GIFT OF 
 
 AUVHOR 
 

 o4 
 
 d 
 
HOW TO KNOW THE STARRY 
 HEAVENS 
 
^. . 
 
FIG. 1. SOLAK PROMINENCES, BY TROUVELOT, OF HARVARD 
 OBSERVATORY 
 
 The white circle represents the size of the Earth on the same scale. 
 
HOW TO KNOW 
 
 THE 
 
 STARRY HEAVENS 
 
 AN INVITATION TO THE 
 
 STUDY OF SUNS AND WORLDS 
 
 BY 
 
 EDWARD IRVING 
 
 WITH CHARTS, COLOURED PLATES, DIAGRAMS, 
 
 AND MANY ENGRAVINGS OF 
 
 PHOTOGRAPHS 
 
 NEW YORK 
 
 FREDERICK A. STOKES COMPANY 
 PUBLISHERS 
 
COPYRIGHT, 1904 
 BY FREDERICK A. STOKES COMPANY 
 
 All rights reserved 
 Published in November, 1904 
 
 THE UNIVERSITY PRESS, CAMBRIDGE, U. S. A. 
 
"Everybody should study astronomy. It is the most delightful 
 of all the sciences. It is the most inspiring of all. It lifts and 
 broadens the mind. It rouses the imagination, and the imagination 
 is the most God-like of human faculties, because it is the most 
 creative. Let no one be deterred by the superstition that it is 
 necessary to be a mathematician in order to understand and enjoy 
 astronomy. You can let the mathematics of the subject severely 
 alone and yet Jind inexhaustible pleasure and advantage in astro- 
 nomical study. It is because they were compelled to begin at the 
 mathematical end of the subject that hundreds of thousands of 
 graduates from schools and colleges have virtually no knowledge of 
 astronomy. Mathematical gifts are rare, but they are not essential 
 to the enjoyment of astronomy." GARRETT P. SERVISS. 
 
PREFACE 
 
 THIS volume is not so much a text-book on Astronomy, as 
 an invitation to read text-books on that subject. In other 
 words, it is a careful selection of the most typical, interesting, 
 and instructive facts and theories concerning the Universe 
 around us. The author has endeavoured to describe and illus- 
 trate these in such a way as to attract, interest, and inform the 
 general reader. But, though intended primarily for beginners, 
 every effort has been made to avoid offending those who are 
 further advanced, by sensationalism or a want of proportion and 
 accuracy. The comparisons and illustrations used are the re- 
 sult of many years' study, and have been successfully used in 
 lectures and classes. They may interest some who are well 
 acquainted with the facts of astronomy, but have not looked at 
 them from the same standpoint. 
 
 Many interesting and important astronomical methods, prin- 
 ciples, and facts have been left out of this volume, to avoid 
 overcrowding and confusion. The main object of the work is 
 not so much to describe individual worlds, as to enable the 
 reader to realise, as far as possible, what the Universe itself is 
 like. In other words, it is to give a bird's-eye view of the 
 celestial forest from a general and philosophical standpoint, 
 so that the individual trees may be afterwards examined more 
 at leisure. Until such a bird's-eye view has been obtained, the 
 learner is apt to be confused by the details. As the old saying 
 has it, he " cannot see the wood for the trees." 
 
 When such a general view has once been obtained, the details 
 no longer confuse, and text-books that were formerly thrown 
 down in disgust become luminous with the ever-growing interest 
 that rightly belongs to the physical sciences. 
 
viii PREFACE 
 
 The figures given in this work are mostly round numbers. 
 They do not claim absolute accuracy, but at the same time 
 every effort has been made to avoid serious errors. 
 
 The distance of the nearest star has been given as about 
 9,000 times as great as that of Neptune. It is quite possible 
 that further investigations may result in other figures being 
 adopted. But even if it should be changed to 8,000 or 10,000, 
 the comparisons used will still serve to illustrate the relative 
 dimensions of the visible Universe. 
 
 The author gratefully acknowledges the kindness of Professor 
 K. G. Aitken and other members of the staff at the Lick Ob- 
 servatory, in reading the manuscript and making suggestions 
 which have materially helped to perfect the work. 
 
 Thanks are due to many who have given advice, suggestions, 
 corrections, and information; also to those who have granted 
 the reproduction of valuable photographs and drawings. Among 
 these are : 
 
 The late Dr. E. Keeler, Director of Lick Observatory, 
 California. 
 
 Dr. W. W. Campbell, Director of Lick Observatory, California. 
 
 Dr. A. 0. Leuschner, Director of Students' Observatory, 
 Berkeley, Cal. 
 
 E. L. Larkin, Director of Lowe Observatory, California. 
 
 C. Burckhalter, Director of Chabot Observatory, Oakland, Cal. 
 
 G. E. Hale, Director of Yerkes Observatory, Wisconsin. 
 
 E. C. Pickering, Director of Harvard Observatory, Massa- 
 chusetts. 
 
 W. H. M. Christie, M.A., Astronomer Eoyal, Greenwich, 
 England. 
 
 E. Walter Maunder, F.K.A.S., Greenwich, England. 
 
 Besides giving an account of well-known and indisputable 
 astronomical facts, the author has touched upon certain specu- 
 lative theories which cannot yet be proved by either experiment 
 or observation. The most that can be said for them is that 
 they give a reasonable explanation of a large number of ob- 
 served phenomena, and must therefore contain a certain amount 
 
PREFACE ix 
 
 of truth. They also help to give us a better idea of the Infinite 
 and Eternal Drama in which our little Earth is playing its 
 obscure and ephemeral part. The reader is not asked to accept 
 these theories if he can explain the observed phenomena by 
 more probable speculations of his own. But he must beware 
 of adopting theories which conflict largely with ascertained 
 facts. 
 
 It only remains to be said that these speculations have 
 everywhere been carefully distinguished from those facts which 
 are so well proved as to be practically indisputable. 
 
 This volume is intended to be the first of a series, by the 
 same writer, dealing with the sciences of astronomy, geology, 
 biology, and sociology. These four were grouped together by 
 the late Herbert Spencer under the name of the Concrete 
 Sciences. Though the vast importance of these subjects is 
 now generally recognised, many otherwise educated people are 
 lamentably deficient in them. This is very unfortunate for the 
 individuals concerned, for, however learned a man may be in 
 all other subjects, it is impossible for him to be truly broad- 
 minded, philosophical, and cosmopolitan, without some knowl- 
 edge of these Concrete Sciences. 1 
 
 A general lack of scientific knowledge injures, not only the 
 individuals themselves, but also society at large. In spite of 
 the great advances made in all directions during the last century, 
 there are still many imperfections remaining in our systems of 
 government, of administrative justice, of national education, and 
 in our entire social and moral organisations. These imperfec- 
 tions are largely due to the fact that many of our statesmen, 
 lawyers, teachers, doctors, and preachers are deficient in the 
 above-mentioned sciences. Let us hope that during the present 
 
 1 As the philosophical A. Zazel truly says : 
 
 " Astronomy, geology, biology, and sociology together form an impregnable 
 bulwark against the inroads of superstition. And where the seeds of that deadly 
 mental disease have been already sown, these sciences form an infallible antidote 
 and cure." 
 
x PREFACE 
 
 century this ignorance may be removed, so that our upward 
 progress may no longer be impeded by the erroneous ideas that 
 have been dragged up with us from the flat world in which our 
 ancestors imagined themselves to be living. 
 
 The second volume will deal with the history of the Third 
 Planet in our System, from its nebulous birth to the advent of 
 Man. Its title will probably be How to Know the Earth's 
 
 History. 
 
 EDWARD IRVING. 
 
 BERKELEY, CAL. (U. S.), 
 October, 1904. 
 
CONTENTS 
 
 CHAPTER P AGK 
 I. APPARENT MOTIONS OF THE HEAVENLY BODIES AS 
 
 SHOWN BY OBSERVATION 1 
 
 II. RIVAL THEORIES TO EXPLAIN THE APPARENT MOTIONS 
 
 OF THE HEAVENLY BODIES 15 
 
 III. PRINCIPLES UTILISED FOR MEASURING THE UNIVERSE 26 
 
 IV. SOME PROBLEMS USED IN CELESTIAL MEASUREMENTS 39 
 V. THE CHARIOT OF IMAGINATION 53 
 
 VI. DIMENSIONS OF THE UNIVERSE ......... 68 
 
 VII. SOME MORE DIMENSIONS 77 
 
 VIII. THE PRINCIPLES AND APPLICATIONS OF THE SPECTRO- 
 SCOPE 87 
 
 IX. A STAR-SPANGLED BANNER 102 
 
 X. CONSTRUCTION OF THE UNIVERSE 114 
 
 XL SOLAR ARCHITECTURE 125 
 
 XII. A REELING WORLD 136 
 
 XIII. KEPLER'S THREE LAWS 155 
 
 XIV. GALILEO'S LAWS OF MOTION 163 
 
 XV. NEWTON'S LAW OF GRAVITATION 167 
 
 XVI. ANCIENT COSMOGONIES, AND THE NEBULAR HYPOTHESIS 178 
 XVII. THEORIES AND DISCOVERIES MODIFYING THE NEBULAR 
 
 HYPOTHESIS 190 
 
 XVIII. MODIFICATIONS OF THE NEBULAR THEORY .... 205 
 
 XIX. THE MESSENGERS OF HEAVEN 219 
 
 XX. LARGE AND SMALL WORLDS 233 
 
x COiNTENTS 
 
 CHAPTER PAGE 
 
 XXI. IGNEOUS FORCES ON THE MOON AND ELSEWHERE . . 243 
 
 XXII. LUNAR GEOLOGY AND GEOGRAPHY 257 
 
 XXIII. INHABITED WORLDS 265 
 
 XXIV. SIZE, IMPORTANCE, SPEED, AND DURATION .... 283 
 XXV. CONCLUSION 290 
 
 APPENDIX A. FACTS AND FANCIES CONCERNING MATTER . . 295 
 
 APPENDIX B. THE GREEK ALPHABET 301 
 
 APPENDIX C. THE LUNAR CRATERS 302 
 
 INDEX . , 309 
 
ILLUSTRATIONS 
 
 FULL-PAGE ILLUSTRATIONS 
 
 FIGURE 
 
 1. Solar Prominences, by Trouvelot, of Harvard Observatory 
 
 frontispiece in colours 
 FACING PAGK 
 
 7. Northern Star-Trails 14 
 
 8. The Dipper, or Great Bear, at Intervals of Six Hours ... 14 
 
 24. Sun, Showing Spots and Faculse 52 
 
 25. Group of Sunspots 58 
 
 26. Solar Flames and Corona, as Seen During Eclipse of May 28, 
 
 1900. (In colours) 56 
 
 27. Eruptive Prominences 58 
 
 28. Solar Corona. Eclipse of May 28, 1900 60 
 
 29. North Polar Streamers of the Corona. May 28, 1900 ... 60 
 
 30. Mercury, the First Planet 62 
 
 31. Venus, the Second Planet 62 
 
 33. Mars, the Fourth Planet 62 
 
 35. The Zone of Asteroids Between Mars and Jupiter .... 64 
 
 36. Jupiter, the Largest Planet 64 
 
 38. Saturn, the Ringed Planet 66 
 
 41. Lick Observatory on Mount Hamilton, California 70 
 
 42. Main Entrance and Great Dome, Lick Observatory .... 70 
 
 43. The Thirty-Six-Inch Refractor at Lick Observatory . . . 72 
 
 44. Eye-Piece of the Great Lick Telescope 74 
 
 45. Yerkes Observatory, Williams Bay, Wisconsin 80 
 
 46. The Forty-Inch Refractor of the Yerkes Observatory: tin- 
 
 Largest in the World 80 
 
 47. Milky Way Surrounding Messier II 
 
 48. The Star-Cluster Messier II 84 
 
 53. Laboratory and Celestial Spectra. (In colours) 94 
 
 54. Tele-Spectroscope 
 
 55. The Mills Spectrograph at Lick Observatory 96 
 
 56. Chief Lines in the Solar Spectrum (Herschel) . 
 
 57. Part of the Spectra of Four Red Stars (Hale and Ellerinan) . 100 
 
 58. Star Spectra Showing Displacement of Lines Due to Star's 
 
 Motion in Line of Sight 
 
xiv ILLUSTRATIONS 
 
 FIOUBE FACING PAGE 
 
 59. Coloured Double Stars. (In colours) 108 
 
 60. Star-Cluster in Hercules 112 
 
 61. Part of the Milky Way in Sagittarius 114 
 
 62. A Rope-like Nebula in Cygnus 114 
 
 63. Spiral Nebula in Triangulum 116 
 
 64. The Great Nebula in Andromeda 118 
 
 65. A Spiral Nebula Seen Edgeways 120 
 
 66. The Ring Nebula in Lyra 120 
 
 67. The Trifid Nebula in Sagittarius -122 
 
 68. Great Nebula in Orion 124 
 
 69. A Typical Sunspot 128 
 
 70. Solar " Flames " or Prominences 132 
 
 75. The Solar Corona During the Eclipse of July 29, 1878 ... 134 
 
 76. Theoretical Section of Solar Photosphere 132 
 
 79. Equatorial Mounting of the Crossley Reflector, Lick Observatory 150 
 
 80. Meridian Circle 150 
 
 82. Drawing an Ellipse 158 
 
 84. Mount Lowe Observatory, in Southern California 168 
 
 85. Spiral Nebula in Ursa Major (M 81) 172 
 
 91. Dumb-Bell Nebula 192 
 
 92. Nova Persei, 1901. Showing Movement of Surrounding Nebu- 
 
 losity. Lick Photographs " 196 
 
 93. Spectra of Nova Persei, Showing Changes 200 
 
 94. The Star- Cluster Omega Centauri 204 
 
 100. A Celestial Messenger Approaching a Star 222 
 
 101. Brook's Comet, 1893 222 
 
 102. Comet 1903 C 222 
 
 106. Donati's Comet, 1858 228 
 
 107. Comet Rordame, 1893 228 
 
 109. The California Meteor of July 27, 1894 232 
 
 113. Full Moon, Showing Radiating Streaks 244 
 
 114. The Moon, at First and Last Quarter 248 
 
 117. Clavius and Tycho 252 
 
 118. Theophilus, a Lunar Crater-With-Cone 254 
 
 122. Mare Crisium, a Lunar Plain 258 
 
 123. Lunar Apennines and Alps 258 
 
 124. Copernicus 260 
 
 125. Schickard and Wargentin 262 
 
 126. Ptolemy, Alphons, and Arzachel 264 
 
 127. Twelve Views of Mars . 268 
 
 128. Disc of the Sun, August 12, 1903 274 
 
ILLUSTRATIONS xv 
 
 CHARTS 
 
 Chart A. The Northern Heavens | PACING PAGE 
 
 Key to Chart A. (In colours) J 282 
 
 Chart B. The Equatorial Constellations. For Spring Evenings ] 
 
 Key to Chart B. (In colours) . j -290 
 
 Chart C. The Equatorial Constellations. For Summer Evenings ) 
 
 Key to Chart C. (In colours) . } 294 
 
 Chart D. The Equatorial Constellations. For Winter Evenings ) 
 
 Key to Chart D. (In colours) } 30 
 
 Chart E. Eastern Half of Moon. (In colours) ) 
 
 Chart F. Western Half of Moon. (In colours) \ 804 
 
 Chart G. The Constellation Figures 308 
 
 ILLUSTRATIONS IN THE TEXT 
 
 FIGURE p AG s 
 
 2. Umbrella-Apparatus for Illustrating (Apparent) Star Move- 
 
 ments 5 
 
 3. The Earth, Showing Relative Positions of Apparatus when Used 
 
 at Equator, Poles, etc 7 
 
 4. Umbrella- Apparatus Modified for Illustrating Apparent Move- 
 
 ments of Sun and Planets 8 
 
 5. Circles of the Celestial Sphere with World in the Centre . . 9 
 
 6. An Adjustable Equatorial, Suitable for any Part of the World 13 
 9. The Ptolemaic System 19 
 
 10. The Tychonic System 20 
 
 11. Copernican System 23 
 
 12. Relative Positions of Earth and Sun at the four Seasons ... 24 
 
 13. Orbits of Mercury, Venus, and Earth 28 
 
 14. Estimating Distances with the Eyes 31 
 
 15. Surveying from a Base-line 32 
 
 16. Daily Positions of Earth and Moon ....*.... 37 
 
 1 7. Arc of Circle 40 
 
 18. Chord of Arc . 41 
 
 19. Sine of Angle 42 
 
 20. Measuring Width of River 43 
 
 21. Measuring Distance of Moon 46 
 
 22. Arc of Circle 47 
 
 23. Sine of Angle 50 
 
 32. Terra, the Third Planet, and Its Satellite or Moon .... 63 
 
 34. Relative Sizes of Earth and Mars 64 
 
 37. Relative Sizes of Jupiter and Earth 65 
 
xvi ILLUSTRATIONS 
 
 FIGURE PAGE 
 
 39. Relative Sizes of Saturn and Earth 66 
 
 40. Relative Sizes of Neptune and Earth 67 
 
 49. A Prism and its Spectrum 90 
 
 50. A One-prism Spectroscope 91 
 
 51. Section of a One-prism Spectroscope 92 
 
 52. A Compound Spectroscope 93 
 
 71. A Solar " Cloud " of Glowing Hydrogen (Professor Young) . . 131 
 
 72. The Same Region 35 Minutes Later (Young) 132 
 
 73. The Same Region 35 Minutes Later (Young) 133 
 
 74. The Same, 15 Minutes Later (Young) 133 
 
 77. Diagram Illustrating Zodiac 137 
 
 78. Diagram Illustrating Precession of Equinoxes and Advance of 
 
 Perihelion 143 
 
 81. Alt- Azimuth Mounting for Small Telescope 153 
 
 83. An Elliptical Orbit, Divided into Twelve Monthly Parts . . . 159 
 
 86. Original Nebula, after its Rotation has Produced a Disc-like 
 
 Form 184 
 
 87. Nebula with Outer Ring, left behind by Contraction and Conse- 
 
 quent Quickening of Rotation 185 
 
 88. Central Condensation Surrounded by Rings 186 
 
 89. Rings Collapsing into Planets, and Central Condensation Turn- 
 
 ing to a Luminous Sun 187 
 
 90. Solar System as it is now 188 
 
 95. Earth-tides, if the Day and Month Were Equal 213 
 
 96. Acceleration of Moon by Forward Pull of Earth-tide . . . . 214 
 
 97. Loop in Apparent Path of Mars 215 
 
 98. Diagram Showing Cause of Loop in Apparent Path of Mars . 216 
 
 99. A Celestial Messenger on a Journey 221 
 
 103. Parabolic Orbit of a Free Comet 227 
 
 104. Elliptical Orbits of Captive Comets 228 
 
 105. Tail of a Comet near Perihelion 229 
 
 108. A Meteor Bursting in the Atmosphere 230 
 
 110. Relative Sizes of Planets 234 
 
 111. Relative Sizes of Sun, Jupiter, and Earth 235 
 
 112. Relative Sizes of the First Four Asteroids and the Earth's Satel- 
 
 lite 236 
 
 115. Section of Earthly Volcanoes 251 
 
 116. Section of Lunar Volcano in full Activity 252 
 
 119. Section of Mountain of Exudation 254 
 
 1 20. Section of Mountain of Elevation 254 
 
 121. Section of Lunar Crater with Cone 255 
 
HOW TO KNOW THE 
 STARRY HEAVENS 
 
 CHAPTER- 
 
 APPARENT MOTIONS OF THE HEAVENLY BODIES AS 
 SHOWN BY OBSERVATION 
 
 " Appearances are deceptive." Old Saying. 
 
 "Ne jugez pas selon 1'apparence, raais jugez selon la justice." 
 
 Fourth Gospel, vii, 24 (Segond). 
 " Things are not what they seem." Longfellow. 
 
 SUPERFICIAL APPEARANCES 
 
 BEFORE describing the Universe as it is, I wish to say a 
 few words about the Universe as it seems. We shall then 
 be better able to judge as to the reasonableness, or otherwise, 
 of the various theories which have from time to time been 
 brought forward to explain the celestial phenomena which are 
 going on around us. It may be well also, before dealing with 
 the dimensions of the Universe, to give a very brief account 
 of the methods used by astronomers to enable them to ascer- 
 tain the distances and dimensions of those celestial bodies 
 which are within a measurable distance of our World. 
 
 The conclusions at which modern astronomy has arrived are 
 not those which would naturally occur to the first observers of 
 the heavenly bodies. The conditions, indeed, are such that 
 superficial observations always lead to wrong conclusions. To- 
 day, in most of our so-called civilised countries, the people in 
 general take it for granted that the Earth is a planet going around 
 the Sun. Many of them have also heard that the stars are far-off 
 suns, floating in practically empty space. Yet not one person 
 
 l 
 
2 HOW TO KNOW THE STARRY HEAVENS 
 
 in a thousand truly realises what these statements mean. They 
 are merely hearsay, accepted in childlike faith, as some of the 
 ancients accepted the statement that the Earth is supported by 
 a number of elephants standing on the back of a big turtle 
 whose legs reach all the way down ! 
 
 Bu.t in those Countries where the secular schools have not 
 familiarised the people' with the accepted teachings of modern 
 astra'nc!ray,.a man who asserts to-day that the Earth goes around 
 the Sun is regarded as either a wag or a lunatic. If people 
 condescend to argue the point with him, they can overwhelm 
 him with apparently good reasons for their incredulity. They 
 can not only give plausible arguments from their own surround- 
 ings and experiences, but can also prove their case by wholesale 
 quotations from the writings of the " inspired " priests and 
 prophets of former times. If he suggests that their surround- 
 ings and experiences are wrongly interpreted, they laugh him 
 to scorn. If he insists that the ancient writers were ignorant 
 and mistaken, they abuse him as an infidel. If, to avoid their 
 resentment, he tells them that the writers of their sacred books 
 did not intend that their statements should be understood 
 literally, they truly and philosophically reply that he is wrest- 
 ing the Scriptures to his own destruction. 
 
 ONLY FACTS WANTED 
 
 Seekers after truth should not be satisfied with mere hear- 
 say. Those who expect to get facts by faith alone generally 
 accumulate fables instead of facts. Where faith is relied on, it 
 is a mere matter of where we are born as to what we believe. 
 Faith may possibly do no harm as regards immaterial or child- 
 ish beliefs, but it is very hurtful when used for material or 
 important matters, which require intelligent scepticism to enable 
 us to sort out the true from the false. 
 
 Even if by accident we should get the Truth by faith alone, 
 it would do us no good. One of the founders of Christianity 
 told his followers to "prove all things" and " hold fast that 
 which is good " (I Thess. v, 21). A better precept was never 
 
APPARENT MOTIONS OF HEAVENLY BODIES 3 
 
 given, though many who profess to walk in his footsteps do not 
 seem very enthusiastic about following his counsel. 
 
 Those who are looking for actual facts concerning the Uni- 
 verse should therefore leave faith to those who are satisfied 
 with pleasant fables and flattering delusions. They should 
 endeavour, by all the means at their command, to ascertain for 
 themselves whether these things are truly as represented, and 
 they should also try to realise what the facts of the case really 
 involve. 
 
 THE MUSIC OF THE SPHERES 
 
 As regards the shape of our Earth, it is not now necessary to 
 prove that it is a sphere. Many of us have travelled enough 
 to satisfy ourselves by actual experience as to its general size 
 and shape. Even those who have lived all their lives in one 
 locality have now plenty of positive evidence that the old 
 theory of its being flat is untenable. As regards the rest of the 
 Universe, however, we still have to rely on observation and 
 abstract reasoning. 
 
 In order to ascertain whether the sky is a hollow rotating 
 sphere surrounding the Earth, or whether it is, as now claimed, 
 a boundless ocean swarming with suns and worlds, let us 
 examine it and the various objects which appear to be " fixed " 
 to it, or to be wandering around on it. 
 
 The most noticeable of the permanent objects in the sky are 
 known as the Sun and Moon. 
 
 The most numerous and steadfast are called the "fixed " stars. 
 They were so named because they do not appear to change 
 places relatively to one another. 
 
 A few objects which very much resemble the stars in appear- 
 ance are distinguishable from them by several peculiarities. 
 For example, they do not twinkle like the stars, but shine with 
 a steady unflinching light. At some periods they shine very 
 much more brilliantly than at other times. And they slowly 
 change their places among the "fixed" stars. For this latter 
 reason they are known as planets, or " wanderers." The best 
 
4 HOW TO KNOW THE STARRY HEAVENS 
 
 known of them go by the names of Latin deities who were 
 formerly identified with them. They are called Saturn, Jupiter, 
 Mars, Venus, and Mercury. 
 
 Oft-repeated observations of the heavenly bodies, from differ- 
 ent parts of our globe, long since proved that they all appear to 
 have certain definite and well-defined motions which have been 
 repeated over and over again for hundreds and thousands of 
 years. There are, to be sure, certain irregularities in some of 
 these motions, but close and long-continued observations show 
 that even these irregularities are themselves regular and cyclic 
 in their action. 
 
 STELLAR MUSIC 
 
 The most obvious of these motions may be imitated by tak- 
 ing two twelve-ribbed umbrellas (real or imaginary), opening 
 them both, and tying their handles together, so that the arrange- 
 ment forms a kind of globe (see Figure 2). 
 
 On the Equator. If the observer lives on the Equator, in 
 that hot circle of the Earth which lies between the Tropics, he 
 can represent the apparent motion of the star-strewn " sphere " 
 by keeping the handles of his umbrellas horizontal in a north- 
 and-south direction, and slowly spinning the whole thing 
 around on its handles, so that the rims of the umbrellas rise 
 in the east and descend in the west. 
 
 The names of the various groups of stars can be chalked on 
 the inside of the umbrellas, and the observer must imagine 
 himself standing (in the centre of the apparatus) on a flat 
 table which prevents him from seeing anything below his own 
 level. The chalk-marks which are near the rims of the um- 
 brellas will then seem to rise in the east, pass overhead, and 
 sink in the west. Those farther north and south will pass 
 more slowly over the handles or " poles " of the apparatus, 
 which lie flat on the central table and do not change their posi- 
 tion at all. 
 
 So long as the observer stays on the Equator there will be 
 no change in the position of the starry sphere, which appears 
 
APPARENT MOTIONS OF HEAVENLY BODIES 5 
 
 to turn completely over in about four minutes less than twenty- 
 four hours. 1 
 
 It is obvious that, if we turn our apparatus so as to keep up 
 with the stars, a fresh rib will pass the Zenith, or point over- 
 head, every two hours (nearly), and that at the same instant 
 
 AS USED ON 
 THE EQUATOR . 
 
 *F 
 
 FIG. 2. UMBRELLA-APPARATUS FOR ILLUSTRATING (APPARENT) STAR 
 MOVEMENTS 
 
 Face the west when using this diagram. By reversing the points of the compass as here 
 given, and facing the east, it will represent the Earth's real motion. 
 
 the opposite rib will pass the Nadir, or point below. Also that 
 one rib will rise above the eastern horizon at the same time, 
 while another will descend below the western horizon. 
 
 1 If it were not for these four minutes' difference we should see the same stars, 
 in the same part of the sky, at the same time of the night, the whole year 
 through, 
 
6 HOW TO KNOW THE STARRY HEAVENS 
 
 At the North Pole. But if the observer travels to the north, 
 the apparatus will not follow the motions of the stars unless 
 he tips it up by raising the northern umbrella. By the time he 
 reaches the frozen regions near the North Pole, he will have 
 to tip up the apparatus so much that the handles will be per- 
 pendicular. The southern umbrella will then be below, out of 
 sight, and the chalk -marks on the northern umbrella will turn 
 around the point overhead. If the observer now holds his 
 watch overhead, with the face down, he will find that the 
 chalk-marks are going the opposite way to the hands of the 
 watch. 
 
 At the South Pole. If the observer returns to the Equator, 
 he will have to turn the northern umbrella down again, and 
 when he sails into the southern seas the southern umbrella will 
 have to be tipped up, to represent the motions of the stars. By 
 the time he reaches the frozen regions around the South Pole, 
 the southern umbrella will be uppermost. A fresh set of chalk- 
 marks will then turn around the point over his head, and they 
 will be found to turn the same way that the hands of the watch 
 revolve when looked at from below. 
 
 During these supposed journeys from the Equator to the Poles, 
 the axis of the apparatus will not really le typed up either way, 
 for the northern stick will point to the North Pole-Star all the 
 time, and the southern stick will be directed toward the same 
 part of the southern skies all the time. The apparent tipping 
 up and down is due to the fact that the surface of the Earth 
 is not flat, but round, and therefore dips toward the Poles. 
 The annexed diagram will show this clearly, the large circle 
 representing the Earth, and the five small objects representing 
 our umbrellas in different parts of the world (see Figure 3). 
 
 SOLAR MUSIC 
 
 On the Equator. Let us suppose that the observer is again 
 on the Equator with his apparatus, and that he wishes to follow 
 the motions of the Sun. It will be necessary to put a hoop 
 over the umbrellas where the twelve pairs of ribs come together. 
 
APPARENT MOTIONS OF HEAVENLY BODIES 7 
 
 This hoop will represent the Celestial Equator. The ribs of the 
 umbrellas should be numbered from 1 to 12. 
 
 Spring " Passover." If it is about the 20th of March, the 
 Sun's position can be represented by hanging a small electric 
 light where the equatorial hoop crosses the first pair of ribs. 
 On turning the apparatus as before, the electric light will rise 
 in the east, pass overhead, and set in the west. While it is 
 
 FIG. 3. THE EARTH, SHOWING RELATIVE POSITIONS OF APPARATUS WHEM 
 USED AT EQUATOR, POLES, ETC. 
 
 above the level of the imaginary observer in the centre of the 
 apparatus, the chalk-marks representing the stars must be 
 supposed to be out of sight, on account of the greater brilliancy 
 of the electric light. When it sets in the west, the chalk- 
 marks above the horizon must be supposed to come into view 
 again. 
 
 Autumnal Equinox. Six months later about Septem- 
 ber 22 the arrangement will be the same, except that the 
 
8 HOW TO KNOW THE STARRY HEAVENS 
 
 light will have to be shifted to where the equatorial hoop 
 crosses the opposite or seventh pair of ribs. That is to say, if 
 the light was where the first pair of ribs come together in 
 March, it will be where the opposite or seventh pair of ribs 
 come together in September. 
 
 FIG. 4. UMBRELLA-APPARATUS MODIFIED FOR ILLUSTRATING APPARENT 
 MOVEMENTS OF SUN AND PLANETS 
 
 Face the west when using this diagram. If used north of the Equator, raise (N) till it 
 points to the North Pole, and vice versa. The feathered arrows indicate the diurnal mo- 
 tion; the plain arrows indicate the annual motion. 
 
 Midsummer Solstice. About June 21 the light will be on 
 the fourth rib, but will be some distance north of the equatorial 
 belt. 
 
 Yuletide Solstice. About December 21 it will be on the 
 tenth rib, but some distance south of the equatorial belt. 
 
APPARENT MOTIONS OF HEAVENLY BODIES 9 
 
 If a second hoop be passed over the umbrellas, so that it will 
 pass over these four places, it will represent the Ecliptic, or 
 annual path of the Sun among the stars (see Figure 4). 
 
 It will be seen that the light representing the Sun does not 
 go its daily round exactly the same as the chalk-marks repre- 
 senting the stars. It moves slowly backward on the second 
 
 SUN 
 
 JUNE. 
 
 FIG. 5. CIRCLES OF THE CELESTIAL SPHERE WITH WORLD IN THE CENTRE 
 
 Only the upper half of the diagram is supposed to be above the horizon of the observer. 
 Face the west when using the diagram. Those living north of the Equator should raise (* 
 until the axis (SN) points to the North Pole-Star, and vice versa. 
 
 hoop, so that the average interval between one " mid-day " and 
 the next is nearly four minutes longer than the " southing " of 
 one of the chalk-marks on two successive " nights." The re- 
 sult is that in the course of 366J revolutions of the umbrellas, 
 which represent the star-sphere, there are only 365J revolutions 
 
10 HOW TO KNOW THE STARRY HEAVENS 
 
 of the light which represents the Sun. In other words, the 
 Sun, whose motions we are trying to represent, creeps slowly 
 back along the Ecliptic, so that in exactly one year it has lost 
 one revolution, having gone completely around the " star-sphere " 
 to the place where it was twelve months before. 
 
 As the Sun's path is not on a line with the Equator, but 
 crosses it obliquely, the Sun not only loses one complete 
 revolution in a year, but also drifts to the north and south 
 of the equatorial belt, which it " passes over " twice in each 
 year, at the spring and autumn " Passover " or Equinox (see 
 Figure 5). 
 
 "THE BURNING ROW" 
 
 In the apparatus just used, the hoop along which the light 
 slowly travels represents the Celestial Ecliptic, or path of the 
 Sun. This hoop lies over twelve sets of chalk-marks repre- 
 senting twelve different constellations of stars. Each set of 
 stars has a name by which it has been known for several thou- 
 sands of years. The twelve form what are collectively known 
 as the Signs of the Zodiac. They are also known as the Twelve 
 Houses (or Mansions) of the Sun. The Book of Job (xxxviii, 32) 
 mentions them under the name of the Mazzaroth. 
 
 It takes the Sun a solar month (a little longer than a lunar 
 month) to travel through each " house " or constellation. In 
 March the Sun enters the constellation known by the Latin 
 name for Fishes (Pisces) ; in June it gets to the group known 
 as the Twins (Gemini) ; in September it reaches the Virgin 
 ( Virgo) ; in December it is with the Archer (Sagittarius); 
 and the following March it enters once more the constellation 
 of Pisces. 1 
 
 1 The Sun is commonly said to be at the "First Point of Aries" (the Ram) 
 at the Spring Equinox. This is true only at certain long distant intervals, as 
 will be explained in Chapter XII. The "point" has reference to the Earth's 
 orbit, and not to the stars. It was named after the constellation which happened 
 at the time to be beyond the Sun in March. 
 
APPARENT MOTIONS OF HEAVENLY BODIES 11 
 
 LUNAR MUSIC 
 
 The positions and motions of the Moon are about the same 
 as those of the Sun, only the Moon hangs back more and loses 
 a revolution in a lunar " moonth," or month, instead of losing 
 one in a year. In its backward drift it therefore catches up 
 with the Sun nearly thirteen times in a solar year. 
 
 Eclipses. The various phases of the Moon show that it is 
 a dark body, like our Earth, lighted up on one side by the Sun. 
 They also show that it is nearer to us than the Sun. Some- 
 times, indeed, it passes exactly between us and the Sun, pro- 
 ducing what is known as an Eclipse of the Sun. When it is 
 opposite to the Sun, the shadow of the Earth sometimes falls 
 on it, producing what is known as an Eclipse of the Moon. The 
 reason why there is not an eclipse at every " conjunction " and 
 " opposition " of the Sun and Moon is that the path of the lat- 
 ter, although nearly on the same plane as that of the Sun, does 
 not exactly coincide with it. The two paths, therefore, appear 
 to cross or intersect, in the same way that the Ecliptic and the 
 Equator cross each other. 
 
 PLANETARY MUSIC 
 
 The larger planets all keep on or near the Sun's path, but 
 their apparent motions are more irregular, and each has a period 
 of its own, varying from a few months to many generations. 
 
 Those known as Mercury and Venus appear to drift back- 
 ward and forward on each side of the Sun. They never go 
 very far from it, and are therefore seen only shortly before sun- 
 rise or soon after sunset. 
 
 The other planets appear to drift eastward among the stars 
 that lie along the path of the Sun and Moon. But when they 
 get nearly opposite to the Sun (that is, when they pass the 
 south about midnight) this eastward drift is reversed for a time, 
 so that each planet appears to make a loop in the star-sphere. 
 But they never go far away from the Ecliptic, or path of the 
 Sun (see Figure 97). 
 
12 HOW TO KNOW THE STARRY HEAVENS 
 
 North and South of the Equator. If our observer takes his 
 apparatus north or south of the Equator, and tips it up as 
 before, when observing the stars, he will find that the positions 
 and motions of Sun, Moon, and planets can all be approximately 
 marked out on the hoop that represents the Ecliptic. This 
 will be true for any and every part of the Earth's surface. The 
 Moon and the large planets are never found in any other part 
 of the sky than on (or close to) the Sun's path, or Ecliptic. The 
 same apparatus will show why the days are long in June north 
 of the Equator, and long in December to the south of that line. 
 
 Going East and West. So far the observer has travelled 
 only north and south. If he travels to the east or west, he will 
 find that no change is needed in his apparatus so long as he 
 does not change his latitude. 
 
 On the Equator, for example, the motions of the heavenly 
 bodies are the same whether the observer is in Africa, the East 
 Indies, or in America. The only difference is in time. If he 
 could telegraph from equatorial Africa at midnight, and get 
 immediate answers from the East Indies and America, he would 
 find that it was already sunrise in the East Indies, whilst it 
 was only sunset in equatorial America. With this exception 
 the phenomena observed are alike on all parts of the Earth 
 lying under the Equator. The same is true of any other 
 latitude. 
 
 Although our apparatus represents very fairly the angular 
 distances and apparent motions of the heavenly bodies, it does 
 not directly throw any light on their actual distances or real 
 motions. 
 
 A PRIMITIVE EQUATORIAL 
 
 It will be well for all who have not made a study of the 
 above phenomena to observe for themselves as many of these 
 apparent motions as can be seen from the part of the world 
 they may happen to live in. All the apparatus that is really 
 necessary is a straight stick set firmly in the ground (or other- 
 wise supported) at such an angle that it will point to the Pole 
 
APPARENT MOTIONS OF HEAVENLY BODIES 13 
 
 Star, and a tube (or telescope) attached to it so that it can be 
 moved in any direction. The tube or telescope can then be 
 rotated so as to follow the diurnal motion of any of the heav- 
 enly bodies. When the tube is at right angles to its support 
 it is pointing to the celestial Equator (see Figure 6). Rude 
 
 Fio. 6. AN ADJUSTABLE EQUATORIAL, SUITABLE FOR 
 ANY PART OF THE WORLD 
 
 The axis is clamped in such a position that its ends point to the 
 poles of the heavens. 
 
 as this method of observation may seem, it is capable of lead- 
 ing intelligent observers to a correct solution of the main prob- 
 lems of astronomy. 
 
 A very interesting method of observing the daily motions of 
 the stars is to point a camera to some part of the sky on a clear 
 starlight night, and leave the plate exposed for an hour or so. 
 On developing the print it will be found that each star has left 
 a trail on the plate. Figure 7 is a photograph of the stars sur- 
 
14 HOW TO KNOW THE STARRY HEAVENS 
 
 rounding the North Pole. The further the star is from the 
 centre of rotation, the longer and straighter is the trail it makes 
 on the plate. 
 
 Figure 8 shows the constellation of the Great Bear (or the 
 Dipper, as it is often called), repeated four times, to show its 
 position in the northern skies every six hours. It will be seen 
 that the two " Pointers " are always in a straight line with the 
 star which happens to be near the axis of rotation. This star 
 is commonly known as (Stella) Polaris, or the Pole Star. 
 
FIG. 7. NORTHERN STAR-TRAILS 
 Photographed by Barnard, with twelve hours' exposure. 
 
 FIG. 8. THE DIPPKR, OR GREAT BEAR, AT INTERVALS OF Six HOURS 
 It will be seen that the two "pointers" are always in a line with the Pole-star. 
 
\ 
 
CHAPTER II 
 
 KIVAL THEORIES TO EXPLAIN THE APPARENT MOTIONS 
 OF THE HEAVENLY BODIES 
 
 (A) THE EARTH-CENTRED THEORIES OF THE UNIVERSE 
 
 "Then the Evening (Erev) and the Morning ( Voker) brought to a close the 
 Third Day ( Yom}. 
 
 "And the Mighty Ones (Elohim) said : ' Let there be luminaries in the Ham- 
 mered Plate (Rakia) of the sky, to separate the Day (Yom) from the Night 
 (Lylah}; 1 let them be for signs and to mark the seasons, Days (Yamim), and 
 years ; let them serve as luminaries, in the Hammered Plate of the sky, to give 
 light upon the Earth.' And it was so. 
 
 " And the Mighty Ones made two great luminaries, the larger one to preside 
 over the Day ( Yom), and the smaller one over the Night (Lylah). [They made] 
 the stars also. 
 
 " The Mighty Ones placed them in the Hammered Plate of the sky, to give light 
 upon the Earth, to preside over the Day (Yarn), and the Night (Lylah}, and to 
 separate the light from the darkness. The Mighty Ones saw that it was good. 
 
 "Then the Evening (Erev} and the Morning (Voker} brought to a close the 
 Fourth Day (Yom}." Book of Origins, I, 13-19 (A. ZazeVs Translation). 
 
 EARLY FLAT-WORLD SUPPOSITIONS 
 
 IN trying to explain the observed motions real (or apparent) 
 of the heavenly bodies the ancients were handicapped by 
 their ignorance of the world itself. This appeared, from their 
 local standpoint, to be a flat though uneven surface, the lower 
 parts of which were filled with water. Their experiences on 
 this Earth also prevented them from realising the possibility of 
 anything solid and heavy remaining suspended in space without 
 falling anywhere. Their entire ignorance as to the nature, 
 dimensions, and distances of the celestial bodies led them to 
 
 1 Lylah was personified by the Israelites as Lilith, the first wife of Adam. 
 Isaiah xxxiv, 14 (R. V. Margin). 
 
16 HOW TO KNOW THE STARRY HEAVENS 
 
 suppose that they were put in the heavens by somebody to throw 
 light on the Earth, or to relieve the monotony of the sky. With 
 them the Earth itself was the Universe, and even those who 
 recognised the importance of some of the most prominent celes- 
 tial objects made the natural mistake of supposing them to be 
 Gods who ruled the Earth from their thrones on high. 
 
 UNDERLYING FACTS 
 
 Yet even three and four thousand years agone there were 
 individuals who had discovered that " things are not what they 
 seem." Some of the real facts relating to the Universe were 
 known to a few learned men among the ancient Babylonians, 
 Egyptians, Chinese, Greeks, and Hindus. But the world was 
 not ready for their teachings, and during the Dark Ages that 
 followed the establishment of Christianity the few truths that 
 were known were trampled under foot, like pearls cast before 
 swine. 
 
 However, trampled pearls are apt to come to light again. 
 Facts are stubborn things, and will not permanently down. 
 So the lost facts have been rediscovered in modern times, and 
 largely supplemented by fresh ones. 
 
 Let us glance briefly at some of the primitive ideas held by 
 the ancients with regard to the Universe, so that we may com- 
 pare them with more modern explanations. We can then decide 
 as to which best fit the observed phenomena, and are, on that 
 account, the most deserving of credence. 
 
 THE CANOPY THEORY 
 
 The world we live in was at first supposed to be flat, or nearly 
 so, with a massive firmament resting on the mountains at the 
 edge and spanning the whole Earth. 
 
 To the ancient Egyptians the sky was the bosom of Neit, a 
 celestial ocean across which the divine Sun, Moon, and planets 
 were carried in boats. In Greece it was supposed to be a solid 
 canopy, across one part of which Helios, the Sun-God, daily 
 
RIVAL THEORIES 17 
 
 drove in a chariot of gold, while his sister Selene, the Moon- 
 Goddess, followed him in a chariot of silver. Mount Olympus 
 was supposed to reach up to the highest part of this canopy. 
 On the summit of this holy mountain was the palace of Zeus, 
 king of all the Gods. There the Greater Deities abode, ruling 
 the world below to suit themselves, and dealing out a very pecu- 
 liar kind of justice to the unfortunate mortals who lived thereon. 
 
 Ancient books, as a rule, did not discuss or assert these things, 
 any more than modern books discuss or assert the conclusions 
 of modern astronomy. They merely alluded to them, taking them 
 for granted as well-ascertained facts which were useful for illus- 
 tration, but which it would be folly to argue about or assert. 
 Thus one of the characters in the Hebrew drama of Job casu- 
 ally mentioned that this firmament was " spread out " (Job ix, 8) 
 "as strong as a molten mirror" (Job xxxvii, 18 R. V.). In 
 the same way the Mohammedan Koran sought to show the fine 
 workmanship of Allah by pointing out that he had stretched the 
 firmament across the entire world without a crack in it. 
 
 The Hebrew word for firmament (Ralda) really means a ham- 
 mered plate of metal (Ex. xxxix, 3), and all its Greek and Latin 
 equivalents have afirm or solid meaning. The modern idea that 
 the writers meant an expanse is seen to be absurd when we notice 
 that it was created (Gen. i, 1), or made (Gen. i, 7) ; that it was 
 spread out over the Earth (Job ix, 8) ; and that it had windows 
 in it (Gen. vii, 11) ; also that the Tower of Babel was intended 
 to reach up to it (Gen. xi, 4) ; and that the top of Jacob's ladder 
 rested against it (Gen. xxviii, 12). The mountains which were 
 supposed to support this " hammered plate of heaven " were natu- 
 rally spoken of as the pillars of heaven (Job xxvi, 11). 
 
 When the writer of the Apocalypse was describing the ap- 
 proaching end of the world he made an earthquake shake the 
 stars out of this firmament on to the ground " as a fig-tree casteth 
 her unripe figs when she is shaken of a great wind." He ended 
 by letting the heavens roll together, as a scroll does when the 
 ends are released (Rev. vi, 13-14 R. V.). 
 
 The Venerable Bede, an eminent Christian writer of the 
 
 2 
 
18 HOW TO KNOW THE STARRY HEAVENS 
 
 seventh century, considered the Earth to be flat (or perhaps 
 convex), with a star-spangled canopy over it. This canopy he 
 supposed to be like an umbrella, with its centre at the Pole 
 Star. The daily motion of the heavenly bodies he explained 
 by supposing the canopy to spin round, like the tent over the 
 " merry-go-rounds " of our country fairs. His ideas on the sub- 
 ject are a curious mixture of accurate observation and childlike 
 speculation. He says : 
 
 " The Creation was accomplished in six days. The Earth is its 
 centre and its primary object. The Heaven is of a fiery and subtile 
 nature, round and equidistant from every part, as a canopy from the 
 centre of the Earth. It turns round every. day with ineffable rapidity, 
 only moderated by the resistance of the seven planets, three above 
 the Sun Saturn, Jupiter, Mars then the Sun ; three below 
 Venus, Mercury, the Moon. The stars go round in their fixed courses, 
 the northern perform the shortest circle. The Highest Heaven . . . 
 contains the angelic virtues. . . . The Inferior Heaven is called the 
 Firmament, because it separates the superincumbent waters from the 
 waters below." 
 
 THE CRYSTAL SPHERES 
 
 Such were the primitive ideas of unenlightened men with regard 
 to the Universe. Sometimes, however, the problem was investi- 
 gated in a scientific spirit. It was then readily seen that the 
 celestial phenomena could not be explained on the canopy 
 theory. 
 
 Observation, as well as theory, ultimately led to the overthrow 
 of this primitive idea of a solid star-strewn firmament resting 
 on the mountains. For many of these so-called "pillars of 
 heaven " had been ascended, and no " hammered plate of 
 heaven" had been found resting on them. 
 
 So new theories arose, each of which came a little nearer the 
 truth than the one before. It was suggested that the world was 
 inside a crystal globe or sphere, to which the stars were attached. 
 The nightly motions of the stars were explained by supposing 
 that this crystal sphere rolled over every twenty-four hours. 
 
RIVAL THEORIES 
 
 19 
 
 This theory explained very well the motions of the stars, but 
 did not fit in with the more varied movements of the Sun, Moon 
 and five planets. Some explained their irregularities of motion 
 by supposing that they were carried around with the stare, but 
 that, instead of being fixed to the revolving sphere, like the stars, 
 they were at liberty to crawl around on it very slowly, like so 
 
 FIG. 9. THE PTOLEMAIC SYSTEM 
 
 many insects. Others suggested that each of these seven wan- 
 derers had a crystal sphere all to himself (see II Cor. xii, 2). 
 The seven spheres were supposed to be one inside the other. 
 Each was thought to share in the general daily rotation, but to 
 lag behind or have a slight independent motion of its own (see 
 Figure 9). 
 
 Even this far-fetched notion did not fit in satisfactorily with 
 the observed phenomena. So Tycho Brahe* suggested that the 
 Earth was a globe, spinning round on its axis every twenty-four 
 
20 HOW TO KNOW THE STARRY HEAVENS 
 
 hours ; that the Sun and Moon went around the Earth in a year 
 and in a month, respectively ; and that the five planets went 
 around the circling Sun (see Figure 10). 
 
 FIG. 10. THE TYCHONIC SYSTEM 
 EPICYCLES 
 
 As even this complex arrangement did not fit in with the 
 observed motions, the planets were then supposed to move in 
 a series of eccentrics around their ideal orbits, with the star- 
 sphere outside of all. For a time this theory was thought to 
 explain the observed motions. But it was such a complex, 
 improbable, lumbering, incomprehensible, and absurd theory 
 that Alphonso, king of Castile, ventured the remark that if he 
 had been consulted by the Creator he could have considerably 
 improved upon the plan. 
 
RIVAL THEORIES 21 
 
 FAUSTUS ON THE SPHERES 
 
 These mediaeval speculations are well illustrated by the fol- 
 lowing dialogue from Marlowe's " Faustus" written toward the 
 close of the sixteenth century. 
 
 " Faust. Tell me, are there many heavens above the Moon ? 
 
 Are all celestial bodies but one globe, 
 
 As is the substance of this centric Earth ? 
 
 Mephistopheles. As are the elements, such are the spheres, 
 
 Mutually folded in each other's orb. 
 
 And, Faustus, 
 
 All jointly move upon one axletree, 
 
 Whose terminine is termed the World's wide pole : 
 
 Nor are the names of Saturn, Mars, or Jupiter 
 
 Feign'd, but are erring stars. 
 
 Faust. But, tell me, have they all one motion, both situ et tempore ? 
 
 MepJi. All jointly move from east to west in twenty-four hours upon 
 the poles of the World, but differ in their motion upon 
 the poles of the zodiac. 
 
 Faust. Tush, these slender trifles Wagner can decide : 
 
 Hath Mephistopheles no greater skill? 
 
 Who knows not the double motion of the planets? 
 
 The first is finished in a natural day; 
 
 The second thus; as Saturn in thirty years, Jupiter in twelve; 
 Mars in four ; the Sun, Venus, and Mercury in a year ; 
 the Moon in twenty-eight days. Tush, these are fresh- 
 men's suppositions. But, tell me, hath every sphere a 
 dominion or intellitjencia ? 
 
 Meph. Aye. 
 
 Faust. How many heavens or spheres are there ? 
 
 Meph. Nine ; the seven planets, the firmament, and the empyreal 
 heaven. 
 
 Faust. Well, resolve me in this question ; why have we not con- 
 junctions, oppositions, aspects, eclipses, all at one time, 
 but in some years we have more, in some less ? 
 
 Meph. Per incequalem motum respectu totius. 
 
 Faust. Well, I am answered." 
 
22 HOW TO KNOW THE STARRY HEAVENS 
 
 The writer of a recent magazine article l sums up these old 
 ideas of the Universe very neatly. He says : 
 
 " To the men of the Middle Ages the world was a little space shut 
 tight within a wheelwork of revolving spheres. It was compendious,, 
 complete, ingenious, like a toy in a crystal box. Beyond the outer 
 shell nothing existed. The heavens were uncorruptible. No change 
 could occur in the whole system, save in the Earth alone. The Uni- 
 verse was created for the sole use of man. It was small and finite." 
 
 THE ROUND WORLD 
 
 While all these speculations were going on, people had been 
 going to and fro on the Earth, and travelling up and down on 
 it. In this way they had discovered for an actual fact that the 
 world is not flat, but is a round ball, 8,000 miles thick, suspended 
 in space, with the starry heavens on every side of it. 
 
 This being the case, it follows that if the stars are fixed to a 
 massive firmament, it is not a mere " dish-cover " or umbrella 
 over a flat Earth, but is in the form of a hollow crystal sphere, 
 rolling over (to the west) every twenty-four hours, with the round 
 World in the centre, supporting itself on nothing. 
 
 (B) THE SUN-CENTRED THEORY OF COPERNICUS. 
 
 "The first formal assertion of the heliocentric theory was made in 
 a timid manner, strikingly illustrative. of the expected opposition. It 
 was by Copernicus, a Prussian, speaking of the revolutions of the 
 heavenly bodies ; the year was about 1536. In his preface ... he 
 complains of the imperfections of the existing system, states that he 
 has sought among ancient writers for a better way, and so had learned 
 the heliocentric theory. ... In their decree prohibiting [the work of 
 Copernicus], ' De RevolutionilmsJ the Congregation of the Index, 
 March 5, 1616, denounced the new system of the Universe as 'that 
 false Pythagorean doctrine utterly contrary to the Holy Scriptures.' 
 . . . The opinions thus defended by the Inquisition are now objects 
 of derision to the whole civilized world." 2 
 
 1 Dr. E. S. Holden, in the " Popular Science Monthly," November, 1903. 
 
 2 Dr. J. W. Draper. 
 
RIVAL THEORIES 23 
 
 " People gave heed to an upstart astrologer who strove to show that 
 the Earth revolves, not the heavens or the firmament, the Sun and 
 Moon. . . . This fool wishes to reverse the entire science of astronomy." l 
 
 The final outcome of all these speculations was that the whole 
 of the Earth-centred theories were thrown overboard, and re- 
 placed by an old Sun-centred theory originally brought from 
 India by Pythagoras. According to this new yet ancient theory, 
 the stars are practically immovable bodies suspended far off in 
 space, and the Sun is the centre around which all the planets, 
 including the Earth itself, revolve (see Figure 11). 
 
 FIG. 11. COPERNICAN SYSTEM 
 Including four of the most tilted orbits of Minor Planets. Neptune's orbit is here omitted. 
 
 It has been found, however, that the Moon does actually go 
 around the Earth, completing a revolution in about a month. 
 The daily motion of all the heavenly bodies is not real, but only 
 apparent. It is explained by the fact that the Earth itself rolls 
 completely over (to the east) every twenty-four hours, at the 
 same time that it travels around the Sun once every year. This 
 daily rotation of the Earth causes all the heavenly bodies to 
 appear to turn in the opposite direction. 
 
 The peculiarities of the Sun's annual drift to the north and 
 south, and the resulting seasons, are readily explained by the 
 
 l Martin Luther. 
 
24 HOW TO KNOW THE STARRY HEAVENS 
 
 fact that the Earth has a. heavy " list " to one side, with reference 
 to its path around the Sun (see Figure 12). The other planets 
 are also drifting around the Sun, in the same general direction, 
 but at different distances from it. 
 
 This Indian system of cosmogony is now known as the Coper- 
 nican Theory, because Copernicus first established its truth in 
 modern Europe. It explains the motions of the heavenly bodies 
 so well that there is no doubt about its being true as far as it 
 
 FIG. 12. RELATIVE POSITIONS OF EARTH AND SUN AT THE FOUR SEASONS 
 
 goes. In spite of the long-continued opposition of unprogres- 
 sive theologians, it has now been adopted by all competent 
 judges, and is accepted, on hearsay, even by those who do not 
 realise the subordinate position to which it reduces our Earth, 
 and by those who do not profess to be competent to judge as to 
 its correctness. 
 
 The adoption of this theory has led to the solution of a mul- 
 titude of otherwise inexplicable phenomena. Without it, the 
 planetary bodies appeared to be swinging around us in a labyrinth 
 of perplexing knots and meaningless tangles. As a result of its 
 adoption, the knots and tangles have all been unravelled, and 
 the structure and dimensions of the Solar System have been 
 
RIVAL THEORIES 25 
 
 tolerably well ascertained. The telescope and other opitical in- 
 struments have now greatly increased our knowledge of the 
 heavenly bodies generally, and have revealed to us similar sys- 
 tems moving in actual conformity with the Copernican Theory. 
 
 This same theory has also enabled astronomers to apply them- 
 selves, not entirely without success, to the task of ascertaining 
 the structure, and measuring the distances and dimensions, of 
 the more distant luminaries known to us by the misleading name 
 of " fixed stars." 
 
 Every observed peculiarity is explained by this theory, without 
 any absurd and impossible suppositions like the " eccentrics " 
 and " epicycles " of other theories. And many facts have been 
 discovered by following it up to its logical conclusions. It is 
 therefore the true explanation of the mechanism of the Universe. 
 
 How and why these movements of the heavenly bodies are 
 kept up will be briefly dealt with in subsequent chapters. 
 
CHAPTER III 
 
 PRINCIPLES UTILISED FOR MEASURING THE UNIVERSE 
 
 "And there was given me a reed like unto a rod, and the angel stood, saying, 
 Rise and measure the temple of God." Rev. xi, 1. 
 
 "And he that talked with me had a golden reed to measure the city, . . . 
 and he measured the city with the reed, twelve thousand furlongs. The length 
 and the breadth and the height of it are equal." Rev. xxi, 15, 16. 
 
 "The measure of the Moon's distance involves no principle more abstruse than 
 the measure of the distance of a tree on the opposite side of a river." Sir George 
 Airy. 
 
 HOW IT IS DONE 
 
 I WILL now say a few words about the way in which as- 
 tronomers have been enabled to find out the distances and 
 dimensions of many of the objects which -compose the L T ni verse. 
 It was very early recognised that the heavenly bodies are not 
 all at the same distance from us. 
 
 STARS ARE BEYOND PLANETS 
 
 The stars, for example, have a far-away look and a fixity of 
 position that would naturally lead one to think that they were 
 beyond the larger, brighter, and more active luminaries which 
 are found on or near the Ecliptic. This was proved beyond a 
 doubt when observers at a distance from one another compared 
 notes. For it was sometimes found that when an observer in 
 the north saw a certain planet a little to the south of a particu- 
 lar star, an observer in the south would see it north of the same 
 star. The only possible explanation of this is that the planet is 
 nearer to us than the stars. 
 
 THE ORDER OF THE PLANETS 
 
 Leaving the " fixed " stars out, there were seven celestial 
 " wanderers " known to the ancients. Of these, two appear to 
 
PRINCIPLES FOR MEASURING THE UNIVERSE 27 
 
 be very much nearer to us than the other five. The Sun, for 
 example, is evidently either very near or very large, bright, and 
 hot. But the Moon is nearer to us than the Sun, for it some- 
 times passes in front and shuts off its light and heat from us. 
 As it also passes between us and every other celestial object 
 that comes in its way, it is evidently the nearest of all the 
 heavenly bodies. 
 
 Now the Moon performs its circuit of the heavens in less time 
 than any other wanderer. It seems natural, then, to suppose 
 that the wanderers which take the most time to perform their 
 circuit are the farthest away from their common centre of 
 revolution. 
 
 This reasoning led the early astronomers to regard slow-moving 
 Saturn as the most distant planet. The stately Jupiter they 
 put next, followed by fiery Mars. As regards the other three, 
 there was some difference of opinion, due to the fact that, on the 
 Earth-centre theory, their real motions were not distinguished 
 from their apparent ones, due to perspective. 
 
 But when once it was recognized that the Sun was the centre 
 around which the planets turned, it became evident that our own 
 populous Earth and pale-faced Moon were travelling in partner- 
 ship, next to Mars ; that " Venus the beautiful " followed ; and 
 that fast-flying Mercury kept nearest to the central Sun. 
 
 COMPARATIVE DISTANCES 
 
 The order of the planets being thus settled, the next thing 
 was to ascertain their distances from the Sun. 
 
 In the case of the inferior or inner planets, Mercury and 
 Venus, their proportional distances from the Sun were easily 
 found. All that had to be done was to point one leg of a pair 
 of dividers, or compasses, at the setting or rising Sun, and the 
 other leg at the planet Venus when at its greatest angular dis- 
 tance from it, as an Evening or Morning Star. The dividers 
 were then laid on a sheet of paper, and two lines drawn 
 to indicate the V shape of the open dividers (see S E V in 
 Figure 13). 
 
28 HOW TO KNOW THE STARRY HEAVENS 
 
 The Earth was then supposed to be at E, where the two lines 
 come together, and the Sun was supposed to be at the other end 
 (S) of one of the lines. Venus would evidently be somewhere 
 on the line E V. 
 
 Taking it for granted that the planetary orbits were circular, 
 a circle was then drawn through E from S as a centre. This 
 
 represented the Earth's or- 
 bit. Another and smaller 
 circle was drawn from the 
 same centre, just large 
 enough to touch the other 
 arm, E V. This circle 
 evidently represented the 
 orbit of the planet Venus. 
 The same process was 
 gone through with the 
 planet Mercury, and the 
 result transferred to the 
 same figure (see S E M). 
 
 On measuring the radii 
 or semi-diameters of these 
 three circles, representing 
 
 the planetary orbits, it was found that their lengths varied 
 in the ratio of 100, 72, and 38. These figures, therefore, 
 represent the relative distances of the Earth, Venus, and 
 Mercury. 
 
 A comparison of the distances with the times of revolution 
 then enabled the relative distances of the superior or outer 
 planets to be computed by means of their times of revolution, 
 taking it for granted that they all obeyed the same law, what- 
 ever that law might be. 
 
 The result was that the distances of the outer planets, when 
 computed on the same scale as the inner ones (=100 to the 
 Earth's distance), were found to be 152, 520, and 953. 
 
 FIG. 13. ORBITS OF MERCURY, VENUS, 
 AND EARTH 
 
PRINCIPLES FOR MEASURING THE UNIVERSE 29 
 
 PLANETS MOVE IN ELLIPSES 
 
 It may be as well to state here, that while the above observa- 
 tions were being made it was discovered that the orbits of the 
 inner planets are not exactly circular, but slightly egg-shaped, 
 or, rather, elliptical. It has since been found that the paths of 
 all the planets share this peculiarity, the cause of which has 
 also been ascertained. 
 
 NEWLY DISCOVERED PLANETS 
 
 Since the invention of the telescope two large planets have 
 been discovered beyond the orbit of Saturn. They bear the 
 names of Uranus and Neptune. On the same scale as that used 
 above, their distances from the Sun are represented by the 
 numbers 1,920 and 3,000. 
 
 A great number of small planets have also been discovered in 
 the interval between the orbits of Mars and Jupiter. Their 
 numbers are so great, their sizes so small, and their orbits so 
 peculiar, that astronomers formerly looked upon them as the 
 scattered fragments of larger planets which had met with an 
 accident. 1 
 
 ACTUAL DISTANCES 
 
 The comparative distances of all the planets having been thus 
 discovered, all that had to be done was to find the real distance 
 of one of them in miles. All the other distances could then be 
 readily computed in miles. 
 
 It took many generations to solve this little problem, and even 
 yet the answer is not as free from error as could be wished. It 
 has, however, been solved, with a very fair amount of accuracy, 
 by several independent methods. The distances usually meas- 
 ured are those of the neighbouring planets when they are at 
 their least distances from us or are otherwise favourably placed. 
 
 1 The orbits of four of these " Asteroids " are shown in Figure 11. It will be 
 noticed that the four represented do not lie in the same general plane as those of 
 the larger planets, but are more or less tilted up, some one way, and some another. 
 These, however, are exceptions. The majority move in or near the general plane. 
 
30 HOW TO KNOW THE STARRY HEAVENS 
 
 There are many people who do not put much faith in celestial 
 measures. They cannot see any possibility of obtaining them, 
 seeing that we cannot stretch a tape-line from one flying world 
 to another. There are, however, a number of ways in which in- 
 accessible distances may be accurately measured. For example, 
 if you wish to measure the height of a tree without ascending 
 it, all you have to do, if the ground is level, is to put a stick 
 upright in the sunshine, and measure the length of its shadow. 
 If a three-foot upright makes a three-foot shadow, then a hun- 
 dred-foot shadow indicates that the tree which casts it is a 
 hundred feet high. And if the Sun is so low down that the 
 three-foot stick makes a six-foot shadow, then a two-hundred- 
 foot shadow will indicate that the tree which casts it is a hundred 
 feet high. 
 
 There are other methods which are just as simple, though 
 most of them require more elaborate apparatus. A little study 
 will show that celestial and other inaccessible measurements 
 may be as accurate as any made with the help of a chain or 
 tape-line. Let us see what are the principles involved and 
 methods employed. 
 
 ESTIMATING DISTANCES 
 
 If you close one eye and keep your head still, you will find 
 that with one eye alone you will be unable to judge as to the 
 distance from you of the object you are looking at. The only 
 exception to this is, that if you already know the size of the 
 object you can estimate its distance by noticing whether it 
 appears to be large or small. 
 
 To be able to estimate your distance from any object, you 
 must either move your head or open the other eye, so as to 
 get another picture of it to compare with the image already ob- 
 tained. Then you can estimate with a tolerable amount of 
 accuracy how far the object is from you (see Figure 14). 
 
 The two eyes form the extremity of a three-inch base-line, 
 and if you draw an imaginary line from each eye to the point 
 you are looking at, you will obtain a three-cornered or triangular 
 
PRINCIPLES FOR MEASURING THE UNIVERSE 31 
 
 figure of known dimensions. That is, you will know (approxi- 
 mately) the length of all its three sides. 
 
 LAND-SURVEYING 
 
 The surveyor, when he wishes to find the width of a river 
 without crossing to the other side, measures off a base-line on 
 his own side of the stream. Then, by noting with his instru- 
 ments the position of an object on the other side of the river, as 
 
 his base-line, he 
 river is. 
 
 either calculate the 
 result by means of 
 
 FIG. 14. ESTIMATING DIS- 
 TANCES WITH THE EYES 
 
 seen from each end of 
 can tell how wide the 
 
 In this case he can 
 distance, or get the 
 a diagram on paper. 
 If he wishes to do the 
 latter, he draws a line 
 to represent his base- 
 line, and from each 
 end of it sets off a line 
 at the same inclination 
 or angle to it as that used on his real base-line. The place 
 where these two lines cross each other represents the position 
 of the object observed on the other side of the river (see Figure 
 15). By measuring the sides of his triangle he gets the dis- 
 tance required in terms of his base. For instance, if the sides 
 of his triangle are 10 times as long as the base thereof, and 
 the latter is 10 yards long, then the width of the river is 100 
 yards. 1 
 
 A whole continent can be surveyed in the same way, by 
 measuring off three-cornered areas of land, and using every dis- 
 tance obtained as a base to measure other distances with. In 
 this way (with certain details and precautions which need not 
 be here specified) the shape and size of the Earth can be 
 obtained. 
 
 1 A right-angled triangle gives the best results. Those who wish for further 
 details will find them in the next chapter, which is written for those who are not 
 afraid of a little simplified trigonometry and diluted mathematics. 
 
HOW TO KNOW THE STARRY HEAVENS 
 
 SKY-SURVEYING 
 
 The astronomer then finds out the distance of the Moon in 
 the same way, by using a measured base-line about 4,000 miles 
 long. As he cannot see one end of his base-line from the other 
 end of it, he gets his angles indirectly, by polar distances, or by 
 observing how much the Moon is displaced among the stars 
 when viewed from different parts of the world at the same time. 
 The same principle, rather differently 
 applied, enables him to tell the distance 
 of the Sun. 
 
 With a 4,000-mile base-line the 
 Moon's distance is found to be about 
 60 times as long as the base-line. On 
 multiplying 4,000 by 60 we get the 
 Moon's distance, 240,000 miles. 1 
 
 With the same base-line of 4,000 
 miles the Sun's distance is found to be 
 about 388 times greater than that of the 
 Moon. It will be seen that the longest 
 base-line we can get is very short when 
 compared with the distance to be meas- 
 ured ; but as it is the longest available, 
 astronomers have to make up for its 
 
 shortness by using different methods and taking advantage of 
 every favourable opportunity to correct their measurements. 
 Now 388 times 240,000 comes to about 93,000,000 miles, which 
 is approximately the Earth's distance from the Sun. 
 
 As we already know the comparative distances of the other 
 planets from the Sun, their actual distances can now be obtained 
 without difficulty. 
 
 The following table gives in one column the relative distances 
 of the planets, the Earth's distance being represented by 1.000. 
 In another column it gives the real distances in miles. They 
 are calculated according to the most recent estimates of the 
 solar parallax, which will be explained in the next chapter. 
 
 1 These figures are not exact, but will serve to show the principles involved. 
 
 FIG. 15. SURVEYING 
 FROM A BASE-LINE 
 
PRINCIPLES FOR MEASURING THE UNIVERSE 33 
 
 PLANETARY DISTANCES 
 
 (Solar Parallax, 8.81") 
 
 
 RELATIVE 
 
 ACTUAL (IN MILES) 
 
 Mercury . 
 
 . . . .387 
 
 . . 35,909,000 
 
 
 
 . . . .723 . 
 
 . . 67,087,000 
 
 Earth 
 
 . . . 1.000 
 
 
 
 . . . 1.523 
 
 . . 141,384,000 
 
 Asteroids 
 
 ( 2.080 . 
 '1 4.262 . 
 
 . . 193,000,000 
 . . 395,470,000 
 
 Jupiter . 
 
 .... 5.203 . 
 
 . . 482,786,000 
 
 Saturn 
 
 .... 9.538 
 
 . . 885,105,000 
 
 Uranus 
 
 .... 19.183 . 
 
 . . 1,779,990,000 
 
 Neptune 
 
 .... 30.055 . 
 
 . . 2,788,800,000 
 
 It will be seen by those who have followed the argument thus 
 far that there is no guessing about the process. It is a mere 
 matter of observation and calculation. In the first instance 
 given, the width of the river can be found by stretching a cord 
 across it, or the result can be tested in various other ways. In 
 the case of the Sun, Moon, and planets, the results can also be 
 tested in other ways, as well as by repeating the experiment 
 under different conditions. As soon as the observations can be 
 carried out without error, the distances can be obtained exactly. 
 But not before. 1 
 
 STAR DISTANCES 
 
 The stars are too far off for their distances to be measured by 
 a 4,000-mile base-line. But as it is found that the Earth in Jan- 
 uary is at an enormous distance from the place which it occupies 
 in July, the positions of the stars are observed at both periods,, 
 and compared together. 
 
 1 A few years ago it was discovered that one of the asteroids, or minor planets, 
 which goes by the name of Eros, moves in an elongated orbit, one part of which is 
 nearer to us than that of Mars. At certain periods this planet (which is only 
 about twenty miles thick) comes within a distance of 14,000,000 miles from the 
 Earth. By its means celestial distances will before long be much more accurately 
 known than they are now, 
 
 8 
 
34 HOW TO KNOW THE STARRY HEAVENS 
 
 This gives a base-line of nearly 186,000,000 miles. But even 
 with this gigantic base there are only a few of the nearest stars 
 whose distances can be even approximately estimated. The 
 distance of the nearest of them is about 135,000 times as great 
 as the length of our enormous base-line. It is 9,000 times as 
 far off as Neptune, the outside planet in our system. About 
 sixty stars have measurable parallaxes, a few more have per- 
 ceptible ones, but all the others are at present out of reach in 
 the unsoundable depths of infinite space. 
 
 If our eyes were as powerful and accurate as the instruments 
 of the astronomer, we could look at a shining grain of sand 
 thirty miles away, and estimate its distance from us by observ- 
 ing how much the eyes had to be drawn together to focus on 
 the object. 
 
 The same principle of triangulation which enables a surveyor 
 to plot off a township or measure the height of a mountain en- 
 ables the astronomer to measure the world and ascertain the 
 distances of the Sun, Moon, planets, and some of the stars. 
 Enormous as many of the distances are, all these measure- 
 ments depend on an ordinary yard-stick, they are all based 
 on the common three-foot rule. 
 
 "E PUR SI MUOVE" 
 
 It should be observed that the above-described method of 
 measuring the distances of the heavenly bodies will in some 
 cases give the same results whether we suppose the Earth to 
 stand still, with the Sun, Moon, planets, and stars swinging 
 around it once every twenty-four hours, or whether we suppose 
 that the diurnal changes are caused by the Earth revolving on 
 its axis. 
 
 But, having once found the distances, it is evident that the 
 latter is the true explanation of the phenomena. For if the 
 planet Neptune distant as it is really goes around the Earth 
 in a day, it must go at the unthinkable speed of 190,000 miles 
 in a second of time. And if the stars, whose distances are so 
 much greater than that of Neptune, also go around the Earth 
 
PRINCIPLES FOR MEASURING THE UNIVERSE 35 
 
 every day, their speed must be thousands and millions of times 
 faster still. 
 
 On the other hand, if it is the Earth that revolves, the motion 
 is nowhere greater than one mile in three seconds. The proba- 
 bilities are evidently altogether in favour of the latter proposi- 
 tion. The former one is impossible and absurd. 
 
 There is only one way of getting over the difficulty. In spite 
 of all who deny it, or fail to realise it, the fact still remains that 
 " the Earth does move." 
 
 MEASURING THE PLANETS 
 
 While measuring the distances of the Sun and planets, astron- 
 omers have been able, by measuring their apparent diameters 
 (in degrees, minutes, and seconds of arc), to ascertain their real 
 diameters in miles. The principle is a very simple one, and 
 may be illustrated in this way. 
 
 A two-inch ball is 8 times as large as a one-inch ball (2 x 
 2x2 = 8). But if a one-inch ball is viewed from a distance of 
 ten feet, it will be just large enough to hide a two-inch ball 
 twice as far away, or a four-inch ball four times as far away. 
 
 Now, suppose that we have found the Moon to be 239,000 
 miles away. Let us get a ball 11 feet 5 inches in diameter, and 
 place it in a conspicuous position on the top of a steep mountain. 
 Having done so, let us measure off 1,262 feet (which is the one- 
 millionth part of the Moon's distance), to a place where the ball 
 will come between us and the rising or setting Moon. It will 
 be found that the ball is just large enough, at that distance, to 
 hide the Moon from us. Now, as the Moon is just a million 
 times as far from us as the ball which hides it, it follows that 
 its diameter is just a million times greater (11 feet 5 inches 
 X 1,000,000 = 2,162 miles). 
 
 So far, so good. It is interesting to note that, in an eclipse 
 of the Sun, the Moon acts the part of the ball just used. 
 It so happens that, while the Sun's average distance from us 
 (92,790,000 miles) is about 388 times that of the Moon (239,000 
 miles), his diameter (864,000 miles) exceeds hers (2,162 miles) 
 
36 HOW TO KNOW THE STARRY HEAVENS 
 
 in about the same proportion. They therefore look as though 
 they were about the same size, although the Sun's diameter is 
 really almost 400 times as long, and his bulk is more than 
 60,000,000 times as great (400 x 400 x 400 = 64,000,000). 
 
 Most of the planets have no measurable diameter when seen 
 by the naked eye, but by means of the telescope their dimen- 
 sions also have been ascertained. The stars cannot be measured 
 in this way, as they are so far off that they have no perceptible 
 size, even when seen through the most powerful telescopes. 
 The amount of light we receive from them is almost the only 
 guide we have to their size, and even this is of no avail unless 
 we know something of their distances from us. 
 
 WEIGHING THE PLANETS 
 
 One of the most astonishing things that astronomers have 
 been able to do is to weigh the Sun and planets, so as to ascer- 
 tain their mass or weight. 1 Yet the principle is as simple as 
 that used in ascertaining their dimensions. 
 
 Get a light straight stick, and make a 'sharp point at each end 
 of it. Then stick a potato on each point, and hang the appa- 
 ratus from the ceiling by a string. Shift the string on the stick 
 till the potatoes balance one another. Now give it a twirl and 
 release it. The two potatoes will swing around the common 
 centre of gravity, where the string is fastened to the stick. 
 
 If the two potatoes are of the same weight, the centre of 
 gravity will be the same distance from each of them, and it 
 will be found that each one swings around the other one in the 
 same sized circle. But if one is heavier than the other, the 
 centre of gravity will be nearer to the heavy one, and it will be 
 found that the small one makes the largest circle. The appa- 
 ratus, indeed, makes a primitive pair of scales with which the 
 relative weight of each potato can be ascertained by noting the 
 size of the circle it makes. 
 
 1 These terms are not absolutely identical. The word mass refers to the amount 
 of matter contained in anything, while weight has reference also to the force of gravi- 
 tation, which varies iu different worlds. The distinction is not important here. 
 
PRINCIPLES FOR MEASURING THE UNIVERSE 37 
 
 Now the Earth aud Moon form a similar weighing-machine. 
 They are all the time swinging around their common centre of 
 gravity, like our two potatoes, and their relative weights can be 
 found by the same process. 
 
 But at the same time that the Earth and Moon are swinging 
 around their common centre of gravity, the Earth-Moon family 
 on the one hand, and the Sun on the other, are also swinging 
 
 FIG. 16. DAILY POSITIONS OF EARTH AND MOON 
 
 It will be seen that the lunar path is always concave towards the Sun. 
 
 around their common centre of gravity. In this case the Earth 
 and Moon together are so small, in comparison with the Sun, 
 that they are doing nearly all the swinging. Nevertheless the 
 Sun is doing his part of the motion, even if it is too small to be 
 easily perceived. 
 
 All the members of our Solar System (including even the 
 Sun) swing around their various centres of gravity and influence 
 one another in the same way, the amount of their influence 
 depending on their mass and distance. The Sun outweighs all 
 the planets 745 times, so that his part of the swinging is very 
 small. Still it exists, and although it is convenient to say that 
 the Moon swings around the Earth, and that the Earth swings 
 around the Sun, it would be more correct to say that the Earth 
 and Moon swing around their common centre of gravity, and 
 that the Earth-Moon family and Sun do the same. 
 
 It will be seen that any family of worlds can be used as a 
 weighing-machine, with which the relative weight of each indi- 
 vidual can be ascertained by its influence over the other mem- 
 bers of the family. Some of the stars, even, can be weighed 
 against one another when they belong to one family. 
 
38 HOW TO KNOW THE STARRY HEAVENS 
 
 ACTUAL WEIGHT 
 
 When we have found the relative masses or weights of the 
 Sun and planets, we can, by finding the actual weight of one of 
 them, in tons, find the actual weight of any, or all of them, in 
 tons. 
 
 The readiest way of doing this is to weigh the Earth and find 
 out how many tons of material it contains. Of course this is a 
 very easy thing to do. All that appears to be necessary is to 
 get a very strong weighing-machine, turn it upside down, so that 
 the Earth rests in the pan, and then adjust the scale and read 
 off the weight. 
 
 This last item must not be taken too seriously. The problem 
 of weighing the Earth is really one of the most difficult tasks 
 astronomers ever undertook. It has been solved, however, by 
 several different methods, 1 and it is interesting to know that the 
 Earth weighs about 6,600 millions of millions of millions of 
 American tons (6,600,000,000,000,000,000,000). And the Sun 
 contains 330,000 times that amount of material. 
 
 1 The best plan is one which employs a torsion -balance to measure the mutual 
 attraction of lead balls at known distances from one another. This is then com- 
 pared with the observed attraction of the Earth for the same lead balls, which are 
 known to be at a distance of about 4,000 miles from the centre of attraction. The 
 mutual attraction of the balls being known, the law of gravitation shows how dense 
 the World must be in order to give the balls their observed weight. (See Chapter 
 XV for the key to this problem. ) 
 
CHAPTER IV 
 
 SOME PROBLEMS USED IN CELESTIAL MEASUREMENTS 
 
 "The methods used for measuring astronomical distances are in some applica- 
 tions absolutely the same as the methods of ordinary theodolite surveying, and are 
 in other applications equivalent to them. . . . There is nothing in their principles 
 which will present the smallest difficulty to a person who has attempted the common 
 operation of plotting from angular measures." Sir George Airy. 
 
 IN order that the beginner may better understand the prin- 
 ciples upon which celestial measures depend, a few examples 
 are given here, going further into details than in the preceding 
 chapter. I do not undertake to say that everyone will be able 
 to follow them all ; but I have simplified them and explained 
 the terms as much as possible, so as to help a non-mathematician 
 who is willing to try. 
 
 DEGREES IN A CIRCLE 
 
 In trigonometry, which deals with the properties of three-sided 
 figures, we (after the Greeks) divide the circumference of a circle 
 into 360 degrees of arc, denoted thus (360). 
 
 These degrees are indicated by straight lines radiating from 
 the centre of the circle, which is supposed to be the point of 
 observation. 
 
 Where two of these radiating lines enclose a square corner or 
 right-angle, that angle evidently contains 90 of arc as measured 
 off on the circumference. 
 
 Each degree is, for convenience, divided into 60 minutes ('), 
 and each minute into 60 seconds (") of arc. These minutes and 
 seconds of arc have nothing whatever to do with minutes and 
 seconds of time. It is a mere accident (and misfortune) that 
 they are called by the same names. 
 
40 HOW TO KNOW THE STARRY HEAVENS 
 
 Each line going from the centre to the circumference (like a 
 spoke in a wheel) is termed a radius (plural radii). 
 
 RADII AND ARC OF CIRCLE 
 
 It has been found that when two radii are so placed that the 
 central corner or angle contains 57 17' 45" (= 206,265"), then 
 the arc of circle cut off by the two radii is just equal in length 
 to one radius. 1 Such an arc is termed a radian. 
 
 FIG. 17. ARC OF CIRCLE 
 
 It naturally follows from this that when the angle is half of 
 that just given then the arc cut off is just half as long as each 
 radius (see Figure 17). 
 
 This is expressed as follows : 
 
 Let A B represent arc of circle 
 " Z " size of angle 
 
 " Y " radius of circle 
 
 " X angle of 57 17' 45" 
 
 Then when Z = X, A B = Y 
 
 When Z = JX, A B = j Y 
 
 WhenZ = JX, A B = JY 
 
 And so on. 
 
 1 That is, the part of the tire which is cut off would be, if straightened out, 
 just as long as one of the spokes, 
 
PROBLEMS IN CELESTIAL MEASUREMENTS 41 
 
 The result is, that if we know the distance of an object in miles, 
 we can tell its diameter in miles by measuring the angle enclosed 
 by its opposite sides. For example, if an object 15 miles away 
 is long enough to subtend an angle of 3 49' 11" (=y a ^ of X), 
 then it must be about a mile long. 
 
 On the other hand, if we know the diameter of an object in 
 miles, we can tell its distance from us in miles. For example, 
 if we know that a certain object is a mile long, and we find by 
 
 FIG. 18. CHORD OF ARC 
 
 our instruments that it subtends an angle of 3 49' 11" (= & of X), 
 then it must be about 15 miles away. 
 
 These two things can be ascertained; however, only when the 
 distant object is near enough to have a measurable size when 
 seen through a telescope. 
 
 THE CHORD OF AN ARC 
 
 For many purposes it is convenient to draw a straight line 
 cpnnecting the outer ends of the two radii. This line is called 
 a chord, and the three straight lines together form what is known 
 as a triangle (see Figure 18). 
 
 In such a triangle the two outside corners or angles, A and B, 
 are equal to one another, and are each sharper or more acute 
 than a right angle. This is true whether the centre angle Z be 
 
42 HOW TO KNOW THE STARRY HEAVENS 
 
 great or small. In fact the greater the central angle is, the more 
 acute become the outer angles. It is useful to remember that if 
 the number of degrees in all the three angles of a triangle be 
 added together, they are always equal to the number contained 
 
 FIG. 19. SINE OF ANGLE 
 
 in two right angles. That is, they always contain exactly 180 
 of arc. 
 
 The chord of an arc is of course shorter than the arc with 
 which it begins and ends. The smaller the angle, the less differ- 
 ence there is between the two, and in very small angles this 
 difference can be neglected, it is so minute. 
 
 The Greeks made great use of chords in their investigations. 
 Ptolemy, the astronomer (/. 127-151 A. D.), constructed tables 
 
PROBLEMS IN CELESTIAL MEASUREMENTS 43 
 
 SHORE. 
 
 giving the length of both arcs and chords for every half-degree 
 up to two right angles. 
 
 THE SINE OF AN ANGLE 
 
 The Hindus, however, simplified their problems by taking 
 the chord of double the angle, and then cutting it in two and 
 discarding one half. The 
 half-chord used (A B) is 
 known as a sine of the angle 
 (A Z B) it measures (see 
 Figure 19). 
 
 The advantage of a sine 
 over a chord is this: In 
 solving problems in trigo- 
 nometry it is often conven- 
 ient to have one of the outer 
 angles a right angle, that is, 
 one containing 90 of arc. 
 Now, as the chord (A F) is 
 cut in the middle by the 
 bisecting radius (Z B), the 
 two lines always cross at 
 right angles (at B), and the 
 resulting triangle (A B Z) is 
 a right-angled one. The 
 result of one of the angles 
 being invariable is that part 
 of the labour is saved, as the 
 calculations are confined to 
 the other two angles. All 
 
 books on trigonometry have tables giving the length of sines, 
 etc., for every degree and fraction of a degree. 
 
 MEASURING INACCESSIBLE DISTANCES 
 
 The advantage of a right-angled triangle is shown in the fol- 
 lowing problem, which is something similar to one given in the 
 preceding chapter : 
 
 BASE 
 
 YDS'. 
 
 FIG. 20. MEASURING WIDTH OF 
 RIVER 
 
44 HOW TO KNOW THE STARRY HEAVENS 
 
 A surveyor wishes to measure the width of a river without 
 crossing to the other side (see Figure 20). 
 
 First he measures off, on his own side of the river, a base-line 
 (A B) 10 yards long. He stands at one end (B) of his base- 
 line, and points his instrument at the other end of it (A). He 
 then turns the instrument one quarter round (90 of arc), and 
 selects an object (Z) on the opposite bank of the river. Having 
 made a note of the number of degrees he has turned the instru- 
 ment (90), he goes over to the other end (A) of the base-line 
 and repeats the operations. He will find that he will not have 
 to turn his instrument so far around to make it point to the 
 object selected (Z). 
 
 Let us suppose that he has to turn it only 89. The two 
 angles at the base will then together equal 179. Now, as the 
 three angles of a triangle, added together, always equal two 
 right angles (180), it is obvious that the opposite angle (Z) 
 must be just 1. 
 
 The problem then stands as follows : 
 
 As the sine of 1 (angle Z) 
 Is to the sine of 89 (angle A), 
 So is 10 yards (length of base A B) 
 To the perpendicular Z B (or Y). 
 
 After obtaining the length of the sines of 1 and 89 (which 
 are given in all books on trigonometry), the problem is solved 
 as follows : 
 
 As 01745 is to 99985, so is 10 yards to the answer, 573 yards, 
 
 which is the width of the river as exactly as it can be found 
 with five-place logarithms. 
 
 PARALLAX 
 
 The angle (Z) opposite the base of such a triangle is called 
 by surveyors and astronomers the parallax of the distant object. 
 The further off the object is, the smaller becomes its parallax. 
 
PROBLEMS IN CELESTIAL MEASUREMENTS 45 
 
 The longer the base from which it is measured, the larger 
 becomes the parallax. 1 
 
 In the problem just considered it is obvious that if the object 
 Z is exactly west of the observer at B, it will no longer be ex- 
 actly west of him when he goes to A. It will be a little to the 
 south of west. It is also obvious that the amount of its displace- 
 ment will depend on its distance from him. The farther off the 
 object is, the less it is displaced when he goes from one end of 
 the base to the other. In other words, as stated before, the 
 more distant the object is, the smaller becomes its parallax. If it 
 is a very long way off, it may appear to be exactly west from both 
 ends of the base-line. In this case it will be necessary to greatly 
 lengthen the base-line in order to measure the distance of the 
 object. 
 
 The word " parallax " is rather a hard one to remember. But 
 astronomers can simplify matters when referring to the Sun's 
 parallax by calling it the " mean equatorial long horizontal solar 
 parallax." This is a useful thing to know. 
 
 A few examples of how astronomers utilize these principles 
 will conclude this chapter, which some may consider to be dryer 
 than a California summer, and more uninteresting than a 
 Baedeker's guide-book to one who never travels. 
 
 MEASURING THE MOON'S DISTANCE 
 
 We will of course start with the problem of finding the Moon's 
 distance from the Earth. 
 
 In Figure 21 the large circle represents a section of the Earth 
 through the two poles of rotation. The small circle in the dis- 
 tance represents the Moon. B and L are the two stations at the 
 ends of the measured base-line B L. We will imagine that they 
 are 4,000 miles apart, and that they are both on the same meri- 
 dian and at the same distance from the equator, which lies 
 between them. 
 
 1 " Parallax may be defined, generally, as the change produced in the apparent 
 place of an object when it is viewed from a point other than that of reference." - 
 ENCY. BRIT., Parallax. 
 
46 HOW TO KNOW THE STARRY HEAVENS 
 
 Let us suppose that, to the observer at L, the Moon's centre is 
 exactly on the celestial equator, and is therefore exactly 90 from 
 the south pole (as well as from the north pole). 
 
 Then, to the observer at B, the Moon's centre will be found to 
 be 57 minutes of arc (nearly 1) south of the equator. That is 
 to say, it will be only 89 3' from the south pole, of which the 
 position is known even when it is out of sight. In the triangle 
 B L M, therefore, the angles B and L lack 57' of making two 
 
 FIG. 21. MEASURING DISTANCE OF MOON 
 
 right angles (180). This 57' is evidently the size of the other 
 angle M. 
 
 We have now a problem absolutely identical in principle with 
 the preceding one, which dealt with the width of a river. It 
 stands as follows: 
 
 As the sine of 51' (the angle M) 
 
 Is to the sine of 89 3' (the angle B), 
 
 So is 4,000 miles (the length of base B L) 
 
 To the perpendicular L M. 
 
 The problem is easily solved with almost the same figures as 
 in that dealing with the width of the river. 
 
 As 01658 is to 99986, so is 4,000 miles to 240,000 miles, 
 
 which is the approximate distance of the Moon at the time when 
 the angles were measured. 1 
 
 1 The above problem has been simplified as much as possible, so that the prin- 
 ciple may be readily grasped. As a matter of fact, the two ends of the base-line 
 
PROBLEMS IN CELESTIAL MEASUREMENTS 47 
 
 For convenience of comparison, all results are reduced to fit a 
 right-angled triangle having a base-line equal to the radius, or 
 semi-diameter, of the Earth at the equator. The parallax is 
 then known as the horizontal equatorial parallax. 
 
 The distances of Mars and Eros are measured in the same 
 way as that of the Moon. But in the case of the Sun the 
 results have to be obtained by taking advantage of a transit of 
 
 Y 
 
 FIG. 22. ARC OF CIRCLE 
 
 Venus, or by some other indirect method. The principles and 
 results are, however, the same. 
 
 ARC PROBLEMS 
 
 The five following problems are worked out by means of two 
 radii and the enclosed arc (see Figure 22). The observer is 
 supposed to be at Z. 
 
 PROBLEM I. Given the angular diameter of Sun or Moon, 
 32' of arc (=1920" of arc), as seen from the Earth, find their 
 distances from us in terms of their own diameter A B (= 1). 
 
 are never exactly on the same meridian. Nor are they ever exactly the same dis- 
 tance north and south of the equator. And the distance required is not from the 
 Moon to the station L, but from the centre of the Moon to the centre of the Earth. 
 Quite a number of corrections and precautions have to be taken to give trust- 
 worthy results. But they need not be given here. It is sufficient if the principle 
 of the problem is thoroughly understood. 
 
48 HOW TO KNOW THE STARRY HEAVENS 
 
 X 20fi 265" 
 
 2 A B = Y. Therefore l J 2(r A B = 107 A B. 
 
 [NOTE. For meaning of letters see the table at page 40.] 
 
 So that the distances of the Sun and Moon from the Earth are 
 both alike in terms of their diameters ; that is to say, the dis- 
 tance of each one of them is 107 times as great as its actual 
 diameter, whatever that may be. 
 
 This problem does not tell us how far they are from us or how 
 large they are. It merely proves that if the Sun (or Moon) is a 
 mile across, then it is 107 miles away from us ; while if it is 
 1,000,000 miles across, then it is 107,000,000 miles away. 
 
 PROBLEM II. Given the real distance of the Sun, 92,790,000 
 miles, and its angular diameter, 32' of arc (=1,920"), find its 
 real diameter in miles. 
 
 MILE$ MILKS 
 
 Z 1 920 
 
 ^ Y = A B. Therefore ^265 92 > 790 > 000 = 863,727 
 
 The following form of this problem may perhaps be better 
 understood : 
 
 As X is to Z, so is Y to A B. 
 
 Worked out, this is as follows : 
 
 MILKS MILES 
 
 As 206,265" : 1,920" : : 92,790,000 : 863,727 
 
 PROBLEM III. Given the real distance of the Moon, 239,000 
 miles, and its angular diameter, 31' 6" (= 1,866"), find its real 
 diameter in miles. 
 
 This is a similar problem to the preceding one. 
 
 MILES MILES 
 
 rj 1 Q A A 
 
 = Y = A B. Therefore 2^265 239 > 000 = 2 > 162 
 Or, by the " rule of three " : 
 
 MILES MILES 
 
 As 206,265" : 1,866" : : 239,000 : 2,162 
 
PROBLEMS IN CELESTIAL MEASUREMENTS 49 
 
 PROBLEM IV. Given the real diameter of the Sun, 863,727 
 miles, and its angular diameter 32' ( 1,920"), find its real dis- 
 tance in miles. 
 
 It will be seen that this is the reverse of Problem II. 
 
 MILES MILES 
 
 X 206,265 
 
 ~ A B = Y. Therefore 863,727 = 92,790,000 
 
 Or, as before : 
 
 MILES MILKS 
 
 As 1,920" : 206,265" : : 863,727 : 92,790,000 
 
 PROBLEM V. Given the real diameter of the Moon, 2,162 
 miles, and its angular diameter, 31' 6" (= 1,866"), find its real 
 distance in miles. 
 
 It will be seen that this is the reverse of Problem III. It is 
 worked the same as Problem IV. 
 
 MILES MILES 
 
 ^A B = Y. Therefore ^f|fjf 2,162 = 239,000 
 
 SINE PROBLEMS 
 
 The following problems are worked out by means of a right- 
 angled triangle constructed of two radii and the sine (or half- 
 chord) of the enclosed angle (see Figure 23 ; lettering same as 
 before). 
 
 PROBLEM VI. Given the Sun's distance, 92,790,000 miles, 
 and angular semi-diameter 16' (= 960"), find its real semi- 
 diameter in miles. 
 
 This is like Problem II, except that the semi-diameter is used 
 instead of the diameter. 
 
 MILKS MILES 
 
 Z 960" 
 
 Y Y = A B. Therefore 9nr 9r - 92,790,000 = 431,863 
 
 .A. ^UDj^OiJ 
 
 PROBLEM VII. Given the Moon's distance, 239,000 miles, 
 and its angular semi-diameter, 15' 33" (= 933"), find its real 
 semi-diameter in miles. 
 
 4 
 
50 HOW TO KNOW THE STARRY HEAVENS 
 
 This is like Problem III, but uses the semi-diameter instead 
 of the diameter. 
 
 MILKS MILES 
 
 Z 933" 
 
 Y = A B. Therefore // 239,000 = 1,081 
 
 FIG. 23. SINE OF ANGLE 
 
 In all the following problems the observers are supposed to be 
 at A and B. Z is supposed to be the centre of the celestial body 
 under observation. 
 
 PROBLEM VIII. Given the Sun's parallax, 8.81", and the 
 Earth's semi-diameter, 3,963 miles, find the Sun's distance in 
 miles. 
 
PROBLEMS IN CELESTIAL MEASUREMENTS 51 
 
 All solar and planetary parallaxes are for convenience reduced 
 to fit the semi-diameter of the Earth. This is here represented 
 by A B, and the parallax by the opposite angle Z. 
 
 MILES MILKS 
 
 X 206 265" 
 
 - A B = Y. Therefore 8 ' 8]// 3,963 = 92,790,000 
 
 PROBLEM IX. Given the Moon's parallax, 57' (= 3,420'% 
 and the Earth's semi-diameter, 3,963 miles, find the Moon's dis- 
 tance in miles. 
 
 This is a similar problem to the preceding one. 
 
 MILES MILES 
 
 X 206,265" 
 
 2~ A B = Y. Therefore 3 ^ 2Q , 3,963 = 239,000 
 
 Here is the same problem worked by logarithms, which must 
 be obtained from published tables of logarithms : 
 
 As the sine of 57' (angle Z) 8.21958 
 Is to base 3,963 miles (A B) 3.59802 
 So is sine of 89 3' (angle A) 9.99994 
 
 13.59796 
 8.21958 
 
 To perpendicular (Z B) 5.37838 = 239,000 miles 
 
 [NOTE. In small angles Z B = Y.] 
 
 PROBLEM X. Given the Sun's distance, 92,790,000 miles, and 
 the Earth's semi-diameter, 3,963 miles, find the Sun's parallax. 
 This is the reverse of Problem VIII. 
 
 4j? X = Z. Therefore ^fg^O 206 > 265 " = 8 ' 81 
 
 PROBLEM XI. Given the Moon's distance, 239,000 miles, and 
 
 the Earth's semi-diameter, 3,963 miles, find the Moon's parallax. 
 
 This is the reverse of Problem IX, and similar to Problem X, 
 
52 HOW TO KNOW THE STARRY HEAVENS 
 
 A B 3,963 
 
 ~~ X = Z. Therefore 206 > 265 " = 57 ' 
 
 [If it is not too late, I would here suggest that those who do 
 not like Mathematics would do well to " skip " the foregoing 
 chapter.] 
 
FIG. 24. SUN, SHOWING SPOTS AND FACUL^C 
 Photographed at Greenwich Observatory, Feb. 13, 1892. 
 
V 
 
CHAPTER V 
 
 THE CHARIOT OF IMAGINATION 
 
 " Before their eyes in sudden view appear 
 The secrets of the hoary deep ; a dark 
 Illimitable ocean, without bound, 
 
 Without dimension, where length, breadth, and height, 
 And time, and place, are lost." Milton, " Paradise Lost," Book IL 
 
 " Oh Deep, whose very silence stuns ! 
 Where Light is powerless to illume, 
 Lost in immensities of gloom, 
 That dwarf to motes the flaring suns ! " 
 
 G. Sterling, " The Testimony of the Suns." 
 
 A LONG JOURNEY 
 
 TO enable us to realise, to some extent, what position man 
 holds with reference to the Universe, let us leave our 
 Earth for a short time, and hasten away, in the Chariot of Im- 
 agination, to a point in space half-way between our Sun and 
 Alpha Centauri, the nearest of the other stars. 
 
 We will take with us a specially constructed chronometer, 
 made to indicate long periods of time ; a special cyclometer, made 
 to fit the wheels of our chariot ; and a number of other scientific 
 instruments which may prove useful in our celestial researches. 
 
 In order that we may not get lost or have any corners to turn, 
 we make our start from Cape Town, South Africa, in the night- 
 time, when the Moon is above the horizon and Alpha Centauri 
 is on the meridian. 
 
 As this may be the first time some of us have travelled through 
 space unaccompanied by Mother Earth, it will be well for us to 
 travel slowly, so that we can get a good view of our surroundings, 
 and at the same time avoid running into unnecessary danger. 
 We will therefore keep a firm hand on the lines, from the start, 
 
54 HOW TO KNOW THE STARRY HEAVENS 
 
 so as to prevent our imaginary steeds from running away with 
 us. On such a long journey the most satisfactory speed for us 
 to keep up will perhaps be that at which light travels, about 
 186,000 miles per second. 
 
 Everything being ready for our trip, the signal is given. " One, 
 two, three. Away we go I " 
 
 Before the words are fairly uttered, we find ourselves at the 
 Moon's distance and in the bright sunshine. By a curious 
 optical delusion we did not seem to move when the word was 
 given, but the moonlit Earth suddenly dropped from beneath 
 our feet. For a fraction of a second it appeared to swell, as dis- 
 tant lands and moonlit seas sprang above the horizon. Then 
 the Sun rose with a jerk, and the crescent Earth began to shrink 
 in size as its distance increased. 1 
 
 At the end of one minute the Earth is still plainly visible in 
 the bright sunlight, but the Moon is almost out of sight. In 
 five minutes nothing is to be seen of either of them. 
 
 For a time we are in the sunshine, but the light soon begins 
 to wane as we recede from the Sun and approach the confines of 
 the Solar System. 
 
 In four hours we are at the distance of Neptune, and the Sun 
 is not much more than a very brilliant star in the gathering 
 twilight. 
 
 Although the Sun continues to dwindle in size as we leave it 
 behind, it shines continuously, there being no horizon to hide it 
 from us. After we have been a month on our journey, as shown 
 by our chronometer, it is practically nothing but a bright star 
 among the multitude of stars by which we are entirely sur- 
 rounded. 
 
 By this time we have discovered that we have left behind 
 many things which seemed very real and important while we 
 remained on terra firma. 
 
 There is now no north or south, no up or down. The star- 
 
 1 For the above effects to be produced, we should really have to travel slower 
 than light, otherwise nothing would be visible in our rear. Every impossible 
 illustration has its discrepancies, as Artemus Ward would say, 
 
THE CHARIOT OF IMAGINATION 55 
 
 sphere has ceased to turn on its axis, so that there are no pole 
 stars. The wandering planets have long- since disappeared. 
 There is no Sun or Moon. Day and night have ceased to roll. 
 Seed-time and harvest come no more. Summer and winter are 
 meaningless terms. Aside from our chronometer, months, years, 
 and centuries have now no significance. Away from our Earth, 
 geological periods trouble the mind no more. 
 
 We keep on in a straight line, at the same speed, for two long 
 years> as registered by our chronometer. The star which used 
 to be our Sun is now directly behind us, but has long ceased to 
 be conspicuous for either size or brilliancy. 
 
 And now the special cyclometer which we brought along tells 
 us that we are at last nearing our goal, the half-way house 
 between the centre of our system and the nearest outside star. 
 
 AMONG THE STARS 
 
 Arrived at our lonely destination, let us check our imaginary 
 horses, hitch them to an imaginary post, and take a survey of 
 our actual surroundings. 
 
 As we did not bring our Earth along with us, our view is not 
 impeded in a downward direction. We can see clearly below 
 and around, as well as above. 
 
 What is there to be seen from our point of vantage ? 
 
 One of the first things to attract our attention is that we do 
 not appear to have any immediate surroundings. We are soli- 
 tary in empty space. 
 
 Instead of being surrounded by houses and trees lighted up 
 by the dazzling glare of a hot Sun, or half-revealed by the soft 
 glamour of a pale Moon, we find ourselves alone in the midst of 
 perpetual starlight, which no Sun or Moon ever interferes with. 
 
 There is no cloud or fog, for all is cold, clear, still, dark, and 
 apparently void. 
 
 But in the far distance there are plenty of objects to make up 
 for an unoccupied " fore-space." 
 
 The " back-space " of sky is all more or less crowded with 
 stars. To the naked eye there are about 6,000 visible. These 
 
56 HOW TO KNOW THE STARRY HEAVENS 
 
 are distributed promiscuously in irregular clusters and hap- 
 hazard groups, without any regard to pattern or symmetry. 
 
 But besides these groups of stars there are, in some parts of 
 the sky, great irregular streaks of nebulous haze. One set of 
 these hazy streaks is so long-drawn-out that its snake-like folds 
 and spirals almost form a girdle around us. 
 
 The unaided eye cannot pierce this haze, and without further 
 insight even the imagination itself is unable to invent a reason- 
 able explanation of this " Milky Way." 
 
 THE EYES OF SCIENCE 
 
 Let us now imagine that our eyes improve in light-grasping 
 power till they equal the most powerful telescopes in existence. 
 What is there now to be seen from our point of vantage ? 
 
 The result is something startling astounding overwhelm- 
 ing. The scene is grand beyond the power of language to 
 describe magnificent beyond the ability of the mind to 
 conceive. 
 
 The Earth we came from is still invisible lost in the depths 
 of infinite space. 
 
 The Sun that ruled our Solar System with such undisputed 
 sway is visible still, but it rules no more. It was a SUN that 
 reigned supreme among a thousand little twinkling stars. It is 
 now but a star among a hundred million fellow-stars. 
 
 But though we have lost our Earth and its Sun, we have 
 gained more than we have lost. For we have revealed before 
 us a goodly portion of the Universe itself. And though we 
 see no more a panoramic succession of days and nights, seasons 
 and years, we do not miss these earthly phenomena. For in their 
 stead we see the stately evolutions of countless squadrons of 
 heavenly orbs, circling through never-ending time in an ocean of 
 limitless space. 
 
 We have here no need of the Sun, neither of the Moon ; for 
 the everlasting glory of the Great Cosmos enlightens us, and the 
 iridescent mantle of Universal Nature enfolds us. 
 
FIG. 26. - SOLAH FLAMES AND COHONA, AS SEEN DUKIXG ECLIPSK OF 
 MAY 28, 1900 
 
 By Burckhardt. (From Comstock's " Text-book of Astronomy,' 11 published by 
 Messrs. D. Applelon & Co.) 
 
VTBRAT7 
 
 or THE 
 
 UNIVERSITY 
 
 or 
 
 JzALirCi* 
 
THE CHARIOT OF IMAGINATION 57 
 
 On every side, above and below, we see stars by the million. 
 They are strewn through endless space like the blinding snow- 
 flakes of a Western blizzard. They are as thick as the leaves 
 of an earthly forest. 
 
 And we know that each and every star is a SUN, more or less 
 like unto our Sun. Many, if not all of them, have subject 
 worlds revolving around them like the planets which compose 
 our own system. 
 
 Gazing on such a picture, words are not equal to express our 
 sense of littleness. As the poet says : 
 
 This is a wondrous sight, 
 
 And mocks all human grandeur." 
 
 Contemplating the star-strewn heavens, the deist may well 
 exclaim with one of old 
 
 " When I contemplate the heavens, 
 
 The work of thy hands, 
 The Moon and the stars, 
 
 That thou hast disposed, 
 What is Man, 
 
 That thou shouldst remember him, 
 The Son of Man, 
 That' thou shouldst watch over him ? " 
 
 Ps. viii, 3 (Segond and Diodati). 
 
 The poet Shelley has beautifully described such a scene. He 
 
 says: 
 
 " Below lay stretched the Universe. 
 There, far as the remotest line 
 That bounds imagination's flight 
 Countless and unending orbs 
 In mazy motion intermingled, 
 Yet each fulfilled immutably 
 Eternal Nature's law. 
 Above, below, around, 
 The circling systems formed 
 A wilderness of harmony ; 
 Each with undeviating aim, 
 In eloquent silence, through the depths of space, 
 Pursued its wondrous way." 
 
58 HOW TO KNOW THE STARRY HEAVENS 
 
 All around us is 
 
 " the abyss of an immense concave, 
 Radiant with million constellations, tinged 
 With shades of infinite colour." 
 
 A RUSH THROUGH SPACE 
 
 After having gazed for a while at the wonderful scene around 
 us? a scene so magnificent that even the words of a Saul among 
 the poets fail to give any adequate conception of it, we un- 
 hitch our imaginary horses from our imaginary post, turn our 
 Chariot of Imagination toward one of the stars, and rapidly 
 approach it. 
 
 ONLY A STAR 
 
 The star we selected for examination was a very ordinary- 
 looking star. It was far smaller than many of its neigh- 
 bours, and did [not shine anything like so brightly as some of 
 them. 
 
 But now that we have arrived in its vicinity it has grown in 
 size and brilliancy till all the other stars have either gone out 
 of sight or become faint dots of light, just perceptible in the 
 growing daylight. It has, indeed, become so overwhelmingly 
 radiant that we have to put on dark spectacles to enable us to 
 use our eyes without being blinded. 
 
 Let us stop and watch this star for a thousand years or so, and 
 see what changes are going on around it as it drifts along in the 
 ocean of space. 
 
 The star itself is a round yellowish-white ball more than 
 800,000 miles in diameter. Its glowing surface, or photosphere, 
 is one vast mass of shining cloud, which has the appearance of 
 being dotted all over with still brighter specks, like rice-grains. 
 This cloud-like photosphere is composed of calcium and other 
 elements, kept in a white-hot state by an unimaginably intense 
 heat rising from the gaseous interior of the star. The white 
 photosphere radiates into outer space about four times as much 
 
FIG. 25. GROUP OF SUNSPOTS 
 
 Photographed with the Greenwich 26-inch Refractor, on Sept. 11, 1898. The largest 
 nucleus was about 24,000 miles long. 
 
 FIG. 27. ERUPTIVE PROMINENCES 
 
 Eclipse of May 28, 1900 (Barnard and Ritchey). The largest of these " hydrogen flames ' 
 is 60,000 miles high. 
 
THE CHARIOT OF IMAGINATION 59 
 
 light and heat as an electric arc-light of the same size would 
 do. 1 
 
 There are some peculiar features about this star as seen from 
 a short distance. Physical and mechanical reactions of incon- 
 ceivable violence are taking place beneath its surface. In some 
 places they give rise to what look like volcanic eruptions on a 
 vast and awe-inspiring scale. To an outside observer these 
 centres of eruption appear like great irregular black blotches 
 scattered about the white cloud-like photosphere. They are sur- 
 rounded by plume-like shadows or penumbrae. By watching 
 these black spots we soon find that the star is spinning slowly 
 around on its axis, completing a revolution in about twenty-seven 
 of our days. 
 
 The light given out by this white photosphere is so dazzling 
 that little more can be made out, even with dark glasses. We will 
 therefore use special instruments to turn it aside, so as to enable 
 us to see more clearly what other phenomena are going on in 
 the neighbourhood. 
 
 We can now see that the entire body of the star is buried 
 under a shoreless ocean of transparent fire of a scarlet hue. This 
 fiery ocean, or atmosphere, is everywhere from 4,000 to 5,000 
 miles deep, and appears to rest on the white cloud-like photo- 
 sphere already described. The storm-tossed surface of this fiery 
 ocean bristles at every point with huge ascending " flames " of the 
 same scarlet colour. Those on our side of the star are not readily 
 examined, on account of the brilliancy of the photosphere, but 
 those around the edges are plainly visible with proper apparatus. 
 Most of them are about 8,000 or 10,000 miles high, but here and 
 there are larger ones, reaching up 60,000 miles or more. These 
 huge ruddy flames assume a great variety of forms. They re- 
 semble jets of steam, fireworks, fountains, ocean breakers, cy- 
 clones, torpedo explosions, and volcanic eruptions, all on a scale 
 of inconceivable magnitude.' 
 
 1 By the way, an electric arc-light the size of a pin's head cannot be examined 
 without the aid of dark glasses, it is so overwhelmingly bright. And its tempera- 
 ture is 6,300 F. But this star is nearly a million miles through and is very 
 much brighter and hotter ! 
 
60 HOW TO KNOW THE STARRY HEAVENS 
 
 As we watch this stormy scene it reminds us of a wind-tossed 
 prairie fire as seen by night through a telescope on our little 
 Earth. The flames rise and dart forward, fall back and roll 
 over ; bend, twist, and curl ; embrace, wrestle, and fling them- 
 selves apart. Before our eyes they change into all imaginable 
 shapes, so that we find it almost impossible to realise their over- 
 whelming magnitudes and the terrific speed of their varied 
 movements. Every once in a while we see great ruddy blasts 
 of fiery gas rise from the surface with tremendous force and in- 
 conceivable velocity. Some of these flaming jets shoot up at 
 the rate of 250 miles in a second of time, and reach an altitude 
 of 200,000 or 300,000 miles. They then branch out in tree-like 
 clouds, and finally break up and scatter in a shower of solar 
 fireworks. The very largest of these flames are long enough to 
 be wrapped sixteen times around our Earth. 
 
 These ruddy flames (though cooler than the white photosphere 
 beneath them) are so inconceivably hot that they do not burn. 
 In fact they would " unburn " any burnt substance which might 
 fall into them, even if it should happen to be as large and heavy 
 as our Earth. No chemical compound could exist for a second 
 in such a terrific heat. No element, even, could remain there in 
 a solid or liquid state. The flames are composed of incandescent 
 hydrogen and helium, while the ruddy sea from which they rise 
 contains also iron, magnesium, sodium, and other metals, all 
 vaporised by the tremendous heat. 
 
 This scarlet ocean of fiery gas is termed a sierra or chromo- 
 sphere. The flames which rise from it are known as prom- 
 inences. 
 
 Outside of all these is a corona, consisting of great hazy radi- 
 ating streaks of some light and apparently gaseous substance, 
 extending a million miles or more into outer space. Owing to 
 their distribution, and to the fact that the star is spinning 
 around on its axis, these " repulsive " streaks are not straight, 
 but slightly curved, and have a very peculiar plume-like 
 appearance. 
 
FIG. 28. SOLAR CORONA. ECLIPSE OF MAY 28, 1900 
 Photographed by Chabot-Dolbeer Eclipse Expedition. 
 
 FIG. 29. XOKTH POLAR STREAMERS OF THE CORONA. MAY 28, 1900 
 Crocker Eclipse Expedition. 
 

 
THE CHARIOT OF IMAGINATION 61 
 
 OFFSPRING OF A STAR 
 
 As we watch the eruptive " freckles " which come and go every 
 eleven years on the surface of the star, we notice a number of 
 small balls sweeping around and around it, all going in the same 
 general direction. These are all worlds, more or less like the 
 one on which we used to live before we began our heavenly 
 wanderings. Let us watch them as they eddy around the star, 
 like moths circling around a lantern in the dark. 
 
 THREE CLASSES OF WORLDS 
 
 The most noticeable of them are four outer or superior planets. 
 These are so much larger and more powerful than the rest that 
 they form a kind of aristocracy, subject only to the reigning 
 monarch in the centre. They do not appear to shine by their 
 own light, yet they are still puffed up with heat. They have 
 followers, or satellites, of their own, so that they are something 
 like petty rulers subject to a higher power. 
 
 Four very insignificant planets form an inner or inferior family 
 of worlds. They give out neither light nor heat of their own, 
 so they may be called terrestrial planets. They are much more 
 under the control of the central ruler, but at the same time may 
 be said to bask in the sunshine of his favour. They are, in fact, 
 the bourgeoisie or well-to-do citizens of the monarchy. 
 
 Between these two families of worlds there is a whole regiment 
 of almost invisible planets, which may be called asteroids, from 
 their small size and star-like appearance. They are the pro- 
 letarians, the working-class of the monarchy, subject not only to 
 the legitimate rule of the sovereign, but also to the overbearing 
 authority of the aristocracy on the one hand, and to the petty 
 bossing of the bourgeoisie on the other. They are in fact " be- 
 tween the upper and the nether millstone." The result is shown 
 by the steep, elongated, and apparently dangerous paths some of 
 them are compelled to follow, with neither hope of relief nor 
 promise of reward. 
 
62 HOW TO KNOW THE STARRY HEAVENS 
 
 Although the four outer planets appear to us to be very large, 
 yet they are extremely small compared with the central star, 
 which is 560 times as large and 745 times as heavy as all the 
 planets put together. 
 
 Let us now examine some of the individuals composing these 
 three classes of worlds, beginning with the inner planets. 
 
 THE INNER PLANETS 
 
 The one which is nearest to the central star is small, and very 
 little can be seen of it. The second is larger, with a dense atmos- 
 phere which somewhat obscures the planet itself. Both of these 
 little wgrlds move at a speed many times greater than that of a 
 cannon-ball, yet it takes them several months to go once around 
 the central star. 
 
 PLANET NUMBER THREE 
 
 Planet No. 3 is slightly larger than No. 2, its diameter being 
 nearly 8,000 miles. It is, indeed, the largest of the inner family 
 of worlds. It is more than 90,000,000 miles from the star 
 around which it is sweeping. It takes just a year to complete a 
 revolution, although it travels at the astounding rate of eighteen 
 miles in a second of time. 
 
 On looking more closely at this world, another and smaller 
 planet is seen buzzing around and around it. This is a moon or 
 satellite, which goes around its primary in the same direction as 
 that is going around the central star. It is a little over 2,000 
 miles thick, so that the principal planet is about fifty times as 
 large as its companion. 
 
 A more attentive look at No. 3 reveals several peculiarities. 
 It is spinning around like a top, turning in the same gen- 
 eral direction as that in which it goes around the central star. 
 The two points which form its poles of rotation are white, as 
 though covered with ice and snow. Its surface is variegated, 
 and is evidently composed of land and water. There are con- 
 tinents, oceans, islands, seas, lakes, rivers, and mountains. The 
 land appears to be more or less covered by vegetation of a green 
 
FIG. 30. MERCURY-, THE FIRST PLANET 
 By Schiaparelli. (From Todd's " Stars and Telescopes," published by Messrs. Little, Brown, <fe Co. ) 
 
 FIG. 31. VENUS, THE SECOND PLANET 
 
 By Autoniadi. (From Comstock's " Text-book of Astronomy," published by 
 Messrs. D. Appleton & Co.) 
 
 FIG. 33. MARS, THE FOURTH PLANET 
 
 By Knobel. (From Todd's " Stars and Telescopes," published by Messrs. Little, Brown, & Co.) 
 
THE CHARIOT OF IMAGINATION 63 
 
 colour, while portions of the surface are hidden by drifting 
 clouds. Altogether, it looks like a world which might be in- 
 habited. Although small compared with the giant planets 
 which circle on the outskirts of the system, yet the diversity of 
 its surface, and the terrific speed with which it circles around 
 
 FIG. 32. TERRA, THE THIRD PLANET, AND ITS SATELLITE 
 OR MOON 
 
 the central star, entitle it to the archangel's song as given in the 
 prologue to Goethe's " Faust " : 
 
 " And swift and swift beyond conceiving, 
 The splendour of the World goes round, 
 Day's Eden-brightness still relieving 
 The awful night's intense profound. 
 The ocean tides in foam are breaking, 
 Against the rock's deep bases hurled, 
 And both, the spheric race partaking, 
 Eternal, swift, are onward whirled." 
 
 Bayard Taylor's Translation. 
 
 PLANET NUMBER FOUR 
 
 Planet No. 4 has a ruddy appearance. It is considerably 
 smaller than the one just described, its diameter being only 
 about 4,000 miles. It has two very small moons circling around 
 it. Like No. 3, it has the appearance of being in a condition 
 suitable for sustaining life. It appears to have an atmosphere, 
 clouds, and variegated continents. Its poles, too, are white, as 
 though covered by ice and snow. 
 
64 HOW TO KNOW THE STARRY HEAVENS 
 
 PLANETOIDS 
 
 After Planet No. 4 there is a great crowd of little worlds 
 which are too small to be of much importance. The most in- 
 teresting thing about them is the speculation whether or not 
 
 they are the fragments of 
 two larger planets that 
 have unsuccessfully tried 
 to occupy the same space 
 MA us at the same time. 
 
 A GIANT PLANET 
 
 Outside this swarm of 
 pigmy worlds there circles 
 and spins a gigantic ball 
 about 1,200 times the size 
 of Planet No. 3. It is not 
 only the largest of all the 
 planets, but is larger than 
 all the rest of them put 
 together. It has a dense 
 impenetrable atmosphere, 
 with bands of clouds around 
 its equatorial regions. 
 There are five moons sweep- 
 ing around it, some of them 
 being of considerable size, 
 far larger than any of the 
 planetoids just mentioned. 
 The main planet, although 
 so large, spins around in a little less than ten hours. This rapid 
 rotation has made its equator bulge out, so that the cloud-like 
 surface of the planet is something the shape of an orange. 
 
 A RINGED PLANET 
 
 After this there is another big globe, only second in size to 
 the one just described. But this one is surrounded by such an 
 
 FIG. 34. RELATIVE SIZES OF EARTH 
 AND MARS 
 
FIG. 35. THE ZONE OF ASTEROIDS BETWEEN MARS AND JUPITEU 
 
 FIG. 36. JUPITER, THE LARGEST I'LANET 
 Showing great red spot and transit of satellite. Lick Observatory. 
 
THE CHARIOT OF IMAGINATION 
 
 65 
 
 astonishing arrangement that one cannot help rubbing his eyes 
 to see if they have not deceived him. It looks as though there 
 was a large round thin disc, with a good-sized round hole in the 
 middle. In the centre of this hole is the planet itself, not quite 
 large enough to fill the hole, and not visibly connected with 
 the disc. On a closer view the disc is seen to have a series of 
 gaps and thin places in it, 
 extending all around, as 
 though it were really a 
 series of discs all lying in 
 the same plane, and hav- 
 ing the planet for a centre, 
 but differing in size and 
 texture. If these concen- 
 tric discs or rings were 
 visibly supported by the 
 planet, they would not 
 seem so extraordinary, 
 but the closest scrutiny 
 fails to discover any phy- 
 sical connection with the 
 globe they surround. The 
 only explanation that 
 seems able to account for 
 their continued existence 
 is that they are composed 
 of countless millions of 
 tiny satellites crowded 
 
 together, and revolving around the planet in the same direction. 1 
 Farther off than these rings there are nine satellites, or 
 moons, revolving at different distances from the planet. The 
 whole family group seems almost a miniature of the solar sys- 
 tem of which it forms a part, with a hint thrown in as to how 
 that system originated. 
 
 1 If they were farther from the planet, they would probably coalesce into 
 regular satellites, but as it is, the tidal action of the huge planet prevents 
 this. 5 
 
 FIG. 37. RELATIVE SIZES OF JUPITER 
 AND EAKTH 
 
66 HOW TO KNOW THE STARRY HEAVENS 
 
 TWO OUTER PLANETS 
 
 There are two more large planets outside the one just described. 
 But they are not so remarkable in appearance, and they are so far 
 from the central star that they are comparatively in the cold and 
 dark. The outside one is about 30 times as far off as Planet 
 No. 3, and is 125 times as large. It moves only a little 
 over three miles in a second of time, and, as it has a large 
 circuit to make, it takes 164 years to go once around the 
 
 central star. 
 
 It is interesting to 
 note that the combined 
 mass of the four out- 
 side planets just men- 
 tioned is about 220 
 times as great as the 
 combined mass of the 
 four inner planets, with 
 .all the visible planet- 
 oids thrown in. Also 
 that the same outside 
 planets together weigh 
 450 times as much as 
 No. 3 alone. If only 
 bulk and mass were 
 
 concerned, it would 'scarcely be worth while to mention the 
 inner planets at all, they are so insignificant. 
 
 SOLAR SYSTEM No. 3,141,592,653 
 
 It is hardly necessary to explain that the star we have been 
 examining, with its attendant worlds, forms our own Solar Sys- 
 tem. The insignificant little globe which I have called " Planet 
 No. 3 " is our own World, once regarded, by its reasoning inhab- 
 itants, as the whole Universe, with nothing outside but the 
 Realms of Chaos. 
 
 If we were to approach any one of the millions upon millions 
 of sovereign suns revealed by the telescope, we should in all 
 
 FIG. 
 
 ). RELATIVE SIZES OF SATURN 
 AND EARTH 
 
H 
 W 
 
 I I 
 
THE CHARIOT OF IMAGINATION 
 
 67 
 
 probability find it to be the centre of a family group more or 
 less similar to ours. Some systems are smaller, but others are 
 far larger, while many are more elaborate and democratic, with 
 two, three, four, a hundred, or a thousand suns circling around 
 their common centre of gravity. 
 
 FIG. 40. RELATIVE SIZES OF NEPTUNE 
 AND EARTH 
 
CHAPTER VI 
 
 DIMENSIONS OE THE UNIVERSE 
 
 "Firstly, we may inquire as to the extent of the Universe of stars. Are the 
 latter scattered through infinite space, so that those we see are merely that por- 
 tion of an infinite collection which happens to be within reach of our telescopes, 
 or are all the stars contained within a certain limited space ? " 
 
 Prof. Simon Newcorrib. 
 
 PLANETARY DISTANCES 
 
 IN the third and fourth chapters I tried to show the principles 
 by which the distances of the heavenly bodies are measured. 
 It was there stated that the Moon's distance from us is about 
 239,000 miles, and that the Sun is about 388 times as far off. 
 The most reliable measurements make the Earth's distance from 
 the Sun 92,790,000 miles. Neptune, the farthest planet in our 
 system, is about 30 times as far from the Sun as we are, so that 
 it is 2,790,000,000 miles away. 
 
 This distance is so tremendous that it is unthinkable. The 
 mind of man cannot grasp it. It is as utterly beyond our com- 
 prehension as infinity itself. Yet when we turn to the stars we 
 find that this vast distance is as nothing when compared to the 
 intervals separating one star from another. 
 
 STELLAR DISTANCES 
 
 It has been ascertained that the nearest star outside our sys- 
 tem is something like 9,000 times as far off as Neptune, whose 
 distance seemed so amazingly great. Alpha Centauri, the nearest 
 of all the stars, is distant from us about 25,000,000,000,000 
 miles. Its light, travelling at the rate of 186,000 miles in a 
 second of time, takes more than four years to come to us. 
 
 The brightest star in all the sky is known as Sirius, or the 
 Dog Star. It is twice as far from us as Alpha Centauri, and is 
 therefore more than eight "light-years " away. 
 
DIMENSIONS OF THE UNIVERSE 69 
 
 The distances of about sixty other stars, ranging up to sixty 
 light-years, have been more or less approximately ascertained. 
 All the others are too far off for our sounding-rods. They are out 
 of reach in the depths of space. All that we know for certain 
 concerning their distances is that none of them are less than 
 4,000,000 times as far from us as our Sun, which is nearly 
 93,000,000 miles away. 1 
 
 COMPARISONS 
 
 Now it is very easy to say that the nearest star outside our 
 system is 25,000,000,000,000 miles away, but it is not so easy 
 to realise what that distance is like. Let us try to do so by 
 means of some simple illustrations. 
 
 In the first place it is necessary to realise the proportionate 
 distances and dimensions of the members of our own Solar 
 System. 
 
 If we take a one-inch ball to represent our Earth, it will 
 require a nine-foot globe to represent the Sun. 
 
 Let us place this nine-foot globe on a level plain that has 
 just had the grass burnt off it, and set up wire circles (on posts) 
 to indicate the various planetary orbits. 
 
 The sizes of the planets and the distances of their orbits from 
 the central globe will be as follows : 
 
 PLANET 
 
 Mercury . 
 Venus 
 
 Earth . . 
 Mars . . 
 
 Asteroids 
 
 Jupiter . . 
 Saturn . 
 Uranus . 
 Neptune . 
 
 1 Investigations are now in progress which promise greatly to extend the list 
 of stars having a measurable parallax. It is possible that the distances of most of 
 the naked-eye, stars will be ascertained before many years have passed. 
 
 SIZE 
 
 DISTANCE 
 
 large pea . 
 
 127 yards 
 
 one-inch ball 
 
 235 " 
 
 one-inch ball 
 
 325 " 
 
 half-inch marble . 
 
 495 " 
 
 small seeds 
 
 676 " 
 1,385 " 
 
 eleven-inch globe 
 
 1 mile (nearly) 
 
 nine-inch globe . 
 
 If miles 
 
 four-inch globe . 
 
 3 " 
 
 five-inch globe . 
 
 5 '< 
 
70 HOW TO KNOW THE STARRY HEAVENS 
 
 On this scale our Moon will be represented by a pea moving 
 in a circle at a distance of 30 inches from the one-inch ball 
 representing the Earth. 
 
 The outside ring of Saturn will be 21 inches in diameter. 
 
 The orbit of Neptune will be 11 miles across, and will take 
 nearly 35 miles of wire to mark it out. 
 
 Let us now make arrangements with an electric light com- 
 pany to cover our nine- foot globe with a complete network of 
 electric lights, so close and compact that every part of the sur- 
 face will give off more light and heat than the brightest part of 
 an arc-light. We will then choose a dark yet clear night, and 
 turn on the current. 
 
 We shall find that all of our toy planets are more or less bril- 
 liantly illuminated on one side by the central light. But of 
 course the outer side of each " planet " will be dark and invis- 
 ible. Let us station ourselves just beneath the one-inch ball 
 which represents our Earth, and take a look around at our 
 miniature "solar system." 
 
 The overpowering effulgence of the nine-foot globe, 325 yards 
 away, makes it necessary for us to put up a shelter to protect us 
 from the light and heat. 
 
 Apart from our electric " sun," the most prominent object 
 visible from our position will be the quarter-inch ball which goes 
 around us at a distance of 30 inches. It will, in fact, look as large 
 as our nine-foot " sun," but will not be anything like as bright. 
 
 As the illuminated side of this imitation " moon " does not 
 always face us, it will show all the phases of the real Moon as 
 it goes around in its little orbit. 
 
 The first of our toy planets (that is, the one nearest to the 
 central globe) will be just visible to us when most favourably 
 placed. The second will shine very brightly when it is at a 
 large angle from our "sun." Both of these toy planets will 
 show lunar phases if examined with the help of a telescope. 
 
 The fourth " planet " (half an inch in diameter), will also be 
 very brilliant when at its nearest, 170 yards away. But at 
 other times it will be rather inconspicuous. 
 
FIG. 41. LICK OBSERVATORY ON MOUNT HAMILTON, CALIFORNIA 
 FIG. 42. MAIN ENTRANCE AND GREAT DOME, LICK OBSERVATORY 
 
DIMENSIONS OF THE UNIVERSE 71 
 
 The first and second of the large planets will also be tolerably 
 conspicuous, although a telescope will be necessary to show 
 details. 
 
 The two outside planets will not be visible at all without a 
 telescope. The farthest of them will not vary much in appear- 
 ance ; its distance at all parts of its orbit being something like 
 5 J miles away from us. 
 
 The nearest star will, on the same scale, be represented by an 
 electric globe, probably 12 feet across, at a distance of about 
 50,000 miles. Sirius will take a similar globe, nearly 30 feet in 
 diameter, about 100,000 miles away. The largest star visible 
 to us may probably be represented by a 100-foot globe, some- 
 where about 1,000,000 miles distant. 
 
 This illustration gives a fair idea of the comparative dimen- 
 sions and distances of the principal bodies forming our Solar 
 System, but fails to convey any definite idea of stellar distances. 
 Let us try some other illustrations. 
 
 A LOCOMOTIVE 
 
 We all know what it is to travel at the rate of 60 miles an 
 hour. At this rate it would take 17 J days and nights to travel 
 around our own world. 
 
 To reach the Moon, travelling at the same rate, it would take 
 166 days, or nearly half a year. 
 
 To reach the Sun, we should have to travel for 176 years. 
 
 To go around the Sun would take about 5 years. 
 
 To go from the Sun to Neptune, the farthest planet, would 
 take 5,000 years, and the railway fare, at one cent a mile, would 
 be nearly $28,000,000. This makes a railroad impracticable. 
 
 A CANNON-BALL 
 
 Now take a cannon-ball travelling at the rate of a mile in five 
 seconds. 
 
 It would go around the Earth in 36 hours, and would reach 
 the Moon in 14 days. 
 
72 HOW TO KNOW THE STARRY HEAVENS 
 
 To get to the Sun would take it 1 5 years, and it would require 
 5 months to go around it. To go from the Sun to Neptune, the 
 farthest planet, it would have to travel at the same speed for 
 415 years. 
 
 AN ARROW OF LIGHT 
 
 A wave of light travels at the enormous velocity of 186,000 
 miles in one second of time. So it would go around our Earth 
 more than seven times in a second. It would reach the Moon 
 in a second and a quarter. 
 
 It takes more than eight minutes for the Sun's light to reach 
 us, and over four hours for it to get to Neptune, the outside 
 planet in our own system. 
 
 At the same rate, 186,000 miles a second, it takes more than 
 four years for the light of the nearest star to reach us. 
 
 Sirius, the brightest star in the sky, is so far off that the light 
 which reaches us to-night has been eight and a half years on the 
 way. If it were to collide with another star now, we should not 
 see the flare-up for eight years and a half. 1 
 
 A PILE OF PAPER 
 
 Now, suppose that we had here a pile of thin paper, with as 
 many sheets in it as there are miles between us and the nearest 
 star. What would be the height of the pile, supposing that it 
 took 200 sheets to measure one inch in thickness ? 
 
 Those people who are naturally reasonable in their ideas and 
 moderate in their estimates might think that the pile would 
 probably be a hundred feet or so in thickness. Others, who are 
 naturally wild in their ideas and extravagant in their guesses, 
 would think that the pile might possibly be a mile thick. As a 
 matter of fact, it would reach up nearly 2,000,000 miles. More 
 exactly, its height would be 1,972,853 miles, 94% yards, and 8 
 inches. 
 
 1 The distance of Sirius is not less than that stated, but there is a possibility 
 that it is greater. 
 
FIG. 43. THE THIRTY-SIX-IXCH REFRACTOR AT LICK OBSERVATORY 
 
 The tube is 5G feet long and weighs several tons. It is equatorially mounted, with a 
 
 driving clock. The entire floor under the dome can be raised or 
 
 lowered 26 feet. It is shown half-way down. 
 
DIMENSIONS OF THE UNIVERSE 75 
 
 As this pile of paper is rather top-heavy, suppose we lay it 
 down on its side. Then it will go nearly 79 times round the 
 Earth. Yet every inch in this great pile of paper represents a 
 distance of 200 miles. The sheets would have to be placed a 
 mile apart before they would reach to the nearest star. 
 
 A STACK OF BLOOD DISCS 
 
 Perhaps a smaller illustration of the same kind may be more 
 within our mental grasp. 
 
 Human blood is an almost colourless fluid, crowded with very 
 small red discs or corpuscles. These discs are flat and coin- 
 shaped. They are so extremely minute that if they were piled 
 up one on the top of another, like a stack of coins, it would take 
 15,000 of them to reach one inch in height. 
 
 If we let each disc stand for one mile, then the height of the 
 pile representing the Moon's distance will be 16 inches. That 
 representing the Sun's distance will reach up 172 yards, and 
 Neptune's pile will be nearly three miles high. But the pile 
 which contains as many discs as there are miles between us and 
 the nearest star will be 26,000 miles in height. If it were laid 
 down on the ground it would go around the world. 
 
 VIOLET WAVES 
 
 The shortest light-waves which affect the eye are those which 
 produce the sensation of violet light. It takes 61,000 of these 
 waves to measure one inch. If a single wave stands for a mile, 
 then the distance of the Moon will be represented by 4 inches ; 
 of the Sun, by 42 yards ; of Neptune, by 1,250 yards ; and of 
 Alpha Centauri, by 6,400 miles. 
 
 Then we must remember that the vast majority of even naked- 
 eye stars are hundreds and thousands of times farther off than 
 the one we have been considering. 
 
 A LONG STRAND 
 
 The cotton factories of Lancashire, England, at present spin 
 about 155,000,000 miles of thread in a day, so that in six seconds 
 
74 HOW TO KNOW THE STARRY HEAVENS 
 
 they make enough to go around the Earth. In one minute they 
 spin enough to reach from here to the Moon. The product of 
 18 days would reach from the Sun to Neptune. Counting 310 
 working days in a year, it would take them, at this rate, 500 
 years to spin enough thread to reach to the nearest star. 
 
 If one end of this thread were to be made fast to some place 
 on our equator, the daily rotation of the Earth would wind up 
 25,000 miles of it every day. At this rate it would take about 
 300 years to wind up that part of the thread between us and 
 Neptune. But to wind up the whole of the thread between us 
 and the nearest star would take ,500,000 years. 
 
 Let us suppose that this thread is all wound around the Earth, 
 and that the size of the thread is such that a rope of it an inch in 
 diameter contains 10,000 threads. Then the entire skein would 
 make a rope nearly 26 feet in diameter around the entire Earth. 
 
 Let us suppose that four miles of this thread weighs one 
 pound. Then that part of it between the Sun and Neptune will 
 weigh 340,000 American tons. And the same-sized thread 
 reaching to the nearest star will weigh -3,000,000,000 American 
 tons. If twenty tons of it were to be loaded on one railroad car, it 
 would take 17,000 cars to carry that part between the Sun and 
 Neptune, and the thread reaching to the nearest star would take 
 150,000,000 cars to hold it all. 
 
 A SPIDER'S THREAD 
 
 These numbers are still too large to be realised by the human 
 mind as at present constituted. Fortunately, however, there is 
 a way of considerably reducing them. 
 
 The thread spun by some spiders is so extremely fine and light 
 that a single pound of it would be long enough to reach around 
 our Eai\h. Let us see if we cannot get more reasonable weights 
 by using this light and invisible thread. 
 
 To reach to our Moon would require nearly 10 pounds of it. 
 To go to the Sun would take 3,712 pounds. Neptune's distance 
 would require 56 American tons of it. 
 
FIG. 44. EYE-PIECE OF THE GREAT LICK TELESCOPE 
 
DIMENSIONS OF THE UNIVERSE 75 
 
 But to reach to the nearest star would take 500,000 tons. 
 At twenty tons to the car, this would take 25,000 cars to carry 
 it all. At 35 feet to the car, these would make a train of cars 
 167 miles in length. This train would require 500 powerful 
 locomotives to move it. 
 
 A QUARTZ FIBRE 
 
 We can get still better results by taking a quartz fibre like 
 those used in a torsion-balance for weighing the Earth. They 
 can be made one-hundred-thousandth of an inch in diameter, 
 with tapering ends which thin off to the millionth of an inch. 
 No microscope can show a fibre of this latter size, but its presence 
 can be made apparent by means of photography. Nine and a 
 half grains of this invisible quartz fibre (equal to one seventieth 
 of a cubic inch) would reach to the Moon. Half a pound of it 
 would go nearly to the Sun. Sixteen pounds would reach to 
 Neptune. But it would take 72 American tons (equal to a cube 
 of 9 feet 4 inches) to go to Alpha Centauri. 
 
 ONE CENT A MILE 
 
 If a railroad could be constructed to the nearest star, and the 
 fare made one cent a mile, a single passage would cost $860000- 
 000,000. This would make a 94-foot cube of pure gold. The 
 coined gold in the world amounts to $4,000,000,000, about equal 
 to a 24-foot cube. It would therefore take more than 60 times 
 the world's stock of coined gold to pay the fare of one passenger. 
 Let us save up our money and go when the line is built ! 
 
 A TIRELESS WHEEL 
 
 One more illustration will bring this chapter to a close. 
 
 Let us suppose a wheel to be turned at the speed of 100 revolu- 
 tions in a second of time. This is equal to 6,000 times in a minute. 
 At that speed it will go around 1,000,000 times in a little less 
 than three hours. To go around as many times as there are 
 miles between us and the Sun would take nearly eleven days. 
 To go around as many times as there are miles between the Sun 
 
76 HOW TO KNOW THE STARRY HEAVENS 
 
 and Neptune, the outside planet, would take nearly eleven 
 months. But to go around as many times as there are miles 
 between us and the nearest star outside our system would take 
 nearly 8,000 years. 
 
 These comparisons will do for the present. Let us take a rest 
 till the next chapter. 
 
CHAPTER VII 
 
 SOME MORE DIMENSIONS 
 
 " That collection of stars which we call the UnfVerse is limited in extent. 
 . . . This does not preclude the possibility that far outside of our Universe there 
 may be other collections of stars of which we know nothing." 
 
 Prof. Simon Newcomb. 
 
 " Then the angel threw up his glorious hands to the Heaven of Heavens, say- 
 ing : ' End is there none to the Universe of God. Lo, also, there is no begin- 
 ning ! ' " De Quincey. 
 
 A LONG SHEET OF PAPER 
 
 AYEEY good way to get an idea of the relative distances 
 of the heavenly bodies is to mark them off, on a small 
 scale, on a long sheet of paper. 
 
 In order to do this properly, get a 1,000-pound roll of paper, 
 like that on which magazines are printed. 1 Set up a bench or 
 table, about 4 miles long, and unroll the paper on it. Draw 
 a straight line down the middle of it, from one end to the 
 other. We can now choose a unit of measure, and mark off 
 the distances along this line. 
 
 Let us make a mark to represent the Sun, and another, one 
 inch away, to represent the Earth. Then one inch will stand 
 for 93,000,000 miles. On the same scale, Mars, the ruddy 
 planet, will be \\ inches off; Jupiter, the largest of the planets, 
 will be 9^ inches distant; Uranus will be 19 inches off; and 
 Neptune, the farthest of all the planets, will be 30 inches 
 away. 2 The distance that light will travel in one year will be 
 
 1 Such a roll is 20,250 feet long and 39 inches wide. 
 
 2 The orbits of all the principal planets are on nearly the same plane. There- 
 fore, on the above scale, the Solar System could be contained inside a round disc 
 of wood five feet in diameter and two inches thick. Very few even of the small 
 planets (asteroids) would ever go outside of this thin disc. 
 
78 HOW TO KNOW THE STARRY HEAVENS 
 
 represented by one mile. The nearest star, on the same scale 
 of one inch to the Sun's distance, will be more than four miles 
 away. And Sirius will be eight and a half miles distant. 
 
 But stay ! Our long sheet of paper is too short. Let us 
 erase these marks and try a smaller scale. 
 
 In order to get the most convenient unit, measure off a 12- 
 inch line and divide it into ten equal parts. Then divide one 
 of these parts also into ten. This will give us the one hundredth 
 of a foot for a unit. -We may regard it as equal to one eighth of 
 an inch, although it is really a trifle shorter. 
 
 If we make this little unit represent a mile, the distance of 
 our Moon from us will be represented by 800 yards. It is quite 
 evident that this scale is too large for our purpose. We must 
 choose a smaller one. 
 
 As our Moon is nearer to us than any of the other heavenly 
 bodies, we will let our little unit represent the Moon's distance. 
 
 First, make a mark, to represent the Sun, at one end of our 
 long sheet of paper. Then put another mark, nearly four feet 
 away, to stand for the Earth, with a quarter-inch circle around 
 it to represent the Moon's orbit. Neptune's place may now be 
 marked out, at a distance of 117 feet from our starting-point. 
 The position of the nearest star will be about 200 miles far- 
 ther on. 
 
 As our paper is again too short, we will reduce the scale, and 
 regard our unit as representing the distance of the Earth from 
 the Sun. Then Neptune's distance will be 3| inches, and that 
 of Alpha Centauri will be 900 yards. 
 
 Even this small scale is too large for some of the star-dis- 
 tances which have been approximately ascertained. So we will 
 try again. This time we will represent the distance of Neptune 
 from the Sun by our unit, so that the entire Solar System will 
 be about the size of a pea. Every eighth of an inch will thus 
 represent 2,790,000,000 miles! 
 
 At last we have succeeded in our efforts to get some of the 
 stars on to our paper. The distance of Alpha Centauri will on 
 this scale be only 90 feet. Sirius, the brightest star in the 
 
SOME MORE DIMENSIONS 79 
 
 heavens, will on the same scale be represented by a microscopic 
 grain of sand- 180 feet away, yet glaring with such an over- 
 whelming intensity of light as sometimes to throw shadows on 
 the invisible point which represents the Earth. 
 
 The great majority of the visible stars, however, on the above 
 scale of one eighth of an inch to the distance of Neptune, will 
 be scores and hundreds of miles away. So that we shall have 
 to try some other way of visibly representing their distances. 
 
 SOME BIG SQUARES 
 
 If, instead of using a straight line on which to represent 
 distances, we use different-sized squares for the same purpose, 
 we shall perhaps be more successful in appealing to the eye. 
 
 Take a square piece of white pasteboard which measures a 
 foot each way. On each edge mark off ten equal divisions. 
 Then with pencil and ruler join the opposite marks, thus 
 making a kind of chess-board with 100 equal squares. In the 
 same way divide up one of these squares into 100 equal squares. 
 Each of these smaller squares will be nearly one eighth of an 
 inch across. 
 
 Taking one of these tiny squares^ as a unit (1), the whole 
 square will contain one hundred units (100), and the entire 
 pasteboard will be equal to ten thousand units (10,000). 
 
 Now if each of these little squares or units be made to repre- 
 sent one mile, it will take a square nearly five feet across to 
 represent the distance of the Moon from the Earth. To repre- 
 sent the Sun's distance from us, it will take a chess-board meas- 
 uring 96 feet each way. Neptune's distance will be represented 
 by a square measuring 525 feet. The distance of the nearest 
 star will take a chess-board measuring 9 J miles each way, and 
 covering 90 square miles of land. It must be remembered that, 
 on this scale, every eighth-of-an-inch square of surface represents 
 a mile between us and the nearest star. 
 
 It is evident that we shall have to try a smaller scale if we 
 are to make the stellar distances visible to the eye by means of 
 squares. If we let one of the tiny squares represent the distance 
 
80 HOW TO KNOW THE STARRY HEAVENS 
 
 between us and the. Sun, then the distance of the nearest star 
 will be represented by a chess-board more than five feet in 
 diameter. 
 
 If we reduce the scale still more, and make our unit represent 
 the distance of Neptune from the Sun, then the distance of 
 Alpha Centauri will be represented by nine tenths of our 12- 
 inch chess-board. 
 
 SOME SOLID COMPARISONS 
 
 In order to bring our measures still more within the reach of 
 the eye, the little unit just used may be cubed. It will then be 
 a solid block, measuring nearly one eighth of an inch every ^way. 
 
 Kegarding this cube as the equivalent of a mile, the Moon's 
 distance will be represented by a 7J-inch cube. The Sun's dis- 
 tance will take a cube 4 feet 6 inches every way, and Neptune's 
 will take a 14-foot cube. The distance of Alpha Centauri will 
 be represented by a cube measuring 290 feet every way. 
 
 A GREAT VOID 
 
 Let us now consider in other ways the vastness of this appar- 
 ently empty space between our system and the nearest star. 
 
 Make a circle, two inches across, on the ground. Let this 
 circle represent our entire Solar System, with the Sun in the 
 centre. Then a similar circle including the nearest star will, 
 on the same scale, be 1,524 feet across. That is to say, it will 
 make a circular race-track nearly a mile around. 
 
 If these circles be regarded as solid spheres or globes, then 
 the larger one, representing the intense loneliness of our Solar 
 System, will be equal to 766,000,000,000 globes like the smaller 
 one that represents the size of our system. 
 
 LONG-RANGE CANNON 
 
 It is difficult for one who is not an astronomer to realise the 
 enormous light-grasping power of our great telescopes. Most of 
 us, indeed, fail to realise even the power of the unaided eye to 
 penetrate space. Here are a few illustrations of both. 
 
FIG. 45. YERKES OBSERVATOKT, WILLIAMS BAY, WISCONSIN 
 
 FIG. 46. THE FORTY-INCH REFRACTOR OF THE YERKES OBSERVATORY: 
 THE LARGEST IN THE WORLD 
 
SOME MORE DIMENSIONS 81 
 
 Suppose that our Sun were to leave us and go off in the direc- 
 tion of Sirius at such a rate as to double its distance in one 
 year. And suppose it were to continue receding at the same 
 rate for an indefinite period. In 100,000 years it would be about 
 as bright as Sirius, though the latter would still be 5| times as 
 far away from us. In 550,000 years it would pass Sirius and 
 appear to us about as bright as the Pole Star. In 3,000,000 
 years it would be just visible to the naked eye, and its light 
 would take 46 years to reach us. After receding for 750,000,000 
 years, it would still be visible to a telescope with a 50-inch ob- 
 ject-glass or mirror, and its light would take more than 11,000 
 years to reach us. 
 
 Suppose that Sirius were to recede from us at the rate of 
 1,500,000 miles per second (eight times the speed of light), so as 
 to double its distance in one year. In 30 years it would be just 
 visible to the naked eye, and its light would take 240 years to 
 reach us. After receding for 7,500 years it would still be visible 
 with a 50-inch telescope, and its light would take about 60,000 
 years to reach us. 1 
 
 Suppose that a star that is just visible to the naked eye were 
 to recede from us at such an inconceivable rate as to double its 
 distance in a year. It would be about 250 years before it would 
 be lost sight of by the same 50-inch telescope. 2 
 
 Let one inch represent the distance of the farthest star visible 
 to the naked eye. Then the distance at which our largest tele- 
 scopes would lose sight of it will be represented by about 21 
 feet. 
 
 This last illustration may be put in another form. If a globe 
 two inches in diameter be supposed to contain all the stars 
 visible to the naked eye, then it will take a globe 42 feet thick 
 to contain all the stars visible to our great telescopes. 
 
 1 It would be more correct to say that stationary stars equal to Sirius would be 
 just visible at those distances, and that their light would take so long to reach 
 us. 
 
 2 The same remark applies here. 
 
82 HOW TO KNOW THE STARRY HEAVENS 
 
 ETERNAL LIGHT 
 
 Suppose that (with the exception of our Sun) every star in 
 the Universe were to be blotted out of existence to-day, we 
 should not know of it for several years. We should continue to 
 receive the light which is already on the way, and the stars 
 would still appear to twinkle as they have always done. In a 
 little over four years the nearest star would suddenly go out of 
 sight. But no one would miss it except the astronomer. After 
 another four years the mysterious disappearance of Sirius would 
 attract more general attention. In a century a few more would 
 be missed, but the majority would remain visible for thousands 
 of years. Some of the stars seen in the most powerful telescopes 
 may be so far off that the light we now see left them when 
 Great Britain was part of the mainland of Europe, and the 
 Britons were fighting the hippopotamus, the hyena, and the sabre- 
 toothed tiger. 
 
 REASON VERSUS IMAGINATION 
 
 I have now given sufficient illustrations of the unthinkable 
 vastness of the visible Universe. It is no use trying to realise 
 even ascertained facts of such immensity. As Dr. J. W. Draper 
 says, " distances and periods such as these are beyond our grasp. 
 They prove to us how far human reason excels imagination, the 
 one measuring and comparing things of which the other can 
 form no conception, but in the attempt is utterly bewildered and 
 lost." 
 
 NUMBERING THE STARS 
 
 " Look now toward heaven, 
 
 And count the stars. 
 Tell the number of them 
 If thou art able." Genesis xv, 5 (A. Zazel). 
 
 The next question is, How many stars are there in the visible 
 and invisible parts of our Universe ? 
 
 This, like many other celestial problems, can be only partially 
 answered. The unaided eye can perceive about 3,000 in each 
 
SOME MORE DIMENSIONS 83 
 
 hemisphere. Argelander's great catalogue contains a list of 6"ver 
 300,000, all visible with a pocket telescope. A good three-inch 
 achromatic telescope brings about 1,000,000 in sight. But they 
 are shown by the giant instruments of our great observatories 
 in such multitudes that they cannot be counted. We have to 
 be satisfied with more or less approximate estimates of their 
 numbers. 
 
 Yet every improvement in light-grasping power brings mil- 
 lions of fresh ones into sight, and shows the " backspace " of sky 
 all glowing with the light of invisible suns too far off to be 
 separately distinguished. 
 
 It has of late years been found possible to attach a photo- 
 graphic apparatus to a telescope, so as to make the luminous 
 bodies in the heavens take their own pictures. Whole groups 
 of stars are photographed on one plate. Complete sets of these 
 star-photographs (embracing every nook and corner of the celestial 
 sphere) are taken every year, and carefully compared with one 
 another, to find out what changes are going on in the heavens. 
 It will not be long before every star photographically visible to 
 the most powerful telescope will have its present position accu- 
 rately defined on these photographic charts. 
 
 By a prolonged exposure of the sensitive plate even invisible 
 stars gradually photograph themselves, so that immense numbers 
 of stars have been discovered which no eye can see, even with 
 the aid of the same telescope. " Many ten thousands " of stars 
 have often registered themselves on a single plate. In one 
 case over 400,000 were actually counted. 
 
 It has been estimated that for every star visible to the naked 
 eye there are at least 50,000 visible to the telescopic camera. 
 This would bring the number of visible stars to about 300,000,000. 
 
 Yet even the picture-taking power of the photographic tele- 
 scope has its limits. In photographing the Milky Way its plates 
 (when long exposed) are sometimes clouded by constellations 
 too faint, through distance, for the individual stars to record 
 themselves. However much the telescope and its adjuncts may 
 be improved in the future, they will always fail to penetrate 
 
84 HOW TO KNOW THE STARRY HEAVENS 
 
 more than a certain distance into space. Beyond that limit there 
 may still be, as George Sterling suggests, the 
 
 " fires of unrecorded suns 
 That light a heaven not our own." 
 
 IS THE UNIVERSE LIMITED IN EXTENT? 
 
 " The centre of space is everywhere, and its circumference nowhere." Blaise 
 Pascal. 
 
 We know, by abstract reasoning, that space is limitless. The 
 question arises, Is there a limit to the distribution of luminous 
 and non-luminous bodies in that limitless space ? In other 
 words, Is -there a limit to the Universe ? 
 
 Professor Newcomb deals with the question as follows. Sup- 
 pose a globe to encircle and include all the stars visible to the 
 naked eye. And suppose another of double radius, a third of 
 treble radius, etc., with similar distribution of stars. As the 
 light received from a given luminous area or surface is in the 
 inverse ratio to the square of the distance, each shell will send 
 us an equal amount of light. If there is no limit, then, unless 
 some cause produces a loss of light, the whole sky will be as 
 bright as the Sun. As this is very far from being the case, it is 
 evident that there is either a limit or a loss of light. 
 
 It is not impossible that light itself may have limits to its 
 continuous flight : that it may be intercepted by dark bodies on 
 its way to us, or that its waves may lengthen out till all vibra- 
 tion ceases. Dr. J. J. See says on this subject : 
 
 11 In the exploration of the sidereal heavens it is found that the 
 more power the telescope, the more stars are disclosed ; and hence 
 the practical indications are that in most directions the sidereal system 
 extends on indefinitely. But the possible uniform extinction of light 
 due to the imperfect elasticity of the luminiferous ether, and the un- 
 doubted absorption of light by dark bodies widely diffused in space, 
 seem to preclude for ever a definite answer to the question of the 
 bounds of creation." 
 
FIG. 47. MILKY WAY SURROUNDING MESSIER II. 
 Photographed with a portrait-leiis, by Barnard, at Yerkes Observatory. 
 
FIG. 48. THE STAR-CLUSTER MESSIER II. 
 Photographed with the great Yerkes refractor, by Ritchey. 
 
SOME MORE DIMENSIONS 85 
 
 So George N. Lowe may be right when he says : 
 
 " Beyond the thirty thousand years 
 
 Of light, the giant systems swing 
 Vast, unknown suns and flaming spheres 
 And great worlds from their girdles fling." 
 
 INCOMPREHENSIBLE, YET TRUE 
 
 I once put the following question to the late Richard A. 
 Proctor : 
 
 " Let u suppose that a man could reach, in one second of time, the 
 remotest star visible. Let us also suppose that he could continue on at 
 the same* speed, in a straight line, to all eternity. Would he ever get 
 to the end of suns and worlds, or would he always have as many in 
 front of him as he had behind him ] The latter proposition seems 
 absurd, yet appears to be a necessary consequence of the theory that 
 'end there is none, nor is there yet beginning.' But if, on the other 
 hand, the last star could be reached in every direction, then the Uni- 
 verse not only has bounds, but is as a mere grain of sand in the infinite 
 desert of space. Of course I use the word Universe in its largest 
 sense." 
 
 Mr. Proctor's reply was as follows : 
 
 " I fear that to this question there is but one answer, ' We don't 
 know.' The infinite, which necessarily is, is necessarily incompre- 
 hensible." l 
 
 QUANTITY OF MATTER IN UNIVERSE 
 
 Of late years an attempt has been made to ascertain the total 
 amount of matter in the Universe by estimating the gravita- 
 tional force acting on individual stars. One of these, known 
 as 1,830 Groombridge, is moving at a speed of 200 miles per 
 second. Let us suppose that it has " fallen " from a practically 
 infinite distance, pulled by the combined attraction of every- 
 thing in our Universe. It has been estimated that more than 
 30,000,000,000 suns like ours would be necessary to produce 
 
 1 See "Knowledge," June 1, 1886, page 254. 
 
86 HOW TO KNOW THE STARRY HEAVENS 
 
 the observed speed. If our Sun be taken as an average star, 
 this would indicate that, for every star visible to the telescope, 
 there are more than a hundred that are invisible, either from 
 distance or because they have ceased to be luminous. 
 
 If this method be trustworthy, it will give us some idea as to 
 the dimensions of our Universe. But it does not disprove the 
 existence of other and similar universes at practically infinite 
 distances from ours, and from one another. For if it did, then 
 the observed motion of a comet visiting our Solar System (being 
 the result of the total attraction of the matter in the system), 
 could be used as a proof of the non-existence of air^hing out- 
 side of the Solar System. And this would hardly be doing 
 justice to the myriads of Stellar Systems which are known to 
 surround our own. 
 
 The Law of Gravitation, which has just been alluded to, will 
 be dealt with in Chapter XV. 
 
 OUTSIDE UNIVERSES 
 
 The study of the visible Universe shows that it is composed 
 of ascending series of similar systems. For example : (1) atoms 
 appear to be spheroidal " star-clusters " of still smaller particles 
 in motion ; (2) suns and worlds are rotating spheroids built up 
 of these atoms ; (3) stellar systems are rotating spheroids built 
 up of suns and worlds ; (4) the visible Universe appears to be 
 a rotating spheroid built up of a Milky Way of stellar systems. 
 
 It is possible that this largest spheroid, which we call the 
 Universe, may be only one out of innumerable similar spheroids, 
 rotating at practically infinite distances from each other, and 
 forming a still vaster rotating spheroid. 
 
 These speculations could be extended ad infinitum at both 
 ends of the series. It would, however, be a waste of time to 
 consider them seriously, they only serve to show how little we 
 really know of the great " Kiddle of the Universe." 
 
CHAPTER VIII 
 
 THE PRINCIPLES AND APPLICATIONS OF THE 
 SPECTROSCOPE 
 
 " And Elohim spake unto Noah and to his sons with him, saying ... I will 
 establish my covenant with you ; neither shall all flesh be cut off any more by the 
 waters of a flood ; neither shall there any more be a flood to destroy the earth. 
 And Elohim said : This is the token of the covenant. . . . I do set my bow in the 
 cloud, and it shall be for a token of a covenant between me and the earth, . . . 
 and I will look upon it, that I may remember the everlasting covenant." - 
 Genesis ix, 8-16. 
 
 THE BRIDGE OF BIFROST 
 
 THE rainbow has always been a source of wonder and ad- 
 miration to mankind. Before history began, men were 
 blindly theorising as to the cause and meaning of the wonder- 
 ful arch of colours which, phantom-like, seemed to span the 
 earth and reach to heaven. Among the old Norsemen it was 
 known as the Bridge of Bifrost, and was supposed to connect 
 the abode of the gods with that of their subjects on earth. No 
 mortal could set his foot on this bridge, but the gods used it 
 when they had business to transact or mischief to work in the 
 lower regions. 
 
 In more recent times its nature and cause have been ascer- 
 tained, and its glorious colours have been reproduced by allow- 
 ing the Sun to shine through a three-cornered glass prism. 
 Marvellous to relate, the fragments of rainbow thus produced 
 have not only helped chemists to solve some of the mysteries 
 concerning matter on earth, but have also enabled astronomers 
 to wrest from high heaven many of the secrets relating to the 
 chemistry, constitution, and movements of the heavenly bodies, 
 some of which still bear the names of the old deities. 
 
88 HOW TO KNOW THE STARRY HEAVENS 
 
 If the old Norse religion had only survived until now, how 
 easily might the priests of Odin have proved the inspiration of 
 the old records ! They could now show that the apparently 
 childish stories (though not literally true) have a hidden sym- 
 bolical meaning and refer to facts that only Gods could have 
 then been acquainted with. 
 
 But, alas ! the new light has come too late. The old narra- 
 tives have been replaced by others. The Bridge of Bifrost is 
 now the only remaining proof that the life of the world was 
 once practically destroyed by .an all-wise Creator, in a justifiable 
 exasperation at the moral imperfections with which he had know- 
 ingly endowed its most perfect inhabitants. 
 
 THE KEYS TO THE UNIVERSE 
 
 The rainbow and its artificial imitations are caused by the 
 refraction of light, a property without which mankind would 
 have been for ever left in the dark as to the outer Universe. 
 The study of the peculiarities of this refraction has given us the 
 telescope and the spectroscope two master keys which are 
 unlocking the mysteries of the Universe to man. The two dis- 
 coveries have indeed been described by enthusiastic scientists as 
 the most important events that have taken place on earth since 
 history began. The telescope, the camera, the spectroscope, and 
 even the human eye itself, would have been impossible without 
 the refraction of light upon which they and the rainbow 
 depend. 
 
 The instrument into which the rainbow-like spectrum has 
 been harnessed is known as the spectroscope. A few words 
 concerning the principles utilised in this instrument will help 
 us to grasp some of the facts which have been brought down 
 from heaven by its means. 
 
 MATTER AND ETHER 
 
 There appear to be in Nature two forms of substance entirely 
 distinct from each other in structure and functions. Every 
 
THE SPECTROSCOPE 89 
 
 nook and corner of infinite space appears to be packed with one 
 or the other of these two forms of substance. 
 
 I. Matter. That with which we are most familiar is com- 
 monly known as matter. It is made up of atoms, possesses 
 weight, and exists as a solid, liquid, or gas, according to sur- 
 rounding conditions. 
 
 II. Ether. The other goes by the name of luminiferous (or 
 light-bearing) ether. This ether is not made up of atoms, but 
 appears to consist of homogeneous particles or corpuscles. These 
 are estimated to be about a thousand times less (in mass) than 
 the smallest atoms of ordinary matter. On account of their 
 being the carriers of so-called negative electricity they are 
 sometimes called negative particles. 
 
 This ether is practically without weight, being millions of mil- 
 lions of times thinner than air. It probably fills to saturation 
 all space which is not occupied by ordinary matter^ even filling 
 the little spaces between the atoms of matter. Some of the 
 phenomena produced by it are explainable only on the theory 
 that it can pass through suns and worlds as water passes 
 through a sieve, or as light passes through a massive sheet 
 of glass. 1 
 
 VIBRATIONS OF ETHER 
 
 All matter has a life of its own and is in continuous motion. 
 The various motions of matter produce corresponding vibrations 
 in the ether, which carries them to inconceivable distances. 
 Some of these vibrations become sensible to us in the form of 
 light; others are recognisable as heat, electricity, magnetism, 
 etc. 
 
 REFRACTION OF LIGHT 
 
 Light may be regarded as produced by wave-like undulations 
 of the elusive ether which appears to fill all space. The un- 
 
 1 This may at first seem incredible, even with our recent experience of Roentgen 
 rays. But it must be remembered that it is not a whit more wonderful than the 
 commonplace yet astounding fact that light can pass, almost without let or hin- 
 drance, through solid glass or ice. 
 
90 HOW TO KNOW THE STARRY HEAVENS 
 
 dulations of light radiate through this ether like the ripples 
 which spread over water when a pebble is thrown into it. Or 
 they may more correctly be likened unto the vibrations of air 
 which start out in all directions from a centre of vibration and 
 ultimately become sensible to the ear as sound. Like the waves 
 of sound, the ethereal undulations of light vary in length. That 
 is to say, the interval between the summit of one wave and that 
 of the next varies in length in different kinds of light. When 
 
 FIG. 49. A PRISM AND ITS SPECTRUM 
 
 a ray of white light passes through a glass prism, the greater 
 density of the medium causes it to be bent or refracted. The 
 light, instead of coming out opposite to where it entered the 
 prism, comes out at an angle, the bend being toward the side 
 where the prism is thickest. The inequality of wave-lengths 
 causes this refraction to be unequal also, and the white light 
 splits up into an infinite number of shades, the best known of 
 which go by the names of violet, indigo, blue, green, yellow, 
 orange, and red (see Figure 49). 
 
 Of these colours the violet rays have the shortest wave-length 
 and are bent the most from their previous course. The red 
 waves are the longest, and are bent the least. 
 
 This visible spectrum is only a part of a much longer spectrum, 
 the rest of which is invisible to the eye, though recognisable by 
 other means. The short waves at the violet end are character- 
 ised by the intensity of their actinic or chemical properties, 
 
THE SPECTROSCOPE 91 
 
 while the long ones at the red end give out more heat. The 
 violet waves are so short that 61,000 of them reach only an 
 inch, while the red ones are so long that there are only 33,000 
 of them to an inch. They all travel at the same speed, 186,000 
 miles in a second of time. 1 
 
 THE SPECTROSCOPE 
 
 For convenience the glass prism is placed at the elbow of an 
 instrument that looks like a bent telescope and is commonly 
 
 FIG. 50. A OXE-PKISM SPECTROSCOPE 
 
 known as a spectroscope (see Figures 50, 51, and 52). A ray of 
 white light entering at one end through a narrow slit passes 
 along the tube until it comes to the prism. There it is bent 
 and split up into the colours of the rainbow. This row of 
 colours is known as a spectrum, and is examined directly from 
 the other end of the " bent telescope." 
 
 The spectroscopes now used are more complicated than the 
 above, with a " battery " of prisms (or with a corrugated mirror 
 
 1 It is interesting to note that if the prism, instead of being straight, is bent 
 around a centre into a lens-form, it 'brings the light to a focus, and forms the 
 basis of the telescope and microscope. In these instruments special means are 
 taken to avoid the separation of the various colours, but in the spectroscope spe- 
 cial means are taken to increase the dispersion. 
 
92 HOW TO KNOW THE STARRY HEAVENS 
 
 called a diffraction grating), but they all depend on the same 
 principle, so need not be here described. 
 
 VARIETIES OF SPECTRA 
 
 Now it is found that different sources of light do not give 
 the same spectrum when examined through the spectroscope. 
 There are, in fact, several distinct classes of spectra, which are 
 here given. 
 
 I. Continuous Spectrum. Light from an incandescent sub- 
 stance in a solid or liquid state, or from a glowing gas which is 
 under great pressure, gives a continuous spectrum, all the colours 
 
 FIG. 51. SECTION OF A ONE-PRISM SPECTROSCOPE 
 
 being fully and evenly represented. In this case it is evident 
 that light of every wave-length is being given off (see Figure 5 3, a). 
 
 II. Emission or Radiation Spectrum. Light from an incan- 
 descent gas which is uncompressed, and therefore free to vibrate 
 at its own rate, does not give a continuous spectrum, as in the 
 first instance. It merely gives a limited number of bright lines, 
 crossing the long streak where the spectrum should have been. 
 These bright lines vary in colour according to their position in 
 the (absent) spectrum. This shows that a glowing gas, when 
 unconfined, only gives out light of certain definite wave-lengths 
 (see Figure 53, b, d, e). 
 
 III. Absorption Spectrum. When light of the first class 
 passes through a mass of uncompressed gas, its otherwise con- 
 tinuous spectrum becomes to a certain extent discontinuous. 
 It is crossed by certain dark lines, making the spectrum look as 
 though there were a ladder in front of it, with numerous black 
 rungs at irregular distances from one another. This shows that 
 light of certain wave-lengths is absent, being absorbed by the 
 
THE SPECTROSCOPE 93 
 
 uncompressed gas through which the light passes (see Figure 
 53, i, etc.). 
 
 IV. When the source of light is partly solid or compressed 
 matter, and partly uncompressed gas, the result is a spectrum 
 crossed by lot h bright and dark lines or bands (see Figure 53, h). 
 
 FIG. 52. A COMPOUND SPECTROSCOPE 
 
 SPECTRUM ANALYSIS 
 
 Chemists have discovered that there are only about eighty 
 different kinds of matter on the accessible parts of our globe, 
 and that only about a quarter of these are abundant or im- 
 portant. All the tens of thousands of different substances on 
 earth (whether solid, liquid, or gaseous) consist of these elements, 
 either separate or in partnership with one another. 
 
 Now the great importance of the spectroscope depends on 
 the fact that every one of the elements, when in the condition 
 
94 HOW TO KNOW THE STARRY HEAVENS 
 
 of glowing gas, produces its own special lines in the spectro- 
 scope. By examining the spectrum of an unknown substance, 
 the elements of which it is composed can be ascertained. This 
 way of examining substances is therefore known as spectrum 
 analysis. 
 
 It has also been found that when light passes through a cer- 
 tain uncompressed gas, that gas absorbs the same rays of light 
 which it naturally emits when it is itself an uncompressed 
 source of light (see Figure 53, b, c). 
 
 Bearing these facts in mind, let us turn back to reconsider 
 the four classes of spectra given above. 
 
 When the spectrum is of the first class (continuous), we do 
 not get much information with regard to the source of light. 
 We know that the light does not proceed from an uncompressed 
 gas, but we cannot tell whether it is given off by a solid, a 
 liquid, or by a compressed gas. 
 
 When it is of the second class (emission), consisting entirely 
 of a limited number of bright lines, we know that the light pro- 
 ceeds from a glowing gas that is not under great pressure. And 
 we can tell what particular elements that gas consists of or con- 
 tarns. Certain lines prove that it contains hydrogen; other 
 lines tell of the presence of sodium. Another set is caused by 
 iron vapour; and so on, with all the elements (see Figure 53, 
 b,d,e,f). 
 
 When the spectrum is of the third class (absorption), it is 
 nearly continuous, but is crossed by dark lines. In this case 
 we know that the luminous body, whatever it is, is surrounded 
 by uncompressed gas which has absorbed certain light-waves 
 and so prevented them from reaching us, and, as in the second 
 class, we can tell what particular elements that gas consists of 
 or contains ; for the element which produced a certain set of 
 bright lines when it was a source of light produces the same set 
 of dark lines when it surrounds the source of light or comes 
 between the source of light and its spectrum. Hydrogen, 
 sodium, iron, etc., are in the one case recognised by their pecu- 
 liar bright lines, and in the other case by identical sets of 
 
THE SPECTROSCOPE 95 
 
 dark lines. The difference is one of condition, not of substance 
 (see Figure 53, 6, c). 
 
 A spectrum of the fourth class, crossed by both bright and 
 dark lines or bands, denotes that the source of light is either a 
 mixture of solid and gas, or of compressed and uncompressed 
 gases. The different sets of lines denote the presence and con- 
 dition of their respective elements, as in the other classes. 
 
 In spite of the one element of uncertainty mentioned, the 
 above results are remarkable achievements, even when applied 
 to substances actually present in the chemist's laboratory. 
 They have led to the discovery of hitherto unknown elements 
 and to a great advance in chemistry generally. But still more 
 remarkable is the fact that this spectrum analysis can be applied 
 to a distant source of light. Large numbers of the terrestrial 
 elements have been recognised in the sierra or atmosphere of 
 our Sun, and even the stars are not too far off to be cross- 
 examined by the spectroscope as to their chemical composition 
 and physical condition. 
 
 The spectrum of a star being very faint, it is observed by a 
 spectroscope attached to a telescope, the combination being 
 known as a tele-spectroscope (see Figure 54). Sometimes the 
 spectrum is photographed for future .examination and com- 
 parison. The instrument which accomplishes this is termed a 
 spectrograph (see Figure 55). 
 
 SPECTRA OF STARS 
 
 Our Sun and the brighter stars, when examined with the spec- 
 troscope, give spectra of the third class (absorption). That is to 
 say, their spectra are fairly continuous, but are crossed by dark 
 lines. This shows that such stars are all related to one another, 
 so that the study of any one of them will throw light on all the 
 rest. They are all suns, somewhat similar to, but not identical 
 with, our Sun (see Figure 53, i,j, Jc, I, m). 
 
 The fainter stars have not yet been satisfactorily examined 
 with the tele-spectroscope, on account of the small quantity of 
 light we receive from them. Still, a certain amount of infor- 
 
96 HOW TO KNOW THE STARRY HEAVENS 
 
 mation has been obtained concerning their composition and 
 condition. - 
 
 SPECTRA OF NEBULAE 
 
 When the heavens are examined with the help of a telescope 
 of some considerable power, enormous numbers of stars are 
 revealed. But, besides these stars, the telescope also brings 
 into sight large numbers of tiny patches of hazy light. These 
 look as though they might be clusters of stars which are too 
 far off to be separately distinguished. From their cloud-like 
 appearance these streaks and patches are termed nebulce. 1 
 
 With two or three exceptions these nebulae are not visible to 
 the naked eye, and the vast majority of them require very 
 powerful instruments to bring them into view. 
 
 Modern telescopes have in many cases proved that they are 
 really composed of stars, and every increase in telescopic power 
 has resolved fresh nebulse into star-clusters. At one time it 
 was thought that all would eventually be proved to be nothing 
 more or less than clusters of faint stars. It has been ascer- 
 tained, however, that there are two main classes of so-called 
 nebulse, and that only those of one class are composed of stars. 
 
 PSEUDO-NEBULAE (Star- Clusters). All of those nebulse which 
 have been shown by the telescope to be really star-clusters give 
 absorption spectra similar to those of the visible stars (Class III), 
 and some nebulae which have not yet been resolved into stars by 
 the telescope have been found to give similar spectra. As a 
 rule the spectrum of a star-cluster is so faint that it consists of 
 a mere streak of light in which the colours and lines are imper- 
 ceptible. 
 
 TRUE OR GASEOUS NEBULAE. Other nebulas, however, show 
 by their bright-line spectra (Class II) that they are not com- 
 posed of suns, but are immense masses of glowing gas, not under 
 pressure. Those which are comparatively bright give a number 
 of bright lines, five of which are much more prominent than the 
 
 1 The Latin word nebula means a cloud, fog, mist, or smoke. It may be regarded 
 as a diminutive of nubes,a. cloud. 
 
FIG. 54. TELE-SPECTROSCOPE 
 Attached to a telescope for the purpose of viewing celestial spectra. Lowe Observatory. 
 
 FIG. 55. THE MILLS SPECTROGKAPH AT LICK OBSERVATORY 
 For photographing spectra of celestial objects. 
 
THE SPECTROSCOPE 97 
 
 rest. In the fainter nebulae only one of the lines is visible, 
 owing to the small quantity of light which reaches us ; but it is 
 readily distinguished from the practically continuous spectrum 
 given by star-clusters, etc. 
 
 CLASSES OF STARS, ETC. 
 
 Stars and other self-luminous heavenly bodies have been 
 divided into a number of classes, according to their colours and 
 spectra ; but no hard-and-fast line can be drawn between them, 
 as there are many which give intermediate spectra. The fol- 
 lowing are perhaps the best defined classes, starting with the 
 youngest. 
 
 A. BLUE-GREEN NEBULA (G-aseous Nebulce). Nearly a hun- 
 dred of the nebulae have a bluish-green tint which distinguishes 
 them from all others. They give an emission spectrum, con- 
 sisting entirely of a few bright lines (Class II) on a dark back- 
 ground. This indicates that they are entirely composed of 
 uncondensed gases, so extremely diffuse as to be transparent in 
 spite of their thickness, which is sometimes many millions of 
 miles. The lines are those belonging to hydrogen, helium, and 
 " nebulum " (see Figure 53, g). The lines are thin, denoting a 
 comparatively low temperature and the absence of pressure. 
 One of these lines, in the blue-green part of the spectrum, is so 
 bright that it gives the blue-green tinge peculiar to nebulas of 
 this class when seen through the telescope. It is due to an 
 unknown substance which has been named " nebulum." 
 
 About half of these gaseous objects are termed planetary 
 nebulce, from the symmetrical planet-like disc which they ex- 
 hibit when seen through a powerful telescope (see Figure 99). 1 
 The rest are generally irregular and shapeless, like the Great 
 Nebula in Orion (see Figure 68), and the Trifid Nebula in Sagit- 
 tarius (see Figure 67). The so-called King Nebula in Lyra is 
 also gaseous. Recent photographs taken at the Ann Arbor 
 Observatory by Professor Schaeberli show that its resemblance 
 
 1 Some of the planetary nebula have a star-like nucleus in the centre, 
 
 7 
 
98 HOW TO KNOW THE STARRY HEAVENS 
 
 to a ring is only apparent, and that it is really a spiral nebula 
 (see Figure 66). 
 
 B. PEAKLY- WHITE NEBULAE. Some thousands of nebulae 
 have a pearly-white appearance when seen through the tele- 
 scope. They give a continuous spectrum, which denotes that 
 they are either composed of matter in a solid state, or of gases 
 under high pressure or great heat. Very little is at present 
 known as to the actual condition of the matter composing 
 these nebula3. But in many cases it appears to be collecting 
 in " centres of condensation," as though stars were in process 
 of formation out of nebulous matter. 
 
 The Great Nebula in Andromeda (see Figure 64) belongs to 
 this class, as do the spiral nebulce generally (see Figure 63). 
 The late Dr. Keeler estimated that there are at least 120,000 
 nebulae within range of the telescopic camera, and that more 
 than half of these show signs of a spiral structure. 
 
 C. NEBULOUS STARS (Orion Stars). These consist of a faint 
 nebulous haze with a star in the centre. They give broader 
 hydrogen and helium lines than Class A, showing that the gases 
 are hotter and more condensed. These stars are still in process 
 of formation, and have not yet drawn in all of the nebulous 
 matter around them. They are therefore buried in the depths of 
 a luminous haze consisting chiefly of hydrogen and helium. 
 Examples, the stars in the Pleiades and those connected with 
 the Great Nebula in Orion. 
 
 D. BLUISH-WHITE STARS (Sirian Stars). About 75 per 
 cent of the brighter stars appear to belong to this class. Their 
 spectra show all seven colours (Class III), but the violet end is 
 the most brilliant. There are four broad dark lines belonging 
 to hydrogen, greatly condensed and very hot. The metal lines 
 are few and faint. One of the magnesium lines indicates a 
 temperature about equal to that of the electric spark, say 
 about 20,000 F. The probability is that these stars are still 
 surrounded by a very deep, dense, and hot atmosphere (chromo- 
 sphere) of hydrogen, and that the high temperature prevents 
 the formation in it of a bright cloud-photosphere of calcium, etc. 
 
w 8 
 
THE SPECTROSCOPE 99 
 
 Examples, Sirius, Vega, Altair, Rigel, and Arided (see Figure 
 
 53,y,*> 
 
 E. YELLOWISH STARS (Solar Stars). This class includes 
 about 23 per cent of the brighter stars. Their spectra show all 
 seven colours (Class III), the middle being the most brilliant. 
 The hydrogen lines are faint, denoting a shallower atmosphere 
 or chromosphere. There are large numbers of very strong dark 
 absorption lines, due to the presence of different metals (in the 
 gaseous state) in the stellar atmospheres. Many of these metal- 
 lic elements have been recognised by their special lines. One 
 of the magnesium lines indicates a temperature not very far 
 from that of the electric arc (6,300 F.), or at least it indicates 
 a temperature lower than that of the electric spark. Probably 
 12,000 F. is not very far from the mark. The comparatively 
 low temperature of the chromosphere due to its shallowness 
 causes the formation of a layer of bright clouds known as 
 the photosphere. This is composed of incandescent solid (or 
 liquid) particles of calcium, etc. 
 
 If all the light from this brilliant photosphere reached us, 
 the Sun and solar stars would all be of a pure white, and their 
 spectra would be continuous (Class I), containing rays of all 
 wave-lengths. But as they are surrounded by a chromosphere 
 (or atmosphere) of metallic gases at a rather lower temperature, 
 some of the light is absorbed. The absorption is greatest among 
 the short waves, so that these stars all have a yellowish tinge. 
 Their spectra are therefore of Class III, with many dark absorp- 
 tion lines due to the metallic gases in their chromospheres. 
 Examples, Capella, our Sun, Procyon, Pollux, and Arcturus 
 (see Figure 53, 1 ; also Figure 56). 
 
 F. ORANGE-RED STARS. This class includes about one per 
 cent of the brighter stars. More than 60 of them are irregular 
 variables of the Mira Ceti class. The spectra show all the seven 
 colours (Class III), with the red end most brilliant. There are 
 no hydrogen lines except when the stars are at their maximum 
 of brilliancy. The metal lines are complex, and there are dark 
 absorption-bands, with a sharp, well-defined edge toward the 
 
100 HOW TO KNOW THE STARRY HEAVENS 
 
 violet. These indicate a dense and complex atmosphere of rela- 
 tively low temperature, with chemical compounds. Examples, 
 Aldebaran, Betelgeuse, Antares, and Mira Ceti (see Figure 
 53, i). 
 
 G. BLOOD-RED STARS. The spectra are similar to those of 
 Class F, but are more or less cut up by dark absorption-bands. 
 These have a sharp, well-defined edge toward the red end of the 
 spectrum, and are due to hydrocarbon vapours in the stellar 
 atmospheres. In some stars these bands are so broad and dark 
 that but little of the spectrum can be seen. Their light is in 
 fact dying out. Examples, Mu Ceph, and 152 Schjellerup (see 
 Figure 53, m ; also Figure 57). 
 
 H. DARK SUNS. These give out little or no light and heat, 
 and therefore have no visible spectra. They are dead or dying 
 suns. We know of their existence only when they have visible 
 companions moving around the same centre of gravity. Ex- 
 ample, one of the companions of the Pole Star. 
 
 RADIAL MOTIONS 
 
 Of late years the tele-spectroscope has given aid to astronomy 
 in another and unexpected direction. Astronomers have long 
 been able to watch and measure the movements (both real and 
 apparent) of the heavenly bodies when those movements were 
 more or less at right angles to the line of sight. But until 
 recently they were unable to detect motions toward or away 
 from us, except indirectly, by the increase or decrease of bril- 
 liancy and size. 
 
 A few years ago, however, it was discovered that, when a 
 source of light is approaching, the lines which cross its spectrum 
 are displaced toward the violet end, and that when it is receding 
 they are displaced toward the red end of the spectrum. 
 
 This is due to the same cause that makes a locomotive whistle 
 appear to fall in pitch the moment it passes the listener. While 
 the engine was approaching the listener, the waves of sound 
 reached his ear at shorter intervals than they would otherwise 
 
fa -U 
 
THE SPECTROSCOPE 101 
 
 have done, and after it has passed him the reverse is the case. 
 Hence the apparent change of pitch. 
 
 In the case of light (spectroscopically observed), j the effect is 
 a slight change of position instead of pitch:, t <yh$;wi\v$s aieiu 
 fact crowded together and made shorter from, crest , to, jerest. . 
 This could not be measured or even recognised in -a cont^u-yds 
 spectrum, but in a banded one it is done with comparative ease 
 by so arranging as to have a normal spectrum on each side of it 
 for comparison (see Figure 58). The result is that we can not 
 only tell that a certain object is approaching or receding from 
 us, but can also tell how many miles it is moving in those 
 directions per second. 
 
 This method of detecting and measuring radial motions (real 
 or apparent) can be applied not only to those heavenly bodies 
 whose distances are known, but also to those which are utterly 
 beyond the reach of our space-measuring instruments. The 
 only limit is that caused by deficiency of light. 
 
 It is possible that this principle may in time be found avail- 
 able for measuring star-distances which are too great for our 
 present methods. It is proposed to measure the orbits of double 
 stars spectroscopically, and then use the major axes as base 
 lines. 
 
 At present, stellar distances can be roughly estimated up to 
 60 light-years, which is 15 times the distance of Alpha Cen- 
 tauri. Dr. See thinks that some day star-distances of 1,000 
 light-years may be determined by this plan. 
 
CHAPTER IX 
 
 A STAR-SPANGLED BANNER 
 
 " The winter sunset fronts the North, 
 The light deserts the quiet sky, 
 From their far gates how silently 
 The stars of evening tremble forth ! 
 
 " Time, to thy sight what peace they share 
 On Night's inviolable breast ! 
 Remote in solitudes of rest, 
 Afar from human change or care. 
 
 "Eternity, unto thine eyes 
 
 In war's unrest their legions surge, 
 Foam of the cosmic tides that urge 
 The battle of contending skies."" 
 
 George Sterling, " The Testimony of the Suns." 
 
 STAR MAGNITUDES 
 
 " One star differeth from another star in glory." I Cor. xv, 41. 
 
 THE stars are at such vast distances from us that in spite 
 of the enormous sizes of some of them they all appear as 
 mere points of light. This is true even with the most power- 
 ful telescope in existence. Only one star in the heavens is 
 near enough to show a measurable disc, and that is the one 
 which rules our own system under the names of Helios, 
 Shemish, Baldur, Father Sol, the Sun of Kighteousness, and a 
 thousand other suggestive names. 
 
 But this does not mean that the stars all look alike, either 
 with the naked eye or with the telescope. There are stars of 
 almost all colours, and even those which appear to be of the 
 same colour differ enormously in brilliancy. Sirius scintillates 
 in the sky like a sparkling jewel, and glares down the telescope 
 
A STAR-SPANGLED BANNER 103 
 
 tube like a little sun, so that he is better examined with a dark 
 glass. A few other stars are not far behind in brilliancy. 
 Large numbers are fairly bright, while swarms of them are com- 
 paratively inconspicuous. Still larger numbers are just visible 
 to the naked eye, and the telescope reveals them in multitudes 
 that no man can number. Yet no two of them send us exactly 
 the same amount or quality of light. 
 
 It has been found convenient to classify the stars according 
 to their brilliancy. At first the classification was rude, but of 
 late years they have been sorted out with considerable accuracy. 
 They are divided into a number of magnitudes, a star of one 
 magnitude being 2 J times as bright as one of the magnitude 
 below it. l 
 
 Thus a star of the first magnitude sends us 100 times as 
 much light as one of the sixth magnitude, which is the faintest 
 star visible without a telescope. And that is 100 times as bright 
 as one of the eleventh magnitude, which in its turn is 100 times 
 as bright as one of the sixteenth. This rule applies to all magni- 
 tudes. Taking Aldebaran as a standard star of the first mag- 
 nitude, the North Pole Star belongs to the second, and the 
 brightest star of the Pleiades to the third. The rest of the 
 bright stars in the same group belong to the fourth. The 
 faintest stars usually seen belong to the fifth, and those just 
 visible by direct vision on very clear nights are of the sixth 
 magnitude. The seventh magnitude stars can just be glimpsed 
 by oblique vision, by unusually keen eyes, on exceptionally 
 clear occasions. 
 
 There are a few stars brighter than Aldebaran, and these are 
 sorted out in the same way, with the numbers reversed and the 
 minus sign ( ) placed in front of them, instead of the plus sign 
 (+), which is sometimes used to denote the regular magnitudes. 
 Thus one magnitude brighter than the first is denoted as (0), 
 the next (1), and so on. On this plan Sirius is denoted by 
 the sign (1.4), his brilliancy being 9.1 times greater than that 
 of Aldebaran. And our Sun is a star of the magnitude 26.4, 
 
 !More exactly, 2.512. 
 
104 HOW TO KNOW THE STARRY HEAVENS 
 
 his apparent brilliancy being about 90,000,000,000 times greater 
 than that of Aldebaran. 
 
 It must be understood that the magnitude of a star does not 
 denote its real size, or its weight, or the actual amount of light 
 given off by it, or its distance from us. It merely denotes the 
 amount of light we receive from it, and this depends on a com- 
 bination of these factors, which are unknown to us in the vast 
 majority of cases. For example, Canopus, which is the second 
 brightest star in the heavens, is at an immeasurable distance 
 from us, and must therefore be many thousands of times larger 
 and brighter than our Sun. And some of the fainter stars 
 visible to the telescope may be even larger than Canopus. On 
 the other hand, some fairly brilliant stars are smaller even than 
 our Sun, their distances from us being comparatively small, as 
 stellar distances go. 
 
 For this reason the actual and apparent motions of the stars 
 form a better guide to their distance, size, and actual brilliancy 
 than do their magnitudes. We have an example of this in the 
 star known as 61 Cygni, which is nearer to us than Sirius, 
 although it is nearly seven magnitudes smaller and sends us 
 nearly 600 times less light. 
 
 The number of visible stars has been already dealt with. It 
 may, however, be interesting to know that there are about 50 
 stars of the second magnitude (from 1.6 to 2.4), and about one 
 third that number of larger ones. Also that, from this down, 
 each magnitude has about three times as many as the one 
 above it. To the fourteenth magnitude (14.5) this would give 
 200,000,000, stars. With the fainter stars, however, the in- 
 crease in numbers appears to be less rapid. The faintest stars 
 visible to the eye in the great Lick telescope are of about the 
 seventeenth magnitude. 
 
 ACTUAL BRILLIANCY OF VISIBLE STARS 
 
 The actual magnitudes of the stars may be considered from 
 three distinct standpoints, (1) Mass or Weight; (2) Size; 
 (3) Brilliancy. We will here consider the brilliancy alone, 
 
A STAR-SPANGLED BANNER 105 
 
 as comparatively little is at present known of the other two 
 factors. 
 
 It must be remembered that stars which now give out little 
 or no radiant energy are not necessarily small. Some of the 
 largest suns in the Universe are feeble from extreme old age, 
 while others are dead and cold, waiting patiently for the resur- 
 rection that comes through collision. 
 
 If the stars were all at the same distance from us, their actual 
 brilliancy would be proportionate to their apparent magnitudes, 
 and could therefore be easily found. On the other hand, if 
 they were alike in actual brilliancy, we could estimate their 
 distances from us by that alone. 
 
 As it is, however, with varying distances and sizes, the prob- 
 lem is a difficult one, and will probably never be solved except 
 in the case of the nearer stars. I can give here only a few 
 illustrations of what has been ascertained concerning the radiant 
 energy of the stars. 
 
 Let us first consider what we may reasonably expect to find, 
 and then compare our expectations with the results actually 
 attained. 
 
 Take a certain distance, A L, and divide it into 11 regularly 
 increasing intervals. Call these shorter distances B, C, D, etc. 
 
 Let us suppose that we are at A, and that there are 10 stars 
 at the distance B. The actual brilliancy of these stars we may 
 suppose to vary regularly, so that (from A) the largest appears 
 equal to Sirius, and the smallest is just visible. If there be a 
 similar set at each of the other distances, only 9 of those at C 
 will be visible. Of those at D only 8 will be seen. And so OD. 
 Those which become invisible will of course be the smallest, 
 but, as the others will appear smaller on account of the greater 
 distance, the effect will be as though the largest were dropped. 
 Beyond the distance K all will be invisible. Out of the 110 
 stars only 55 (one half) will be visible to us. We may expect, 
 therefore, to find all sizes of stars among those nearest to us, 
 while at the limit of visibility only the very largest will be 
 visible, and they will appear very faint. For every star visible 
 
106 HOW TO KNOW THE STARRY HEAVENS 
 
 there will be at least one invisible. This reasoning may be 
 applied to telescopic stars as well as to visible ones. 
 
 First Step. It is found, however, that there are no very 
 large stars among those which are near to our System. The 
 largest, both actually and apparently, is Sirius, which equals 
 about 30 suns like ours. Procyon, Altair, and Alpha Centauri 
 are also brighter than our Sun. The fifth-magnitude star known 
 as 61 Cygni is small, and some of the binaries and multiple 
 systems contain stars which give out hundreds and thousands 
 of times less light than our Sun. 
 
 Second Step. If we examine those which are very much 
 farther away, but are still at a measurable distance from us, we 
 find stars which have much more actual brilliancy than any of 
 the nearest stars. And some of them, in spite of their great 
 distances, are equal in apparent brilliancy to any of the nearest 
 stars, with the single exception of Sirius. Those known as 
 Arcturus, Eegulus, Antares, and Gamma Cassiopeise, are each of 
 them about equal in brilliancy to 1,000 suns like ours, rolled 
 into one huge globe. 
 
 Third Step. Among those which are at absolutely immeas- 
 urable distances from us we should not expect to find any stars 
 equal in apparent magnitude to those which are so much closer 
 to us. But here we meet with another surprise. For some of 
 them are among the brightest stars in the heavens. They in- 
 clude, indeed, the second brightest star in the sky. Rigel, Can- 
 opus, and Arided are each of them many thousands of times 
 larger and more brilliant than our Sun. In fact they are so 
 large and brilliant that they exceed our Sun as much as it 
 exceeds the planets which yield to its authority. They are so 
 enormous that the mind cannot grasp their immensity. They 
 may be the centres of systems of a higher order than ours, with 
 mighty suns for planets, huge planets for satellites, and perhaps 
 secondary satellites revolving around the primary ones. 
 
 Yet, for all we know to the contrary, some of the faint stars 
 that fill the back-space of sky may exceed them as much as 
 they exceed our Sun. 
 
A STAR-SPANGLED BANNER 107 
 
 We have now taken three huge steps into the visible Uni- 
 verse, and at each step have found larger suns than we had 
 come across before. And the fact that some of those that are 
 at an immeasurably great distance from us are quite brilliant 
 when seen from the Earth shows that several more such steps 
 will have to be taken before we get beyond the great mass of 
 fairly visible stars. This is true of those seen without the aid 
 of the telescope, and it is much more true of telescopic stars. 
 
 DARK SUNS AND PLANETS 
 
 It has been already mentioned that some stars are not now 
 luminous, their heat having radiated into space and left them 
 dark and cold. There is some reason to believe that the Uni- 
 verse is crowded with these dead and dying suns, and that they 
 are in fact vastly more numerous than the living ones. Besides 
 these, there are the planets which probably swarm around each 
 and every star, living and dead. Our own star has countless 
 millions of such bodies revolving around it. Probably about a 
 thousand of these are large enough and near enough to be de- 
 tected by our telescopes, the smallest one visible (a satellite of 
 Mars) being about seven miles thick. All the rest are too 
 small or too distant to be seen by us. The only evidence we 
 have of their existence is that they occasionally run up against 
 our atmosphere, and are turned to flaming gas by the friction. 
 Sometimes fragments of them reach the Earth's surface in a 
 solid state, unaltered except at the original surface, which is 
 vitrified by the heat. 
 
 VARIABLE STARS 
 
 While sorting out the stars according to their magnitudes, 
 astronomers have discovered that large numbers of them vary 
 in brightness at different times. They are therefore called 
 " variables," to distinguish them from those which give out a 
 steady unfluctuating light. 
 
108 HOW TO KNOW THE STARRY HEAVENS 
 
 REGULAR (SHORT-PERIOD) VARIABLES 
 
 Algol Variables. Some of these variables are periodic and 
 regular in their changes. For example, Algol, which is usually 
 of the 2.3 magnitude, fades every three days to the 3.5 magni- 
 tude, and recovers its normal brightness in a few hours. The 
 spectroscope shows that between these minima it is alternately 
 approaching and receding from us. 
 
 It is evident that in this case there are two stars revolving 
 around their common centre of gravity, but that one of them is 
 smaller and gives out little or no light. When it passes be- 
 tween us and Algol it partly eclipses the latter. 
 
 The period of revolution (three days), and the speed at which 
 Algol moves to and from us, show that they are about 3,000,000 
 miles apart. The invisible companion appears to be about the 
 size of our Sun, and Algol larger. But their masses, taken to- 
 gether, are probably less than half that of our Sun alone. 1 
 
 Speetroscopic Double Stars. Beta Lyrae is also a periodic 
 variable, with partial eclipses every 6^ days. But in this case 
 only the alternate minima are equal. The spectroscope shows 
 the usual spectral lines to be doubled. There appear to be two 
 unequal self-luminous stars revolving around each other, about 
 30,000,000 miles apart. 
 
 It is obvious that these two classes of variables, which are 
 both regular in their fluctuations, are only apparently variable, 
 through change of position. Their actual brilliancy remains 
 the same. Most of them are white stars. 
 
 Stars below a certain magnitude cannot be satisfactorily ex- 
 amined spectroscopically, on account of the faintness of their 
 spectra. Among the stars which have been so examined, about 
 one in seven shows some inequality of radial motion, due to 
 large invisible companions. 
 
 IRREGULAR (LONG-PERIOD) VARIABLES 
 
 Mir a Ceti Variables. Other variable stars (which are 
 generally red) differ from the above in being irregular, both as 
 
 1 One variable of this type has a period of only 4 hours. 
 
FIG. 59. COLOURED DOUBLE STARS 
 
A STAR-SPANGLED BANNER 109 
 
 to time and brilliancy of maxima and of minima. Mira Ceti, 
 for example, has a maximum varying from the second to the 
 fifth magnitude, and a minimum varying from the eighth to 
 the ninth magnitude. Its period also varies irregularly, -being 
 usually about eleven months. 
 
 The cause of such irregular fluctuations must be violent 
 physical and chemical reactions such as take place on all large 
 cooling bodies at certain critical temperatures. Even our Earth 
 has passed through such crises in the past, and our Sun has 
 slight spasms every eleven years from the same cause. Some 
 day, when chemical compounds are formed on the cooling sur- 
 face of the Sun, these fluctuations will be vastly greater than 
 they are now. 
 
 NEW STARS 
 
 " Vague on the night the mist we mark 
 
 That tells where met the random suns." G. Sterling. 
 
 Allied to these irregular long-period variables are the new 
 stars which occasionally flash out in a hitherto vacant part of 
 the sky, attain a maximum brilliancy in a few days, and then 
 slowly die out again. These either disappear altogether or re- 
 main as telescopic stars. The New Star in Perseus is a familiar 
 example of this class. Inside of five days it increased from 
 telescopic invisibility to be the brightest star in the Northern 
 Hemisphere (magnitude 0). It then faded gradually away, and 
 in a few months became invisible to the naked eye. 
 
 While this star was increasing in brilliancy, the spectroscope 
 showed an almost continuous spectrum, like that of other stars 
 (Class III). But bright and dark bands gradually appeared 
 in it (Class IV), and it ended by resembling the spectra of 
 the true nebulae (Class II). 
 
 This star's sudden appearance was not due to its coming 
 toward us out of the depths of space. It was probably caused 
 by a sudden and stupendous discharge of light and heat from 
 a previously existing star or stars. Such an outburst may be 
 produced in several ways. 
 
ilO HOW TO KNOW THE STARRY HEAVENS 
 
 For example : (1) two stars or planets may come into more 
 or less direct collision, and spread out rapidly into a huge 
 nebula of flaming gas. This will cool down in a short time to 
 the temperature of space. Or (2) the colliding stars may strike 
 a glancing blow and cut slices out of each other. In this case 
 the slices alone will turn to gas, while the wounded stars will 
 enter into partnership, revolving around their common centre 
 of gravity. Or (3), the stars may not strike, but pass so close 
 to one another that their solid crusts are rent asunder by tidal 
 action, exposing the molten interior of one or both of them. 
 Or (4), a dark star may, in the course of its wanderings, dash 
 through an immense swarm of "pocket planets," commonly 
 known as meteoric bodies. Such a collision will turn the 
 meteorites into gas, and, if they are numerous enough, their 
 dissipation will cause a temporary brilliancy like that observed. 
 Or (5), a single cooling body may reach one of its " critical " 
 periods, and flare up from sudden physical or chemical reactions, 
 like those attributed to Mira Ceti, only more severe. 
 
 Collisions and minor interferences between all kinds of 
 heavenly bodies must, in the very nature of things, take place 
 now and then, seeing what multitudes of suns and worlds are 
 hurtling through space, in all directions, without any one on 
 board to guide them. And at the same time collisions appear 
 to be necessary to prevent the Universe from dying of old age. 
 The dead or dying hulks collide, turn to gaseous nebulae, and 
 start afresh to form new systems of suns and worlds. 
 
 DOUBLE AND MULTIPLE STARS 
 
 " Those double stars 
 Whereof the one more bright 
 Is circled by the other." Tennyson. 
 
 In dealing with periodically variable stars it was shown that 
 they are really double-star systems with orbits turned edgeways 
 to us. There are immense numbers of similar systems which 
 do not happen to be so situated, and are therefore not recognis- 
 able as " doubles " by the spectroscope. Some of them, however, 
 
A STAR-SPANGLED BANNER 111 
 
 are so near to us, or have such large orbits, that the telescope 
 itself enables us to detect their "duplicity" and follow their 
 motions. There are over 10,000 double stars now known. In 
 about fifty cases the time of mutual revolution has been deter- 
 mined with some certainty. The periods vary from 5.7 years 1 
 (the shortest telescopically visible) to 1,500 years. Many bi- 
 naries take thousands of years to complete a revolution, and 
 their motions have not been followed long enough to fix their 
 orbits and periods. 
 
 Those dual systems of suns which started as partners not 
 by direct collision, but by tidal division, are twins, their gase- 
 ous contents having, at first, the same -heat and condition. It 
 takes longer for a large mass to condense into a sun, and then 
 cool off and die of old age, than it does for a smaller one. There- 
 fore the larger of the two bodies is relatively younger than its 
 companion, and the centre of brilliancy of its spectrum should 
 be nearer to the violet end. Dual systems which started in 
 other ways would not necessarily have this spectral peculiarity. 
 
 For some unexplained reason there is much more variety of 
 colour in double stars than in single ones. They are sometimes 
 of a green, blue, or violet colour (see Figure 59). 
 
 In some cases there are more than two suns in the same sys- 
 tem. The North Pole Star, for example, has two companions 
 large enough to be classed as suns, though one of them has 
 ceased to give out any appreciable light and heat. 
 
 There appears to be every gradation of solar systems visible 
 to the telescope. They vary from simple ones like ours, to 
 highly complex star-clusters, like the one in the constellation 
 of Hercules. This has over 6,000 visible suns, and appears to 
 be surrounded by long spirally radiating wisps of nebulous mat- 
 ter in which other stars are entangled. 
 
 SOLAR DRIFT. 
 
 It has long been known that some of the nearer stars are 
 not absolutely fixed, but are slowly changing their positions in 
 
 l Delta Equulei. 
 
112 HOW TO KNOW THE STARRY HEAVENS 
 
 the heavens. And the spectroscope has told us that, while some 
 stars are coming nearer to us, others are retreating. From the 
 nature of the evidence we may safely assume that all stars are 
 in motion, and that our Sun partakes in this stellar drift, 
 carrying its planets along with it. 
 
 If our sun be assumed to be motionless, then the observed 
 motion of a star must be real, due to its own drift through space. 
 But if our System is also adrift, the observed motion of a star 
 may be only apparent, due to our own change of place. Or it 
 may be partly real and partly apparent. 
 
 It is obvious that, if our Sun is drifting in one direction 
 (carrying us along with it), the stars toward which it is drifting 
 will appear to open out or separate, while those from which it is 
 retreating will appear to close up. At the same time those 
 which we are passing will appear to drift backward. 
 
 Now the telescope shows that all three of these peculiarities 
 are actually taking place. The stars around Vega, in the con- 
 stellation of the Lyre, are gradually separating from one an- 
 other, those on the opposite side of the heavens are as gradually 
 closing up, and those at right angles to this line of march are 
 drifting backward. 
 
 The conclusion is obvious. The motions of the stars are, at 
 least in part, only apparent. Our whole System is drifting in 
 the direction of Vega. 
 
 Lest we should have made a mistake, let us inquire of the 
 tele-spectroscope, and find out which stars are approaching us 
 and which are receding. 
 
 According to the spectroscope and spectrograph, the major- 
 ity of the stars about Lyra are approaching us at the aver- 
 age speed of about 12J miles a second. And the majority 
 of stars opposite that constellation are receding from us at 
 about the same rate. In the circle of the heavens between 
 these two points there is no decided motion either to or 
 from us. 
 
 We thus see that two absolutely independent sets of evidence 
 both point to the same conclusion. Our Sun is drifting toward 
 
FIG. 60. STAR- CLUSTER IN HERCULES 
 Lick photograph. 
 
A STAR-SPANGLED BANNER 113 
 
 Vega at the rate of 12| miles a second, and all the planets share 
 in the " solar drift." 
 
 On account of this solar drift, the orbit of the Earth, in- 
 stead of being an ellipse, is really of a corkscrew shape, the 
 axis of the " corkscrew " being in the direction of the constel- 
 lation Lyra. 1 
 
 STELLAR DRIFT 
 
 After allowing for the apparent motions of the stars, due to 
 our own drift, there remain certain real motions of the stars, 
 due to their own drift. 
 
 For instance, the telescope shows that the star known as 
 1,830 Groombridge is moving steadily along at the rate of over 
 200 miles a second. Some other stars have motions as real, 
 though not as rapid. The spectroscope shows that some stars 
 are actually approaching us, while others are as actually reced- 
 ing from us. 
 
 In some cases a number of stars are drifting along together, 
 showing that they form a family group. The Pleiades form 
 a familiar example of this social drift through space. 
 
 1 The Cluster of Hercules is not very far away from the part of the sky which 
 we are approaching. It is possible that our System may form a distant part of 
 one of its encircling wisps of star-strewn nebulous matter. In this case we may 
 eventually be drawn into the cluster. 
 
CHAPTER X 
 
 CONSTRUCTION OF THE UNIVERSE 
 
 "Secondly, . . . what is the arrangement of the stars in space? Especially, 
 what is the relation of the Galaxy to the other stars ? In what senses, if any, 
 can the stars be said to form a permanent system ? Do the stars which form the 
 Milky Way belong to a different system from the other stars, or are the latter a 
 part of one universal system ? " Prof. Simon Newcomb. 
 
 DISTRIBUTION OF STARS 
 
 IN the stellar population of the visible Universe there are 
 very great differences of distribution. Although it would 
 be difficult to point a powerful telescope to any part of the sky 
 and find the field of view absolutely hare of stars or nebulae, 
 yet in some directions they are very much more scarce than in 
 others. In fact the visible inhabitants of space are as unevenly 
 distributed as is the human population of Usona. There are 
 belts of sky that are swarming with cities, towns, and villages 
 of social stars, and have the intervening spaces well peopled 
 with more independent families. And there are large tracts 
 of sky that are comparatively thinly inhabited with visible suns. 
 Some of the star-clusters are almost as crowded as are our cities. 
 In some of the thickly settled tracts nearly all the stars are well 
 developed, while in others large numbers of the inhabitants are 
 in a nebulous embryonic stage. 
 
 ALL SORTS AND CONDITIONS OF SUNS 
 
 In that part of the Universe which is at present visible from 
 our Earth, there are many different structures and styles of 
 architecture. And all stages of construction and development 
 are represented. There are systems that appear to be still in 
 the throes of birth; systems in young and vigorous growth; 
 
CONSTRUCTION OF THE UNIVERSE 115 
 
 systems in the strength and pride of maturity ; systems that are 
 tottering toward the grave ; and systems that are cold in death 
 and waiting for the resurrection that will surely come. 
 
 THE CONSTELLATIONS 
 
 The stars that are visible to the naked eye have long been 
 divided up by man, for his own convenience, instruction, and 
 amusement, into groups or constellations. About 48 of these 
 are extremely ancient, and the rest are quite modern. 
 
 The ancient constellations appear to have had a priestly origin 
 and an important religious significance. The stars were divided 
 into groups, each of which was supposed to form a picture of 
 some person, animal, or inanimate object. The 48 constella- 
 tions contained 54 figures, which formed a huge sky-picture 
 whose mystic meaning has long been lost sight of by the 
 multitude. 
 
 These fanciful figures appear to have been invented by a 
 people who lived south or southeast of the Caspian Sea, nearly 
 5,000 years ago. As the stars near the South Pole were invisi- 
 ble from their part of the world, they naturally left that section 
 of the sky unfigured. The size of the circle which was left 
 blank shows us that the constellation-makers lived about 39 
 north of % the Equator. And the animals, etc., which they pic- 
 tured in the sky, tell us their longitude on the earth ; for they 
 naturally depicted the animals with which they were acquainted, 
 and none others. Even the animal monstrosities were combi- 
 nations of familiar animals. 
 
 Owing to what is known as the Precession of the Equinoxes 
 (described in Chapter XII), this circular blank space does not 
 now centre at the South Pole, and the amount of its drift tells 
 us that the constellations were completed about 2800 B. c. 
 
 The first groups of stars to be pictured out were evidently the 
 twelve Signs of the Zodiac, likewise known as the "Mansions 
 of the Sun." The picture-makers were, astronomers of no mean 
 ability. They had already determined the length of the year 
 
116 HOW TO KNOW THE STARRY HEAVENS 
 
 with some degree of accuracy. They had recognised the fact 
 that the stars are in the sky during the daytime, though they 
 cannot then he seen under ordinary circumstances. They had 
 even traced out the annual path of the Sun among the stars. 
 This was a remarkable achievement which few of us would have 
 the patience and ingenuity to accomplish unaided. To do it they 
 must have rigged up some sort of equatorial mounting, with 
 a number of pointers directed to the most prominent stars. 
 
 To enable them to ascertain the Sun's position in this path, 
 or Ecliptic, all the year round, they divided up the neighbouring 
 stars into twelve constellations. This made it easier to keep 
 track of the months, seasons, and years. It also enabled them 
 to find the four critical days in which the seasons culminated. 
 Being Sun-worshippers, like nearly all the nations of antiquity, 
 they were very anxious to ascertain the exact date of the sab- 
 baths, new moons, equinoxes, and solstices ; for otherwise they 
 could not time their feasts, fasts, and sacrifices so as to have 
 them credited in the heavenly ledger. They regarded the Sun 
 as a Great Spirit labouring for the good of mankind, and fight- 
 ing the powers of cold and darkness with varying success. Each 
 summer he got the upper hand, but in the winter he lost his 
 strength, like his Semitic prototype, Samson, when he was shorn 
 of his flowing locks. As the very existence of the human race 
 depended on the Sun-God's success, the struggle was watched 
 with never-flagging interest and anxiety. 
 
 The year was then reckoned to begin in the spring, at the 
 time when the days and nights were equal. The Sun-God was 
 then in the centre of a group of stars which they pictured out 
 as a Bull (Taurus)}- At the longest day their God was in the 
 centre of a group which they named the Lion (Leo). At the 
 autumn equinox he was in the centre of a group which they 
 imagined to represent a Scorpion (Scorpio). And on the short- 
 est day in winter he was in the midst of a group which they 
 called the Water- Carrier (Aquarius). 
 
 1 Subsequent generations long inherited the tradition that each year was opened 
 by a bull with golden horns. 
 
FIG. 63. SPIRAL NEBULA IN TRIANGULUM 
 Lick photograph. 
 
V\BRT7> 
 Or TME 
 
 UNIVERSITY 
 
 or 
 
CONSTRUCTION OF THE UNIVERSE 117 
 
 These significant symbols became famous in mythology, and 
 are several times mentioned in the Hebrew Bible and early 
 Christian writings. The brightest star in or near each of the 
 four groups has been known ever since as a " royal " star, though 
 its significance was lost when the Precession of the Equinoxes 
 dethroned the celestial Bull and set the heavenly Ram in the 
 place of honour. These royal stars were Aldebaran, Eegulus 
 Antares, and Fomalhaut. 
 
 The Zodiacal groups having been satisfactorily marked out, 
 the northern stars were made into a great winged Dragon 
 (Draco), which was supposed to guard the pole of the heavens. 1 
 The rest of the constellations were then figured off in other 
 parts of the sky. They were all connected together, each figure 
 forming a portion of the same great mythological sky picture. 
 As a rule they were all upright when on the meridian, either 
 north or south. 2 
 
 The picture-makers of 2800 B. a, looking south at midnight 
 at the spring equinox, imagined a huge man in the sky, crush- 
 ing a scorpion with his left foot, and strangling an enormous 
 serpent which was coiled around his body. The same observers, 
 on turning to the north, pictured a second man, kneeling on one 
 knee, and pressing the head of a winged dragon with the other 
 foot. 3 The stars which were faintly visible above the southern 
 horizon were afterward worked into the picture, and the knowl- 
 edge of it was handed down, from generation to generation, as 
 a divine revelation, to change or add to which would be sacrilege. 
 
 These picture-makers appear to have domesticated cattle, 
 sheep, goats, dogs, and horses. They hunted bears, lions, and 
 
 1 In after years the Precession of the Equinoxes made this winged dragon slip 
 off the pole of the heavens. He was then said to have been overcome by the 
 stalwart Michael and thrown into a pit that had no bottom. One rather lurid 
 writer tells us that "his tail drew the third part of the stars of heaven, and did 
 cast them to the Earth." 
 
 2 See the Constellation Chart at the end of this book. 
 
 8 The head of this winged dragon was then turned threateningly toward the 
 man, and had two bright stars for eyes. Its wings have since then been cut off, 
 in order to make room for other constellations. Its head has also been turned 
 around, for the same reason, so that its fierce basilisk stare has been lost. 
 
118 HOW TO KNOW THE STARRY HEAVENS 
 
 hares, using bows and arrows, as well as spears. They do not 
 appear to have been acquainted with the tiger, elephant, camel, 
 hippopotamus, or crocodile. To their north lay a sea, and they 
 were familiar with ships and with sea-monsters. They sacri- 
 ficed on altars ; knew the stories of the Fall and of the Deluge, 
 and probably devised many of the constellations to keep record 
 of them. 
 
 These constellations became known to the Greeks. They are 
 described in a poem of Aratus (260 B. c.), and are mentioned in 
 the star-catalogue of Ptolemy (150 A. D.). In modern times 
 their religious significance has been lost. From time to time 
 their irregular and arbitrary boundaries have been changed, and 
 a number of other groups have been formed, to fill in the vacant 
 places. About 90 constellations are now recognised. 1 
 
 Most of the larger stars are known by names which were 
 given them by the Arab astronomers. Large numbers are dis- 
 tinguished by the genitive form of the name of the constella- 
 tion in which they occur, with a Greek letter prefixed to it. 
 Many thousands are known only by numbers in certain star- 
 catalogues. The great majority of telescopic stars have no 
 names at all. 
 
 It is not necessary to describe the constellations here, as they 
 are best studied by night, under the blue heavens, with an oc- 
 casional reference to a star atlas. The four star charts given 
 at the end of the book will be a help to beginners who live 
 in the Northern Hemisphere. One of them gives the North 
 Polar heavens, and the other three include all the Equatorial 
 constellations. In order to avoid confusion, no names or di- 
 visions are marked on these charts, but each one is accom- 
 panied by a key, giving all necessary particulars. 
 
 The first of the Equatorial Charts is intended to be used in 
 the spring (from December to March), the second in the sum- 
 
 1 Those interested in the ancient constellations should read an article by the 
 late Richard A. Proctor, in his "Myths and Marvels of Astronomy," and another 
 by E. W. Maunder (F.E.A.S.), entitled "The Oldest Picture Book of All," in 
 the "Nineteenth Century Magazine" for September, 1900. 
 
FIG. 64. THE GREAT NEBULA IN ANDROMEDA 
 
CONSTRUCTION OF THE UNIVERSE 119 
 
 mer (from April to July), and the third in the autumn (from 
 August to November). The Polar Chart can be used all the 
 year round. 
 
 In order to understand these charts, the learner should go 
 outside on a clear starlight evening, about nine o'clock, and 
 seat himself in a rocking-chair, facing the south. If he can tilt 
 the chair back against some trustworthy support, it will be an 
 advantage, as he may otherwise see the wrong kind of stars. 
 A dark lantern will be an assistance, to enable him to see the 
 charts and keys at intervals. 
 
 Let the beginner now select the Equatorial Chart which is 
 suitable for the time of the year. At the foot of the chart 
 he will find a number of dates. Selecting the date which comes 
 nearest to that of his observation, he will find that the stars 
 represented above it agree with those in the heavens in front of 
 him, from the horizon to the point overhead. 
 
 When the beginner wishes to identify the stars which are 
 farther north than the point overhead, he should take the Polar 
 Chart and turn it till the proper date is at the foot of the chart. 
 He can then lean well back in his chair, when he will be able 
 to recognise the resemblance between the brightest of the stars 
 above him and those represented on the chart. With the help 
 of the proper key the names of the stars and constellations can 
 be gradually and pleasantly acquired. 
 
 A good way to make a beginning is to get acquainted with 
 the names and positions of the brighter stars on clear evenings, 
 to divide them up into squares, triangles, etc., and then to fill 
 in with the fainter ones. After having done this in the Polar 
 regions, they can be connected with stars farther south, giving 
 particular attention to those on or near the Equator and Ecliptic. 1 
 
 1 The Equator can easily be found by fastening a stick or pointer to the top 
 of a fence, so that it points to the northwestern star in the Band of Orion, when 
 it is due south. All the Equatorial stars will occupy the same position when 
 they come to the local meridian. The Ecliptic can easily be found (approximately) 
 by noting the position of the Moon among the stars every night that it is visible. 
 The large planets are also on or near the Ecliptic. To prevent their being mis- 
 taken for stars it should be remembered that they do not twinkle, but shine with 
 
120 HOW TO KNOW THE STARRY HEAVENS 
 
 In the course of a year the greater part of the heavens will 
 thus come under observation without the necessity of staying 
 up late at night. 1 
 
 Most of the stars in these constellations are only visually 
 connected, so that an observer in a distant solar system would 
 find them altogether differently arranged. There are many 
 natural groupings, however, like that known as the Pleiades, 
 and another including several of the brighter stars in the con- 
 stellation of the Great Bear. Such natural groups are being 
 discovered by the fact that the stars composing them are drift- 
 ing in the same direction and at the same speed. 
 
 Most of the telescopic star-clusters are evidently family 
 groups, as are also the thousands of double, treble, and quad- 
 ruple stars which revolve around their common centres of 
 gravity. 
 
 THE GALAXY 
 
 " A broad and ample road whose dust is gold, 
 And pavement stars." Milton. 
 
 The largest and most important structure in the visible Uni- 
 verse is that nebulous haze of invisible suns which is known as 
 the Via Lactea, the Galaxy, or the Milky Way. In fact, if the 
 Universe were no larger than the visible part of it, we might al- 
 most say that the Universe itself consisted of the Milky Way 
 and its appendages. 
 
 With the naked eye the Galaxy forms the most conspicuous 
 object of the midnight heavens. It is an irregular hazy ring 
 crossing the celestial sphere in a great circle. This circle is 
 like that containing the Signs of the Zodiac, but is very much 
 more tipped up with reference to the equator. A telescope of 
 
 a steady unflinching light. It will soon be found that they gradually change 
 their positions among the stars that lie near the Ecliptic. 
 
 1 "Astronomy without a Telescope," by E. W. Maunder, F.R.A.S., will be 
 found to make the subject more interesting. This may be followed by the study 
 of "Astronomy with an Opera Glass," and "The Pleasures of the Telescope," 
 both bv Garrett P. Serviss. 
 
CONSTRUCTION OF THE UNIVERSE 
 
 moderate power shows that it consists of a "blinding snow- 
 storm " of suns and star-clusters. 
 
 This Milky Way was formerly considered to form a kind of 
 irregular disc or " grindstone," with our Solar System not very 
 far from its centre. More accurate observations, however, have 
 caused this theory to be discarded. It is now believed to con- 
 sist of long spiral wisps or serpent-like streams of nebulous 
 haze, of more or less circular section, and considerably distorted 
 by projection. In one place the main stream splits in two, but 
 finally comes together again. This split portion has a number 
 of narrow nebulous channels crossing the dark interval which 
 separates them, and dividing it into irregular islands, or " coal- 
 sacks." If we were on one side of this Milky Way, instead of 
 being inside it, we should probably see it as a vast ring-like spiral 
 nebula, with its centre of rotation still comparatively empty. 
 
 If the observer is favourably situated, nearly all of the Milky 
 Way may be seen from one .station in the course of a long 
 winter night. Such an observation will soon show that, al- 
 though very irregular, these " flowing robes of infinite space " 
 form, on the whole, a nearly complete girdle around our part of 
 the Universe. 
 
 With a telescope it is easily seen that the Galaxy consists 
 of an innumerable host of telescopic stars, promiscuously dis- 
 tributed, with thicker clusters or aggregations here and there 
 (see Figures 47, 48, and 61). Even the naked-eye stars (with 
 the exception of the nearest) are found to be most numerous in 
 and around the Milky Way, and to thin out gradually as we 
 approach its poles on either side. The same is true of the 
 stellar nebulae. The entire visible system probably resembles 
 a watch in shape, slowly rotating on its axis, and condensing 
 into a flat spiral disc. 
 
 THE NEBULA 
 
 While it is found that the stars and stellar nebulae are most 
 numerous near the Milky Way, it is rather startling to find 
 that with the Gaseous Nebulae the reverse is true. There are 
 
HOW TO KNOW THE STARRY HEAVENS 
 
 very few of them in or near the Milky Way, and they increase 
 in numbers toward its poles. 
 
 The Magellanic Clouds, in the Southern Hemisphere, greatly 
 resemble the Milky Way in appearance ; but, instead of being 
 composed of stars and stellar nebulae, they consist of stars and 
 gaseous nebulae. 
 
 Some nebulae are diffuse and sprawling, as though the central 
 attraction was not strong enough to draw them together or had 
 been overpowered by some outside influence. One of them has 
 been traced along the starry sphere for a length of 8 degrees. 
 Supposing that its distance from us is only two million times 
 the Sun's distance (and it can hardly be less), it must be as 
 long as from here to the nearest star. Though many of the 
 gaseous nebulas are of enormous thickness, they all appear to 
 be transparent. 
 
 The late Professor Keeler, a short time before his death, 
 found that the telescopic camera showed twenty times as many 
 nebulae as the telescope alone. The number within the range 
 of the photographic telescope is now put at 120,000 or more, 
 and the majority of them are more or less spiral, like those 
 represented in Figures 63 and 85. 
 
 The Great Nebula in Andromeda has a condensed nucleus 
 (giving a continuous spectrum) surrounded by a swirl of nebu- 
 lous matter. In fact, it looks not unlike the planet Saturn 
 surrounded by its rings (see Figure 64). It is, however, im- 
 mensely larger than our entire Solar System, and is probably a 
 galaxy of suns. 
 
 When a spiral nebula is turned edgeways to us, it is not 
 recognisable as a spiral, but has a more or less lenticular shape 
 (see Figure 65). The remarkable Ring Nebula in Lyra re- 
 sembles in telescopic appearance one of the familiar vortex 
 rings which occasionally rise from the smoke-stack of a steam- 
 engine. Like most of the ring-nebulae, it has a faint star in its 
 centre. But photographs recently taken by Professor Schae- 
 berli at Ann Arbor, Michigan, show that a two-branched spiral 
 originates at and surrounds this central star. The visible nebu- 
 
FIG. 67. THE TRIFID NEBULA IN SAGITTARIUS 
 
 Composed of glowing gas. The rifts were probably caused by stars drifting through 
 body of nebula. 
 
CONSTRUCTION OF THE UNIVERSE 
 
 lous ring is the most prominent part of this double spiral (see 
 Figure 66). 
 
 Other nebulae have very irregular outlines, at some places clean 
 cut, and elsewhere fading gradually away. Some are split up 
 by sharp fractures, as though they had been torn asunder by 
 some wandering star drifting through them. Such is the Trifid 
 Nebula in Sagittarius (see Figure 67). The Great Nebula in 
 Orion also has some of these peculiarities, and has several nebu- 
 lous stars connected with it. Its present irregular outlines may 
 be partly due to the disrupting influence of these stars, or it is 
 possible that the neighbouring nebula may have collided with 
 it. Seen through a powerful telescope, it forms one of the most 
 magnificent objects in the heavens. Its real size is so enormous 
 that the mind cannot realise its vastness. It has been estimated 
 that if a million discs as large as the orbit of Neptune were 
 placed in front of the nebula, they would not be sufficient to 
 hide it from us. The spectroscope shows that the matter com- 
 posing it is in the form of gas so diffuse as to be almost a 
 vacuum (see Figure 68). 
 
 It was formerly supposed that all nebulae are at an intense 
 heat, causing the peculiar glow which makes them visible to us. 
 It seems probable, however, that the more diffuse of them are 
 at the temperature of space ( 230 F.), and that their light is 
 an electrical phenomenon due to a rain of negatively charged 
 particles driven off from the stars (in the form of coronas) by 
 the repulsive action of light. This would explain the simple 
 nature of their spectra, as the glow would be chiefly confined to 
 the surface, where the lighter gases, like hydrogen and helium, 
 collect. 
 
 UNSOLVABLE PROBLEMS 
 
 Although a great many facts bearing on the distribution and 
 relationships of the visible stars and nebulae have been discov- 
 ered in the last few years, we are not yet in a position to give 
 a satisfactory answer to the questions asked in the quotation at 
 the beginning of this chapter. At present we can only say, with 
 the late Richard A. Proctor : 
 
124 HOW TO KNOW THE STARRY HEAVENS 
 
 "The sidereal system is altogether more complicated and more 
 varied in structure than has hitherto been supposed : in the same 
 region of the stellar depths co-exist stars of many orders of real mag- 
 nitude ; all the nebulse, gaseous or stellar, planetary, ring-formed, 
 elliptical, and spiral, exist within the limits of the sidereal system ; 
 and, lastly, the whole system is alive with movements the laws of 
 which may one day be recognised, though at present they are too com- 
 plex to be understood." 
 
 The Universe is so vast that a bird's-eye view of it cannot be 
 obtained from a single standpoint, and though that standpoint 
 is being swept along through the lofty corridors at a speed fifty 
 times as great as that of a cannon-ball, the life of the human 
 race is hardly long enough to profit by the change of position. 
 We are like the man in the forest who said that he could not 
 see the wood for the trees. Even in those parts where we 
 imagine that we can see a limit to the celestial forest, we can- 
 not be sure that it is not a mere clearing in the woods, or a gap 
 between our forest and the next one. And the situation is com- 
 plicated by the fact that the celestial trees are not anchored fast 
 to a visible ground, but are drifting around in all directions, 
 while we are prisoned on a conveyance whose movements we 
 are utterly unable to control. 
 
 To use the simile of Sir Isaac Newton, we can learn some- 
 thing of the celestial pebbles that lie around us, but the great 
 ocean is beyond. The finite cannot grasp the infinite, nor can 
 the ephemeron comprehend the eternal. And if it could, what 
 then? 
 
FIG. 68. GREAT NEBULA IN ORION 
 Lick photograph. 
 
 Irregular mass of glowing gases. Many millions of times larger than Solar System. 
 Irregularities possibly due to collision with neighbouring nebula. 
 
CHAPTER XI 
 
 SOLAR ARCHITECTURE 
 
 "We know the Sun to be infinitely more complex in structure . . . than it 
 was formerly supposed to be. ... We have learned that . . . the glowing veil 
 of air hides by day . . . the largest (though not the most massive) part of that 
 Sun." Richard A. Proctor. 
 
 THE individual construction of the stars themselves can 
 best be found by studying our Sun and comparing its 
 peculiarities with those of more distant suns. This comparison 
 has led to the discovery that no two stars are at precisely the 
 same stage of evolution. 
 
 INTERIOR OF SUN 
 
 Our Sun appears to be still gaseous with heat, from centre to 
 circumference. But its constituent gases are so compressed by 
 the attraction of its huge mass, that it is, on the average, denser 
 than water. It has in fact the density of a liquid with the 
 mobility of a gas. In other words, it is composed of glowing 
 "gaseous-liquids," the central layers of which are extremely 
 dense (for gases), while the outer layers are only moderately so. 
 
 The gaseous-liquid nature of the interior is shown by the 
 average density of the Sun, which is 1.4 that of water. This is 
 about what might be expected for a huge mass of intensely hot 
 gas, but is far too small for solids or liquids, taking into con- 
 sideration the fact that solar gravitation is more than 27 times 
 as great as that of the Earth. 
 
 That the interior is not solid may also be seen from the fact 
 that the surface heat is kept up by a continuous supply of hot 
 material from below. This interior heat is actually due to the 
 contraction or shrinkage of the outer layers of the Sun as they 
 
126 HOW TO KNOW THE STARRY HEAVENS 
 
 cool off. The whole Sun may be said to boil, the hot gases 
 forcing their way (explosively or otherwise) to the surface, cool- 
 ing off somewhat, and then sinking. If the interior were solid, 
 or if a solid crust were to form, this " boiling " circulation would 
 cease, the heat would not be so free to rise, and the surface 
 would lose its heat and become dark. Some day this will take 
 place, and we shall then have to look for another source of heat, 
 or get used to the intense cold of interstellar space. 
 
 This is the period referred to by George Sterling when he 
 says: 
 
 " The Night inevitable waits 
 
 Till fails the insufficient Sun, 
 And darkness ends the toil begun 
 By Chaos and the morning Fates. 
 
 " And star ward drifts the stricken world, 
 Lone in unalterable gloom, 
 Dead, with a Universe for tomb, 
 Dark, and to vaster darkness whirled." 
 
 The Testimony of the Suns. 
 
 Judging from the Sun's outer characteristics, it is almost cer- 
 tain that there are no compound substances in its interior. It 
 is even possible that the so-called elements themselves are dis- 
 sociated, by the intense heat, into one primitive form of matter, 
 which exists only in the gaseous-liquid state. 
 
 THE PHOTOSPHERE 
 
 The solar photosphere is a dazzlingly incandescent globular 
 shell surrounding and concealing the main body of the Sun. It 
 is indeed the only part of the Sun which is usually visible to 
 us. It is composed of closely packed clouds of intensely hot 
 metallic vapours. 
 
 These photospheric clouds are probably long and pillar-like, 
 floating upright in the metallic atmosphere of permanent gases 
 which surrounds the main body of the Sun. Under ordinary 
 circumstances only the bright tops of these radial clouds are 
 visible to us. As the spaces between them are comparatively 
 
SOLAR ARCHITECTURE 127 
 
 dark, the result is that the entire surface of the Sun has a 
 granulated or mottled appearance when seen through a power- 
 ful telescope. It looks, indeed, like a piece of grey cloth stretched 
 over a hoop, with rice-grains or snowflakes thickly scattered 
 over it. 
 
 The particles composing these upright floating clouds probably 
 rise (in a gaseous state) from the inconceivably hot interior of 
 the Sun, and gradually cool off' through expansion and outward 
 radiation. At a certain elevation the diminished pressure and 
 temperature cause them to condense into the brilliant vaporous 
 clouds whose tops form the visible photosphere. 
 
 As the rising, cooling, and condensing processes go on all 
 around the solar nucleus, there is probably a continuous del- 
 uge of white-hot metallic " rain " descending Sunward from the 
 chilled summits of these radial luminous clouds. 
 
 It is possible that in the case of refractory elements like car- 
 bon, calcium, etc., the liquid drops " freeze " and descend in a 
 "hailstorm" of genuine diamonds and solid metal shot. If 
 this is so, it is evident that the falling " hail " will be remelted 
 and vaporised as soon as it reaches a sufficiently hot layer of 
 gases. The extraordinary brilliancy of the solar photosphere 
 may be largely due to the clash of these diamonds and metal- 
 lic shot, as they fall back in a continuous incandescent hail- 
 storm onto the ascending gases beneath them. 
 
 FACUL.E AND SUN-SPOTS 
 
 The intense activity of internal physical action is sometimes 
 indicated by the appearance of certain dark blotches on the 
 otherwise fair face of the photosphere. These are commonly 
 known as Sun-spots, and are usually surrounded by brilliant 
 eruptive patches of piled-up photospheric clouds or faculce. 
 
 The Sun-spots are more or less irregular black hollows which 
 occasionally form in the cloudy photosphere on each side of the 
 solar equator, and are seen to drift around as the Sun rotates 
 on its axis (see Figure 24). They are most abundant at rather 
 irregular intervals of about eleven years. At the beginning of 
 
128 HOW TO KNOW THE STARRY HEAVENS 
 
 one of the Sun-spot periods the spots are some distance north 
 and south of the Equator. Later on, the Sun-spot areas move 
 nearer to it, so that the last spots seen, in one such period, are 
 not far from the Equator. 
 
 The Sun-spots usually break out in the midst of a piled-up 
 mass of brilliant faculce. At first they appear as irregular black 
 openings in the bright photosphere. They gradually increase in 
 size and become more circular in outline. The lower ends of 
 the long perpendicular clouds which (presumably) compose the 
 surrounding photosphere gradually drift into the opening, so that 
 the spot becomes a saucer-shaped depression. The black bottom 
 of this saucer is known as the Sun-spot nucleus, and the semi- 
 dark fringed sides form what is known as the penumbra. 
 
 The nucleus itself is sometimes 40,000 to 50,000 miles in 
 diameter, the surrounding penumbra being occasionally 150,000 
 miles across. 1 
 
 Sun-spots vary in depth from 500 to 2,000 miles, and are 
 filled with cooler and therefore less luminous gases, which ab- 
 sorb the light from below. The blackness is only the result of 
 contrast, for their gaseous contents are really hotter and brighter 
 than molten steel. There appears to be a spiral uprush of hot 
 gas all around the spot, with a descending current in the mid- 
 dle. They are evidently related to the cyclones, tornadoes, 
 etc., in the temperate regions of our Earth. The surrounding 
 penumbra consists of jets, swirls, and cataracts of luminous 
 vapour surging into the abyss. Long plume-like " bridges " of 
 superheated gas occasionally shoot out from the sides and cross 
 the cavity, which is finally covered up by dazzling masses of facu- 
 Ise (see Figures 25 and 69). When these brilliant inrushes of 
 vapour are crossing the abyss, they produce an electrical activ- 
 ity which extends far out into space. On our Earth it produces 
 the polar phenomena known as the Aurora, and causes power- 
 ful currents in all kinds of electrical apparatus. These latter are 
 commonly known as electrical storms. 
 
 1 If the great Sun-spot of 1858 had been 35 times larger, it would have cov- 
 ered the entire surface of the Sun, and practically put it out of business for the 
 time, so far as illuminating and heating purposes are concerned. 
 
SOLAR ARCHITECTURE 129 
 
 ROTATION 
 
 An examination of the time which it takes the spots and 
 granulations of the photosphere to move across the disc as 
 the Sun rotates shows that the clouds at a distance from the 
 Equator take a longer time to complete a rotation than those 
 on or near to the Equator. While the Equatorial granulations 
 rotate in 25J days, the spots take more than a day longer to 
 complete their rotation. And the granulations near the Poles 
 take about 40 days to go once around. This shows the gaseous 
 mobility of a great part, and probably of the entire mass, of the 
 Sun. 
 
 THE CHROMOSPHERE 
 
 I have said that the dazzling white clouds which form the 
 visible photosphere float in an atmosphere of uncondensed gases. 
 This metallic atmosphere, or veil, is ruddy, but tolerably trans- 
 parent. It extends 4,000 or 5,000 miles above the luminous 
 clouds, and has a ragged storm-tossed surface (see Figure 27). 
 It is known as the chromosphere, sierra, or solar atmosphere, 
 The lower portion of it (about 500 miles thick) is known as 
 the " reversing layer." a The spectroscope has shown that this 
 lower and denser portion consists of metallic gases,- with some 
 non-metallic elements, all free and uncombined on account of 
 the intense heat. The most abundant (or at least the most 
 recognisable), are hydrogen, calcium, iron, manganese, nickel, 
 and titanium. The following are also present : barium, carbon, 
 chromium, cobalt, germanium, helium, magnesium, platinum, 
 silicon, silver, sodium, and zinc. There is also strong evidence 
 of the presence of aluminium, cadmium, copper, lead, molybde- 
 num, oxygen, palladium, uranium, and vanadium. 
 
 In addition to these elements, there are lines indicating the 
 existence of substances as yet unknown on Earth. 
 
 1 This name is derived from the fact that a spectrum formed from its light alone 
 has the usual dark solar absorption lines reversed into bright radiation lines. This 
 ' ' flash spectrum " can be obtained for only a few seconds at the beginning or end 
 of a solar eclipse. 
 
 9 
 
130 HOW TO KNOW THE STARRY HEAVENS 
 
 There are no signs of chlorine, nitrogen, gold, mercury, phos- 
 phorus, sulphur, and some other elements. This does not, 
 however, prove that they are not present in other parts of the 
 Sun. 
 
 The upper and thinner portion of the sierra does not contain 
 the numerous metals found in its lower " reversing layer." It 
 is composed of hydrogen, helium, and one or two other perma- 
 nent gases. 1 
 
 ERUPTIVE PROMINENCES (METALLIC FLAMES) 
 
 In the Sun-spot zones on either side of the Equator, immense 
 red jets of glowing gas rise between the white clouds of the 
 photosphere, pass through the sierric atmosphere, and extend 
 many thousands of miles above it. They are known as eruptive 
 prominences or metallic flames (see Frontispiece and Figures 26, 
 27, and 70). The highest one ever seen rose more than 
 350,000 miles above the general surface. 
 
 These red metallic flames are best seen when on the edge of 
 the Sun. When they are on our side they are invisible with 
 the telescope, but their upper surfaces can be photographed (at 
 different elevations) with the aid of Professor Hale's spectro- 
 heliograph. In this position they are known as Eruptive Cal- 
 cium Flocculi (see Figure 128). 
 
 These eruptive flames, or flocculi, consist chiefly of gaseous 
 calcium, hydrogen, sodium, magnesium, and iron. They ap- 
 pear to be forced up by explosive physical changes below the 
 photosphere, but their great elevation is probably due to the re- 
 pulsive action of light on the small particles of which they 
 consist. 
 
 CLOUD PROMINENCES (HYDROGEN FLAMES) 
 
 Above the sierra or chromosphere there are also to be seen huge 
 ruddy clouds consisting of hydrogen and helium. When they 
 are seen in profile, at the edge of the Sun, they are known as 
 
 1 The non-metallic elements are here printed in italics. 
 
SOLAR ARCHITECTURE 131 
 
 cloud prominences or hydrogen flames. When they are on 
 our side of the Sun, and are photographed from overhead 
 by means of the spectroheliograph, they are called hydrogen 
 flocculi. 1 They are not confined to latitudinal belts or zones, 
 like the eruptive ones just mentioned, but are to be found over 
 all parts of the Sun's surface. There does not seem to be any 
 atmosphere for them to float in. Like the eruptive prom- 
 inences, they appear to be composed of extremely small particles 
 of matter, upborne by the repulsive action of the Sun's light. 
 
 FIG. 71. A SOLAR "CLOUD" OF GLOWING HYDROGEN 
 (PROFESSOR YOUNG) 
 
 About 100,000 miles long and 54,000 miles high. Notice the 
 bright uprush below one end of it. 
 
 In 1871 Professor Young observed a hydrogen cloud about 
 100,000 miles long, with its summit about 54,000 miles above 
 the sierra. It was connected with this latter by a number of 
 vertical columns that looked like water-spouts (see Figure 71). 
 Thirty-five minutes later the cloud had been blown to pieces 
 by an eruption, and the fragments were scattered to a height of 
 207,000 miles (see Figure 72). They gradually faded away as 
 they rose, leaving an eruptive prominence 50,000 miles in height 
 (see Figure 73). The flame-like summit of this eruptive mass 
 rolled over like a breaking wave (see Figure 74), and in a few 
 minutes faded out of sight. These changes all took place in 
 about two hours. 
 
 1 For further particulars concerning the spectroheliograph and the latest 
 results obtained with its aid, see an illustrated article by Professor Hale in the 
 "Popular Science Monthly," for May, 1904. 
 
132 HOW TO KNOW THE STARRY HEAVENS 
 
 THE CORONA 
 
 The white spherical cloud-surface of the Sun has now been 
 described, and also the ruddy atmosphere and the two kinds of 
 
 prominences which rise 
 from it. But outside of 
 all these there is a ra- 
 diating halo of pearly 
 light sometimes ex- 
 tending more than 
 2,000,000 miles in every 
 direction (see Figures 
 26, 28, and 75). This 
 is known as the corona. 
 Like the eruptive prom- 
 inences, it appears to 
 start from volcanic 
 outbursts; but, its 
 particles being smaller, 
 instead of being merely 
 upheld by the radiant 
 energy of the Sun, they 
 are violently repelled, 
 so that they stream 
 forth continuously and 
 pass away into outer 
 space. When Sun- 
 spots are numerous, the 
 visible corona does not 
 extend so far as when they are absent or scarce. The greatest 
 development of the corona is over the Sun-spot zones north and 
 south of the Equator. The rotation of the Sun causes the 
 coronal streamers to bend in a plume-like manner. They are 
 not so crowded together near the poles of the Sun, so that 
 the polar streamers are very distinct (see Figure 29). 
 
 When the spectroscope is turned to this coronal halo it shows 
 a continuous spectrum crossed by bright lines. The former 
 
 FIG. 72. THE SAME REGION 35 MINUTES LATER 
 
 (YOUNG) 
 
 Rising wisps of glowing hydrogen, reaching a height 
 of 207,000 miles. The eruptive mass below is growing 
 larger. 
 
FIG. 70. SOLAK "FLAMES" OR PROMINENCES 
 
 By Zoellner. (From Comstock's " Text-book of Astronomy," published by 
 Messrs. D. Appleton & Co. ) 
 
 FIG. 76. THEORETICAL SECTION OF SOLAR PHOTOSPHERE 
 By Trouvelot. 
 
 Clouds of carbon, etc., floating in an atmosphere of metallic gases. Hot gases from 
 
 interior forcing their way out. (From Todd's " New Astronomy," 
 
 published by The American Book Co.) 
 
SOLAR ARCHITECTURE 
 
 133 
 
 FIG. 73. THE SAME REGION 35 
 MINUTES LATER (YOUNG) 
 
 The uprush has developed into a mass 
 of rolling and ever-changing "flame," 
 50,000 miles in height. 
 
 indicates the presence of solid or liquid particles, and the 
 bright lines are those of glowing hydrogen gas. There is also 
 a bright green line due to an 
 unknown gas which has been 
 provisionally named "coro- 
 nium." The atoms of these sub- 
 stances are so far apart that the 
 corona is practically a vacuum. 
 
 SOLAR ENERGY 
 
 As in the lime-light, or oxy- 
 
 calcium lamp (used for magic 
 
 lanterns, etc.), the brilliancy of 
 
 the Sun's photosphere is largely 
 
 due to incandescent calcium. 
 
 The intense bluish-white light 
 
 of this hollow cloudy sphere 
 
 forces its way through the ruddy transparent atmosphere and 
 
 prominences. In doing so it loses much of its intensity and 
 
 becomes slightly yellow. 
 It passes through the 
 coronal streamers with 
 but little loss, and 
 spreads out evenly in 
 all directions. 
 
 The planets catch a 
 little of this scattered ra- 
 diance, but the bulk of 
 it is lost in the outer 
 darkness of space. If 
 the portion of light and 
 heat received by the 
 Earth be represented by 
 the figure 1, the part 
 
 which misses the Earth will be represented by 2,200,000,000. 
 
 So that what we get is equal to one cent out of twenty-two 
 
 F IG . 74. _ THE SAME, 15 MINUTES LATER 
 (YOUNG) 
 
 In half an hour this curling prominence faded entirely 
 away. 
 
134 HOW TO KNOW THE STARRY HEAVENS 
 
 millions of dollars. What all the planets catch is equal to ten 
 cents out of the same amount of money. All the rest escapes 
 into outer space and is apparently wasted. 
 
 The amount of " waste " may be conceived from the fact that 
 (in spite of the loss by absorption in passing through the sierra, 
 etc.) every square foot of the Sun's surface continually sends 
 out into space about 10,000 horse-power of radiant energy, 
 while a square foot of our Earth's surface receives about a 
 quarter of one horse-power. 1 
 
 CAUSE OF SOLAR HEAT 
 
 Although we cannot see what is taking place beneath the 
 photosphere of the Sun, we can learn something of its anatomy 
 and physiology by indirect methods. All the surface phenom- 
 ena, revealed by the telescope and spectroscope, are due to 
 deep-seated mechanical and physical processes. Our knowledge 
 of the effects of known mechanical and physical laws enables 
 us to form some idea of what is going on below. The whole 
 body of the Sun appears to be composed of concentric gaseous 
 layers, like the coats of an onion. Each shell is denser than 
 the layer above it, and therefore thinner than the one below. 
 As the outer layers cool off by the radiation of their heat into 
 space, they settle down onto the lower layers and urge them to 
 a quicker rotation. This makes the Sun a huge electrical 
 machine, generating an enormous amount of energy, which 
 manifests itself in different forms. When the various layers 
 have reached a certain density, there is a periodical overheating 
 of the lower layers through the progressive cooling of the upper 
 ones. This periodical overheating causes the layers to react 
 on one another with great violence. The overheated gases 
 escape at every weak place, and these periodical outbursts of 
 energy are visible on the surface in the form of eruptive promi- 
 nences, Sun-spots, etc. (see Figure 76). 
 
 1 This latter would in one year lift GO short tons one mile high ; the former 
 would lift 40,000 times as much. 
 
SOLAR ARCHITECTURE 135 
 
 So much for the physical constitution of the Sun. If the 
 reader will now turn back to the section entitled " Classes of 
 Stars," in Chapter VIII, he will be able to form some idea as to 
 the physical condition of nebulae, stars, and planets, at different 
 stages of evolution. 
 
 OLD AND DYING SUNS 
 
 The common variability of red stars is evidently the outer 
 manifestation of the death-struggles of old and waning suns. 
 The vital forces of the aged stars are no longer able to prevent 
 the various elements from forming chemical combinations, 
 resulting in periodic fluctuations. Their interior forces are 
 making tremendous but unsuccessful efforts to throw off the 
 cooling vapours above, which are gradually choking the life out 
 of the dying suns. Some of them are nearly invisible, except 
 when these paroxysms are at their height. During these peri- 
 odical spasms, they glare out strangely into the darkness for a 
 time, and then subside. Their struggles grow feebler as time 
 goes on, and finally their uneasy flickering subsides into the 
 calmness and tranquillity of solar death. 
 
CHAPTER XII 
 
 A REELING WORLD 
 
 " Learned Faustus, 
 To know the secrets of astronomy, 
 Graven in the book of Jove's high firmament, 
 Did mount himself to scale Olympus' top, 
 Being seated in a chariot burning bright, 
 Drawn by the strength of yoked dragons' necks. 
 
 When Faustus had with pleasure ta'en the view 
 Of rarest things, and royal courts of kings, 
 He stayed his course and so returned home ; 
 Where such as bare his absence but with grief, 
 I mean his friends and near'st companions, 
 Did gratulate his safety with kind words, 
 And in their conference of what befel, 
 Touching his journey through the world and air, 
 They put forth questions of astrology, 
 Which Faustus answer'd with such learned skill 
 As they admir'd and wonder'd at his wit." 
 
 Marlowe, ' ' Faustus. " 
 
 A BIRD'S-EYE VIEW 
 
 IN order to ascertain some more particulars about our own 
 Earth, let us go back, for a time, to our Chariot of Imagi- 
 nation, and once more watch our Solar System from a short 
 distance away. 
 
 Let us suppose that we are so situated in space that the Sun 
 and planets appear as though they were floating in front of us, 
 on the surface of a sheet of perfectly clear water. And let us 
 suppose that (owing to a slight eddy in the water) the planets 
 are all circling slowly around the Sun. When they are between 
 us and the Sun, they drift to the right, but when they are beyond 
 it they go to the left. The surface of this imaginary sheet of 
 
A REELING WORLD 
 
 137 
 
 water will, to an inhabitant of the Third Planet, represent the 
 plane of the Ecliptic, the so-called path of the Sun. 
 
 From our supposed position in space, we can not only see our 
 own Solar System spread out before us, but also, in the far dis- 
 tance, the innumerable starry systems which surround it. Those 
 
 Pisces. 
 FIG. 77. DIAGRAM ILLUSTRATING ZODIAC 
 
 stars which are on or near the horizon of our imaginary sheet 
 of water may be conveniently divided into twelve equal groups 
 or constellations. 1 
 
 Among these twelve Signs of the Zodiac, or Ecliptic, are 
 those which bear the names of Sagittarius, Virgo, Gemini, and 
 Pisces. As these constellations will hereafter be used to indi- 
 
 1 Named as follows : 
 
 1. Aries, the Ram. 5. Leo, the Lion. 9. Sagittarius, the Archer. 
 
 2. Taurus, the Bull. 6. Virgo, the Virgin. 10. Capra, the Goat. 
 
 3. Gemini, the Twins. 7. Libra, the Balance. 11. Aquarius, the Water-Bearer. 
 
 4. Cancer, the Crab. 8. Scorpio, the Scorpion. 12. Pisces, the Fishes. 
 
138 HOW TO KNOW THE STARRY HEAVENS 
 
 cate planetary motions, their relative positions on the Ecliptic 
 are here indicated (see Figure 77). 
 
 Keeping these positions in mind, let us now turn our eyes 
 back to our own Solar System. 
 
 If we get out our telescopes and watch the Third Planet, which 
 is now known to us as the Earth, we shall see that its North 
 Pole is uppermost, but that it has a heavy list to the right. As 
 the globe spins around, the markings on its near side move to 
 the right, with a slight downward tendency due to the planet's 
 inclination. 
 
 One result of the planet not floating quite erect is that the 
 rotation causes its tropical regions to be continually dipping 
 into the water and emerging from it, while the rest of the globe 
 remains all the time either above or below the surface, which 
 represents the plane of the Ecliptic. 
 
 On turning to the other planets for comparison, we find that 
 they are rotating in the same direction. Some of them have 
 satellites, or moons, and these appear to drift around their 
 primaries in the same direction, as though the rotation of each 
 planet caused a secondary eddy in the water. It will be seen, 
 therefore, that all these movements (1) the revolution of the 
 planets around the Sun, (2) their rotation around their axes, and 
 (3) the revolutions of the satellites around their primaries are 
 in the opposite direction from that taken by the hands of a 
 watch. 1 
 
 A closer view of the satellites would show that their rotation 
 also agrees in direction with the three motions just described. 
 Some of the satellites have adjusted the speed of their rotation 
 to that of their revolution, so that they always show the same 
 side to the world they attend. 2 
 
 It is hardly necessary to say that all these agreements are not 
 
 1 The satellites of the two outside planets do not at present conform to the 
 general rule, though they probably will in the course of time. These planets ap- 
 pear to have been formed later than any of the others. 
 
 2 The two inner planets appear to have done the same thing, so that they 
 always turn the same side to the Sun. 
 
A REELING WORLD 139 
 
 accidental. There is a cause for them, as will be seen in a later 
 chapter. 
 
 If we stay where we are, and watch the movements of the 
 Earth for a few years, we shall see that while it drifts around 
 the Sun its axis keeps the same position. The result is that a 
 person living at the North Pole would have the same star over- 
 head all the year round. 
 
 When the Earth is to the right of the Sun, it is obvious that 
 the North Pole is in the dark, and that it is winter in the North- 
 ern Hemisphere (see Figure 12). When the Earth gets beyond 
 the Sun, both poles are just lighted up by it, and the days and 
 nights are equal all over the globe. This is known in the North- 
 ern Hemisphere as the Spring Equinox. When it arrives at 
 the left of the Sun, the North is enjoying its summer, and the 
 South Pole is in the dark. Finally, when the Earth reaches 
 our side of the Sun, the days and nights are again equal all 
 over the globe. This is known in the North as the Autumnal 
 Equinox. As already stated, the axis of the Earth does not 
 share in any of these movements of the planet, but remains fixed 
 with regard to the stars. 
 
 Let us now see what ideas the inhabitants of this Third Planet 
 are likely to have with regard to the various movements just 
 described. The rotation of the planet itself they will not be 
 able to perceive, so that, as it spins toward the east, they will 
 naturally fall into the delusion that the stars themselves are roll- 
 ing over toward the west. They will also naturally think that 
 the Sun and planets are doing the same thing. But as they are 
 also ignorant of the fact that their Earth is leaning over to one 
 side, they will be surprised and puzzled to find that the Sun 
 gradually drifts toward the north and south as summer and 
 winter approach. They will also find it hard to account for the 
 erratic manner in which the planets appear to move, or for the 
 fact that they always keep on or near the Sun's path. 
 
 To an outside observer these circumstances seem to be too 
 simple to require explanation, but to an inhabitant who can 
 neither see, hear, nor feel that his own world is moving, the 
 
140 HOW TO KNOW THE STARRY HEAVENS 
 
 whole of the celestial motions are puzzling to the last degree. 
 It speaks well for the intelligence of the inhabitants that many 
 of them have at last managed to find out the real facts of the 
 case. 
 
 As the Earth rolls over every day there are two points on the 
 surrounding " star-sphere " which, to an inhabitant of the planet, 
 do not appear to move, but seem to be centres of rotation. These 
 two points are opposite the North and South Poles of rotation. 
 If we let the eye follow the direction of the axis, in an upward 
 (but slanting) direction, till it reaches the stars, it will be found 
 that there happens to be a tolerably bright star near the point 
 around which the other stars appear to move. To an inhab- 
 itant of the Earth this star therefore becomes known as the 
 North Pole-Star. Let us keep this in mind, for if the axis of 
 the Earth never changes its position this star will always re- 
 main the North Pole-Star so far as the Earth is concerned. 1 
 
 There is another peculiarity about the Earth's motions that is 
 worth mentioning. The World, like all the other planets, does 
 not go around the Sun in an exact circle, but in a nearly circular 
 ellipse or oval. The result of this is that at one part of the 
 year the Earth is about 3,000,000 miles nearer to the Sun than 
 it is six months earlier or later. 
 
 From our chosen point of observation the Earth is to the 
 right of the Sun on the 21st day of December in each year, and 
 its North Pole is then turned exactly away from the Sun. This 
 part of the Earth's orbit is termed the Winter Solstice, and we 
 will call it the point A. From the Earth, the Sun then 
 appears to be in the sign or constellation of Sagittarius (see 
 Figure 77). 
 
 A few days later the Earth reaches that part of its orbit where 
 it is nearest to the Sun. This part of the orbit is termed its 
 Perihelion, and we will call it the point B. 
 
 1 In "Julius Caesar," Shakespeare makes one of his characters say: 
 
 " I am constant as the Northern Star, 
 Of whose true-fixed and resting quality 
 There is no fellow in the Firmament." 
 
A REELING WORLD 141 
 
 OUR FIRST VISIT (A.D. 1900) 
 
 Let us note the relative position of these two points in the 
 year 1900 A.D. (10 apart, measured from the Sun). Then we 
 will wait for a few thousand years, so as to see whether the two 
 phenomena always continue to happen in the same places. 
 
 SECOND VISIT (A.D. 8400) 
 
 After amusing ourselves by travelling among the stars for 
 6,500 sidereal years we return to our System (in the year 8400 
 A. D.), and look for the Third Planet. It is still spinning away 
 like a top that is wound up for ever. But, strange to say, there 
 has been a remarkable change in the position of the two points 
 A and B. The northern end of the polar axis, instead of point- 
 ing away from the Sun when the Earth was to our right (see 
 Figure 12), has reeled slowly back (or retrograded) through a 
 quarter circle. Its opposition (A) to the Sun, therefore, takes 
 place when the Earth is between us and the Sun. If we regard 
 the Earth as the hand of a watch (going around the Sun once a 
 year, the opposite way to the hands of our watches), it is evi- 
 dent that this watch has gained a quarter of a year (90 of arc, 
 measured from the Sun). For the inhabitants will tell you that 
 it is the 21st day of December, while it is evident that it ought 
 to be the 22d of September so far as the earthly revolutions are 
 concerned. 
 
 The result of this is that the Earth has now another Pole-Star, 
 and the old one appears (to the creatures on the Earth) to go 
 circling around it like all the other stars. The twelve monthly 
 " mansions of the Sun " have also swung a quarter round, so that 
 they are occupied by different sets of stars. From the Earth, 
 the December Sun now appears to be in the constellation of 
 Virgo instead of being in Sagittarius as before (see Figure 77). 
 
 Let us see whether there has been any change in the peri- 
 helion (B), the place where the Earth is nearest to the Sun. Yes, 
 it has moved forward in the orbit about 20 of arc. The two 
 points A and B, which were only 10 apart, are now 120 apart 
 
142 HOW TO KNOW THE STARRY HEAVENS 
 
 (10 +90+20=120 ). The combined result of the two changes 
 is that, instead of being nearest to the Sun at the beginning of 
 January, the Earth is now in perihelion toward the end of 
 April. 
 
 THIRD VISIT (A.D. 14900) 
 
 Let us now go away a second time for 6,500 years, and then 
 come back to our Solar System again (in the year 14900 A. D.). 
 
 The points A and B have gone on separating at the same 
 rate, so that the angle between them is now 230 of arc (10+ 
 110 +110 = 230 ), measured, as before, from the Sun. It is 
 therefore December 21 when the Earth is to the, left of the Sun. 
 A third and distant Pole-star has replaced the second one. The 
 December Sun is now in the constellation of Gemini, and the 
 Earth is nearest to the Sun in August. 
 
 FOURTH VISIT (A.D. 21400) 
 
 A third time we retire for the same length of time, and then 
 go back to our old acquaintance (A. D." 21400). By this time 
 the Earth-clock has gained three quarters of a year with refer- 
 ence to the stars, or nearly a year with reference to its peri- 
 helion (10+110 +110 +110 = 340). The Earth is now beyond 
 the Sun in December. A fourth Pole-star has replaced the 
 third one. The December Sun is now in the constellation of 
 Pisces, and the Earth is again nearest to the Sun in December. 
 
 FIFTH VISIT (A.D. 27900) 
 
 Once more we go away for the same length of time. On our 
 return (in the year A.D. 27900), the points A and B have passed 
 each other. The Earth-clock has gained a whole year with 
 reference to the stars, so that the inhabitants tell us we are a 
 year overdue. December 21 has at last reached its old camping- 
 ground to the right of the Sun (as in Figure 12). The old Pole- 
 star, that we knew so well 26,000 years ago, has returned to its 
 place of duty. And so have the twelve Signs of the Zodiac, so 
 that the December Sun is once more in the constellation of 
 
A REELING WORLD 
 
 143 
 
 Sagittarius. But the points A and B are now 90 apart, so that 
 the Earth, instead of being nearest to the Sun at the opening of 
 the year (as at our first visit, in the year A. D. 1900), does not 
 reach its perihelion until March. Figure 78 shows the posi- 
 tions of A and B at the various dates mentioned. 
 
 FIG. 78. DIAGRAM ILLUSTRATING PRECESSION OP EQUINOXES AND 
 ADVANCE OF PERIHELION 
 
 The places marked A 1, 2, 3, 4, 5, are the positions of the Earth at the Winter 
 Solstice, at the dates mentioned. The places marked B 1, 2, 3, 4, 5, are the posi- 
 tions where the Earth is nearest to the Sun at the dates mentioned. 
 
 We have now followed the backward reeling of the Earth's 
 axis for one complete re volution, which has taken 26,000 years. 1 
 This reeling of the Earth's poles around the poles of the Ecliptic 
 is known as the Precession of the Equinoxes, because it makes 
 
 1 More exactly, 25,868 years. 
 
144 HOW TO KNOW THE STARRY HEAVENS 
 
 the spring and autumn equinoxes come a little sooner every 
 revolution than they would otherwise do. It is in some respects 
 similar to the slow wabbling motion of a child's top. We may 
 almost say that our World is a big top which spins and wabbles 
 as it swings around the Sun. 1 
 
 EIGHTEENTH VISIT 
 
 If we were to keep up our periodical visits to the Earth till 
 the point B, where it is nearest to the Sun, has advanced one 
 complete revolution to its old place, it would take about 13 more 
 visits, 6,500 years apart. For this point, called the Earth's 
 perihelion, takes 109,000 years to complete its circuit. 
 
 MILLIONS OF YEARS LATER 
 
 Suppose that we now leave our System for say x millions 
 of years and then come back to it. What changes shall we 
 find on our return ? 
 
 In the first place we shall have some trouble in finding our 
 Solar System at all, for in the meantime it has drifted so far 
 that, if its curved path were straightened out, it would be equal 
 in length to Sx times the distance of Sirius. And its Sun has 
 changed from a yellowish-white star to a dark-red one, with 
 periodical spasms of brilliancy. 
 
 In the second place, when we have found it, picked out the 
 wizened relic of our once-beautiful Earth, and taken our star- 
 photographs, we shall discover that the almost inperceptible 
 drifting of the stars has by this time completely changed the 
 face of the heavens. The " sweet influences " of the Pleiades 
 (Job xxxviii, 31) have now been dissipated and lost. The 
 " Bands of Orion " are loosed for ever. The " Mazzaroth " (or 
 Signs of the Zodiac) are no more waiting to be led forth in 
 their season. And the Great Bear, with her cub, no longer re- 
 mains to be led around the " pole." Of all the constellations 
 
 1 The cause of the Precession of the Equinoxes will be dealt with in chapter 
 XV. 
 
A REELING WORLD^ 145 
 
 we used to know so well, not one is now recognisable, though 
 myriads of shining suns still sparkle in the ebon " vault." 
 
 On this our last visit to the Solar System we not only find 
 that the Sun has changed its colour and lost much of its former 
 size and brilliancy, but that the planets are not in the same 
 condition they were in before. The Third Planet, for example, 
 rotates very much slower than it used to, and its Moon is farther 
 from it. The result is that the Earth's day and month are now 
 the same length (equal to about 57 of our days). The Moon 
 still shows but one side to the Earth, and the Earth now shows 
 but one side to the Moon. They move around their common 
 centre of gravity like a huge dumb-bell with an invisible 
 handle. The Earth's oceans have partly frozen, and partly 
 soaked into the cold interior. And its atmosphere has congealed 
 into a solid snow-like substance. Like its Moon, it is a dead 
 world, waiting for the inevitable crash that is to bring it back 
 to some other form of life and usefulness. 
 
 ORBITS VARY 
 
 It may be as well to mention here that the Earth's orbit is 
 not always the shape it is now. Sometimes it is almost circu- 
 lar, while at other periods its ellipticity is so great as to make 
 the Earth's distance from the Sun vary 14,000,000 miles, instead 
 of 3,000,000 miles as at present. This change (combined with 
 the Precession of the Equinoxes, and various geographical 
 changes) produces considerable variations in the Earth's climate 
 at long-distant periods. 
 
 If we regard the Solar System as a machine, we shall see 
 that one of its eccentrics takes 109,000 years to go once around. 
 Yet there are people on Planet Number Three who think that 
 the whole Universe, stars and all, was made and wound up 
 6,000 years ago, and that in another thousand years the entire 
 machine will have run down and worn out ! 
 
 ORBITS ARE TILTED 
 
 Before quitting my illustration of a floating Solar System it 
 may be as well to say that, besides being unreal (a mere detail) 
 
 10 
 
146 HOW TO KNOW THE STARRY HEAVENS 
 
 it is faulty, even for an illustration, in one rather important 
 particular. I have imagined the various planets to be floating 
 on the surface of water. Now the fact is that the plane, or level, 
 or surface, on which one planet moves, is not exactly the plane or 
 surface on which the others move, so that, if the Earth be re- 
 garded as floating evenly on this ecliptic plane, each of the 
 other planets will be found to rise a little above its surface at 
 one part of its orbit, and to sink a little below it at another. 
 
 This is the reason why there is not an eclipse of the Sun 
 every new-moon, and an eclipse of the Moon every full-moon. 
 It is only at the two nodes, where the plane of the Moon's 
 orbit crosses the plane of the Earth's orbit, that eclipses can 
 occur. For elsewhere the Moon passes below or above the 
 straight line connecting the Earth and Sun. The same is true 
 of the " transits " and " occupations " of the planets in front 
 of, or behind, the disc of the Sun. 
 
 SAME POLE-STARS EVERY 26,000 YEARS 
 
 Now suppose that the first time we visited the Solar System 
 we took a complete set of photographs of the stars as seen from 
 Planet Number Three. And suppose that on each of our sub- 
 sequent visits we take a fresh set of photographs. On compar- 
 ing these we shall find that the stars themselves are about the 
 same, but that what should be called (but are not) their celes- 
 tial " latitudes and longitudes " are changing all the time. This 
 is of course due to the fact that the North and South Poles are 
 all the time slowly circling around the poles of the Ecliptic. 1 
 But if we make many visits with the same interval between 
 them, we shall find every fourth set practically the same. Thus 
 the first and fifth sets will be nearly alike, and so will be the 
 second and sixth, the third and seventh, and the fourth and 
 eighth. The reason for this is obvious, for when the poles 
 have " wabbled " around a complete revolution they come back 
 to the same place on the " star-sphere," and the twelve monthly 
 
 1 See North Polar Star Chart. 
 
A REELING WORLD 147 
 
 " mansions of the Sun " again coincide with the same constella- 
 tions of the Zodiac. 
 
 STARS ARE DRIFTING 
 
 But if we make a closer examination of our different sets of 
 star-maps we shall find that the stars themselves are slowly 
 moving about in space. One group of stars is drifting in this 
 direction, and another in that. Some are coming nearer to us, 
 and others are receding. Even in a group of drifting stars the 
 individuals are moving slowly around among themselves, like 
 the motes in a sunbeam. This slow drift will eventually make 
 the heavens unrecognisable. 
 
 THE GREAT PYRAMID 
 
 It is interesting to know that when the Great Pyramid of 
 Egypt was constructed, the North Pole of the Earth was nearly 
 as represented in our third return to the planet. The building 
 was "oriented " (that is, adjusted to the points of the compass) 
 by making a descending passage, down which the pole-star of 
 the period (Alpha Draconis, also known as Thuban) shone at 
 its lowest meridian passage. A temporary pool of water was 
 formed some distance down the passage, and the image of the 
 star reflected up a second (but ascending) passage. The result 
 was that the Pyramid was better oriented than any other build- 
 ing put up before the invention of the telescope. This peculi- 
 arity fixes the date at which the Pyramid was built at 3,400 
 B. c., the December Sun being then in the constellation of 
 Aquarius (Number 11 in Figure 77). 
 
 The long, narrow, but lofty gallery which formed a continua- 
 tion of the ascending passage was the most perfect transit 
 instrument ever made, leaving out those provided with magnify- 
 ing instruments. The large square platform at the top, probably 
 provided with corner-posts and observing-stations, was also an 
 excellent arrangement for the study of the heavenly bodies. 
 By the long-continued use of this truncated pyramid the science 
 
148 HOW TO KNOW THE STARRY HEAVENS 
 
 of astronomy might have been largely developed. But unfor- 
 tunately it was covered up for a tomb as soon as its childish 
 astrological purpose had been served. 
 
 THE FIRST POINT OF ARIES 
 
 In this chapter I have kept track of the planetary motions 
 by referring to the constellation which the Sun appears to 
 occupy in December. In practice it is found more convenient 
 to note what stars are beyond the Sun at the Spring Equinox. 
 Four thousand years ago the March Sun was in the constel- 
 lation of Taurus (the Bull). The Apis worship of Egypt was 
 probably founded on this fact. In Europe it was handed down 
 from father to son by such poetical expressions as " the White 
 Bull opens the year with his golden horns." Two thousand 
 years later, when the same equinox had moved back to the 
 constellation of Aries (the Earn), Jupiter Ammon was repre- 
 sented with a ram's horns. At present the spring equinox is in 
 the constellation of Pisces (the Fishes), and is moving in the 
 direction of Aquarius (the Water-Carrier). 
 
 When this slow-moving point was on the margin between 
 Aries and Pisces, it acquired the name of " the First Point of 
 Aries," and it still retains this now misleading name. 
 
 It may perhaps prevent a misunderstanding if we regard the 
 Sun (when viewed from the earth) as advancing from right to 
 left into a fresh " house " every month, while the solar houses 
 themselves are hooked on to the equinoxes and solstices, and 
 therefore drift backward at an extremely slow rate. As the 
 constellations of stars do not share in this backward drift, the 
 effect is as though the celestial bull, ram, fishes, etc., were drift- 
 ing forward from one house to another, entering a fresh " house " 
 every 2,155 years. Or we may imagine that there are twelve 
 picture frames fastened on to the Ecliptic, and that the Sun 
 goes from one frame to another in a month, going from right to 
 left. It will thus occupy one frame every January, the next 
 one, to the left, every February, etc. In this case the stars 
 
A REELING WORLD 149 
 
 form the framed pictures, and they very slowly drift in the 
 same direction, staying in each frame a little more than 2,000 
 years. 
 
 DECLINATION AND RIGHT ASCENSION 
 
 In mapping out the heavens it has been found convenient to 
 divide them into 360 " longitudinal " degrees (or into 24 hours), 
 by imaginary lines passing through the Celestial Equator to the 
 poles. The zero of these divisions crosses the Equator and 
 Ecliptic where they cross each other at the so-called First 
 Point of Aries. The same number of " latitudinal " degrees are 
 used to denote the distance of any celestial object north or 
 south of the Celestial Equator. These celestial circles are 
 identical with the terrestrial longitudes and latitudes which are 
 used to denote the position of any place on our Earth. For 
 convenience, the earthly longitudes have their zero at Green- 
 wich, England. 
 
 For the sake of simplicity, let us suppose, for a time, that we 
 are living at Greenwich. We shall find that, owing to the 
 daily rotation of the Earth, the First Point of Aries appears to 
 cross the local meridian every twenty-three hours and fifty-six 
 minutes. At the moment of crossing, the two longitudinal 
 zeros coincide, and all the stars which are on the local (Green- 
 wich) meridian at that instant might be said to have a longi- 
 tude of 0, or of hours. To prevent confusion, however, they 
 are said to have a Right Ascension of 0, or of hours. 
 
 The number of hours and minutes which elapse before a 
 certain star passes the same (Greenwich) meridian is termed 
 the right ascension of that particular star. For example, a star 
 which is on the meridian of Greenwich six hours later than the 
 Equinoctial Colure which contains the First Point of Aries is 
 said to have a right ascension of 6 hours, or of 90. 
 
 The number of degrees separating a star, etc., from the celestial 
 equator might be known as its latitude, but for convenience it is 
 really known as its North (or South) Declination. For exam- 
 ple, if it is 20 south of the Celestial Equator, it is said to have 
 a south declination of 20. 
 
150 HOW TO KNOW THE STARRY HEAVENS 
 
 By measuring the position of a star or other object in these 
 two ways, its position in the heavens can be registered with an 
 accuracy which is limited only by the imperfections of the 
 observers and their instruments. 1 
 
 CELESTIAL LATITUDES AND LONGITUDES 
 
 It will be noticed that both of these celestial measurements 
 start from zeros which move around with the Precession of the 
 Equinoxes. The result is that both the declination and right 
 ascension of every star change very slowly as the Earth's axis 
 reels round the poles of the ecliptic. To avoid this objection, 
 it would be necessary to use latitudes and longitudes based on 
 the ecliptic and its poles. For most purposes, however, the 
 equatorial and polar measurements are most convenient. 
 
 IMPROVED EQUATORIAL INSTRUMENT 
 
 At the close of the First Chapter I described a very primi- 
 tive form of equatorial instrument which could be used to 
 " place " the various heavenly bodies, and to follow their motions, 
 both real and apparent (see Figure 6). 
 
 This instrument can be greatly improved, so far as right 
 ascension is concerned, by fixing a cog-wheel with 24 teeth at 
 one end of the polar axis, and placing a spring so that it presses 
 against one of the teeth. On turning the telescope or pointer 
 around toward the east, the spring will click off the hours of 
 right ascension. When the pointer is directed to Alpheratz, 
 the upper left-hand star in the Square of Pegasus, or at the 
 most westerly star in the W of Cassiopeia, it is at the zero of 
 right ascension, which passes through the First Point of Aries. 
 One click will bring it to the right ascension of Mirach, in 
 
 1 When the observer does not live at Greenwich, he has to allow, in all his 
 calculations, for the difference in time and latitude. For, on the one hand, it is 
 obvious that if the First Point of Aries is on the meridian of Greenwich, it can- 
 not at the same time be on the meridian of New York or San Francisco. And, 
 on the other hand, it is also obvious that a star that is on the zenith at Greenwich 
 is a long way from the zenith of Cape Town, 
 
A REELING WORLD 151 
 
 Andromeda. Another click will bring it in a line with Alpha 
 Arietes, also known as Hamal. Between the fifth and sixth 
 clicks it will pass Kigel and Betelgeuse. At the tenth click 
 Kegulus will be in line. Soon after the fourteenth, Arcturus 
 will line up. Between the eighteenth and nineteenth, Vega 
 will be passed; and at the twenty-third click the two right- 
 hand stars of the Square of Pegasus will fall in line. Each 
 click will of course represent one hour (or 15) of right ascen- 
 sion (see Star Charts and Keys). 
 
 The same instrument can also be greatly improved, so far as 
 north and south declination is concerned, by fixing a similar 
 cog-wheel and spring where the telescope or pointer turns on 
 the polar axis. On turning the telescope or pointer to the 
 north or south, the spring will click off every 15 degrees. When 
 it points to Mintaka, the northwestern star in the Belt of Orion, 
 it will be on the equatorial zero. One click to the north will 
 bring it to the declination of Aldebaran, in Taurus, and of the 
 southern stars in the Square of Pegasus. One click to the 
 south of the equator will almost bring Sirius in line. Three to 
 the north will give the equatorial distance of Capella and Arided. 
 Two clicks to the south will bring it to the declination of 
 Fomalhaut (see Star Charts and Keys). 
 
 By having three times as many teeth in the two cog-wheels, 
 every click will represent 5 degrees, and the positions of the 
 stars, etc., can be more accurately ascertained. Many modern 
 telescopes have wheels or circles so finely divided that the 
 divisions have to be read off with the help of a microscope. 
 And their polar axis is turned by clockwork, so as to keep up 
 with the (apparent) diurnal motion of the heavens (see Figures 
 43, 46, and 79). 
 
 The right ascension and north and south declination of 
 " many ten thousands " of stars are accurately recorded in star 
 catalogues. By turning the two axes of an equatorial telescope 
 till the index fingers point to the position of a star as given in 
 these catalogues, it is at once placed in the centre of the tele- 
 scope's field of view. This can be done even in the daytime, 
 
152 HOW TO KNOW THE STARRY HEAVENS 
 
 and some of the stars and planets can be found and observed 
 telescopically while the Sun is above the horizon. 
 
 MERIDIAN INSTRUMENTS 
 
 If the instrument described above is pointed to the zenith 
 (or point overhead), and the polar axis is then permanently 
 clamped, the range of the telescope is reduced to a straight 
 north-and-south line, forming one half of a great circle of the 
 heavens. It can be pointed to the northern horizon, to the 
 polar axis of the heavens, to the point overhead, to the southern 
 horizon, or to any intermediate point. But it cannot be directed 
 to any part of the heavens either east or west of the local merid- 
 ian. In order to observe any heavenly body with this crippled 
 equatorial it is necessary to wait until the apparent diurnal 
 motion of the heavens brings the object to the meridian. Sup- 
 posing that we are still at Greenwich, let us wait till the zero 
 of right ascension passes the field of view, and then turn the 
 hands of a 24-hour clock till they point to 24 o'clock. The 
 clock will then register what is known as sidereal time. 1 
 
 As the northeast star in the Square of Pegasus is at present 
 close to that zero, we can start the sidereal clock when that 
 star crosses the field of view. It will be found that the star 
 known as Mirach passes at one o'clock (sidereal), Alpha Arietes 
 at two, Regulus at ten, and Arcturus at fourteen o'clock. These 
 stars are therefore said to have so many hours of right ascen- 
 sion, and by measuring the number of degrees they are north or 
 south of the Equator (90 from each of the Poles) we can ascer- 
 tain their north or south declination. 
 
 These two classes of observation are so important that greater 
 precision is obtained by using a special instrument, with no 
 polar axis, but with large and carefully constructed declination 
 circles. This instrument is called a Meridian Circle (see Fig- 
 ure 80). It is mounted on a horizontal axis lying east and 
 west. This axis rests on the top of two massive piers, so that 
 
 1 It should be regulated so as to gain four minutes in 24 hours of solar time. 
 
A REELING WORLD 
 
 153 
 
 the arrangement is similar to that of a cannon mounted on its 
 carriage. 
 
 When this meridian circle is being used as a transit instru- 
 ment, the exact sidereal time when a celestial body crosses 
 the centre of the field of 
 view is observed, and the 
 star or planet is said to have 
 a right ascension of that 
 number of hours, minutes, 
 and seconds. 
 
 When this meridian cir- 
 cle is used as a mural circle, 
 to find the distances of 
 stars, etc., from the Celestial 
 Poles or Equator, the clock 
 is disregarded, but their 
 distances from the local 
 zenith are carefully read 
 off on the large declination 
 circles attached to the axis 
 of the telescope. As the 
 distances of the local zenith 
 from the Celestial Pole and 
 Equator have been pre- 
 viously ascertained, the ze- 
 nith distance of any object 
 can easily be turned into 
 either " polar distance " or 
 declination (north or south), 
 as may be preferred. 
 
 ALT-AZIMUTH TELESCOPE 
 
 FIG. 81. ALT-AZIMUTH MOUNTING FOK 
 SMALL TELESCOPE 
 
 One of the screw motions changes the altitude, 
 and the other, the azimuth or point of the compass. 
 
 There is another form of 
 telescope-mounting known 
 
 as the alt-azimuth. As its name implies, this gives two mo- 
 tions, one around a perpendicular axis, changing the " azimuth " 
 
154 HOW TO KNOW THE STARRY HEAVENS 
 
 or point of the compass, and the other around a horizontal axis, 
 changing the " altitude " (see Figure 81). This form of mount- 
 ing, though very handy for terrestrial purposes, is inconvenient 
 for celestial objects, which almost always move at an angle 
 with the horizon. For any one living at the North or South 
 Pole, however, it is the best form, as the perpendicular axis 
 becomes a polar axis, and the instrument is transformed into 
 an equatorial. 
 
 USES OF INSTRUMENTS 
 
 It will be seen from the above that both the alt-azimuth and 
 the equatorial are capable of being directed to any part of the 
 sky, and can be made to keep a celestial object in view for any 
 length of time, provided that it is above the horizon. The alt- 
 azimuth is, however, difficult to use for most" astronomical pur- 
 poses, as the diurnal motions can be followed only by turning 
 both axes at the same time. The equatorial form is therefore 
 commonly used for general observational purposes. The various 
 attachments used for celestial photography and spectroscopy 
 are all applied to telescopes so mounted, with a clockwork 
 movement to the polar axis, to neutralise the apparent motions 
 due to the Earth's rotation. 
 
 The meridian circle, however, moves solely on the local me- 
 ridian, and no celestial object can be seen through its telescope 
 except for a few seconds every 24 hours, as it crosses the field 
 of view from east to west. Of course such a telescope is of no 
 use for " star-gazing." Its chief purpose is for measuring the 
 polar distances and] hour angles of the heavenly bodies on the 
 celestial " sphere." 
 
CHAPTER XIII 
 
 KEPLER'S THREE LAWS 
 
 " In the phenomena presented to him, man must [have early noticed] two 
 kinds of relation. Some things show themselves with other things, and some 
 things follow other things. These two kinds of relation we call relations of co- 
 existence, and relations of succession or sequence. Since what continues is not so 
 apt to attract our attention as what changes, it is probable that the first of these 
 two relations to be noticed is that of succession. . . . Now of the sequences which 
 we notice in external nature, some are variable, . . . while some are invari- 
 able. ... As to these invariable sequences, which we properly call con-sequences, we 
 give a name to the causal connection, between what we apprehend as effect and 
 what we assume as cause, by calling it a Law of Nature. ... In original meaning 
 the word law refers to human will, and is the name given to a command or rule 
 of conduct imposed by a superior upon an inferior, as by a sovereign or State 
 upon those subject to it. At first the word law doubtless referred only to human 
 law. But when, later in intellectual development, men came to note invariable 
 co-existences and sequences in the relations of external things, they were, of the 
 mental necessity already spoken of, compelled to assume as cause a will superior* 
 to human will, and, adopting the word they were wont to use for the highest 
 expression of human will, called them laws of Nature. Whatever we observe as 
 an invariable relation of things, of which in the last analysis we can only affirm 
 that ' it is always so/ we call a law of Nature." Henry George. 
 
 UNCHANGING LAWS 
 
 PEEHAPS the most striking thing in the study of astronomy 
 is the fact that everywhere there are evidences that the 
 whole Universe is absolutely ruled by unchanging laws. There 
 is no such thing as chance. Hesitation and uncertainty are 
 unknown. Knowing the forces which are at work, the as- 
 tronomer can calculate with certainty the positions and move- 
 ments of the other planets in our System for thousands of 
 years to come. And even beyond our System, at distances 
 which are too vast for the imagination itself to fathom, he can 
 
156 HOW TO KNOW THE STARRY HEAVENS 
 
 follow up the movements of some of the stellar groups and 
 predict their future positions and relations. 
 
 In order to do these things he has to cast aside all ideas of 
 chance or miracle, and rely entirely on the immutability of the 
 laws of Nature. 
 
 These natural laws must not be confounded with mere 
 human decrees, which are all more or less arbitrary, change- 
 able, and local, as well as ineffective. Human laws may to-day 
 decree that in a certain country one kind of stealing shall be 
 legal and praiseworthy, while another kind of stealing shall 
 be criminal and punishable ; and to-morrow the decree may be 
 reversed, if the rulers think fit. For example, in Old Testa- 
 ment times it was against the law to charge interest (usury). 
 At present it is a legal and even respectable custom. Some 
 day it may again become a crime. 
 
 But natural laws exist without any decree being promulgated. 
 They are not the creation or invention of mind, but the inevi- 
 table result of mathematical necessity. They rule alike the 
 entire Universe. All matter is absolutely subject to them, 
 whether it be dead or living. They are the same to-day as they 
 were a billion or a trillion years ago, and they will be the same 
 a billion or a trillion years to come. For example, 2 + 2 = 4, 
 always and everywhere. Omnipotence itself could not invent 
 or change this natural law. It would be just as true if nothing 
 existed. 
 
 George N. Lowe says of Natural Law 
 
 " The Law no contract knows, no lease 
 Of being, waning past its prime 
 She moves but in Eternities ; 
 Supreme, she hath no need of Time." 
 
 Dr. J. W. Draper, in his " Conflict Between Religion and 
 Science," says : 
 
 " Astronomical predictions of all kinds depend on the admission of 
 this fact that there never has been, and never will be, any interven- 
 tion in the operation of natural laws. The scientific philosopher 
 
KEPLER'S THREE LAWS 157 
 
 affirms that the condition of the [Universe] at any given moment is 
 the direct result of its condition in the preceding moment, and the 
 direct cause of its condition in the subsequent moment. Law and 
 chance are only different names for mechanical necessity." 
 
 KEPLER'S LAWS 
 
 It was Kepler l who first discovered the music which regu- 
 lates the whirling of the worlds through space. His explana- 
 tions of the planetary motions are known as Kepler's Three 
 Laws. They are as follows: 
 
 I. The orbit of every planet is an ellipse, with the Sun in one of 
 its foci. 
 
 II. An imaginary line drawn from the Sun to a planet will sweep 
 over equal areas in equal times. 
 
 III. The squares of the numbers representing the periodic times 
 of the planets vary as the cubes of the numbers representing their 
 mean or average distances. 
 
 These laws are easily stated, and, to one who understands 
 the meaning of the terms employed, are not difficult to com- 
 prehend. To us, indeed, they seem as obvious, natural, and 
 inevitable as the statement that two and two make four. 
 
 Yet it was not always so. For thousands of years intelligent 
 astronomers, of many nationalities, were seeking diligently for 
 these three laws, but never found them. After every other 
 theory, probable and improbable, had failed to explain the 
 apparent motions of the planets, Kepler found that the move- 
 ments of Mars could all be accounted for on the theory that 
 each planet moves in an elliptical orbit around the Sun with 
 a velocity varying with its distance from that body. Let us 
 examine his conclusions. 
 
 FIRST LAW 
 " The orbit of every planet is an ellipse, with the Sun in one of the foci." 
 
 In order to comprehend this we must clearly understand 
 what an ellipse really is. 
 
 1 Born in 1571 ; died in 1630. 
 
158 HOW TO KNOW THE STARRY HEAVENS 
 
 Get a piece of white pasteboard. Stick a pin upright on one 
 side of it, near the centre. Tie the two ends of a piece of thread 
 together, so as to make a loop three inches long. Pass one end 
 of this loop over the pin, and insert the point of a pencil through 
 the other end of it. Let the pencil-point touch the card, and 
 move it around the centre-pin so as to make a six-inch circle. 
 This circle is really an ellipse with no eccentricity. 
 
 Now stick two more pins in the pasteboard, one on each side 
 of the first, so that each is the eighth of an inch from the 
 centre one. Pass the loop over them all, insert the point of a 
 pencil as before, and again move it around on the card, keep- 
 ing the string stretched all the time. The resulting figure 
 looks like a circle, but it will be found, on measuring it, that 
 it is a trifle narrower one way than another. And instead of 
 having one centre, or focus, it has two eccentric foci, each one 
 being an eighth of an inch away from the centre of the figure. 
 The apparent circle is really an ellipse of small eccentricity. 
 
 By increasing the interval between the two pins, or foci, we 
 can produce a great variety of ellipses. When the two foci 
 are two inches apart, the resulting figure, instead of being a 
 six-inch circle, is an ellipse measuring 4 inches one way, and 
 3^ inches the other way. As each focus is some distance from 
 the centre, the figure is termed an ellipse of great eccentricity 
 (see Figure 82). 
 
 We are now in a position to understand Kepler's First Law, 
 that each planet moves in an ellipse, with the Sun in one of 
 the foci. 1 
 
 SECOND LAW 
 
 " An imaginary line drawn from the Sun to a planet will sweep over equal 
 areas in equal times." 
 
 The simplest form in which we can study this law is where 
 the elliptical orbit has no eccentricity ; that is to say, when 
 
 1 In most astronomical calculations, one focus alone is of importance, the 
 other one being placed on the shelf, along with the so-called " fourth dimension 
 of space." 
 
FIG. 82. DRAWING AN ELLIPSE 
 
KEPLER'S THREE LAWS 159 
 
 the ellipse is a true circle, with the two foci together at the 
 centre. 
 
 An ordinary carriage-wheel with twelve spokes will do to 
 illustrate this form of ellipse. The spokes of such a wheel 
 are all of the same length and are the same distance apart. 
 
 FIG. 83. AN ELLIPTICAL ORBIT, DIVIDED INTO TWELVE 
 
 MONTHLY PARTS 
 
 This ellipse is more eccentric than the majority of planetary orbits, 
 but is less so than the orbits of comets. 
 
 The spaces between them are therefore all the same size ; that 
 is, they all contain the same number of square inches. 
 
 If an insect should crawl straight along the tire of this 
 wheel at a uniform speed, it is obvious that it would always 
 take the same interval of time to go from one spoke to another, 
 and an imaginary line between the insect and the centre of the 
 wheel would always sweep over the same number of square 
 inches per second. 
 
 It is the same in the case of a planet. " An imaginary line 
 drawn from the Sun to a planet will sweep over equal areas in 
 
160 HOW TO KNOW THE STARRY HEAVENS 
 
 equal times." So when this line has swept over one twelfth of 
 the area of the orbit, one twelfth-part of the planet's revolu- 
 tionary period has passed away. 
 
 When the wheel is not a circular ellipse, but an eccentric 
 one, the details are rather different, though the law is the same. 
 In this case the spokes radiate from one of the foci instead of 
 from the centre (see Figure 83). And if the area (or number 
 of square inches) between each of the spokes is to remain the 
 same, it follows that the long spokes must be set closer to- 
 gether than the short ones. 
 
 From this it is evident that if the insect wishes to go from 
 one spoke to another in the same interval of time, it must 
 crawl slowly when on that part of the tire where the spokes 
 are long and close together, and increase its speed as it goes 
 to where the spokes are short and far apart. 
 
 It is the same in the case of a planet. The speed increases 
 and diminishes according to the planet's distance from the 
 Sun, so that, in this case too, " an imaginary line drawn from the 
 Sun to a planet will sweep over equal areas in equal times." 
 And, as in the case of a circular orbit, when this line (called a 
 radius vector) has swept over one twelfth of the area of the 
 orbit, one twelfth-^&rt of the planet's revolutionary period has 
 passed away. 
 
 Figure 83 is an exaggerated view of the Earth's orbit, with 
 12 "spokes" (or radius vectors) radiating from the Sun, which 
 occupies one of the foci. The Earth goes from one " spoke " 
 to another in an average month (about 30J days), and there- 
 fore travels faster when nearest to the Sun (in perihelion) 
 than it does six months later, when it is at its greatest distance 
 from the Sun (in aphelion). 1 
 
 1 If any orbit is correctly marked out in pasteboard, and the twelve wedge- 
 shaped pieces are then cut out, they will all be found to weigh alike, because, 
 though different in shape, they all have the same size or area. 
 
KEPLER'S THREE LAWS 161 
 
 THIRD LAW 
 
 " The squares of the numbers representing the periodic times of the planets 
 vary as the cubes of the numbers representing their mean or average distances." 
 
 The law which we have just discussed deals with the vary- 
 ing velocity of one planet alone. The one we have now come 
 to compares together the periodic times of different planets, 
 and shows that they have a definite relation to the distances of 
 the planets from the Sun. It also enables us to compare the 
 mean or average velocity of one planet with the mean or 
 average velocity of any other planet. The periodic time of a 
 planet is of course the time it takes to go once around the Sun. 
 In other words, it is the length of the planet's year. 
 
 The outer planets have a longer journey to make than the 
 inner ones. And they move with less rapidity. Consequently 
 their years or periodic times are considerably longer. 
 
 Observation has shown that Jupiter, which is 5.2 times as 
 far from the Sun as our Earth, takes 11.86 times as long to 
 complete a revolution. In other words, Jupiter's journey is a 
 little over 5 times as long as ours, but his year is nearly 12 
 times as long. 
 
 Let us see how Kepler's Third Law fits in with this. If 
 we square the periodic times, 1 and 11.86, we get (omitting 
 fractions) the numbers 1 and 140. And if we cube the distances, 
 1 and 5.2, we get 1 and 140. These results are identical. 
 
 In the above example the smaller period and distance are 
 both represented by unity (1) to save figuring. Here is another 
 example, given in miles and days. The distances of Mercury 
 and Venus from the Sun are 46,000,000 and 67,000,000 miles 
 respectively. When these numbers are cubed, the latter ex- 
 ceeds the former 6J times. Their periods of revolution are 
 88 and 225 days, respectively. When these numbers are 
 squared, the latter exceeds the former 6J times. These results 
 (like those in the Earth-Jupiter example) are identical, and if 
 we perform the operation with any two planets we get a similar 
 
 11 
 
162 HOW TO KNOW THE STARRY HEAVENS 
 
 result. So we find that " the squares of the periodic times are 
 in the same proportion as the cubes of the distances." 
 
 The velocity of a planet is easily computed when we know 
 the size of its orbit and the length of its year. Jupiter has 
 5.2 times as far to go as the Earth, so that if he moved with 
 the same velocity he would complete a revolution in 5.2 of our 
 years. As his year is 2.28 times as long as that, the average 
 velocity of the Earth in its orbit is evidently 2.28 times that of 
 Jupiter. Accordingly we find that while Jupiter travels 486 
 miles per minute, our Earth travels 1,108 miles in the same 
 interval of time (486 x 2.28 = 1108). 1 
 
 Kepler not only discovered that the planets move in ellipti- 
 cal orbits (according to the laws which he formulated), but also 
 convinced himself that their notions were due to mutual 
 attraction between them and the Sun. Unfortunately he was 
 not able to demonstrate this. It was, with him, a probable but 
 unproved theory. 
 
 1 It was afterward discovered by Newton that Kepler's Third Law is the 
 result of the solar attraction alone, so that it is only strictly correct in the case of 
 planets consisting of single infinitesimal particles. Where the planet is large, its 
 attraction must be allowed for as well. The correction does not make much 
 difference in the result, so far as the above examples are concerned, but it enables 
 us to extend the law to the satellites of planets and to stellar systems. The de- 
 tails of this correction will be found in most modern text-books. 
 
CHAPTER XIV 
 
 GALILEO'S LAWS OF MOTION 
 
 " When we find in Nature certain invariable sequences, whose cause of being 
 transcends the power of the will testified to by our own consciousness ; such, for 
 instance, as that stones and apples always fall toward the Earth ; that the square 
 of a hypothenuse is always equal to the sum of the squares of its base and per- 
 pendicular ; . . . and, so on through the list of invariable sequences that these 
 will suggest, we say for it is really all that we can say that these sequences 
 are invariable because they belong to the order or system of Nature ; or, in 
 short, that they are Laws of Nature. . . . 
 
 Why is it that some things always co-exist with other things ? The Moham- 
 medan will answer : ' It is the will of God.' The man of our western civilisation 
 will answer : ' It is a law of Nature.' The phrase is different, but the answer 
 one." Henry George. 
 
 ARISTOTLE'S THEORY OF MOTION 
 
 FEOM very ancient times men have tried to find the laws 
 which regulate motion, both on Earth and in the heavens. 
 Aristotle, the founder of science, gave the following as his view 
 of the subject : 
 
 "All simple motion must be rectilinear or circular, either to a 
 centre or from* a centre, each of which is rectilinear, or about a centre. 
 It is natural for two of the elements earth and water to tend to 
 a centre ; two air and fire which are light, to tend/rom a centre. 
 As the motion of all terrestrial elements is therefore rectilinear, it 
 seems reasonable that the celestial bodies, which are of a different 
 nature, should have the only other simple motion possible, namely, 
 circular motion." 
 
 This reasoning sounds strange to-day, though it held its own 
 until the time of Kepler. That philosopher finally threw aside 
 the celestial part of it, and substituted his laws of planetary 
 motion, dealt with in the preceding chapter. 
 
164 HOW TO KNOW THE STARRY HEAVENS 
 
 GALILEO'S LAWS 
 
 The terrestrial part of Aristotle's law also had to give way 
 about the same time. Galileo l discovered that on our Earth all 
 bodies move, or abstain from moving, according to the follow- 
 ing laws, which were put in their present shape by Sir Isaac 
 Newton. 
 
 I. Every body continues in its state of rest, or of uniform 
 motion in a straight line, unless it is compelled to change that 
 state by forces impressed thereon. 
 
 II. The alteration of motion is ever proportional to the 
 motive force impressed, and is made in the direction of the 
 straight line in which that force is impressed. 
 
 III. To every action there is always opposed an equal re- 
 action, or the mutual actions of two bodies are always equal 
 and directed to contrary parts. 
 
 FIRST AND SECOND LAWS OF MOTION 
 
 One result of the first law of motion is that a body which is 
 at rest will stay where it is until it is acted upon by some 
 force. This is obvious enough, but there is another result 
 which does not seem so clear. It is that if a body be once set 
 in motion with a certain velocity it will (if not acted on by any 
 other force) continue to move for ever in a straight line and at 
 the same velocity. This tendency to resist change (either of 
 rest or motion) is known as inertia. 
 
 We have no means of testing this first law by itself, for when 
 we examine an object which appears to be at rest we find that 
 the attraction of the Earth is holding it in its place ; and when 
 we set anything in motion we are unable to prevent other forces 
 from acting on it. If we fire a bullet out of a gun, it is acted 
 on not only by the initial impulse of the exploding powder 
 behind it, but also by the continuous attraction of the Earth 
 beneath it. It has also to contend with the continuous resist- 
 ance of the air in front of it. If any wind is blowing, it may 
 
 l Born in 1564; died in 1642. 
 
GALILEO'S LAWS OF MOTION 165 
 
 be affected by a lateral force as well. All of these modify and 
 finally overcome what (according to this law) would otherwise 
 have been a uniform motion in a straight line. 
 
 But, according to the second law of motion, any secondary 
 force impressed on the flying object produces a change of mo- 
 tion proportional to its own strength. So that, if we can ascer- 
 tain how much this second force has drawn the bullet from its 
 path, we can find where it would have gone if the second force 
 had not acted on it. 
 
 It has been found by experiment that if a bullet (or any 
 other object heavy enough practically to neutralise the resist- 
 ance of the atmosphere) is dropped from a height, the attraction 
 of the Earth will cause it to fall 16 feet in a second of time. 
 And we have seen that this force acts on the bullet even when 
 in motion. 
 
 Let us, then, select a perfectly level piece of ground (which 
 does not share in the convexity of the Earth's surface), and fire 
 a gun horizontally at a height of 16 feet above the ground. 
 We shall find that the bullet (instead of keeping on in a 
 straight line parallel with the ground) will bend down so as to 
 strike the ground in exactly one second of time. If the act of 
 firing the gun is made to release another bullet at the same in- 
 stant and from the same elevation, both bullets will reach the 
 ground at the same instant, one of them some distance away, 
 and the other beneath the gun. So far as regards the time in 
 which the first-mentioned bullet reaches the ground, it will 
 make no difference whether the charge of powder used is large 
 or small, though of course a large charge will make the bullet 
 strike farther away than it would with a small charge. 
 
 Now if we could have prevented the attraction of the Earth 
 from pulling the flying bullet 16 feet out of its course, it would 
 have kept in a straight line at the same distance from the 
 ground. 
 
 Thus we see that although the first law of motion cannot be 
 experimentally proved by itself, it can readily be tested in con- 
 junction with the second law. The only difficulty in the ex- 
 
166 HOW TO KNOW THE STARRY HEAVENS 
 
 periment is to make a correct allowance for the atmospheric 
 friction. To get the most accurate results, the experiment 
 should be performed in a vacuum, but this is easier said than 
 done. 
 
 THIRD LAW OF MOTION 
 
 The Third Law, concerning reaction, is true of both attrac- 
 tion and repulsion. It is not only true that a magnet will 
 draw a piece of iron to it, but it is also true that a piece of 
 iron will draw a magnet to it. When a gun is fired, the back- 
 ward kick of the gun is equal to the forward impulse of the 
 bullet, and if the gun and bullet were of the same weight they 
 would both go the same distance, but in opposite directions. 
 
 If two bullets are connected by a string, and then swung 
 into the air, they will circle around each other as they fly. If 
 both are of the same weight, they will swing around the centre 
 of the string. If one is heavier than the other, then the lighter 
 one will make the larger circles. In the latter case the influ- 
 ence of the small bullet will be exerted on a greater mass, and 
 will consequently draw it less out of its course. But neverthe- 
 less it is obvious that, as in the case of the bullet fired from a 
 gun, the action and reaction will be equal. 1 
 
 It is rather singular that Galileo, while discovering and 
 fighting for his laws of motion, entirely ignored Kepler's dis- 
 covery of the three laws of planetary motion, dealt with in the 
 preceding chapter. This has been charitably attributed, not 
 to vulgar jealousy, but to " a certain unconscious intellectual 
 egotism, not always unknown to the greatest minds." Ency. 
 Brit. art. " Galileo." 
 
 1 If anyone still finds these laws of motion hard to understand, he may find 
 his difficulties melt away as he reads them in the simple form in which they were 
 first given to an admiring world. They were published as follows : 
 
 I. Corpus omne perseverare in statu quo quiescendi vel movendi uniformiter 
 in directum, nisi quatenus illud a viribus impressis cogitur statum suum mutare. 
 
 II. Mutationem motus proportionalem esse vi motrici impress, et fiere sectm- 
 dum lineam rectam qua vis ilia imprimitur. 
 
 III. Actioni contrariam semper et aequalem esse reactionem ; sive corporum. 
 duorum actiones in se mutuo semper esse aequales et in partes contrarias dirigi. 
 
CHAPTER XV 
 
 NEWTON'S LAW OF GRAVITATION 
 
 " The force of gravitation acts on every particle of matter, and hence it is not 
 confined to our own World. By its action the heavenly bodies are bound to one 
 another, and thus kept in their orbits. It may help us to conceive how the Earth 
 is supported, if we imagine the Sun letting down a huge cable, and every star in 
 the heavens a tiny thread, to hold our globe in its place. ... So we are bound 
 to them, and they to us. Thus the worlds throughout space are linked together 
 by these cords of mutual attraction, which, interweaving in every direction, make 
 the Universe a unit." J. Dorman Steele. 
 
 THE LAW AND ITS PROOF 
 
 THE three laws of motion discussed in the preceding chapter 
 were at first confined to sublunary dynamics. But Sir 
 Isaac Newton 1 showed that the heavenly bodies also are subject 
 to them. He theorised, and after many years of labour proved, 
 that while they were the cause of the peculiarities described in 
 Kepler's Laws, they were themselves the result of a general 
 principle known as the Law of Gravitation. 
 According to this universal law 
 
 " All bodies in the material Universe gravitate toward each other 
 with a force which is directly proportional to their masses, and inversely 
 proportional to the squares of their distances from one another." 
 
 Perhaps the simplest form in which this law can be correctly 
 stated is that " every particle of matter in the Universe pulls 
 every other particle toward it with a force which decreases as 
 the square of the distance increases." 
 
 When the law of gravitation was first brought forward in a 
 theoretical manner, it seemed to be very feasible, but, at the 
 same time, to be incapable of proof. The assumption that the 
 
 1 Born in 1642; died in 1727. 
 
168 HOW TO KNOW THE STARRY HEAVENS 
 
 attracting force varies directly in proportion to the masses 
 hardly required any proof ; it simply meant that a body com- 
 posed of three atoms would attract three times as strongly as a 
 body composed of one atom. It could no more be questioned 
 than the statement that three equal masses of iron will, under 
 similar conditions, weigh three times as much as one such mass 
 alone. But the assumption that the attraction of one body for 
 another varies in the inverse proportion to the square of the 
 distance separating them was neither obvious nor easily proved. 
 There was this to be said in favour of the proposition, however, 
 that light, heat, and similar forces vary in intensity according 
 to this rule. For example, if a small lamp shines through a 
 square twelve-inch hole in a screen one yard away, so as to 
 light up part of another screen two yards from the lamp, it will 
 be found that the area illuminated on the second screen contains 
 four square feet. It is therefore four times as large as the hole 
 in the first one, and the intensity of the light is obviously 
 reduced to one quarter of what it was at half the distance. If 
 the second screen be moved to a distance of three yards from 
 the lamp, it will be found that the area illuminated measures 
 nine square feet. It is therefore nine times as large as the hole 
 in the first screen, and the intensity is evidently only one ninth 
 of what it was at one third the distance. The rule holds good 
 for any distance, provided that none of the light is absorbed by 
 fog, etc. 
 
 Newton theorised that the attraction of all the atoms com- 
 posing the Earth would act as though the pull came from the 
 centre of the Earth. Now this attraction is strong enough to 
 cause a body on the surface (about 4,000 miles from the centre of 
 attraction) to fall 16 feet in one second of time. If this law 
 of gravitation is true, then an object twice as far from the centre 
 of the Earth should drop only one quarter as far in the same 
 interval of time, an object three times as far from the centre 
 should fall only one ninth as far in a second, and so on for all 
 distances. 
 
 Newton could easily have proved or disproved this theory if 
 
FIG. 84. MOUNT LOWE OBSERVATORY, IN SOUTHERN CALIFORNIA 
 
NEWTON'S LAW OF GRAVITATION 169 
 
 he could have gone up 4,000 and 8,000 miles to see how far the 
 Earth's attraction would cause a body at those distances to fall 
 in a second. But unfortunately he was not able to do this. 
 
 Finally he found a way to get over the difficulty by taking 
 advantage of the presumed fact that our Moon is kept in her 
 orbit by the attraction of the Earth. It has been already shown 
 that on the Earth's surface a bullet fired horizontally from a gun 
 is, in one second, pulled 16 feet out of its direct course by the 
 attraction of the Earth beneath. That is to say, it falls just as 
 fast when it is flying through the air as when it is simply 
 dropped from the hand. Now the Moon is 60 times as far from 
 the centre of the Earth as we are. Let us look on it as a big 
 bullet fired horizontally at that height. We shall then see that 
 the Earth's attraction is pulling it out of the straight course 
 it would follow if suddenly left to itself. The theory is that 
 the Earth's attraction decreases as the square of the distance 
 increases. The square of 60 is 3,600, so that the Moon should, 
 in one second of time, be pulled out of its straight course the 
 3,600th part of 16 feet. This is about one twentieth part of an 
 inch, and it fits in exactly with the observed motion of the 
 Moon in its orbit. The theory is therefore true, so far as the 
 Earth and Moon are concerned. 1 
 
 The law has since been applied to all the planets revolving 
 around our Sun. The satellites of Jupiter, etc., are found to 
 
 1 Although this law of gravitation was unknown before Newton, its existence 
 and universality were suspected by Galileo and hinted at in his " Dialogo dei 
 Massimi Sistemi." In one place he says: 
 
 " Le parti della Terra hanno tal propensione al centre di essa, che quando ella 
 cangiasse luogo, le dette parti, benche lontane dal globo nel tempo delle muta- 
 tioni di esso, lo seguirebbero per tutto ; esempio di ci6 sia il seguito perpetuo delle 
 Medicee, ancorche separate continuamente da Giove. L'istesso si deve dire della 
 Luna, obligata a seguir la Terra." 
 
 Rather freely translated, this reads : 
 
 " The different parts of the Earth have such a propensity toward its centre 
 that, though it should change its place, the said parts, although far from the globe 
 in the time of its change, would follow it everywhere. An example of this is the 
 perpetual following of the satellites of Jupiter, although always separate from the 
 planet. There is a similar instance in the case of the Moon, obliged to follow 
 the Earth." ' 
 
170 HOW TO KNOW THE STARRY HEAVENS 
 
 conform to it, and the cometary messengers of heaven are bound 
 by it. Even the starry systems appear to circle in complete 
 bondage to this universal law of gravitation. 
 
 PLANETS SECURELY TETHERED 
 
 We now come to two questions which often puzzle those who 
 have not made a study of the subject. Why does not a planet, 
 when it reaches its perihelion, continue to approach the Sun in 
 a closing spiral till it finally falls into it ? And why does it 
 not, when at its aphelion, continue to recede in an opening 
 spiral, and finally go off into the outer darkness of space ? So far 
 as the principles involved are concerned) these questions are not 
 difficult to answer satisfactorily. But mathematics are neces- 
 sary if we wish to go into details and prove every point. 
 
 Let us take a single planet moving in a very eccentric orbit. 
 We will suppose that it has passed its aphelion and is approach- 
 ing that part of its orbit where it will be nearest to the Sun. 
 As its distance decreases, the increasing, attraction of the Sun 
 (being in the same general direction as that in which the planet 
 is moving) gradually increases its speed, and therefore straightens 
 its path. For, the deflection Sunward being so many inches 
 per minute, if the planet moves faster its course will be straighter. 1 
 The result is that the planet sweeps by the Sun with a rush 
 that the increased attraction cannot check. 2 
 
 As the planet's distance from the Sun increases, the decreasing 
 attraction (being almost opposite to the direction in which the 
 planet is moving) gradually checks its speed. It therefore 
 bends in toward the Sun and finally begins to approach again. 
 
 Where the planet moves in an orbit of small eccentricity, the 
 
 1 This is seen on our Earth, where a large charge of powder will send a bullet 
 swifter and therefore straighter than a small charge. If we could stand on the 
 summit of a lofty mountain, and fire a cannon horizontally with just sufficient 
 charge, the projectile would sweep around the Earth, and (possibly) knock in the 
 breech-plug of the cannon from behind. 
 
 2 A similar thing takes place with the pendulum of a clock. The Earth's at- 
 traction brings it down on one side with a rush that carries it up on the other 
 side. 
 
I UNlv . votTY 
 
 L 
 
 NEWTON'S LAW OF GRAVITATION 171 
 
 above phenomena are not so marked, but the principle .is 
 the same. In the absence of a resisting medium there is not 
 the slightest possibility of a planet getting into a closing spiral. 
 And an opening one is only possible where tidal influences are 
 very strong. So we need not be afraid of either falling into the 
 Sun or of breaking loose and drifting into the outer darkness. 
 These are only possibilities of the remote future, long after the 
 human race shall have passed away from other causes. 
 
 Where a number of planets are revolving around the same 
 sun, at different distances, their mutual attractions slightly 
 interfere with their orbits, producing certain periodical jper^wr- 
 JataVws. It was the study of some of these irregularities which 
 led to the discovery of the planet Neptune, 1,000,000,000 miles 
 beyond Uranus, which had previously been regarded as the out- 
 side planet of our system. 
 
 WHAT IS GRAVITATION? 
 
 It appears certain that all matter is under the absolute con- 
 trol of the attraction of gravitation. Atoms and suns are alike 
 ruled by this law. Every motion is regulated by it, every non- 
 motion is the result of it. 
 
 Although gravitation is now thoroughly understood, both as 
 to its mode of action and the measure of its power, there is yet 
 some uncertainty as to its nature. It is generally regarded as a 
 universal property inherent in matter itself, but some think that 
 it may be an independent energy controlling matter from the 
 outside. 
 
 The original idea was that gravitation reaches out from one 
 particle to another, even when they are separated by great dis- 
 tances, with nothing to connect them, in fact that there is 
 action at a distance without a medium. This idea has had to 
 be abandoned, for it is evident that a thing cannot act where it 
 is not present. So a connecting ether has been " invented " to 
 carry the energy of gravitation (and what is known as radiant 
 energy) across from one particle of matter to another. Whether 
 
172 HOW TO KNOW THE STARRY HEAVENS 
 
 this ether really exists, what it is like, and how it acts, are 
 questions that still keep scientists busy, and will probably not 
 be settled for some time to come. 
 
 EFFECTS OF GRAVITATION 
 
 Whatever it is, the action of gravitation is always mutual, 
 and appears to be instantaneous. It operates at all distances 
 and through all substances. 
 
 Its tendency, suddenly applied to scattered bodies previously 
 at rest, would be to bring together all the suns and worlds of 
 which the Universe is composed. But, if applied to bodies al- 
 ready in motion, its effect would be to change direct motions 
 into curved orbits like those of the planets. 
 
 Its effect on any isolated body (like the Sun, or our Earth) 
 is to cause its particles to arrange themselves in the form of a 
 sphere, more or less flattened when there is any considerable 
 rotation. In this sphere the densest forms of matter naturally 
 gravitate toward the centre, and, while "the globe possesses any 
 considerable amount of internal heat, there may be an outer 
 layer of liquid, with expansive gases outside of all. 
 
 On the surface of such isolated bodies its effects are almost 
 inappreciable, the only noticeable effect being that every par- 
 ticle of matter clings to the planet with an intensity varying 
 directly with the mass of the planet, and inversely with the 
 square of the distance between the body and the centre of the 
 planet. On the same globe all things on the surface are at prac- 
 tically the same distance from the centre. Therefore they are all, 
 whether heavy or light, attracted with the same intensity, and 
 (in a vacuum) fall with the same velocity. The weight of an 
 object equals its mass multiplied by the force of gravity. If it 
 were removed to a planet where the force of gravity was twice as 
 great, its weight would be doubled, though its mass would re- 
 main the same. 
 
FIG. 85. SPIRAL NEBULA IN URSA MAJOR (M 81) 
 Lick photograph. 
 
NEWTON'S LAW OF GRAVITATION 173 
 
 INTENSITY OF GRAVITATION 
 
 As regards the strength of the attraction of gravitation, it is 
 really very small, being more than a million times weaker than 
 that of magnetism. Two masses, each of 465,000 American 
 tons, attract each other with a force of one pound when they 
 are a mile apart. If the distance between them be doubled, 
 the attraction is reduced to four ounces. If the distance be 
 reduced to half a mile, it is increased to four pounds. If one 
 of the masses be doubled in size and weight the attractive force 
 is doubled, while if both masses be doubled, the attraction is 
 quadrupled. 
 
 OMNIPOTENCE OF GRAVITATION 
 
 The above example, taken by itself, might lead one to suppose 
 that the attraction of gravitation is of very slight importance in 
 a Universe where the distances separating the suns and worlds 
 are so vast. But other forces are local, or operate only under 
 certain conditions, while gravitation appears to be universal and 
 to act under all conditions. It therefore becomes an all-control- 
 ling force whose immensity the mind of man cannot realise. It 
 possesses some of the attributes of Deity, being omnipotent, 
 omnipresent, and eternal. It controls the infinitely great and 
 the infinitely small. It regulates the movements of every speck 
 of dust that dances in a sunbeam, and, at the same time, of 
 every sun that sweeps through the boundless depths of space. 
 
 The following illustration will give some faint idea of the im- 
 mense power of the attraction of gravitation : 
 
 In going around the Sun, the Earth travels about 19 miles in 
 a second of time. During the same interval the Sun pulls the 
 Earth toward him about one eighth of an inch. The power 
 exerted to produce this insignificant change of direction is so 
 enormous that if the solar gravitation were to be replaced by 
 steel telegraph wires they would have to be attached to the 
 entire Sunward side of the Earth, considerably closer together 
 than the stalks in a flourishing wheat field. If the bond con- 
 
174 HOW TO KNOW THE STARRY HEAVENS 
 
 sisted of a single cast-iron rod, it would have to be thicker than 
 the Earth itself in order to stand the strain. Yet the mutual 
 attraction of the two bodies keeps them together without any 
 visible bond. 
 
 Professor Duffield says of this law : 
 
 " We cannot but regard it as the most important truth in the 
 whole book of Nature, and its discovery as the most interesting event 
 in the history of physical science. As there is but one material 
 Universe, and the law of gravitation solves the enigma of its struc- 
 ture, no other problem of equal interest and importance can ever 
 occupy the attention of the student of Nature." 
 
 The above quotation, while paying a just tribute to Newton's 
 discovery, really overrates the scope and importance of the law 
 of gravitation. As Ernst Haeckel says : 
 
 " Newton had the immortal merit of establishing the law of gravi- 
 tation and embodying it in an indisputable mathematical formula. 
 Yet this dead mathematical formula, on" which most scientists lay 
 great stress, as so frequently happens, gives us merely the quantitative 
 demonstration of the theory ; it gives us no insight whatever into the 
 qualitative nature of the phenomena. The action at a distance with- 
 out a medium, which Newton deduced from his law of gravitation, 
 and which became one of the most serious and most dangerous 
 dogmas of later physics, does not afford the slightest explanation of the 
 real causes of attraction ; indeed it long obstructed our way to the 
 real discovery of them." 
 
 The fact is that we are yet groping almost in the dark, and 
 need a second Newton to tell us why the law of gravitation 
 acts as he proved it to act. 
 
 PRECESSION AND NUTATION 
 
 In Chapter XII the slow reeling of the Earth's axis was 
 described, without any explanation except the remark that it 
 was allied to the wabbling of a child's spinning-top. As the 
 phenomenon is one of the results of the law of gravitation, and 
 
NEWTON'S LAW OF GRAVITATION 175 
 
 was first explained by Newton, a few words concerning its 
 cause may not be out of place here. It should be remembered 
 that the intensity of the Sun's attraction on a planet varies with 
 the square of the distance. And it should not be forgotten 
 that it acts independently on each and every individual atom 
 composing the planet. An atom at the planet's centre is 
 attracted less than an atom on the surface facing the Sun, and 
 is attracted more than an atom on the surface away from the 
 Sun. The difference in intensity produces the same result as 
 though the nearest atom was attracted, and the farthest atom 
 was repelled. In a perfectly spherical planet these differences 
 would neutralise one another, and the effect would be the same 
 as though all the atoms were at the centre of the planet. 
 When the planet's equator is bulged out by rotation, the effect 
 is the same, providing that the equator of the planet coincides 
 with the plane of its orbit. But when the planet's equator is 
 tipped up at an angle with the p]ane of the orbit (as is the 
 case with our Earth), the relative attraction and repulsion, on 
 the equatorial bulging, tend to reduce the angle at which the 
 equator is tipped. The rotation of the planet, however, modi- 
 fies the movement, so that (in summer and winter) an atom 
 on the surface, at the equator, makes a lower curve and 
 crosses the ecliptic a trifle behind the place where it would 
 otherwise have crossed. This of course has the effect of mak- 
 ing the polar axis reel slowly back, as already described. The 
 effect is trifling, but cumulative, so that in the course of time 
 the axis wabbles completely round. In the case of our Earth 
 the process is greatly helped by the attraction of the Moon, yet 
 it is so slight that it takes 26,000 years for the poles to make 
 one wabble. At the equinoxes the action ceases, so that the 
 circles described by the polar axis have a tremulous or wavy 
 outline. As the Moon's orbit is a little inclined to the Ecliptic 
 and has a " precession " of its own, another irregularity is pro- 
 duced every 19 years. These two irregularities in the Earth's 
 precession are together known by the name of nutation. 
 
176 HOW TO KNOW THE STARRY HEAVENS 
 
 CAUSE OF REPULSION 
 
 At first sight, the theory of gravitation does not seem to ex- 
 plain such phenomena as the solar flames and corona. These, 
 and especially the latter, are evidently acted upon by a repellent 
 force of enormous intensity. The explanation seems to be that 
 radiant light tends to push away any substance that it strikes. 
 In large bodies this repulsion is very small when compared with 
 the force of gravitation. But the former acts according to the 
 surface, and the latter to the mass. As bodies decrease in size, 
 the repellent force of light decreases by the square, while the 
 force of gravitation decreases by the cube. On extremely small 
 particles gravitation is overpowered by a continuous repulsion 
 two, ten, or twenty times as great, according to their size. They 
 are therefore driven off like a bullet out of a rifle, only hundreds 
 of times more rapidly. 
 
 Corona. In the case of the corona, the eruptive particles 
 are so minute that they appear to be driven clear away into 
 interstellar space. On the way, some of them are intercepted 
 by the planets. As they are charged with negative electricity, 
 and the planets are huge "electrical machines," they arrange 
 themselves according to the lines of force, and produce such 
 electrical phenomena as the Zodiacal Light, the Gegenschein, 
 the Aurora Borealis, etc. All the luminous stars send off simi- 
 lar negatively electrified particles, and when these, in their 
 travels, come across a large mass of uncompressed matter, they 
 cause its surface to glow like the rarefied gas in a vacuum tube. 
 This appears to be the reason why nebulae are luminous, though 
 cold with the fearful cold of interstellar space. 
 
 Solar Flames. In the case of the solar flames, the eruptive 
 particles are probably larger, and therefore come to a standstill 
 sooner or later. They are then buoyed up, not by an atmos- 
 phere, as our clouds are, but by the pressure of light radiating 
 from below. If they join together to form larger particles, they 
 fall back to the surface of the Sun, like the raindrops from our 
 watery clouds. 
 
NEWTON'S LAW OF GRAVITATION 177 
 
 A WREATH OF SMOKE 
 
 Sometimes, on a quiet evening, just before sundown, when 
 hardly a breath of air was stirring, I have watched the blue 
 rings and spirals of tobacco-smoke, slowly curling, twining, and 
 eddying in the level glints of dying sunshine. 
 
 Now if you will imagine that the atoms of carbon in that 
 wreath of tobacco-smoke are mighty suns in every stage of solar 
 life, from the spiral nebulae of solar infancy to the dark, cold, 
 and lifeless wrecks of superannuated suns, then the curling 
 and eddying smoke will represent the Universe. 
 
 For the great telescopes of our observatories show us star- 
 clusters and nebulae extended through space in gigantic rings, 
 eddies, and spirals. If we could watch this celestial cloud of 
 smoke for a few millions of years, it is almost certain that we 
 should see these curves and spirals change from form to form 
 like wreaths of smoke. Through all eternity the star-dust of 
 which the Universe is composed is eddying and circling through 
 space that has no limits. 
 
 And the very same laws which regulate the curling of the blue 
 tobacco-smoke regulate the eddying and circling of the innu- 
 merable nebulae, suns, and worlds which compose our mighty 
 COSMOS. 
 
 NOTE. The laws briefly dealt with in the above three chapters are more fully 
 discussed and illustrated in Sir George Airy's " Popular Astronomy," which was 
 written for non-mathematical readers; in George C. Comstock's more recent 
 " Textbook of Astronomy ; " and in many other works. 
 
 
 12 
 
CHAPTER XVI 
 
 ANCIENT COSMOGONIES, AND THE NEBULAR 
 HYPOTHESIS 
 
 " In the intellectual infancy of a savage state, Man transfers to Nature his 
 conceptions of himself, and, considering that everything he does is determined 
 by his own pleasure, regards all passing events as depending on the arbitrary 
 volition of a superior but invisible power. . . . After Reason, aided by Experi- 
 ence, has led him forth from these delusions as respects surrounding things, he 
 still clings to his original ideas as respects objects far removed. ... But as 
 reason led him forth from fetishism, so in due time it again leads him forth from 
 star-worship. . . . Philosophically speaking, he is exchanging, by ascending 
 degrees, his primitive doctrine of arbitrary volition for the doctrine of law." 
 Dr. J. W. Draper. 
 
 FACTS VERSUS THEORIES 
 
 THE human race is not old enough to have watched the 
 development of suns and worlds to any appreciable 
 extent. We cannot therefore know for an absolute certainty 
 that such a process is at work throughout the Universe. Yet 
 thinking men are naturally led, by their earthly experiences 
 and celestial observations, to believe in such a development, 
 and to theorise as to how the Universe has reached its present 
 condition. They have even gone beyond the present, and 
 speculated as to the changes which it will undergo in the 
 future. 
 
 Even a false theory has its value as a stepping-stone to lead 
 to a true one. It is well, therefore, to theorise even where we 
 have no direct method of proving the truth or falsity of our 
 speculations. When a theory gives a reasonable explanation of 
 observed phenomena, it must have some truth in it. And 
 when it not only explains all known phenomena, but also 
 enables us to discover and explain fresh ones, we may regard it 
 
COSMOGONIES, AND NEBULAR HYPOTHESIS 179 
 
 as a valuable help for the upbuilding of the Temple of 
 Knowledge. 
 
 Still it is well for us to remember that an unproved theory 
 is not necessarily a permanent part of that Temple of Knowl- 
 edge. It may be only a piece of scaffolding that will have to 
 come down when the building is further advanced. 
 
 One of the great troubles in the past has been the tendency 
 to mistake unproved theories for known facts, and to stretch, 
 twist, or ignore all facts which refuse to fit in with them. 
 This is evidently a serious mistake. As Sir William Crookes 
 said at Berlin, a short time ago : 
 
 " It must never be forgotten that theories are only useful as long as 
 they admit of the harmonious correlation of facts into a reasonable 
 system. Directly a fact refuses to be pigeon-holed, and will not be 
 explained on theoretic grounds, the theory must go, or it must be 
 revised to admit the new fact." 
 
 With this necessary warning I will now proceed to outline 
 a few of the theories which have been held with regard to the 
 past, present, and future history of the Universe. 
 
 HISTORICAL SPECULATIONS 
 
 There are in existence several different classes of what pro- 
 fess to be histories of the Universe in general and of our World 
 in particular. Some of them have come down to us from pre- 
 historic times, while others are quite modern. They differ so 
 much from one another that it is evident they cannot all be 
 historical. If one is true, the others must be more or less 
 fictitious. 
 
 Some of the more ancient of the " historians " professed to 
 start from the very beginning of things, although they found it 
 a difficult thing to do. They began either with a primeval 
 Chaos that always existed, or with a world-egg that no hen 
 ever laid. Out of one of these they evolved the Earth and 
 all that is therein, along with such trifles as the Sun, Moon, 
 planets, and stars. 
 
180 HOW TO KNOW THE STARRY HEAVENS 
 
 The more modern ones do not profess to know of any original 
 Chaos, and they doubt the veracity of the primitive-egg story. 
 They modestly content themselves with stating what they be- 
 lieve to have been the course of events since a certain time, 
 beyond which they admit that they have no direct knowledge. 
 And as far as possible they adopt those theories which appear 
 to be supported by evidence, and to be in harmony with the 
 laws of Nature as we know them here and now. 
 
 These different "histories" may be more or less definitely 
 divided into the following four classses. 
 I. Primitive Creationism. 
 II. Pseudo Creationism. 
 
 III. Evolutionary Creationism. 
 
 IV. Modern Evolutionism. 
 
 I must here content myself with giving a very brief sketch 
 of the leading varieties of these classes, beginning with the 
 various forms of Creationism, which I have divided into Primary, 
 Secondary, and Tertiary. 
 
 I. PRIMITIVE CREATIONISM (PRIMARY STAGE) 
 
 In early times, when unenlightened men first began to 
 speculate as to the origin and history of the World and its 
 surroundings, they found no one to tell them where the Earth 
 had come from or how it had come into being. 
 
 The wise men of each tribe naturally had to answer many 
 inquiries on the subject. If they had frankly admitted that 
 they did not know the origin and destiny of all things, they 
 would have lost their reputation for wisdom. So it was abso- 
 lutely necessary for them to invent some story which, if it did 
 not satisfy the mind of a child, would at least put a stop to its 
 questions. This is probably the way in which all creation 
 stories have originated, fresh details being gradually, and often 
 unconsciously, added by successive generations. 
 
 From their own limited observations and experiences, these 
 primitive men naturally inferred that the World could not 
 always have existed as they found it. They concluded that it 
 
COSMOGONIES, AND NEBULAR HYPOTHESIS 181 
 
 must some time, some where, and in some manner have 
 been either hatched or born. The only other explanation they 
 could think of was that it might have been made by the Father 
 of the Gods, for his own amusement. 
 
 As a rule the ancients were entirely ignorant of all except 
 their immediate surroundings. This ignorance compelled them 
 to view all things from a flat-world standpoint, which natu- 
 rally and necessarily decided the character of their specula- 
 tions on the origin of things in general. Having no one to 
 tell them the facts of the case, they gradually evolved from 
 their own inner consciousness a number of mythical his- 
 tories whose ephemeral nature fitted in with their insignificant 
 Cosmos. 
 
 The best known of these, so far as our part of the World 
 is concerned, is an old Semitic legend, the modern form of 
 which has been poetically narrated by Milton in his "Paradise 
 Lost." 
 
 According to this account the World (including its attendant 
 Sun, Moon, and stars) is a manufactured contrivance, invented 
 and constructed by one who is known as the Architect, or 
 Creator, of the Universe. Although the account professes to 
 start from the beginning, it leaves the origin of the Creator 
 himself in the primeval darkness, and even intimates that he 
 had no origin, but always existed. 
 
 This Architect of the Universe is said to have " created " the 
 World and its appurtenances. This prodigious work having 
 been accomplished in six days, the Creator, we are told, " rested 
 on the seventh day, and was refreshed." He now keeps it in 
 existence and repair, and personally superintends everything 
 that takes place on it. 
 
 Owing to the machinations of an ambitious and unscrupu- 
 lous servant, whom he had himself brought into existence, 
 things did not run smoothly in the newly created World. Its 
 history (past, present, and future) embraces six thousand years 
 of strife and one millennium of peace, corresponding to the six 
 days of work and one of rest. At the close of the seven thou- 
 
182 HOW TO KNOW THE STARRY HEAVENS 
 
 sand years the World and its Sun, Moon, and stars will be 
 destroyed, and will be succeeded by " a new Heaven and a 
 new Earth," to endure for ever. 
 
 II. PSEUDO CREATIONISM (SECONDARY STAGE) 
 
 The above is only one out of a number of primitive creation 
 stories. In the course of time these childlike " histories " 
 became looked upon as not only true but also " inspired." It 
 was actually made a punishable offence to doubt their truth 
 and inspiration. So, when men came to know something as to 
 the actual dimensions of the Universe, and the relative im- 
 portance of the Earth in that Universe, they recognised the 
 improbable nature of these stories, yet hesitated about rejecting 
 them as untrue and uninspired. The accounts were therefore 
 " spiritually interpreted," to fit in with the new order of things. 
 In some cases considerable ingenuity has been used to accom- 
 plish this. For example, when Astronomy had to be accepted, 
 the seven thousand years of strife and- peace were declared to 
 refer to our World alone. When Geology had to be accepted, 
 the seven days of creation and rest were " spiritualised " into 
 meaning seven immense periods of time, long enough for suns 
 and worlds to develop out of "fire-mist." The inconvenient 
 fact that the Sun and stars were treated as mere appendages 
 of the Earth, was explained as a " pious fraud " on the part of 
 the inspired writer, rendered necessary by the ignorance of his 
 readers. 
 
 Some people still accept these stories as true history. Others 
 have forced themselves to the curious conclusion that they are 
 not true historically, but that they are allegories, containing 
 spiritual truths, perceptible only to those who are spiritually 
 minded. All intelligent and well-informed people now know 
 that these accounts are simply primitive speculations about 
 the unknown past. But many of them refrain from hurting the 
 feelings of others by openly saying so. 
 
COSMOGONIES, AND NEBULAR HYPOTHESIS 183 
 
 in. EVOLUTIONARY CREATIONISM (TERTIARY STAGE) 
 
 Among those who have rejected Oreationism in both its 
 primary and secondary forms, there are many who still adhere 
 to it in an attenuated tertiary form. For want of time or lack 
 of inclination to formulate a better and truer theory, they take 
 it for granted that in a very remote past an Infinite and Eternal 
 Being created an all-pervading substance, or matter out of 
 nothing, and endowed it with certain permanent qualities and 
 energies. He then allowed it to evolve without any further 
 interference. The resulting physical and chemical movements 
 of this matter have since produced the Universe as we know it. 
 
 Some, however, think that at one stage in each world there 
 was a second creative act, the introduction of organic life in 
 its lowest form. From this primitive single-celled organism 
 all the various forms of animal and vegetable life have since 
 developed by natural laws. 
 
 Another interference with mundane events is believed in by 
 some, the implanting of an immortal soul in man after his 
 body had sufficiently developed by the operation of natural 
 laws. This immortal soul was then left to work out its own 
 salvation or condemnation, without interference. 
 
 This tertiary and evolutionary creationism is upheld, in one 
 or other of its forms, by a more intelligent class of people than 
 those who are still in the primary and secondary stages, but it 
 appears to share with those beliefs the disadvantage of not 
 being either reasonable or true. 
 
 However, the truth itself is so astounding to finite creatures 
 like us, and long-inherited prejudices are so strong, that the 
 majority of people are not yet able to grasp or ready to receive 
 it. In the meantime this evolutionary creation-story serves 
 very well for a temporary basis on which to build a truer and 
 more reasonable history of the Universe. It will be thrown 
 away as soon as it has outgrown its usefulness, and the super- 
 structure can then be fitted on to the eternal foundation of 
 actual fact. 
 
184 HOW TO KNOW THE STARRY HEAVENS 
 
 THE ORIGINAL NEBULAR THEORY 
 
 On the basis of a single creative act, Kant, Laplace, and 
 Herschel I. founded their celebrated Nebular Theory, which 
 first attracted notice about the end of the eighteenth century. 1 
 It is rather remarkable that these three great men arrived at 
 practically the same conclusions by independent and entirely 
 different routes. 
 
 FIG. 86. ORIGINAL, NKBULA, AFTER ITS ROTATION 
 HAS PRODUCED A DISC-LIKE FORM 
 
 Immanuel Kant 2 was led to it in his youth by abstract 
 philosophical speculations. He outlined the theory in a work 
 which was published in 1755, but as it did not excite any 
 interest, he turned his attention to other speculations. 
 
 Pierre Laplace 3 was led to its consideration by mathematical 
 
 1 Kepler and Tycho Brahe had previously speculated that the Sun and stars 
 were condensations from celestial vapours. 
 
 2 Born in 1724; died in 1804. 
 8 Born in 1744; died in 1827. 
 
COSMOGONIES, AND NEBULAR HYPOTHESIS 185 
 
 reasoning, in middle age, and published it in a modest footnote 
 in his " Systeme du Monde," 1796. 1 
 
 Sir William Herschel 2 was led to it by his lifelong tele- 
 scopic observations. He discussed it in his papers to the Koyal 
 Society. 
 
 The assumption was that " in the beginning " an inconceiv- 
 ably vast and attenuated mass of intensely heated gas was 
 
 FIG. 87. NEBULA WITH OUTER RING, LEFT BEHIND BY CON- 
 TRACTION AND CONSEQUENT QUICKENING OF ROTATION 
 
 created and put in motion. This original motion led with- 
 out any further interference to its gradual condensation into 
 a number of rotating lens-shaped nebulae of thin gas. One of 
 these has since shrunk and developed into our Solar System, 
 others have condensed and developed into the stellar systems 
 which surround us, and thousands (having for some reason 
 failed to develop) still exist as glowing gaseous nebulae. They 
 
 1 He suggested it cautiously, " avec la defiance que doit inspirer tout ce qui 
 n'est poiut un resultat de 1'observation ou du calcul." 
 
 2 Born in 1738; died in 1822. 
 
186 HOW TO KNOW THE STARRY HEAVENS 
 
 all move according to the natural laws originally imparted to 
 matter by the Creator, and eventually discovered by Kepler, 
 Galileo, and Newton. 
 
 As one of these primary rotating nebulae (subject to the 
 mutual attraction of its own particles) gradually condenses into 
 a spheroidal form, it naturally increases in density and speed 
 
 Fio. 88. CENTRAL CONDENSATION SURROUNDED BY RINGS 
 
 of rotation. Much of its energy is also turned into heat, which 
 radiates into space. 
 
 The tendency of every moving body to continue in a straight 
 line (First Law of Motion) produces a centrifugal force which 
 increases with the increasing speed of rotation. At last the 
 equatorial part of the spheroid breaks away in a ring, which 
 may continue to rotate around the shrinking central body. 
 Generally, however, it breaks up into a secondary rotating 
 spheroid, or planet, which continues to revolve around the 
 primary one, or sun. Each planet goes through the same 
 process of condensation, throwing off similar rings, which 
 
COSMOGONIES, AND NEBULAR HYPOTHESIS 187 
 
 generally collapse into tributary satellites or moons (see Fig- 
 ures 86 to 90). 
 
 In all these secondary and tertiary bodies the original heat 
 is gradually dissipated by radiation into outer space. The later 
 rings are smaller than the earlier ones, and give rise to smaller 
 planets and moons, which go through the various stages more 
 rapidly than the larger ones. 
 
 In time the formation of rings ceases, but the central spheroid 
 continues to decrease in size and increase in density. Although 
 
 FIG. 89. RINGS COLLAPSING INTO PLANETS, AND CENTRAL 
 CONDENSATION TURNING TO A LUMINOUS SUN 
 
 still gaseous, it has long ceased to be a glowing transparent 
 nebula, and is a compact bluish-white sun, radiating an im- 
 mense amount of light and heat into space. 
 
 Later on, its colour changes to a yellowish white, and after- 
 ward to yellow. The radiation of heat into outer space goes 
 on continuously, so that in time it cools off to a reddish tinge. 
 The colour deepens to crimson and gradually fades away. The 
 star liquefies and then becomes solid. The crust no longer 
 
188 HOW TO KNOW THE STARRY HEAVENS 
 
 glows with light and heat, so that the star ceases to be visible 
 from outer space. 
 
 Meanwhile the various worlds to which it has given rise 
 have cooled off, become liquid, crusted over, and finally solid- 
 ified. Life has made its appearance on their surfaces, developed, 
 flourished, and died away in the growing cold. They are now 
 dead worlds revolving about a dying sun. 
 
 /x^"- xN\ 
 
 I . N :.'...*f^WKf w..- . / s 
 
 \\:<::r :>'// 
 
 :. .?%. .' tr 
 
 FIG. 90. SOLAR SYSTEM AS IT is NOW 
 
 In the course of millions of years the sun itself cools to its 
 centre, and shrinks till it is but a shadow of its former self. All 
 forms of energy die away, the times of rotation of the planets 
 and moons become equal to their periods of revolution, and the 
 entire system is dead and cold. 
 
 Lord Byron once wrote, of this period : 
 
 " I had a dream which was not all a dream. 
 The bright Sun was extinguished, and the stars 
 Did wander darkling in the eternal space, 
 Rayless and pathless, and the icy Earth 
 Swung blind and blackening in the moonless air." 
 
COSMOGONIES, AND NEBULAR HYPOTHESIS 189 
 
 The other nebulae which surrounded it have passed through 
 the same stages and are also dead. The Universe is one vast 
 cemetery of dead suns and worlds. 
 
 " Time was, time is, and time shall be no more. " 
 
 Such is the evolutionary history of our Universe which has 
 been theoretically built up on the most modern form of Crea- 
 tionism. It is not all true, yet it probably contains more truth 
 than any of its predecessors. And it is perhaps about as near 
 the truth as the majority of us are able to get without being 
 overwhelmed by the awful realities of eternal time and infinite 
 space. 
 
 Many of those who pursue the truth wherever it may 
 lead them, regardless of prejudices and consequences, have 
 changed and enlarged the original Nebular Theory to make 
 it fit in with the discoveries of the nineteenth century. When 
 thus changed it is no longer in the third stage of Evolution- 
 ary Creationism, but rests entirely on the fourth and last basis 
 of Modern Evolutionism. It will be dealt with in Chapter 
 XVIII. 
 
CHAPTER XVII 
 
 THEOKIES AND DISCOVERIES MODIFYING THE NEBULAR 
 
 HYPOTHESIS 
 
 " We must bear in mind that scientific hypotheses as to the underlying causes 
 of phenomena are subject to the law of evolution, and have their birth, maturity, 
 and decay. Theory necessarily succeeds theory, aud while no hypothesis can be 
 looked upon as expressing the whole truth, neither is any likely to be destitute 
 of all truth if it sufficiently reconciles a large number of observed facts. 
 
 " The notion that we can reach an absolutely exact and ultimate explanation 
 of any group of physical effects is a fallacious idea. We must ever be content 
 with the best attainable sufficient hypothesis that can at any time be framed to 
 include the whole of the observations under our notice. Hence the question, 
 ' What is electricity ? ' no more admits of a complete and final answer to-day than 
 does the question, ' What is life? ' Though this idea may seem discouraging, it 
 does not follow that the trend of scientific thought is not in the right direction. 
 We are not simply wandering round and round, chasing some illusive will-o'-the- 
 wisp, in our pursuit after a comprehension of the structure of the Universe. 
 Each physical hypothesis serves as a lamp to conduct us a certain stage on the 
 journey. It illuminates a limited portion of the path, throwing a light before and 
 behind for some distance, but it has to be discarded and exchanged at intervals, 
 because it has become exhausted and its work is done." Professor J. A. Fleming. 
 
 SINCE the original Nebular Theory, outlined at the close of 
 the preceding chapter, was formulated by Kant and La- 
 place, great additions have been made to our knowledge of 
 natural laws. And these additions have led to important 
 modifications of the theory. 
 
 Some of the most important of these modifying discoveries 
 and theories will now be briefly sketched. The reader is par- 
 ticularly desired to bear in mind Professor Fleming's words as 
 given at the head of this chapter. 
 
 MATTER AND ETHER 
 
 Although it cannot be proved, it is now generally agreed that 
 substance, or matter, exists in two forms, one of which has 
 many subdivisions while the other appears to be homogeneous. 
 
MODIFYING THE NEBULAR HYPOTHESIS 191 
 
 I. The first and most obvious division contains all forms of 
 what may be termed ponderable matter, or, for convenience, 
 simply matter. It includes all kinds of substance which are 
 obvious to our senses. All solids, liquids, and gases belong to 
 this division. 
 
 This sensible matter is supposed to consist of a variety of 
 very small but perfectly distinct atoms. Those substances 
 which are built up entirely of one kind of atom are known as 
 elements, while those containing two or more kinds of atoms 
 are known as compounds. It possesses such characteristics 
 as go by the name of gravity, inertia, molecular heat, and 
 chemical affinity. 
 
 II. The other form of substance may be termed ethereal 
 matter, though it is commonly known as ether ^ It does not 
 consist of a variety of atoms, like the ponderable matter just 
 mentioned. It is practically imponderable and is absolutely 
 imperceptible to the senses. We have therefore only indirect 
 proofs of its existence. 
 
 According to one of the most modern theories concerning this 
 ether it is composed of particles which are very much smaller 
 than atoms and are all exactly alike in every respect. These 
 are supposed to be so crowded together that they act like one 
 continuous substance. It has also been likened to an incon- 
 ceivably thin elastic transparent jelly, filling all space not occu- 
 pied by ponderable matter. It even fills the spaces between 
 the atoms of the latter. Its existence appears to be proved by 
 the action of gravitation across apparently empty spaces, and 
 also by its wave-like movements, which are recognisable as 
 radiant energy, in the forms of chemism, 2 light, heat, electricity, 
 and magnetism. 
 
 Although we do not know that the above theory is correct, 
 we are compelled, by reasoning on observed phenomena, to 
 believe that, in one or other of its two forms, this indestructible 
 
 1 Not the bottled ether of the chemist, but the luminiferous ether of the 
 astronomer. 
 
 2 Producing chemical action. It is also known as actinism. 
 
192 HOW TO KNOW THE STARRY HEAVENS 
 
 substance, or matter, fills all the infinity of space, without any 
 void whatsoever. 
 
 ATOMIC THEORY 
 
 The science of chemistry deals with ponderable matter only. 
 It has ascertained by experiment that all the varied substances 
 known are composed of about 80 " elementary " forms of matter. 
 These exist either separately, as elements, or combined, in cer- 
 tain fixed proportions, to form chemical compounds. And it 
 has explained the observed phenomena of chemical combination 
 by what is known as the Atomic Theory, formulated by Dalton 
 in 1808. This theory is that each of the elements is composed 
 of separate and infinitesimal atoms. These are all supposed to 
 be exactly the same in size, weight, shape, and properties, but 
 to be entirely different, in size, weight, shape, and properties, 
 from the atoms of any other element. These atoms may com- 
 bine to form molecules, but seem to be incapable of further 
 analysis. 
 
 PERIODIC SYSTEM OF ELEMENTS 
 
 Although one element cannot be changed into any other ele- 
 ment, yet the different elements do not appear to be absolutely 
 independent of one another. When they are arranged according 
 to their combining weights, they fall naturally into family 
 groups, reminding one of the octaves of music, where the eighth 
 notes are related to one another. It is probable, therefore, that 
 the elements are not ultimate unchangeable forms of matter, 
 but that their atoms consist of variously arranged groups of one 
 primitive form of matter. This, when uncondensed, may possi- 
 bly form the substance of the luminiferous ether. 
 
 THE LAW OF SUBSTANCE 
 
 One of the most far-reaching of modern discoveries is that of 
 the Law of Substance, commonly known as the Law of the 
 Conservation of Matter and Energy. 
 
 Indestructibility of Matter. One half of this law of sub- 
 
FIG. 91. DUMB-BELL NEBULA 
 Lick photograph. 
 
MODIFYING THE NEBULAR HYPOTHESIS 193 
 
 stance was discovered much earlier than the other half, and is 
 still known as the Law of the Persistence or Indestructibility 
 of Matter. It was worked out experimentally, with the balance, 
 in the laboratory of Lavoisier, as early as 1789. This first half 
 of the law affirms that no substance is ever created or destroyed ; 
 that the Universe always contains exactly the same quantity of 
 matter ; and that chemical processes do not increase or decrease 
 its quantity, but merely change its condition. 
 
 The modern science of Chemistry has been largely built on 
 this half of the law of substance, and it is now accepted by all 
 thinking men. 
 
 Conservation of Energy. The other half of the law of sub- 
 stance is known as the Law of the Persistence of Force or 
 Conservation of Energy. It was worked out experimentally, in 
 the workshop of Eobert Mayer, in 1842. This second half of 
 the law of substance affirms that no force is ever created or 
 destroyed ; that the Universe always contains exactly the same 
 amount of energy ; and that chemical and mechanical changes 
 do not increase or decrease its amount. They merely change 
 its condition from potential to actual, or from actual to potential, 
 leaving the sum total of the two forms of energy eternally the 
 same. 
 
 The physical sciences have been largely built on this half of 
 the law of substance, and it is now adopted (either as a fact or 
 as a working hypothesis) by all thinking men. 
 
 Actual energy manifests itself in several different ways, and 
 one kind of it can readily be changed into another. Sound, 
 heat, light, chemical action, electricity, magnetism, etc., are all 
 manifestations of energy, and any one of them can be converted 
 into any other without actual loss of energy. 
 
 Some one may here say, " That sounds like perpetual motion, 
 which we know to be an absurdity." 
 
 It is true that perpetual motion is an absurdity so far as 
 machinery constructed by man is concerned. That, however, 
 is not because any of the energy is destroyed, but because it is 
 turned into a form which is not available to us. It still exists, 
 
 13 
 
194 HOW TO KNOW THE STARRY HEAVENS 
 
 and accurate measurement will show that there is no loss of 
 energy whatever. 
 
 All forms of energy are available to Nature, so that the Uni- 
 verse as a whole is not only a " perpetual-motion machine," but 
 is the only one that can possibly exist. 
 
 SPECTROSCOPIC DISCOVERIES 
 
 The discovery of the dark lines in the solar spectrum, by 
 Wollaston and Frauiihofer, and their explanation by Kirchhoff 
 and others, after fifty years of study, have put the atomic theory 
 on a solid basis, and given an immense help in solving the 
 riddle of the Universe. KirchhofFs discovery, in fact, deserves 
 to rank with the discovery of the law of gravitation by Newton. 
 While the one enables us to weigh the suns and worlds in a 
 balance, and to find out their past, present, and future move- 
 ments, the other tells us what they are made of and the 
 condition they are in. It also enables us to detect celestial 
 phenomena and movements that the telescope by itself fails 
 to reveal. These achievements have, however, been already 
 described in former chapters, so need not be further dwelt on 
 here. 
 
 KINETIC (OR VIBRATORY) THEORY OF SUBSTANCE 
 
 It is now concluded that all the different forms of energy 
 gravitation, sound, heat, light, chemical action, electricity, 
 and magnetism are only different manifestations of one 
 primitive force. This is commonly conceived to be a vibratory 
 motion of the atoms of matter dancing to and fro in empty 
 space, and influencing one another at a distance without any 
 medium. 
 
 When this theory is examined, however, some parts of it 
 prove not only mysterious, but improbable, if not impossible. 
 We can find no satisfactory answer to the question, How can a 
 thing act where it is not present ? 
 
MODIFYING THE NEBULAR HYPOTHESIS 195 
 
 PYKNOTIC (OR CONDENSATION) THEORY OF SUBSTANCE 
 
 To overcome this objection it has been suggested that all 
 space is filled with a simple primitive continuous substance, 
 which has a tendency to contract or condense around infinitesi- 
 mal centres. These centres of condensation are the atoms of 
 ponderable matter, and they are supposed to float in the uncon- 
 densed matter, which goes by the name of ether. The condensa- 
 tion of the atoms causes a stretching of the surrounding ether. 
 The efforts of the atoms to complete their condensation are 
 therefore opposed by the resistance of the ether to the further 
 increase of its strain. The result is the accumulation of an 
 immense amount of potential energy around the atoms, and of 
 actual energy in the ether. These two forms of energy are 
 continually varying, but the sum of them is ever the same. 
 They manifest themselves as light, heat, gravitation, and all the 
 other modes of motion with which we are acquainted, and 
 thereby produce all the varied phenomena of Nature. 
 
 These two theories of substance are now being tried in the 
 crucible of experiment and observation. Fresh facts are being 
 discovered every day, and a satisfactory and comprehensive 
 theory will probably be constructed before very long. 
 
 ELECTRO-MAGNETIC THEORY OF LIGHT 
 
 Until 1872, "chemism," light, heat, electricity, and mag- 
 netism, were almost universally regarded as separate and dis- 
 tinct entities. We now look upon them as merely sensations 
 or effects due to one solitary form of radiant energy, which is 
 given off by all radiant suns, and manifests itself differently 
 according to the way in which we observe it. 
 
 According to Maxwell's electro-magnetic theory of light 
 (which is now generally accepted), heat, light, magnetism, etc., 
 are simply different manifestations of electricity generated and 
 sent out by the huge electrical machines which we know as 
 suns or stars. They are, in fact, due to stresses and strains in 
 the luminiferous ether. 
 
196 HOW TO KNOW THE STARRY HEAVENS 
 
 It will be seen that the tendency now is not to seek for 
 mechanical explanations of electrical phenomena, but to look 
 for electrical explanations of mechanical phenomena. 
 
 ULTRA-ATOMIC (OR ELECTRONIC) THEORY 
 
 Kathode Rays. If a wire which carries a current of elec- 
 tricity be cut in two, and the ends kept apart, the flow is of 
 course stopped. But if the cut ends (or terminals) are inside 
 a closed glass vacuum-tube, the current leaps across the almost 
 empty space, and the tube is filled with a phosphorescent glow. 
 Sir W. Crook es, and Professor Thomson, after years of experiment 
 with these vacuum-tubes, concluded that this cold light is due 
 to a torrent of small negatively electrified particles of radiant 
 matter, chipped off the " kathode " or negative terminal. 
 
 These kathode particles resemble ordinary matter in possess- 
 ing inertia, and will turn a toy windmill when they strike it. 
 By allowing some of them to pass through a slit in a mica 
 diaphragm, and then to skim along the surface of a screen 
 coated with zinc sulphate, their course becomes visible (in the 
 dark) to the naked eye. Ordinarily the particles travel in a 
 straight line, so that their course resembles a straight jet of 
 steam. But when a magnet (or a plus pole) is brought near, 
 the jet of luminous particles bends toward it, as a horizontal 
 jet of water bends toward the earth. The amount of the 
 deflection depends on the strength of the attracting current, 
 the mass of the particles, and the speed at which they travel. 
 It has thus been ascertained that the particles are from 700 to 
 1000 times less (in mass) than an atom of hydrogen, and that < 
 they travel at a speed comparable with that of light. The 
 torrent gives a negative electric charge to any bodies it may 
 strike, and it appears to be virtually an electric current. 
 Metals are transparent to it, and even after passing through 
 them it affects a photographic plate more powerfully than 
 ordinary light. 
 
 Rontgen or X Rays. Any object struck by these kathode 
 particles gives off what are thought to be invisible ether waves. 
 
FIG. 92. NOVA PERSEI, 1901. SHOWING MOVEMENT OP 
 SURROUNDING NEBULOSITY 
 Lick photographs. 
 
 (a) Nov. 7-8, 1901. Exposure 7 h. 19 m. 
 
 (6) Jan. 31 and Feb. 2, 1902. Exposure 9 h. 45 m. 
 
MODIFYING THE NEBULAR HYPOTHESIS 197 
 
 These are commonly known as Rontgen or X Rays. They 
 radiate from their source in straight lines, and are not deflected 
 by a magnet or electrical field. They can pass through wood, 
 metal, leather, and flesh without losing their power of affecting 
 a photographic plate. They do not impart negative charges to 
 the bodies on which they fall, but they discharge charged 
 bodies by making gases better conductors of electricity. 
 
 Becquerel Rays (Alpha, Beta, and Gramma). Besides the two 
 kinds of STIMULATED radio-activity just described, some forms of 
 matter possess a SPONTANEOUS radio-activity. All compounds 
 containing the heavy elements known as radium, thorium, 
 cerium, and (perhaps) actinium, give out, continuously and 
 spontaneously, three distinct kinds of radiant energy. These 
 are known as 
 
 Alpha, or Atomic Rays. 
 
 Beta, or Kathodic Rays, and 
 
 Gamma, or Rontgen Rays. 
 
 Alpha or Atomic Rays. These are the most noticeable of 
 the spontaneous radiations, and appear to consist of atomic 
 projectiles shot out in all directions from the radio-active 
 substances. They move in a straight line with a velocity of 
 about 20,000 miles per second. They are not ordinarily drawn 
 aside by a magnet or by an electrically charged body, but in 
 a very stroDg electrical field they are deflected toward the 
 negative pole. The direction and amount of this deflection, 
 with a current whose intensity is known, prove that they con- 
 sist of positively electrified atoms whose mass is two or three 
 times as great as that of hydrogen atoms. 1 On account of their 
 great size they cannot pass between the atoms of ordinary mat- 
 ter. They can therefore be stopped by a sheet of paper. They 
 affect a photographic plate more slowly than the beta particles, 
 but discharge electrically charged bodies more quickly. 
 
 1 They may possibly be atoms of the newly discovered metal helium, whose 
 atomic weight is four times that of hydrogen. This element is never found except 
 in company with the heavy radio-active elements we are discussing, and its 
 spectral line has been found in the gaseous emanations from radium. 
 
198 HOW TO KNOW THE STARRY HEAVENS 
 
 Beta or Kathodic Rays. These are identical with the kathode 
 rays of the Crookes tube. They therefore consist of negatively 
 electrified particles about 2,000 times smaller (in mass), than 
 the alpha atoms. They travel in a straight line at about the 
 speed of light. They can pass through a plate of platinum or 
 an inch of solid iron, and then strongly affect a photographic 
 plate. On account of their small size they cannot discharge 
 electrified bodies so quickly as the more ponderous alpha 
 projectiles. 
 
 Gramma or Rontgen Rays. These are identical with the 
 x rays of the Crookes tube. They are probably ether-waves 
 caused by the breaking up of the atoms. They can pass 
 through six inches of iron and then affect a 'photographic 
 plate. 
 
 Of all the radio-active elements yet discovered, radium is by 
 far the most active. It is indeed so active that its compounds 
 are measurably warmer than surrounding objects. In the dark 
 they give off a faint light like that of a glow-worm. When 
 they are placed near a screen covered with zinc sulphide, the 
 impact of the bombarding projectiles on the zinc crystals gives 
 a display which (seen through a microscope) resembles a sky 
 full of shooting-stars. 
 
 The available evidence seems to show that those elements 
 whose atoms are very heavy and complex were built up under 
 conditions very different from the present ones, and are now 
 very slowly disintegrating, by stages, into lighter and simpler 
 elements. 1 This would explain the apparently inexhaustible 
 supply of energy possessed by the radio-active elements. 
 
 In this connection Professor R A. Millikan says : 
 
 " The disintegration of a gram of uranium, or thorium, or radium, 
 sets free at least a million times as much energy as that which is 
 represented in any known chemical change taking place within a 
 gram weight of any known substance. The experiments of the last 
 
 1 This would be analogous to the complex molecules which are built up by 
 living organisms (at the expense of solar energy) only to disintegrate into simpler 
 ones at the first available opportunity. 
 
MODIFYING THE NEBULAR HYPOTHESIS 199 
 
 eight years have then marked a remarkable advance in science, in 
 that they have proved the existence of an immense store of sub-atomic 
 energy." l 
 
 Glowing metals and other hot bodies give off radiant matter 
 somewhat similar to some of the forms described above. Cold 
 metals do the same when they are exposed to ultra-violet light. 
 It is possible that all forms of matter may emit similar particles 
 all the time. 
 
 It would be absurd to suppose that these bodies can give out 
 either radiations or particles continuously without any loss of 
 energy or weight, but the loss may sometimes be so small that 
 they may appear to do so. In some cases the radiations may 
 have been previously received from the Sun, and the vibrations 
 changed to a rate which our senses or instruments are capable 
 of perceiving or registering. 
 
 The particles of which most radiant matter is composed are 
 variously known as electrical corpuscles, electrons, ions, or 
 negative particles. It is worthy of note that different sub- 
 stances do not give out different kinds of corpuscles, but that 
 the latter appear to be all alike, whatever their source. 
 
 An atom of hydrogen is the smallest of all known atoms. In 
 decomposing water by electricity, an atom of hydrogen carries 
 a certain definite and indivisible charge of electricity, which is 
 known as an electron. Now it has been found that one of our 
 newly discovered corpuscles [although it is from 700 to 1000 
 times less (in mass) than an atom of hydrogen] carries the same 
 amount of electricity. This, however, is always what is known 
 as a negative charge. Positively charged corpuscles have not 
 yet been discovered, and they probably do not exist in a free 
 state. 
 
 It is possible that all the various forms of " elementary " 
 atoms composing ponderable matter are built up of concentric 
 layers of corpuscles, the layers being alternately positive and 
 
 1 "Recent Discoveries in Radiation," Popular Science Monthly, April, 1904. 
 Perhaps this advance will help to set at rest the long-standing dispute between 
 the astronomers and the geologists as to the duration of geologic times. 
 
200 HOW TO KNOW THE STARRY HEAVENS 
 
 negative. In this case we may assume that the outside layer 
 is always composed of negative corpuscles, so that the atoms 
 all attract one another at a distance, but mutually repel when 
 close together, especially when they are of the same sign. For 
 otherwise the atoms would mingle and lose their individuality. 
 If this is so, then the vibrations which produce light, etc., are 
 not vibrations of the atom itself, but of the electrons or cor- 
 puscles of which it is composed. 
 
 According to this Electronic Theory, electrons or corpuscles 
 are the ultimate particles of which all kinds of atoms consist. 
 The atoms themselves are " star-clusters " of electrons in stable 
 orbital motion at planetary distances from one another. On 
 this hypothesis a cluster of about 700 electrons forms an atom 
 of hydrogen. An atom of oxygen contains about 11,200 of 
 them. An atom of gold contains about 137,200. And so on. 
 
 It appears probable that, besides the corpuscles which are 
 built up into atoms, there are such vast quantities of free nega- 
 tive corpuscles that they fill all space . to saturation. If so, 
 then the luminiferous ether itself consists of these electrons or 
 negative particles. 1 
 
 1 This Electronic or Ultra-Atomic Theory appears to have needlessly alarmed 
 many people, who think that it will lead to the overthrow of the Atomic Theory 
 and of the Law of Substance. They may perhaps be set at ease by the following 
 words by Sir Oliver Lodge, F.R.S., at the close of an article on " Radium and its 
 Lessons." He says: 
 
 " Let me conclude by asking readers to give no ear to the absurd claim of 
 paradoxers and others ignorant of the principles of physics, who, with misplaced 
 ingenuity, will be sure to urge that the foundations of science are being uprooted, 
 and long-cherished laws shaken. Nothing of the kind is happening. The new 
 information now being gained in so many laboratories is supplementary and stim- 
 ulating, not really revolutionary, nor in the least perturbing to mathematical 
 physicists, whatever it may be to chemists ; for on the electric theory of matter it 
 is the kind of thing that ought to occur. And one outstanding difficulty about 
 this theory, often previously felt and expressed by Professor Larmor, that 
 matter ought to be radio-active and unstable if the electric theory of its constitu- 
 tion were true, this theoretical difficulty is being removed in the most brilliant 
 possible way." Nineteenth Century Magazine, July, 1903, 
 
FIG. 93. SPECTRA OF NOVA PERSEI, SHOWING CHANGES 
 Yerkes Observatory. 
 
 Feb. 27. 
 Feb. 28. 
 
 Mar. 6. 
 Mar. 15. 
 
 r. 28. 
 
MODIFYING THE NEBULAR HYPOTHESIS 201 
 
 REPULSION OF LIGHT 
 
 It has been discovered, first by theory and afterward by ex- 
 periment, that when the vibrations of light strike any object 
 they push against it with a force which varies according to the 
 square of its diameter. And as the attraction of gravitation, 
 acting on the same object, varies as the cube of its diameter, it 
 follows that, if the object is small enough, it will be violently 
 repelled from the source of light. 
 
 These facts form a simple and sufficient explanation of many 
 physical phenomena, both terrestrial and celestial, and have 
 been several times alluded to in the preceding chapters. 
 
 EVOLUTION OF LIFE, ATOMS, AND WORLDS 
 
 About the beginning of the nineteenth century, Goethe, 
 Lamarck, and some other naturalists rejected the theory of the 
 special creation of the different species of plants and animals. 
 They contended that all have developed, by natural means, 
 from the simplest forms of life, which originally came from 
 non-living matter. This development, they claimed, was car- 
 ried on by means of the interaction of heredity and adaptation. 
 
 In 1859 Charles Darwin proved the truth of this theory of 
 descent, as far as such a theory is capable of proof, and showed 
 that it was caused by a struggle for existence and the resulting 
 natural selection by the survival of the fittest. 
 
 The late Herbert Spencer first recognised that the same law 
 of evolution dominates the entire Universe. He showed that 
 its transformations are exhibited, not only by the Universe as 
 a great whole, but in all its details. They can be traced in the 
 Solar System, and in the inorganic Earth ; in the organic world 
 as a whole, and in each individual organism ; in society at 
 large, and in the individual mind. They are also clearly recog- 
 nisable in all the products of social activity. 
 
 From suns and worlds to molecules and atoms, all things 
 struggle for existence, and survive or perish according to their 
 
202 HOW TO KNOW THE STARRY HEAVENS 
 
 fitness. The reason why atoms and suns are in a state of 
 stable equilibrium that seems to be the result of mental con- 
 trivance is that all the forms which do not possess that " fitness 
 to survive " are promptly changed into forms that are not 
 mutually interfering. In both atoms and suns there is an 
 unconscious struggle for existence leading to an equally un- 
 conscious survival of the fittest. 
 
 PRIMEVAL TIDES 
 
 The shape, size, condition, and movements of any heavenly 
 body are due to the forces which act (or have acted) upon the 
 individual particles of which it consists. The mathematical 
 study of these forces has led to the discovery that the develop- 
 ment of suns and worlds is largely controlled by tidal action 
 while they are still in a gaseous or liquid-gaseous condition. 
 
 In a solar system like ours, and in a binary system or star- 
 cluster, the various bodies are moving with a certain regularity 
 along practically non-interfering lines. . This is not the result 
 of skilful manoeuvring by clever world-pilots. There is no one 
 steering them out of danger. Their apparent security is simply 
 due to the fact that interfering movements soon lead to catas- 
 trophes which effectually remove the insecure members of the 
 family circle, but leave the others alone. It is simply an in- 
 stance of the struggle for existence and of the survival of the 
 fittest. 
 
 But the sovereign suns which roam at large through space 
 all appear to be flying at random. So far as we know they 
 have no regular orbit, but each one is apparently dashing 
 blindly in the direction of least resistance to the surrounding 
 centres of attraction. They may be likened to a cloud of 
 mosquitoes or a vast swarm of bees. 
 
 Let us suppose that two gaseous suns are approaching one 
 another from opposite directions. Each one is sailing majes- 
 tically along in a practically straight line, and at the same 
 time is serenely spinning around on its axis. 
 
 If there were pilots on board, who could control them by 
 
MODIFYING THE NEBULAR HYPOTHESIS 205 
 
 means of a steering-apparatus, they would probably get in a 
 flurry sometimes, steer wildly, and cause a collision. But as 
 there is no one in charge to make trouble, an "accident" of 
 this kind seldom takes place. 
 
 It seems natural to suppose that if the two suns do not 
 actually collide they will pass each other and go on their way 
 as though they had never met. This is the case, indeed, when 
 they are a great distance apart. But if they pass very near to 
 one another the law of gravitation compels them to salute each 
 other. Their original speed is added to by their mutual attrac- 
 tion. They swing in toward one another, pass like a flash, and 
 go off on a curve which soon becomes practically a straight 
 line. 
 
 So far the only effect noticed has been a change of direction. 
 But there appear to be other changes produced. When the 
 two bodies were making their bow to each other, the central 
 particles in each of the suns were attracted less than the 
 nearest particles, but more than the farthest. The intensity 
 of the pull varies in the inverse ratio to the square of the dis- 
 tance (see Chapter XV). The result is the same as though 
 the nearest and farthest particles in each body were strongly 
 repelled from one another. The two suns therefore lose their 
 original orange-shape (due to attraction modified by rotation) 
 and become more or less the shape of a pear. After they have 
 passed each other, never to meet again, they continue to rotate 
 as before, and- the small end of each pear-shaped star swings 
 around as a mighty tidal wave. The centrifugal tendency is 
 so strong that the two ends gradually draw the central matter 
 to them, forming a dumb-bell arrangement which finally breaks 
 in two. The result is that each star becomes a " binary " or 
 double star, in which both of the partners rotate in the same 
 direction as that in which the parent moved. The telescope 
 and spectroscope show the heavens to be crowded with such 
 binary systems. In some cases the rotation is so rapid as to 
 show that the partners are still clinging together like Siamese 
 Twins. 
 
204 HOW TO KNOW THE STARRY HEAVENS 
 
 The binary system known as V Puppis appears to be in this 
 stage of evolution. The combined mass of the two partners is 
 equal to that of 66,000 worlds like ours, and they are still in 
 a distended gaseous state. Yet they are shown to revolve (or 
 rotate) in the remarkably short period of 35 hours. 
 
 The theory of tidal evolution (on which the above descrip- 
 tion of "puppation" is founded) was demonstrated mathe- 
 matically by Professor George Darwin from an examination 
 of the interaction between the tides and the motions of the 
 Earth and Moon. 
 
I 
 
 
 
 
 
 
 
CHAPTER XVIII 
 
 MODIFICATIONS OF THE NEBULAR THEORY 
 
 " Worlds on worlds are rolling ever, 
 
 From creation to decay, 
 Like the bubbles on a river, 
 
 Sparkling, bursting, borne away." P. B. Shelley. 
 " Without beginning, aim or end ; 
 Supreme, incessant, un begot ; 
 The systems change, but goal is not, 
 Where the Infinities attend." G. Sterling. 
 
 IMMORTALITY OF THE UNIVERSE 
 
 THE discoveries and speculations I have just sketched, and 
 others which have not been mentioned, have led to some 
 important modifications and developments of the original Neb- 
 ular Theory. 
 
 Among other changes, the foundation of Creationism has 
 been rejected by the foremost minds, so that the whole theory 
 is evolutionary. We now recognise no beginning and acknowl- 
 edge no end. We can conceive of no space which is not occu- 
 pied by matter in one or other of its two forms. We can admit 
 of no exhaustion of energy leading to a dead Universe. We 
 have come to the conclusion that nothing exists apart from 
 matter and its energies. Mind, in the form of desires and in- 
 clinations, exists not only throughout the animal and vegetable 
 kingdoms, but likewise in so-called dead matter. Even the 
 molecules, atoms, and corpuscles have a kind of sensation and 
 will. 
 
 -FROM DEATH UNTO LIFE" 
 
 The secret of the perpetual youth of the Universe appears to 
 lie in the fact that the millions upon millions of heavenly 
 
206 HOW TO KNOW THE STARRY HEAVENS 
 
 bodies do not move in paths of eternal regularity, but that they 
 interfere with one another. This causes their orbits to be 
 changeable, and, to some extent, irregular. The result is that 
 every once in a while two of them come into violent collision, 
 thus changing a large amount of potential into actual energy. 
 
 If two trains travelling at the speed of a mile a minute were 
 to meet " head on," it is obvious that an enormous amount of 
 latent energy would be turned to actual energy. If they were 
 travelling 750 times faster (which is the speed at which our 
 Sun is going toward Vega), the amount of actual energy pro- 
 duced by the shock would be 540,000 times greater ( = 750x 
 750). And if the two trains were to be loaded down till they 
 each equalled our Sun in weight, the energy produced would 
 be proportionately increased. It would be equal to that caused 
 by a direct collision between our Sun and another star of the 
 same mass and travelling at the same speed; 
 
 The result of such a collision could be calculated mathe- 
 matically, but the most vivid imagination could not picture it. 
 Yet there are suns many thousands of times larger, travelling 
 at a speed many times as great, and apparently liable at any 
 time to come together with a crash, or to glance by one another 
 with a result almost as disastrous. In the event of such a 
 collision the temperature of the colliding bodies would be raised 
 many thousands of degrees. They would expand into a huge 
 mass of thin gas, which would, in time, cool off to the tempera- 
 ture of space (probably about 230 F.). That is to say, the 
 old and feeble perhaps dead suns would spring into new 
 youth and drift away as a more or less diffuse and shapeless 
 mass of glowing gas. This would gradually assume the form 
 of a rotating spiral nebula, and begin once more the great drama 
 of evolution. 
 
 This picture is no freak of the imagination, but appears to be 
 an illustration of an actual fact. In all probability such things 
 have always been taking place, are taking place now, and will 
 be taking place when our Solar System has for ever disappeared 
 and been forgotten. 
 
MODIFICATIONS OF THE NEBULAR THEORY 207 
 
 We thus see that the evolution of suns and worlds does not 
 necessarily take place once and then cease. It is apparently 
 repeated over and over again ; here, there, and everywhere. As 
 Ernst Haeckel says, " while the rotating masses move toward 
 their destruction and dissolution in one part of space, others 
 are springing into new life and development in other quarters 
 of the Universe." 
 
 SOME NEBULA ARE COLD 
 
 The Nebular Theory of Laplace was that the nebulae were 
 extremely hot, and rotated in lens-shaped masses which threw 
 off regular rings. It has since been modified for both theoreti- 
 cal and observational reasons. 
 
 In the first place it is evident that, however hot a thin nebula 
 may be at its first formation (due to the collision of mighty 
 suns), there is nothing to prevent that heat from radiating away 
 into outer space. When it has done so there is no fresh supply 
 of heat to draw from except that produced by the action of 
 gravitation drawing its spirals back into condensed centres, and 
 it takes millions of years for that to produce any great increase 
 of temperature. So in the meantime it may be invisible except 
 at the outer surface. There a rain of negatively electrified cor- 
 puscles (sent out by the myriads of radiant suns) probably 
 causes it to glow with a cold light akin to many other corpus- 
 cular radiations. 1 
 
 In the second place it has been found that the most common 
 form of nebula seen in the telescope is not lens-shaped, but 
 spiral. While some of the nebulae (like the Great Nebula in 
 Andromeda) seem to be condensing into a vast central globe 
 surrounded by tolerably even rings, others (like the Spiral 
 Nebula in Canes Venatici) appear to be condensing around a 
 number of centres, as though forming a social system or star- 
 cluster (see Figures 63, 64, and 85). 
 
 1 Among these may be mentioned the Solar Corona, the tail of a comet, the 
 Zodiacal Light, the Gegenschein, the Aurora Borealis and Australis, St. Elmo's 
 fires, the phosphorescence of fishes and other animals, the kathode rays of our 
 electricians, etc. 
 
208 HOW TO KNOW THE STARRY HEAVENS 
 
 EVOLUTION OF SOLAR SYSTEM 
 
 When our Sun was in its first nebular stage (perhaps due to 
 collision), it was probably a hot and more or less spherical mass 
 of inconceivably thin gas, immensely larger than the whole Solar 
 System is now. Its particles would then be so far apart that 
 the most perfect vacuum we can produce would be dense in 
 comparison. Seen from a great distance, it would probably re- 
 semble the symmetrical planetary nebulae which are revealed 
 by our telescopes (see Figure 99). 
 
 Presuming that this planetary nebula was not interfered with 
 from outside, it would not lose its regularity of form, but would 
 gradually condense and acquire a spiral structure. But if any 
 wandering stars had happened to pass through it, it might for a 
 time have assumed the torn explosive appearance of the great 
 Trifid Nebula (see Figure 67), and if it had collided with a 
 neighbouring nebula it might possibly "have acquired an irregu- 
 lar form like that of the Great Nebula in Orion (see Figure 68), 
 but of course it would have been on a much smaller scale. 
 Unless very much scattered, however, the mutual attraction of 
 its particles would, in the course of time, again bring about a 
 regularity of form and structure. 
 
 When a cricket-ball is struck by a bat, the size, shape, and 
 density of the two bodies, and their position, speed, and direc- 
 tion, determine the flight of the ball and the subsequent adven- 
 tures it may meet with. In the same way the colliding bodies 
 which we assume to have given birth to the nebulous mass 
 under consideration must have received a certain moment of 
 momentum which has produced every peculiarity now possessed 
 by the Solar System which has developed from it. 
 
 After the explosive energy of the original collision had pro- 
 duced the hypothetical nebula, every gaseous particle in it was 
 left at a certain temperature and in a certain position. It was 
 also moving in a certain direction with a certain velocity. The 
 varied and irregular nature of these movements led to innumer- 
 able collisions between the particles. Some of the energy pos- 
 
MODIFICATIONS OF THE NEBULAR THEORY 209 
 
 sessed by the particles was thus turned to heat, which, like the 
 original heat of the nebula, radiated away into outer space. The 
 varied movements of the particles, and the resulting collisions, 
 naturally ended in the survival of the movements which did not 
 interfere with one another. The mass therefore gradually at- 
 tained a rotating disc-like form, lying on a plane and moving 
 in a direction determined by its original " moment of momen- 
 tum." In this way every particle moved in the path of least 
 resistance, and therefore with the least, expenditure of energy. 
 
 By this time the temperature of the nebula was very much 
 reduced by radiation into outer space. It was probably invisi- 
 ble except near the surface, where the radiant energy from sur- 
 rounding suns made the light surface-gases glow with a cold 
 radiance akin to that of the kathode rays of our vacuum tubes. 
 
 The dissipation of the original heat by radiation led to the 
 contraction and condensation of the entire mass. The decrease 
 in size of course led to an increase of the density and speed of 
 rotation. As the speed was greatest toward the centre, a rotat- 
 ing and indrawing spiral was the result (see Figures 63 and 85). 
 
 The centre of this spiral became a vast condensation which, 
 in the case of our System, drew to it the great mass of the neb- 
 ula. Four important subordinate centres of condensation were 
 also formed, as well as a great number of lesser ones. These 
 centres gradually absorbed the nebuldus matter around them, 
 and thereby increased continuously in density. 
 
 At first these centres of condensation did not have any rota- 
 tion except that due to the spiral indrawing revolution of the 
 whole mass. That is to say, each subordinate centre rotated at 
 the same speed that it revolved. But as its particles were drawn 
 in toward the centre, the rotation grew more rapid, because they 
 had a shorter journey to go and were nearer the local centre of 
 attraction. All the subordinate condensations, therefore, ac- 
 quired an ever-quickening speed of rotation in the same direction 
 as the revolution of the whole system. In the case of the 
 central condensation there would be no distinction between 
 rotation and revolution. 
 
210 HOW TO KNOW THE STARRY HEAVENS 
 
 As the particles in one of these condensations gradually fell in 
 toward its centre, their friction with one another turned a large 
 part of its energy into heat. So much heat was produced in this 
 way that it could not all radiate into space. Its temperature, 
 therefore, rose, slowly but steadily, till it glowed like a little sun. 
 
 As a result of the changes outlined in the preceding three 
 paragraphs, the centres of condensation, though they decreased 
 in size, continually increased in density, speed (of rotation and 
 revolution), and heat. 
 
 So far we have theoretically traced the evolution of the origi- 
 nal nebula into a system of thin, hot, and bright gaseous planets 
 revolving around a huge gaseous centre. This central conden- 
 sation was even hotter than the planets, and was destined in 
 time to become a central sun, luminous with an inconceivable 
 intensity of heat. 
 
 The small amount of nebulous matter which still remained, 
 outside the planetary centres, was gradually drawn in by them 
 in a spiral manner, and condensed into similar but smaller 
 centres. They acquired the same peculiarities of revolution 
 and rotation, and in fact repeated the original history of the 
 whole system on a smaller scale. This appears to be the origin 
 of the satellites which now attend the larger planets, and of the 
 rings of Saturn, which consist of innumerable small satellites. 
 
 After a certain amount of condensation the production of 
 frictional heat in each subordinate centre became less in 
 amount. As the radiation continued unchecked, a maximum of 
 heat was reached, and the satellites and planets then began 
 to cool off. The smaller a body is, the larger becomes its 
 surface in proportion to its mass. The satellites and smallest 
 planets therefore cooled off the quickest. Their surfaces solidi- 
 fied and became solid rock. This, being a bad conductor of heat, 
 somewhat checked their loss of heat by radiation, but did not al- 
 together prevent it. In time they therefore became solid to 
 the centre and gradually approximated to the temperature of 
 outer space. 
 
 The larger planets are now going through the same cooling 
 
MODIFICATIONS OF THE NEBULAR THEORY 
 
 and solidifying process. But the central Sun is still producing 
 about as much heat by its contraction as it loses by radiation 
 into outer space. It is still kept in an incandescent gaseous 
 form by this heat, and the only elements in it which have 
 reached a solid state are the carbon and silicon which are ex- 
 posed to the cold of outer space above a certain elevation in 
 its atmosphere of metallic gases. Their chilled particles are 
 apparently frozen into solid incandescent beads that form the 
 glittering clouds which we term the solar photosphere. 
 
 We thus see that the heat of the Sun is not due to com- 
 bustion. In fact combustion is like organic life, it cannot 
 exist above or below a certain range of temperature. The heat 
 of the Sun is at present far too great to allow a comparatively 
 cold process like combustion to take place anywhere near it. 
 
 When the Sun formed the bulk of the original nebula its 
 energy was all potential. Its circling particles have been 
 falling ever since, as they " spirated " around the centre of 
 gravity of the mass. Their friction in falling is the cause of 
 all the heat, etc., which has since been produced and radiated. 
 The same amount of heat is produced by the friction of adja- 
 cent particles, whether a body falls rapidly or slowly, directly 
 or indirectly. As the Sun's mass has not changed and is 
 known, the amount of potential energy changed into actual 
 energy can be computed. The radiant energy developed by 
 the contraction of the Solar System from a thin nebula is equal 
 to the energy necessary to force its particles asunder and return 
 it to a nebular condition. 
 
 After the contraction had gone on for many millions of years, 
 the various planets were left outside of the central condensing 
 nucleus in the way already described. When this nucleus 
 had contracted to the size of the Earth's present orbit, it was 
 still about 12,000 times thinner than our atmosphere at the 
 sea level. It was therefore about as dense as the most perfect 
 vacuum we can make with an air-pump. As it continued to 
 shrink in size, the crowding atoms gradually gave rise to long 
 heat-waves. In the course of ages the short light-waves were 
 
HOW TO KNOW THE STARRY HEAVENS 
 
 also produced, turning the gaseous mass into a nebulous sun. 
 It has been estimated that when it had contracted to the size 
 of the present orbit of Mercury it gave off about one eightieth 
 of its present radiant energy, and when the continuous con- 
 traction had reduced it to a thousand times its present size its 
 average density became equal to that of our atmosphere at the 
 sea level. 
 
 As the light gases around it were gradually absorbed, it 
 slowly changed from a nebulous star into a brilliant bluish- 
 white star, and afterward into a yellowish-white one. It is 
 now, on the average, about one and a half times as dense as 
 water. Its particles, therefore, fall more slowly, but produce 
 more friction and radiance. 
 
 The Sun's contraction in size has now fallen off to about 
 9 inches per day say a mile in twenty years. This is so 
 small that it would take nearly 10,000 years to recognise the 
 shrinkage, from the Earth, with our present instruments. The 
 maximum of heat appears to have been passed, and the light 
 has begun to wane and turn yellow. Some day, in the dim and 
 distant future, spasms of chemical combination will take place 
 in the reddening Sun. It will gradually liquefy from the 
 centre up to the surface, and afterwards solidify from the sur- 
 face down to the centre. It will then cease to contract and to 
 give out light and heat, its potential energy having all turned 
 into actual energy, and radiated away into space. By that time 
 its average density will have probably increased to about twenty 
 times that of water. 
 
 Although satellites or moons are common in the Solar System, 
 our Moon appears to be, in some respects, an exceptional one. 
 It is very much larger, in proportion to the Earth, than the 
 satellites of the other planets "are when compared with their 
 primaries, and it appears to have had a different origin. Before 
 it was born, the still molten Earth appears to have shrunk 
 until it rotated in about four or five hours. Its equatorial parts 
 then bulged out and became almost weightless, through the 
 centrifugal force resulting from the rapid rotation. The pull of 
 
MODIFICATIONS OF THE NEBULAR THEORY 213 
 
 the Sun on this weightless mass raised a huge tide on the Sun- 
 ward side of the Earth. This gradually grew in size, so that 
 the Earth assumed something of a pear shape. Finally the 
 rotation became so rapid that the tidal wave was wrenched 
 loose from the main body of the Earth and became our Moon. 
 This tidal parentage is known as a " fission " process, and was 
 first brought to light by Professor George Darwin. 
 
 The Earth and Moon, while still very close together, and 
 still molten, produced huge tides in each other. The Earth- 
 raised Moon-tides acted as a brake on the Moon and checked 
 its rotation. At last its rotation and revolution periods became 
 equal, so that it always turned the same face to the Earth. 
 The Earth-tides which the Sun and Moon raised acted as a 
 brake on the Earth itself, and at the same time quickened 
 the forward motion of the Moon, thereby increasing its distance 
 and period. 
 
 The Earth and Moon have now solidified, so that the tides 
 on the Moon have ceased, and those on the Earth are almost 
 
 FIG. 95. EARTH-TIDES, IF THE DAY AND MONTH WERE EQUAL 
 The moon's orbit would remain constant. 
 
 entirely confined to the large open bodies of water on its sur- 
 face. Yet the ocean tides still continue to act as a brake to 
 check the Earth's rotation. The effect, though small, is cumu- 
 lative, and will in time lengthen the Earth's day and the 
 Moon's " moonth " till they are both equal to about 55 of our 
 days. The lengthening will then cease, and both bodies, 
 though still revolving around their common centre of gravity, 
 
214 HOW TO KNOW THE STARRY HEAVENS 
 
 will be relatively immovable, like the two ends of a dumb-bell, 
 which always present the same face to each other. 
 
 It is not difficult to understand that the tides on each body 
 should act as a brake and check rotation. But it is not so 
 obvious that the Earth- tides should pull the Moon forward, 
 and, by so doing, increase the size of its orbit and the period of 
 its revolution. The principle is as follows : 
 
 A particle of matter at the centre of the Earth is pulled 
 toward the Moon with a certain force. A particle on the side 
 nearest the Moon is pulled with a greater force. And a parti- 
 
 CUtt-TAttion 
 
 )MOON 
 
 FIG. 96. ACCELERATION OF MOON BY FORWARD PULL OF EARTH-TIDE 
 Moon's orbit forms a slowly opening spiral. 
 
 cle on the side away from the Moon is pulled with less force, 
 and is therefore (relatively) repelled. Consequently, if the 
 Earth rotated at the same speed at which the Moon revolved, 
 the water would bulge out, not only on the side nearest the 
 Moon, but also on the side farthest from it (see Figure 95). 
 
 Owing, however, to the relative rapidity of the Earth's rota- 
 tion, the tides are dragged forward by molecular friction. The 
 tide nearest the Moon is therefore a little in front of the line 
 joining the centres of the Earth and Moon (see Figure 96). 
 It is the forward pull of this Earth-tide on the Moon which 
 quickens the motion of the latter. By so doing it very slowly 
 enlarges the Moon's orbit and lengthens its period of revolution 
 around the centre of gravity of the Earth and Moon. The 
 action (like that of the Earth-brake) is absolutely imperceptible, 
 
MODIFICATIONS OF THE NEBULAR THEORY 215 
 
 but is, at the same time, real and cumulative. It is therefore 
 only a question of time for great changes to be produced. And 
 of time there is no end. 1 
 
 By the time the Earth and Moon have reached the dumb- 
 bell stage, the lunar tidal-friction on the Earth will come to an 
 end, and the Moon's path will cease to be an opening spiraL 
 
 FIG. 97. LOOP IN APPARENT PATH OF MARS 
 
 As he approaches opposition, his direct (easterly) motion amongst 
 the stars slackens and soon ceases. He then appears to move back 
 towards the west. After opposition this retrograde motion also slack- 
 ens and ceases. His direct motion then recommences, and is kept up 
 till the next opposition. He thus appears to make a loop every 584 days. 
 
 But until our oceans are frozen solid, the Earth's solar tides 
 will still continue to act as a brake and check its rotation. So 
 at last the time may come when the Earth's day will equal its 
 year, and the same side will always be turned toward the Sun. 2 
 It is rather uncertain what changes will take place after this 
 stage has been reached. If no accident should happen, in the 
 form of a collision with some outside body, the probability is 
 that the satellites and planets will very slowly draw in toward 
 their centres of revolution. 3 In this case the Moon's path will 
 
 1 The tide which is away from the Moon tends to counteract this pull, but is 
 too weak to overcome it altogether. 
 
 2 Mercury and Venus appear to have already reached this stage. 
 
 8 This theory is based upon the supposition of a resisting medium, ethereal or 
 otherwise. 
 
216 HOW TO KNOW THE STARRY HEAVENS 
 
 gradually get smaller, and it will, in time, reach the surface of 
 the Earth. The two bodies will grind each other into super- 
 heated gas, which will afterward cool down and solidify. The 
 resulting body will gradually get nearer to the Sun, and even- 
 tually grind its way into the body of its parent. 1 
 
 By the time all the planets have returned to the Sun, and 
 the last disturbance has subsided, one second of Eternity will 
 
 w 
 FIG. 98. DIAGRAM SHOWING CAUSE OF LOOP IN APPARENT PATH OF MARS 
 
 The positions of Earth and Mars given at intervals of ten days. Mars appears to ad- 
 vance amongst the stars from 1 to 7, to retrograde from 7 to 11, and then to advance as 
 before. 
 
 have passed away since it was in the same stage before. The 
 Solar System will then be represented by a cold, dark, solid 
 mass containing the same amount of matter as the original 
 nebula. This dead hulk will drift around in the long cold star- 
 light night (like a derelict on the broad ocean) until some simi- 
 lar body collides with it and turns it all into gas again. It will 
 
 1 If this theory is correct, the matter of which our bodies are composed once 
 formed part of what is now the Sun, and will in time return to it. 
 
MODIFICATIONS OF THE NEBULAR THEORY 217 
 
 then be ready to live its life over again and give birth to an- 
 other Solar System perhaps twice as large as the present one. 
 These cycles will presumably take place an infinite number of 
 times, the same matter being used over and over again to all 
 eternity. This is probably true not only of the future but of 
 the past ; not only of our System but of all the systems of the 
 Universe; not only of our Universe but of all the universes 
 that may exist in infinite space. 
 
 Now that I am through with the Nebular Hypothesis, it may 
 be well to remind the reader again that it is still an unproved 
 theory. As a working hypothesis it is one of the grandest and 
 most valuable theories ever reasoned out by the mind of man, 
 and in its main features it is almost certainly true as far as it 
 goes. But from the very nature of the case we are not in a 
 position to prove its truth, and it is doubtful if we ever shall 
 have anything except indirect evidence concerning it. 
 
 SUMMARY 
 
 I cannot do better than close this chapter with a summary, 
 by Ernst Haeckel, of the most important conclusions at which 
 science is arriving with regard to the constitution and evolu- 
 tion of the Great Cosmos. It is as follows: 
 
 " I. The extent of the Universe is infinite and unbounded ; it is 
 empty in no part, but everywhere filled with substance. 
 
 " II. The duration of the Universe is equally infinite and unbounded; 
 it has no beginning and no end : it is eternity. 
 
 II III. Substance is everywhere and always in uninterrupted move- 
 ment and transformation : nowhere is there perfect repose and rigid- 
 ity ; yet the infinite quantity of matter and of eternally changing 
 force remains constant. 
 
 " IV. This universal movement of substance in space takes the 
 form of an eternal cycle or of a periodical process of evolution. 
 
 " V. The phases of this evolution consist in a periodic change of 
 consistency, of which the first outcome is the primary division into 
 mass and ether, the ergonomy of ponderable and imponderable 
 matter. 
 
218 HOW TO KNOW THE STARRY HEAVENS 
 
 " VI. This division is effected by a progressive condensation of 
 matter as the formation of countless infinitesimal ' centres of conden- 
 sation,' in which the inherent primitive properties of substance feel- 
 ing and inclination are the active causes. 
 
 "VII. While minute and then larger bodies are being formed by 
 this pyknotic process in one part of space, and the intermediate ether 
 increases its strain, the opposite process the destruction of cosmic 
 bodies by collision is taking place in another quarter. 
 
 " VIII. The immense quantity of heat which is generated in this 
 mechanical process of the collision of swiftly moving bodies represents 
 the new kinetic energy which effects the movement of the resulting 
 nebulae and the construction of new rotating bodies. The eternal 
 drama begins afresh." * 
 
 1 " The Kiddle of the Universe," pp. 242, 243. 
 
CHAPTER XIX 
 
 THE MESSENGERS OF HEAVEN 
 
 " In the old mythologies the Universe consisted merely of a flat World, resting 
 on an infernal bowl, and covered by a celestial vault or canopy. 
 
 " The Gods who ruled this mundane Universe generally resided on the top of 
 the firmamental dish-cover. There the supreme Deity had his throne, and pre- 
 sided over the councils of the Gods. 
 
 " As none of these Gods were omniscient or omnipresent, they had to provide 
 themselves with angelic messengers to keep them posted as to what was going on 
 iii the World beneath, and to carry out their commands when they had come to 
 an agreement as to what kind of left-handed justice should be meted out to the 
 mortals below. 
 
 " These messengers of heaven were no loafers round the throne when they had 
 a duty to perform. They could fly on the wings of the wind and outstrip the 
 fiercest tempest. 
 
 " We now know that these angelic messengers, like the Gods they were supposed 
 to serve, have no existence except in the imaginations of ignorant and superstitious 
 people. But Science has revealed to us that there are messengers of heaven more 
 swift than the wing-footed Mercury, more restless than the cloven-hoofed Satan, 
 and more long-lived than the Father of the Gods himself." A. Zazel. 
 
 VISITORS FROM AFAR 
 
 IN a former chapter I spoke about the intense loneliness of 
 our Solar System in the midst of an immense multitude of 
 similar systems scattered through space. 
 
 Is there, then, no physical communication between the vari- 
 ous systems of worlds ? Are they entirely and for ever cut off 
 from one another? Are there no messengers of heaven that 
 can serve the bidding and carry the messages of the sunny-faced 
 Gods of ethereal space ? 
 
 Yes, there are wanderers who go from star to star and from 
 constellation to constellation. There are beings which spend 
 almost an eternity in going to and fro in the Universe, and in 
 flying up and down through it. 
 
220 HOW TO KNOW THE STARRY HEAVENS 
 
 A VOYAGE OF FIVE MILLION YEARS 
 
 In order to learn something of these interstellar wanderers, 
 let us suppose that we are back in our Chariot of Imagination, 
 half way between our Sun and the nearest outside star. Let us 
 also suppose that the clock has been turned back several 
 millions of years ; that we have plenty of time at our disposal ; 
 and that we have laid in a goodly supply of Job's patience. 
 
 We are surrounded, as before, by countless systems of worlds, 
 but they are all in the remote distance. Let us move around 
 a little, and see if our immediate neighbourhood is really as 
 empty as it seems. 
 
 With the naked eye we might have to look for a long time 
 before finding anything near us. But with suitable instruments 
 we soon find that although there are no suns or large worlds in 
 our neighbourhood there are, here and there, small fragments of 
 hard rock floating in the otherwise empty darkness. These 
 stones sometimes contain a large percentage of iron, and greatly 
 resemble the meteoric stones that occasionally fall onto our 
 Earth. They vary greatly in size, some of them being no larger 
 than grains of sand. As there is no large world near to attract 
 them, they are destitute of weight and simply float in empty 
 space. 
 
 If we search long enough we may possibly come across one or 
 two similar rock masses of considerable size, for there does not 
 appear to be any break between these " pocket-planets" and the 
 huge suns and worlds with which we are distantly acquainted. 
 
 In some places these airy particles of sand and gravel are 
 thousands of miles apart, but sometimes they are so crowded 
 together that they are only twenty or thirty miles from one 
 another. 
 
 As these fragments of floating rock are familiar in appearance, 
 small in size, non-aggressive in disposition, and sedentary in 
 habit, we will not concern ourselves any more with them at pres- 
 ent, but will stop in one place and sweep the neighbourhood with 
 a searchlight to see if anything more important passes our way. 
 
THE MESSENGERS OF HEAVEN 
 
 We may have to watch for what seems to us a big part of 
 eternity, or our search may be successful before an earthly year 
 has passed away. 
 
 At last our patience is rewarded by seeing something coming 
 in our direction. It is approaching so leisurely that we have 
 plenty of time to observe it, as it almost imperceptibly drifts by 
 our lonely station. 
 
 With the help of suitable instruments we can see that our 
 visitor consists of a nucleus of fragmentary solids surrounded 
 by a thin but misty atmosphere which emits a faintly phos- 
 phorescent glow. The density of the whole mass is so small 
 that the solid nucleus is apparently in the form of dust or ashes, 
 with perhaps a nucleolus of larger fragments. All are practi- 
 cally without weight, and rest on one another 
 as gently as so much feathery down. 
 
 Our visitor is not very far away from us, as 
 celestial distances go, and yet it appears to 
 be almost at a standstill. Considering its 
 size it really seems to be the quietest, laziest, 
 deadest object we have yet come across in the 
 Universe. With the exception of the tiny ^ 99. A CELES- 
 meteoric stones just mentioned, we have never TIAL MESSENGER ON 
 seen its equal in these respects. 
 
 Let us follow this strange object in its do^iVpSntta^Vei^ 
 leisurely travels through space. But be care- ula - it should be viewed 
 
 , , J . . r . , from a distance. 
 
 lul lest your impatience at its slowness does 
 not bring on that kind of nervous attack which is known by 
 western deer-hunters as the "buck-ager," for you might pos- 
 sibly scare the lazy-looking object, which is not as dead as it 
 looks, and is indeed capable of travelling at a speed that would 
 almost leave the Chariot of Imagination behind. 
 
 After keeping the new arrival in view for a million years or 
 so, it becomes evident that its drifting motion is not due to any 
 energy of its own, but is caused by the gravitational attraction 
 of the far distant stars. 
 
HOW TO KNOW THE STARRY HEAVENS 
 
 KEARING PORT 
 
 In the course of long and weary ages the object we are 
 investigating gradually and imperceptibly enters the area 
 where the attractive energy exerted by one star is greater than 
 that of all the other stars put together. The result is that it 
 now moves faster than before, and (like a messenger-boy near- 
 ing his destination) begins to look as though it were going 
 somewhere. 
 
 It yields itself without a struggle to the growing influence, 
 and imperceptibly quickens its speed with every mile it goes. 
 As the time passes away, the now progressive messenger leaves 
 the cold and midnight darkness of outer space, and enters the 
 serene twilight that reigns eternal at the portals of the solar 
 system it is visiting. 
 
 As it approaches the brilliantly glowing star and comes within 
 the radius of its circling family of worlds, it increases still more 
 the rapidity of its forward movement. Faster and yet faster it 
 speeds through the gathering light. The intense cold of inter- 
 stellar space has now moderated. The new arrival feels the 
 growing warmth, and begins to unfold itself before the cheerful 
 influence. The surrounding haze gradually melts away into a 
 glowing gas which forms a huge luminous atmosphere around 
 the loose and scattering nucleus. 
 
 By this time the outer members of the solar family have been 
 safely passed. The now rushing messenger is hastening faster 
 and yet faster toward the central star. The milestones of space 
 fall behind as the pickets of a fence flicker when seen close at 
 hand from an express train. 
 
 The so-called Asteroids are passed with a fearful disregard 
 for possible collisions. Then, with still gathering intensity of 
 ever-increasing speed, our celestial messenger flashes like a 
 winged sword of fire through the midst of the inner planets as 
 they circle serenely around their central sun. So great is the 
 speed of the messenger's body that its flowing robes of luminous 
 particles now trail behind for many millions of miles. They 
 
FIG. 100. A CELESTIAL MESSENGER APPROACHING A STAR 
 
 FIG. 101. BROOK'S COMET, 1893 
 
 Lick photograph. The tail was distorted, probably 
 by collision with a swarm of meteoric bodies. 
 
 FIG. 102. COMET 1903 C 
 Lick photograph. 
 
THE MESSENGERS OF HEAVEN 223 
 
 look, indeed, like the " wake " of a fast-moving steamer on 
 smooth water (see Figure 100). 
 
 A CELESTIAL MESSENGER APPROACHING A STAR 
 
 The inhabitants of the minor planets tremble by night as 
 they see what looks like a mighty two-edged sword of fire 
 flaming in the starlit sky. Some of the more ignorant of 
 them pray to their Gods to deliver them from the threatening 
 monster. Others, with more self-reliance, beat their tom-toms 
 to scare away the intruder from their neighbourhood. But, all 
 unconscious of the commotion it has caused among the self- 
 important microbes that cling around the circling cobble-stones, 
 the mighty visitor sweeps majestically by on its appointed 
 path, leading to the central star. 
 
 A HOT RECEPTION 
 
 At last, with a still more energetic rush that almost rivals 
 the flight of the swift- winged arrows of light, the messenger of 
 the Gods swoops down down down, and is lost to sight 
 in the blasting heat and dazzling light of the solar furnaces. 
 
 To all appearances our messenger of the Gods has met with 
 such a fiery reception that his reappearance is not to be looked 
 for. His fall seemed to be as disastrous as that of the fabled 
 Adversary, whom (according to Milton) 
 
 "the Almighty Power 
 
 Hurled headlong flaming from the ethereal sky, 
 With hideous ruin and combustion, down 
 To bottomless perdition, there to dwell 
 In adamantine chains and penal fire, 
 Who durst defy the Omnipotent to arms." l 
 
 One thing, however, we noticed as our celestial messenger 
 disappeared in the solar light, and that was that he did not fall 
 prone into the solar flames, as the traditional Adversary crashed 
 into the molten crater of the hellish Kilauea. He seemed, in- 
 
 1 " Paradise Lost," Book I. 
 
224, HOW TO KNOW THE STARRY HEAVENS 
 
 deed, to fall to one side, as though he meant to skim along the 
 surface, deliver his message, and rush out on the other side 
 before the terrific heat could burn him up. 
 
 Knowing, however, how fearful is the heat of that stu- 
 pendous globular furnace, it does not seem worth while staying 
 to see if he has survived the ordeal. Indeed, it is uncomfort- 
 ably hot even fifty millions of miles away from the blazing 
 star. We shall have to back out of the stellar heat lest our 
 Chariot of Imagination should catch fire, or we should lose 
 control of the horses thereof and share the fate of the presump- 
 tuous Phaethon when he tried to drive the chariot of the Sun. 
 
 ANOTHER VOYAGE 
 
 But stay ! Something has just come into sight on the other 
 side of the star. What is it ? Surely it cannot be that our 
 messenger has safely skimmed the vast and fiery furnace, and 
 has already reappeared on the other side, a million miles away 
 from where he disappeared but an hour ago ! It seems im- 
 possible, and yet it is evidently the same messenger, hasten- 
 ing away in safety from the fiery ordeal through which he has 
 passed. 
 
 So far from being injured by the encounter, he (like the 
 grand hero of " Paradise Lost "), 
 
 " With fresh alacrity and force renewed, 
 Springs upward, like a pyramid of fire, 
 Into the wild expanse, and through the shock 
 Of fighting elements, on all sides round 
 Environed, wins his way ; harder beset 
 And more endanger'd than when Argo passed 
 Through Bosphorus, betwixt the justling rocks; 
 Or when Ulysses on the larboard shunn'd 
 Charybdis, and by the other whirlpool steered." 1 
 
 Strange to relate, our fast-retreating messenger has been 
 beaten in the race by his flowing garments. These, instead of 
 trailing behind in the solar furnaces, are now extended in front 
 
 1 " Paradise Lost," Book II. 
 
THE MESSENGERS OF HEAVEN 225 
 
 of him for many a million miles, as though anxious to get 
 back into the outer cold and darkness. 
 
 Let us turn our chariot and trace him as he recedes from the 
 star. We have not followed him very far before we find that 
 his speed begins to slacken, and that he is apparently gathering 
 in his garments. By the time that we are once more in the 
 dark, outside the stellar system, he is again nothing but a 
 round mass of faintly glowing haze, drifting idly through the 
 midnight sky. 
 
 So he keeps on, century after century, drifting drifting 
 drifting, like a ship becalmed by night in the solitude of a 
 tropic sea. 
 
 On our little Earth and perhaps on millions of similar 
 worlds scattered through space continents appear above the 
 seas and are pounded to pieces by the waves. New and higher 
 forms of life develop, and give way in their turn to still more 
 specialised species. The huge reptiles of the Earth's Oolite 
 yield to the warm-blooded mammalia of the Tertiary period. 
 The four-footed tree-dwellers develop ape-like peculiarities. 
 The sharpest of the four-handed apes desert the trees and adapt 
 themselves once more to live on the ground. Pithecanthropus 
 erectus develops into Palaeolithic Man. Neolithic Man is 
 driven into the mountains by those who have chariots of iron. 
 Nations, empires, and races come into existence, nourish for a 
 time, and pass away, like ephemeric clouds in a summer sky. 
 The chattel-slave and his master develop into the serf and his 
 lord. The wage-slave and his " boss " become economic equals 
 in the Industrial Commonwealth. And still this hazy mass is 
 drifting drifting drifting, through ethereal realms of star- 
 lit space. 
 
 A million times our World goes around its Sun, and still our 
 lazy messenger is imperceptibly drifting through endless night. 
 For two three four five millions of Earth-timed years 
 he drifts drifts drifts along, and then, coming once more 
 under the influence of a star, he repeats his former rush, but 
 around another sun. Again he goes into the outer darkness, 
 
 15 
 
226 HOW TO KNOW THE STARRY HEAVENS 
 
 drifts through almost endless years, and again he rushes around 
 another star. And so he spends what seems to us almost an 
 eternity of time. 
 
 A CAPTIVE MESSENGER 
 
 Sometimes the influences which surround a star cause him 
 to close his orbit and circle around and around the same star in 
 a long narrow orbit. But some time or other the attraction of 
 a planet turns him out of his closed orbit, and he once more 
 goes off and drifts drifts drifts through endless space. 
 
 COMETS 
 
 It is hardly necessary to state that our Messenger of the 
 Gods is nothing more or less than what is known to us as a 
 comet. Such bodies exist throughout the Universe in hundreds 
 of millions. Until recently we were entirely in the dark as to 
 their composition, origin, and movements. Their nuclei, it is 
 true, were known to submit to the law of gravitation, but 
 hardly a guess could be made as to the nature of the repulsive 
 force which produces and dominates over their tails. Even yet 
 we have much to learn concerning comets generally. But some 
 of the main facts have been ascertained, and a reasonable 
 theory has been formed which throws a good deal of light 
 upon them. 
 
 The probability is that they are huge collections of loose 
 meteoric dust and gravel, with large quantities of hydrocarbons 
 and free hydrogen. All this loose material has been ejected 
 into space from solar or planetary volcanoes. In the intense 
 cold of outer space (which is at least 230 below zero on the 
 Fahrenheit scale, and may possibly be 461), the hydrogen 
 and hydrocarbons naturally cling evenly around the solider 
 material. 
 
 On approaching a star, the radiant energy from the central 
 sun causes them to spread in all directions around the scatter- 
 ing nucleus. They thus form the cloudy haze of which all 
 
THE MESSENGERS OF HEAVEN 227 
 
 telescopic comets consist. When still nearer, the spreading 
 particles in front are further dissipated by the heat. At last 
 they are so small that the radiant energy of the sun overcomes 
 their gravity, and violently repels them into outer space. 
 There, lighted up by the sun, and glowing with a soft electric 
 light of their own, they form the tremendous hollow luminous 
 
 FIG. 103. PARABOLIC ORBIT OF A FREE COMET 
 
 It is practically an ellipse with the two foci at an infinite 
 distance from each other. Hence the orbit is closed at only 
 one end. 
 
 trumpet-shaped appendage known as the tail of the comet. 
 The shape of the tail, and its direction in space, depend on the 
 strength of the repelling force, and that varies with the size of 
 the particles composing the tail. Sometimes there are several 
 tails, extending in different directions, or, rather, in different 
 curves. There appear to be three different types of tail, differ- 
 ing in direction, shape, and material. The straightest ones are 
 probably composed of hydrogen. They are repelled with the 
 greatest force, and therefore extend almost directly away from 
 the Sun. The next are more curved, and are supposed to con- 
 
228 HOW TO KNOW THE STARRY HEAVENS 
 
 sist of varying hydrocarbons. They are repelled with about 
 one quarter the force of the hydrogen tail. The third type is 
 still more curved, and probably consists of chlorine and iron. 
 The repulsion is only about one sixteenth that of the hydrogen 
 tail. All of these tails are hollow cones, of which only the 
 sides are generally visible. 
 
 FIG. 104. ELLIPTICAL ORBITS OF CAPTIVE COMETS 
 
 As fresh particles are being sent out into each tail all the 
 time, it naturally follows that after the head of the comet has 
 begun to recede from the Sun its newly formed tails stretch out 
 in front of it. In the meantime the old ones have been driven 
 off and dispersed. 
 
 As before stated, the main body of a comet obeys the same 
 laws that control the motions of all the heavenly bodies. The 
 luminous gas of which a comet is largely composed is so thin 
 and transparent when within the Solar System that the faintest 
 stars can be seen through millions of miles of its substance. 
 The whole comet is so light in weight that it can sweep by the 
 
FIG. 106. DONATI'S COMET, 1858 
 By Bond. (From Comstock's " Text-book of Astronomy," published by Messrs. D. Appleton & Co.) 
 
 FIG. 107. COMET RORDAME, 1893 
 By Hussey, at Lick Observatory. 
 
THE MESSENGERS OF HEAVEN 
 
 planet Saturn without disturbing the motions of his numerous 
 family of moons, while these same moons, small as they are, 
 are able to deflect it from its original path if it should happen 
 to pass near them. 
 
 PERIODIC COMETS 
 
 " Amid the radiant orbs 
 That more than deck, that animate the sky, 
 The life-infusing suns of other wcfrlds ; 
 Lo ! from the dread immensity of space, 
 Returning with accelerated course, 
 The rushing comet to the Sun descends ; 
 And as he sinks below the shading Earth, 
 With awful train projected o'er the heavens, 
 The guilty nations tremble." Thomson, "The Seasons" Summer. 
 
 Some of the comets that move in closed orbits around our 
 Sun have had their elliptical paths traced out by the astron- 
 omers. They are not confined to the Ecliptic, like the planets, 
 but are inclined at all angles 
 to it. Their regular coming can 
 be anticipated, though their 
 movements are never to be de- 
 pended on, owing to the ease 
 with which they are turned 
 out of their course by the plan- 
 ets they happen to come near. 
 
 Several of the periodical 
 
 comets have paths extending 
 
 ,, , ., \ . _. 6 FIG. 105. TAIL OF A COMET NEAR 
 
 to the orbit of Jupiter. Others PERIHELION 
 
 go away as far as Saturn and 
 
 Uranus. This is one of the peculiarities which gave rise to 
 the theory that they were originally thrown out from those 
 giant planets by tremendous volcanic eruptions, like those 
 which are constantly taking place on the apparent surface of 
 our Sun. This theory is now generally abandoned, on account 
 of the tremendous force necessary to overcome the gravitation 
 of such huge planets. 
 
 They are now believed to have been captured by the planets 
 
230 HOW TO KNOW THE STARRY HEAVENS 
 
 to which they are related. Tempel's comet, which is connected 
 with the Leonid meteors and which goes away as far as the 
 orbit of Uranus has had its orbit traced back to the year 
 126 A. D. At that date the two bodies were very near together, 
 and the planet appears to have drawn it (and the Leonids 
 accompanying it), out of the original parabolic orbit into an 
 elliptical orbit having a period of about 33 years. Such 
 changes of orbit appear to be not uncommon among comets. 
 
 The spectra of comets .contain three bright hydrocarbon 
 bands well denned at the red end. There are also several 
 bright iron lines, and one due to manganese. When a comet is 
 near the Sun, the bright sodium lines are sometimes seen. In 
 addition to this emission or radiation spectrum, there is 
 generally a faint absorption spectrum visible, with dark lines. 
 
 METEORS 
 
 Another peculiarity of these erratic wanderers is that some 
 of them are intimately connected with meteor showers. When 
 
 FIG. 108. A METEOR BURSTING IN THE ATMOSPHERE 
 
 Seen through a telescope. 
 
 our Earth passes through the path of one of these captive 
 comets, vast multitudes of so-called " shooting-stars " enter our 
 atmosphere and burn up with the heat generated by atmospheric 
 friction. Where fragments of meteors happen to reach the. 
 
THE MESSENGERS OF HEAVEN 231 
 
 surface of the Earth, they are found to consist of volcanic sub- 
 stances like those thrown out by earthly volcanoes. Many of 
 them consist of irregular fragments cemented together. Some 
 contain considerable iron, and carbon has been found in a few. 
 Even mineral veins have been found in them. 
 
 Our Earth has now lost a great part of its volcanic activity, 
 yet the eruption of Krakatoa, a few years ago, was almost 
 powerful enough to cast its debris clear of the planet's 
 attraction. 
 
 Supposing such a thing to take place, the cast-out masses, 
 both gaseous and solid, would naturally turn toward the Sun, 
 rush around that mighty globe, and, if not consumed by its 
 heat, return to the place where the Earth was when they were 
 ejected. Not finding the planet where it had been, the stream 
 of meteoric matter would naturally turn to the Sun again, and 
 continue in the same orbit until its Earth-derived particles were 
 all picked up again by the Earth or Moon. 
 
 If these comets and clouds of meteoric dust should originate 
 in the way described, it follows that moderate-sized worlds of 
 other systems must be equally capable of casting out similar 
 masses of cometary gas and meteoric solids. This would explain 
 the great abundance of comets and meteoric streams in our own 
 system. 
 
 There is some evidence that both comets and meteoric streams 
 gradually waste away when travelling through solar systems. 
 At each approach to a star, a comet appears to lose the repelled 
 matter which forms its dissipated tail or tails. After a certain 
 number of perihelia the supply of hydrogen and hydrocarbons 
 fails. Short-period comets are therefore generally tailless. A 
 comet has also been known to split up into two separate bodies 
 which gradually drifted apart. In some cometary orbits there 
 appear to be several comets, all moving in the same path, but 
 at long distances apart. Sometimes the solid bodies forming 
 the nucleus of a comet appear to spread out along its orbit until 
 the comet disappears and nothing remains but a long trail of 
 invisible meteoric matter. Meteoric streams also waste away 
 
232 HOW TO KNOW THE STARRY HEAVENS 
 
 to some extent, owing to the capture or deflection of fragments 
 by passing planets. The captured fragments of course form the 
 meteors and " shooting-stars " with which we are so familiar on 
 Planet Number Three. 
 
 It seems, therefore, that, long-lived as the comets are, they 
 too have a limit in duration. They are not " built for eternity," 
 but are as ephemeral as the suns and worlds among which they 
 wander. But the loss is evidently made up by the constant 
 formation of fresh comets and meteoric streams in various parts 
 of the Universe. 
 

CHAPTER XX 
 
 LARGE AND SMALL WORLDS 
 
 " There are worlds so vast that beside them our Earth would seem but a toy. 
 There are worlds so small that they might serve as marbles for our children to 
 play with." A. Zazd. 
 
 IT has been already shown that both suns and worlds vary 
 enormously in size and in the amount of matter they con- 
 tain. But it is very hard to realise how vast these differences 
 are. In our own System, while some planets are immensely 
 larger than our Earth, others are too small to be visible with 
 any telescope unless they happen to be massed together in mil- 
 lions, as in the rings of Saturn. It may be well to illustrate 
 some of these differences, paying special attention to the Third 
 Planet, the largest planet, and the Sun. 
 
 MICROSCOPIC WORLDS 
 
 There are " planets " going around the Sun which are so small 
 that if we had them in our hands we could not see them with- 
 out a microscope. They are commonly called meteoric bodies, 
 yet they really and truly are worlds like ours, revolving in or- 
 bits more or less similar to ours. They are subject to the same 
 laws, and may have had a separate existence as long as the 
 Earth on which we live. 
 
 At the same time there are planets, going around the same 
 Sun, so vast that our Earth would appear utterly insignificant 
 beside them. 
 
 OUR INSIGNIFICANT EARTH 
 
 Jupiter, the largest planet in our system, weighs 300 times 
 as much as our Earth. Not having yet cooled down so much 
 as the Earth, it is more than 1,200 times as large. 
 
234 HOW TO KNOW THE STARRY HEAVENS 
 
 Our Sun weighs 330,000 times as much as the Earth, and 
 for the same reason is 1,250,000 times as large. 
 
 Two or three illustrations may make these comparisons 
 plainer. 
 
 If our Earth be represented by a ball one inch in diameter, 
 Jupiter's weight will be represented by a globe, of the same 
 
 SATURN. 
 
 * 9 f| @ 6 
 
 ASTEROIDS. MARS. MOON. EARTH. VENUS. MERCURY. 
 
 FIG. 110. RELATIVE SIZES OF PLANETS 
 
 density, 4.2 inches thick, and that of the Sun by a globe 5 feet 
 9 inches across. 
 
 With the same one-inch ball for our Earth, Jupiter's size will 
 be represented by a globe 11 inches thick, and that of the Sun 
 by a globe 9 feet across. 
 
 If we were to place in a straight line enough of these one- 
 inch globes to represent the weight of Jupiter, they would 
 extend 25 feet, while if we were to put in a line enough to 
 represent the size of Jupiter, they would reach 100 feet. 
 
 To represent the Sun's weight in the same way, we should 
 
LARGE AND SMALL WORLDS 
 
 235 
 
 reguire a string of them more than five miles long. And for 
 its size, nearly twenty miles of them. 
 
 The difference between the mass of the Sun and that of the 
 Earth may also be illustrated in this way. A weight dropped 
 from a height on our Earth falls a little over 16 feet in the first 
 second. But on the Sun it 
 would fall 452 feet in the 
 same interval of time. An ob- 
 ject which, on account of the 
 Earth's attraction, here 
 weighs one pound, if removed 
 to the apparent surface of 
 our Sun, and weighed by a 
 spring balance, would be 
 found to have increased its 
 weight to 28 pounds on ac- 
 count of the greater mass 
 and attraction of the Sun. 
 
 These two illustrations do 
 not really do justice to the 
 difference between the mass 
 of the Earth and that of the 
 Sun. For the Sun's centre of 
 attraction is 108 times as far 
 from the object on its surface 
 as in the case of the Earth. 
 
 To get over this difficulty, let us imagine the Sun to be com- 
 pressed until it is the same size as the Earth, without dimin- 
 ishing its mass. It will then be 330,000 times as dense as the 
 Earth. The object which, on the Earth, weighed a pound, will 
 now, when removed to this compressed Sun, be found to weigh 
 165 American tons. And a weight dropped from a height will 
 fall 1,000 miles in the first second. 1 
 
 1 This compressed illustration is of course impossible, but it will serve to show 
 the immense difference in the quantity of material contained in the Earth and 
 Suu. 
 
 FIG. 111. RELATIVE SIZES OF SUN, 
 JUPITER, AND EARTH 
 
236 HOW TO KNOW THE STARRY HEAVENS 
 
 All the other planets in our System, taken together, weigh 
 about 450 times as much as our Earth, yet the Sun outweighs 
 them all 745 times. If all the planets be represented by a 
 heap of boulders weighing 450 pounds, a little one-pound pebble 
 will stand for the Earth. And on the same scale the Sun will 
 be represented by a mighty rock weighing about 170 American 
 tons. 
 
 Our Moon is 2,162 miles in diameter, and looks, from here, 
 as though it were the same size as the Sun, yet the latter ex- 
 ceeds it in bulk more than 
 60,000,000 times, and in weight 
 27,000,000 times. 
 
 Go out on an unusually clear 
 night, when the Moon is below 
 the horizon. Notice what a 
 multitude of stars can be seen 
 by the naked eye alone. Imag- 
 ine every star visible to be 600 
 times as large as our Earth. 
 Then all of them rolled together 
 into one vast globe would not 
 be as large as the Sun. 
 
 Yet our Sun is comparatively 
 a small star. Canopus, one of 
 the bright stars in the southern 
 hemisphere, gives out many 
 
 thousands of times as much light. If its lustre is equal to that 
 of the Sun, it must be many thousands of times larger. 
 
 FIG. 112. RELATIVE SIZES OF THE 
 FIRST FOUK ASTEROIDS AND THE 
 EARTH'S SATELLITE. BY BARNARD 
 
 The black circle represents the Moon, 
 and the white ones the Asteroids. 
 
 OUR MIGHTY GLOBE 
 
 We thus see that our planet is a very insignificant world 
 compared with some of the other heavenly bodies. Yet it con- 
 tains what seems to us to be a considerable amount of material. 
 
 Let us suppose the Earth to be drawn out into a long square 
 column a mile thick each way. This column would reach from 
 
LARGE AND SMALL WORLDS 237 
 
 the Sun to a distance 93 times as great as that of the planet 
 Neptune. 
 
 Let us suppose that this long column was put on suitable 
 flat-cars and started off at 50 miles an hour. Then suppose we 
 saw it coming, and decided not to cross the track till it had 
 passed by. We should have to wait 590,000 years before 'the 
 line would be clear. 
 
 A signal-light flashed from one end of this train, at the usual 
 speed of 186,000 miles in a second of time, would not be seen 
 at the other end for sixteen days. 
 
 If our Earth could be crushed under foot till it was flattened 
 out, so as to be only a mile thick, it would form a round flat 
 disc, 565,000 miles across, considerably larger than the 
 Moon's orbit. 
 
 So that if our Earth is of but slight importance in the Uni- 
 verse, it must be admitted that it is a considerable size when 
 looked at from a human standpoint. 
 
 THE CRASH OF WORLDS 
 
 Theoretically, every atom of matter in the Universe influences 
 every other atom of matter in the Universe. And practically 
 it influences all within x millions of miles. 
 
 Yet as a rule the myriads of suns and worlds do not interfere 
 with one another. They keep on in the even tenor of their 
 way from century to century. For many ten thousands of 
 millenniums they keep out of one another's way. 
 
 Still, accidents will happen even among solar systems. 
 There appear to be times when suns and planets come into col- 
 lision, when even worlds suffer shipwreck. 
 
 Some of the stellar systems are drifting along at the rate of 
 two hundred miles in one second of time. Therefore such catas- 
 trophes are liable to give rise to a considerable amount of light 
 and heat. 
 
 Whenever you see what is miscalled a shooting -star dart 
 across the sky and disappear, you witness the destruction of a 
 " pocket-planet " which may be as old as our Earth. 
 
238 HOW TO KNOW THE STARRY HEAVENS 
 
 Whenever you see the fiery rush of a meteor, and hear its 
 distant crash, you may know that another little world has met 
 its doom and ceased to have an independent existence. 
 
 Whenever a star suddenly increases in brilliancy, and for a 
 time gives out many thousands of times its former light, you 
 may feel tolerably certain that mighty suns have crashed into 
 mutual destruction. 
 
 Yet nothing is really destroyed. The " shooting-star " still 
 exists as vapour or dust in our atmosphere ; the meteor settles 
 down to form part of oUr Earth; the crashing suns, though 
 turned to naming gas, unite and begin once more the same end- 
 less cycle of evolution and devolution. There is no end, nor 
 was there yet beginning. 
 
 STARS ARE SOLITARY 
 
 " His soul was like a star, and dwelt apart." 
 
 Many people still have the old idea that the stars, although 
 a long way from us, are comparatively close to one another. 
 This is not at all correct, in spite of the fact that in thousands 
 of cases two, three, or more stars form one system. 
 
 Some of the star-clusters appear to be democratic systems 
 composed of vast numbers of comparatively small suns revolv- 
 ing around their common centres of gravity. Thus the cluster 
 Omega Centauri consists of more than 6,000 stars, of which at 
 least 125 are variables (see Figure 94). In cases like this it is 
 not likely that the individual suns have planets revolving 
 around them, or, at least, not habitable ones. 
 
 But leaving these multiple systems out of consideration, it 
 may be said that each star is, with the exception of its subject 
 worlds, solitary in space. If we could take our stand at a com- 
 fortable distance from any one of these sovereign stars, we 
 should imagine the system to be in the centre of a huge void, 
 surrounded, at an enormous distance, by a hollow sphere of 
 crowded stars. Or, in other words, the heavens would look 
 about the same as they do from our Solar System. In the case 
 
LARGE AND SMALL WORLDS 239 
 
 of a neighbouring star, only an expert could detect any changes 
 in the constellations. 
 
 When we see two stars which appear to be near to each 
 other, we must remember that in many cases one star is two, 
 ten, twenty, or a hundred times as far from us as the other one. 
 It may even be that the brighter one is the most distant. 
 
 On this account the apparent brightness of a star as seen from 
 our Earth is a very unreliable guide as to its distance or size. 
 As a matter of fact, no two stars are alike in actual size, bril- 
 liancy, colour, or any other peculiarity. 
 
 STABS ARE MIGHTY SUNS 
 
 " The stars of heaven fell to the ground, as green figs fall jvhen the tree is 
 shaken by a mighty wind." Rev. vi, 15. 
 
 Then we must remember that every one of these sovereign 
 stars is a SUN more or less like our Sun. Every one seen is at 
 least something like 1,000,000 times as large as our Earth. 
 The smallest visible is worthy of the name of SUN ; is large 
 enough, powerful enough, hot enough, and bright enough, to 
 hold sway over worlds as beautiful as Venus, as fiery as Mars, 
 as vast as Jupiter, as magnificent as Saturn, as distant as Nep- 
 tune, and as populous as the little Earth on which we live. 
 
 Every star visible is blazing with a light peculiar to itself, 
 different from the light of any other. In the vast majority of 
 cases this light is intense enough to make the Columbian 
 search-light look black by comparison. 
 
 Each of these suns is throbbing with quaking blasts of fer- 
 vent heat that would make the molten interior of a Bessemer 
 converter seem cold by comparison. The eruptions of Mont 
 Pe'le'e, fearful as they seemed to us, were but the sputterings of 
 a bunch of Fourth of July fire-crackers when compared with the 
 awful cannonading which goes on, every day in the year, all 
 around the average star. 
 
 So intense is the heat of our own central star that if the 
 Earth were to be checked in its career and left to fall toward 
 
240 HOW TO KNOW THE STARRY HEAVENS 
 
 the Sun, it would never reach the photosphere in a solid state, 
 but would be turned into flaming gas, and driven off again, like 
 a hailstone falling toward a mass of molten steel. Sir John 
 Herschel showed that if an icicle 45 miles in diameter could 
 be driven endways into the Sun with the velocity of light 
 (186,000 miles per second), it would be melted off as quickly as 
 it advanced. Some of the larger stars could dispose of an icicle 
 more than 100 miles in diameter. 
 
 Every star is continuously roaring and throbbing with ear- 
 rending detonations and world-jarring convulsions that are 
 greater, in one short hour, than all our thunder and lightning, 
 earthquakes and volcanic eruptions, for millions of years gone 
 by. Every one is dragging its attendant family of worlds 
 through the wilderness of space at a speed that the mind of 
 man cannot realise, it is so tremendous. 
 
 A TINY GLOBE 
 
 "The Earth is my foot-stool." (The Later] Isaiah, Ixvi, 1. 
 
 In all this splendour of molten orbs, our Earth, fortunately 
 for us, has no part. Silent, dark, and invisible (except to three 
 or four of its nearest companions), it is of no measurable im- 
 portance in the economy of Nature. So far as other worlds are 
 concerned, its existence is no benefit, its disappearance would 
 cause no anxiety, its destruction would be no loss, its absence 
 would give no trouble. 
 
 Yet, fastened to the radiant skirts of the glorious Sun by 
 invisible yet unbreakable bonds, it has been dragged for many 
 millions of years, through the wilds of space, at a speed incon- 
 ceivably great. Small though it is, it is teeming with life of 
 every kind. It contains almost boundless oceans and con- 
 tinents. It has mountains and valleys, rivers and lakes, islands 
 and seas, beautiful beyond the power of words to describe. It 
 has a history extending back millions upon millions of years. 
 It has a future almost without end. 
 
LARGE AND SMALL WORLDS 
 
 HUMAN ACHIEVEMENTS 
 
 So far I have considered only the smallness and insignificance 
 of man. But there is another side to the question. A thing 
 may be small and yet wonderful. The ancestors of man were 
 all Earth-born. He himself is but the creature of a day, and 
 has all his life been on one insignificant planet with no pros- 
 pect of ever leaving it. Yet, considering his situation, he has 
 done some wonderful things. Leaving out of consideration all 
 his earthly achievements, he has eaten of the fruit of the Tree 
 of Celestial Knowledge to a far greater extent than might have 
 been expected. Cooped up in his invisible cage, he has con- 
 templated the visible parts of the Universe to such good effect 
 that he has solved many of its mysteries. Not satisfied with 
 the eyes provided by Nature, he has constructed artificial 
 instruments which increase their light-grasping power more 
 than 40,000 times. With their help he is measuring the depths 
 of space, analysing the stars as though they were in his labora- 
 tory, weighing suns and worlds in a balance, and photographing 
 celestial objects that are invisible even with his instruments. 
 He traces the wanderings of the planets both in the remote 
 past and the distant future. He is finding out the life-history 
 of a sun from its cradle to its grave. He watches the stars so 
 closely that millions of them are unable to move without his 
 knowledge. The infinitely great and the infinitely small are 
 alike compelled to submit to his scrutiny. Slowly but surely 
 he is compelling Nature to give up her innermost secrets. He 
 is gradually solving the mystic riddle of the Universe. 
 
 These be no light achievements for man to have even par- 
 tially accomplished. The Gods of Greece and Eome never 
 attempted such tasks. Odin and Thor never dreamed of such 
 vast undertakings. The labours of Heracles and feats of Shem- 
 ishon cannot be mentioned on the same page without provoking 
 a smile. The actual achievements of man surpass those 
 fabulously attributed to the Gods and heroes of antiquity. 
 
 16 
 
HOW TO KNOW THE STARRY HEAVENS 
 
 TWO STANDPOINTS 
 
 " The Hebrews looked upon themselves as Yahveh's Peculiar People, which 
 they probably were. 
 
 " The Chinese regard the ' Celestial Empire ' as the most important part of the 
 World, which it is to them. 
 
 " Every little Boston is thought, by its own people, to be the ' Hub of the Uni- 
 verse/ which it possibly may be to those that dwell therein. 
 
 "But a Citizen of the GREAT COSMOS though compelled to view all things 
 from his own physical standpoint can see them also from a spiritual standpoint 
 which is Universal and Eternal." A. Zazel. 
 
 To the ancients, the World was visible only from a local 
 standpoint, with the eyes of an epheineron. From their posi- 
 tion it appeared to be vast beyond comparison, fixed beyond the 
 possibility of removal, changeless as the decrees of destiny, 
 eternal as time itself. 
 
 We, who have eaten of the fruit of the Tree of Knowledge, 
 have acquired the power of observing the Earth from both a 
 local and a universal standpoint. We have learned of its 
 insignificance , yet we better comprehend its vastness. We 
 know that it is ever on the wing, yet we understand the un- 
 deviating fixity of the paths in which it travels. We watch its 
 lands and seas come and go like drifting clouds, yet we are 
 aware of the changelessness of the laws to which those changes 
 are due. We know it as a transient bubble on the River of 
 Eternity, yet we have discovered a history that staggers even 
 the imagination itself, and can foresee a future that shall rival 
 its past. 
 
CHAPTER XXI 
 
 IGNEOUS FORCES ON THE MOON AND ELSEWHERE 
 
 " He scarce had ceased, when the superior fiend 
 Was moving toward the shore : his ponderous shield 
 Ethereal temper, massy, large, and round, 
 Behind him cast ; the broad circumference 
 Hung on his shoulders like the Moon, whose orb 
 Through optic glass the Tuscan artist views 
 At evening from the top of Fesole', 
 Or in Val d' Arno, to descry new lands, 
 Rivers, or mountains, in her spotty globe." 
 
 Milton, " Paradise Lost," Bk. I. 
 
 BY this time we should have a very fair idea of the construc- 
 tion, dimensions, distances, and histories of the various 
 celestial mansions which compose the visible part of the Grand 
 Temple of the Universe. It is now time to turn nearer home 
 and find what there is to be seen and learned of the satellite 
 which is such a faithful attendant on the Third Planet of the 
 Solar System. 
 
 Some details have already been given about our Moon, but 
 little has been said concerning its present appearance and 
 condition, or about the changes that have taken place on it 
 since it left the embrace of its earthly parent. 1 
 
 The history of the Moon, like the histories of its ancestors 
 the Earth, the Solar System, and the Universe is not 
 recorded in books that were written by eye-witnesses. It has 
 to be obtained by carefully observing its present appearance 
 and condition, and then by reasoning as to the way in which 
 natural laws (known and unknown) can have brought about 
 
 1 Since the Moon owes its separate existence to the gravitational attraction of 
 the Sun on the body of the Earth, it shares with many of the heroes of antiquity 
 the honour (?) of having a heavenly father and an earthly mother. 
 
244 HOW TO KNOW THE STARRY HEAVENS 
 
 that appearance and condition. The most that we can reason- 
 ably hope for, under these circumstances, is to get a fairly 
 accurate idea of the main sequence of events without laying 
 too much stress on minor details. Indeed we must not be 
 surprised if we find that recognised authorities sometimes differ 
 with regard to the course of events, as well as to the relative 
 importance of the different agencies that have been at work 
 on it. Past experience has shown that incorrect theories will 
 sooner or later be found out, and replaced by others that are 
 nearer the truth. 
 
 LUNAR FEATURES 
 
 If we examine the Moon with the unaided eye, when our 
 side of it is fully illuminated by the Sun, we can see very little 
 as to its condition except that it appears to be a tolerably 
 bright round disc with some irregular dark patches on it. 
 Each of these dark patches remains permanently in about the 
 same part of the disc, and has been there since history began. 
 It is therefore evident that the Moon always turns the same 
 side to us. The only considerable change is in the direction 
 from which it is illuminated by the Sun as it revolves around 
 the circling Earth. 
 
 With the help of an opera-glass (also used at full moon), 
 these lunar patches become very much plainer, and appear to 
 have a somewhat circular outline. There also comes into 
 sight a star-like series of bright radiating streaks, having their 
 centre near the south of the visible disc. These two pecu- 
 liarities together give the full moon a strong resemblance to a 
 peeled orange that has been badly bruised. 1 
 
 1 If two photographs of the Moon are taken from rather different standpoints, 
 and then combined so as to be used in the stereoscope, this resemblance to a bruised 
 orange becomes quite startling. Thus viewed, the Moon loses the flat disc-like 
 appearance due to its immense distance, and stands out as a solid sphere just as 
 it would appear to a giant whose eyes were thousands of miles apart. The same 
 principle has also been applied to planets and comets, so as to show them as they 
 really are, standing out solidly between us and the more distant background of 
 stars. Efforts are now being made to get similar stereoscopic pictures of the 
 stars, by coupling photographs taken at intervals of many years. 
 
FIG. 113. FULL MOON SHOWING RADIATING STREAKS 
 
IGNEOUS FORCES ON THE MOON 245 
 
 With a small telescope the whole surface is seen to consist 
 of solid land like that of our continents. The Moon is there- 
 fore a solid sphere (or spheroid) like our Earth, but without 
 any oceans or seas. The dark patches are now recognised to 
 be tolerably level plains of a darker material than the rest of 
 the surface. Some of these plains are more or less surrounded 
 by mountain chains, or lesser elevations. 
 
 The telescope also brings into view a large number of smaller 
 and more regular circles scattered on all parts of the visible 
 surface. Those, however, which are near the edge of the disc 
 are distorted into ellipses by perspective. The largest of these 
 rings are easily seen to consist of a circular embankment or 
 rampart surrounding a saucer-like depression in the centre of 
 which there is often an irregular conical elevation. 
 
 When the Sun shines obliquely on these circular ramparts, 
 their shadows are seen extended on the plains beyond, as well 
 as on the floor of the interior. Where they are numerous the 
 scene reminds one of a plaster-of-paris surface that has been 
 filled with bubble-holes by means of citrate of magnesia. 
 When such a surface is illuminated from one side by a power- 
 ful electric light, it makes an almost perfect representation of 
 some parts of the lunar disc. 
 
 Those who are acquainted with volcanic districts on our 
 Earth will have no difficulty in recognising these hollow cir- 
 cular objects as volcanic craters with or without central lava 
 cones. 
 
 These lunar craters are extremely numerous and vary greatly 
 in size. The largest are considerably over one hundred miles 
 across, and below this all sizes are represented down to invisi- 
 bility, the smallest seen being less than a mile across. 
 
 On and near the dark plains these craters are tolerably 
 plentiful, but toward the southern part of the Moon's disc they 
 are so astonishingly numerous that they crowd together and 
 overlap one another. The large ones are often filled with, and 
 surrounded by, swarms of little ones, which even perch on the 
 summits and slopes of their ramparts. 
 
246 HOW TO KNOW THE STARRY HEAVENS 
 
 Several of the larger craters form centres for bright star-like 
 radiating streaks extending along the surface for hundreds of 
 miles. The most extensive set of these has already been men- 
 tioned as giving the full moon the appearance of a peeled 
 orange. Its longest streak can be traced for over 2,000 miles. 
 
 With a powerful telescope long narrow cracks are also visible 
 on the Moon's surface, as well as crust foldings and all kinds 
 of small irregularities which need not be here described. They 
 are beautifully pictured in Nasmyth and Carpenter's splendid 
 but expensive work entitled " The Moon." 
 
 IGNEOUS FORCES 
 
 Now it is evident that most, if not all, of the lunar features 
 just mentioned are of exclusively igneous or volcanic origin. 1 
 There is no single feature or peculiarity which can with cer- 
 tainty be ascribed to either air or water. Oceans, seas, lakes, 
 marshes, rivers, planes of denudation, snow-patches, ice-sheets, 
 clouds, mists, and such-like aqueous features and phenomena, 
 are conspicuous by their total absence. 
 
 On our Earth the various aqueous agencies have for millions 
 of years waged an unceasing conflict with the igneous agencies, 
 and have now almost won the fight. But on the Moon the 
 igneous forces have had all the field to themselves, and have 
 had to deal with a force of gravitation only one sixth as great 
 as that on our Earth. We therefore find that all the lunar 
 features are such as would be produced by volcanic forces 
 working under peculiarly favourable conditions. When com- 
 pared with similar volcanic features here they are seen to be on 
 a vastly greater scale, differently proportioned, and more per- 
 fectly preserved. 
 
 Before dealing further with the condition, peculiarities, 
 origin, and development of these lunar features, it may be well 
 to say a few words about the various ways in which volcanic 
 forces are likely to act under widely different conditions. We 
 
 1 The word " volcanic " is here used in its widest sense. 
 
IGNEOUS FORCES ON THE MOON 247 
 
 shall then be better able to understand the unfamiliar shapes, 
 sizes, and other peculiarities of the lunar relics of igneous 
 action. 
 
 HOW A MOLTEN WORLD SOLIDIFIES 
 
 The cooling off of a luminous gaseous sun or planet, first into 
 a liquid and then into a solid state, is an exceedingly protracted 
 process. An appreciable part of it has never been witnessed 
 by ephemeral man. This being the case, it must be borne in 
 mind that the following account is almost entirely theoretical. 
 No one can prove its truth, though the greater part of it is 
 supported by many forms of indirect evidence. The most that 
 can be said for it is that it is exceedingly probable. 
 
 After a gaseous sun-like world has cooled off sufficiently to 
 allow its most combustible elements to burn themselves into 
 chemical compounds, it still continues to cool off by radiation 
 into space. So in time the bulk of its material leaves the 
 gaseous state and forms a spherical white-hot molten globe. 
 This is extremely dense and compressed at the centre, where 
 the heavier elements and compounds naturally tend, and com- 
 paratively thin and " watery " near the surface, where the pres- 
 sure is small. When the molten globe is of any considerable 
 size it is surrounded by an atmosphere composed of those gases 
 which liquefy only at a low temperature. 
 
 If the world under consideration is only a subordinate centre 
 of condensation, it still continues to revolve around the main 
 centre, as in its gaseous youth. Its rotation not only continues, 
 but (if not counteracted by tidal action) increases in rapidity 
 as it cools and shrinks. And any tides that may have been 
 previously produced in it by large neighbouring bodies will 
 still continue to affect it. 
 
 In time the radiation of heat into space will chill, and even- 
 tually freeze, the surface of the molten world. The time occu- 
 pied in solidifying will depend on the mass of the cooling world 
 and on the resulting density of its atmosphere. 
 
 The solid outside crust will gradually get thicker, but, if 
 
248 HOW TO KNOW THE STARRY HEAVENS 
 
 neighbouring worlds cause any considerable tides beneath, it 
 will be liable to be fractured as soon as it loses some of its 
 flexibility. The cooling and freezing processes, however, go 
 on at the surface without interruption, though considerably 
 hindered by the more or less violent physical and chemical 
 reactions below. 
 
 At last a tolerably solid crust is formed, covering the entire 
 world to a considerable depth. This crust is all the time en- 
 croaching on the molten nucleus inside it, and will eventually 
 replace it to the very centre. 
 
 But before that can take place there will be a terrible struggle 
 for supremacy between the cooling and crushing shell, and the 
 crushed and overheated nucleus. 
 
 For the laws of cooling and contraction are such that just 
 before a liquid turns to a solid it swells out and occupies more 
 room than it did before, and that after it has solidified it shrinks 
 as it continues to cool off. 1 
 
 Owing to these peculiarities the solid outside crust at first 
 contracts faster than the nucleus inside it. The strain produced 
 by this cause (assisted by the presence of confined gases) is 
 tremendous beyond conception, and appalling in its world-wide 
 effects. When at its greatest intensity it causes the world to 
 throb and quiver from centre to circumference. The crust frac- 
 tures and gapes from pole to pole. Near the centres of force 
 the surface-blocks jump like the lid of a pan full of boiling 
 water. The molten rock and its confined gases (which consist 
 partly of the vapour of water) force their way through the 
 cracks and gaping fissures. Where their escape is strongly op- 
 posed, they issue in explosive fountains of fiery solids, liquids, 
 and gases, and bombard the heavens with an incessant and 
 ear-rending cannonading that defies description. If an eye- 
 witness could view the stormy scene from a safe distance, he 
 might think that the throes of Eagnarok were at their height. 
 
 1 The freezing of water and solidification of type-metal sufficiently illustrate 
 the former peculiarity, and the cooling of almost any solid substance exemplifies 
 the latter. 
 
H 
 
 GO 
 
 < 
 
 - 
 
 5 
 
 H I 
 K 
 
 :l 
 
 < es 
 
 1 1 
 
^TBRATT^ 
 
 or THE 
 
 UNIVCP.S/TY 
 
 S+ or 
 
IGNEOUS FORCES ON THE MOON 249 
 
 And in fact he would not be far wrong, for the old Norsemen 
 probably got the germ of that grand conception from the world- 
 rocking convulsions of the Icelandic volcanoes. 
 
 In the course of time the solidifying process gets nearer the 
 centre of the world. The igneous forces are therefore hampered 
 by the increasing weight of the solid crust above. The molten 
 nucleus now contracts faster than the solid crust, and the latter 
 crumples and folds as it settles down on the outside of it. The 
 strains produced by both contraction and expansion vary in di- 
 rection and intensity, and the surface phenomena vary accord- 
 ingly. The igneous manifestations in time become less violent, 
 and the conflict gradually dies away into feeble and intermittent 
 spasms, which at last entirely cease. 
 
 The natural features resulting from the above conflict vary 
 according to the intensity of gravitation, the density of the at- 
 mosphere, the amount of water above and below the surface, 
 and such like peculiarities, and these, in their turn, depend 
 largely on the size of the cooling sphere. 
 
 TIME OCCUPIED IN SOLIDIFYING 
 
 On a little world, like our Moon, for example, the force of 
 gravitation is small. Consequently the gases and vapours appear 
 to leave the planet as they are liberated. It is therefore ex- 
 posed to the intense cold of outer space, and, as its surface is 
 large when compared with its mass, it cools off in a compara- 
 tively short time. 
 
 On a somewhat larger world, like the Earth or Venus, gravi- 
 tation is more powerful, and retains all the gases except the 
 very lightest. It is therefore surrounded by a dense, foul, and 
 cloudy atmosphere, which retards and lengthens the cooling 
 process. But, as soon as the surface temperature is low enough 
 the aqueous vapour in this atmosphere turns to liquid drops 
 and rains down on to the solid surface. At first this surface is 
 too hot to retain the water, and it is driven off again in the 
 form of steam. But after a time it collects into rivers of hot 
 
250 HOW TO KNOW THE STARRY HEAVENS 
 
 water and flows into any depressions there may be in the crust. 
 There it forms oceans, seas, and lakes, of more or less saline 
 water. This, by its alternate evaporation and condensation, 
 produces on the dry land all the well-known phenomena of 
 aqueous denudation. 
 
 On a still larger world, like Saturn or Jupiter, the process is 
 still more hampered and prolonged by the intensity of gravita- 
 tion and by the extent and density of the cloud-packed atmos- 
 phere. 1 
 
 In the case of huge bodies like our Sun, and of still larger 
 ones like Canopus and Rigel, the time taken to cool off (first to 
 a liquid, and then to a solid state) is so enormous that it is 
 beyond the comprehension of ephemeral beings. Reason may 
 be able to estimate the period in years, but even the imagination 
 fails to grasp and realise its vastness. 
 
 COMPARATIVE EFFECTS OF IGNEOUS FORCES 
 
 When this conflict was at its height on our Earth, the cen- 
 tral attraction of gravitation was (as now) considerable when 
 compared with that of the Moon, and there was a dense acrid 
 atmosphere all around, which at first contained all the water 
 now in the oceans. These features would act as a check on 
 the igneous forces, prolong tbeir action, and make their per- 
 manent records less conspicuous. Yet geology shows that some 
 tremendous results were produced even when the conflict was 
 dying away. 
 
 Leaving the more ancient and important effects out of con- 
 sideration, the crater of Haleakala, which has an area of 16 
 square miles, is an awe-inspiring evidence of past volcanic 
 
 1 The low density of the large outer planets shows that they are still in a 
 gaseous state with possibly a small molten nucleus. Owing to their rapid rotation 
 the dense clouds by which they are surrounded are whirled into more or less per- 
 manent latitudinal belts, which compose the only visible part of the planet. The 
 belts on each side of the Equator exhibit more frequent changes than elsewhere. 
 The Sun has a somewhat similar peculiarity, as the sun-spots and eruptive promi- 
 nences are mainly confined to the same " sub-tropical " regions. 
 
IGNEOUS FORCES ON THE MOON 251 
 
 power. The eruption of Krakatoa, a few years ago, shook the 
 Earth to its very centre and from pole to pole. Its upward 
 cannonading was so terrific that it was heard 3,000 miles away, 
 and it almost shot its projectiles into outer space. The Japan- 
 ese earthquakes, even now, are active enough to cause the 
 islands to be facetiously termed " The Lid of Sheol." Even the 
 sputterings of Mont Pele'e and Vesuvius are sometimes violent 
 enough to inspire our respect. Who, then, can describe, or 
 even imagine, the world-wrecking violence of the igneous forces 
 when they were at the height of their strength and activity, 
 before geology began ? 
 
 On a much larger world than ours, with heavier rocks and a 
 still denser atmosphere, the igneous forces are even more 
 cramped than here, and the radiating surface is smaller in com- 
 parison with the mass. The process, therefore, continues for a 
 much longer time, and the resulting evidences are compar- 
 atively insignificant. 
 
 FIG. 115. SECTION OF EARTHLY VOLCANOES 
 Built up of ashes and cinders, with interstratified lava streams. 
 
 But on a smaller world, like our Moon, the igneous forces 
 appear to be practically unfettered. As the material there is 
 only one sixth as heavy as it would be on our globe, it can be 
 moved with only one sixth the effort. 
 
 If two volcanoes, one on the Moon and the other on the 
 Earth, were each to eject the same kind of material with the 
 same amount of force and under the same atmospheric condi- 
 tions, the lunar projectiles would go six times as far as the 
 earthly ones. But as there is no resisting atmosphere on the 
 Moon, the lunar volcano will scatter its debris to an even 
 greater distance than the difference in weight would indicate. 
 
HOW TO KNOW THE STARRY HEAVENS 
 
 The result is that a violent, explosive, and long-continued 
 eruption will not (as here) build up a huge mountain of debris 
 with a small crater on its summit. It will tear out an enor- 
 mous circular funnel-shaped hollow, surrounded by a massive 
 rampart just at the edge of the volcano's field of force. 
 
 FIG. 116. SECTION OF LUNAR VOLCANO IN FULL ACTIVITY 
 
 It may be well to give one or two illustrations of these dif- 
 ferences in size and proportion between the earthly and the 
 lunar volcanoes. 
 
 The largest volcanic crater on our globe is an extinct one in 
 the Hawaiian Islands, that goes by the musical name of Hal- 
 eakala. Its size, however, has been increased and its shape 
 altered by an explosion like that which blew the head off the 
 original Mount Vesuvius. The crater as it now exists is 7^ 
 miles across, one way, and 2i miles the other. It has an area 
 of about 16 square miles, and the depth is about 2,700 feet. 
 There are 16 conical hills scattered about its interior, from 500 to 
 600 feet in height. It is perched on the summit of a mountain 
 20 miles across and 10,000 feet above the sea-level. 
 
 In the southern part of the Moon is a crater to which has 
 
FIG. 117. CLAVIUS AND TYCHO 
 
 The former is the large walled plain near the bottom of the picture. The latter is the 
 
 centre crater. It is the source of the chief lunar radiating streaks, which are 
 
 only visible at full moon. Photographed at Yerkes Observatory. 
 
T\B R ATT?* 
 
 CK THE 
 
 UNIVERSITY 
 
 or 
 
 *Li 
 
IGNEOUS FORCES ON THE MOON 253 
 
 been given the name of Clavius. It is one of the largest on our 
 side of the Moon, and has several smaller and more recent 
 craters scattered about its interior. It is more than 140 miles 
 across, and has an area of about 16,000 square miles. Its ram- 
 part in some places reaches a height of 17,000 feet above the 
 inside floor, which is about two miles below the level of the 
 outside plain. 
 
 This crater, like all the very large ones on our side of the 
 MOOD, has no central cone. It is thought by some that these 
 coneless craters are not the result of explosive volcanic erup- 
 tions, but that they were formed as seething lakes of molten 
 lava, like the crater of Kilauea in the Hawaiian Islands. 
 
 There are many, however, which have inside cones, indicating 
 that they are true volcanic craters. It may be as well to give 
 the dimensions of one of the largest of these. 
 
 Theophilus, one of the most perfect craters on the Moon, is 
 64 miles across, and has an area of about 3,200 square miles. 
 Some of the peaks on its rampart reach an elevation of 18,000 
 feet above the floor of the crater. One of the cone-shaped 
 mountains in its centre is 6,000 feet high, yet its summit is 
 4,000 feet below the level of the outside plain. A number of 
 similar craters are scattered around, but they are smaller or in 
 a less perfect state of preservation. Besides these, there are 
 swarms of craters so small that only a very powerful telescope will 
 show them. But, small as they are, they are equal in size to the 
 craters of the largest earthly volcanoes. 
 
 VARIETIES OF IGNEOUS ACTION 
 
 The solid crust which first forms on a solidifying world is 
 more or less flexible on account of its thinness and high tem- 
 perature. As it cools off and loses this flexibility it is cracked 
 in all directions by the tides and other strains to which it is 
 exposed. The cracks are filled up with molten rock, which 
 sometimes reaches the surface and spreads over it in thin 
 sheets. As this liquid matter cools and consolidates, it cements 
 the crust solidly together again. The process goes on till the 
 
254 HOW TO KNOW THE STARRY HEAVENS 
 
 whole shell is traversed in every direction with dykes and 
 veins of mineral matter. 
 
 When the crust has become thicker, and the interior strains 
 are greater, the molten matter exudes in greater volume from 
 
 FIG. 119. SECTION OF MOUNTAIN OF EXUDATION 
 
 the cracks. It solidifies quickly on the cold surface, and piles 
 itself up in great heaps, forming ridges and sometimes moun- 
 tains of exudation. The action is something like that of our 
 mud- volcanoes, only the material is plastic through heat instead 
 of water. 
 
 In time the molten nucleus becomes small, in proportion to 
 the outside shell. It then contracts faster than the crust, and 
 leaves the latter to fold and shrink upon it like the skin of a 
 
 FIG. 120. SECTION OF MOUNTAIN OF ELEVATION 
 
 wizened apple. This folding or crumpling produces what are 
 known as mountains of elevation , consisting of more or less 
 parallel ranges of folded rock. 1 
 
 The molten matter, instead of exuding quietly up wide cracks 
 to the surface, and there cooling off on the mountain slopes, is 
 
 1 The character, distribution, and condition of these folded rocks will depend 
 upon whether or not the world has a permanent atmosphere and a large amount 
 of water on its surface. Also on whether it has any external source of heat and 
 light, to keep those agencies in a state of activity. 
 
V 1 J f ' 
 
 feV$i&'i 
 
 
 s i Y- . 
 
 FIG. 118. THEOPHILUS, A LUNAR CRATER-WITH-CONK 
 
 64 miles across. Yerkes photograph. 
 
IGNEOUS FORCES ON THE MOON 255 
 
 now forcibly ejected from a series of blow-holes along the 
 closed or choked cracks. 1 The result is that instead of piling 
 up mountains of exudation it forms volcanoes of eruption. 
 
 The funnel-shaped hollow or crater formed at the top of one 
 of these blow-holes is surrounded by a rampart composed of 
 the ejected material. While the explosive force is increas- 
 ing, the hollow gets larger, and the rampart is pushed farther 
 back. The size of the crater is therefore a measure of the energy 
 of the volcano at the height of its power, during its most 
 violent paroxysms. 
 
 When the explosive force abates somewhat, small craters are 
 formed inside the large one. When the violent eruptions give 
 way to a quiet yet considerable oozing of molten rock, it fills 
 up the crater till the rampart gives way, and then floods the 
 surrounding country with more or less liquid lava. When there 
 is not enough lava to overflow the crater, it simply solidifies 
 inside, forming a nearly level floor. And when the lava flow is 
 
 FIG. 121. SECTION OF LUNAR CRATER WITH CONE 
 
 too small or viscid to spread over the crater, it solidifies into 
 conical peaks above the central vent. 
 
 Sometimes a volcano becomes inactive, not because the energy 
 is exhausted, but because it is intermittent and the vent has 
 become plugged up during a quiet interval. A subsequent dis- 
 turbance, if powerful enough, will either blow out the obstruc- 
 tion or force a vent in some other part of the line of weakness. 
 In the latter case the crust will be fractured afresh, and other 
 
 1 The violence of its action depends largely on the quantity of water which 
 gets to the hot interior, and on the volume and character of the gases produced 
 by chemical action. 
 
256 HOW TO KNOW THE STARRY HEAVENS 
 
 craters will be formed. The old one will then remain dormant 
 or become extinct. 
 
 As the volcanic forces become exhausted, the craters formed 
 are, of course, smaller than the old ones. And so at last the 
 igneous action ceases to be visible on the surface of the now 
 solid world. 
 
 The subsequent history of the world in question will depend 
 upon the presence or absence of air and water in a state of 
 activity. With them, the surface structures reared by igneous 
 action will be gradually obliterated. Without them, the only 
 changes will be landslides due to variations of temperature act- 
 ing on the piled-up crater ramparts and precipitous mountain 
 slopes. With this exception the volcanic structures will be 
 perfectly preserved for as many millions of years as the petrified 
 world containing them continues to have a separate existence. 
 
CHAPTER XXII 
 
 LUNAR GEOLOGY AND GEOGRAPHY 
 
 " Speaking by our own lights, from our own experience and reasoning, we are 
 disposed to conclude that in all visible aspects the lunar surface is unchangeable ; 
 that in fact it arrived at its terminal condition eons of ages ago ; and that in the 
 survey of its wonderful features, even in the smallest details, we are presented 
 with the sight of objects of such transcendent antiquity as to render the oldest 
 geological features of the Earth modern by comparison." Nasmyth and Car- 
 penter, " The Moon." 
 
 BIRTH OF THE MOON 
 
 WHEN the Moon still formed part of the Earth, the whole 
 mass was probably in a molten condition, and surrounded 
 by an extremely dense atmosphere which contained all the 
 water now in the oceans, seas, and lakes. The atmospheric 
 pressure must then have been equal to about 5,000 pounds to 
 the square inch. 
 
 Owing to the rapid and increasing rotation the molten body 
 was very much spread out at the equator, and the atmosphere 
 was deeper and denser there than near the poles. The loss of 
 internal heat by radiation was therefore greatest at and near the 
 poles. This probably led to great convectional currents in the 
 molten globe. The same cause led to atmospheric currents 
 the lowest of which were from the northeast to the southwest 
 in the northern hemisphere, and vice versa in the southern. 
 
 The attraction of the Sun, acting on the molten rock of which 
 the rotating spheroid consisted, presumably raised a huge and 
 ever-increasing tide on the side nearest to it. As the rotation 
 quickened, this solar tidal wave of molten rock grew in size 
 until it was finally thrown off and became the Moon, as de- 
 scribed in a previous chapter. 
 
 17 
 
258 HOW TO KNOW THE STARRY HEAVENS 
 
 Now the material which went to form the Moon was not 
 taken from the heavy central metallic rock (8.2), but from the 
 lighter envelope of molten silicates, with a density of a little 
 over three times that of water (3.2). And the heavy atmos- 
 phere of steam and other gases was either retained or drawn 
 back by the Earth on account of its superior size and attraction. 
 The lunar silicates, however, were probably heavily charged 
 with steam, etc., owing to the enormous atmospheric pressure to 
 which they had previously been subjected. 
 
 The orbit of the new-born Moon gradually increased in size, 
 from the tidal action. The molten silicates composing the 
 Moon, being relieved from the tremendous atmospheric pressure, 
 gradually expelled the steam and gases with which they were 
 charged. They thus formed a huge globe of "boiling" rock, 
 which cooled off on every side, by radiation into space, until 
 the surface matter solidified. 
 
 THE GREAT PLAINS 
 
 The escaping gases, assisted by the earth-tides, probably 
 broke up the first crust, and the fragments floated and drifted 
 on the still molten surface. Large open lakes of boiling rock 
 may thus have been left between them. These molten lakes 
 would be something like that in the crater of Kilauea, but of 
 vastly greater dimensions. They were sometimes many hun- 
 dreds of miles across, and were more or less surrounded by 
 rocky ramparts. These may have been built up of solid blocks 
 driven to the sides by the violent ebullition and diverging 
 surface currents. 
 
 In the course of time these hypothetical molten lakes cooled 
 off and solidified. They form the dark level plains visible from 
 the Earth with the naked eye. Before the invention of the 
 telescope they were thought to be seas ; and the Latin name 
 for a sea has stuck to them ever since. 1 
 
 1 Even Kepler shared in this erroneous belief. In one place he says "Do 
 maculas esse maria, do lucidas esse terras." Galileo, on the contrary, appears to 
 have discovered that there are no visible bodies of water on our side of the Moon, 
 
3 1 
 
LUNAR GEOLOGY AND GEOGRAPHY 259 
 
 Most of these great plains have either a circular outline or 
 are more or less surrounded by semicircular bays. Mare 
 Serenetatis (the Sea of Serenity) is an example of the former, 
 and Mare Imbrium (Sea of Showers) of the latter. This 
 circular feature is not the result of accident. Whatever differ- 
 ences of opinion there may be as to the way in which they 
 originated, it is certain that they are the result of (igneous or 
 other) forces acting from local centres. 
 
 THE WALLED PLAINS 
 
 Mare Crisium, one of the smallest and most regular of the 
 great plains, connects them with the crater-like watted plains, 
 of which the best examples are known by the names of Ptolemy, 
 G-rimaldiy Clavius, Schiller, and Schickard. Most of these are 
 over 100 miles in diameter. 
 
 In spite of the enormous -surface dimensions of these walled 
 plains, and of the fact that they have a practically level floor 
 with no central cone, their appearance is so crater-like that it is 
 impossible to draw a satisfactory dividing-line between them 
 and the smaller volcanic craters which were subsequently 
 formed. Their resemblance is so marked that it is evidently 
 due to relationship. 
 
 RADIATING STREAKS 
 
 After the surface had cooled off and consolidated, the cooling 
 process went on below, adding to the solid crust at the expense 
 of the molten nucleus. The varying ratios of contraction, etc., 
 gave rise to violent strains which resulted in immense cracks 
 radiating in all directions from the local centres of force. The 
 molten lava welled up through the cracks and spread over the 
 
 for his friend Milton carefully avoided mentioning lunar oceans and seas. He 
 made Raphael watch the Earth 
 
 " as when by night the glass 
 Of Galileo, less assured, observes 
 Imagined lands and regions in the Moon." 
 
 " Paradise Lost," Bk. V. 
 
260 HOW TO KNOW THE STARRY HEAVENS 
 
 surface for some little distance in thin watery sheets. These 
 of course soon solidified, and are now visible when the Moon is 
 at its full. 
 
 MOUNTAINS OF EXUDATION 
 
 At a later time, when the conditions were rather different, 
 the solid crust appears to have been again fractured in some 
 parts of the Moon, and immense quantities of molten lava 
 welled out onto the surface. There it cooled off and solidified, 
 like spring water that comes to the surface in a severe frost. 
 In this way long ridges of solidified lava were formed, with 
 open vents all along the summit. Through these vents the 
 quiet exudation of lava continued until the ridges became 
 mighty ranges of mountains. Such are the Leibnitz Mountains, 
 in the extreme south of the Moon. These have an elevation 
 of 31,000 feet above the general surface. They are therefore 
 higher in proportion than any mountains on the Earth. 
 
 Another important range is known as the Lunar Apennines, 
 a little to the north of the centre of our, side of the Moon. 
 It is an extremely wild and precipitous range of mountains 
 about 480 miles long and of considerable width. It contains 
 about 3,000 peaks, which probably represent the widest parts 
 of the elongated cracks through which the liquid silicates rose 
 to the surface. Some of these summits are 18,000 feet above 
 the level of the plains below. 
 
 The Caucasus Range and the Lunar Alps are similar 
 mountains of exudation. The latter range contains 700 peaks 
 and is almost cut in two by a remarkable straight valley with 
 a level floor and precipitous sides 11,000 feet high. It is 80 
 miles long and about 5 miles wide at the bottom. 
 
 With perhaps the exception of the first mentioned, all these 
 ranges of mountains have a steep precipitous slope toward the 
 Moon's west, 1 and a long gradual slope on the side toward 
 which they are carried by the Moon's rotation. In this respect 
 they resemble the Andes of South America. 
 
 1 Toward the east as seen from the Earth. 
 
liili 
 
 :fi'l 
 
 
 
 m - 
 
 
 
 
 !OTs 
 
 MmMM 
 
 FIG. 124. COPERNICUS 
 
 By Nasniyth and Carpenter. (From " The Moon," by Nasmyth and Carpenter, 
 published by John Murray. ) 
 
LUNAR GEOLOGY AND GEOGRAPHY 261 
 
 ISOLATED PEAKS 
 
 A few isolated peaks were also formed, perhaps by the same 
 quiet exudation of rather viscid lava. They rise rather abruptly 
 from the level plain, like some vast cathedral. There is one in 
 the north which goes by the name of Pico. It rises almost 
 precipitously to a height of 8,000 feet. 1 
 
 EXPLOSIVE VOLCANIC ERUPTIONS 
 
 After these mountain ranges and isolated peaks had been 
 more or less quietly formed on the northern plains the increas- 
 ing shrinkage of the nucleus appears to have closed up the 
 wide cracks and made egress to the surface more difficult. 
 The result was that the volcanic forces became violent, and the 
 molten lava, instead of quietly oozing up all along the cracks, 
 was forced up explosively at distant centres. Owing to the feeble 
 gravitation, and to the absence of atmospheric pressure, the 
 resulting volcanic craters were so tremendous in size that we 
 have nothing on Earth anywhere approaching them. 
 
 After the volcanic forces had passed their maximum the 
 large craters were choked up, and smaller ones were formed on 
 their flanks, to be in time superseded by still smaller ones. 
 There are sometimes strings of them, evidently formed along 
 the same crust-fractures. 
 
 QUIET VOLCANIC EXUDATIONS 
 
 The explosive volcanic eruptions were sometimes succeeded 
 by the quiet exudation of lava through the same volcanic vents. 
 Where the flow was very abundant the crater was filled till the 
 lava broke down the rampart and flooded the outside plains. 
 In the case of one crater, which has been named Wargentin, 
 the lava rose to the very brim of the crater and there solidified, 
 forming a round table-mountain 53 miles across. 
 
 1 The lunar peaks are not really as precipitous as one would think from the 
 long shadows they causet 
 
HOW TO KNOW THE STARRY HEAVENS 
 
 In cases where the flow of lava was less abundant the craters 
 were partly filled up, and have now either a level or a slightly 
 convex floor. 1 Very often this has a number of little craters 
 scattered about it, and has also a cone, or series of cones, over 
 the central vent. 
 
 As no two of the lunar craters were formed under exactly 
 the same conditions, it is not surprising to find that each one 
 has an individuality of its own. Yet if we except the great 
 differences in size, which are easily explained, it will be found 
 that their resemblances are much more marked than their 
 differences. There is not the shadow of a doubt as to their 
 volcanic origin, and geologists can learn many a lesson as to 
 the history of the Earth by studying the volcanoes on the 
 Moon. 
 
 OPEN CRACKS 
 
 After all volcanic activity had died away on the Moon's sur- 
 face (and probably after the Moon had solidified to its centre), 
 large numbers of surface cracks were formed by the continued 
 contraction. Many of them are of such a tremendous size that 
 they are visible to our telescopes. Some can be traced for 
 more than a hundred miles, being from one to two miles wide 
 and of great but unknown depth. 
 
 These open cracks in some cases cut clear through the 
 previously formed craters. Not only are some of the large 
 and early craters thus intersected, but also some of the small 
 and more recent ones. 
 
 With the formation of these open cracks the Moon's activity 
 apparently ceased and it became what it is to-day and what 
 our Earth will be to-morrow a dead world. 
 
 TYPICAL FEATURES 
 
 The study of lunar geology leads naturally to lunar geography, 
 which is its product. The principal features can be best learned 
 with the help of a good telescope, assisted, and preceded, by 
 
 1 Due to imperfect fluidity. 
 
t>' * iio 
 
 x *u *) . i: 
 
 * 
 
 as 
 
 FlO. 125. SCHICKAUD AND WARGENTIN 
 
 By Nasmyth and Carpenter. (From " The Moon," by Nasmyth and Carpenter, 
 published by John Murray.) 
 
LUNAR GEOLOGY AND GEOGRAPHY 263 
 
 the study of lunar charts and photographs. It may he well, 
 however, to point out some of the best illustrations of the 
 peculiarities already mentioned. 
 
 The G-reat Plains are conspicuous objects on account of 
 their great size and dark hue. Most of them can be made out 
 with an opera glass, or even with the naked eye. Their names 
 will be found on the lunar charts at the end of the book. 
 
 The bright streaks which have been mentioned radiate from 
 the craters which bear the celebrated names of Tycho, Coper- 
 nicus, Aristarchus, Kepler, and Proclus. These craters de- 
 veloped after the streaks were formed, but owe their positions 
 to the weakness and open state of the crust at the centre of 
 fracture. 
 
 There are over 100 streaks radiating from Tycho. They 
 spread over a great part of the Moon's surface. One of them 
 passes under the distant crater Menelaus, stretches clear across 
 the " Sea of Serenity," and is finally lost to sight at the north- 
 ern edge of the Moon. 
 
 The streaks radiating from Copernicus are next in importance. 
 They are so intricate as to be uncountable. 
 
 The Aristarchus streaks appear to have been formed after 
 those of Copernicus but before those of Kepler. 
 
 The craters-with-cones vary in size from the giant Petavius, 
 78 miles across, to the little companion to Hell, 1-f miles in 
 diameter. There are probably many smaller ones which the 
 telescope fails to reveal. 
 
 Copernicus, 56 miles across, is one of the grandest objects on 
 our side of the Moon. It is remarkable not only for its radiat- 
 ing streaks, but also for the landslides on both sides of its 
 rampart, for its radial spurs extending for 100 miles, for the 
 open cracks in its neighbourhood, and for the thousands of tiny 
 craters which surround it. 
 
 Plato, 60 miles across, is a coneless crater easily recognised, 
 at full moon, as a dark oval spot near the northern edge. 
 Like all other craters, it is better seen when the sunshine falls 
 on it at an angle, and throws the black shadows of its sur- 
 
264 HOW TO KNOW THE STARRY HEAVENS 
 
 rounding peaks on the smooth inside floor and on the hill 
 country beyond. It has a considerable landslide on the inner 
 side of its rampart, and there are thirty very small craters 
 scattered about on its level floor. The Lunar Alps are close by, 
 cut hi two by the curious straight valley already mentioned. 
 
 Aristarchus, 28 miles across, is as easily recognised by its 
 brilliant chalk-like hue, that almost dazzles the eye. The sur- 
 face outside appears to be folded into parallel ridges, and there 
 is a curiously contorted crack, not far away, which is about two 
 miles in width. 
 
 Ptolemy, Alphons, and Arzacha,el, near the centre of ou~ 
 side of the Moon, form one end of a more or less continuoui 
 chain of large craters extending to the south. Near the last 
 named is a huge circle with a scarcely perceptible rampart. 
 Across this almost smooth circle there runs what looks like a 
 straight railroad embankment, about 60 miles long and 2,000 
 feet high. From its artificial appearance it is commonly known 
 as The Railway. 
 
 Every part of the Moon's surface is full of objects that are 
 interesting when seen through a good telescope with the right 
 illumination. With the exception of the bright streaks, all the 
 lunar features are best observed when they are near the chang- 
 ing " terminator," so that the light falls on them at an acute 
 angle. 
 
FIG. 126. PTOLEMY, ALPHONS, AND ARZACHEL 
 
 By Nasmyth and Carpenter. (From " The Moon," by Nasmyth and Carpenter, 
 published by John Murray.) 
 
CHAPTER XXIII 
 
 INHABITED WORLDS 
 
 " As there are other globes like our Earth, so there are other [family groups] 
 like our Solar System. There are self-luminous suns exceeding in number all 
 computation. The dimensions of this Earth pass into nothingness in comparison 
 with the dimensions of the Solar System, and that system, in its turn, is only an 
 invisible point if placed in relation with the countless hosts of other systems. 
 Our Solar System, far from being alone in the Universe, is only one of an exten- 
 sive brotherhood, bound by common laws and subject to like influences. Even in 
 the very verge of creation, where imagination might lay the beginning of the 
 realms of Chaos, we see unbounded proofs of order, a regularity in the arrange- 
 ment of inanimate things, suggesting to us that there are other intellectual 
 creatures like us, the tenants of those islands in the abysses of space." Dr. J. W. 
 Draper. 
 
 ARE OTHER WORLDS INHABITED? 
 
 IN ancient times our Earth was supposed to be the only world 
 in existence. In fact the Universe was thought to consist 
 solely of our Earth and its appendages. But in the course of 
 time it was discovered that the Earth is only one member of a 
 family of worlds, and that there are other families of worlds 
 outside of our own. 
 
 These two discoveries naturally gave rise to a lively discus- 
 sion as to whether those worlds are, as a rule, inhabited by 
 living organisms. 
 
 At first, pride and theological prejudice led many people to 
 deny emphatically the existence of any kind of life on other 
 worlds. Even after the consideration of probabilities had led 
 to the abandonment of this position, the existence of rational 
 life was strongly contested. 
 
 After this came a time when the most progressive minds 
 went to the other extreme. They claimed that life probably 
 
266 HOW TO KNOW THE STARRY HEAVENS 
 
 exists on every world of any size, at a certain stage in its 
 development. 
 
 The first of these extreme views concerning the plurality of 
 worlds has long been abandoned by all intelligent and well- 
 informed persons. The last is now being somewhat modified 
 by astronomers. They consider that, while it is absurd to sup- 
 pose that our Earth is the only inhabited world in the Universe, 
 the opposite extreme is not supported by the available evidence 
 as to the conditions existing on other worlds. 
 
 While the extreme affirmative side was in the ascendency, 
 certain imaginative astronomers (and other imaginative persons 
 who were not astronomers) stated that they had recognised 
 indications of life on the Moon. A little later, some of our 
 very best observers constructed charts of Mars showing the 
 dark markings on it connected together by very artificial-looking 
 " cobwebs." Schiaparelli gave the Italian name canali (mean- 
 ing " channels " ) to these elusive markings. English-speaking 
 people mistook the Italian canali for the. English word " canals," 
 and jumped to the conclusion that Mars is inhabited by very 
 enterprising engineers who eke out a small water-supply by 
 means of large irrigating canals. The theory was afterward 
 made less absurd by the supposition that the markings were 
 not the canals themselves, but the belt of vegetation on each 
 side of the main ditch. 
 
 Made enthusiastic by this supposed identification, one or two 
 sensational astronomers went a step farther, and asserted that 
 the Martians were trying to attract our attention by displaying 
 geometrical signals constructed on a world-wide scale. 
 
 The supposed evidences of life on the Moon were easily 
 proved to be wholly imaginative. In one rather notorious case, 
 indeed, they turned out to be nothing but a hoax, gotten up to 
 test the credulity of the general public. 
 
 With regard to the " canals " of Mars, the belief is now grow- 
 ing stronger among astronomers that they are largely subjective 
 phenomena that in fact the majority of them are optical 
 delusions caused by the observers over-straining their eyes in 
 
INHABITED WORLDS 267 
 
 the effort to make the best use of their telescopes. The rest of 
 them are probably due to close sequences of spots too faint to 
 be separately visible. 
 
 The truth appears to be that our optical appliances, powerful 
 as they may be, are yet very far from the degree of perfection 
 required in order to detect evidences of life in other worlds. 
 The probability is that they always will be unequal to the task. 
 We have therefore no means of actually proving or disproving 
 the theory that other worlds are inhabited. There appears to 
 be some positive evidence that the Earth is inhabited, and that 
 its Moon is not. But apart from these two planets we have no 
 actual positive evidence that life exists, or does not exist, any- 
 where in the Universe. And we never shall have. 
 
 This being the case, about the only way we can deal with 
 the problem is to try to find out the conditions necessary for 
 life as we know it, and to see whether those conditions exist on 
 any of the other planets hi our System. We shall then be in a 
 better position for speculating on the probability, or otherwise, 
 of these worlds being inhabited by living organisms allied to 
 those on our Earth. 
 
 When that question is disposed of, there will still remain 
 the more obscure problem whether any of the worlds are 
 tenanted by entirely different forms of life. 
 
 ESSENTIALS TO LIFE AS WE KNOW IT 
 
 Among the things which are absolutely essential to organic 
 life here are the four elements known as carbon, hydrogen, 
 nitrogen, and oxygen. 
 
 Of these, oxygen, in a free gaseous state, is essential to all 
 forms of animal life. 
 
 Carbon and oxygen, in combination, form carbon-dioxide 
 (C0 2 ), which, as a gas, is equally essential to all forms of 
 vegetable life. 
 
 Hydrogen and oxygen combine to form water (H 2 0), which 
 both plants and animals require in a liquid state. 
 
268 HOW TO KNOW THE STARRY HEAVENS 
 
 Carbon and hydrogen form the basis of numerous compounds 
 which, by their formation and oxidation, alternately accumulate 
 energy and expend it in motion, etc. These two processes are 
 together known by the name of energy-traffic. 
 
 Nitrogen is necessary, in a free gaseous state, to keep in 
 check the all-devouring energy of free oxygen. It is also neces- 
 sary, in combination with the hydrocarbons, to regulate and 
 control their energy-traffic. It is specially adapted for this 
 office on account of its sensitiveness to changes of energy and 
 the resulting instability of its compounds. 
 
 All the life on our globe is based on protoplasm, which con- 
 sists of these four elements. A number of other elements 
 occur in most forms of life, but do not seem to be so essential 
 to it. 
 
 An intermittent supply of radiant energy also appears to be 
 necessary to life as we know it. The plants derive their 
 energy, either directly or indirectly, from the Sun, and the 
 animals get it at second-hand, from the plants. 
 
 The energy-traffic mentioned above can only be carried on 
 within a certain range of temperature. Life based on proto- 
 plasm cannot exist where the temperature is permanently 
 above 150 K, or below 32 F. High temperatures break up 
 the protoplasm into less complex compounds. Low temper- 
 atures check and eventually put a stop to its activity. 
 
 A certain intensity of the force of gravitation also seems to 
 be essential to life as we know it. For worlds which are very 
 much smaller than ours do not appear to be able to retain the 
 vapours and gases necessary to living organisms, and on worlds 
 that are very much larger, the same organisms would be 
 crushed to death by their own weight. 
 
 DO LIFE-ESSENTIALS EXIST ON OTHER WORLDS? 
 
 When we examine the other planets in our System, we find 
 that some of these essentials are lacking in every one, and 
 always will be lacking. 
 
Fastigium Ceryor 
 
 30 Margaritifer-Sinus 
 
 60 Ganges 
 
 90 Solis Lasus 
 
 120 Nodus Gordii 
 
 150 Mare Sirenum 
 
 FIG. 127. TWELVE VIEWS OF MARS 
 
 By Lowell. (From Todd's " Stars and Telescopes," published by 
 Messrs. Little, Brown, & Co.) 
 

 180 Atlantis 
 
 210 Trivium Charontis 
 
 300 Syrtis Major 330 Phisoner Euphrates 
 
 FIG. 127. TWELVE VIEWS OF MARS 
 
 By Lowell. (From Todd's "Stars and Telescopes," published by 
 Messrs. Little, Brown, & Co.) 
 
f\BR ATTp 
 Of THE 
 
 UNIVERSITY 
 
 or 
 
INHABITED WORLDS 269 
 
 Our nearest neighbour, the Moon, shows no signs of having 
 either air or water. This is probably due to the fact that it is 
 unable to retain them, except in a solid state. Owing to their 
 absence, and to the slowness of the planet's rotation, the range 
 of temperature is too great for any form of life based on the 
 carbon compounds. 
 
 Mercury and Mars probably have a very scanty supply of 
 both air and water. There are no perceptible oceans or seas on 
 Mars, and Dr. Campbell, of Lick Observatory, has shown that 
 the atmospheric pressure on its surface is very small. It ap- 
 pears, in fact, to be less than that at the summit of Mount 
 Everest, the highest mountain on our globe. This being the 
 case, it is possible that the planet is unable to retain the vapour 
 of water, and that its " snowy poles " are nothing but frozen 
 carbon-dioxide (C0 2 ), an inch or two in thickness. 
 
 Venus probably has a good supply of both air and water. 
 But as it appears to keep one side always turned to the Sun, it 
 has not the intermittent supply of radiant energy which is nec- 
 essary for life on our globe. The Sunward side must be too 
 hot for protoplasm to exist, and the dark side must be cold 
 enough to freeze both water and air. Mercury also appears to 
 possess the same unfavourable coincidence between its rotation 
 and revolution. 
 
 The Asteroids receive much less light and heat than the 
 Earth. They have probably neither air nor water, as their 
 gravitation is too small to prevent these from escaping into 
 space, as free hydrogen does from our Earth. 
 
 Jupiter may be said to be all atmosphere, as it appears to be 
 still in a hot gaseous state, surrounded by thick cloudy conden- 
 sations. The intensity of the Sun's light and heat is 27 times 
 less there than on our Earth. Its five moons must therefore 
 appear as mere wandering stars. 
 
 Saturn is not as dense even as Jupiter. And it is still less 
 favourably situated as regards solar radiation, in spite of its 
 enormous satellite-rings and numerous moons. For the intensity 
 of solar light and heat is 90 times less than here. 
 
270 HOW TO KNOW THE STARRY HEAVENS 
 
 Uranus and Neptune are little more, at present, than huge 
 masses of rotating gas, slowly revolving in the gloomy outskirts 
 of the Solar System. The intensity of Neptune's sunshine 
 is 900 times less than that which we enjoy. Its lot would 
 therefore be a cold one if it were not for its store of internal 
 heat, continually replenished by the gradual contraction of the 
 planet. 
 
 This concludes our survey of the Solar System in search of 
 the essentials of life. If we wait until the outer planets have 
 reached the present stage of the Earth, we shall still find the 
 conditions utterly unfavourable to life as we know it. For the 
 force of gravitation will still be tremendously greater than 
 here, and the radiant energy from the distant and waning Sun 
 will then be insufficient to keep the otherwise dense atmos- 
 pheres from settling down over their entire surfaces, in a solid 
 mass of never-melting " snow." 
 
 We have then good reason to think that in our own System 
 the Earth is the only planet on which the conditions are 
 favourable for life as we know it. That is to say, if life must 
 necessarily be based on protoplasmic combinations of oxygen, 
 hydrogen, nitrogen, and carbon, the other planets in our System 
 appear to be uninhabitable. 
 
 Among the many millions of solar systems which surround 
 our own, it may be regarded as certain that there is no single 
 world where the conditions sue identical with those on Earth. 
 But it is possible that there may be quite a number of worlds 
 where the conditions are somewhat similar to those found 
 here. 
 
 In such worlds we should probably find living organisms 
 based on the same four elements, but developing along some- 
 what different lines. For earthly forms of life have grown up 
 under certain conditions, and cannot exist where those condi- 
 tions do not prevail. On other planets life would start under 
 different conditions and develop accordingly. In other words, 
 the various forms of life on our globe are the result of general 
 laws operating under special conditions, and the same general 
 
INHABITED WORLDS 
 
 laws would, under different conditions, result in different forms 
 of life. 
 
 But although the number of such worlds in the Universe may 
 be numerically large, it must be relatively small. We know 
 that the Universe contains hundreds of millions of luminous 
 suns, and we have reason to believe that they are many times 
 outnumbered by dark planetary worlds. Let us deduct from 
 these latter the comparatively small number on which the con- 
 ditions are presumably somewhat similar to those on our Earth. 
 The question now remains whether the rest are entirely with- 
 out life of any kind, or whether they are tenanted by forms of 
 life which are based on other elements and require altogether 
 different conditions. 
 
 For my part, I must say that the latter seems the most rea- 
 sonable supposition, considering the resourcefulness of Nature 
 in our part of the Universe. Yet we have reason to believe 
 that even our World is entirely uninhabited, except on the thin 
 surface layer. And it is only habitable there for a compara- 
 tively snort time. Nature may be as wasteful of worlds as it 
 is of sunshine. 
 
 The fact is that we none of us know anything at all about 
 this last question. And we never shall know. 
 
 WHERE IS THE EARTH? 
 
 " Beelzebub. ' There is a place 
 (If ancient and prophetic fame in heaven 
 Err not), another world, the happy seat 
 Of some new race, called Man. 
 
 Thither let us bend all our thoughts, to learn 
 What creatures there inhabit, of what mould 
 Or substance, how endued, and what their power.' 
 
 Satan. ' Whom shall we send 
 
 In search of this new world? Whom shall we find 
 
 Sufficient? Who shall tempt with wandering feet 
 
 The dark, unbottomed, infinite abyss, 
 
 And through the palpable obscure find out 
 
 His uncouth way, or spread his aery flight 
 
HOW TO KNOW THE STARRY HEAVENS 
 
 Upborne with indefatigable wings, 
 Over the vast abrupt, ere he arrive 
 The happy isle? 
 
 I abroad 
 
 Through all the coasts of dark destruction seek 
 Deliverance for us all : this enterprise 
 None shall partake with me.'" Milton, "Paradise Lost," Bk. II. 
 
 So far the entire subject of inhabited worlds has been treated 
 from an earthly standpoint. It may be an advantage to con- 
 sider it briefly from the outside. 
 
 Let us suppose for a moment that our Earth is the only 
 world in the Universe which is inhabited by living organisms. 
 And let us suppose that from some distant spirit-land a flying 
 messenger is sent to hunt up our World, without any special 
 instructions for finding it. Let us also suppose that he can 
 travel through space at a speed equal to that of light. He may 
 travel from star to star, for hundreds, thousands, and millions 
 of years, without being able to find it. " If in the course of time 
 he comes to our System, he may see the larger and more showy 
 planets, and yet fail to notice our little World. 
 
 If it were to be pointed out to him as the specially favoured 
 world, he would hardly be able to convince himself of the fact 
 without a close examination. For the only unusual feature 
 about it, as seen from a distance, would be that it was attended 
 by a satellite which was large in proportion to its primary. 
 Apart from this peculiarity, which may be common in other 
 systems, the Earth would seem to be merely an insignificant 
 attendant on a star which was itself almost indistinguishable 
 from millions of other stars. 
 
 That our Earth is the only inhabited world is therefore an 
 extremely unlikely supposition to be entertained by anyone 
 who is at all conversant with the dimensions, construction, and 
 duration of the Universe. It appears reasonable only to one 
 who is almost entirely ignorant of all except his immediate 
 surroundings. 
 
 Yet there are people on our Earth (even in so-called enlight- 
 
INHABITED WORLDS 273 
 
 ened and civilised countries) who not only think that it was 
 created expressly for the use of man, but also believe that the 
 entire Universe visible and invisible was made for his 
 service and edification ! There are persons who actually believe 
 that the Sun was made to rule an earthly day, the Moon to 
 adorn an earthly night, the planets to serve as oracles of earthly 
 fortunes, and the stars to relieve the monotony of an earthly 
 sky ! The sciences of astronomy and geology show that 
 natural as these ideas may seem to unenlightened people 
 they are as baseless as the airy fabrics of a midnight dream. 
 
 SUMMARY 
 
 Dr. F. J. Allen, in a recent article in the " Popular Science 
 Monthly," l has ably summed up the argument as to " Life in 
 Other Worlds." He says : 
 
 " 1. If life is essentially a function of the elements nitrogen, oxy- 
 gen, carbon, and hydrogen, acting together, then it can probably 
 occur only on exceptional worlds, with conditions closely resembling 
 those of our own Earth. Such conditions are not present in any 
 other world in our own Solar System, nor can they be expected to 
 occur frequently in members of other systems. 
 
 " 2. On the other hand, if different conditions can awaken a capac- 
 ity for exalted energy-traffic among other elements than those just 
 named, then the Universe seems to provide immense possibilities of 
 life, whose variety and magnificence may far exceed anything that we 
 can imagine." 
 
 OTHER-WORLD SPECULATIONS 
 
 I think that it has now been satisfactorily shown that we 
 have no direct knowledge whatsoever concerning inhabited 
 worlds outside of our own, and that we are never likely to 
 obtain such knowledge. 
 
 But on the other hand it has also been shown that it would 
 be preposterous to suppose our Earth to be the only inhabited 
 
 1 November, 1903. 
 
 18 
 
274 HOW TO KNOW THE STARRY HEAVENS 
 
 world in the Universe. As a matter of probability, we may 
 safely take it for granted that there are, at the present time, 
 myriads of inhabited worlds, a certain percentage of which 
 have developed reasoning beings. We may also take it for 
 granted that there have been myriads of such worlds in the 
 limitless past, and will be in the limitless future. 
 
 This being so, the question naturally arises, is the life on 
 those worlds likely to develop along the same lines as here, 
 or has each world its own special line of development, not con- 
 ceivable by the inhabitants of any other planet ? In other 
 words, is it probable that a visitor to one of those worlds would 
 there find two ascending series of organisms, the one culmi- 
 nating in flowering shrubs and trees, and the other in back- 
 boned quadrupeds, headed and more or less controlled by 
 a reasoning biped like man ? 
 
 At first sight it does not seem as though any time could be 
 profitably spent in considering the question. It looks, indeed, 
 as though it would be only another case of arguing about the 
 politics of the people who live or do not live on the other 
 side of the Moon. 
 
 Yet a close study of the development of life on our Earth 
 appears to afford considerable indirect and circumstantial 
 evidence that the course of organic evolution may be very 
 similar, even where the physical and chemical conditions are 
 widely different. This similarity is rendered probable by the 
 fact that organic peculiarities, both internal and external, have 
 not been developed so much by the inorganic as by the organic 
 surroundings. The evolution is mainly the result of a struggle 
 for existence, which must go on wherever there is life. There- 
 fore if the physical environment be a tolerably permanent one, 
 favouring the processes of organic chemistry, the resulting life- 
 forms may be similar, whatever may be the temperature or the 
 active chemical elements. 
 
 On our Earth, Nature has long been unconsciously experi- 
 menting with innumerable kinds of organic life. Without 
 either mercy or spite she has pitted one form against the other 
 
Fi<;. 128. Disc OF THE SUN, AUGUST 12, 1903 
 
 Showing brilliant calcium flocculi. Middle (H) level. Taken with Hale'a spectroheliograph, 
 at Yerkes Observatory. 
 
\TBRA;?> 
 
 0- r- <E ' 
 
 UNIVERSITY 
 
 or 
 *J 
 
INHABITED WORLDS 275 
 
 under a great variety of local conditions, allowing the fittest to 
 survive and the rest to perish. The " experiments " have been 
 ceaselessly carried on for many millions of years, with a super- 
 abundance of material, and with a physical and chemical 
 environment that has been almost unchanging. 
 
 This being the case, the course of development and final 
 result may have been inevitable rather than the effects of 
 chance. Earthly forms of life may be practically duplicated 
 on a million worlds that were, and are, and are to be. 
 
 There is not room in this chapter to go into details on the 
 question, and it would be out of place in any other part of this 
 volume. But a few hints may be given as to the way in which 
 organic life is likely to develop on a world where the condi- 
 tions prove favourable. 
 
 Whatever the temperature and active elements may be, it 
 seems certain that organic life must be based on the cell or its 
 equivalent, and that the first cells must originate from and in 
 non-living compounds of those active elements. 
 
 A. The first living forms must be single-celled PROTISTA, 
 having their home in water or some similar fluid. 
 
 The energy necessary to carry on the processes of life must 
 come from a chemical change similar to the oxidation of tissues. 
 The wasting tissues must be renewed by the absorption of 
 soluble inorganic compounds. 
 
 Each single-celled organism must go through a life-cycle 
 ending either in death or in division. This must lead to re- 
 production by fission, or by some similar process involving a 
 less expenditure of energy than the original spontaneous 
 generation. 1 
 
 The multiplying individuals must adjust themselves to local 
 conditions, and thus give rise to varieties, species, etc. When 
 they have multiplied till food becomes scarce, some will be 
 compelled to feed on their neighbours. Only those will survive 
 which can obtain food and protect themselves from being 
 eaten. The result of this " cannibalism " is a division into 
 
 1 And capable of being carried on under less favourable conditions. 
 
276 HOW TO KNOW THE STARRY HEAVENS 
 
 plants, which live on soluble inorganic food, and animals, 
 which live, either directly or indirectly, on the plants. 
 
 When single-celled possibilities have all been long and 
 fully tried, the only possible advance will be found in combina- 
 tion. Some of the dividing organisms will remain in contact 
 and partnership, giving rise to many-celled plants and animals. 
 These compound individuals will by co-operation and division 
 of labour find greater safety and economy, resulting in a 
 better living than their simple competing neighbours. They will 
 therefore get the upper hand, and continue to advance in size 
 and complexity of organisation. 
 
 Nature may be said to have issued two irrevocable decrees 
 with regard to organic evolution. One of these is that " where 
 there is no necessity there shall be no development." The 
 other is that " where there is necessity there shall be either 
 development or death." 
 
 The plants living by the absorption of soluble inorganic 
 compounds, which are all around them require no special- 
 sense organs, or apparatus for thinking, moving, eating, digest- 
 ing, etc., and they do not develop them. But they are usually 
 compelled to anchor themselves to the sea-bottom where the 
 surroundings are favourable, to spread themselves out so as to 
 obtain a large absorbing surface, to protect themselves from 
 their animal foes, and to modify their methods of growth and 
 reproduction wherever the local conditions require it. 
 
 The animals being compelled to find suitable organic food 
 or starve will develop means of locomotion and all the 
 physical and mental peculiarities necessar}^ for obtaining and 
 utilising the available supply. Like the plants, they will find 
 it necessary to protect themselves from their animal foes, and 
 to modify their methods of growth and reproduction wherever 
 the local conditions require it. 
 
 The animals will therefore rise to a higher plane than the 
 vegetables, and the free-moving and offensive forms will develop 
 more, in every direction, than the fixed, sluggish, and defensive 
 forms, 
 
INHABITED WORLDS 277 
 
 So far as shape is concerned, there appear to be only two 
 general organic types possible, either here or in any other 
 world. These are the radial and the elongated bilateral. 
 
 Among the animals, the radial type has given rise, on our 
 planet, to two branches. 
 
 B. One of these is termed the CCELENTERATA. It contains 
 such forms as the jelly-fishes, sea anemonies, and corals. These 
 have only one opening to the stomach. 
 
 0. The other branch is the ECHINODERMATA. It includes 
 the crinoids, starfishes, and sea-urchins. They have the stomach 
 open at both ends. 
 
 All the forms in these two branches are either fixed or 
 sluggish. Other-world forms of this radial type would probably 
 be the same. 
 
 The elongated bilateral type, although very unpromising in 
 its earlier stages, has much greater possibilities. In fact all 
 our higher forms of animal life belong to this type. 
 
 D. The simplest form is that of a marine worm, which is 
 little more than a long sack with a hole at each end of it. At 
 this stage it is naturally a very sluggish animal. 
 
 E. When the worm-like animal develops tentacles or arms 
 around its mouth, it becomes a MOLLUSK, represented on Earth 
 by the clams, snails, and cuttle-fish. Some of these forms are 
 rather more active than those already mentioned, but the limit 
 of advancement is soon reached. 
 
 F. When the worm-like form develops a segmented structure, 
 with a tough skin, and numerous jointed legs arranged along 
 its two sides, it becomes the more active ARTHROPODA, repre- 
 sented in our seas by the lobster family and some insects. 
 
 Gr. When the same worm-like form retains its simpler 
 structure but develops an internal skeleton, with a tail and two 
 pairs of lateral limbs, it becomes a VERTEBRATE fish-like ani- 
 mal. This is capable of great activity, and appears to be the 
 highest form of life which can be developed under oceanic 
 conditions. 1 
 
 1 For many millions of years this fish-like vertebrate has made very little 
 progress with us, in spite of the relative immensity of our oceans and the great 
 
278 HOW TO KNOW THE STARRY HEAVENS 
 
 From this it appears probable that on those worlds which 
 are nearly or entirely covered by water or some similar liquid, 
 the highest form of life will be a rather stupid fish-like animal 
 with an internal skeleton, simple organisation, a tail, and two 
 pairs of lateral fins. 
 
 On those planets which have large masses of land rising oat 
 of the ocean, some forms of life will be gradually crowded out 
 of the water and modified so that they can live without being 
 constantly submerged. In the course of time both plants and 
 animals will spread over the continents and islands, relying on 
 an occasional rainstorm to keep them from drying up. 
 
 On our Earth, only the elongated worm-like type sent repre- 
 sentatives out of the water to seek a living on the dry land. 
 Its four branches (D, E, F y and G) now constitute the entire 
 population of the dry land, as well as all the more active resi- 
 dents of the ocean. The arthropods and vertebrates have been 
 the most successful of the dry-land colonists, and have risen, 
 both physically and mentally, far above their relatives who still 
 remain below the sea level. 
 
 Most of the dry-land ARTHROPODS became parasites of the 
 land vegetation. 1 As a result of the struggle for existence they 
 developed into an immense variety of insect-lite. At the same 
 time they compelled the plants to protect themselves, and so 
 caused the development of an equally immense variety of 
 flowering plants. But their complex organisation and parasitic 
 mode of life limited their size and prevented them from de- 
 veloping further than the bee and the ant. On other worlds 
 the same causes would probably result in similar limitations. 
 
 It would be a mistake to suppose that the animal with the 
 most complex organisation is necessarily the highest and most 
 progressive form of life. The most progressive animal, both 
 physically and mentally, is likely to be the one which has the 
 
 variety of forms which have arisen therein. Its development appears to have 
 been checked by the limitations of its habitat. Even the land mammals which 
 have gone back to live in the sea have degenerated, both physically and mentally. 
 1 Some of them afterward became parasites on other animals. 
 
INHABITED WORLDS 279 
 
 very simplest and best arranged machinery that is really 
 effective in accomplishing the desired ends. 
 
 On our world the arthropods, with their many segments and 
 numerous limbs, were compelled (like the fishes in the sea) to 
 waste their energies in mere multiplication of non-progressive 
 species. The fish-like VERTEBRATES, on the other hand, with 
 their simple, well-arranged, and centralised organisation, and 
 with the smallest effective number of limbs, made rapid prog- 
 ress as soon as they had adapted themselves to living on the 
 dry land. Their gills were replaced by lungs, and their lateral 
 fins developed into legs, with five toes on each foot. The more 
 varied conditions to which they were exposed in their new 
 habitat, combined with the violent struggle for existence which 
 soon arose, led to great developments in size and strength or in 
 nimbleness and cunning. Their internal organs became more 
 effective, and their organs of sense more acute. They developed 
 into amphibians, reptiles, birds, and mammals. Many of them 
 became carnivorous, and developed claws and teeth suitable for 
 their bloodthirsty profession. This led to the survival of those 
 vegetarian forms which were most successful in defence, con- 
 cealment, or flight. A great variety of species arose from this 
 struggle for existence. 
 
 Some of the tree-dwelling quadrupeds learned to use their 
 feet for climbing, and for swinging from tree to tree. When 
 they were subsequently forced to live on the treeless plains, 
 they walked upright on their hind legs, and used their front 
 feet for grasping weapons and tools. Their mental develop- 
 ment was so much hastened by this new use for their front 
 feet that they gradually learned to utilise the forces of Nature 
 in addition to their own strength. They also learned to convey 
 their thoughts to one another by a constantly increasing variety 
 of vocal sounds, and mutually to co-operate for the attainment 
 of any desired end. As they were now able to protect them- 
 selves from the elements, and from all kinds of difficulties and 
 dangers, they soon spread from land to land without under- 
 going any great physical modifications. Their descendants are 
 
280 HOW TO KNOW THE STARRY HEAVENS 
 
 now to be found all over the continents and islands of the 
 Third Planet, and the species is known to science by the name 
 of Homo sapiens. 
 
 Now the innumerable modifications that have, on our Earth, 
 led from the first protista to the latest man, are entirely the 
 result of the struggle for existence. This struggle may at the 
 very first have been entirely physical and chemical. But when 
 once any particular part of the World became crowded with 
 living organisms, there arose a much more terrible struggle, 
 between the different species, and also between the individuals 
 composing those species. This struggle was one for the neces- 
 saries of life, such as food, water, air, and light. All kinds 
 of organic life were blindly and intensely prolific, but the 
 World was small, and the necessaries of life were strictly 
 limited in amount. The entire Earth therefore became like 
 the Black Hole of Calcutta, packed with a struggling mass of 
 starving and suffocating organisms. For every one that lived 
 long enough to propagate its species, a -thousand perished in 
 infancy. Only those that were strong, savage, nimble, cunning, 
 unscrupulous, or uneatable, could survive and hand down their 
 peculiarities to their posterity. The surviving forms are there- 
 fore those which are best fitted to carry on the struggle. 
 
 The physical and mental peculiarities which have been most 
 successful here would probably be most successful in a similar 
 struggle for existence on any other world. And the course of 
 organic evolution would therefore be somewhat similar. Hence 
 we may say, with George Morris : 
 
 " There is considerable reason to believe that the beings which 
 answer to man upon any of the planets of the Universe must at least 
 approach man somewhat closely in physical configuration. ... It 
 certainly seems as if a human traveller, if he could make a tour of 
 the Universe, would find beings whom he could hail as kindred upon 
 a thousand spheres." * 
 
 1 Those who wish to follow up this subject should read an article by Mr. 
 Morris in the Popular Science Monthly for April, 1904. 
 
INHABITED WORLDS 281 
 
 A POET'S DREAM 
 
 The astronomer, as such, has nothing to say of the unknown 
 citizens of these unknown worlds. Accustomed, as he is, to 
 test his theories by observation, he holds lightly to unprovable 
 speculations, however probable they may be. 
 
 The speculative poet, however, trusts himself in airy flights 
 that extend far beyond the limits of the known. He not only 
 wrestles boldly with half-seen facts, but also concerns himself 
 with invisible probabilities. With an imagination that knows 
 no fetters except those of natural law, he sees, beyond the 
 utmost range of telescope and camera, the 
 
 " fire of unrecorded stars 
 
 That light a heaven not our own." 
 
 He beholds, with a certainty that is based on mathematics 
 
 and physics 
 
 "the hidden gyre 
 Of bulks that strain in Algol's toils." 
 
 He glimpses, with a probability that is born of his earthly 
 observations, the 
 
 " seas that flash on alien eyes 
 The riven sunlight of Altair." 
 
 In many a far-off globe he sees a dawn of life, followed by a 
 physical and mental evolution which culminates in the develop- 
 ment of reasoning beings. On many an unknown world he 
 watches an age of faith slowly change to an age of reason. On 
 many a sun-kissed planet he hears infantile stories of a one- 
 world creation give way to more mature discussions of a vast 
 and abiding Universe. He imagines these unknown phi- 
 losophers discussing the whence, the where, the what, the 
 why, and the whither of all things even as some of us do 
 here. 
 
 He sees these lengthy discussions brought to a futile close by 
 the gathering darkness and cold of everlasting night to be as 
 
282 HOW TO KNOW THE STARRY HEAVENS 
 
 fruitlessly brought up, again and again, on other worlds, in 
 systems yet to come. For the great " Eiddle of the Universe " 
 can never be fully solved by finite minds. As Olive Schreiner 
 says of the drama that is being enacted on our own Earth : 
 
 " What the name of the play is, no one knows. If there sits a spec- 
 tator who knows, he sits so high that the players in the gaslight 
 cannot hear his breathing." 
 
 George Sterling, in his immortal " Testimony of the Suns," 
 
 " So dreamt thy sons on worlds destroyed, 
 Whose dust allures our careless eyes, 
 As, lit at last on alien skies, 
 The meteor melts athwart the void. 
 
 " So shall thy seed on worlds to be, 
 At altars built to suns afar, 
 Crave from the silence of the star 
 Solution of thy mystery. 
 
 " And crave unanswered, till, denied 
 By cosmic gloom and stellar glare, 
 The brains are dust that bore the prayer, 
 And dust the yearning lips that cried." 
 
CHAPTER XXIV 
 
 SIZE, IMPORTANCE, SPEED, AND DURATION 
 
 SIZE AND IMPORTANCE RELATIVE 
 
 " The appearance of things depends altogether on the point of view we oc- 
 cupy. He who is immersed in the turmoil of a crowded city sees nothing but the 
 acts of men. . . . But he who ascends to a sufficient elevation . . . discovers that 
 the importance of individual action is diminishing as the panorama beneath him 
 is extending. And if he could attain to the truly philosophical, the general point 
 of view, . . . rising high enough to see the whole world at a glance, his acutest 
 vision would fail to discover the slightest indication of man, his free will, or his 
 works. In her resistless onward sweep, in the clock-like precision of her daily 
 and nightly revolution, in the well-known pictured forms of her continents and 
 seas, now no longer dark and doubtful, but shedding forth a planetary light, well 
 might he ask what had become of all the aspirations and anxieties, the pleasure 
 and agony of life. As the voluntary vanished from his sight, and the irresistible 
 remained, well might he incline to question . . . whether beneath the vast- 
 ness, energy, and immutable course of a moving world there lay concealed the 
 feebleness and imbecility of man. Yet it is none the less true that these contra- 
 dictory conditions co-exist Free-will and Fate, Uncertainty and. Destiny. It is 
 only the point of view that has changed, but on that how much has depended." 
 Dr. J. W. Draper. 
 
 THE human family is an ephemeral form of organic life 
 entirely confined to one insignificant planet in an incon- 
 spicuous stellar system. And the still more ephemeral individ- 
 uals composing it are generally cooped up in a small corner of 
 this little planet. It is therefore very difficult for those who 
 take an interest in cosmical affairs to get correct and undistorted 
 ideas as to the relative sizes and importance of the objects com- 
 posing the Universe. Nor is it easy for them to accept the 
 teachings of Astronomy with regard to the enormous speed with 
 which some of these objects move through space, or the im- 
 mense duration of the heavenly bodies in general. It may not, 
 
284 HOW TO KNOW THE STARRY HEAVENS 
 
 therefore, be out of place to conclude our bird's-eye examination 
 of the Universe with a few words on these subjects. 
 
 Man is a very important personage in his own [estimation. 
 As a general thing he is so wrapped up in the petty details of 
 his own mundane existence, that he fails to realise his own 
 insignificance, either in the Universe at large or in the little 
 World on which he lives and moves and has his being. 
 
 Yet a man is only one out of some 1,400,000,000 of similar 
 beings. And as knowledge and wisdom bring modesty, he who 
 thinks himself better and more important than his fellows is 
 generally of very little account. t 
 
 The same is true of the entire living race. All the men, 
 women, and children on Earth are but a handful to those who 
 have gone before, and will come hereafter in the ages yet to 
 come. Future generations will look back with pity on our 
 boasted wisdom and knowledge, even as we do on the wisdom 
 and knowledge of former times. 
 
 The human race, as a whole, believes itself to be the raison 
 d'etre of the Universe, " the end and aim of all creation." 
 Yet it is but a thing of yesterday, doomed to perish to-morrow 
 and be forgotten. For millions of years the Earth spun around 
 its reeling axis, and circled around its little twinkling star, in 
 company with a crowd of other planets. It did all this without 
 the presence of man, and it will continue to circle and spin 
 when the human family has passed away, like a streak of morn- 
 ing cloud, into the infinite azure of the past. 
 
 Our World is a very mighty world to us. How mighty it 
 is, only those who have traversed its oceans and continents can 
 truly realise. 
 
 Yet, compared with the rest of the Universe, it is very, very 
 small. 
 
 So small is it that the mind cannot grasp the idea of its 
 littleness. 
 
SIZE, IMPORTANCE, SPEED, AND DURATION 285 
 
 It is as a single leaf, compared with all the leaves of the 
 forest. 
 
 It is as a blade of grass that withereth away, compared with 
 all the grasses of the World. 
 
 It is as a drop of water, compared with all the oceans and 
 seas. 
 
 It is as a grain of sand, compared with a world of similar 
 grains. 
 
 Our Sun is 1,250,000 times as large as our Earth, and con- 
 tains 330,000 times as much matter. 
 
 Though it is more than 90,000,000 miles away, it is bright 
 enough to make the electric light seem black by contrast. 
 
 It is hot enough to turn our entire Earth into fire-mist if it 
 were dropped into it. It is powerful enough to keep the planet 
 Neptune in bondage, although thirty times as far from it as 
 our Earth. 
 
 Yet this mighty Sun of ours is only one out of millions of 
 similar suns. It is only a star among a Universe of stars. 
 
 Space is endless limitless bottomless. It has no bounds, 
 either visible or invisible. It is a sea without surface or 
 bottom, an ocean without a shore. And our telescopes and 
 spectroscopes show that, all around us in the depths of this 
 shoreless ocean, living suns like ours are strewed in hundreds 
 of millions, while nebulae and dead suns exist beyond all com- 
 putation. 
 
 SPEED IS RELATIVE 
 
 When we hear that our World goes around the Sun at the 
 speed of 18 J miles in a second of time, and that the Solar 
 System itself is speeding toward the constellation of Lyra at 
 the rate of 12 1 miles per second, we naturally compare such 
 motions with the rush of a bullet or cannon-ball. The result 
 of the comparison is that the statements appear almost unbe- 
 lievable. But if we change the comparison, and note that the 
 Earth is seven minutes in moving the length of her own diam- 
 
286 HOW TO KNOW THE STARRY HEAVENS 
 
 eter, and that the Sun is 16 hours in doing the same thing, the 
 celestial velocities seem very moderate. The first comparison 
 calls to mind the sharp " ping " of an invisible projectile. The 
 second reminds one of the stately and almost imperceptible 
 drift of a family of icebergs through the arctic seas. 
 
 In this case the figures do not become smaller, but the stand- 
 point is changed, and that makes a wonderful difference in the 
 result. 
 
 It is true that astronomy shows us instances of extremely 
 small bodies travelling at even greater speed than the large 
 ones. But in these cases it will be found that the small bodies 
 are not moving by any energy of their own, or by any initial 
 force that soon ceases to act. They are under the continuous 
 influence of some celestial giant whose power is almost im- 
 measurably great. The energy exerted is not merely initial 
 but continuous and cumulative. The push or pull is therefore 
 unimaginably vast, compared with any force that man can 
 bring to bear on such an object. This being the case, it is quite 
 natural and reasonable that the resulting motions should be 
 almost beyond his comprehension and belief. 
 
 DURATION IS RELATIVE 
 
 " A generation passeth away, 
 And a generation cometh, 
 But the Earth abideth 
 For ages of ages. Eccles. i, 4 (A. Zazel). 
 
 " But yestermorn, O boastful clay, 
 
 Thy planet from its parent broke 
 O, insect of a summer's day, 
 
 Thy vaunted glories pass like smoke ! " George N. Lowe. 
 
 To some low forms of animal life a day represents an entire 
 lifetime. In one day an entire generation is born, flourishes, 
 and dies. 1 
 
 1 In some of the single-celled monera the average life of an individual is about 
 four minutes, so that there are 360 generations in a day of 24 hours. One of our 
 days is therefore equal to 12,000 years with them. 
 
SIZE, IMPORTANCE, SPEED, AND DURATION 287 
 
 Yet, to a man, a day seems a very short period of time 
 that gets still shorter as he advances in years. 
 
 To a youth who is just entering into life, seventy years seem 
 to make an almost endless stretch of time. There appear to be 
 hardly any limits to what may be accomplished in threescore- 
 and-ten long, long years. 
 
 But to the old man that life is little more than a dream 
 
 of high hopes unfulfilled of noble aspirations that have been 
 
 abandoned of great expectations that have come to nought 
 
 of tardy realisations that have turned to ashes in the 
 
 mouth. 
 
 In the lifetime of one individual many events take place 
 among men, many changes occur in the World on which he 
 lives. 
 
 Yet all the world-wide occurrences during such a lifetime 
 form but a page of that history which in Egypt and elsewhere 
 goes back more than 6,000 years. 
 
 Six thousand years of human activities almost becloud the 
 mind. Through the mists of antiquity the early actors loom 
 vague and vast. To the unenlightened they seem as Gods who 
 wield the thunderbolt, control the tempest, and forge the chains 
 of human destiny. 
 
 Yet 6,000 years form but a fragment of the history of man 
 as revealed by the study of his remains. The human family is 
 very, very ancient. So ancient indeed is it that many people 
 refuse to accept the evidence they cannot overthrow. 
 
 If we assume that 6,000 generations of men have lived on 
 this Earth and the time cannot have been much less than 
 that we are utterly bewildered when we endeavour to realise 
 such an abyss of time. 
 
 Yet such an interval is but a watch in the night when we 
 compare it with the vast geological periods intervening between 
 the dawn of life on Earth and the days when man first stood 
 erect on terra firma. It must have taken millions of years to 
 deposit the Carboniferous rocks alone, and they represent but a 
 small fragment of geologic time. 
 
288 HOW TO KNOW THE STARRY HEAVENS 
 
 Before the dawn of life on this globe there was a period 
 during which the first gaseous and then molten Earth was but 
 " a bare lurid ball in the vast wilds of space." During fathom- 
 less ages it slowly cooled off, till at last the surface became 
 solid, and the vaporous ocean above was no longer kept off the 
 blistering surface. 
 
 How long that period lasted we are utterly ignorant. For all 
 we know it may have exceeded geological times as geological 
 times exceeded the era of man. 
 
 Before the Earth was born as a gaseous centre of conden- 
 sation in a swirling mist, subsequently to shrink into a fiery 
 globe was a long, long period, during which a vast and shape- 
 less nebula turned into a flat and symmetrical indrawing spiral. 
 
 And before that shapeless nebula was, the Universe is. 
 
 As E. A. Proctor says : 
 
 " The whole duration of this Earth's existence is but as a single 
 pulsation in the mighty life of the Univer.se. Nay, the duration of 
 the Solar System is scarcely more. Countless other such systems 
 have passed through all their stages, and have died out, untold ages 
 before the Sun and his family began to be formed out of their mighty 
 nebula; countless others will come into being after the life has 
 departed from our system. Nor need we stop at solar systems, since 
 within the infinite Universe, without beginning and without end, not 
 suns only, but systems of suns, galaxies of such systems, to higher 
 and higher orders endlessly, have long since passed through all the 
 stages of their existence as systems, or have all these stages yet to 
 pass through." 
 
 It appears certain that matter and energy always existed and 
 always will exist. They were never created and will never be 
 destroyed. We have reason to believe that through all time 
 the Universe contains exactly the same number of corpuscles, 
 the same amount of energy. Suns and worlds come and go, 
 like bubbles, on the Eiver of Eternity. But the matter of 
 which they are composed endures for ever and ever. The 
 energy they contain neither waxes nor wanes. The one and 
 the other are eternal everlasting imperishable. Science 
 
SIZE, IMPORTANCE, SPEED, AND DURATION 289 
 
 teaches us that though the heavens change and the worlds 
 decay, neither a corpuscle of matter nor an iota of energy will 
 ever cease to exist. 
 
 SUMMARY 
 
 We thus see that size, importance, speed, and duration are 
 all relative terms, denoting attributes that are either great or 
 small according to the standpoint from which they are viewed. 
 
 The object of this work is to enable us to view all subjects 
 from as many different standpoints as possible, so that we may 
 not be deceived in the conclusions at which we arrive, about 
 the Universe in general and our World in particular ; about the 
 human race as a grand total, and an individual as a minute 
 fraction of it; about Eternity as a limitless whole, and our 
 Earth-measured years as microscopic parts thereof. 
 
 19 
 
CHAPTER XXY 
 
 CONCLUSION 
 
 "An undercut astronomer is mad." E. Young. 
 
 " Most of the religions of the world are more or less derived from Astronomy 
 in its astrological childhood. The majority of their deities were once identified 
 with the sun, moon, planets, or stars. Their temples, vestments, feasts, fasts, 
 ceremonies, and writings, contain multitudes of celestial fossils which only astrono- 
 mers can recognise and explain." A. Zazel. 
 
 "It is Astronomy which will eventually be the chief educator and emancipator 
 of the race." Sir Edwin Arnold. 
 
 I HAVE now finished an account that is little more than a bare 
 outline of what Science has to say about the Universe. Is 
 it not a wonderful story, even when poorly told ? Is it not a 
 sublime picture, though seen as through a glass, darkly ? 
 
 The astronomer of to-day is a cosmopolitan in the widest 
 sense of the word. He is a citizen of the Great Cosmos a 
 traveller on the Ocean of Space an explorer of what was but 
 yesterday an unknown Universe. Though he is physically a 
 prisoner on Earth, he is mentally free to roam through all the 
 mansions of the skies. Though he is but one of a multitude 
 of world-mites, he is the privileged spectator of the greatest of 
 all the dramas. Though he is but an ephemeron, he can watch 
 the mystic whirling of the myriad worlds through endless time 
 and space. In the grandest of all temples he can hear the 
 sublime " music of the spheres " echoing for ever through 
 the lofty aisles. From his celestial watch-towers he surveys 
 the wonders of " the house not made with hands, eternal in the 
 heavens." He stands before the INFINITE ; he contemplates the 
 ETERNAL. 
 
 The human race owes much more to astronomy and its kindred 
 sciences than it is aware of. All the production, transportation, 
 
CONCLUSION 291 
 
 and distribution of the necessaries of life are regulated by the 
 clock of the astronomer. Every train that crosses the conti- 
 nents with speed and safety does it through his observations. 
 Every ship that crosses the otherwise trackless oceans is guided 
 to port by his instruments and calculations. His predictions 
 of astronomical phenomena are published in the "Nautical 
 Almanac " several years before they occur, so that navigators 
 may be able to correct the errors of their chronometers in 
 whatever part of the World they may happen to be. 
 
 A single mistake in these predictions may bring death and 
 disaster in any part of the globe. An improved method of cal- 
 culation or observation may bring increased speed, certainty, 
 and safety to the commerce of all the World. 
 
 The science of human history is largely indebted to astron- 
 omy for the correction of its dates. .For some of the eclipses, 
 comets, etc., which are mentioned in ancient documents and 
 traditions, have been identified by calculating back, and the 
 exact dates have been ascertained. When these have once 
 been fixed, all the neighbouring dates can be adjusted to those 
 which have been ascertained astronomically. 
 
 Some departments of science appear, at first sight, to be 
 practically useless, because they have, or appear to have, no 
 direct bearing on the welfare of the race. Yet even these bring 
 indirect benefits which are too vast to be easily realised. Pure 
 science can be cultivated only for itself, but it forms the foun- 
 dation on which all practical science is based. Then the les- 
 sons that science teaches, on the art of getting at the truth, are 
 as valuable as its most practical discoveries and practicable 
 inventions. This is especially the case with astronomy. Even 
 the necessary ills of life are lessened by a knowledge of the 
 heavens, for in the presence of the illimitable and eternal Uni- 
 verse it seems absurd to worry about the little earthly troubles 
 that we cannot remedy. We learn to accept the inevitable and 
 make the best of it. 
 
 It may indeed be truthfully said that a fair knowledge of 
 astronomy and geology will double the pleasures of life and 
 
292 HOW TO KNOW THE STARRY HEAVENS 
 
 halve its troubles. At the same time it will entirely remove 
 the creed-made terrors of death. 
 
 There are not many of us who can do much toward gaining 
 fresh knowledge of the secrets of Nature. But there is no 
 reason why we should not enlighten, broaden, and refresh our- 
 selves by taking an interest in the scientific discoveries which 
 are revolutionising the world and revealing the Universe to 
 man. 
 
 The study of the Universe will not only make us enlightened 
 citizens of the Great Cosmos, but will also make us better citi- 
 zens of our own World. It will do this by teaching us to observe 
 correctly the surrounding social and economic phenomena, 
 instead of blindly trusting to the assertions of prejudiced and 
 perhaps interested persons. It will also train us to reason cor- 
 rectly and impartially as to the causes and effects of the 
 observed phenomena. We find ourselves, at the commence- 
 ment of the twentieth century, confronted by serious industrial, 
 economic, and social problems which demand solution at our 
 hands. These problems are largely the result of scientific 
 instruments of production and distribution, invented and 
 developed during the last two centuries. We cannot solve 
 these problems satisfactorily and equitably till we recognise 
 the fact that human progress is subject to evolution that it 
 is in fact ruled by natural laws just as inexorable as those 
 which govern suns and worlds. It is therefore necessary for 
 us to ascertain what these laws are, and then to solve our in- 
 dustrial and social problems in accordance with them. When 
 this is done, our wonderful advance in the arts and sciences 
 will be paralleled by as rapid an advance toward universal 
 prosperity and happiness. But not before. 
 
 NOTE. Those who wish to continue the study of the starry heavens will do 
 well to get the popular works of Airy, Ball, and Serviss; also Comstock's 
 " Text-book of Astronomy," which, at its close, gives a list of some of the best 
 works on astronomy, both general and special. 
 
CONCLUSION 293 
 
 ASTRONOMY 
 
 BY GEORGE N. LOWE 
 
 (By permission') 
 
 Great Antidote for ignorance and fears, 
 
 We look to thee to lead us to the day. 
 
 Before thy light the darkness melts away 
 Thy ceaseless labour Life's great pathway clears. 
 The shackles fall as pass the stately years, 
 
 Thy gaze uplifts, lo ! Yega's distant day 
 
 Comes, captive, where thy mystic colours play 
 The sombre gloom of ages disappears. 
 
 What though the thrones of false gods shake and fall, 
 
 Though useless, hoary, man-made creeds may fade ? 
 
 Calm Reason knows no sorrow, reck, or ruth. 
 
 Thy touch, Boon Science, liberates the thrall ; 
 
 Thy broadening beam illumes the unknown shade ; 
 
 Patient, thy finger pointeth to the Truth. 
 
APPENDIX A 
 
 FACTS AND FANCIES CONCERNING MATTER 
 
 " What is Matter ? Never mind. 
 What is Mind ? No matter." Old Queries. 
 
 " What is Matter ? Only a cloud of Corpuscles. 
 What are Corpuscles ? Only Electricity. 
 What is Electricity ? Only Matter. 
 What are they all ? No matter. Never mind ! " New Queries. 
 
 ONLY A ROCK 
 
 TAKE up a small rock in your hand and examine it care- 
 fully with the naked eye. 
 
 It appears to consist of a number of irregular granules, dif- 
 fering in size and shape, but alike in colour and texture. It is 
 only a piece of rock, rough, heavy, more or less hard and com- 
 pact, and altogether insignificant. 
 
 Such a rock might serve a teamster very well to throw at 
 his off leader, or a small boy might use it as a nucleus for a 
 vicious snow-ball, but otherwise it is of no value to man or 
 beast. 
 
 TWO STANDPOINTS 
 
 Yet these ideas concerning its insignificance are all owing 
 to the fact that we view it from a human standpoint, without 
 even the aid of science. 
 
 If we could examine it from the standpoint of one who 
 possessed the all-seeing eye popularly attributed to some of the 
 Gods, we should perhaps come to very different conclusions 
 concerning its size, condition, and importance. 
 
296 HOW TO KNOW THE STARRY HEAVENS 
 
 In order to do this, we shall have to increase our powers of 
 vision and analysis by resorting to the microscope and other 
 scientific instruments. 
 
 A MAGNIFIED ROCK 
 
 On applying a powerful magnifying-glass to the rock, we 
 find that it no longer appears small and insignificant. In fact 
 it is now so large that we can examine only a small part of it 
 at once. 
 
 Its granulated surface has swelled into rugged rock-masses 
 divided by narrow gulches and clefts. The surface of these 
 masses of rock has the same granulated appearance that the 
 whole rock had to the naked eye. 
 
 We will now select the smallest visible speck, and examine 
 it with the microscope. The result is that the speck, which 
 was almost invisible with the single magnifying-glass, is now 
 a huge mass of rocky hills separated by gloomy gorges. 
 
 On closely observing the rocks which compose these hills, we 
 see that the whole mass is honeycombed with crevices which 
 were invisible before. Each mighty rock is seen to be com- 
 posed of small granules loosely connected together. 
 
 A WORLD IN ITSELF 
 
 By vastly increasing the power of our microscope the hills 
 become mountain-chains whose lofty peaks extend away into 
 the remote distance. The stone which could be held in the 
 hand has become a world in itself, shutting out the firmament 
 from view. 
 
 Again and again we select the smallest visible granule, and 
 subject it to examination with higher magnifying power. 
 Each time we do so the almost invisible particle selected swells 
 into an enormous mass that fills the field of view. Each suc- 
 cessive particle is seen to consist of hills and gorges of more 
 or less solid rock, composed of scarcely visible granules. But 
 the substance of these granules is still the same as that com- 
 posing the whole rock. 
 
FACTS AND FANCIES CONCERNING MATTER 297 
 
 The magnifying powers of the most powerful microscope in 
 existence are at last exhausted. We have to continue our 
 examination by means of the spectroscope and other instru- 
 ments, and view the results of our investigations with the eye 
 of the imagination. 
 
 Confining ourselves to the smallest sub-granule revealed by 
 the most powerful microscope, we see it gradually unfold itself 
 as the magnifying power of the imagination is applied to it. 
 When it becomes too large for minute examination, we select 
 an almost invisible particle of it, and watch it grow till it fills 
 the entire field of view. Again and again we do the same 
 thing, each successive particle getting too large for inspection 
 as it swells under the scrutiny of the scientific imagination. 
 
 As this process goes on, we notice a progressive change, not 
 in the substance, but in the structure of what we are examining. 
 It slowly loses its original solid appearance and becomes a 
 dense nebulous haze. 
 
 MOLECULES 
 
 This haze gradually opens out, and finally resolves itself into 
 a universe of small separate bodies which are commonly known 
 as molecules. These appear to float in empty space without 
 touching one another. 
 
 ATOMS 
 
 As the magnifying power of our imagination goes on increas- 
 ing, each molecule is seen to be a group of shining atoms, 
 clinging together in " radical " bunches, yet avoiding actual 
 contact. These atoms are altogether different in appearance 
 and properties from the molecules which they compose. They 
 may be sorted out into several different species, the individual 
 atoms of each kind being all absolutely alike, but different in 
 size, weight, and other particulars from those of the other 
 species. 
 
 CAPTIVE CORPUSCLES 
 
 The question now arises, What are these different kinds of 
 atoms which constitute the molecules of which our rock is 
 
298 HOW TO KNOW THE STARRY HEAVENS 
 
 built up ? Are they single and indivisible, independent and 
 unrelated, or are they, too, composed of still smaller particles? 
 
 In order to decide this question we pick out a single atom in 
 one of the molecules and confine our attention to it exclusively. 
 At the same time we once more increase the separating power 
 of the imagination. 
 
 The atom now loses its indivisible character and is seen to 
 consist of a star-cluster of minute corpuscles. These appear to 
 have a regular orbital motion, at planetary distances, around 
 their centre of gravity. They are kept together, and yet 
 separate, by a combination of forces which is not yet under- 
 stood. 
 
 These sub-elementary corpuscles are all identical in form, 
 weight, and attributes. The only suspicion of difference is that 
 they act as though one half of them were positively, and the 
 other half negatively, electrified. They seem to cling together 
 in pairs and form alternate layers around the centre of the 
 cluster, the layers being far apart and sparsely occupied. 
 
 We now leave the atom we have just resolved into corpuscles, 
 and devote our attention to the other species of atoms which 
 build up the molecules of matter. They are all resolvable into 
 star-clusters of corpuscles which are exactly the same as those 
 which composed the atom first examined. The only difference 
 appears to be in the number and arrangement of the corpuscles 
 which compose the different kinds of atoms. The smallest 
 known atoms contain about a thousand corpuscles. 
 
 The outside layer of corpuscles in an atom appears to be 
 always composed of negatively electrified corpuscles, some of 
 which have the power of flitting from one atom to another, 
 and of flying off into space as free and independent corpuscles. 
 
 FREE CORPUSCLES 
 
 Besides the corpuscles which go to build up the various 
 atoms, there is an immense multitude of negatively electrified 
 corpuscles which exist in a free state. The atoms of matter 
 
FACTS AND FANCIES CONCERNING MATTER 299 
 
 move through this " dust-cloud " of free corpuscles as readily as 
 a sieve moves through water without displacing it. The other- 
 wise unoccupied space between the atoms of matter is filled to 
 saturation with these free negative particles, which carry the 
 vibrations of ponderable matter from one atom to another. 
 They form the luminiferous ether which fills all space. 
 
 ULTIMATE PARTICLES 
 
 We now seem to have at last reached a stage where all 
 matter is identical in substance, form, weight, appearance, and 
 properties. The ultimate particles of which matter is composed 
 appear to be revealed to the eyes of the imagination. But we 
 are still entirely in the dark as to the nature of these ultimate 
 and identical particles, and the reason why they group them- 
 selves as they do, to build up the atoms and molecules of 
 ponderable matter. We are now face to face with the unsolved 
 Riddle of the Universe. We are dealing with the mysterious 
 astronomy of the atoms. We have found the simple bricks out 
 of which the elaborate structures of the Universe are built, but 
 cannot tell whence, nor why, nor what they are. Even the 
 imagination has at last reached the limit of its power, and we 
 are hopelessly lost in trying to solve the great Problem of 
 Substance. 
 
 A TINY UNIVERSE 
 
 Now, for all we know to the contrary, the nebulous cloud of 
 matter we have been examining may be a Universe like ours. 
 Its molecules may be aggregations of atomic star-clusters like 
 those revealed by the telescope. Its electrical corpuscles may 
 be suns like ours, sending forth their radiant energy to invisible 
 worlds, some of which may be inhabited by unreasoning 
 creatures like man. 
 
 If such should be the case (and it would not be very easy to 
 disprove it), then an inhabitant of one of these invisible worlds 
 probably thinks that his Earth is the only one in existence ; 
 
300 HOW TO KNOW THE STARRY HEAVENS 
 
 that he is the one for whom all things were created ; that his 
 eternal well-being is the chief concern of the Creator ; and that 
 his moment of life is a big part of Eternity. 
 
 So much for the rock we have been studying. Let us now 
 throw it away and turn our attention to some of the more 
 pressing problems of lunar politics. 
 
 WHO KNOWS? 
 
 Yet before doing so I would like to ask, How do you know 
 that our mighty Universe is not a similar pebble on the shore 
 of some gigantic world ? It may seem to some that absurdity 
 could go no further than this suggestion. Yet it is a surmise 
 logically based on the generally accepted infra-atomic " star- 
 clusters" of our foremost scientists. As such I cheerfully 
 submit it to them for their prayerful consideration. If their 
 corpuscular theory of atoms is true and I should be the last 
 to deny it then this celestial application of it may be true 
 also. Or it may not. ^ Quien sale ? 
 
THE GREEK ALPHABET 301 
 
 APPENDIX B 
 
 THE GREEK ALPHABET 
 
 THE study of the Star Charts requires a knowledge of 
 the Greek alphabet. It is therefore printed here for 
 reference, with the name and sound of each letter. 
 
 GREEK 
 A a 
 
 B j3 
 
 r y 
 
 A d 
 
 E s or e 
 
 Z f 
 
 H r) 
 
 e #or 6 
 
 1 i 
 
 K K 
 
 A X 
 
 M 11 
 
 N v 
 
 * 
 O o 
 
 n TT 
 p P 
 
 2 a- or $ 
 T T 
 
 Y v 
 
 * 
 X 
 
 NAME 
 
 ENGLISH 
 
 Alpha 
 Beta 
 
 a 
 b 
 
 Gamma 
 Delta 
 
 g 
 d 
 
 Epsilon 
 Zeta 
 
 u 
 z 
 
 Eta 
 
 e 
 
 Theta 
 
 th 
 
 Iota 
 
 i 
 
 Kappa 
 Lambda 
 
 k 
 1 
 
 Mu 
 
 m 
 
 Nu 
 
 n 
 
 Xi 
 
 X 
 
 Omicron 
 
 6 
 
 Pi 
 Rho 
 
 P 
 r 
 
 Sigma 
 Tau 
 
 s 
 t 
 
 Upsilon 
 Phi 
 Chi 
 
 u 
 
 ph 
 
 ch 
 
 Psi 
 
 Omega 
 
 ps 
 o 
 
302 HOW TO KNOW THE STARRY HEAVENS 
 
 APPENDIX C 
 
 THE LUNAR CRATERS 
 EXPLANATION OF THE FIRST FOUR TABLES 
 
 THE number before the name of a crater indicates its place on 
 the charts. 
 
 The craters which have no number before them are lettered on 
 the charts. 
 
 Small odd numbers (1 to 81) indicate craters on the north half of 
 the western chart. 
 
 Large odd numbers (83 to 169) indicate craters on the south half 
 of the 'western chart. 
 
 Small even numbers (2 to 68) indicate craters on the north half of 
 the eastern chart. 
 
 Large even numbers (70 to 176) indicate craters on the south half 
 of the eastern chart. 
 
 The names in italics indicate craters near the centre of the lunar 
 disc. 
 
 The names in roman type indicate craters near the circumference 
 of the lunar disc. 
 
 Small numbers in parentheses, ( ), denote the diameter of the 
 crater in miles. 
 
 Large numbers in brackets, [ ], denote the extreme height of the 
 rampart (in feet) above the floor of the crater. 
 
 TABLE I 
 CRATERS ON THE NORTHWEST QUARTER OF THE MOON 
 
 [See Chart F] 
 
 1 Barrow (40) 
 
 3 Strabo 
 
 5 Aristoteles (60), [11,000] 
 
 7 Endymion (80) 
 
 9 Atlas (55), [11,000] 
 
 11 Hercules (46), [11,000] 
 
 13 Berg 
 
 15 Eudoxus (40) 
 
THE LUNAR CRATERS 
 
 303 
 
 17 Messala 
 
 19 Cassini (36), [4,000] 
 
 21 Gauss (110) 
 
 23 Berzelius 
 
 25 Thesetetus 
 
 27 Gemiims 
 
 29 Aristillus (34), [11,000] 
 Posidonius (60), [6,000] 
 
 31 Autolycus (23), [4,000] 
 
 33 Linne 
 
 35 Burckhardt 
 
 37 Tralles 
 
 39 Cleomenes (80), [10,000] 
 
 41 Roemer 
 
 43 Macrobius (40), [13,000] 
 
 45 Bessel 
 
 47 Maraldi 
 
 49 Sulpicius Gallus 
 
 51 Peirce 
 
 53 Vitruvius 
 
 Proclus 
 55 Alhazen 
 57 Dawes 
 
 Menelaus (20) 
 59 Hansen 
 61 Picard 
 
 Plinius (30), [6,000] 
 
 Manilius (25) 
 63 Condorcet 
 65 Julius Ccesar 
 67 Firmicus 
 69 Taruntius 
 71 Silberschlag 
 73 Hyginus 
 75 Ariadceus 
 77 Agrippa (30) 
 79 Triesnecker (20) 
 81 Godin (22) 
 
 TABLE II 
 CRATERS ON THE SOUTHWEST QUARTER OF THE MOON 
 
 [See Chart F] 
 
 83 Webb 
 
 85 Messier 
 
 87 Delambre 
 
 89 Hipparchus (100) 
 
 91 Hypatia 
 
 93 Langrenus (90), [10,000] 
 
 95 Torricelli 
 
 97 Taylor 
 
 99 Isadorus 
 
 101 Guttemberg (45) 
 
 103 Goclenius (28) 
 
 Theophilus (64), [18,000] 
 
 105 Cyrillus (60) 
 
 107 Albategnius (65), [15,000] 
 
 109 Abulfeda 
 
 111 Vendelinus 
 
 113 Catharina (65) 
 
 115 Almamon 
 
 117 Sacrobosco 
 
 119 Santbeck 
 
 121 Fracastorius 
 
 123 Apianus 
 
 125 Humboldt [16,000] 
 
 Petavius (78) 
 
 127 Pontanus 
 
 129 Werner (45) 
 
 131 Aliacensis [16,000] 
 
 133 Piccolomini [15,000] 
 
 135 Zagut 
 
 137 Reichenbach 
 
 139 Walter (100) 
 
 141 Lindenau 
 
 143 Gemma 
 
 145 Frisius 
 
 147 Neander 
 
 149 Rabbi Levi 
 
304 HOW TO KNOW THE STARRY HEAVENS 
 
 151 Stiborius 
 
 153 Furnerius 
 
 155 Rheita 
 
 157 Maurolycus (150), [14,000] 
 
 159 Stofler (110) 
 
 161 Fabricius 
 
 163 Clairaut 
 
 165 Pitiscus 
 
 167 Bacon 
 
 169 Curtius 
 
 TABLE III 
 CRATERS ON THE NORTHEAST QUARTER OF THE MOON 
 
 [See Chart E] 
 
 2 Philolaus 
 
 4 Pythagoras 
 
 6 Fontanelle 
 
 8 Condamine 
 
 Plato (60), [7,000] 
 
 10 Harpalus 
 
 12 Bianchini 
 
 14 Sharp 
 
 16 Leverrier 
 
 18 Helicon 
 
 20 Mairan 
 
 22 Herschel(17) 
 
 24 Gruithuisen 
 
 26 Lichtenberg 
 
 Archimedes (52), [4,000] 
 
 28 Delisle 
 
 30 Beer 
 
 32 Timocharis (23), [7,000] 
 
 34 Diophantus 
 
 36 Lambert (17) 
 
 38 Euler (19) 
 
 Aristarchus (28) 
 40 Herodotus 
 42 Pytheas 
 44 Tobias Mayer 
 46 Eratosthenes (37), [16,000] 
 48 Bessarion 
 50 Marius 
 52 Stadius 
 
 Copernicus (56), [12,000] 
 54 Galileo 
 
 Kepler (22) 
 56 Reiner 
 58 Schroeter 
 60 Reinhold 
 62 Kunowsky 
 64 Encke 
 66 Hevel 
 68 Gambert 
 
 TABLE IV 
 CRATERS ON THE SOUTHEAST QUARTER OF THE MOON 
 
 [See Chart E] 
 
 70 Landsberg 
 72 Mosting 
 74 Lalande 
 
 76 
 
 78 
 80 
 
 Fra Mauro 
 
 Parry 
 
 Bonpland 
 
_< 'Saiy o/ Ctt*apk< e 'Pit A 
 Rai * * 
 
 CHART E. EASTERN HALF OF MOON 
 
C=>c-_ C^> <-> 
 g? -J 
 
 ^ tA or i" ^^%^, 
 
 touViiL^K_\^^ 
 
 a ^.-V;P!S-.- .^i- 
 
 ^e-<ri 
 
 D> P P * 
 r> '/ g "? 
 
 ro p^ 
 
 <=4 W-* ,O ^ 
 
 ". -J13 '' n*, L * V 1 
 
 CHART F. WESTERN HALF OK MOON 
 
THE LUNAR CRATERS 
 
 305 
 
 82 Flamsteed 
 
 84 Damoiseau 
 Grimaldi (150) 
 
 86 Euclides 
 
 Ptolemy (115) 
 
 88 Guerike 
 
 90 Letronne 
 
 92 Hansteen 
 Alphons (83) 
 
 94 A Ipetragius 
 
 96 Lassell 
 
 98 Billy 
 
 Arzachel (65) 
 
 100 Gassendi (54) 
 
 102 Fontana 
 
 104 Thebit (30) 
 
 106 Birt 
 
 108 Nicollet 
 
 110 Bullialdus (38), 
 
 112 Agath archides 
 
 114 Mersenius (40) 
 
 116 Eichstadt 
 
 118 Purbach (60) 
 
 120 Regiomontanus 
 
 122 Pilatus 
 
 124 Mercator 
 
 126 Vitello (24) 
 
 128 Vieta 
 
 [8,000] 
 
 130 Hell 
 
 132 Cichus 
 
 134 Lexell 
 
 136 Ball 
 
 138 Capuanus 
 
 140 Lagrange 
 
 142 Lacroix 
 
 144 Piazzi 
 
 146 Bouvard 
 
 148 Heinsius 
 
 150 Saussure 
 
 Tycho (54), [17,000] 
 
 152 Hainzel 
 
 Schickard (134), [9,000] 
 
 154 Wilhelml. 
 
 156 Inghirami 
 
 158 Maginus (100) 
 
 Wargentin (53) 
 
 160 Longimontanus 
 
 162 Schiller 
 
 Clavius (140), [17,000] 
 
 164 Scheiner 
 
 166 Bettinus 
 
 168 Bailly 
 
 170 Kircher 
 
 172 Moretus 
 
 174 Casatus 
 
 176 Newton [24,000] 
 
 TABLE V 
 
 ALPHABETICAL LIST OF CRATERS 
 
 Abulfeda, 109 
 Agatharchides, 112 
 Agrippa, 77 
 Albategnius, 107 
 Alhazen, 55 
 Aliacensis, 131 
 Almamon, 115 
 Alpetragius, 94 
 Alphons 
 Apianus, 123 
 Archimedes 
 Ariadceus, 75 
 
 Aristarchus 
 Aristillus, 29 
 Aristoteles, 5 
 Arzachel 
 Atlas, 9 
 Autolycus, 31 
 
 Bacon, 167 
 Bailly, 168 
 Ball, 136 
 Barrow, 1 
 Beer, 30 
 
 20 
 
 Berzelius, 23 
 Bessarion, 48 
 Bessel, 45 
 Bettinus, 166 
 Bianchini, 12 
 Billy, 98 
 Birt, 106 
 Bonpland, 80 
 Bouvard, 146 
 Bullialdus, 110 
 Burckhardt, 35 
 Burg, 13 
 
306 HOW TO KNOW THE STARRY HEAVENS 
 
 Capuanus, 138 
 
 Hainzel, 152 
 
 Messala, 17 
 
 Casatus, 174 
 
 Hansen, 59 
 
 Messier, 85 
 
 Cassini, 19 
 
 Hansteen, 92 
 
 Moretus, 172 
 
 Catharina, 113 
 
 Harpalus, 10 
 
 Hosting, 72 
 
 Cichus, 132 
 
 Heinsius, 148 
 
 
 Clairaut, 163 
 
 Helicon, 18 
 
 Neander, 147 
 
 Clavius 
 
 Hell, 130 
 
 Newton, 176 
 
 Cleomenes, 39 
 
 Hercules, 11 
 
 Nicollet, 108 
 
 Condamini, 8 
 
 Herodotus, 40 
 
 
 Condorcet, 63 
 
 Herschel, 22 
 
 Parry, 78 
 
 Copernicus 
 
 Hevel, 66 
 
 Peirce, 51 
 
 Cur-tins, 169 
 
 Hipparchus, 89 
 
 Petavius 
 
 Cyrillus, 105 
 
 Humboldt, 125 
 
 Philolaus, 2 
 
 
 Hyginus, 73 
 
 Piazzi, 144 
 
 Damoiseau, 84 
 
 Hypatia, 91 
 
 Picard, 61 
 
 Dawes, 57 
 
 
 Piccolomini, 133 
 
 Delambre, 87 
 
 Inghirami, 156 
 
 Pilatus, 122 
 
 Delisle, 28 
 
 Isadorus, 99 
 
 Pitiscus, 165 
 
 Diophantus, 34 
 
 
 Plato 
 
 
 Julius Ccesar, 65 
 
 Plinius 
 
 Eichstadt, 116 
 
 
 Pontanus, 127 
 
 Encke, 64 
 
 Kepler 
 
 Posidonius 
 
 Endymion, 7 
 
 Kircher, 170 
 
 Proclus 
 
 Eratosthenes, 46 
 
 Kunowsky, 62 
 
 Ptolemy 
 
 Euclides, 86 
 
 
 Purbach, 118 
 
 Eudoxus, 15 
 
 Lacroix, 142 
 
 Pythagoras, 4 
 
 Euler, 38 
 
 Lagrange, 140 
 
 Pytheas, 42 
 
 
 Lalande, 74 
 
 
 Fabricius, 161 
 
 Lambert, 36 
 
 Rabbi Levi, 149 
 
 Firmicus, 67 
 
 Landsberg, 70 
 
 Regiomontanus, 120 
 
 Flamsteed, 82 
 
 Langrenus, 93 
 
 Reichenbach, 137 
 
 Fontana, 102 
 
 Lassell, 96 
 
 Reiner, 56 
 
 Fontanelle, 6 
 
 Letronne, 90 
 
 Reinhold, 60 
 
 Fracastorius, 121 
 
 Leverrier, 16 
 
 Rheita, 155 
 
 Fra Mauro, 76 
 
 Lexell, 134 
 
 Roemer, 41. 
 
 Frisius, 145 
 
 Lichtenberg, 26 
 
 
 Furnerius, 153 
 
 Lindenau, 141 
 
 Sacrobosco, 117 
 
 
 Linne, 33 
 
 Santbeck, 119 
 
 Galileo, 54 
 
 Longimontanus, 160 
 
 Saussure, 150 
 
 Gambert, 68 
 
 
 Scheiner, 164 
 
 Gassendi, 100 
 
 Macrobius, 43 
 
 Schickard 
 
 Gauss, 21 
 
 Maginus, 158 
 
 Schiller, 162 
 
 Geminus, 27 
 
 Mairan, 20 
 
 Schroeter, 58 
 
 Gemma, 143 
 
 Manilius 
 
 Sharp, 14 
 
 Goclenius, 103 
 
 Maraldi, 47 
 
 Silberschlag, 71 
 
 Godin, 81 
 
 Marius, 50 
 
 Stadius, 52 
 
 Grimaldi 
 
 Maurolycus, 157 
 
 Stiborius, 151 
 
 Gruithuisen, 24 
 
 Menelaus 
 
 Stofler, 159 
 
 Guerike, 88 
 
 Mercator, 124 
 
 Strabo, 3 
 
 Guttemberg, 101 
 
 Mersenius, 114 
 
 Sulpicius Gallus, 49 
 
THE LUNAR CRATERS 
 
 307 
 
 Taruntius, 69 
 Taylor, 97 
 Thesetetus, 25 
 Thebit, 104 
 Theophilus 
 Timocharis, 32 
 Tobias Mayer, 44 
 Torricelli, 95 
 
 Tralles, 37 
 Triesnecker, 79 
 Tycho 
 
 Vendelinus, 111 
 Vieta, 128 
 Vitello, 126 
 Vitruvius, 53 
 
 Walter, 139 
 Wargentiu 
 Webb, 83 
 Werner, 129 
 Wilhelm I, 154 
 
 Zagut, 135 
 
CHART G. THE C 
 
 Astrological He 
 to explain t 
 
 PERSIAN, JEW 
 
 RE 
 
 P&le Nord - - 
 
 North Pole. 
 
 Voye Lacte 
 
 Milky Way. 
 
 Hydre - - 
 
 Hydra. 
 
 Taureau 
 
 Taurus; Bull. 
 
 Orion ; Nemrod - 
 
 Orion ; Nimrod. 
 
 Gemeaus 
 
 Gemini. 
 
 Crab ou Cancer 
 
 Crab or Cancer 
 
 Bellier; Agneau de 
 
 Ram ; Lamb of God ; 
 
 Dieu 
 
 Aries. 
 
 Pers^e; Cherubin - 
 
 Perseus ; Cherubim. 
 
 Etable d'louseph 
 
 Joseph's Stable ; Auriga. 
 
 Lion - 
 
 Lion; Leo. 
 
 Nortnern Hemisphere. 
 
 Translation. 
 
 Ours ; Sanglier ; Ane ; 
 
 Typhon - 
 Poissons - 
 Andromede 
 Dragon des Hesperides 
 Vierge; Eve; Sybille; 
 
 Isis, &c. 
 
 Bootes; Adam; Osiris; 
 Couronne 
 Hercule 
 Serpent d'Eve ; Ahri- 
 
 man ; Satan 
 
 Bear ; Boar ; Ass ; 
 
 Typhon. 
 
 Pisces the Fishes. 
 Andromeda. 
 
 Dragon of the Hesperides 
 Virgin ; Eve ; Sybil ; 
 
 Isis, &c. 
 
 Bootes ; Adam ; Osiris. 
 Corona Borealis. 
 Hercules. 
 Eve's Serpent ; Ahri- 
 
 manes; Serpentinus. 
 
STELLATION FIGURES. 
 
 of the 
 of the Ancients 
 
 r yslertes of the 
 
 AND CHRISTIAN 
 ONS. 
 
 Southern Hemisphere. 
 
 Translation, 
 
 hien ; Sirius 
 
 Dog; Sirius. 
 
 Corbeau de No 
 
 Noah's Raven ; Corvus 
 
 ridan ... 
 
 Eridanus. 
 
 Verseau ... 
 
 Aquarius, the Water- 
 
 aleine ... 
 
 Whale ; Cetus. 
 
 
 bearer. 
 
 il - - - 
 
 Nile. 
 
 Capricorne 
 
 Capricornus. 
 
 oupe ... 
 
 Crab; Cup. 
 
 Sagittaire 
 
 Sagittarius, the Archer 
 
 aisseau ; Argo ; Arche 
 
 Vessel ; Argo ; Navis ; 
 
 Voye Lact6e 
 
 Milky Way. 
 
 
 Ark. 
 
 Scorpion - 
 
 Scorpio. 
 
 uiopus - 
 
 Canopus. 
 
 Balance 
 
 Scales; Libra. 
 
 .le Sud - - 
 
 South Pole. 
 
 
 
INDEX 
 
 ABSORPTION or STARLIGHT, 84 
 
 Absorption spectra, 92 
 
 Airy, Sir George, 26, 39 
 
 Aldebaran, 103 
 
 Algol, 108 
 
 Allen, Dr. F. J., 273 
 
 Alpha Centauri, 53, 78 
 
 Alpha Draconis, 147 
 
 Alphonso, King, 20 
 
 Alt-azimuth telescope, 153 
 
 Andromeda, nebula in, 122 
 
 Angles, measurement of, 31, 39 
 
 Angular diameter, 41 
 
 Aphelion, 160 
 
 Apocalypse, 17, 26, 239 
 
 Apparent motions, 4 
 
 Appearances, superficial, 1 
 
 Aratus, 118 
 
 Arc, chord of, 41 ; of circle, 40 
 
 Arc problems, 47 
 
 Aries, First Point of, 10, 148 
 
 Aristarchus, lunar crater, 264 
 
 Aristotle, 163 
 
 Ascension, right, 149 
 
 Asteroids, 29, 61, 64 
 
 Astronomy, Egyptian, 16; Greek, 16, 
 
 42 ; Hindu, 23, 43 
 Atomic theory, 192 
 Autumnal equinox, 7, 139 
 
 BALANCE, TORSION, 38 
 Base line, 31, 32, 34 
 Becquerel rays, 197 
 Bede, Venerable, 17 
 Beta Lyrae, 108 
 Bifrost, Bridge of, 87 
 Binaries, 108, 110 
 Blood discs, stack of, 73 
 Brahe, Tycho, 19 
 
 Bridge of Bifrost, 87 
 Byron, Lord, 188 
 
 CALCIUM FLOCCOLI, 130 
 
 " Canals " of Mars, 226 
 
 Cannon-ball, speed of, 71 
 
 Canopus, 104 
 
 Canopy theory, 16 
 
 Celestial distances, measurement of, 
 
 32 
 
 Celestial equator, 7, 119 
 Celestial latitude and longitude, 150 
 Chariot of imagination, 53, 136, 220 
 Chord of arc, 41 
 
 Chromosphere, or sierra, 60, 129 
 Circle, arc of, 40; meridian, 152 
 Clavius, lunar crater, 253 
 Clouds, Magellanic, 122 
 Clusters of stars, 1 1 1 
 Colliding stars, 110, 206, 237 
 Colours of stars, 98,111 
 Comets, 221 
 
 Comparisons, planetary, 69, 77 
 Constellations, 115, 137 
 Copernican system, 24 . 
 
 Copernicus, lunar crater, 263 
 Corona, 60, 131, 176 
 Corpuscles, or negative particles, 89, 199 
 Craters, lunar, 245, 253, 254, 264 
 Creation, 18 
 Creationism, 180 
 Crookes, Sir William, 179, 196 
 Crystal spheres, 18 
 
 DARK STARS, 107, 135 
 Darwin, Charles, 201 
 Darwin, George, 204, 213 
 Declination, north and south, 149 
 DeQuincey, Thomas, 77 
 
310 
 
 INDEX 
 
 Dipper, the, 14 
 
 Distances, estimating, 30 ; measurement 
 of celestial, 32 ; measurement of in- 
 accessible, 31, 43 ; of stars, 123 
 
 Distribution of stars and nebulae, 114, 
 121 
 
 Diurnal motion, 4 
 
 Double stars, 108, 110; spectroscopic, 
 108 
 
 Draco, 117 
 
 Draper, Dr. John W., 22, 156, 178, 265, 
 283 
 
 Drift, solar, 111 ; stellar, 113, 147 
 
 Duffield, Prof., 174 
 
 EARTH, 62, 69, 139 ; centre of system, 
 15 ; measuring the, 31 ; revolution of, 
 23, 138; rotation of, 23, 138; shape 
 of, 3 ; weight of, 38 
 
 " Ecclesiastes," 286 
 
 Eclipses, 11, 146 
 
 Ecliptic, 8, 9, 119, 138 
 
 Egyptian astronomy, 16 
 
 Electro-magnetic theory, Maxwell's, 
 195 
 
 Electronic theory, 200 
 
 Elements, in sun, 1 29 ; periodic system 
 of, 192 
 
 Ellipse, 158 
 
 Equator, celestial, 7, 119 
 
 Equatorial telescope, 12, 150 
 
 Equinoxes, 7, 139; precession of, 141, 
 174 
 
 Eros, 33 
 
 Estimating distances, 30 
 
 Ether, 89, 171, 191, 195 
 
 Evolution of organic life, 201, 274 
 
 Evolution of solar system, 208 
 
 Evolution, tidal, 202, 213 
 
 FACUL,E AND FLOCCULI, 127, 130 
 " Faust," Goethe's, 63 
 "Faustus," Marlowe's, 21, 136 
 Fibre, quartz, 75 
 Firmament, massive, 15, 16 
 Flames, solar, 59, 130, 176 
 Flat-world ideas, 15 
 Fleming, Prof. J. A., 190 
 
 Flocculi and facute, 127, 130 
 Fraunhofer, Joseph von, 194 
 
 GALAXY, the, 56, 120 
 
 Galileo, 169, 258; his laws of motion, 164 
 
 " Genesis," 15, 82, 87 
 
 George, Henry, 155, 163 
 
 Goethe's " Faust," 63 
 
 Gravitation, law of, 167 
 
 Great Bear, 14, 120 
 
 Great Pyramid, 147 
 
 Greek astronomy, 16, 42 
 
 HAECKEL, ERNST, 174, 207, 217 
 Helium, 197 
 
 Hercules, cluster in, 111 
 Herschel, Sir William, 185 
 Hindu astronomy, 23, 43 
 Holden, Dr. Edward S., 22 
 Human laws, 156 
 
 INERTIA, 164 
 
 "Jos," 17 
 
 Jupiter, 27, 64, 69, 233 
 
 KANT, IMMANUEL, 184 
 
 Kathode rays, 196 
 Keeler, Prof. James E., 122 
 Kepler, Johann, 258; Laws of, 157 
 Kinetic theory of substance, 194 
 Kirchhoff, Gustav R., 194 
 Koran, the, 17 
 
 LAND-SURVEYING, 31 
 
 Laplace, Pierre, 184 
 
 Latitude, celestial, 150 
 
 Lavoisier, Antoine L., 193 
 
 Law of gravitation, 167 
 
 Law of substance, 192 
 
 Laws, human, 156; of motion, 164; of 
 
 nature, 155 
 
 Life, evolution of organic, 201, 274 
 Light, refraction of, 89 ; speed of, 54, 
 
 72 
 Light waves, lengthening of, 84 ; violet, 
 
 73, 91 
 Light years, 68 
 
INDEX 
 
 311 
 
 Line of sight, motion in, 100 
 
 Locomotive, speed of, 84 
 
 Lodge, Sir Oliver, 200 
 
 Longitude, celestial, 150 
 
 Lowe, Geo. N., 85, 156, 286, 293 
 
 Lunar craters, 245, 253, 263, 264 
 
 Lunar mountains, 260 
 
 Lunar plains, 245 
 
 Luther, Martin, 23 
 
 Lyre, constellation of, 112 
 
 MAGELLANIC CLOUDS, 122 
 
 Magnitude, stellar, 102, 103 
 
 Marlowe's "Faustus," 21, 136 
 
 Mars, 27, 63, 69 ; " canals " of, 226 
 
 Mass and weight, 36 
 
 Massive firmament, 15, 16 
 
 Matter, 89, 191, 295; pyknotic theory 
 of, 195 
 
 Maunder, E. W., 118, 120 
 
 Maxwell's electro-magnetic theory, 
 195 
 
 Mayer, Robert, 193 
 
 Measurement, of angles, 31,39 ; of celes- 
 tial distances, 32 ; of inaccessible dis- 
 tances, 31, 43 ; of the earth, 31 
 
 Mercury, 27, 69 
 
 Meridian circle, 152 
 
 Meteorites, 220, 230 
 
 Meteors, 230 
 
 Midsummer solstice, 8 
 
 Milky Way, 56, 120 
 
 Millikan, R. A., 198 
 
 Milton, John, 53, 120, 223, 224, 243, 
 271 
 
 Mira Ceti, 108 
 
 Moon, the, 244; birth, 257; distance, 
 45; motions, 11, 23; size and mass, 
 35 
 
 Morris, George, 280 
 
 Motion, diurnal, 4 ; in line of sight, 
 100; laws of, 164; of sun, 6, 7 
 
 Motions, apparent, 4 
 
 Mural circle, 1 53 
 
 NADIR, 5 
 
 Nasmyth, James, 257 
 
 Nature, laws of, 155 
 
 Nebulae, 12 J -123; classes of, 97; dis- 
 tribution of stars and, 114, 121; 
 planetary, 97 
 
 Nebular hypothesis, 184, 207 
 
 Negative particles, 89, 199 
 
 Neptune, 66, 69 
 
 New stars, 109 
 
 Newcomb, Prof. Simon, 68, 77, 84, 114 
 
 Newton, Sir Isaac, 124, 162; his law of 
 gravitation, 167 
 
 North and south declination, 149 
 
 Nutation, 175 
 
 OBLIQUITY OF -ECLIPTIC, 8, 138 
 Organic life, evolution of, 201, 274 
 Orientation of pyramid, 147 
 Orion nebula, 123 
 
 PAPER, pile of, 72 ; roll of, 77 
 
 Parallax, 44 
 
 Particles, negative, 89, 199 
 
 Pascal, Blaise, 84 
 
 Passover, spring, 7, 139 
 
 Perihelion, 140, 160 
 
 Periodic system of elements, 192 
 
 Perturbations of planets, 171 
 
 Photographing stars, 83 
 
 Photosphere of sun, 59, 126 
 
 Planetary comparisons, 69, 77 
 
 Planetary nebulae, 97 
 
 Planets, 3, 61, 211; comparative dis- 
 tances, 27, 33, 77 ; density, mass, and 
 size, 35, 36 ; inferior and superior, 
 27, 28, 61 ; motions of, 11, 138; move 
 in ellipses, 29, 157 ; order of, 26 ; 
 perturbations of, 171; real distances 
 of, 29, 33, 68 
 
 Plato, lunar crater, 263 
 
 Pleiades, the, 103, 120 
 
 Pointers, the, 14 
 
 Polaris, 14, 103, 111 
 
 Pole-stars, different, 141, 147 
 
 Poles of rotation, 140 
 
 Precession of equinoxes, 141, 174 
 
 Prisms, 87 
 
 Proctor, Richard A., 85, 118, 124, 125, 
 288 
 
 Prominences, solar, 59, 130, 176 
 
312 
 
 INDEX 
 
 " Psalms," the, 57 
 Ptolemaic system, 1 8 
 Ptolemy, 42, 118 
 Pyknotic theory of matter, 195 
 Pyramid, the Great, 147 
 Pythagoras, 23 
 
 QUARTZ FIBRE, 75 
 
 RADIAL MOTIONS, 100 
 
 Radian, 40 
 
 Radiant energy of sun, 133 
 
 Radiation, spectrum, 92 
 
 Radium, 198 
 
 Radius vector, 160 
 
 Railroad to Neptune, 71 ; to nearest 
 
 star, 75 
 Rainbow, 87 
 
 Rays, Becquerel, 197 ; kathode, 196 
 Red light-waves, 91 
 Refraction of light, 89 
 Repulsion, 176 
 Reversing layer of sun, 129 
 Revolution of the earth, 23, 138 
 Revolving wheel, 75 
 Right Ascension, 149 
 Ring nebula in Lyra, 122 
 Rontgen rays, 196 
 Rotation, of the earth, 23, 138 ; of 
 
 planets, 138, 209; of sun, 129; poles 
 
 of, 140 
 
 SATELLITES, or Moons, 61, 62, 65 
 
 Saturn, 27, 64, 69 
 
 Schaeberli, Prof., 122 
 
 Schiaparelli, 266 
 
 " Seasons, The," 229 
 
 Seasons on the earth, 139 
 
 See, Dr. J. J., 84, 101 
 
 Serviss, Garrett P., 120 
 
 Shakespeare, 140 
 
 Shelley, Percy B., 57, 205 
 
 Shooting stars, 230 
 
 Sierra, or chromosphere, 60, 129 
 
 Sight, motion in line of, 100 
 
 Signs of zodiac, 10, 137 
 
 Sine of angle, 43 
 
 Sine problems, 49 
 
 Sirius, 68, 78, 103 
 
 Solar flames or prominences, 59, 130, 
 176 
 
 Solar system, drift of, 111 ; evolution 
 of, 208 
 
 Solstice, midsummer, 8; winter, 140 
 
 Spectroscope, 88, 194 
 
 Spectroscopic binaries, 108 
 
 Spectrum, 88 ; continuous, 92 ; of nebu- 
 lae, 96; stellar, 95; of star-clusters, 
 96 
 
 Spectrum, absorption, 92 
 
 Spectrum analysis, 93 
 
 Spectrum, emission, or radiation, 92 
 
 Spectrum, flash, of sun, 129 
 
 Spencer, Herbert, 201 
 
 Spheres, crystal, 18; umbrella, 4 
 
 Spider's thread, 74 
 
 Spiral nebulas, 98, 122 
 
 Spots in the sun, 127 
 
 Spring passover, 7, 139 
 
 Starlight, absorption of, 84 
 
 Stars, 3 ; beyond planets, 26 ; classes 
 of, 98; clusters of, 111; colliding, 
 110, 206, 237; colours of, 98, 111; 
 dark, 107, 135; distances of, 23; dis- 
 tribution of, 114, 121; double, 108, 
 110; drift of, 113, 147; magnitudes, 
 102, 103 ; nearest, 34, 68 ; new, 109 ; 
 number of, 82 ; photographing, 83 ; 
 telescopic, 83 ; trails, 13; variable, 
 107 ; visible, 55, 82 
 
 Steele, J. D., 167 
 
 Stellar drift, 113, 147 
 
 Sterling, George, 53, 84, 102, 109, 126, 
 205, 281, 282 
 
 Substance, law of, 192; theories of, 
 194, 195 
 
 Sun, annual motion, 7 ; bulk and mass, 
 37 ; chromosphere or sierra, 60, 129; 
 corona, 60, 131, 176 ; daily motion, 
 6 ; diameter, 35 ; distance, 32 ; ele- 
 ments in, 129; faculae and flocculi, 
 127, 130; flames, 59, 130, 176; inte- 
 rior, 125, 134 ; photosphere or visible 
 surface, 59, 126; prominences or 
 solar flames, 59, 130, 176; radiant 
 energy, 133 ; -reversing layer, 129; 
 rotation, 129; spots, 127 
 
INDEX 
 
 313 
 
 Suns, colliding, 110, 206, 237 
 Superficial appearances, 1 
 
 TELESCOPE MOUNTINGS, alt-azimuth, 
 153; equatorial, 12, 150; meridian 
 circle, 152 ; mural circle, 153 ; transit 
 instrument, 153 
 
 Telescopic stars, 83 
 
 Tele-spectroscope, 95 
 
 Tennyson, Alfred, 110 
 
 " Testimony of the Suns," 53, 84, 102, 
 109, 126, 205, 281, 282 
 
 Theophilus, lunar crater, 253 
 
 Thomson, Prof., 196 
 
 Thomson, James, " The Seasons," 229 
 
 Thread, quartz, 75 ; spider's, 74 ; a 
 strand of, 74 
 
 Tidal evolution, 202, 213 
 
 Time, difference in, 5, 12 
 
 Torsion balance, 38 
 
 Trails, star, 13 
 
 Transit instrument, 153 
 
 Triangulation, 31 
 
 Trifid Nebula, 123 
 
 Trigonometry, 39 
 
 Tycho Brahe, 19 
 
 UMBRELLA SPHERES, 4 
 
 Universes, outside, 86 
 Uranus, 66, 69 
 
 VARIABLE STARS, 107 
 
 Vega, 112 
 
 Venerable Bede, 17 
 
 Venus, 27, 69 
 
 Vernal equinox, 7, 139 
 
 Via Lactea, 120 
 
 Vibratory theory of substance, 195 
 
 Violet light- waves, 73, 91 
 
 WEIGHT AND MASS, 36 
 Wheel, revolving, 75 
 Winter solstice, 140 
 Wollaston, 194 
 
 YOUNG, PROF. CHARLES A., 131 
 
 Yule-tide solstice, 8 
 
 ZAZEL, A., ix. 219, 233, 242, 290 
 
 Zenith, 5 
 
 Zodiac, signs of the, 10, 137 
 
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