext": "144 THE PLANETS.\\nstar, and presents no inequalities by widen its diurnal\\nmotion can be discovered. Its orbit is very nearly\\ncircular, and is inclined less than a degree to the\\necliptic.\\n181. The Satellites of Uranus. Sir William Her-\\nschel announced the discovery of six satellites belong-\\ning to Uranus. But only four have been identified\\nby later astronomers. The remarkable facts relating\\nto these satellites are, that their orbits are nearly at\\nright angles to the plane of the ecliptic, and that in\\nthe orbits the motions of the satellites are retrograde;\\nthat is, from east to west. Their periods of revolu-\\ntion vary from 2J days to 13J days, and their dis-\\ntances from 130,000 to 396,000 miles.\\nNEPTUNE.\\n182. Discovery. Neptune was discovered in 1846.\\nThe circumstances which led to the discovery were\\nbriefly as follows After the orbit of Uranus had\\nbeen carefully computed, and corrections made for\\nthe disturbing influence of Jupiter and Saturn, the\\nplanet was found to depart from the calculated path\\nin a manner not to be accounted for except by sup-\\nposing some other disturbing force. It was for some\\ntime suspected that there must be a planet superior\\nto Uranus, whose attraction caused the change of its\\norbit. At length, two mathematicians, Le Verrier, of\\nFrance, and Adams, of England, each without any\\nknowledge of what the other was attempting, engaged\\n181. By what is it attended", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0156.jp2"}, "155": {"fulltext": "NEPTUNE. 145\\nin the arduous labor of calculating what must be the\\nelements of a planet which should produce the given\\ndisturbance of the motions of Uranus. They reached\\nresults which agreed remarkably with each other D\\nLe Verrier communicated to Galle, of the Berlin ob-\\nservatory, the place in the sky in which the disturb-\\ning body should be situated and in the evening of\\nthe same day, Galle found it within a degree of the\\npredicted longitude.\\nThe planet thus discovered explains fully the dis-\\nturbances in the motions of Uranus.\\nIt soon appeared that Neptune had repeatedly\\nbeen entered in catalogues as a fixed star. The ear-\\nliest of these records, in 1795, afforded material aid\\nat once in determining its mean distance and its peri-\\nodic time.\\nNeptune is attended by one satellite, which was\\nalso discovered in 1846. It is nearly as far from the\\nprimary as the moon is from the earth, and revolves\\nin 5d. 21h.\\nSo far as known, Neptune is the most remote-\\nplanet of the solar system, its distance from the sur\\nbeing 30 times as great as that of the earth. Its\\ntime of revolution is 164 years.\\nMUTUAL ACTION OF THE PLANETS.\\n183. Motions of the Planets Disturbed. On ac-\\ncount of the universal gravitation of matter, it mighl\\nbe expected that the planets, in describing theii\\n182. When was Neptune discovered? What led to the discov\\nry? Give an account of it. State other particulars respecting\\nNeptune.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0157.jp2"}, "156": {"fulltext": "146 THE PLANETS.\\norbits about the sun, would disturb each other s mo-\\ntions. It is true that they do and one of the most\\ndifficult and laborious parts of practical astronomy is\\nto calculate and allow for these disturbances. No\\none of all the planets pursues the same elliptic orbit\\nwhich it would describe if the sun were the only other\\nbody in the system.\\nOne kind of disturbance is this The plane of an\\norbit changes its position in such a manner that the\\nnodes, in which the planet cuts the plane of the\\necliptic, move backward that is, from east to west.\\nAnother is, that the perihelion and aphelion of most\\nplanetary orbits advance, or move from west to east.\\nStill another disturbance is, that the eccentricity of an\\norbit changes, becoming at one time greater, and at\\nanother time less. And others beside these might be\\nnamed.\\n184. Stability of the System, Notwithstanding\\nthese disturbances, it has been proved that they do\\nnot tend to cause the destruction of the system, as\\nwas once supposed. The reasons why the stability\\nand permanency of the system are not endangered\\nare the following\\n1. The planets are exceedingly small compared\\nwith the central body, the sun being more than 700\\ntimes greater than all of them together.\\n2. The largest planets are very distant from the\\n183. What effect do the planets produce on each other? State\\nthe different kinds of disturbance caused by them.\\n184. Do they tend to destroy the system Why The first rea-\\nson the second.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0158.jp2"}, "157": {"fulltext": "STABILITY OF THE SYSTEM. 147\\nsmall ones and from each other, and move in orbits\\nvery nearly circular, and very nearly in one plane.\\nFor these reasons the disturbances are all very\\nsmall and such of them as might ultimately become\\ndangerous by accumulating for a long time, are pre-\\nvented from accumulating by oscillating back and\\nforth that is, they increase for a time in one direc-\\ntion, and then in the opposite.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0159.jp2"}, "158": {"fulltext": "CHAPTEK XIII.\\nCOMETS SHOOTING STARS.\\n185. A Comet Defined. A comet is a body which\\nconsists of nebulous matter, and revolves about the\\nsun in a very eccentric orbit. Most comets present a\\nroundish ill-defined appearance, often having a bright\\ncentral part, called the Nucleus. The fainter part,\\nsurrounding the nucleus, is called the Coma (hair)\\nand the Tail, which distinguishes many comets, is\\nmerely the extension of the coma. It is the stream-\\ning appearance of the tail, resembling hair, which\\ngave the name comet to this class of bodies. The\\nnucleus has been sometimes supposed to be solid\\nbut it probably consists always of nebulous matter in\\na more condensed state than the other parts. The\\nnucleus and coma are called the Bead of the comet.\\n186. Number of Comets. Many hundreds of com-\\nets have been recorded, most of them, of course, vis-\\nible to the naked eye. But lately it is observed that\\nmost comets are telescopic objects. And many, which\\nwould otherwise be seen, escape observation by being\\nabove the horizon only in the daytime. The whole\\nnumber, therefore, belonging to the solar system is\\n185. Define a comet and its parts.\\n186. What is said of the number of comets", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0160.jp2"}, "159": {"fulltext": "TAILS OF COMETS\\n149\\nundoubtedly to be reckoned by thousands, or tens of\\nthousands.\\n187. Eccentricity of Orbit. All known cometary\\norbits are more eccentric than any planetary orbit\\nand most of them are exceedingly so, their perihelion\\nbeing as near the sun as Mercury and Yenus, or\\nnearer, and their aphelion as far off as the most dis-\\ntant planets, or even beyond. And some appear to\\nbe ellipses of infinite length.\\nOn account of this great eccentricity, comets are\\nnot seen except when they are near the perihelion.\\n188. Form and Direction of Tails of Comets.\u00e2\u0080\u0094 -The\\nforms of tails belonging to different comets are ex-\\nceedingly varied. In general, however, the sides\\ndiverge from the head, so that the most distant and\\nfaintest part is broadest, as in the comets of 1680 and\\nFig. 38.\\nCOMET OF 1680.\\n187. What is the form of their orbits? When are the comets\\ninvisible\\n188. Describe the general appearance and direction of the tail.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0161.jp2"}, "160": {"fulltext": "COMET OF 1811.\\n1811 (Figs. 38, 39). But sometimes the divergence is\\nvery slight, as in the comet of 1843 (see Fig. 40). In\\na few instances, the tail has appeared to be divided\\ninto two or more branches diverging from each other.\\nThe general direction of the tail is from the sun; so\\nthat, as a comet approaches the sun, the tail follows\\nit; but as it recedes, the tail is directed forward.\\nThe axis of the tail is not, however, a straight line,\\nbut more or less curved backward, so that the convex\\nside of the curve is foremost in the motion.\\n189. Dimensions of Comets. The dimensions of\\ncomets are various, and, on account of their nebulous\\ncharacter, they never admit of accurate measurement.\\nThe nucleus of a large comet is sometimes 5.000\\nmiles, and the coma 200,000 miles, in diameter, while\\nthe tail has, in one case, attained the extraordinary\\nlength of 200,000,000 miles.\\n189. What is said of tlie dimensions of comets Over how long\\nan arc does the tail sometimes extend", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0162.jp2"}, "161": {"fulltext": "MATTER IN COMETS. 151\\nThe apparent length of a comet s tail is often suf-\\nficient to span an arc of 20\u00c2\u00b0 or 30\u00c2\u00b0 on the sky, and\\nsometimes much more than this. The comet of 1680\\nextended 97\u00c2\u00b0, and that of 1861, 106\u00c2\u00b0. The fainter\\npart, in all cases, is seen only by indirect vision.\\nIt is obvious that the real length cannot be inferred\\nfrom the apparent, until the distance from us, and the\\nobliquity to our line of vision, are obtained.\\n190. Light of the Comets. These bodies, like the\\nplanets and satellites, shine by solar light which they\\nreflect to us. But, unlike all planetary bodies, they\\nare in a condition so attenuated that the sun s rays\\npenetrate every part of them without obstruction.\\nThe brightness of a star is not diminished in the least\\nwhen seen through the tail or coma of a comet. In\\na few instances, a star has been seen through the nu-\\ncleus, and even then was not essentially dimmed.\\n191. Quantity of Matter in Comets.\u00e2\u0080\u0094 Though some\\nof the largest comets surpass all other bodies in the\\nsolar system in magnitude, yet in respect to their mass\\nthey are too small to have produced, as yet, the\\nslightest perceptible effect. They sometimes come\\nvery near planets and their satellites, but are never\\nknown to exert the least influence on them. They\\ndo, of course, attract the planets, because they are\\nattracted by them, and suffer great disturbances from\\nthem. But until they themselves produce some effect\\nwhich is appreciable, their mass must be regarded as\\ninfinitely small.\\n190. What is said of tlie light of the comets\\n191. What proof is given that their mass is very small Do we\\nka that they attract at all?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0163.jp2"}, "162": {"fulltext": "152 COMETS.\\n192, Directions of Cometary 3Iotions. The com-\\netary orbits are unlike the planetary, not only in the\\ndegree of their eccentricity, but in the varied posi-\\ntions of their planes. Instead of being limited to a\\nnarrow zone like the zodiac, they make every variety\\nof angle with the ecliptic, so that a comet is as likely\\nto pass round the sun from north to south as from\\nwest to east. And whether the orbit is much or little\\ninclined, the comet s motion in it is as often retro-\\ngrade as direct.\\n193* T7ie Determination of a Comet s Orbit,\u00e2\u0080\u0094 From.\\nthe observations of right ascension and declination of\\na comet, which are repeatedly made while it is in\\nsight near the perihelion, the form of its orbit and\\nthe time of describing it can be calculated. But the\\npart in which it is visible is so small, compared with\\nthe whole orbit, that the results of calculation are\\nquite uncertain, until the comet is identified on its re-\\nturn. When a comet is thus identified, its periodic\\ntime is, of course, known and from that the length\\nand form of its orbit can be computed.\\nThe periods of most comets, however, appear to\\nbe so long that only a few have returned since\\nthe time when accurate observations began to be\\nmade. Hence it is that by far the greater part of all\\nthe recorded comets are unknown in respect to the\\nextent of their orbits and the time of describing\\nthem. And the few which are known have com-\\n192. How are their orbits situated\\n193. What observations are made in order to calculate their or-\\nbits Are the results certain When can the orbits be exactly\\ndetermined Have many been determined?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0164.jp2"}, "163": {"fulltext": "EEMAKKABLE COMETS. 153\\nparatively small orbits, and describe them in short\\nperiods.\\n194. Comets of Known Period. The following\\ntable contains the names of the only comets whose\\nperiodic times are certainly known\\nPeriod Perihelion Aphelion\\nComet. in years. Distance. Distance.\\nHalley s 75 56,000,000 3,400,000,000\\nEncke s 3\u00c2\u00a3 32,000,000 390,000,000\\nBiela s 6-J 85,000,000 570,000,000\\nFaye s 7i 161,000,000 565,000,000\\nBrorsen s 5^ 62,000,000 538,000,000\\nD Arrest s 6i 111,000,000 546,000,000\\nWinnecke s 5\u00c2\u00a3 73,000,000 526,000,000\\nOf the above, Halley s is by far the most interest-\\ning, on account of its brightness and length of tail,\\nand also on account of its long period. Its last re-\\nturn to the perihelion was in 1835, and it will not be\\nseen again till 1910. The other six contained in the\\ntable considerably resemble each other. Their pe-\\nriods are short, they are accompanied by little or no\\ntail, and they are all too faint to be seen except by\\na telescope. Hence, they are of little interest except\\nto the astronomer.\\n195. Other Remarkable Comets. The comet of\\n1680 was unusually brilliant, and was the first whose\\norbit was calculated by Sir Isaac Newton. (See\\nFig. 38.)\\nThe comet of 1744 was so bright as to be seen in\\n194. Name the comets whose orbits are known. Which is the\\nmost interesting Why What is said of the others", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0165.jp2"}, "164": {"fulltext": "154 COMETS.\\nthe daytime. Its tail was divided into six distinct\\nand divergent parts.\\nThe comet of 1770 was remarkable for having its\\norbit twice changed by the attraction of Jupiter first\\nfrom a period of 48 years to one of 6 years, and then\\nagain to one of 20 years. While its period was six\\nyears, it came twice to the perihelion, but was never\\nseen before, and has never been seen since.\\nThe comet of 1843 was so bright as to be seen by\\nday, and passed so near the sun at perihelion as to\\nFig. 40\\ntouch it. Its tail was very slender and straight, as\\nshown in Fig. 40.\\nThe comet of 1858, called, also, Donati s comet,\\npresented a series of envelopes, one within another.\\nIts period is computed to be about 2,000 years.\\nThe comet of 1861 was remarkable for the great\\napparent length of its tail, viz., 106\u00c2\u00b0. It came so\\n195. Describe tlie comet of 1680\u00e2\u0080\u0094 of 1744\u00e2\u0080\u0094 of 1770\u00e2\u0080\u0094 of 1843\u00e2\u0080\u0094 of\\n1858\u00e2\u0080\u0094 of 1861.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0166.jp2"}, "165": {"fulltext": "GASEOUS\\nETEORS.\\n155\\nnear the earth that the latter\\nis supposed to have passed\\nthrough a part of its tail. Its\\nappearance is presented in\\nFig. 41.\\nFig. 41.\\n196. Shooting Stars.\u00e2\u0080\u0094 This\\nis the popular name given to\\nthose bodies which appear\\nlike stars or planets moving\\nacross some part of the sky,\\nand then vanishing. They\\nare equally well known by\\nthe name of meteors. They\\nmay be seen in any clear\\nnight, by watching an hour\\nor two, especially if the moon\\nis not shining. The heights\\nof meteors are found to be\\ngenerally about 50 miles, and\\ntheir velocities 20 or 30 miles\\nper second. Coming into the\\nair with such great velocity,\\nthey are almost instantly set\\non fire, and their substance\\nbecomes incorporated with\\nthe atmosphere. From the\\nmeteors, it is found that they\\naround the sun.\\nJill! 1\\nIftllillljll:\\nI\\nm\\ni;?%-..;.\\nm\\niBl ili\\n11111 jiiii\\nobserved motions of\\nare bodies revolving\\n197. Gaseous Meteors. If the ordinary meteors\\n196. What are shooting stars How high are they generally\\nWhat is their velocity Around what do they revolve", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0167.jp2"}, "166": {"fulltext": "156 SHOOTING STARS.\\nwere more dense than a gas, they would hardly lose\\nall their motion, as they do, before reaching the earth.\\nThe most interesting fact relating to this class of\\nbodies is, that they sometimes come in showers; that\\nis, hundreds of thousands of them are seen in a\\nsingle night. These showers seem to have periodical\\nreturns. The most remarkable date is November\\n12th or 13th, at which time, every 33 or 34 years, they\\nappear in immense numbers on some part or other of\\nthe earth s surface. 1799, 1833, and 1866 were the\\nthree last times of great meteoric showers.\\n198. Solid Meteors. There is another class of\\nmeteoric bodies which afford indubitable evidence of\\nbeing solid. Like the gaseous meteors, they plunge\\ninto the atmosphere with great velocity, and are in-\\nflamed by the violent friction. Before reaching the\\nearth they usually explode, and scatter their frag-\\nments. Some of them, however, appear to lose only\\nsmall portions of their mass by explosion, and pass\\non in their orbits round the sun, greatly disturbed, of\\ncourse, by the earth s attraction.\\n199. Aerolites. This is the name usually given to\\nthe fragments thrown down by solid meteors though,\\nin rare instances, an aerolite obviously constitutes\\nthe entire meteor itself. Aerolites consist of iron,\\nsilex, and a few other materials, which are all known\\namong terrestrial substances. But they are always\\ndistinguishable from terrestrial bodies by their pecu-\\n197. Describe meteoric showers. What are the dates of their\\noccurrence\\n198. How is it known that any meteors are solid", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0168.jp2"}, "167": {"fulltext": "AEEOLITES. 157\\nliar structure. Since the great velocities of meteors,\\nsolid as well as gaseous, have become known, the\\nformer theories as to the origin of meteoric stones,\\nor aerolites, have been abandoned. Such velocities,\\nif they could be generated at all on the earth, could\\nnever exist in horizontal or downward directions.\\nBoth solid and gaseous meteors are, therefore, con-\\nsidered as describing orbits about the sun. The inter-\\nplanetary spaces, which have been generally reckoned\\nas vacant, may perhaps be to a great extent occupied\\nby innumerable bodies, of a grade far below that of\\ncomets and planetoids.\\n199. What are aerolites Of what do they consist How is\\ntheir material distinguishable from terrestrial substances", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0169.jp2"}, "168": {"fulltext": "CHAPTEB XIV.\\nTHE EJXED STAES\u00e2\u0080\u0094 CONSTELLATIONS.\\n200. The Stellar Universe. The bodies described\\nin the foregoing chapters all belong to the solar sys-\\ntem. If our investigations are extended outside of\\nthis system, we find that there are other systems,\\ngreater or less than this, unlimited in number, and\\nseparated from the solar system and from each other\\nby solitudes so vast that each system is only a point\\nin comparison with the distances between them. The\\ncentral sun in each of these countless systems is a\\nfixed star.\\nThe word universe is employed to express the\\nsum total of all these systems, the number of which,\\nand the extent of space occupied by them, are utterly\\nbeyond the reach of human comprehension.\\n201* The Fixed Stars, and their Magnitudes. The\\nfixed stars are so called because, to common observa-\\ntion, they always maintain the same situations with\\nrespect to each other. All the thousands of bright\\npoints ordinarily seen in the sky by night are fixed\\nstars, with the exception of two or three, possibly\\nfour, which are planets.\\nSCO. What is there outside of the solar system? What is the\\nmeaning of universe", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0170.jp2"}, "169": {"fulltext": "UNEQUAL BEIGHTNESS. 159\\nThe fixed stars are classified according to magni-\\ntudes, though the word, when thus used, signifies only\\ndegrees of brightness. The stars which can be seen by\\nthe naked eye, in the most favorable circumstances,\\nare divided into six magnitudes. Those which can\\nbe seen only by the aid of the telescope, called tele-\\nscopic stars, are arranged into several more so that\\nall the magnitudes are 16 or 18.\\nStars of the same magnitude are not equally bright\\nfor there is a continual gradation in respect to bright-\\nness so that, if the intensity were accurately meas-\\nured, probably the light of but very few would be\\nfound exactly equal.\\nStars of the first magnitude are fewest in number,\\nand, generally, the smaller the magnitude, the larger\\nthe number of stars included under it. The limits of\\nthe successive magnitudes differ somewhat, according\\nto different astronomers but the following round\\nnumbers do not vary widely from any of them\\nFirst magnitude 20\\nSecond magnitude 40\\nThird magnitude 140\\nFourth magnitude 300\\nFifth magnitude 950\\nSixth magnitude 4,450\\nIn all, near 6,000, visible to the naked eye. The\\nnumbers of the telescopic stars increase at so rapid a\\nrate that they have to be reckoned by millions.\\n202. Cause of Unequal Brightness. We might\\nsuppose either that the stars are themselves unequal\\nin respect to the quantity of light which they emit, or\\n201. Why are the fixed stars so called How are they classified?\\nWhat are telescopic stars Give the numbers included under each\\nof the first six magnitudes.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0171.jp2"}, "170": {"fulltext": "160 CONSTELLATIONS.\\ntliat they appear unequally bright on account of their\\ndifferent distances. It is undoubtedly true that there\\nis some diversity in the bodies themselves and yet,\\nthe rapid increase of numbers as the magnitudes are\\nless, indicates that difference of distance is the chief\\ncause of inequality in brightness. If there is any\\napproach to a uniform distribution of the stars in\\nspace, those which are nearest should be fewest in\\nnumber, and should, in general, appear brightest.\\n203. Constellations. The fixed stars are also\\nclassed topographically in constellations. This divi-\\nsion is very ancient and some of the constellations\\nare mentioned by the earliest writers. The names\\ngiven to them are those of the animals, heroes, and\\nother objects of pagan mythology.\\nWithin each constellation, the brightest stars are\\ndesignated by the letters of the Greek alphabet in\\nthe order of brightness. Thus, Alpha Lyrse is the\\nbrightest star in Lyra Beta Scorpionis, the brightest\\nbut one in Scorpio, c. After the Greek letters are\\nall used, Roman letters, and then numerals, are em-\\nployed. In some cases the order of brightness does\\nnot accord with the order of the alphabet. This may\\nresult from a change of brightness which has taken\\nplace since the stars were first named. When a cap-\\nital letter follows a number, there is reference to the\\ncatalogue of some astronomer. Thus, 84H is the star\\n84, of a certain constellation in Herschel s catalogue.\\nA few conspicuous stars are still known by the indi-\\n202. What is the principal cause of unequal brightness in stars\\n203. What are constellations How are stars in each designated", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0172.jp2"}, "171": {"fulltext": "THE ZODIAC. 161\\nvidual names given to them in ancient times as Arc-\\nturus, Antares, Sirius, Yega, c.\\n204, Star Catalogues. The first catalogue of stars\\nwas made by Hipparchus, before the time of Christ,\\nand contained 1,022 of the most conspicuous stars.\\nCatalogues of the present day contain hundreds of\\nthousands of stars, whose right ascensions and de-\\nclinations are given for a certain date.\\n203. Descriptions of Constellations. The remain-\\nder of this chapter is devoted to brief descriptions of\\nthe most prominent constellations which can be seen\\nin about latitude 40\u00c2\u00b0 N., accompanied by a few dia-\\ngrams to show the relative position of some of the\\nprincipal stars contained in them. These are in-\\ntended to afford the learner some aid in studying the\\nconstellations in the sky. But in order to become\\nwell acquainted with this branch of astronomy, a\\ncelestial globe or a series of star maps is necessary.\\nCONSTELLATIONS OF THE ZODIAC.\\n206. Aries (The Main) the first Aeies.\\nconstellation of the Zodiac, is known\\nby two bright stars, Alpha, on the a fi%\\nnortheast, and Beta, on the southwest,\\n4\u00c2\u00b0 apart, forming the head. South of 7\\nBeta, at the distance of 2\u00c2\u00b0, is a smaller star, Gamma.\\n204. Who made the first catalogue of stars Compare the num-\\nber in that and modern catalogues.\\n205. What is the purpose of the following descriptions What\\nmore is needed, in order to learn the constellations thoroughly\\n206. Describe Aries.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0173.jp2"}, "172": {"fulltext": "162 CONSTELLATIONS.\\nThe next brightest star of the Kam, Delta, is in the\\ntail, 15\u00c2\u00b0 southeast of Alpha. The feet of the figure\\nrest on the head of the Whale.\\nt 207. Taurus (The Bull) will be readily found by\\nthe seven stars, or Pleiades, which lie in the neck, 24\u00c2\u00b0\\neastward of Alpha Arietis. The largest star in Tau-\\nrus is Aldebaran, of the first magnitude, in the Bull s\\neye, 10\u00c2\u00b0 southeast of the Pleiades. It has a reddish\\ncolor, and resembles the planet Mars. The other eye\\nTaurus. Pleiades.\\n6%\\nof the figure is Epsilon, 3\u00c2\u00b0 northwest of Aldebaran.\\nFive small stars, situated a little west of Aldeba-\\nran, in the face of the Bull, constitute the Hyades.\\nAlthough the Pleiades are usually denominated the\\nseven stars, yet it has been remarked, from a high an\\ntiquity, that only six are present.\\nSome persons, however, of remarkable powers of\\nvision, are still able to recognize seven, and even a\\ngreater number. With a moderate telescope, not less\\nthan 50 or 60 stars, of considerable brightness, may\\nbe counted in this group, and a much larger number\\nof very small stars are revealed to the more pow-\\nerful telescopes. The beautiful allusion, in the Book\\nof Job, to the sweet influences of the Pleiades, and\\n207. Describe Taurus.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0174.jp2"}, "173": {"fulltext": "THE ZODIAC. 163\\nthe special mention made of this group by Homer\\nand Hesiod, show how early it had attracted the\\nattention of mankind. The liorns of the Bull are two\\nstars, Beta and Zeta, situated 25\u00c2\u00b0 east of the Pleiades,\\nbeing 8\u00c2\u00b0 apart. The northern horn, Beta, also forms\\none of the feet of Auriga, the Charioteer.\\n208. Gemini (The Twins) is re- The Twins.\\npresented by two well-known stars,\\nCastor and Pollux, in the head of\\nthe figure, 5\u00c2\u00b0 asunder. Castor, the\\nnorthern, is of the first, and Pollux\\nof the second magnitude. Four\\nconspicuous stars, extending in a\\nline from south to north, 25\u00c2\u00b0 south-\\nwest of Castor, form the feet, and\\ntwo others, parallel to these, at the\\ndistance of 6\u00c2\u00b0 or 7\u00c2\u00b0 northeastward,\\nare in the knees.\\n7#\\n209. Cancer (The Crab). There are no large stars\\nin this constellation, and it is regarded as less re-\\nmarkable than any other in the Zodiac. The two\\nmost conspicuous stars, Alpha and Beta, are in the\\nsouthern claws of the figure and in its body are the\\nnorthern and southern Asellus, which may be readily\\nfound on a celestial globe. But the most remark-\\nable object in this constellation is a misty group\\nof very small stars, so close together, when seen by\\nthe naked eye, as to resemble a comet, but easily sep-\\narated by the telescope into a beautiful collection of\\nbrilliant points. It is called Prossepe, or the Beehive.\\n208\u00e2\u0080\u0094209. Describe Gemini\u00e2\u0080\u0094 Cancer.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0175.jp2"}, "174": {"fulltext": "164: CONSTELLATIONS.\\n210. Leo (The Lion) is a very large constellation,\\nand has many interesting members. Regulus (Alpha\\nLeonis) is a star of the first magnitude, which lies\\nThe L*ion.\\nj\\nvery near the ecliptic, and is much used in astronom-\\nical observations. North of Regulus lies a semicircle\\nof five bright stars, arranged in the form of a sickle,\\nof which Regulus is the handle, and extending over\\nthe shoulder and neck of the Lion. Denebola, a con-\\nspicuous star in the Lion s tail, lies 25\u00c2\u00b0 east of Regu-\\nlus. Twenty bright stars in all help to compose this\\nbeautiful constellation. It ranges from west to east\\nalong the Zodiac, over more than 40\u00c2\u00b0 of longitude,\\nall parts of the figure excepting the feet lying north\\nof the ecliptic.\\n211, Virgo (Hie Virgin) extends along the Zodiac\\neastward from the Lion, covering an equally wide re-\\ngion of the heavens, although less distinguished by\\nbrilliant stars. Spica, however, is a star of the first\\nmagnitude, and lies a little east of the vernal equi-\\nnox. Vindemiatrix, in the arm of Virgo, 18\u00c2\u00b0 east of\\nDenebola, and 23\u00c2\u00b0 north of Spica, is easily found\\nand directly south of Denebola 13\u00c2\u00b0, is Beta Virgims;\\n210\u00e2\u0080\u0094211. Describe Leo\u00e2\u0080\u0094 Virgo.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0176.jp2"}, "175": {"fulltext": "THE ZODIAC. 165\\nwhile four other conspicuous stars, in the form of a\\ntrapezium, between this and Vindemiatrix, lie in the\\nwing and shoulders of the figure. The feet are near\\nthe Balance.\\n212* Libra (TJie Balance) is composed of a few\\nscattered members situated between the feet of Yirgo\\nand the head of Scorpio, but has no very distinctive\\nmarks. Two stars of the second magnitude, Alpha,\\non the south, and Beta, 8\u00c2\u00b0 northeast of Alpha, to-\\ngether with a few smaller stars, form the scales.\\n213, Scorpio (TJie Scorpion) is one of the finest\\nof the constellations of the Zodiac, and is manifestly\\nso called from its resemblance to the animal whose\\nThe Scorpion.\\n*v\\nname it bears. The head is composed of five stars,\\narranged in a line slightly curved, which is crossed in\\n212\u00e2\u0080\u0094213. Describe Libra\u00e2\u0080\u0094 Scorpio.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0177.jp2"}, "176": {"fulltext": "166 CONSTELLATIONS.\\nthe center by the ecliptic, nearly at right angles, a\\ndegree south of the brightest of the group, Beta Seor-\\npionis. Nine degrees southeast of this is a remarka-\\nble star of the first magnitude, called Antares, and\\nsometimes the Heart of the Scorpion. It is of a red\\ncjlor, resembling the planet Mars. South and east of\\nthis, a succession of not less than nine bright stars\\nsweep round in a semicircle, terminating in several\\nsmall stars forming the sting of the Scorpion. The\\ntail of the figure extends into the Milky Way.\\n214. Sagittarius (The Archer). Ten degrees east-\\nward of the Scorpion s tail, on the eastern margin of\\nMilky Way, we come to the hoiv of Sagittarius, con-\\nsisting of three stars, about 6\u00c2\u00b0 apart, the middle one\\nbeing the brightest, and situated in the bend of the\\nbow, while a fourth star, 4\u00c2\u00b0 westward of it, consti-\\ntutes the arrow. The archer is represented by the\\nfigure of a Centaur (half horse and half man) and\\nproceeding about 10\u00c2\u00b0 east from the bow, we come to\\na collection of seven or eight stars of the second and\\nthird magnitudes, which lie in the human or upper\\npart of the figure.\\n215. Capricornus (The Goat), represented with the\\nhead of a goat and the tail of a fish, comes next to\\nSagittarius, about 20\u00c2\u00b0 eastward of the group that\\nform the upper portions of that constellation. Two\\nstars of the second magnitude, Alpha, on the north,\\nand Beta, on the south, 3\u00c2\u00b0 apart, constitute the head\\nof Capricornus, while a collection of stars of the\\n214 215, Describe Sagittarius Capricornus.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0178.jp2"}, "177": {"fulltext": "THE ZODIAC. 167\\nthird magnitude, lying 20\u00c2\u00b0 southeast of these, form\\nthe tail.\\n216. Aquarius (The Water Bearer) is closely in\\ncontact with the tail of Capricornus, immediately\\nnorth of which, at the distance of 10\u00c2\u00b0, is the western\\nshoulder (Beta), and 10\u00c2\u00b0 further east is the eastern\\nshoulder (Alpha) of Aquarius. About 3\u00c2\u00b0 southeast of\\nAlpha is Gamma Aquarii, which, together with the\\nother two, makes an acute triangle, of which Beta\\nforms the vertex. In the eastern arm of Aquarius\\nare found four stars, which together make the figure\\nT, the open part being westward, or towards the\\nshoulders of the constellation. Aquarius ranges\\nnearly 30\u00c2\u00b0 from north to south, being nearly bisected\\nby the ecliptic.\\n217. Pisces (TJie Fishes). Three figures of this\\nkind, at a great distance apart, two north and one\\nsouth of the ecliptic, compose this constellation. The\\nsouthern Fish, Piscis Australia, otherwise called Fo-\\nmalhaut, lies directly below the feet of Aquarius, and\\nbeing the only conspicuous star in that part of the\\nheavens, is much used in astronomical measurements.\\nIt is 30\u00c2\u00b0 south of the equator.\\nAbout 12\u00c2\u00b0 east of the figure Y in the arm of Aqua-\\nrius, is an assemblage of five stars, forming a pretty\\nregular pentagon, which is one of the northern mem-\\nbers of the Constellation Pisces and far to the\\nnortheast of this figure, north of the head of Aries,\\nlies the third member, the three being represented as\\n216 217. Describe Aquarius Pisces.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0179.jp2"}, "178": {"fulltext": "168 CONSTELLATIONS.\\nconnected together by a ribbon, or wavy band, com-\\nposed of minute stars.\\nCONSTELLATIONS NORTH OF THE ZODIAC.\\n218. Ursa Minor (The Little Bear).\u00e2\u0080\u0094 The Pole-star\\n(Polaris) is in the extremity of the tail of the Little\\nBear. It is of the third magnitude, and being within\\nless than a degree and a half of the North Pole of\\nThe Little Beak,\\n7\\nPole Star\\nthe heavens, it serves, at present, to Indicate the po-\\nsition of the pole. It will be recollected, however,\\nthat on account of the precession of the equinoxes,\\nthe pole of the heavens is constantly shifting its place\\nfrom east to west, revolving about the pole of the\\necliptic, and will in time recede so far from the pole-\\nstar that this will no longer retain its present distinc-\\ntion. Three stars in a straight line, 4\u00c2\u00b0 or 5\u00c2\u00b0 apart,\\ncommencing with Polaris, lead to a trapezium of four\\nstars, the whole seven together forming the figure of\\na dipper, the trapezium being the body, and the three\\nfirst-mentioned stars being the handle.\\n219. Ursa Major (The Great Bear) is one of the\\n218. Describe Ursa Minor.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0180.jp2"}, "179": {"fulltext": "NORTH OF THE ZODIAC. 169\\nlargest and most celebrated of the constellations. It\\nis usually recognized by the figure of a larger and\\nmore perfect dipper than the one in the Little Bear\\nThe Gkeat Beab.\\n4\\na\\nf\\nMs-\\ny\\nP\\nthree stars, as before, constituting the handle, and\\nfour others, in the form of a trapezium, the body of\\nthe figure. The two western stars of the trapezium,\\nranging nearly with the North Star, are called the\\nPointers and beginning with the northern of these\\ntwo, and following round from left to right through\\nthe whole seven, they correspond in rank to the suc-\\ncession of the first seven letters of the Greek alpha-\\nbet Alpha, Beta, Gamma, Delta, Epsilon, Zeta, Eta.\\nSeveral of them also are known by their Arabic\\nnames. Thus, the first in the tail, corresponding to\\nEpsilon, is Alioth, the next (Zeta) Mizar, and the last\\n(Eta) Benetnascli. These are all bright and beautiful\\nstars, -Alpha being of the first magnitude, Beta,\\nGamma, Delta, of the second, and the three forming\\nthe tail, of the third. But it must be remarked that\\nthis very remarkable figure of a dipper, or ladle, com-\\nposes but a small part of the entire constellation, be-\\ning merely the hinder half of the body and the tail of\\nthe Bear. The head and breast of the figure, lying\\n219. Describe Ursa Major.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0181.jp2"}, "180": {"fulltext": "170 CONSTELLATIONS.\\nabout ten or twelve degrees west of the Pointers, con-\\ntain a great number of minute stars in a triangular\\ngroup. One of the fourth magnitude, Omicron, is in\\nthe mouth of the Bear. The feet of the figure may\\nbe looked for about 15\u00c2\u00b0 south of those already de-\\nscribed, the two hinder paws consisting each of two\\nstars very similar in appearance, and only a degree\\nand a half apart. The two paws are distant from\\neach other about 18\u00c2\u00b0; and following westward about\\nthe same number of degrees, we come to another very\\nsimilar pair of stars, which constitute one of the fore\\npaws, the other foot being without any corresponding\\npair.\\nIn a clear winter s night, when the whole constella-\\ntion is above the pole, these various parts may be\\neasily recognized, and the entire figure will be seen to\\nresemble a large animal, readily accounting for the\\nname given to this constellation from the earliest\\n220. Draco (The Dragon) is also a very large con-\\nstellation) extending for a great length from east to\\nwest. Beginning at the tail, which lies half way be-\\ntween the Pointers and the Pole-star, and winding\\nround between the Great and the Little Bear, by a\\ncontinued succession of bright stars from 5\u00c2\u00b0 to 10\u00c2\u00b0\\nasunder, it coils around under the feet of the Little\\nBear, sweeps round the pole of the ecliptic, and ter-\\nminates in a trapezium formed by four conspicuous\\nstars, from 30\u00c2\u00b0 to 35\u00c2\u00b0 from the North Pole. A few of\\nthe members of this constellation are of the second,\\n220. Describe Draco.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0182.jp2"}, "181": {"fulltext": "NORTH OF THE ZODIAC. 171\\nbut the greater part of the third magnitude, and be-\\nlow it.\\n221. Cepheus (The King) is bounded north by the\\nLittle Bear, east by Cassiopeia, south by the Lizard,\\nand west by the Dragon. The head lies in the Milky\\nWay, and the feet extend toward the pole. It con-\\ntains no stars above the third magnitude.\\n222. Cassiopeia is bounded north and west by\\nCepheus, east by Camelopardalus, and south by An-\\ndromeda, and is one of the constellations of the Milky\\nWay. It is readily distinguished by the figure of a\\nCassiopeia.\\nH J\\nchair inverted, of which two stars constitute the back,\\nand four, in the form of a square, the body of the\\nchair. It is on the opposite side of the pole from the\\nGreat Bear, and nearly at the same distance from it.\\n223. Camelopardalus (The Giraffe) is bounded\\nnorth by the Little Bear, east by the head of the\\nGreat Bear, south by Auriga and Perseus, and west\\nby Cassiopeia. Although this constellation occupies\\na large space, yet it has no conspicuous stars.\\n221 222 223. Describe Cepheus Cassiopeia Camelopardalus.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0183.jp2"}, "182": {"fulltext": "172 CONSTELLATIONS.\\n224. Andromeda is bounded north by Cassiopeia,\\neast by Perseus, south by Pegasus, and west by the\\nLizard. The direction of the figure is from south-\\nwest to northeast, the head coming down within 30\u00c2\u00b0\\nof the equator, and being recognized by a star of\\nthe second magnitude, which forms the northeastern\\ncorner of the great square in Pegasus, to be described\\nhereafter. At the distance of six or seven degrees\\nfrom the head are three conspicuous stars in a row,\\nranging from north to south, which he in the breast of\\nthe figure and about the same distance from these,\\nand parallel to them, three more, which constitute the\\ngirdle of Andromeda. Near the northernmost of the\\nthree is a faint, misty object, often mistaken for a\\ncomet, but is a nebula, and one of the most remarka-\\nble in the heavens.\\n225. Perseus is bounded north by Cassiopeia, east\\nby Auriga, south by Taurus, and west by Andromeda.\\nThe figure extends from north to south, and is repre-\\nsented by a giant holding aloft a sword in his right\\nhand, while his left grasps the head of Medusa, a group\\nof stars on the western side of the figure, embracing\\nthe celebrated star Algol. A series of bright stars\\ndescend along the shoulders and the waist, and there\\ndivide into the two legs. The western foot is 8\u00c2\u00b0\\nnorth of the Pleiades. The eastern leg is bent at the\\nknee, which is distinguished by a group of small\\nstars. Near the sword handle, under Cassiopeia s\\nchair, is a fine cluster of stars, so close together as\\nscarcely to be separable by the eye.\\n224 225. Describe Andromeda Perseus.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0184.jp2"}, "183": {"fulltext": "NORTH OF THE ZODIAC. 173\\n228. Auriga {Tlie Wagoner) is bounded north by\\nCamelopardalus, east by the Lynx, south by Taurus,\\nand west by Perseus. He is represented as bearing\\non his left shoulder the little Goat Capella, a white\\nand beautiful star of the first magnitude, while Beta\\nforms the right shoulder, 8\u00c2\u00b0 east of Capella. These\\ntwo bright stars form, with the northern horn of the\\nBull, at the distance of 18\u00c2\u00b0, an isosceles triangle.\\n227. Leo Minor {The Lesser Lion) is bounded\\nnorth by Ursa Major, east by Coma Berenices, south\\nby Leo, and west by the Lynx. It lies directly under\\nthe hind feet of the Great Bear, and over the sickle\\nin Leo, and is easily distinguished. Four stars in the\\ncentral part of the figure, from 4\u00c2\u00b0 to 5\u00c2\u00b0 apart, form a\\npretty regular parallelogram.\\n228. Canes Venatici {The Greyhounds,)- -This con-\\nstellation lies between the hind legs of the Great\\nBear, on the west, and Bootes, on the east. Cor\\nCaroli, a solitary star of the third magnitude, 18\u00c2\u00b0\\nsouth of Alioth, in the tail of the Great Bear, will\\nserve to mark this constellation.\\n229. Coma Berenices {Berenice s Hair) is a cluster\\nof small stars, composing a rich group, 15\u00c2\u00b0 northeast\\nof Denebola, in the Lion s tail, in a line between this\\nstar and Cor Caroli, and half way between the two.\\n230. Bootes is bounded north by Draco, east by\\nthe Crown and the head of Serpentarius, south by\\n226\u00e2\u0080\u0094227\u00e2\u0080\u0094228\u00e2\u0080\u0094229. Describe Auriga\u00e2\u0080\u0094 Leo Minor\u00e2\u0080\u0094 Canes Vena-\\ntici Coma Berenices.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0185.jp2"}, "184": {"fulltext": "174: CONSTELLATIONS.\\nVirgo, and west by Coma Berenices and the Hounds.\\nIt reaches for a great distance from north to south,\\nthe head being within 20\u00c2\u00b0 of the Dragon, and the feet\\nextending to the Zodiac. In the knee of Bootes is\\nArcturus, a star of the first magnitude. The next\\nbrightest star, Beta, is in the head of Bootes, 23\u00c2\u00b0\\nnorth of Arcturus, and 15\u00c2\u00b0 east of the last star in the\\ntail of the Great Bear.\\n231, Corona Bor calls (The The Crown.\\nNorthern Crown) is bounded effc\\nnorth and east by Hercules,\\nsouth by the head of Serpenta- 7^ f\u00c2\u00b0\\nrius, and west by Bootes. It Q\\nis formed of a semicircle of\\nbright stars, six in number, of which Gamma, near\\nthe center of the curve, is of the second magnitude.\\n232, Hercules is bounded north by Draco, east by\\nLyra, south by Ophiuchus, and west by Corona Bore-\\nalis. It is a very large constellation, and contains\\nsome brilliant objects for the telescope, although its\\ncomponents are generally very small. The figure lies\\nnorth and south, with the head near the head of\\nOphiuchus, and the feet under the head of Draco.\\nBeing between the Crown and the Lyre, its locality is\\neasily determined. The eastern foot of Hercules\\nforms an isosceles triangle with the two southern\\nstars of the trapezium in the head of Draco while\\nthe head of Hercules is far in the south, within 15\u00c2\u00b0\\nof the equator, being 6\u00c2\u00b0 west of a similar star which\\nconstitutes the head of Ophiuchus.\\n230 231 232. Describe Bootes Corona Borealis Hercules.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0186.jp2"}, "185": {"fulltext": "NOETH OF THE ZODIAC. 175\\n233. Lyra {The Lyre) is bounded north by the\\nhead of Draco, east by the Swan, south and west by\\nHercules. Alpha Lyrce, or Vega, is of the first mag-\\nnitude. It is accompanied by a small acute triangle\\nof stars. Its color is a shining white, resembling Ca-\\npella and the Eagle.\\n234. Cygnus {The Swan) extends along the Milky\\nWay, below Cepheus, and immediately eastward of\\nThe Swan.\\nthe Lyre, and has the figure of a large bird flying\\nalong the Milky Way from north to south, with out-\\nstretched wings and long neck. Commencing with\\nthe tail, 25\u00c2\u00b0 east of Lyra, and following down the\\nMilky Way, we pass along a line of conspicuous stars\\nwhich form the body and neck of the figure; and\\nthen returning to the second of the series, we see two\\nbright stars at 8\u00c2\u00b0 or 9\u00c2\u00b0 on the right and left (the three\\ntogether ranging across the Milky Way), which form\\nthe wings of the Swan. This constellation is among\\nthe few which exhibit some resemblance to the ani-\\nmals whose names they bear.\\n233\u00e2\u0080\u0094234. Describe Lyra\u00e2\u0080\u0094 Cygnus.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0187.jp2"}, "186": {"fulltext": "176 CONSTELLATIONS.\\n235. Vulpecula {The Little Fox) is a small constel-\\nlation, in which a fox is represented as holding a\\ngoose in his mouth. It lies in the Milky Way, be-\\ntween the Swan, on the north, and the Dolphin and\\nthe Arrow, on the south.\\n236* Aquila {The Eagle) stretches across the Milky\\nWay, and is bounded north by Sagitta, a small con-\\nstellation which separates it from the Fox, east by\\nthe Dolphin, south by Antinous, and west by Taurus\\nPoniatowski (the Polish Bull), which separates it from\\nOphiuchus. It is distinguished by three bright stars\\nin the neck, known as the three stars, which lie in\\na straight line about 2\u00c2\u00b0 apart, on the eastern margin\\nof the Milky Way. The central star is of the first\\nmagnitude. Its Arabic name is Altair.\\n237. Antinous lies across the equator, between the\\nEagle, on the north, and the head of Capricorn, on\\nthe south.\\n238. Delphinns (Tlie Dolphin) is situated east and\\nnorth of Altair, and is composed of five stars of the\\nthird magnitude, of which four, in the form of a\\nrhombus, compose the head, and the fifth forms the\\ntail.\\n230. Pegasus (TJie Flying Horse) is a very large\\nconstellation, and is bounded north by the Lizard and\\nAndromeda, east and south by Pisces, west by the\\nDolphin. The head is near the Dolphin, while the\\n235\u00e2\u0080\u0094236\u00e2\u0080\u0094237\u00e2\u0080\u0094238\u00e2\u0080\u0094239. Describe Vulpecula Aquila Anti-\\nnous Delpliinus Pegasus.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0188.jp2"}, "187": {"fulltext": "SOUTH OF THE ZODIAC. 177\\nback rests on Pisces, and the feet extend towards\\nAndromeda.\\nA large square, composed of four conspicuous mem-\\nbers, one (Marhab) of the first, and three others of\\nthe second magnitude, distinguish this constellation.\\nThe corners of the square are about 15\u00c2\u00b0 apart, the\\nnortheastern corner being in the head of Andromeda.\\n240. Ophiuchus is another very large constella-\\ntion, the head being near the head of Hercules, and\\nthe feet reaching to Scorpio, the western foot being\\nalmost in contact with Antares. The figure is that of\\na giant holding a serpent in his hands. The head of\\nthe serpent is a little south of the Crown, and the tail\\nreaches far eastward towards the Eagle.\\nCONSTELLATIONS SOUTH OF THE ZODIAC.\\n241. Cetus {The Whale) is distinguished rather for\\nits extent than its brilliancy, occupying a large tract\\nof the sky south of the constellations Pisces and\\nAries. The head is directly below the head of Aries,\\nand the tail reaches westward 45\u00c2\u00b0, being about 10\u00c2\u00b0\\nsouth of the vernal equinox. Menhir (Alpha Ceti), the\\nlargest of its components, is situated in the mouth,\\n25\u00c2\u00b0 southeast of Alpha Arietis and Mira (Omicron\\nCeti), in the neck, 14\u00c2\u00b0 west -of Menkar, is celebrated\\nas a variable star, which exhibits different magnitudes\\nat different times.\\n242. Orion is one of the most magnificent of the\\nconstellations, and one of those that have longest\\n240\u00e2\u0080\u0094241. Describe Ophiuchus Cetus", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0189.jp2"}, "188": {"fulltext": "178 CONSTELLATIONS.\\nattracted the admiration of mankind, being alluded\\nto in the Book of Job, and mentioned by Homer.\\nThe head of Orion lies southeast of Taurus, 15\u00c2\u00b0 from\\nAldebaran, and is composed of a cluster of small\\nstars. Two very bright stars, Betelgeuse, of the first,\\nOrion.\\n7*\\nft*\\nand Bellatrix, of the second magnitude, form the\\nshoulders three more, resembling the three stars of\\nthe Eagle, compose the girdle and three smaller\\nstars, in a line inclined to the girdle, form the sword.\\nBigel, of the first magnitude, makes the west foot,\\nbut the corresponding star, 9\u00c2\u00b0 southeast of this,\\nwhich is sometimes taken for the other foot, is above\\nthe knee, this foot being concealed behind the Hare.\\nOrion s club is marked by three stars of the fifth\\nmagnitude, close together, in the Milky Way, just\\nbelow the southern horn of the Bull. Orion is a\\nfavorite constellation with the practical astronomer,\\n242. Describe Orion.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0190.jp2"}, "189": {"fulltext": "SOUTH OF THE ZODIAC. 179\\nabounding, as it does, in addition to the splendor of\\nits components, with fine nebulse, double stars, and\\nother objects of peculiar interest, when viewed with\\nthe telescope. It embraces 70 stars, plainly visible to\\nthe naked eye, including two of the first, four of the\\nsecond, and three of the third magnitude.\\n243, Lepus {TJie Hare). Below Bigel, the western\\nfoot of Orion, is a small trapezium of stars, which\\nforms the ears of the Hare and an assemblage of\\nnine stars, of the third and fourth magnitudes, south\\nand east of these, make up the remaining parts of\\nthe figure.\\n244, Cants Major {The Greater Dog) lies directly\\neast of the Hare, and is highly distinguished by con-\\ntaining Sirius, the most splendid of all the fixed\\nstars, which lies in the mouth of the figure. In the\\nfore paw, 6\u00c2\u00b0 west of Sirius, is a star of the second\\nmagnitude {Beta Ganis Majoris), and from 10\u00c2\u00b0 to 15\u00c2\u00b0\\nsouth of Sirius is a collection of stars of the second\\nand third magnitude, which make up the hinder por-\\ntions of the figure. The Egyptians, who anticipated\\nthe rising of the Nile by the appearance of Sirius in\\nthe morning sky, represented the constellation by the\\nfigure of a dog, the symbol of a faithful watchman.\\n245* Canis Minor {The Lesser Dog). About 25\u00c2\u00b0\\nnorth of Sirius is the bright star Procyon, also of the\\nfirst magnitude, which marks the side of the Lesser\\nDog. A star of the third magnitude (Beta), 4\u00c2\u00b0 north-\\nwest of this, in the head of the figure, forms, with\\n243 244 245. Describe Lepus Canis Major Canis Minor.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0191.jp2"}, "190": {"fulltext": "180 CONSTELLATIONS.\\nProcyon, the lower side of an elongated parallelo-\\ngram, of which Castor and Pollux, 25\u00c2\u00b0 north, form\\nthe upper side.\\n246. Monoceros is a large constellation, occupying\\nthe space between the Greater and the Lesser Dog,\\nbut has no conspicuous members.\\n247. Hydra occupies a long space south of Leo,\\nVirgo, and Libra. Its head, which is south of the\\nfore paws of the Lion, consists of four stars of the\\nfourth magnitude, of nearly uniform appearance and\\nabout 15\u00c2\u00b0 southeast of these is the Heart (Cor Hydrce),\\n23\u00c2\u00b0 south of Eegulus. Besting on Hydra, and south\\nof the hind feet of Leo, is Crater (the Cup), consist-\\ning of six stars of the fourth magnitude, arranged in\\nthe form of a semicircle and a little further east,\\nalso perched on the back of Hydra, is Corvus (the\\nCrow), the two brightest components of which are\\nsituated in one of the wings of the figure, in a line\\nbetween Crater and Spica Yirginis.\\nEVENING CONSTELLATIONS OF THE DIFFERENT\\nSEASONS.\\n248. Since the sun passes from west to east round\\nthe heavens once in a year, the constellations of the\\nevening sky will continually vary with the season.\\nHence one portion of the heavens can be best studied\\nin the spring, another in the summer, a third in the\\nautumn, and the fourth and remaining part in the\\n246 247. Describe Monoceros Hydra.\\n248. Why do we see different constellations in the evenings of\\neach season", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0192.jp2"}, "191": {"fulltext": "EVENING CONSTELLATIONS. 181\\nwinter. The following general descriptions, adapted\\nto the times of the equinoxes and solstices, may\\nafford some aid in these studies\\n249\u00c2\u00bb Evening Constellations of Autumn* For the\\nMiddle of September, from 8 to 10 d clock. At 8 o clock\\nScorpio is near setting in the southwest, Antares be-\\ning near 10\u00c2\u00b0 high. The bow of Sagittarius is on the\\neastern margin of the Milky Way, the arrow being\\ndirected to a point a little below Antares. At 9\\no clock the horns of the Goat come upon the me-\\nridian and at 10 o clock, the western shoulder of\\nAquarius. The other shoulder, and the figure Y in\\nthe a*rm, may also be easily found from the descrip-\\ntion given (Art. 216) also, the Pentagon, in Pisces,\\nand Fomalhaut (the Southern Fish), a solitary bright\\nstar far in the south, only 16\u00c2\u00b0 above the horizon. The\\nhead of Aries appears in the east, and the Pleiades\\nare but little above the horizon, while Aldebaran is\\njust rising. Keturning now to the west (at 10 o clock),\\nthe Crown is seen a little north of west, about 20\u00c2\u00b0\\nhigh Lyra is 30\u00c2\u00b0 west of the zenith the Swan is\\nnearly overhead and following down the Milky Way,\\nthe Eagle is seen on its eastern margin over against\\nLyra on the western and the Dolphin, a little east-\\nward of the Eagle, and as far above the horns of\\nOapricornus as the latter are above the southern\\nhorizon. Following on the east of the meridian, the\\ngreat square in Pegasus may next be identified and\\nsince the northeastern corner of the square is in the\\nhead of Andromeda, this constellation may next be\\n249. Describe the appearance in a September evening.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0193.jp2"}, "192": {"fulltext": "182 CONSTELLATIONS.\\nlearned and then Perseus and Auriga, which appear\\nstill further east. Directly north of Perseus is Cas-\\nsiopeia s chair; and next to that we may take the\\nPole-star, the Little Bear, and the Great Bear, the\\nDipper only being traced for the present. Com-\\nmencing now at the tail of the Dragon, we may trace\\nround this figure, between the two Bears, to the\\nhead, which brings us back to Lyra and the feet of\\nHercules.\\n250, Evening Constellations of Winter, For the\\nMiddle of December, from 7 to 10 o clock. Of the con-\\nstellations of the Zodiac, Taurus and Gemini are now\\nfavorably situated for observation in the east. At 7\\no clock the tail of Cetus just reaches the meridian, its\\nhead being seen below the feet of Aries. Orion is\\njust risen in the southeast. At 9 o clock, just above\\nthe western horizon, are seen in succession, from\\nsouth to north, Aquarius, the Dolphin, the Eagle, the\\nLyre, and the Dragon s head. Between the Eagle\\nand the Lyre, at a little higher altitude, we perceive\\nthe Swan, flying directly downwards. Between the\\ntail of the Swan and the Pole-star is Cepheus and\\nfrom the pole, along the meridian, we trace Cassio-\\npeia, the feet of Andromeda, the head of Aries, and\\nthe neck of the Whale. At 10 o clock Perseus has\\nreached the meridian, the star Algol, in the head of\\nMedusa, being directly overhead. The Pleiades are\\nbut little eastward of the zenith and following along\\nsouth from the pole, at the interval of from one to\\ntwo hours east of the meridian, we may trace in suc-\\n250. Describe tlio appearance in a December evening.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0194.jp2"}, "193": {"fulltext": "EVENING CONSTELLATIONS. 183\\ncession, Camelopard, Auriga, Taurus, Orion, and the\\nHare. Turning along the eastern horizon, we find\\nCanis Major, Monoceros, Canis Minor, the head of\\nHydra (just rising), Cancer, Leo, the sickle just ap-\\npearing about 3\u00c2\u00b0 north of the east point. Leo Minor\\nand Ursa Major complete the survey and we may\\nnow advantageously trace out the various parts of the\\nGreat Bear, as described (Art. 219) the two stars\\ncomposing its hindmost paw being scarcely above the\\nhorizon.\\n251. Evening Constellations of Spring. For the\\nMiddle of March, from 8 to 10 o clock. At 8 o clock\\nwe see the Twins nearly overhead, and Procyon\\nand Sirius, at different intervals, towards the south.\\nAlong the west we recognize the neck and head of\\nthe Whale, the head of Aries, and the head of An-\\ndromeda next above these, Orion, Taurus, Perseus,\\nCassiopeia, and Cepheus and north of the head of\\nOrion, we see Auriga and Camelopard. In the\\nsouth, Hydra is now fully displayed and following\\non north, we obtain fine views of the Greater and\\nthe Lesser Lion, and the Great Bear. At 9 o clock\\nCrater and Corvus appear in the southeast, on the\\nback of Hydra Yirgo extends from Leo down to the\\nhorizon, Spica Yirginis being about 5\u00c2\u00b0 high and\\nnorth of Virgo, we trace in succession Coma Bere-\\nnices, Cor Caroli, Bootes, with Arcturus and the\\nCrown lying far in the northeast.\\n252. Evening Constellations of Summer. For the\\nMiddle of June, from 9 to 10 o clock. At 9 o clock,\\n251. Describe tlie appearance in a March evening.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0195.jp2"}, "194": {"fulltext": "184: CONSTELLATIONS.\\nBootes, Corona Borealis, the head of Libra, the Ser-\\npent, and Scorpio, lie along on either side of the me-\\nridian. Castor and Pollux are just setting, and Leo\\nis about an hour high. East of Leo, Yirgo is seen\\nextending along towards the meridian, Spica being\\nabout 30\u00c2\u00b0 above the southern horizon. North of Leo\\nand Yirgo, we recognize Leo Minor, Coma Berenices,\\nCor Caroli, and Ursa Major. At 10 o clock, we trace\\nalong the eastern side of the meridian, Draco, Her-\\ncules, and Ophiuchus and east of these, the Lyre,\\nthe Eagle, Antinous, Sagittarius, and Capricornus.\\nNorth of the Eagle, and round to the east, we find\\nCepheus and Cassiopeia, Andromeda rising in the\\nnortheast, Pegasus in the east, and Aquarius in the\\nsoutheast.\\n252. Describe tlie appearance in a June evening.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0196.jp2"}, "195": {"fulltext": "CHAPTEE XV.\\nDISTANCES AND MOTIONS OF STARS DOUBLE STAES,\\nCLUSTERS, AND NEBULAE.\\n253. Effect of Telescopic Power on Fixed Stars.\\nOne indication of the vast distance of fixed stars is,\\nthat no power of a telescope has ever sensibly magni-\\nfied them. Even under a power which increases the\\ndiameter of a body 5,000 times, they appear no larger\\nthan to the naked eye. It is inferred that they fill\\nan angle so small that 5,000 times that angle is still\\ntoo minute to be perceived. Any appearance of dish\\nwhich a star presents, either with a telescope or with-\\nout, is the effect of the light upon the retina of the\\neye. It is called a spurious disk, since an increase of\\nmagnifying power causes no increase of its diameter.\\n254:. Annual Parallax. Another proof that the\\nfixed stars are at an immense distance from us is the\\nfact that while we shift our position every six months\\nfrom one side of the earth s orbit to the opposite, a\\ndistance of 190,000,000 miles, there is no perceptible\\nchange in the relation of the stars to each other. It\\nis only after long-continued and most accurate ob-\\n253. Wiiat is the effect of the telescope on the fixed stars", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0197.jp2"}, "196": {"fulltext": "186 DISTANCES OF THE STAES.\\nservation that a few stars have been discovered to\\nsuffer an annual change of position, which is clearly\\nof the nature of parallax.\\nThe annual parallax of a star is the angle, at the\\nstar, subtended by the radius of the earth s orbit.\\nAs this angle is, in almost all cases, too small to be\\ndetected, it shows that the earth s orbit, seen from\\nthe distance of the stars, appears as a mere point.\\nIt is justly reckoned among the greatest achieve-\\nments in practical astronomy that the annual parallax\\nhas, in a few cases, not only been clearly detected as\\nexisting, but has been satisfactorily measured, though\\nit is never so great as 1 The greatest parallax yet\\nmeasured is that of Alpha Centauri, which is 0.91\\nThe parallax of a star is most satisfactorily deter-\\nmined when it is in the same telescopic field with\\nother stars for then the distances between the stars\\nmay be measured with great precision by a microme-\\nter, and all errors arising from refraction and other\\ndisturbing causes are wholly avoided, because all the\\nstars in the same field are affected alike. Parallax is\\nis the only circumstance which can produce an an-\\nnual change in their relative positions. The star 61\\nCygni is, in this respect, very favorably situated, and\\nits parallax is thought to be quite accurately deter-\\nmined. It is 0.35\\n255. Distances of the Stars. When the parallax\\nof a body is found, its distance can be computed by\\ntrigonometry. It is thus ascertained that Alpha Cen-\\n254. What is annual parallax What is the greatest parallax of\\na star", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0198.jp2"}, "197": {"fulltext": "NATURE OF FIXED STARS. 187\\ntauri, the nearest star, is about 22,000,000,000,000\\nmiles from us and 61 Cygni, the next nearest, is\\n57,000,000,000,000 miles distant. Light, moving at\\nthe rate of 192,500 miles per second, would require\\nabout 3J years to come to us from Alpha Centauri,\\nand 9 J years from 61 Cygni.\\nAs to all other stars, it is only known that they are\\nstill more distant. There is no improbability that,\\nfrom the remotest telescopic stars yet seen, light may\\noccupy thousands of years in coming to us. There-\\nfore, we see all the stars as they were years ago per-\\nhaps not as they are now. And if at any time a\\nchange has been detected in the aspect or place of\\na star, that change occurred, not when it was seen,\\nbut 10, 100, or 1,000 years before, according to its\\ndistance.\\n256* Nature of the Fixed Stars. The stars are\\nsituated at such vast distances from the solar system\\nthat if they merely reflected the light of the sun,\\nthey would be invisible. In order to exhibit such\\nbrightness as they do, they must not only shed light,\\nbut a very intense light of their own. They cannot be\\ncompared with any one of the bodies in the solar sys-\\ntem except the sun itself. All the fixed stars, there-\\nfore, are to be considered as suns, and probably the\\ncenters of systems resembling the solar system. It is\\n255. Which, is the nearest star What is its distance Which\\nis the next nearest Its distance How long would light require\\nto come from each What is known of other stars\\n258. What is the nature of the stars? Why are they suns?\\nCompare Alpha Centauri and Sirius with the sun. At the distance\\nof the stars, how would the sun appear", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0199.jp2"}, "198": {"fulltext": "188 DOUBLE STAES.\\nascertained, respecting some of those stars whose dis-\\ntance is known, that they shed more light than the\\nsun. For example, Alpha Centanri has been found\\nto shed near four times as much light as the sun and\\nSirius one hundred times as much. On the other hand,\\nif the sun were removed from us to the nearest fixed\\nstar, its apparent diameter would be only T |V an\\ntherefore, it would be a star having no sensible mag-\\nnitude, and having only J- of the brightness of Sirius.\\n257* Double Stars. It is discovered, in a great\\nnumber of instances, that a fixed star, when exam-\\nined by the telescope, really consists of two stars,\\nvery close to each other. If the distance between\\nthem does not exceed 32 such stars are called double\\nstars. Their distance apart is often less than 1 and\\nsome are so close that the highest power of the tele-\\nscope and the most acute vision are requisite to sepa-\\nrate them. Hence, certain double stars are habitu-\\nally used as tests of the excellence of an instrument.\\nWhen Sir William Herschel first began his observa-\\ntions on this class of objects, in 1780, he knew of\\nonly four but he extended the list to 500 himself,\\nand the number now known exceeds 6,000.\\nThe two stars which compose a doable star usually\\ndiffer from each other in magnitude, and sometimes\\nin color.\\n258* Ttvo Ways in ivliich Stars might- Appear\\nDouble. The two stars which compose a double star\\n257. What are double stars Speak of their discovery. What\\nis their number How do the two members of a double star often\\ndiffer?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0200.jp2"}, "199": {"fulltext": "BINAEY STABS. 189\\nmay be supposed either to be really near each other,\\nor only to appear near together, because they fall\\nalmost into the same line of vision, while one is actu-\\nally at an immense distance beyond the other. In\\nthe latter case, the stars are said to be optically\\ndouble. When Sir William Herschel commenced\\nexamining double stars, he very naturally supposed\\nthat, in the very few cases known, one star happened\\nthus to be nearly in the same visual line with the\\nother and he began the work of observing them\\nwith the expectation of detecting annual parallax in\\nobjects so favorably situated. For, if the nearer star\\nis perceptibly affected by parallax, it would exhibit an\\nannual motion relatively to the more distant star in a\\nmanner not to be mistaken.\\n259. Binary Stars, It soon became evident, how-\\never, that double stars are too numerous to allow the\\nsupposition that they appear near to each other acci-\\ndentally. But the question was soon set at rest by\\nanother most interesting discovery, namely, that some\\nof the double stars exhibit motions which indicate a\\nrevolution of one around the other or, rather, of the\\ntwo around a common center, and in periods of vari-\\nous lengths, having no connection whatever with the\\nearth s annual motion. Such motion cannot be par-\\nallactic it must be real and such stars are not opti-\\ncally, but physically double. They are called Binary\\n258. In what two ways might stars appear double What did\\nHerschel anticipate when he first saw them\\n259. What did he discover What are binary stars What are\\ntheir orbits What law prevails among the stars", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0201.jp2"}, "200": {"fulltext": "190 STELLAE OEBITS.\\nStars, and are to be regarded as the centers of double\\nstellar systems.\\nThe orbits of the binary stars are ellipses. It is\\nknown, therefore, that the law of gravitation outside\\nof the solar system is the same as within it.\\n260. Periods of Binary Stars. The shortest pe-\\nriod known is that of Zeta Herculis, about 31 years.\\nThe period of Eta Coronae is 43 years; that of Xi\\nUrssB Majoris 58 years. These, and a few others of\\nshort period, have completed their revolutions once\\nor twice since they were discovered. The orbits of\\nsuch are quite accurately determined. Alpha Cen-\\ntauri has not yet made a revolution since its discov-\\nery. Its period is calculated to be 77 years. A large\\nnumber of binary stars, whose periods are computed\\nto be some hundreds or thousands of years, have\\nbeen observed as yet only through a short arc hence\\ntheir periodic times, and the forms of their orbits, are\\nquite uncertain.\\n261. Dimensions of Stellar Orbits. There are two\\nbinary stars whose parallax has been so satisfactorily\\nmeasured that their distances from us may be consid-\\nered as well known. These are Alpha Centauri and\\n61 Cygni. Hence, by the angular length of the semi-\\nmajor axes of their orbits, we may find the mean\\nradius vector of each. That of Alpha Centauri is\\nabout 1,500,000,000 miles, and that of 61 Cygni is\\nabout 4,200,000,000 miles.\\n260. State the periods of some of the double stars.\\n261. What orbits of double stars are known How large are\\nthey?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0202.jp2"}, "201": {"fulltext": "TEMPORARY STARS. 191\\n262. Triple and Quadruple Stars. There are a\\nfew instances of three or four stars, which are known\\nto be physically connected, and to constitute a sys-\\ntem. Zeta Cancri is triple, and Epsilon Lyrse is\\nquadruple. In each of these, the component stars\\nhave a slow motion about each other.\\n263 o Periodic and Temporary Stars. There are\\namong the fixed stars several instances in which there\\nappear to be revolutions of another sort, the nature\\nof which is not understood. Stars which exhibit\\nthese changes are called periodic stars. A remarka-\\nble example occurs in the star Omicron Ceti. It\\npasses through its changes of brightness in about 11\\nmonths. When brightest, it is of the second magni-\\ntude, and remains so for two weeks. It then dimin-\\nishes during three months to the tenth magnitude,\\nremains thus five months, and increases again during\\nthree months to its maximum of brightness.\\nAlgol (Beta Persei) has a very short period, occu-\\npying only 2d. 20h. 48m. Its changes succeed each\\nother with great regularity, thus\\nDuring 2d. 14A. Qm it remains of the second magnitude.\\nQd. %Ji. 24m. diminishes from second to fourth.\\nQd. Sh. 24m. increases from fourth to second.\\n2d. 207i. 48m. whole period.\\niSome of this class of stars have periods of only a\\nfew days, while in others the changes go on very\\n262. Are there any combinations more complex still\\n263. State what is meant by periodic stars. Describe two. What\\nothers are probably of this class", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0203.jp2"}, "202": {"fulltext": "192 NEBULA.\\nslowly, and appear to require several years. The\\nperiods of some are quite uniform, and of others\\nirregular.\\nTo this class probably belong those stars which are\\ncalled temporary stars. That of 1572 is celebrated.\\nIt appeared so suddenly, and of such brilliancy, as to\\nattract the attention of common people, and rapidly\\nincreased, till in a few weeks it surpassed Jupiter in\\nbrightness. It then faded slowly, and, after about 1 J\\nyears, entirely disappeared. Several other cases less\\nmarked than this are on record. And the earlier\\ncatalogues contain numerous stars which are not to\\nbe found at the present day.\\n264. Clusters of Stars.\u00e2\u0080\u0094 The fixed stars are fre-\\nquently grouped together in clusters; such as the\\nPleiades, in Taurus Presepe, in Cancer and Coma\\nBerenices. If a telescope of low power is used, the\\nnumber of stars appears greatly increased.\\nThere are others which, to the naked eye, appear\\nto be nebulous, but, by the use of the telesccope, are\\nplainly seen to be clusters and in some of them the\\nstars are so numerous as not to be easily counted.\\nThe clusters in Perseus and Hercules are fine exam-\\nples. For the latter, see Fig. 1, frontispiece.\\n285. Nehulw. These are faint patches of light,\\nhaving generally an ill-defined edge, and, in ordinary\\ntelescopes, presenting the same nebulous aspect\\nwhich the closer clusters do to the naked eye. As\\nthe powers of the telescope are increased, many neb-\\n264. Mention some clusters of stars.", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0204.jp2"}, "203": {"fulltext": "THE GALAXY. 193\\nulae are resolved into clusters of stars, while many\\nothers retain their nebulous appearance under every\\npower yet employed. The number of nebulae now\\nknown exceeds 4,000. The forms of nebulae are vari-\\nous, and may be classified as follows\\n1. Globular, These appear circular in their outline,\\nand generally grow brighter from the edges toward\\nthe center. The Planetary Nebvke have a well defined\\nedge, and no bright center. The Nebulous Stars have\\nonly a bright point at the center, and a uniform nebu-\\nlosity about it.\\n2. Elliptical. A large number of the nebulae have\\nthis form, the most remarkable example of which is\\nthe great nebula of Andromeda.\\n3. Spiral. This form is becoming more frequent as\\ntelescopes are improved, and the more delicate fea-\\ntures traced. The whirlpool nebula, near the tail of\\nthe Great Bear, is a fine example. See Fig. 2,\\nfrontispiece.\\n4. Annular. A few nebulae appear ring-like, being\\nmore luminous on the edges than in the center. The\\nnebula of Lyra is annular.\\n5. Irregular. All the previous forms imply the\\nexistence of revolution in the material of which the\\nnebula is composed. But there are others which are\\nwholly irregular. None is more remarkable than the\\ngreat nebula of Orion.\\n268. TJie Galaxy, This is a belt, or zone, of neb-\\nulous appearance, which encircles the heavens, nearly\\n265. What are nebulae? Name the several forms. What re-\\nmarkable ones of these forms", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0205.jp2"}, "204": {"fulltext": "194 THE GALAXY.\\ncoincident with a great circle, and cuts the plane of\\nthe equator afc an angle of 63\u00c2\u00b0. It is usually called\\nthe Milky Way. Near the constellation Cygnus, it\\ndivides into two parts, which continue separate nearly\\na semicircle (150\u00c2\u00b0), and then reunite. Its edges are\\ngenerally ill-defined, and also quite crooked and\\nirregular, having many projections and indentations.\\nThe telescope shows that the whiteness of the\\ngalaxy is due to unnumbered stars, too faint to be\\nseen individually. Their distribution is quite un-\\nequal the stars, in some parts, being crowded very\\nclosely together, while here and there spaces occur\\nwhich contain but few. These inequalities are most\\nmarked in the southern hemisphere. In the most\\nluminous parts, Sir William Herschel estimated that,\\nwithin an area of less than T part of the hemi-\\nsphere, there passed the field of his telescope 50,000\\nstars, large enough to be distinctly seen. The whole\\nnumber of stars in the Milky Way is to be reckoned\\nby millions.\\n266. What is the galaxy? Describe its extent. What does it\\nconsist of?", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0206.jp2"}, "205": {"fulltext": "", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0207.jp2"}, "206": {"fulltext": "", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0208.jp2"}, "207": {"fulltext": "", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0209.jp2"}, "208": {"fulltext": "", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0210.jp2"}, "209": {"fulltext": "", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0211.jp2"}, "210": {"fulltext": "", "height": "3525", "width": "2094", "jp2-path": "compendiumofas00olms_0212.jp2"}}