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diff --git a/77004-0.txt b/77004-0.txt new file mode 100644 index 0000000..dc71c0f --- /dev/null +++ b/77004-0.txt @@ -0,0 +1,10998 @@ + +*** START OF THE PROJECT GUTENBERG EBOOK 77004 *** + + + + + + [Illustration: HIPPARCHUS IN THE OBSERVATORY OF ALEXANDRIA.] + + + + + THE STORY + + OF THE + + SUN, MOON, AND STARS + + BY + + AGNES GIBERNE + + AUTHOR OF “THE STARRY SKIES,” “THE WORLD’S FOUNDATIONS,” + “RADIANT SUNS,” ETC. + + [Illustration] + + WITH COPIOUS ADDITIONS + + Fully Illustrated + + CINCINNATI + + NATIONAL BOOK COMPANY + + + + + COPYRIGHT, 1898, + BY J. T. JONES. + + + + +INTRODUCTION. + +BY CHARLES PRITCHARD, M. A., F. R. S., + +PROFESSOR OF ASTRONOMY IN THE UNIVERSITY OF OXFORD. + + +The pages of this volume on a great subject were submitted to my +criticism while passing through the press, with a request from a friend +that I would make any suggestions which might occur to me for its +improvement. Naturally, such a request was entertained, in the first +instance, with hesitation and misgiving. But after a rapid perusal +of the first sheet, I found my interest awakened, and then gradually +secured; for the book seemed to me to possess certain features of +no ordinary character, and, in my judgment, held out the promise of +supplying an undoubted want, thus enabling me to answer a question +which I have been often asked, and which had as often puzzled me, +to the effect, “Can you tell me of any book on astronomy suited to +beginners?” I think just such a book is here presented to the reader; +for the tale of the stellar universe is therein told with great +simplicity, and perhaps with sufficient completeness, in an earnest and +pleasant style, equally free, I think, from inaccuracy or unpardonable +exaggeration. We have here the outlines of elementary astronomy, +not merely detailed without mathematics, but to a very great extent +expressed in untechnical language. Success in such an attempt I regard +as a considerable feat, and one of much practical utility. + +For the science of astronomy is essentially a science of great +magnitude and great difficulty. From the time of Hipparchus, some +century and a half before the Christian era, down to the present +day, the cultivation of astronomy has severely taxed the minds of a +succession of men endowed with the rarest genius. The facts and the +truths of the science thus secured have been of very slow accretion; +but like all other truths, when once secured and thoroughly understood, +they are found to admit of very simple verbal expression, and to lie +well within the general comprehension, and, I may safely add, within +the sympathies of all educated men and women. + +Thus the great astronomers, the original discoverers of the last +twenty centuries, have labored, each in his separate field of the +vast universe of nature, and other men, endowed with other gifts, +have entered on their labors, and by systematizing, correlating, and +simplifying the expression of their results, have brought the whole +within the grasp of cultivated men engaged in other branches of the +varied pursuits of our complicated life. It is in this sort of order +that the amelioration and civilization of mankind have proceeded, and +at the present moment are, I hope and believe, rapidly proceeding. + +It was, I suspect, under this point of view, though half unconsciously +so, that my attention was arrested by the book now presented to the +reader; for we have here many of the chief results of the laborious +researches of such men as Ptolemy, Kepler, Newton, Herschel, +Fraunhofer, Janssen, Lockyer, Schiaparelli, and others--no matter +where accumulated or by whom recorded--filtered through the mind of +a thoughtful and cultured lady, and here presented to other minds in +the very forms wherein they have been assimilated and pictured in her +own. And these forms and pictures are true. It is in this way that the +intellectual “protoplasm” of the human mind is fostered and practically +disseminated. + +And, then, there is still another point of view from which this general +dissemination of great truths in a simple style assumes an aspect of +practical importance. I allude to the influences of this process on the +imaginative or poetic side of our complex nature. + +Wordsworth, in one of his prefaces, has stated so clearly the truth +on this subject that I can not do better than give his words. “If the +time should ever come,” he says, “when what is now science becomes +familiarized to men, then the remotest discoveries of the chemist, the +botanist, the mineralogist, will be as proper objects of the poet’s +art as any upon which it can be employed. He will be ready to follow +the steps of the man of science; he will be at his side, carrying +sensation into the midst of the objects of science itself. The poet +will lend his divine spirit to aid the transfiguration, and will +welcome the being thus produced as a dear and genuine inmate of the +household of man.” + +It is for reasons such as here stated that I heartily commend this +book to the attention of those who take an interest in the advancement +of the intellectual progress and culture of society. The story of the +Kosmos is told by the authoress in her own language and after her own +method. I believe, as I have said, the story is correct. + +OXFORD UNIVERSITY. + + + + +CONTENTS. + + + CHAPTER. PAGE. + + I. THE EARTH ONE OF A FAMILY, 13 + + II. THE HEAD OF OUR FAMILY, 24 + + III. WHAT BINDS THE FAMILY TOGETHER, 34 + + IV. THE LEADING MEMBERS OF OUR FAMILY.--FIRST + GROUP, 46 + + V. THE LEADING MEMBERS OF OUR FAMILY.--SECOND + GROUP, 55 + + VI. THE MOON, 62 + + VII. VISITORS, 73 + + VIII. LITTLE SERVANTS, 83 + + IX. NEIGHBORING FAMILIES, 95 + + X. OUR NEIGHBORS’ MOVEMENTS, 106 + + XI. MORE ABOUT THE SOLAR SYSTEM, 122 + + XII. MORE ABOUT THE SUN, 133 + + XIII. YET MORE ABOUT THE SUN, 148 + + XIV. MORE ABOUT THE MOON, 157 + + XV. YET MORE ABOUT THE MOON, 164 + + XVI. MERCURY, VENUS, AND MARS, 180 + + XVII. JUPITER, 199 + + XVIII. SATURN, 214 + + XIX. URANUS AND NEPTUNE, 225 + + XX. COMETS AND METEORITES, 240 + + XXI. MORE ABOUT COMETS AND METEORITES, 246 + + XXII. MANY SUNS, 267 + + XXIII. SOME PARTICULAR SUNS, 278 + + XXIV. DIFFERENT KINDS OF SUNS, 291 + + XXV. GROUPS AND CLUSTERS OF SUNS, 304 + + XXVI. THE PROBLEM OF SUN AND STAR DISTANCES, 310 + + XXVII. MEASUREMENT OF STAR DISTANCES, 320 + + XXVIII. THE MILKY WAY, 329 + + XXIX. A WHIRLING UNIVERSE, 337 + + XXX. READING THE LIGHT, 344 + + XXXI. STELLAR PHOTOGRAPHY, 355 + + XXXII. THE DAWN OF ASTRONOMY, 363 + + XXXIII. MODERN ASTRONOMY, 375 + + XXXIV. SIR ISAAC NEWTON, 382 + + XXXV. LATER ASTRONOMY, 393 + + + + +LIST OF ILLUSTRATIONS. + + + PAGE. + + Hipparchus in the Observatory at Alexandria _Frontispiece._ + + The Solar System 15 + + The Pleiades 19 + + Sun-spots 29 + + Phases of Mercury before Inferior Conjunction--Evening Star 50 + + Appearance of the Full Moon 63 + + One Form of Lunar Crater 69 + + The Earth as Seen from the Moon 71 + + Passage of the Earth and the Moon through the Tail of a Comet 76 + + Passage of the Comet of 1843 Close to the Sun 79 + + Meteor Emerging from Behind a Cloud 84 + + The Great Shower of Shooting-stars, November 27, 1872 90 + + Constellation of the Great Bear 108 + + The Great Bear 50,000 Years Ago 109 + + The Great Bear 50,000 Years Hence 109 + + Constellation of Orion as it Appears Now 110 + + Constellation of Orion 50,000 Years Hence 111 + + Position of Planets Inferior to Jupiter--Showing the Zone of the + Asteroids 123 + + Comparative Size of the Planetary Worlds 130 + + A Typical Sun-spot 135 + + A Solar Eruption 138 + + Sun-flames, May 3, 1892 143 + + Solar Corona and Prominence 152 + + Comparative Size of the Earth and Sun 155 + + The Moon--an Expired Planet 159 + + The Lunar Crater Copernicus 170 + + Lunar Eruption--Brisk Action 172 + + Lunar Eruption--Feeble Action 173 + + Nicolaus Copernicus 176 + + Phases of Venus 186 + + Mars and the Path of its Satellites 191 + + General Aspect of Jupiter--Satellite and its Shadow 200 + + Satellites of Jupiter Compared with the Earth and Moon 206 + + The System of Jupiter 208 + + Orbits of Nine Comets Captured by Jupiter 213 + + Saturn and the Earth--Comparative Size 215 + + Ideal View of Saturn’s Rings and Satellites from the Planet 222 + + Great Astronomers of Earlier Times 227 + + The Great Comet of 1811 247 + + Donati’s Comet, 1858 249 + + Great Comet of 1744 254 + + The First Comet of 1888--June 4 255 + + Great Comet of 1680 260 + + Great Comet of 1769 261 + + Baron Alexander Von Humboldt 264 + + A Telescopic Field in the Milky Way 270 + + Cygnus, Constellation of 279 + + Stars whose Distances are Best Known 281 + + Lyra, Constellation of 297 + + Constellations in the Northern Hemisphere 300 + + A Cluster of Stars in Centaurus 305 + + The Great Nebula in Andromeda, Compared with Size of the Solar + System 307 + + A Cluster of Stars in Perseus 332 + + Hercules, Constellation of 338 + + The Great Bear, Constellation of 341 + + The Prism and Spectrum 344 + + The Spectroscope 345 + + Spectra, Showing the Dark Lines 347 + + Great Astronomers of Later Times 377 + + Sir Isaac Newton 386 + + Eye-piece of Lick Telescope 407 + + Lick Observatory 409 + + Professor E. E. Barnard 410 + + + + +THE STORY + +OF THE + +SUN, MOON, AND STARS. + + +CHAPTER I. + +THE EARTH ONE OF A FAMILY. + + +What is this earth of ours? + +Something very great--and yet something very little. Something very +great, compared with the things upon the earth; something very little, +compared with the things outside the earth. + +And as our journeyings together are for a while to be away from earth, +we shall find ourselves obliged to count her as something quite small +in the great universe, where so many larger and mightier things are +to be found,--if indeed they are mightier. Not that we have to say +good-bye altogether to our old home. We must linger about her for a +while before starting, and afterwards it will be often needful to come +back, with speed swifter than the flight of light, that we may compare +notes on the sizes and conditions of other places visited by us. + +But first of all: what _is_ this earth of ours? + +It was rather a pleasant notion which men held in olden days, that +we--that great and important “We” which loves to perch itself upon +a height--stood firm and fixed at the very center of everything. The +earth was supposed to be a vast flat plain, reaching nobody could tell +how far. The sun rose and set for us alone; and the thousands of stars +twinkled in the sky at night for nobody’s good except ours; and the +blue sky overhead was a crystal covering for the men of our earth, +and nothing more. In fact, people seem to have counted themselves not +merely to have had a kind of kingship over the lower animals of our +earth, but to have been kings over the whole universe. Sun, stars, and +sky, as well as earth, were made for man, and for man only. + +This was the common belief, though even in those olden days there were +_some_ who knew better. But the world in general knows better now. + +Earth the center of the universe! Why, she is not that of even the +particular family in the heavens to which she belongs. For we do not +stand alone. The earth is one of a family of worlds, and that family is +called THE SOLAR SYSTEM. And so far is our earth from being the head of +the family, that she is not even one of the more important members. She +is merely one of the little sisters, as it were. + +Men not only believed the earth, in past days, to be at the center +of the universe; but also they believed her to remain there without +change. Sun, moon, stars, planets, sky, might move; but never the +earth. The solid ground beneath their feet, _that_ at least was firm. +Every day the sun rose and set, and every night the stars, in like +manner, rose and set. But this was easily explained. We on our great +earth stood firm and still, while sun, moon, stars, went circling +round us once in every twenty-four hours, just for our sole and +particular convenience. What an important personage man must have felt +himself then in God’s great universe! Once again, we know better now! + +[Illustration: THE SOLAR SYSTEM.] + +For it is the earth that moves, and not the sun; it is the earth that +moves, and not the stars. The daily movements of sun and stars, rising +in the east, traveling over the sky, and setting in the west, are +no more real movements on their part than, when we travel in a rail +way-train, the seeming rush of hedges, telegraph posts, houses, and +fields is real. They are fixed and we are moving; yet the movement +appears to us to be not ours but theirs. + +Still more strongly would this appear to be the case if there were no +noise, no shaking, no jarring and trembling, to make us feel that we +are not at rest. Sometimes when a train begins to move gently out of +a station, from among other trains, it is at the first moment quite +impossible to say whether the movement belongs to the train in which we +are seated or to a neighboring train. And in the motions of our earth +there is no noise, no shaking, no jarring--all are rapid, silent, and +even. + +If you were rising through the air in a balloon, you would at first +only know your own movement by seeing the earth seem to drop away from +beneath you. And just so we can only know the earth’s movements by +seeing how worlds around us _seem_ to move in consequence. + +When I speak of the Universe, I mean the whole of God’s mighty creation +as far as the stars reach. Sometimes the word is used in this sense, +and sometimes it is used only for a particular part of creation nearer +to us than other parts. At present, however, we will put aside all +thought of the second narrower meaning. + +The wisest astronomer living can not tell us how far the stars reach. +We know now that there is no firm crystal covering over our heads, +dotted with bright points here and there; but only the wide open sky +or heaven, containing millions of stars, some nearer, some farther, +some bright enough to be seen by us all, some only visible through a +telescope. + +People talk often of the stars being “set in space;” and the meaning of +“space” is simply “room.” Where you are must be space, or you could not +be there. But it is when we get away from earth, and travel in thought +through the wide fields of space, where God has placed his stars, that +we begin to feel how vast it is, and what specks we are ourselves--nay, +what a speck our very earth is, in this great and boundless creation. + +For there is no getting to the borders of space. As one telescope after +another is made, each one stronger in power and able to reach farther +than the last, still more and more stars are seen, and yet more and +more behind and beyond, in countless millions. + +It is the same all round the earth. The old notion about our world +being a flat plain has been long since given up. We know her now to be +a round globe, not fixed, but floating like the stars in space. + +When you look _up_ into the sky, you are looking exactly in the +opposite direction from where you would be looking _up_ if you were +in Australia. For Australia’s “up” is our “down,” and our “down” is +Australia’s “up.” Or, to put it more truly, “up” is always in the +direction straight away from this earth, on whatever part of it you may +be standing; and “down” is always towards the center of the earth. + +All round the globe, in north, south, east, west, whether you are in +Europe, Asia, Africa, or America, though you will see different stars +in certain different quarters of the earth, still overhead you will +find shining countless points of light. + +And now, what are these stars? This is a matter on which people are +often confused, and on which it is well to be quite clear before going +one step farther. + +Some of the stars you have most likely often noticed. The seven chief +stars of the Great Bear are known to a large number of people; and +there are few who have not admired the splendid constellation of Orion. +Perhaps you also know the W-shape of Cassiopeia, and the brilliant +shining of Sirius, and the soft glimmer of the Pleiades. + +The different constellations or groups of principal stars have been +watched by men for long ages past. They are called the fixed stars, for +they do not change. How many thousands of years ago they were first +arranged by men into these groups, and who first gave them their names, +we can not tell. + +True, night by night, through century after century, they rise, and +cross the sky, and set. But those are only seeming movements. Precisely +as the turning round of the earth upon her axis, once in every +twenty-four hours, makes the sun appear to rise and cross the sky and +set, in the day-time; so also the same turning of the earth makes the +stars appear to do the same in the night-time. + +There is another seeming movement among the stars, which is only in +seeming. Some come into view in summer which can not be seen in +winter; and some come into view in winter which can not be seen in +summer. For the sun, moving on his pathway through the sky, hides those +stars which shine with him in the day-time. The zodiac is an imaginary +belt in the heavens, sixteen or eighteen degrees wide, containing the +twelve constellations through which the sun passes. And as he passes +from point to point of his pathway, he constantly conceals from us +fresh groups of stars by day, and allows fresh groups to appear by +night. Speaking generally, however, the stars remain the same year +after year, century after century. The groups may still be seen as of +old, fixed and unchanging. + +[Illustration: THE PLEIADES.] + +What are these stars? Stars and planets have both been spoken about. +There is a great difference between the two. + +Perhaps if you were asked whether the sun is most like to a star or a +planet, you would be rather at a loss; and many who have admired the +brilliant evening star, Venus, often to be seen after sunset, would be +surprised to learn that the evening star is in reality no star at all. + +A star is a sun. Our sun is nothing more nor less than a star. Each one +of the so-called “fixed stars,” that you see shining at night in the +sky, is a sun like our sun; only some of the stars are larger suns and +some are smaller suns than ours. + +The main reason why our sun looks so much larger and brighter than the +stars is, that he is so very much nearer to us. The stars are one and +all at enormous distances from the earth. By and by we will go more +closely into the matter of their distance, compared with the distance +of the sun. + +At present it is enough to say that if many of the stars were placed +just as near to us as our sun is placed, they would look just as large +and bright; while there are some that would look a great deal larger +and brighter. And if our sun were to travel away from us, to the +distance of the very nearest of the little twinkling stars, he would +dwindle down and down in size and brilliancy, till at last we should +not be able to tell him apart from the rest of the stars. + +I have told you that the stars are called “fixed” because they keep +their places, and do not change from age to age. Though the movement +of the earth makes them seem all to sweep past every night in company, +yet they do not travel in and out among one another, or backwards +and forwards, or from side to side. At all events, if there be such +changes, they are so slow and so small as to be exceedingly difficult +to find out. Each group of stars keeps its own old shape, as for +hundreds of years back. + +But among these fixed stars there are certain stars which do go to and +fro, and backwards and forwards. Now they are to be seen in the middle +of one constellation, and now in the middle of another. These restless +stars were long a great perplexity. Men named them Planets or Wanderers. + +We know now that the planets are in reality not stars at all, and also +that they are not nearly so far away from us as the fixed stars. In +fact, they are simply members of our own family--the Solar System. They +are worlds, more or less like the world we live in; and they travel +round and round the sun as we do, each more or less near to him; and +they depend upon him for heat and light, in more or less the same +manner as ourselves. + +Therefore, just as our sun is a star, and stars are suns, so our earth +or world is a planet, and planets are worlds. EARTH is the name we +give to that particular world or planet on which we live. Planets may +generally be known from stars by the fact that they do not twinkle. +But the great difference between the two lies in the fact that a star +shines by its own radiant, burning light, whereas a planet shines +merely by light reflected or borrowed from the sun. + +But how were the earth and the other worlds made? Let us imagine an +immense gaseous mass placed in space. Attraction is a force inherent in +every atom of matter. The denser portion of this mass will insensibly +attract towards it the other parts, and in the slow fall of the more +distant molecules towards this more attractive region, a general motion +is produced, incompletely directed towards this center, and soon +involving the whole mass in the same motion of rotation. The simplest +form of all, even in virtue of this law of attraction, is the spherical +form. It is that which a drop of water takes, and a drop of mercury if +left to itself. + +The laws of mechanics show that, as this gaseous mass condenses and +shrinks, the motion of rotation of the nebula is accelerated. In +turning, it becomes flattened at the poles, and gradually takes the +form of an immense lens-shaped mass of gas. It has begun to turn so +quickly as to develop at its exterior circumference a centrifugal force +superior to the general attraction of the mass, as when we whirl a +sling. The inevitable consequence of this excess is a rupture of the +equilibrium, which detaches an external ring. This gaseous ring will +continue to rotate in the same time and with the same velocity; but +the nebulous mother will be henceforth detached, and will continue to +undergo progressive condensation and acceleration of motion. The same +feat will be reproduced as often as the velocity of rotation surpasses +that by which the centrifugal force remains inferior to the attraction. +It may have happened also that secondary centers of condensation would +be formed even in the interior of the nebula. + +In our system the rings of Saturn still subsist. + +The successive formation of the planets, their situation near the +plane of the solar equator, and their motions of translation round the +same center, are explained by the theory which we are discussing. The +most distant known planet, Neptune, would be detached from the nebula +at the epoch when this nebula extended as far as the planet, out to +nearly three thousand millions of miles, and would turn in a slow +revolution requiring a period of 165 years for its accomplishment. The +original ring could not remain in the state of a ring unless it was +perfectly homogeneous and regular; but such a condition is, so to say, +unrealizable, and it did not delay in condensing itself into a sphere. +Successively, Uranus, Saturn, Jupiter, the army of small planets, Mars, +would thus be detached or formed in the interior of this same nebula. +Afterwards came the earth, of which the birth goes back to the epoch +when the sun had arrived at the earth’s present position. Venus and +Mercury would be born later. Will the sun give birth to a new world? +This is not probable. + + + + +CHAPTER II + +THE HEAD OF OUR FAMILY. + + +People began very early in the history of the world to pay close +attention to the sun. And no wonder. We owe so much to his heat and +light that the marvel would be if men had not thought much about him. + +Was the sun really any larger than he looked, and if so, how much +larger was he? And what was his distance from the earth? These were two +of the questions which puzzled our ancestors the longest. If once they +could have settled exactly how far off the sun really was, they could +easily have calculated his exact size; but this was just what they +could not do. + +So one man supposed that the sun must be quite near, and very little +larger than he looked. Another thought he might be seventy-five miles +in diameter. A third ventured to believe that he was larger than the +country of Greece. A fourth was so bold as to imagine that he might +even outweigh the earth herself. + +After a while many attempts were made to measure the distance of the +sun; and a great many different answers to this difficult question +were given by different men, most of them very wide of the mark. It +is only of late years that the matter has been clearly settled. And, +indeed, it was found quite lately that a mistake of no less than three +millions of miles had been made, notwithstanding all the care and all +the attention given. But though three millions of miles sounds a great +deal, yet it is really very little--only a tiny portion of the whole. + +For the distance of the sun from the earth is no less than about +NINETY-THREE MILLIONS OF MILES. Ninety-three millions of miles! Can +you picture that to yourself? Try to think what is meant by a thousand +miles. Our earth is eight thousand miles in diameter. In other words, +if you were to thrust a gigantic knitting-needle through her body, +from the North Pole to the South Pole, it would have to be about eight +thousand miles long. + +To reach the thought of one million, you must picture _one thousand +times one thousand_. Our earth is about twenty-five thousand miles +round. If you were to start from the mouth of the River Amazon, in +South America, and journey straight round the whole earth on the +equator, till you came back to the same point, you would have traveled +about twenty-five thousand miles. But that would be a long way off from +a million miles. You would have gone only once round the earth. Now a +cord one million miles in length could be wrapped, not once only, but +_forty times_, round and round the earth. And when you have managed +to reach up to the thought of one million miles, you have then to +remember that the sun’s distance is ninety-three times as much again. +So, to picture clearly to ourselves the actual meaning of “ninety-three +millions of miles” is not so easy. + +Suppose it were possible to lay a railroad from here to the sun. If +you could journey thither in a perfectly straight line, at the rate +of thirty miles an hour, never pausing for one single minute, night or +day, you would reach the sun in about three hundred and forty-six years. + +Thirty miles an hour is a slow train. Suppose we double the speed, and +make it an express train, rushing along at the pace of sixty miles +an hour. Then you might hope to reach the end of your journey in one +hundred and seventy-three years. If you had quitted this earth early in +the eighteenth century, never stopping on your way, you would be, just +about now, near the end of the nineteenth, arriving at the sun. + +So much for the sun’s distance from us. Now as to his size. + +I have already mentioned that our earth’s diameter--that is, her +_through measure_, as, for instance, the line drawn straight from +England through her center to New Zealand--is about eight thousand +miles. This sounds a good deal. But what do you think of the diameter +of the sun being no less than _eight hundred and fifty-eight thousand +miles_? The one is eight thousand miles, the other over eight hundred +thousand! + +Suppose you had a long slender pole which would pass through the middle +of the earth, one end just showing at the North Pole and the other at +the South Pole. You would need more than a hundred and eight of such +poles, all joined together, to show the diameter of the sun. + +The sun seems not to be made of nearly such heavy materials as the +earth. He is what astronomers call less “dense,” less close and compact +in his make, just as wood is less dense and heavy than iron. Still, +his size is so enormous, that if you could have a pair of gigantic +scales, and put the sun into one scale and the earth with every one of +her brother and sister planets into the other, the sun’s side would go +down like lightning. He would be found to weigh seven hundred and fifty +times as much as all the rest put together. And, it would take more +than twelve hundred thousand little earths like ours, rolled into one +huge ball, to make a globe as large as the sun. + +In the beginning of the seventeenth century a man named Fabricius was +startled by the sight of a certain black spot upon the face of the +sun. He watched till too dazzled to look any longer, supposing it to +be a small cloud, yet anxious to learn more. Next day the spot was +there still, but it seemed to have moved on a little way. Morning after +morning this movement was found to continue, and soon a second spot, +and then a third spot, were observed creeping in like manner across +the sun. After a while they vanished, one at a time, round his edge, +as it were; but after some days of patient waiting on the part of the +lookers-on, they appeared again at the opposite edge, and once more +began their journey across. + +Fabricius seems to have been the first, but he was not the last, to +watch sun-spots. Many astronomers have given close attention to them. +Modern telescopes, and the modern plan of looking at the sun through +darkened glass, have made this possible in a way that was not possible +two or three hundred years ago. + +The first important discovery made through the spots on the sun, was +that the sun turns round upon his axis, just in the same manner that +the earth turns round upon hers. Instead of doing so once in the course +of each twenty-four hours, like the earth, he turns once in the course +of about twenty-five days. + +It must not be supposed that the spots seen now upon the sun are the +same spots that Fabricius saw so long ago. There is perpetual change +going on; new spots forming, old spots vanishing; one spot breaking +into two, two spots joining into one, and so on. Even in a single hour +great alterations are sometimes seen to take place. + +Still, many of the spots do remain long enough and keep their shapes +closely enough to be watched from day to day, and to be known again as +old friends when they reappear, after being about twelve days hidden on +the other side of the sun. So that the turning of the sun upon his axis +has become, after long and careful examination, a certain known fact. + +For more than thirty years one astronomer kept close watch over the +spots on every day that it was possible to see the sun. Much has been +learned from his resolute perseverance. + +Now what are these spots? + +One thing seems pretty sure, and that is that they are caused by some +kind of tremendous storms or cyclones taking place on the surface of +that huge ball of fire. + +[Illustration: SUN SPOTS.] + +The first attentive observer of the sun, Scheiner, at first regarded +the spots as satellites--an indefensible opinion, which, however, +some have attempted to revive. Galileo attributed them to clouds or +vapors floating in the solar atmosphere; this was the best conclusion +which could be drawn from the observations of that epoch. This opinion +met for a long time with general approval; it has even been renewed +in our day. Some astronomers, and among them Lalande, believed, on +the contrary, that they were mountains, of which the flanks, more +or less steep, might produce the aspect of the penumbra--an opinion +irreconcilable with the proper motion which the spots sometimes possess +in a very marked manner. It is not usual, in fact, to see mountains +traveling. Derham attributed them to the smoke issuing from the +volcanic craters of the sun, an opinion revived and maintained in +recent times by Chacornac. Several _savants_, regarding the sun as a +liquid and incandescent mass, have also explained the spots by immense +cinders floating on this ocean of fire. But a century had scarcely +elapsed after the epoch when the spots were observed for the first +time, when an English astronomer, Wilson, showed with certainty that +the spots are hollow. + +We do not know with any certainty whether the sun is through and +through one mass of glowing molten heat, or whether he may have a solid +and even cool body within the blazing covering. Some have thought the +one, and some the other. We only know that he is a mighty furnace of +heat and flame, beyond anything that we can possibly imagine on our +quiet little earth. + +It seems very sure that no such thing as “quietness” is to be found on +the surface of the sun. The wildest and fiercest turmoil of rushing +wind and roaring flame there prevails. The cyclones or hurricanes which +take place are sometimes so rapid and so tremendous in extent, tearing +open the blazing envelope of the sun, and showing glimpses of fiery +though darker depths below, that we, on our far-distant earth, can +actually watch their progress. + +Astronomers speak of the “quivering fringe of fire” all around the edge +of the sun, visible through telescopes. But the sun is perpetually +turning on his axis, so that each hour fresh portions of his surface +thus pass the edge, showing the same appearance. What conclusion +can we come to but that the whole enormous surface of the sun is one +restless, billowy sea of fire and flame? + +It sounds to us both grand and startling to hear of the mighty +outbreaks from Mount Vesuvius, or to read of glowing lava from a +volcano in Hawaii pouring in one unbroken stream for miles. + +But what shall be thought of rosy flames mounting to a height of fifty +or a hundred thousand miles above the edge of the sun? What shall be +thought of a tongue of fire long enough to fold three or four times +round our solid earth? What shall be thought of the awful rush of +burning gases, sometimes seen, borne along at the rate of one or two or +even three hundred miles in a single second across the sun’s surface? +What shall be thought of the huge dark rents in this raging fiery +ocean, rents commonly from fifty to one hundred thousand miles across, +and not seldom more? + +Fifty thousand miles! A mere speck, scarcely visible without a +telescope; yet large enough to hold seven earths like ours flung in +together. The largest spot measured was so enormous that eighteen +earths might have been arranged in a row across the breadth of it, like +huge boulders of rock in a mountain cavern; and to have filled up the +entire hole about one hundred earths would have been needed. + +It is well to grow familiar with certain names given by astronomers to +certain parts of the sun. + +The round shining disk or flat surface, seen by all of us, is called +the _photosphere_, or “light-sphere.” It has a tolerably well-defined +edge or “limb,” and dazzles the eye with its intense brightness. + +Across the photosphere the spots move, sometimes many, sometimes +few, in number. Besides the dark spots, there are spots of extreme +brilliancy, standing out on even that dazzling surface, which causes +a piece of white-hot iron to look black and cold by contrast. These +extra-radiant spots which come and go, and at times change with great +rapidity, are named _faculæ_--a Latin word meaning “torches.” + +At the edge of the photosphere astronomers see what has been already +mentioned, that which is sometimes called the _chromotosphere_, which +one has named “the _sierra_,” and which another has described as “a +quivering fringe of fire.” The waves of the sea, on a stormy day, seen +in the distance rising and breaking the horizon-line, may serve as an +illustration; only in the sun the waves are of fire, not water. What +must their height be, to be thus visible at a distance of ninety-three +millions of miles? + +Outside the _sierra_ are seen, at certain seasons, bright, +“rose-colored prominences” or flames of enormous height. During an +eclipse, when the dark body of the moon comes between the sun and us, +exactly covering the photosphere, these red tips stand out distinctly +beyond the edge of sun and moon. Their changes have been watched, and +their height repeatedly measured. Some are so lofty that ten little +earths such as ours might be heaped up, one upon another, without +reaching to their top. Whether they are in character at all like the +outbursts from our own volcanoes it is hard to say. To compare the +two would be rather like comparing a small kitchen fire with a mighty +iron-smelting furnace. The faculæ, the sierra, and the prominences are +visible only through a telescope. + +Outside these red flames or “prominences” is the corona, commonly +divided into the inner and outer coronas. + +Many different explanations have been offered of this beautiful crown +of light round the sun, plainly visible to the naked eye during an +eclipse. But here again we know little, and must be content to watch +and wait. + + + + +CHAPTER III. + +WHAT BINDS THE FAMILY TOGETHER? + + +What is it which binds together all the members of the Solar System? +Ah, what? Why should not the sun at any moment rush away in one +direction, the earth in a second, the planets in half a dozen others? +What is there to hinder such a catastrophe? Nothing--except that +they are all held together by a certain close family tie; or, more +correctly, by the powerful influence of the head of the family. + +This mysterious power which the sun has, and which all the planets +have also in their smaller degrees, is called Attraction. Sometimes +it is named Gravitation or Gravity. When we speak, as we often do, +of the _law_ of attraction or gravitation, we mean simply this--that +throughout the universe, in things little and great, is found a certain +wonderful _something_, in constant action, which we call a “law.” What +the “something” may be, man can not tell; for he knows it only by its +effects. But these effects are seen everywhere, on all sides, in the +earth and in the universe. It is well named in being called a “law;” +for we are compelled to obey it. None but the Divine Lawgiver who made +this law can for a single moment suspend its working. + +What causes an apple to fall to the ground when it drops from the +branch? Why should it not, instead, rise upwards? Because, of course, +it is heavy, or has weight. But what _is_ weight? Simply this--that +the earth draws or drags everything downwards towards herself by the +power of attraction. Every substance, great or small, light or heavy, +is made up of tiny atoms. Each one of these atoms attracts or draws all +the other atoms towards itself; and the closer they are together, the +more strongly they pull one another. + +The atoms in a piece of iron are much closer than the atoms in a piece +of wood; therefore the iron is called the “more _dense_” of the two, +and its weight or “mass” is greater. The more closely the atoms are +pressed together, the greater the number of them in a small space, and +the more strong the drawing towards the earth; for the earth draws each +one of these atoms equally. That is only another way of saying that +a thing is “heavier.” If you drop a stone from the top of a cliff, +will it rise upwards or float in the air? No, indeed. The pull of the +earth’s attraction, dragging and still dragging downward, makes it rush +through the air, with speed quickening each instant, till it strikes +the ground. Every single atom in every single body _pulls_ every other +atom, whether far or near. The nearer it is, the stronger always the +pulling. + +We do not always feel this, because the very much greater attraction of +the earth hides--or smothers, as we may say--the lesser attraction of +each small thing for another. But though you and I might stand side by +side upon earth, and feel no mutual attraction, yet if we could mount +up a few thousands of miles, far away from earth, and float in distant +space, there we should find ourselves drawn together, and unable to +remain apart. + +Now precisely as an apple falling from a tree and a stone dropping +from a cliff are dragged downward to the earth, just so our earth and +all the planets are dragged downwards towards the sun and towards each +other. The law of the earth’s attraction of all objects on its surface +to itself was indistinctly suspected a very long time ago; but it was +the great Newton who first discovered that this same law was to be +found working among the members of the whole Solar System. The sun +attracts the earth, and the earth attracts the sun. But the enormous +size of the sun compared with our earth--like a great nine-foot globe +beside a tiny one-inch ball--makes our power of attraction to be quite +lost sight of in his, which is so much greater. + +The principle of gravitation is of far wider scope than we have yet +indicated. We have spoken merely of the attraction of the earth, and +we have stated that its attraction extends throughout space. But the +law of gravitation is not so limited. Not only does the earth attract +every other body, and every other body attract the earth, but each of +these bodies attracts each other; so that, in its more complete shape, +the law of gravitation announces that “every body in the universe +attracts every other body with a force which varies inversely as the +square of the distance.” It is impossible for us to overestimate the +importance of this law. It supplies the clue by which we can unravel +the complicated movements of the planets. It has led to marvelous +discoveries, in which the law of gravitation has enabled us to +anticipate the telescope, and, indeed, actually to feel the existence +of bodies before those bodies have even been seen. + +We come now to another question. If the sun is pulling with such power +at the earth and all her sister planets, why do they not fall down upon +him? What is to prevent their rolling some day into one of those deep +rents in his fiery envelope? Did you ever tie a ball to a string, and +swing it rapidly round and round your head? If you did, you must have +noticed the steady outward pull of the ball. The heavier the ball, and +the more rapid its whirl, the stronger the pull will be. Let the string +slip, and the rush of the ball through the air to the side of the room +will make this yet more plain. Did you ever carry a glass of water +quickly along, and then, on suddenly turning a corner, find that the +water has not turned with you? It has gone on in its former direction, +leaving the glass, and spilling itself on the floor. + +The cause in both cases is the same. Here is another “law of nature,” +so-called. Though we can neither explain nor understand why and how +it is so, we see it to be one of the fixed rules of God’s working in +every-day life throughout his universe. The law, as we see it, seems +to be this: Everything which is at rest must remain at rest, until +set moving by some cause outside of, or independent of itself; and +everything which is once set moving, must continue moving in a straight +line until checked. + +According to this a cannon-ball lying on the ground ought to remain +there until it is set in motion; and, once set in motion by being fired +from a cannon, it ought to go on forever. Exactly so--if nothing +stops it. But the earth’s attraction draws the cannon-ball downward, +and every time it strikes the ground it is partly checked. Also each +particle of air that touches it helps to bring it to rest. If there +were no earth and no air in the question, the cannon-ball might rush on +in space for thousands of years. + +Why did the water get spilled? Because it necessarily continued moving +in a straight line. Your sudden change of direction compelled the solid +glass to make the same change, but the liquid water was free to go +straight on in its former course; so it obeyed this law, and _did_ go +on. Why did the ball pull hard at the string as you swung it round? +Because at each instant it was striving to obey this same law, and to +rush onward in a straight line. The pull of the string was every moment +fighting against that inclination, and forcing the ball to move in a +circle. + +Just such is the earth’s movement in her yearly journey round the sun. +The string holding in the ball pictures the sun’s attraction holding +in the earth. The pulling of the ball outward in order to continue +its course in a straight line, pictures the pulling of our earth each +moment to break loose from the sun’s attraction and to flee away into +distant space. + +For the earth is not at rest. Each tick of the clock she has sped +onward over more than eighteen miles of her pathway through the sky. +Every instant the sun is dragging, with the tremendous force of his +attraction, to make her fall nearer to him. Every instant the earth is +dragging with the tremendous force of her rapid rush, to get away from +him. These two pullings so far balance each other, or, more strictly, +so far combine together, that between the two she journeys steadily +round and round in her nearly circular orbit. + +If the sun pulled a little harder she would need to travel a little +faster, or she would gradually go nearer to him. If the earth went +faster, and the sun’s attraction remained the same as it is now, she +would gradually widen her distance. Indeed, it would only be needful +for the earth to quicken her pace to about five-and-twenty miles a +second, the sun’s power to draw her being unchanged, and she would then +wander away from him for ever. Day by day we on our earth should travel +farther and farther away, leaving behind us all light, all heat, all +life, and finding ourselves slowly lost in darkness, cold, and death. + +For what should we do without the sun? All our light, all our warmth, +come from him. Without the sun, life could not exist on the earth. +Plants, herbage, trees, would wither; the waters of rivers, lakes, +oceans, would turn to masses of ice; animals and men would die. Our +earth would soon be one vast, cold, forsaken tomb of darkness and +desolation. + +We may not think so, but everything which moves, circulates, and lives +on our planet is the child of the sun. The most nutritious foods come +from the sun. The wood which warms us in winter is, again, the sun in +fragments. Every cubic inch, every pound of wood, is formed by the +power of the sun. The mill which turns under the impulse of wind or +water, revolves only by the sun. And in the black night, under the rain +or snow, the blind and noisy train, which darts like a flying serpent +through the fields, rushes along above the valleys, is swallowed up +under the mountains, goes hissing past the stations, of which the pale +eyes strike silently through the mist,--in the midst of night and cold, +this modern animal, produced by human industry, is still a child of the +sun. The coal from the earth which feeds its stomach is solar work, +stored up during millions of years in the geological strata of the +globe. + +As it is certain that the force which sets the watch in motion is +derived from the hand which has wound it, so it is certain that all +terrestrial power proceeds from the sun. It is its heat which maintains +the three states of bodies--solid, liquid, and gaseous. The last +two would vanish, there would be nothing but solids; water and air +itself would be in massive blocks,--if the solar heat did not maintain +them in the fluid state. It is the sun which blows in the air, which +flows in the water, which moans in the tempest, which sings in the +unwearied throat of the nightingale. It attaches to the sides of the +mountains the sources of the rivers and glaciers, and consequently the +cataracts and the avalanches are precipitated with an energy which +they draw directly from him. Thunder and lightning are in their turn +a manifestation of his power. Every fire which burns and every flame +which shines has received its life from the sun. And when two armies +are hurled together with a crash, each charge of cavalry, each shock +between two army corps, is nothing else but the misuse of mechanical +force from the same star. The sun comes to us in the form of heat, +he leaves us in the form of heat; but between his arrival and his +departure, he has given birth to the varied powers of our globe. + +I have spoken before about the old-world notion that our earth was a +fixed plain, with the sun circling round her. When the truth dawned +slowly upon some great minds, anxious only to know what really was the +truth, others made a hard struggle for the older and pleasanter mode +of thinking. It went with many sorely against the grain to give up all +idea of the earth being the chief place in the universe. Also there was +something bewildering and dizzying in the notion that our solid world +is never for one moment still. But truth won the victory at last. Men +consented slowly to give up the past dream, and to learn the new lesson +put before them. + +We still talk of the sun rising and setting, and of the stars doing the +same. This is, however, merely a common form of speech, which means +just the opposite. For instead of the sun and stars moving, it is the +earth which moves. + +The earth has two distinct movements. Indeed, I ought to say that she +has three; but we will leave all thought of the third for the present. +First, she turns round upon her axis once in every twenty-four hours. +Secondly, she travels round the sun once in about every three hundred +and sixty-five days and a quarter. No wonder our ancestors were +startled to learn that the world, which they had counted so immovable, +was perpetually spinning like a humming-top, and rushing through space +like an arrow. + +You may gain some clear notions as to the daily rising and setting of +our sun, with the help of an orange. Pass a slender knitting-needle +through the orange, from end to end, and hold it about a yard distant +from a single candle in a room otherwise darkened. Let the needle or +axis slant somewhat, and turn the orange slowly upon it. + +The candle does not move; but as the orange turns, the candle-light +falls in succession upon each portion of the yellow rind. Half of the +orange is always in shade, and half is always in light; while at either +side, if a small fly were standing there, he would be passing round out +of shade into candle-light, or out of candle-light into shade. + +Each spot on our earth moves round in turn into half-light, full-light, +half-light, and darkness; or, in other words, has morning-dawn, +midday-light, evening twilight, and night. Each spot on our earth would +undergo regularly these changes every twenty-four hours throughout the +year, were it not for another arrangement which so far affects this +that the North and South Poles are, by turns, cut off from the light +during many months together. + +Thus the sun is in the center of the Solar System, turning slowly on +his axis; and the earth and the planets travel round him, each spinning +like a teetotum, so as to make the most of his bright warm rays. But +for this spinning movement of the earth, our day and night, instead of +being each a few hours long, would each last six months. + +You may notice that, as you turn the orange steadily round, the outside +surface of the skin has to move much more slowly in those parts close +to the knitting-needle, than in those parts which bulge out farthest +from it. Near the North and South Poles the surface of our earth +travels slowly round a very small circle in the course of twenty-four +hours. But at the equator every piece of ground has to travel about +twenty-five thousand miles in the same time; so that it rushes along at +the rate of more than one thousand miles an hour. A man standing on the +earth at the equator is being carried along at this great speed, not +_through_ the air, for the whole atmosphere partakes of the same rapid +motion, but _with_ the air, round and round the earth’s axis. + +Now about the other movement of the earth--her yearly journey round the +sun. While she moves, the sun, as seen from the earth, seems to change +his place. First he is observed against a background of one group of +stars, then against a second, then against a third. Not that the stars +are visible in the daytime when the sun is shining, but their places +are well known in the heavens; and also they can be noted very soon +after he sets, or before he rises, so that the constellations nearest +to him may each day be easily found out. + +Of course, in old times the sun was thought to be really taking this +journey among the stars, and men talked of “the sun’s path” in the +heavens. This path was named “the Ecliptic,” and we use the word still, +though we know well that the movements are not really his, but ours. + +As the earth’s daily movement causes day and night, so the earth’s +yearly movement causes spring, summer, autumn, and winter. A few pages +back I mentioned, in passing, one slight yet important fact which lies +at the root of this matter about the seasons. The earth, journeying +round the sun, travels with her axis _slanting_. Put your candle in the +middle of the table, and stand at one end, holding your orange. Now let +the knitting-needle, with the orange upon it, so slant that one end +shall point straight over the candle, towards the upper part of the +wall at the farther end of the room. Call the upper end so pointing the +North Pole of your orange. You will see that the candle-light falls +chiefly upon the upper half of the orange; and as you turn it slowly, +to picture day and night, you will find that the North Pole has no +night, and the South Pole has no day. That is summer in the northern +hemisphere, and winter in the southern. + +Walk round next to one side of the table, towards the right hand, +taking care to let the knitting-needle point steadily still in exactly +the same direction, not towards the same _spot_, for that would alter +its direction as you move, but towards the same _wall_. Stop, and you +will find the candle lighting up one-half of your orange, from the +North to the South Poles. Turn it slowly, never altering the slope of +the axis, and you will see that every part of the orange comes by turns +under the light. This is the Autumnal Equinox, when days and nights all +over the world are equal in length. + +Walk on to the other end of the table, still letting the needle slope +and point steadily as before. Now the candle-light will shine upon the +lower or South Pole, and the North Pole will be entirely in the shade. +This is summer in the southern hemisphere, and winter in the northern. + +Pass on to the fourth side of the table, and once more you will find +it, as at the second side, equal light from North Pole to South Pole. +This will be the Spring Equinox. + +It is an illustration that may be easily practiced. But everything +depends upon keeping the slant of the needle or axis unchanged +throughout. If it be allowed to point first to right, and then to left, +first towards the ceiling, and then towards the wall, the attempt will +prove a failure. + + + + +CHAPTER IV. + +THE LEADING MEMBERS OF OUR FAMILY--FIRST GROUP. + + +The chief distinction between stars and planets is, as before said, +that the stars shine entirely by their own light, while the planets +shine chiefly, if not entirely, by reflected light. The stars are suns; +mighty globes of glowing flame. The planets simply receive the light of +the sun, and shine with a brightness not their own. + +A lamp shines by its own light; but a looking-glass, set in the sun’s +rays and flashing beams in all directions, shines by reflected light. +In a dark room it would be dark. If there were no sun to shine upon +Mars or Venus, we should see no brightness in them. The moon is like +the planets in this. She has only borrowed light to give, and none of +her own. + +Any one of the planets removed to the distance of the nearest fixed +star, would be invisible to us. Reflected light will not shine nearly +so far as the direct light of a burning body. There may be thousands or +millions of planets circling round the stars--those great and distant +suns--just as our brother-planets circle round our sun. But it is +impossible for us to see them. The planets which we can see are close +neighbors, compared with the stars. I do not mean that they are near in +the sense in which we speak of nearness upon earth. They are only near +in comparison with what is so very much farther away. + +For a while we must now leave alone all thought of the distant stars, +and try to gain a clear idea of the chief members of our own Family +Circle--that family circle of which the sun is the head, the center, +the source of life and warmth and light. There are two ways in which +astronomers group the planets of the Solar System. One way is to divide +them into the Inferior Planets, and the Superior Planets. + +As the earth travels in her pathway round the sun, two planets travel +on their pathways round the sun nearer to him than ourselves. If the +pathway or orbit of our earth were pictured by a hoop laid upon the +table, with a ball in the center for the sun; then those two planets +would have two smaller hoops of different sizes _within_ ours; and the +rest would have larger hoops of different sizes _outside_ ours. The two +within are called inferior planets, and the rest outside are called +superior planets. + +A round hoop would not make a good picture of an orbit. For the yearly +pathway of our earth is not in shape perfectly round, but slightly +oval; and the sun is not exactly in the center, but a little to one +side of the center. This is more or less the case with the orbits of +all the planets. + +But the laying of the hoops upon the table would give no bad idea of +the way in which the orbits really lie in the heavens. The orbits of +all the chief planets do not slope and slant round the sun in all +manner of directions. They are placed almost in the same _plane_ as it +is called--or, as we might say, in the same _flat_. In these orbits +the planets all travel round in the same direction. One may overtake a +second on a neighboring orbit, and get ahead of him, but one planet +never goes back to meet another. + +In speaking of the orbits, I do not mean that the planets have visible +marked pathways through the heavens, any more than a swallow has a +visible pathway through the sky, or a ship a marked pathway through the +sea. Yet each planet has his own orbit, and each planet so distinctly +keeps to his own, that astronomers can tell us precisely whereabouts in +the heavens any particular planet will be, at any particular time, long +years beforehand. + +There is also another mode of grouping the planets, besides dividing +them into superior and inferior planets. By this other mode we find two +principal groups or quartets of planets, separated by a zone or belt of +a great many very small planets. + + { Mercury. + First Group { Venus. + { Earth. + { Mars. + + The Asteroids or Planetoids. + + { Jupiter. + Second Group { Saturn. + { Uranus. + { Neptune. + +The first four are small compared with the last four, though much +larger than any in the belt of tiny Asteroids. + +It was believed at one time that a planet had been discovered nearer to +the sun than Mercury, and the name Vulcan was given to it. But no more +has been seen of Vulcan, and his existence is so doubtful that we must +not count him as a member of the family without further information. + +Mercury is very much smaller than our Earth. The diameter of the earth +is eight thousand miles, but the diameter of Mercury is only about +three thousand miles--not even half that of the earth. Being so much +nearer to the sun than ourselves, the pulling of his attraction is much +greater, and this has to be balanced by greater speed, or Mercury would +soon fall down upon the sun. Our distance from the sun is ninety-three +millions of miles. Mercury’s distance is only about one-third of ours; +and instead of traveling, like the earth, at the rate of eighteen miles +each second, Mercury dashes headlong through space at the mad pace +of twenty-nine miles each second. It is a good thing the earth does +not follow his example, or she would soon break loose from the sun’s +control altogether. + +The earth takes more than three hundred and sixty-five days, or twelve +months, to journey round the sun in her orbit. That is what we call +“the length of our year.” But Mercury’s year is only eighty-eight days, +or not quite three of our months. No wonder!--when his pathway is so +much shorter, and his speed so much greater than ours. So Mercury +has four years to one year on earth; and a person who had lived on +Mercury as long as five earthly years, would then be twenty years old. +The increased number of birthdays would scarcely be welcome in large +families, supposing we could pay a long visit there. + +The sun, as seen from Mercury, looks about four and a half times as +large as from here; the heat and glare being increased in proportion. +No moon has ever been found, belonging to Mercury. + +The planet Mercury is, like the earth and the moon, a globe of dark +matter which only shines and is visible by the illumination of the +solar light. Its motion round the central star, which brings it +sometimes between the sun and us, sometimes in an oblique direction, +sometimes at right angles, and shows us a part incessantly variable, +of its illuminated hemisphere, produces in its aspect, as seen in a +telescope, a succession of phases similar to those which the moon +presents to us. The cut represent the apparent variations of size and +the succession of phases, visible in the evening after sunset; when the +planet attains its most slender crescent, it is in the region of its +orbit nearest to the earth, and passes between the sun and us; then, +some weeks afterwards, it emerges from the solar rays and passes again +through the same series of phases in inverse order, as we see them by +reversing the figure. + +[Illustration: PHASES OF MERCURY BEFORE INFERIOR CONJUNCTION--EVENING +STAR.] + +Venus, the second inferior planet, is nearly the same size as our +earth. Seen from the earth, she is one of the most brilliant and +beautiful of all the planets. Her speed is three miles a second faster +than ours, and her distance from the sun is about two-thirds that of +our own; so that the orbit of Venus lies half-way between the orbit of +Mercury and the orbit of the earth. The day of Venus is about half an +hour shorter than ours. Her year is nearly two hundred and twenty-five +days, or seven and a half of our months. One or two astronomers have +fancied that they caught glimpses of a moon near Venus; but this is +still quite doubtful, and indeed it is believed to have been a mistake. + +Venus and Mercury are only visible as morning and evening planets. +Venus, being farther from the sun, does not go before and follow after +him quite so closely as Mercury, and she is therefore the longer within +sight. + +When Venus, traveling on her orbit, comes just between the sun and us, +her dark side is turned towards the earth, and we can catch no glimpse +of her. When she reaches that part of her orbit which is farthest from +us, quite on the other side of the sun, her great distance from us +makes her light seem less. But about half-way round on either side, she +shows exceeding brilliancy, and that is the best view we can get of her. + +Seen through a telescope, Venus undergoes phases like those of Mercury, +or of our moon. That is to say, we really have “new Venus,” “quarter +Venus,” “half Venus,” “full Venus,” and so on. + +Of all the luminaries in the heavens, the sun and moon excepted, the +planet Venus is the most conspicuous and splendid. She appears like +a brilliant lamp amid the lesser orbs of night, and alternately +anticipates the morning dawn, and ushers in the evening twilight. +When she is to the westward of the sun, in winter, she cheers our +mornings with her vivid light, and is a prelude to the near approach +of the break of day and the rising sun. When she is eastward of that +luminary, her light bursts upon us after sunset, before any of the +other radiant orbs of heaven make their appearance; and she discharges, +in some measure, the functions of the absent moon. The brilliancy of +this planet has been noticed in all ages, and has been frequently +the subject of description and admiration both by shepherds and by +poets. The Greek poets distinguished it by the name of Phosphor, +“light-bringer,” when it rose before the sun, and Hesperus, “the west,” +when it appeared in the evening after the sun retired. It is now +generally distinguished by the name of the Morning and Evening Star. + +Next to the orbit of Venus comes the orbit of our own Earth, the third +planet of the first group. + +Mars, the fourth of the inner quartet, but the first of the superior +planets, is a good deal smaller than Venus or the earth. The name Mars, +from the heathen god of war, was given on account of his fiery reddish +color. Mars is better placed than Venus for being observed from earth. +When he is at the nearest point of his orbit to us, we see him full in +the blaze of sunlight; whereas Venus, at her nearest point, turns her +bright face away. + +The length of the day of Mars--or, in other words, the time he takes +to turn upon his axis--is only forty minutes longer than that of +earth. Mars’ journey round the sun is completed in the course of six +hundred and eighty-seven days, not much less than two of our years. +His distance from the sun is about one hundred and forty millions of +miles, and his speed is fourteen miles a second. We shall find, with +the increasing distance of each planet, that the slower pace balances +the lessened amount of the sun’s attraction. + +Passing on from Mars, the last of the first group of planets, we reach +the belt of Asteroids, sometimes called Planetoids, Minor Planets, or +Telescopic Planets. They are so tiny that Mercury is a giant compared +with the largest among them. + +The zone of space containing all these little planets is more than a +hundred millions of miles broad. Their orbits do not lie flat in almost +the same plane, but slant about variously in a very entangled fashion. +If a neat model were made of this zone, with a slender piece of wire to +represent each orbit, it would be found impossible to lift up one wire +without pulling up all the rest with it. Those asteroids lying nearest +to the sun take about three of our years to travel round him, and those +lying farthest take about six of our years. + +New members of the group are very often found. The number of asteroids +now known amounts to about three hundred and twenty. Ceres is estimated +by Professor Barnard, of the Yerkes Observatory, Chicago University, to +be six hundred miles in diameter. Vesta is about two hundred and fifty +miles in diameter. Meta, on the other hand, is less than seventy-five +miles. There are some smaller ones that do not measure twenty miles in +diameter, and it is probable that there are many which are so small as +to be absolutely invisible to the best telescopes, and which measure +only a few hundred rods in diameter. Twenty thousand Vestas would be +needed to make one globe equal to our earth in size. + +Are they _worlds_? Why not? Is not a drop of water, shown in the +microscope, peopled with a multitude of various beings? Does not a +stone in a meadow hide a world of swarming insects? Is not the leaf +of a plant a world for the species which inhabit and prey upon it? +Doubtless among the multitude of small planets there are those which +must remain desert and sterile, because the conditions of life (of any +kind) are not found united. But we can not doubt that on the majority +the ever-active forces of nature have produced, as in our world, +creations appropriate to these minute planets. Let us repeat, moreover, +that for nature there is neither great nor little. And there is no +necessity to flatter ourselves with a supreme disdain for these little +worlds; for in reality the inhabitants of Jupiter would have more right +to despise us than we have to despise Vesta, Ceres, Pallas, or Juno. +The disparity is greater between Jupiter and the earth than between the +earth and these planets. A world of two, three, or four hundred miles +in diameter is still a continent worthy to satisfy the ambition of a +Xerxes or a Tamerlane. + + + + +CHAPTER V. + +THE LEADING MEMBERS OF OUR FAMILY--SECOND GROUP. + + +Leaving behind us the busy zone of planetoids, hurrying round and round +the sun in company, we cross a wide gap, and come upon a very different +sight. + +The distance from the sun which we have now reached is little less than +four hundred and fifty millions of miles, or about five times as much +as the earth’s distance; and the sun in the heavens shows a diameter +only one-fifth of that which we are accustomed to see. Slowly--yet not +slowly--floating onwards through space, in his far-off orbit, we find +the magnificent planet Jupiter. + +Is eight miles each second slow progress? Compared with the wild whirl +of little Mercury, or even compared with the rate of our own earth’s +advance, we may count it so; but certainly not, compared with our +notions of speed upon earth. Eight miles each second is five hundred +times as fast as the swiftest express-train ever made by man. No mean +pace that for so enormous a body. For Jupiter is the very largest of +all the members of the Solar System except the sun himself--quite +the eldest brother of the family. His diameter is about eighty-five +thousand miles, his axis being nearly eleven times as long as that of +earth. Though in proportion to his great bulk not nearly so heavy as +our earth, yet his bulk is so vast that more than twelve hundred earths +would be needed to make one Jupiter. + +It must not, however, be forgotten that there is a certain amount of +uncertainty about these measurements of Jupiter. He seems to be so +covered with a dense atmosphere and heavy clouds that it is quite +impossible for us to learn the exact size of the solid body within. + +Jupiter does not travel alone. Borne onwards with him, and circling +steadily around him, are five moons; the smallest with a probable +diameter of about one hundred miles; one about the same size as our +own moon, and the others all larger. The nearest of the five, though +distant from the center of the planet over one hundred and twelve +thousand miles, revolves about him in twelve hours; the second, though +farther from Jupiter than our moon from the earth, speeds round him +in less than two of our days. The most distant, though over a million +miles away, takes scarcely seventeen days to accomplish its long +journey. Jupiter and his moons make a little system by themselves--a +family circle within a family circle. + +Like the smaller planets, Jupiter spins upon his axis; and he does this +so rapidly that, notwithstanding his great size, his day lasts only ten +hours, instead of twenty-four hours like ours. But if Jupiter’s day +is short, his year is not. Nearly twelve of our years pass by before +Jupiter has traveled once completely round the sun. So a native of +earth who had just reached his thirty-seventh year, would, on Jupiter, +be only three years old. + +Passing onward from Jupiter, ever farther and farther from the sun, +we leave behind us another vast and empty space--empty as we count +emptiness, though it may be that there is in reality no such thing as +emptiness throughout the length and breadth of the universe. The width +of the gap which divides the pathway of Jupiter from the pathway of his +giant brother-planet Saturn is nearly five times as much as the width +of the gap separating the earth from the sun. The distance of Saturn +from the sun is not much less than double the distance of Jupiter. + +With this great space in our rear, we come upon another large and +radiant planet, the center, like Jupiter, of another little system; +though it can only be called “little” in comparison with the much +greater Solar System of which it forms a part. + +Saturn’s diameter is less than that of Jupiter, but the two come near +enough to be naturally ranked together. Nearly seven hundred earths +would be needed to make one globe as large as Saturn. But here again +the dense and cloudy envelope makes us very uncertain about the +planet’s actual size. Saturn is like Jupiter in being made of lighter +materials than our earth; and also in his rapid whirl upon his axis, +the length of his “day” being only ten and a half of our hours. + +From Jupiter’s speed of eight miles each second, we come down in the +case of Saturn to only five miles each second. And Jupiter’s long +annual journey looks almost short, seen beside Saturn’s long journey +of thirty earthly years. A man aged sixty, according to our fashion of +reckoning time, would on Saturn have just kept his second birthday. + +The system or family of Saturn is yet more wonderful than that of +Jupiter. Not five only but eight moons travel ceaselessly round Saturn, +each in its own orbit; and in addition to the eight moons, he has +revolving round him three magnificent rings. These rings, as well as +the moons, shine, not by their own brilliancy, for they have none, but +by borrowed sunlight. The farthest of the moons wanders in his lonely +pathway about two millions of miles away from Saturn. The largest of +them is believed to be about the same size as the planet Mars. Of the +three rings circling round Saturn, almost exactly over his equator, the +inside one is dusky, purplish, and transparent; the one outside or over +that is very brilliant; and the third, outside the second, is rather +grayish in hue. + +Another vast gap--more enormous than the last. It is a wearisome +journey. From the orbit of Jupiter to the orbit of Saturn at their +nearest points, was five times as much as from the sun to the earth. +But from the orbit of Saturn to the orbit of Uranus, the next member of +the sun’s family, we have double even that great space to cross. + +Still, obedient to the pulling of the sun’s attractive power, Uranus +wanders onward in his wide pathway round the sun, at the rate of four +miles a second. Eighty-four of our years make one year of Uranus. +This planet has four moons, and thus forms a third smaller system +within the Solar System; but he may have other satellites also, as yet +undiscovered. In size he is seventy-four times as large as our earth. + +One more mighty chasm of nine hundred millions of miles, for the same +distance which separates the pathway of Saturn from the pathway of +Uranus, separates also the pathway of Uranus from the pathway of +Neptune. Cold, and dark, and dreary indeed seems to us the orbit on +which this banished member of our family circle creeps round the sun, +in the course of one hundred and sixty-five years, at the sluggish rate +of three miles a second. + +On the planet Saturn, the quantity of light and heat received from +the sun is not much more than a hundredth part of that which we are +accustomed to receive on earth. But by the time we reach Neptune, the +great sun has faded and shrunk in the distance until to our eyes he +looks only like an exceedingly brilliant and dazzling star. + +We know little of this far-off brother, Neptune, except that he is +rather larger than Uranus, being one hundred and five times as big as +the earth; that he has at least one moon; and also that, like Uranus, +he is made of materials lighter than those of earth, but heavier than +those of Jupiter or Saturn. + +After all, it is no easy matter to gain clear ideas as to sizes and +distances from mere statements of “so many miles in diameter,” and “so +many millions of miles away.” A “million miles” carries to the mind a +very dim notion of the actual reality. + +Now if we can in imagination bring down all the members of the Solar +System to a small size, keeping always the same proportions, we may +find it a help. “Keeping the same proportions” means that all must be +lessened alike, all must be altered in the same degree. Whatever the +supposed size of the earth may be, Venus must be still about the same +size as the earth, Saturn seven hundred times as large, and so on. +Also, whatever the distance of the earth from the sun, in miles, or +yards, or inches, Mercury must still be one-third as far, Jupiter still +five times as far, and thus with the rest. + +First, as to size alone. Suppose the earth is represented by a small +globe, exactly three inches in diameter. It will be a very small globe. +Not only men and houses, but mountains, valleys, seas, will all have to +be reduced to so minute a size, as to be quite invisible to the naked +eye. + +Fairly to picture the other members of the Solar System, in due +proportion, you will have them as follows: + +Mercury and Mars will be balls smaller than the earth, and Venus nearly +the same size of the earth. Uranus and Neptune will be each somewhere +about a foot in diameter. Saturn will be twenty-eight inches and +Jupiter thirty-two inches in diameter. The sun will be a huge dazzling +globe, _twenty-six feet_ in diameter. No wonder he weighs seven hundred +and fifty times as much as all his planets put together. + +Next let us picture the system more exactly on another and smaller +scale. First, think of the sun as a brilliant globe, about nine feet, +or three yards, in diameter, floating in space. + +About one hundred yards from the sun travels a tiny ball, not half +an inch in diameter, passing slowly round the sun--slowly, because +as sizes and distances are lessened, speed must in due proportion be +lessened also. This is Mercury. About two hundred yards from the sun +travels another tiny ball, one inch in diameter. This is Venus. Nearly +a quarter of a mile from the sun travels a third tiny ball, one inch +again in diameter; and at a distance of two feet and a half from it a +still smaller ball, one quarter of an inch in diameter, journeys round +it and with it. These are the earth and the moon. About half as far +again as the last-named ball, travels another, over half an inch in +diameter. This is Mars. + +Then comes a wide blank space, followed by a large number of minute +objects, no bigger than grains of powder, floating round the sun in +company. These are the Asteroids. Another wide blank space succeeds the +outermost of them. + +About one mile distant from the sun journeys a globe, ten inches in +diameter. Round him, as he journeys, there travel five smaller balls, +the largest of which is about the third of an inch in diameter. Their +distances from the bigger globe vary from one and a third to twelve and +a half feet. These are Jupiter and his moons. + +Nearly two miles distant from the sun journeys another globe, about +eight and a half inches in diameter. Eight tiny balls and three +delicate rings circle round him as he moves. These are Saturn and his +belongings. About four miles distant from the sun journeys another +globe, four inches in diameter, with four tiny balls accompanying +him--Uranus and his moons. Lastly, at a distance of six miles from +the sun, one more globe, not much larger than the last, with one tiny +companion, pursues his far-off pathway. + +These proportions as to size and distance will serve to give a clear +idea of the Solar System. + + + + +CHAPTER VI. + +THE MOON. + + +Come, and let us pay a visit to the moon. We seem to feel a personal +interest in her, just because she is, in so peculiar a sense, our own +friend and close attendant. The sun shines for us; but, then, he shines +for all the members of the Solar System. And the stars--so many as we +can see of them--shine for us too; but no doubt they shine far more +brilliantly for other and nearer worlds. The moon alone seems to belong +especially to ourselves. + +Indeed, we are quite in the habit of speaking about her as “our moon.” +Rather a cold and calm friend, some may think her, sailing always +serenely past, whatever may be going on beneath her beams; yet she has +certainly proved herself constant and faithful in her attachment. + +We have not very far to travel before reaching her,--merely about +two hundred and forty thousand miles. That is nothing, compared with +the weary millions of miles which we have had to cross to visit some +members of our family. A rope two hundred and forty thousand miles +long would fold nearly ten times round the earth at the equator. You +know the earth’s diameter--about eight thousand miles. If you had +thirty poles, each eight thousand miles long, and could fasten them all +together, end to end, one beyond another, you would have a rod long +enough to reach from the earth to the moon. + +Let us take a good look at her before starting. She is very beautiful. +That soft silvery light, so unlike sunlight or gaslight, or any other +kind of light seen upon earth, has made her the darling of poets and +the delight of all who love nature. Little children like to watch +her curious markings, and to make out the old man with his bundle of +sticks, or the eyes, nose, and mouth of the moon--not dreaming what +those markings really are. And in moods of sadness, how the pure calm +moonlight seems to soothe the feelings! Who would suppose that the +moon’s beauty is the beauty rather of death than of life? + +[Illustration: APPEARANCE OF THE FULL MOON.] + +The stars have not much chance of shining through her bright rays. It +is well for astronomers that she is not always at the full. But when +she is, how large she looks--quite as large as the sun, though in +reality her size, compared with his, is only as a very small pin’s +head compared with a school globe two feet in diameter. Her diameter is +little more than two thousand miles, or one quarter that of our earth; +and her whole surface, spread out flat, would scarcely equal North and +South America, without any of the surrounding islands. + +The reason she looks the same size as the sun, is that she is so very +much nearer. The sun’s distance from us is more than one-third as many +_millions_ of miles as the moon’s distance is _thousands_ of miles. +This makes an enormous difference. + +We call our friend a “moon,” and say that she journeys round the earth, +while the earth journeys round the sun. This is true, but it is only +part of the truth. Just as certainly as the earth travels round the +sun, so the moon also travels round the sun. And just as surely as +the earth is a planet, so the moon also is a planet. It is a common +mode of expression to talk about “the earth and her satellite.” A no +less correct, if not more correct, way would be to talk of ourselves +as “a pair of planets,” journeying round the same sun, each pulled +strongly towards him, and each pulling the other with a greater or less +attraction, according to her size and weight. For the sun actually does +draw the moon with more force than that with which the earth draws her. +Only as he draws the earth with the same sort of force, and nearly in +the same degree, he does not pull them apart. + +The moon, like the other planets, turns upon her axis. She does this +very slowly, however; and most singularly she takes exactly the same +time to turn once upon her axis that she does to travel once round +the earth. The result of this is, that we only see one face of the +moon. If she turned upon her axis, and journeyed round the earth in two +different lengths of time, or if she journeyed round us and did not +turn upon her axis at all, we should have views of her on all sides, +as of other planets. But as her two movements so curiously agree, it +happens that we always have one side of the moon towards us, and never +catch a glimpse of the other side. + +And now we are ready to start on our journey of two hundred and forty +thousand miles. An express train, moving ceaselessly onward night and +day, at the rate of sixty miles an hour, would take us there in about +five months and a half. But no line of rails has ever yet been laid +from the earth to the moon, and no “Flying Dutchman” has ever yet plied +its way to and fro on that path through the heavens. Not on the wings +of steam, but on the wings of imagination, we must rise aloft. Come--it +will not take us long. We shall pass no planets or stars on the road, +for the moon lies nearer to us than any other of the larger heavenly +bodies. + +Far, far behind us lies the earth, and beneath our feet, as we descend, +stretch the broad tracts of moonland. For “downward” now means towards +the moon, and away from the distant earth. + +What a strange place we have reached! The weird, ghastly stillness +of all around, and the glaring, dazzling, cloudless heat, strike us +first and most forcibly. Nothing like this heat have we ever felt on +earth. For the close of the moon’s long day--on this side of its +globe--is approaching, and during a whole fortnight past the sun’s +fierce rays have been beating down on these shelterless plains. Talk +of sweltering tropics on earth! What do you call _this_ heat? Look +at the thermometer: how the quicksilver is rising! Well, that is not +a common thermometer which we have brought with us. The mercury has +stopped--three hundred degrees above boiling water! + +Not a cloud to be seen overhead; only a sky of inky blackness, with a +blazing sun, and thousands of brilliant stars, and the dark body of +our own earth, large and motionless, and rimmed with light. Seen from +earth, sun and moon look much the same size; but seen from the moon, +the earth looks thirteen times as large as our full moon. Not even a +little mistiness in the air to soften this fearful glare! Air! why, +there is no air; at least not enough for any human being to breathe +or feel. If there were air, the sky would be blue, not black, and the +stars would be invisible in the daytime. It looks strange to see them +now shining beside the sun. + +And then, this deadly stillness! Not a sound, not a voice, not a murmur +of breeze or water. How could there be? Sound can not be carried +without air, and of air there is none. As for breeze--wind is moving +air, and where we have no air we can have no wind. As for water--if +there ever was any water on the moon, it has entirely disappeared. We +shall walk to and fro vainly in search of it now. No rivers, no rills, +no torrents in those stern mountain ramparts rising on every side. All +is craggy, motionless, desolate. + +How very, very slowly the sun creeps over the black sky! And no +marvel, since a fortnight of earth-time is here but one day, answering +to twelve hours upon earth. Can not we find shelter somewhere from +this blazing heat? Yonder tall rock will do, casting a sharp shadow +of intense blackness. We never saw such shadows upon earth. There the +atmosphere so breaks and bends and scatters about the light, that +outlines of shadows are soft and hazy, even the clearest and darkest of +them, compared with this. + +When will the sun go down? But he is well worth looking at meanwhile. +How magnificent he appears, with his pure radiant photosphere, fringed +by a sierra of dazzling pink and white, orange and gold, purple +and blue. For here no atmosphere lies between to blend all into +yellow-white brightness. And how plainly stand out those prominences +or tongues of tinted flame, not merely rose-colored, as seen from +earth, but matching the sierra in varying hues; while beyond spreads +a gorgeous belt of pink and green, bounded by lines and streams of +delicate white light, reaching far and dying slowly out against the jet +background. The black spots on the face of the sun are very distinct, +and so also are the brilliant faculæ. + +We must take a look around us now at moonland, and not only sit gazing +at the sun, though such a sky may well enchain attention. How unlike +our earthly landscapes! No sea, no rivers, no lakes, no streams, no +brooks, no trees, bushes, plants, grass, or flowers; no wind or breeze; +no cloud or mist or thought of possible rain; no sound of bird or +insect, of rustling leaves or trickling water. Nothing but burning, +steadfast, changeless glare, contrasting with inky shadows; sun and +earth and stars in a black heaven above; silent, desolate mountains and +plains below. + +For though we stand here upon a rough plain, this moon is a mountainous +world. Ranges of rugged hills stretch away in the distance, with +valleys lying between--not soft, green, sloping, earthly valleys, but +steep gorges and precipitous hollows, all white dazzle and deep shade. + +But the mountains do not commonly lie in long ranges, as on earth. The +surface of the moon seems to be dented with strange round pits, or +craters, of every imaginable size. We had a bird’s-eye view of them as +we descended at the end of our long journey moonward. In many parts +the ground appears to be quite honeycombed with them. Here are small +ones near at hand, and larger ones in the distance. The smaller craters +are surrounded by steep ramparts of rock, the larger ones by circular +mountain-ranges. We have nothing quite like them on earth. + +Are they volcanoes? So it would seem; only no life, no fire, no action, +remain now. All is dead, motionless, still. Is this verily a blasted +world? Has it fallen under the breath of Almighty wrath, coming out +scorched and seared? Is it simply passing through a certain burnt-out, +chilled phase of existence, through which other planets also pass, or +will pass, at some stage of their career? Who can tell? + +We will move onward, and look more closely at that towering mass of +rugged rocks, beyond which the sun will by and by go down. Long jetty +shadows lie from them in this direction. No wonder astronomers on +earth can through their telescopes plainly see these black shadows +contrasting with the glaring brightness on the other side. + +A “mass of rocks” I have said; but as, with our powers of rapid +movement, we draw near, we find a range of craggy mountains sweeping +round in a vast circle. Such a height in Switzerland would demand many +hours of hard climbing. But on this small globe attraction is a very +different matter from what it is on earth; our weight is so lessened +that we can leap the height of a tall house without the smallest +difficulty. No chamois ever sprang from peak to peak in his native +Switzerland with such amazing lightness as that with which we now +ascend these mighty rocks. + +[Illustration: ONE FORM OF LUNAR CRATER.] + +Ha! what a depth on the other side! We stand looking down into one of +the monster craters of the moon. A sheer descent of at least eleven +thousand feet would land us at the bottom. Why, Mont Blanc itself +is only about fifteen thousand feet in height. And what a crater! +Fifty-six miles across in a straight line, from here to the other side, +with these lofty rugged battlements circling round, while from the +center of the rough plain below a sharp, cone-shaped mountain rises to +about a quarter of the height of the surrounding range. + +It is a grand sight; peak piled upon peak, crag upon crag, sharp rifts +or valleys breaking here and there the line of the narrow, uplifted +ledge; all wrapped in silent and desolate calm. There are many such +craters as this on the moon, and some much larger. + +The sun slowly nears his setting, and sinks behind the opposite range. +How we shiver! The last ray of sunlight has gone and already the ground +is pouring out its heat into space, unchecked by the presence of air +or clouds. The change takes place with marvelous quickness. A deadly +chill creeps over all around. A whole fortnight of earth-time must pass +before the sun’s rays will again touch this spot. Verily the contrasts +of climate in the moon, during the twelve long days and nights which +make up her year, are startling to human notions. + +But though the sun is gone we are not in darkness. The stars shine with +dazzling brightness, and the huge body of the earth, always seeming to +hang motionless at one fixed point in the sky, gives brilliant light, +though at present only half her face is lit up and half is in shadow. +Still her shape is plainly to be seen, for she has ever round her a +ring of light, caused by the gathered shining of stars as they pass +behind her thick atmosphere. She covers a space on the sky more than a +dozen times as large as that covered by the full moon in our sky. + +[Illustration: THE EARTH AS SEEN FROM THE MOON.] + +It would be worth while to stay here and watch the half-earth grow +into magnificent full-earth. But the cold is becoming fearful--too +intense for even the imagination to endure longer. What must be the +state of things on the other side of the moon, where there is no bright +earth-light to take the place of the sun’s shining, during the long two +weeks’ night of awful chill and darkness? + +It seems probable that a building on the moon would remain for century +after century just as it was left by the builders. There need be no +glass in the windows, for there is no wind and no rain to keep out. +There need not be fireplaces in the rooms, for fuel can not burn +without air. Dwellers in a city in the moon would find that no dust +can rise, no odors be perceived, no sounds be heard. Man is a creature +adapted for life in circumstances which are very narrowly limited. +A few degrees of temperature, more or less; a slight variation in +the composition of air, the precise suitability of food, make all +the difference between health and sickness, between life and death. +Looking beyond the moon, into the length and breadth of the universe, +we find countless celestial globes, with every conceivable variety of +temperature and of constitution. Amid this vast number of worlds with +which space teems, are there any inhabited by living beings? To this +great question science can make no response save this: We can not tell. + +Time for us to wend our way homewards from this desolate hundred-fold +arctic scene. We have more to learn by and by about our friend and +companion. For the present--enough. + + + + +CHAPTER VII. + +VISITORS. + + +We come next to the very largest members of our Solar System. + +From time to time in past days--and days not very long past +either--people were startled by the sight of a long-tailed star, moving +quickly across the sky, called a comet. We see such long-tailed stars +still, now and then; but their appearance no longer startles us. + +It is hardly surprising, however, that fears were once felt. The great +size and brilliancy of some of these comets naturally caused large +ideas to be held as to their weight, and the general uncertainty about +their movements naturally added to the mysterious notions afloat with +respect to their power of doing harm. + +A collision between the earth and a comet seemed no unlikely event; and +if it happened--what then? Why, then, of course, the earth would be +overpowered, crushed, burnt up, destroyed. So convinced were many on +this point that the sight of a comet and the dread of the coming “end +of the world” were fast bound together in their minds. + +Even when astronomers began to understand the paths of some of the +comets, and to foretell their return at certain dates, the old fear +was not quickly laid to rest. So late as the beginning of the present +century, astronomers having told of an approaching comet, other people +added the tidings of an approaching collision. “If a collision, then +the end of the world,” was the cry; and one worthy family, living and +keeping a shop in a well-known town on the south coast of England, +packed up and fled to America--doubtless under full belief that the +destruction of the Old World would not include the destruction of the +New. + +The nature of these singular bodies is somewhat better known in the +present day; yet even now, among all the members of the Solar System, +they are perhaps the ones about which we have most to learn. The +nucleus, or bright and star-like spot, which, with the surrounding +coma or “hair,” we sometimes call the “head” of the comet, is the +densest and heaviest part of the whole. The comets are of immense size, +sometimes actually filling more space than the sun himself, and their +tails stream often for millions of miles behind them; nevertheless, +they appear to be among the lightest of the members of the Solar System. + +This excessive lightness greatly lessens the comet’s power of +harm-doing. In the rebound from all the old exaggerated fears, men +laughed at the notion of so light and delicate a substance working any +injury whatever, and even declared that a collision might take place +without people on earth being aware of the fact. It is now felt that +we really know too little about the nature of the said substance to +be able to say what might or might not be the result of a collision. +A certain amount of injury to the surface of the earth might possibly +take place. But of the “end of the world,” as likely to be brought +about by any comet in existence, we may safely banish all idea. + +The word “comet” means “a hairy body,” the name having been given from +the hairy appearance of the light around the nucleus. About seventeen +hundred different comets have been seen at different times by men--some +large, some small; some visible to the naked eye, but most of them only +visible through telescopes. These hundreds are, there is no doubt, but +a very small number out of the myriads ranging through the heavens. + +If you were seated in a little boat in mid-ocean, counting the number +of fishes which in one hour passed near enough in the clear water for +your sight to reach them, you might fairly conclude, even if you did +not know the fact, that for every single fish which you could see, +there were tens of thousands which you could not see. + +Reasoning thus about the comets, as we watch them from our earth-boat +in the ocean of space, we feel little doubt that for each one which we +can see, millions pass to and fro beyond reach of our vision. Indeed, +so long ago as the days of Kepler, that great astronomer gave it as his +belief that the comets in the Solar System, large and small, were as +plentiful as the fishes in the sea. And all that modern astronomers can +discover only tends to strengthen this view. + +Why should the comets be called “visitors?” I call them so simply +because many of them _are_ visitors. Some, it is true, belong to the +Solar System. But even in their case, strong doubts are felt whether +they were not once visitors from a distance, caught in the first +instance by the attraction of one of the larger planets, and retained +thenceforward, for a time at least, by the strong attraction of the sun. + +[Illustration: PASSAGE OF THE EARTH AND THE MOON THROUGH THE TAIL OF A +COMET.] + +Every comet, like every planet, has his own orbit or pathway in the +heavens, though the kind of orbit varies with different comets. There +are, first, those comets which travel round and round the sun in +“closed orbits”--that is, in a ring with joined ends. Only the ring is +always oval, not round. There are, secondly, those which travel in an +orbit which _may_ be closed; but if so, the oval is so long and narrow, +and the farther closed end is at so great a distance, that we can not +speak certainly. There are, thirdly, those which decidedly are mere +visitors. They come from the far-off star-depths, flash once with their +brilliant trains of light through our busy Solar System, causing some +little excitement by the way, and go off in another direction, never to +return. + +Only a small part of the orbits of these comets can be seen from +earth; but by careful attention astronomers learn something of the +shape of the curve in which they travel. It is in that way possible to +calculate, sometimes certainly, and sometimes uncertainly, whether a +comet may be expected to return, or whether we have seen him for the +first and the last time. By looking at _part_ of a curve, the rest of +which is hidden from us, we are able to judge whether that part belongs +to a circle or an oval, or whether the two ends pass away in different +directions, and do not join. + +The comets, whether members of our family circle or visitors from a +distance, are altogether very perplexing. They are often extremely +large, yet they are always extremely light. They reflect the sun’s +brightness like a planet, yet in some measure they seem to shine by +their own light, like a star. They obey the attraction of the sun, yet +he appears to have a singular power of driving the comets’ tails away +from himself. + +For, however rapidly the comet may be rushing round the sun, and +however long the tail may be, it is almost always found to stream in an +opposite direction from the sun. An exception to this rule was seen in +the case of a certain comet with two tails, one of which did actually +point towards the sun; but the inner tail may have been only a “jet” of +unusual length, like in kind to the smaller jets often thus poured out +from the nucleus. + +Very curious changes take place in comets as they journey, especially +as they come near the sun. One was seen in the course of a few days to +lose all his hair, and also his tail. Another was seen to break into +two pieces, both of which pieces at last disappeared. Sometimes the one +tail divides into two tails. + +Traveling, as the comets do, from intense cold into burning heat, +they are very much affected by the violent change of climate. For the +paths of the comets are such long ovals, or ellipses, that, while they +approach the sun very closely in one part of their “year,” they travel +to enormous distances in the other part. + +“Halley’s Comet,” which takes seventy-six of our years to journey round +the sun, comes nearer to him than Venus, and goes farther away from him +than Neptune. As this comet draws gradually closer, he has to make up +for the added pull of the sun’s increasing attraction by rushing onward +with greater and greater rapidity, till he whirls madly past the sun, +and then, with slowly slackening speed, journeys farther and farther +away, creeps at length lazily round the farther end of his orbit in the +chill, dark, neighborhood of Neptune, and once more travels towards the +sun with growing haste. + +“Encke’s Comet” has a year of only three and a half of our years, so +he may be said to live quite in our midst. But many comets travel much +farther away than the one named after Halley. It is calculated of some +that, if they ever return at all, it can not be for many hundreds of +years. + +[Illustration: PASSAGE OF THE COMET OF 1843 CLOSE TO THE SUN (FEBRUARY +27TH, 10 HOURS, 29 MINUTES.)] + +“Newton’s Comet,” seen about two centuries ago, has a journey to +perform of such length that he is not expected again to appear for +several thousand years. Yet, at the nearest point in his orbit, he +approached the sun so closely, that the heat which he endured was +about two thousand times that of red-hot iron. Changes were seen to be +taking place in his shape, as he drew near to the sun, and disappeared. +Four days he was hidden in the sun’s rays. He vanished, with a tail +streaming millions of miles behind him. He made his appearance again +with a tail streaming millions of miles in front of him. But how this +wonderful movement took place is beyond man’s power to explain. + +The comet of 1843 was one of the most attractive seen during the +present century. It was first observed in March, and it appeared with +a suddenness which had quite a startling effect. It was an imposing +object in the southern regions. The comet was seen in Italy on the 28th +of February; at Washington, on the 6th of March; at Oporto, on the +14th; but owing to unfavorable weather, it was not visible in England, +or any of the northern countries of Europe, previous to the 17th. A +little after sunset on that day the tail was observed in the western +sky, but the head had already sunk below the horizon. The whole of the +comet appeared on the following evenings for a short time, for it was +traveling away from the sun with great velocity, having doubled the +solar orb before it became visible; and about the beginning of April it +finally disappeared. + +The appearance of this startling stranger, as observed at Washington, +is thus described by Lieutenant Maury, of the Hydrographical Office in +that city: “On Monday morning, March 6th, our attention was called to +a paragraph in the newspapers, stating that a comet was visible near +the sun at midday with the naked eye. The sky was clear; but not being +able to discover any thing with the unassisted eye, recourse was had to +the telescope, but with no better success. About sunset in the evening, +the examination was renewed with great diligence, but to no purpose. +The last faint streak of day gilded the west; beautiful and delicate +fleeces of cloud curtained the bed of the sun; the upper sky was +studded with stars, and all hopes of seeing the comet that evening had +vanished. Soon after we had retired, the officer of the watch announced +its appearance in the west. The phenomenon was sublime and beautiful. +The needle was greatly agitated, and a strongly marked pencil of light +was streaming up from the path of the sun in an oblique direction to +the southward and eastward; its edges were parallel. It was 30° long. +Stars could be seen twinkling through it, and no doubt was at first +entertained that this was the tail of the comet.” + +The tail, as seen in northerly countries, spread over an arc of the +heavens of about 40°; but in southern latitudes it extended to from 60° +to 70°. It had an absolute length of two hundred millions of miles; so +that, had it been coiled around the earth like a serpent, it would have +girdled it eight thousand times at the equator. This comet approached +still nearer the sun than that of Newton, and must therefore have been +exposed to a heat of greater intensity. Its center is computed to +have been within a hundred thousand miles of the solar surface; and +according to Sir John Herschel’s calculations, it was then exposed to a +heat equal to that which would be received by an equal portion of the +earth’s surface, if it were subject to the influence of forty-seven +thousand suns, placed at the common distance of the actual sun. It is +difficult to conceive how a flimsy substance in such circumstances +could escape being entirely dissipated. But such was its velocity that +it wheeled round the sun in less than two hours. + +The general question of the probability and the consequences of a +collision with a comet may be legitimately entertained. With reference +to the first point, it can not be denied that collision is possible; +but, at the same time, it is so extremely improbable that it may be +safely dismissed from apprehension. The fact of such an event not +having been experienced in the known course of terrestrial history is +surely some guarantee against its occurrence. Another may be found in +the small volume of the earth and of comets when compared with the +immensity of space in which they move. According to the well-understood +principles of probabilities, Arago has calculated that, upon the +appearance of a new comet, the odds are as 281,000,000 to 1, that it +will not strike against our globe. But even supposing collision to +occur, all that we know of the constitution of comets justifies the +conclusion that the encounter would involve no terrestrial convulsion, +nor any result incompatible with full security to life and happiness. + +So much for the largest members of our circle--largest, though +lightest; members some, visitors others. Now we turn to the smallest. + + + + +CHAPTER VIII. + +LITTLE SERVANTS. + + +If you walk out any night after dark, and watch the bright stars +shining in a clear sky--shining as they have done for ages past--you +will probably see, now and then, a bright point of light suddenly +appear, dart along a little distance, and as suddenly vanish. +That which you have seen was not the beginning of a story, but in +ninety-nine cases out of a hundred it was the end of a story. The +little shooting-star was in existence long before you saw him, whirling +through space with millions of little companions. But he has left them +all, and dropped to earth. He is a shooting-star no longer. + +If such a journey to the moon as the one described two chapters back +were indeed possible, the voyage aloft would hardly be so easily and +safely performed as is there taken for granted. Putting aside the +thought of other difficulties, such as lack of conveyance and lack of +air, there would be the danger of passing through a very considerable +storm of missiles--a kind of “celestial cannonade”--which, to say the +least, would prove very far from agreeable. + +These “starlets” and “meteor planets,” as they have been called, are +not visible in a normal condition, because of their minuteness. But on +entering our atmosphere they are rendered luminous, owing to the heat +evolved by the sudden and violent compression of the air in front of +the moving body. According to this view, shooting-stars, which simply +dart across the heavens, may be regarded as coming within the limits of +the atmosphere, and carried out of it again, by their immense velocity, +passing on in space. Meteoric showers may result from an encounter with +a group of these bodies, while aërolites are those which come so far +within the sphere of the earth’s attraction as to fall to its surface. +More than two thousand years ago the Greeks venerated a famous stone +which fell from the heavens on the river Ægos. + +[Illustration: METEOR EMERGING FROM BEHIND A CLOUD (NOV. 23, 1877).] + +It will scarcely be believed what numbers of these shooting-stars or +meteorites constantly fall to the earth. As she travels on her orbit, +hurrying along at the rate of nineteen miles each second, she meets +them by tens of thousands. They too, like the earth, are journeying +round the great center of our family. But they are so tiny, and +the earth by comparison is so immense, that her strong attraction +overpowers one after another, drags it from its pathway, and draws it +to herself. + +And then it falls, flashing like a bright star across the sky, and +the little meteorite has come to his end. His myriads of companions, +hastening still along their heavenly track--for the meteorites seem to +travel commonly in vast flocks or companies--might, had they sense, +mourn in vain for the lost members of their family. + +Any one taking the trouble to watch carefully some portion of the sky +after dark, may expect to see each hour about four to eight of these +shooting-stars--except in the months of August and November, when the +number is much larger. About six in an hour does not sound a great +deal. But that merely means that there have been six in one direction, +and near enough for you to see. Somebody else, watching, may have +seen six in another direction; and somebody else, a few miles away, +may have seen six more. It is calculated that, in the course of every +twenty-four hours, about four hundred millions of meteorites fall to +earth, including those visible only through telescopes. + +This is rather startling. What if you or I should some day be struck +by one of these solid, hard little bodies, darting as they do towards +earth with speed swifter than that of a cannon-ball? True, they are not +really stars, neither are they really planets. But they are, to say +the least, often much larger than a cannon-ball, and a cannon-ball can +destroy life. + +Four hundred millions every twenty-four hours! Does it not seem +singular that we do not see them constantly dropping to the ground? +The truth is, we _should_ see them, and feel them too, and dire would +be the danger to human life, but for a certain protecting something +folded round this earth of ours to ward off the peril. That “something” +is the earth’s atmosphere. But for the thick, soft, strong, elastic +air through which the meteorites have to pass, they would fall with +fearful violence, often doing terrible mischief. As it is, we are +guarded. The shooting-star, drawn by the earth’s attraction, drops into +her atmosphere, darting with tremendous speed. In consequence of this +speed and the resistance of the air, it catches fire. That is when we +first see it. The meteorites are believed to appear at a height of +about seventy miles, and to disappear at a height of about fifty miles. +So that, in one instant’s flash, the shooting-star has traveled some +twenty miles toward us. Then the light goes out. The little meteorite +is burnt. It falls to earth still; but only as fine dust, sinking +harmlessly downward. + +The meteorites do not always vanish so quickly. Now and then a larger +one--too large to be rapidly burnt--does actually reach the ground. If +any man were struck by such a stone he would undoubtedly be killed. + +When meteorites thus fall to earth they are usually called _aërolites_. +Some are found no bigger than a man’s fist, while others much exceed +this size. There is one, kept carefully in the British Museum, which +weighs three tons and a half; and we hear of another, lying in South +America, between seven and eight feet in length. Such a sky-visitant +would be very unwelcome in any of our towns. + +We must remember that, whatever size an aërolite may be when it reaches +the earth, it must have been far greater when journeying round the sun, +since a good part of it has been burnt away during its rush downward +through the earth’s atmosphere. + +Meteors, or bolides, or fireballs, are of much the same nature as +meteorites; but they are larger, longer to be seen, and slower in +movement. Also, it is not uncommon for them to burst with a loud +explosion. Early in the present century such a meteor visited Normandy. +It exploded with a noise like the roll of musketry, scattering +thousands of hot stones over a distance of several miles. A great +number of them were collected, still smoking. The largest of these +stones weighed no less than twenty pounds. Happily no one seems to have +been injured. Other such falls have taken place from time to time. +Sometimes bright, slowly-moving meteors have been seen, looking as +large as the moon. + +A remarkable fireball appeared in England on November 6, 1869. This +fireball was extensively seen from different parts of the island, and +by combining and comparing these observations, we obtain accurate +information as to the height of the object and the velocity with which +it traveled. It appears that this meteor commenced to be visible at +a point ninety miles above Frome, in Somersetshire, and that it +disappeared at a point twenty-seven miles over the sea, near St. Ives, +in Cornwall. The whole length of its course was about 170 miles, which +was performed in a period of five seconds, thus giving an average +velocity of thirty-four miles a second. A remarkable feature in the +appearance which this fireball presented was the long, persistent +streak of luminous cloud, about fifty miles long and four miles wide, +which remained in sight for fully fifty minutes. We have in this +example an illustration of the chief features of the phenomena of a +shooting-star presented on a very grand scale. It is, however, to be +observed that the persistent luminous streak is not a universal, nor, +indeed, a very common characteristic of a shooting-star. + +If we may liken comets to the _fishes_ of the Solar System--and in +their number, their speed, their varying sizes, their diverse motions, +they may be fairly so likened--we may perhaps speak of the meteorites +as the _animalcula_ of the Solar System. For, in comparison with the +planets, they are, in the matter of size, as the animalcula of our +ponds in comparison with human beings. In point of numbers they are +countless. + +Take a single drop of water from some long-stagnant pond, and place +it under a powerful microscope. You will find it to be full of life, +teeming with tiny animals, darting briskly to and fro. The drop of +water is in itself a world of living creatures, though the naked eye +of man could never discover their existence. So with the meteorites. +There is good reason to believe that the Solar System fairly teems with +them. We talk of “wide gaps of empty space,” between the planets; but +how do we know that there is any such thing as empty space to be found +throughout all the sun’s domain? + +Not only are the meteorites themselves countless, a matter easily +realized, but the families or systems of meteorites appear to be +countless also. They, like the systems of Jupiter and Saturn, are +each a family within a family--a part of the Solar System, and yet a +complete system by themselves. Each circles round the sun, and each +consists of millions of tiny meteorites. When I say “tiny,” I mean it +of course only by comparison with other heavenly bodies. Many among +them may possibly be hundreds of feet and even more in diameter, but +the greater proportion appear to be much smaller. It is not impossible +that multitudes beyond imagination exist, so small in size that it is +impossible we should ever see them, since their dying flash in the +upper regions of our atmosphere would be too faint to reach our sight. + +The earth, traveling on her narrow orbit round the sun, crosses the +track of about one hundred of these systems, or rings. Sometimes she +merely touches the edge of a ring, and sometimes she goes into the very +thick of a dense shower of meteorites. Twice every year, for instance, +on the 10th of August and the 11th of November, the earth passes +through such a ring, and very many falling stars may be seen on those +nights. Numbers of little meteorites, dragged from their orbits and +entangled in the earth’s atmosphere, like a fly caught in a spider’s +web, give their dying flash, and vanish. It used to be supposed that +the August and November meteorites belonged to one single system; but +now they are believed to be two entirely distinct systems. + +[Illustration: THE GREAT SHOWER OF SHOOTING-STARS, NOVEMBER 27, 1872.] + +The comet discovered on February 27, 1827, by Biela, and ten days later +at Marseilles by Gambart, who recognized that it was the same as that +of 1772 and 1805, returned six and a half years later, in 1832. In +fact it crossed, as we have seen, the plane of the terrestrial orbit +at the respectable distance of fifty millions of miles from the earth; +but if there was any danger in this meeting, it was rather for it +than for us; for it was certainly strongly disturbed in its course. +It returned in 1839, but under conditions too unfavorable to enable +it to be observed--in the month of July, in the long days, and too +near the sun. It was seen again in 1845, on November 25th, near the +place assigned to it by calculation, and its course was duly followed. +Everything went on to the general satisfaction, when--unexpected +spectacle!--on January 13, 1846, _the comet split into two_! What had +passed in its bosom? Why this separation? What was the cause of such a +celestial cataclysm? We do not know; but the fact is, that instead of +one comet, two were henceforth seen, which continued to move in space +like two twin-sisters--two veritable comets, each having its nucleus, +its head, its coma, and its tail, slowly separating from each other. On +February 10th there was already a hundred and fifty thousand miles of +space between the two. They would seem, however, to have parted with +regret, and during several days a sort of bridge was seen thrown from +one to the other. The cometary couple, departing from the earth, soon +disappeared in the infinite night. + +They returned within view of the earth in the month of September, 1852. +On the 26th of this month the twins reappeared, but much farther apart, +separated by an interval of twelve hundred and fifty thousand miles. + +But this is not the strangest peculiarity which this curious body +presented to the attention of astronomers. The catastrophe which was +observed in 1846 was only a presage of the fate which awaited it; for +now its existence is merely imagined, the truth being that _this comet +is lost_. Since 1852 all attempts to find it again have been unavailing. + +To be lost is interesting, especially for a comet. But this, doubtless, +was not enough; for it reserved for us a still more complete surprise. +Its orbit intersects the terrestrial orbit at a point which the earth +passes on November 27th. Well, nothing more was thought about it--it +was given up as hopeless, when, on the evening of November 27, 1872, +there fell from the sky a veritable _rain of shooting stars_. The +expression is not exaggerated. They fell in great flakes. Lines of fire +glided almost vertically in swarms and showers--here, with dazzling +globes of light; there, with silent explosions, recalling to mind those +of rockets; and this rain lasted from seven o’clock in the evening +till one o’clock next morning, the maximum being attained about nine +o’clock. At the observatory of the Roman College, 13,892 were counted; +at Montcalieri, 33,400; in England a single observer counted 10,579, +etc. The total number seen was estimated at _a hundred and sixty +thousand_. They all came from the same point of the sky, situated near +the beautiful star Gamma of Andromeda. + +On that evening I happened to be at Rome, in the quarter of the Villa +Medicis, and was favored with a balcony looking towards the south. This +wonderful rain of stars fell almost before my eyes, so to say, and I +shall never cease regretting not having seen it. Convalescent from +a fever caught in the Pontine Marshes, I was obliged to go into the +house immediately after the setting of the sun, which on that evening +appeared from the top of the Coliseum to sleep in a bed of purple +and gold. My readers will understand what disappointment I felt next +morning when, on going to the observatory, Father Secchi informed me +of that event! How had he observed it himself? By the most fortunate +chance: A friend of his, seeing the stars fall, went to him to ask +an explanation of such a phenomenon. It was then half-past seven. The +spectacle had commenced; but it was far from being finished, and the +illustrious astronomer was enabled to view the marvelous shower of +nearly _fourteen thousand_ meteors. + +This event made a considerable stir in Rome, and the pope himself did +not remain indifferent; for, some days afterwards, having had the +honor of being received at the Vatican, the first words that Pius IX +addressed to me were these: “Have you seen the shower of Danaë?” I had +admired, some days before in Rome, some admirable “Danaës,” painted by +the great masters of the Italian school in a manner which left nothing +to be desired; but I had not had the privilege of finding myself under +the cupola of the sky during this new celestial shower, more beautiful +even than that of Jupiter. + +What was this shower of stars? Evidently--and this is not doubtful--the +encounter with the earth of myriads of small particles of matter moving +in space along the orbit of Biela’s comet. The comet itself, if it +still existed, would have passed twelve weeks before. It was not, then, +to speak correctly, the comet itself which we encountered, but perhaps +a fraction of its decomposed parts, which, since the breaking-up of the +comet in 1846, would be dispersed along its orbit behind the head of +the comet.[1] + +[1] No doubt can remain of the identity of this swarm of shooting-stars +with the comet of Biela. On November 27, 1885, the same encounter +occurred. A magnificent shower of stars was observed all over Europe +just at the moment when the earth crossed the comet’s orbit. + +Once in every thirty-three years we have a grand display of meteorites +in November; tens of thousands being visible in one single night. The +meteorites in that ring have their “year” of thirty-three earthly +years, and once in the course of that long year our earth’s orbit +carries her deep into their midst. In this single November ring there +are myriads upon myriads of meteorites, spreading through millions of +miles of space. + +Yet this system is but one among many. There is no reason whatever +to suppose that the streams of meteorites cluster more thickly about +the orbit of the earth, than in other parts of the Solar System. No +doubt the rest of the planets come across quite as many. Indeed, +the wonderful rings of Saturn are probably formed entirely of +meteorites--millions upon millions of them whirling round the planet +in a regular orbit-belt, lit up by the rays of the sun. Also it is +believed that the meteorite families cluster more and more closely in +the near neighborhood of the sun, rushing wildly round him, and falling +by millions into the ocean of flame upon his surface. It has even been +guessed that they may serve in part as fuel to keep up his mighty +furnace heat. + +There is a curious cone-shaped light seen sometimes in the west after +sunset. It is called the “Zodiacal Light,” and men have often been much +puzzled to account for it. The shining is soft and dim, only to be +seen when the sky is clear, and only to be seen in the neighborhood of +the sun. This, too, _may_ be caused by reflected light from countless +myriads of meteorites gathering thickly round the sun. + + + + +CHAPTER IX. + +NEIGHBORING FAMILIES. + + +We have now to take flight in thought far, far beyond the outskirts of +our little Solar System. Yes, our _great_ Solar System, with its mighty +sun, its planets, its moons, its comets and meteorites, its ceaseless +motions, its vast distances,--even all this sinks to littleness beside +the wider reaches of space which now have to be pictured to our minds. +For our sun, in all his greatness, is only a single star--only one star +among other stars--and not by any means one of the largest of the stars. + +How many stars are there in the sky? Look overhead some cloudless +night, and try to count the brilliant points of light. “Millions,” you +would most likely give as your idea of their number. Yet you would be +wrong; for you do not really perceive so many. The stars visible to +man’s naked eye have been mapped and numbered. It is found that from +two to three thousand are, as a rule, the utmost ever seen at once, +even on a favorable night, and with particularly good sight. + +But what is actually the full number of the stars? Two or three +thousand overhead. Five or six thousand round the whole world. So +much visible to man’s unaided eyes. Ah, but take a telescope, and see +through it the opening fields of stars beyond stars. Take a stronger +telescope, and note how, as you pierce deeper into space, fresh stars +beyond fresh stars shine faintly in the measureless distance. Take the +most powerful telescope ever made, and again it will be the same story. + +There has been a chart or map drawn of known stars in the northern +hemisphere--including those visible in telescopes down to a certain +magnitude--containing over three hundred thousand. But that is only a +part of even what man can see. Sir William Herschel calculated roughly +that the number of stars within reach of his powerful telescope, round +the whole earth, amounted probably to something like twenty millions. + +Twenty millions of suns! For that is what it really means. Twenty +millions of radiant, burning, heavenly bodies--some the same size as +our sun; some larger, perhaps very much larger; some smaller, perhaps +very much smaller; but all SUNS. And any number of these suns may have, +just like our own, families of planets traveling round them, enjoying +their light and their heat. + +We talk about stars of the first, second, and other magnitudes. Stars +can be seen without a telescope as low down as the sixth magnitude; +after that they become invisible to the naked eye. This word +“magnitude” is rather misleading. “Magnitude” means size, and whatever +the real size of the stars may be, they have to our sight no seeming +size at all. So when we speak of different _magnitudes_, we really mean +different _brightnesses_. The brightest stars are those of the first +magnitude, the next brightest those of the second magnitude, and so on. +No doubt many a star of the third or fourth magnitude is really much +larger than many a star of the first or second magnitude, only being +farther away it shines more dimly, or the higher-magnitude star may in +itself possess greater natural brilliancy. + +Of first-magnitude stars there are altogether about twenty; of +second-magnitude stars about sixty-five; of third-magnitude stars about +two hundred; and so the numbers increase till of the sixth-magnitude +stars we find more than three thousand. These are all that can be +commonly seen with the naked eye, amounting to five or six thousand. +With telescopes the numbers rise rapidly to tens of thousands, hundreds +of thousands, and even millions. + +For a long while it was found quite impossible to measure the distances +of the stars. To this day the distances of not over two dozen, among +all those tens of thousands, have been discovered. The difficulty of +finding out the distance of the sun was as nothing compared with the +difficulty of finding out the distances of the stars. + +No base-line sufficient for the purpose could for years be obtained. +I must explain slightly what is meant by a “base-line.” Suppose you +were on the brink of a wide river, which you had no means of crossing, +though you wished to discover its breadth. Suppose there were on the +opposite brink a small tree, standing alone. As you stood, you would +see the tree seeming to lie against a certain part of the country +beyond. Then, if you moved along your bank some fifty paces, the tree +would seem to lie against quite a different part of the country beyond. + +Now if you had a long piece of string to lay down along the fifty paces +you walked, and if two more pieces of string were tied, one from each +_end_ of the fifty paces, both meeting at the tree, then the three +pieces of string would make one large triangle, and the “fifty paces” +would be the “base” of your triangle. + +If you could not cross the river, you could not of course tie strings +to the tree. But having found your _base-line_, and measured its exact +length, and having also found the shape of the two angles at its two +ends, by noting the seeming change of the tree’s position, it would +then be quite easy to find out the distance of the tree. The exact +manner in which this calculation is made can hardly be understood +without some slight knowledge of a science called trigonometry. The +tree’s distance being found, the breadth of the river would be known. + +This mode of measuring distance was found comparatively easy in the +case of the moon. But in the case of the sun there was more difficulty, +on account of the sun’s greater distance. No base-line of ordinary +length would make the sun seem to change his position in the sky in the +slightest degree. Nor till the very longest base-line on the earth was +tried could the difficulty be overcome. That base-line is no less than +eight thousand miles long. One man standing in England looking at the +sun, and another man standing in Australia looking at the sun, have +such a base-line lying between them, straight through the center of the +earth. + +In the case of the stars this plan was found useless. So closely has +the sky been mapped out, and so exactly is the place of each star +known, that the tiniest change would have been at once noticed. Not +a star showed the smallest movement. The eight thousand miles of the +earth’s diameter was a mere point with regard to them. + +A bright idea came up. Here was our earth traveling round the sun, in +an orbit so wide that in the middle of summer she is over one hundred +and eighty millions of miles away from where she is in the middle of +winter. Would not that make a magnificent base-line? Why not observe +a star in summer and observe the same star again in winter, and then +calculate its distance. + +This, too, was done. For a long while in vain! The stars showed no +signs of change, beyond those due to causes already known. Astronomers +persevered, however, and with close and earnest care and improved +instruments, success at last rewarded their efforts. A few--only a few, +but still a few--of those distant suns have submitted to the little +measuring-line of earth, and their distance has been roughly calculated. + +Now, what is their distance? Alpha Centauri, the second star which was +attempted with success, is the nearest of all whose distance we know. +You have heard how far the sun is from the earth. The distance of Alpha +Centauri is _two hundred and seventy-five thousand times as much_. Can +you picture to yourself that vast reach of space--a line ninety-three +millions of miles long, repeated over and over again two hundred and +seventy-five thousand times? + +But Alpha Centauri is one of the very nearest. The brilliant Sirius is +at least twice as far away. Others utterly refuse to show the smallest +change of position. It is with them, as had been said, much the same as +if a man were to look at a church-steeple, twenty miles distant, out +of one pane in a window, and then were to look at it out of the next +pane. With the utmost attention he would find no change of position in +the steeple. And like the base-line of two glass panes to that steeple, +so is the base-line formed by our whole yearly journey to thousands +of distant stars. We _might_ measure how far away they are, only the +longest base-line within our reach is too short for our purpose. + +The planet Neptune has a wider orbit than ours. But even his orbit, +seen from the greater number of the stars, would shrink to a single +point. After all, how useless to talk of two hundred and seventy-five +thousand times ninety-three millions of miles! What does it mean? We +can not grasp the thought. + +Let us look at the matter from another view. Do you know how fast light +travels--this bright light shining round us all day long? Light, so far +as we know, does not exist everywhere. It travels to and fro, from the +sun to his planets, from the planets to one another; from the sun to +the moon, from the moon to the earth, and from the earth to the moon +again. + +Light takes time to travel. This sounds singular, but it is true. Light +can not pass from place to place in no time. Light, journeying through +space, is invisible. Only when it strikes upon something, whether a +solid body or water or air, does it become visible to our eyes. The +shining all round us in the day-time is caused by the sunlight being +reflected, not only from the ground, but from each separate particle +of air. If we had no atmosphere, we should see still the bright rays +falling on the ground, but the sky above would be black. Yet that black +sky would be full of millions of light-rays, journeying hither and +thither from sun and stars, invisible except where they alight upon +something. + +The speed of light is far beyond that of an express train, far beyond +that of the swiftest planet. In one tick of the clock, Mercury has +rushed onward twenty-nine miles. In one tick of the clock, storm-flames +upon the surface of the sun will sweep over two or three hundred miles. +But in one tick of the clock a ray of light flashes through one hundred +and eighty-six thousand three hundred and thirty-seven miles. + +One hundred and eighty-six thousand miles! That is the same as to say +that, during one single instant, a ray of light can journey a distance +equal to about eight times round and round our whole earth at the +Equator. + +By using this wonderful light-speed as a measurement, we gain clearer +ideas about the distances of the stars. A ray of light takes more +than eight minutes to pass from the sun to the earth. Look at your +watch, and note the exact time. See the hand moving slowly through the +minutes, and imagine one single ray of light, which has left the sun +when first you looked, flashing onward and onward through space, one +hundred and eighty-six thousand miles each second. Eight minutes and a +half are over. The ray falls upon your hand. In those few minutes it +has journeyed ninety-three millions of miles. + +So much for the sun’s distance. How about the stars? Alpha Centauri, +a bright star seen in the southern hemisphere, is one of our nearest +neighbors. Yet each light-gleam which reaches the eye of man from that +star, left Alpha Centauri four years and a third before. During four +years and a third, from the moment when first it quitted the surface +of the blazing sun, it has flashed ceaselessly onward, one hundred and +eighty-six thousand miles each second, dwindling down with its bright +companion-rays from a glare of brilliancy to a slender glimmer of light +till it reaches the eye of man. Four years and a third sounds much, +side by side with the eight minutes’ journey from the sun. Sound would +take more than three millions of years to cross the same abyss. At +the constant velocity of thirty-seven miles an hour, an express-train +starting from the sun Alpha Centauri would not reach the earth until +after an uninterrupted course of nearly seventy-five millions of years. + +This is our _neighbor_ star. The second, the nearest after it, is +nearly double as far, and is found in quite another region of space, in +the constellation of Cygnus, the Swan, always visible in our northern +hemisphere. If we wish to understand the relative situation of our sun +and the nearest two, let us take a celestial globe, and draw a plane +through the center of the globe and through Alpha Centauri and 61 +Cygni. We shall thus have before us the relation which exists between +our position in infinitude and those of these two suns. The angular +distance which separates them on the celestial sphere is 125°. Let +us make this drawing, and we shall discover certain rather curious +particulars. In the first place, these two nearest stars are in the +plane of the Milky Way, so that we can also represent the Milky Way on +our drawing; again, this celestial river is divided into two branches, +precisely in the positions occupied by these two nearest stars, the +division remaining marked along the whole interval which separates +them. This drawing shows us, further, that if we wish to trace the +curve of the Milky Way with reference to the distance of our two stars, +it will be nearer to us in the constellation of the Centaur than in +that of the Swan; and, in fact, it is probable that the stars of that +region of the sky are nearer than those of the opposite region. Another +very curious fact is, that both the nearest stars are double. + +But look at Sirius, that beautiful star so familiar to us all. The +light which reaches you to-night, left his surface from nine to ten +years ago. Look at the Little Bear, with the Pole-star shining at the +end of his tail. That ray of soft light quitted the Pole-star some +forty years ago. Almost half a century it has been speeding onward and +ever onward, with ceaseless rapidity, till its vast journey is so far +accomplished that it has reached the earth. Look at Capella, another +fair star of the first magnitude. The light which reaches you from her +has taken over thirty years to perform its voyage. Ten, thirty, forty +years--at the rate of 186,000 miles per second! + +These stars are among the few whose distance can be roughly measured. +Others lie at incalculable distances beyond. There are stars whose +light must, it is believed, have started hundreds or even thousands of +years before the soft, faint ray at length reaches the astronomer’s +upturned eye through the telescope. + +Look at Capella, how gently and steadily she shines! You see Capella, +not as she is _now_, but as she _was_ thirty years ago. Capella may +have ceased to exist meantime. The fires of that mighty sun may have +gone out. If so, we shall by and by learn the fact--more than thirty +years after it happened. Look at the Pole-star. Is there any Pole-star +now? I can not tell you. I only know there _was_ one, forty years ago, +when that ray of light started on its long journey. Stars have ceased +to shine before now. What may have happened in those forty years, who +can say? Look at that dim star, shining through a powerful telescope +with faint and glimmering light. We are told that in all probability +the tiny ray left its home long before the time of Adam. + +There is a strange solemnity in the thought. Hundreds of years +ago--thousands of years ago--some say, even tens or hundreds of +thousands of years ago! It carries us out of the little present into +the unknown ages of a past eternity. + +If the neighboring stars are placed at tens and hundreds of trillions +of miles from us, it is at quadrillions, at quintillions of miles +that most of the stars lie which are visible in the sky in telescopic +fields. What suns! what splendors! Their light comes from such +distances! And it is these distant suns which human pride would like +to make revolve round our atom; and it was for our eyes that ancient +theology declared these lights, invisible without a telescope, were +created! No contemplation expands the thought, elevates the mind, and +spreads the wings of the soul like that of the sidereal immensities +illuminated by the suns of infinitude. We are already learning that +there is in the stellar world a diversity no less great than that +which we noticed in the planetary world. As in our own Solar System +the globes already studied range from 6 miles in diameter (satellites +of Mars) up to 88,000 miles (Jupiter)--that is to say, in the +proportion of 1 to 14,000--so in the sidereal system the suns present +the most enormous differences of volume and brightness: 61 Cygni, the +stars numbered 2,398 in the catalogue of Lalande, and 9,352 in the +catalogue of Lacaille, and others of the eighth or ninth magnitude, are +incomparably smaller or less luminous than Sirius, Arcturus, Capella, +Canopus, Rigel, and the other brilliants of the firmament. + + + + +CHAPTER X. + +OUR NEIGHBORS’ MOVEMENTS. + + +How high! how distant! how mighty! How little we know about them, yet +how overwhelming the little we know, and how wonderful that we do know +it! + +We have now to consider the movements of these distant +neighbors--first, their seeming movements; secondly, their real +movements. + +I have already spoken about the seeming motions of the stars as a +whole, once believed to be real, and now known to be only caused by the +motions of our earth. For just as the turning of the earth upon her +axis makes the sun seem to rise every morning in the east, and to set +every evening in the west, so that same continued turning makes the +stars seem to rise every evening in the east and to set every morning +in the west. + +When we speak of the stars as rising in the east, we do not mean that +they all rise at one point in the east, but that all rise, more or +less, in an easterly direction--northeast, east, and southeast. So also +with respect to the west. It is to the east and west of the earth as a +whole that they rise and set--not merely to the east and west of that +particular spot on earth where one man may be standing. All night long +fresh stars are rising, and others are setting, and if it were not for +the veil of light made by the sunshine in our atmosphere, we should see +the same going on all day long as well. + +There are some constellations, or groups of stars, always visible at +night in our northern hemisphere; and there are some constellations +never visible to us, but only seen by people living in the southern +hemisphere--in Australia, for instance. There are other constellations +which appear in summer and disappear in winter, or which appear in +winter and disappear in summer. This change is caused by our earth’s +journey round the sun. It is not that the constellations have altered +their place in the heavens with respect to the other constellations, +it is merely that the earth has so altered its position in the heavens +that the groups of stars which a short time ago were above the horizon +with the sun by day are now above the horizon without him by night. + +Mention has been a good many times made of the axis of the earth ending +in the North and South Poles. If this axis were carried straight onward +through space, a long, slender pole passing upwards into the sky +without any bend, from the North Pole in one direction and from the +South Pole in the other,--this would be the pole of the heavens. The +places of the stars in the sky are counted as “so many degrees” from +the North and South Celestial Poles, just as the places of towns on +earth are counted as “so many degrees” from the North and South Poles +of earth. There are atlases of the sky made as well as atlases of the +earth. + +The constellation of the Great Bear is known to all who have ever used +their eyes at all to watch the heavens. Almost equally well known +are the two bright stars in this constellation named the Pointers, +because, taken together, they point in nearly a straight line to a +certain important star in the end of the Little Bear’s tail, not very +distant. + +This star, important less from its brightness than from its position, +lies close to that very spot in the heavens where the celestial North +Pole passes. It is called the Pole-star. Night after night, through +the year, it there remains, all but motionless, never going below +the horizon for us in the northern hemisphere, or northern half of +the earth; never rising above the horizon for those in the southern +hemisphere. It shines ever softly and steadily in its fixed position. +If you travel further south, the Pole-star sinks downward towards the +horizon. If you travel further north, the Pole-star rises higher above +the horizon. If you were at the North Pole, you would see the Pole-star +exactly overhead. + +[Illustration: CONSTELLATION OF THE GREAT BEAR.] + +Very near the Pole-star is the constellation of the Great Bear, +with Cassiopeia nearly opposite on the other side of the Little +Bear, and other groups between the two, completing the circle. These +constellations do not, to us who live in the northern hemisphere, +rise or set; for they simply move in a circle round and round the +Pole-star, never going below the horizon. All day and all night long +this circling movement continues, though only visible at night. It is +caused entirely by the earth’s own motion on her axis. + +[Illustration: THE GREAT BEAR 50,000 YEARS AGO.] + +[Illustration: THE GREAT BEAR 50,000 YEARS HENCE.] + +Lower down, or rather further off from the Pole-star, comes another +ring of constellations. These in just the same manner appear to +travel round and round the Pole-star. But being further away, each +dips in turn below the horizon--or, as we call it, each sets and +rises again. And by the time we come to yet another circle of leading +constellations, we reach those which are so far affected by the +earth’s yearly journey as to be only visible through certain months, +and to be hidden during other months. + +[Illustration: CONSTELLATION OF ORION, AS IT APPEARS NOW.] + +If we could stand exactly at the North Pole, during part of its six +months’ night, we should see the Pole-star just overhead, and all the +constellations circling round it once in every twenty-four hours. Those +nearest would move slowly, in a small ring. Those furthest, and lowest +down, would in the same length of time sweep round the whole horizon. +But the stars would not there seem to rise or set. If we were standing +at the South Pole, we should see exactly the same kind of seeming +movement, only with altogether a different set of stars. If we were +standing on the Equator at night, we should see the rising and setting +very plainly. The whole mass of stars would appear to rise regularly +and evenly in an easterly direction, to pass steadily across the sky, +each taking its own straightforward path, and to set in a westerly +direction. + +We who are placed midway between the Pole and the Equator, see a +mixture of these two motions. Some stars seem to circle round and +round, as all would do if we stood at the North Pole. Some stars seem +to rise and set, as all would do if we stood at the Equator. So much +for the seeming movements of the stars. + +But now, about their real movements. Are the stars fixed, or are they +not? These seeming daily and yearly motions do not affect the question, +being merely caused by our own motions. Trees and hedges may appear to +move as we rush past them in a train, yet they are really fixed. + +[Illustration: CONSTELLATION OF ORION 50,000 YEARS FROM NOW.] + +During a long while, after it was found out that the quick, daily +movements of all the stars in company were merely apparent, men +believed that they really had no “proper motions”--that is, no +movements of their own. For century after century the constellations +remain the same. Hundreds of years ago the seven chief stars of the +Great Bear shone in company as they shine now. Who could suppose that +each one of those seven stars is hurrying on its path through space +with a speed exceeding far that of the swiftest express-train? Yet so +it is. Hundreds of years ago the grand group of Orion, with belt and +sword, gleamed brilliantly night by night as it gleams in these days; +and Cassiopeia had her W form, and Hercules and Draco and Andromeda +were shaped as they are shaped still. Who would imagine that through +those hundreds of years each star of these different constellations was +hastening with more or less of speed along its heavenly road? Yet so it +is. + +Cases have been decisively ascertained of stars changing their places +among the other stars by a slow and gradual motion. Three of the most +conspicuous of them--Sirius, Arcturus, and Aldebaran--have been proved, +by the comparison of modern with some ancient observations, to have +experienced a change of place to the southward, to the extent of more +than the breadth of the moon in all the three. And during the period of +accurate modern measurement, other instances have been ascertained of +steady change of place by the effect of proper motion. + +But if the stars are thus rapidly moving in all directions, how is it +that we do not _see_ them move? How is it that, night after night, year +after year, century after century, even thousand years after thousand +years, the shapes of the constellations remain unaltered? + +Suppose you and I were standing on the seashore together, watching +the movements of scores of sea-craft, little boats and large boats, +steamers, yachts, and ships. Suppose we stood through a full quarter +of an hour looking on. Some might move, it is true, very slowly; yet +their movements in every case would plainly be seen. There could be no +possibility of mistaking the fact, or of supposing them to be “fixed.” +Just so we see the nearer planets move. Little danger of our supposing +them to be “fixed stars.” + +In the matter of the stars themselves, we must carry our illustration +further. Come with me up to the top of that lofty hill on the border +of the sea, and let us look from the cliff. We see still the movements +among boats and smacks, yachts and steamers, only the increased +distance makes the movements seem slower. But our view is widened. Look +on the far horizon and see three distant dots, which we know to be +ships--one and two close together, and a third a little way off, making +a small constellation of vessels. Watch them steadily for a quarter of +an hour. You will detect no movement, no increased distance or nearness +between any two of the three. The group remains unchanged. + +Are they really moving? Of course they are, more or less rapidly, +probably with differing speed and in different directions. But at +so great a distance, one quarter of an hour is not long enough for +their motions to become visible to the naked eye. If we could watch +longer--say, for two or three hours--ah, that would make all the +difference! If only we could watch longer! But the hundreds, and even +thousands of years during which men have watched the stars, sink, at +our vast distance, into no more than one quarter of an hour spent in +watching the far-off ships from the high hilltop. The motions can not +be detected. In ten thousand years you might see something. In fifty +thousand years you might see much. But four or five thousand years are +not sufficient. + +One other mode there is, by means of which the movements of the ships +on the horizon might be made plain. Suppose you had no more than the +quarter of an hour to spare, but suppose you had at your command a +powerful telescope. Then you may practically bring the ships nearer, +and by magnifying the small, slow, distant motions, you may make them, +as it were, larger, quicker, more easy to see. + +Telescopes will do this for us, likewise, in the matter of the stars. +By means of telescopes, with the assistance of careful watching and of +close calculation it has been found that the stars are really moving +quickly, each one in his own pathway. The very speed of some of them +has been measured. + +Arcturus is one of those stars, the motions of which are most plainly +to be seen. In the course of about one thousand years he changes +visibly his place in the sky by a space equal to the apparent diameter +of the moon. The seeming movement of Arcturus in one thousand years is +the same as the seeming width of the round moon that we see. + +But the actual speed with which Arcturus rushes through space is said +to be no less than fifty-four miles each second, or not far from two +hundred thousand miles an hour. That is nearly three times as fast as +our own earth’s motion round the sun. How enormous the distance must be +which can shrink such speed to such seeming slowness! + +Another beautiful star, Capella, is believed to travel at the rate of +thirty miles each second. The speed of Sirius is slower, being only +fourteen miles a second. The Pole-star creeps along at the rate of only +one mile and a half each second. + +So also with the rest of the stars. There seems good reason to believe +that every star we see shining in the heavens, every star visible in +powerful telescopes, is perpetually hastening onward. But hastening +whither? God knows! We do not. + +In all probability not one of the tens of millions of stars which +may be seen through telescopes is in repose. This is a matter of +conjecture, of reasoning from analogy, and of reasoning also from +the working of known laws. We _know_, as a consequence of direct +observation, apart from the new spectroscopic method, that at least +hundreds are upon the wing. We _assume_, as a matter of the greatest +possible likelihood, that all the millions besides, which can not be +actually seen to stir, are equally on the move. Knowing what we do know +of the laws by which the universe of stars is governed, it seems to us +an absolute impossibility that any single star, amid the whole vast +host, can be or could be permanently at rest. + +If by any means a star were brought to repose--what then would happen? +It would inevitably start off again, drawn by the attraction of other +stars. From whatever direction the strongest pull came, the impulse +would be given. Lengthened repose would be out of the question. And +this, it seems to us, must be true, not of one star only, here or +there, but of every star in the enormous host of radiant suns which +make up the mighty Stellar System. + +Our forefathers, one thousand years ago, could not measure the precise +positions of individual stars, as astronomers now are able to do. +They had no modern observatories, no telescopes, no spectroscopes, no +photographic appliances. These methods of observation we shall explain +in another chapter. Their measurements at best were rough, their +scientific knowledge was crude. Had we any such accurate observations +handed down from one thousand years ago as are made in these days, we +should no doubt see clearly many slight differences in the positions +of many stars which are not now apparent. But even then we should see +no changes sufficient in amount to affect the general outlines of the +leading constellations. + +A star, which in the course of a century makes visible advance over a +space in the sky equal to only a small portion of the breadth of the +full moon, is looked upon as a fast voyager. One hundred times this +degree of movement, if it took place in a considerable number of stars +in our sky, would not in centuries very materially change the face of +our midnight heavens. + +And all motions which would in the remotest degree affect the shapes of +constellations, must be sideway motions. Those line-of-sight motions, +of which the spectroscope alone tells us, could never have been +discovered by simple observation of the sky. Until the new method came +to light we had no means whatever of perceiving such movements among +the stars. + +Suppose you are looking at two men in the distance, upon a wide, flat +plain. One of the two is walking very slowly _across_ your line of +vision. The second man is moving very slowly straight _towards_ you. +If you watch with care you may find out both the movements. The sideway +walking will be apparent first and most easily, because, as the man +moves, he has constantly a fresh part of the horizon behind him. But +in time the advance of the second man towards you will also become +apparent; for although he is seen still against precisely the same spot +on the horizon, he slowly occupies a larger spot on the retina of your +eye,--in other words, he seems to grow bigger. And that, as you know +from long experience, can only mean increasing nearness. + +If a star seemed to grow larger as it drew nearer, we should then be +able to perceive that movement also. But no star in the sky ever does +seem to grow any larger. Every star is to us but one point of light. +It may be rushing towards us at an enormous rate of speed, yet still +as a single point it remains, always at the same point in our sky. +Therefore we have no chance of perceiving its movement; or rather, we +_had_ no chance until the discovery of this new method. In fact, the +very nearest known star is at so enormous a distance that, supposing it +to be coming towards us at the rate of one hundred miles each second, +it would still gain, in the course of a century, only one-fortieth part +more of brightness than it has now. It would not increase at all in +apparent size. + +When we leave behind us the thought of starry motions, as we faintly +detect them at this great distance, and picture to ourselves the actual +far-off whirl of all those glorious suns, the effect upon the mind is +overwhelming. Stars are found to be rushing hither and thither, at +every degree of speed, in every imaginable direction: stars to right, +and stars to left; stars towards us, and stars away from us; stars +alone, and stars in company,--all this, and more, deciphered out of +the tiny gleam of quivering light, which streams through the vast +abyss of space from each distant orb to earth. So real star-motions +were known--first, through telescopic observation; secondly, through +spectroscopic observation; and now, lastly, photography has stepped in, +bringing with it much increase of exactitude. + +But if all the stars are moving, what of our sun? Our sun is a star. +And our sun also is moving. He is pressing onward, in a wide sweep +through space, bearing along with him his whole vast family--planets, +satellites, comets, meteorites--round or towards some far distant +center. For aught we know, every star in the heavens may have a like +family traveling with him. + +In infinite space the stars are strewn in immense clusters, like +archipelagoes of islands in the ocean of the heavens. To go from one +star to another in the same archipelago light takes years; to pass +from one archipelago to another it takes thousands of years. Each of +these stars is a sun similar to ours, surrounded, doubtless, at least +for the most part, by worlds gravitating in its light; each of these +planets possesses, sooner or later, a natural history adapted to its +constitution, and serves for many ages as the abode of a multitude of +living beings of different species. Attempt to count the number of +stars which people the universe, the number of living beings who are +born and die in all these worlds, the pleasures and pains, the smiles +and tears, the virtues and vices! Imagination, stop thy flight! + +The sun is not one of the most quickly-moving stars. His rate of speed +has not been found out with any certainty, but it is believed to be +about four or five miles a second. + +And where are we going? This has been in part discovered. If you and +I were driving through a forest of trees, we should see the trees on +each side of us seeming to move backward, while behind they would close +together, and in front they would open out. + +Astronomers--and first among them, William Herschel--reasoned that +if our Solar System were really in motion, we ought to be able to +see these changes among the stars. And some such changes have become +visible through careful watching--not so much those ahead and behind as +those at the sides. + +It is not actually so simple a matter as looking at the trees in a +forest, because the trees would be at rest, whereas each star has his +own particular real motion, as well as his seeming change of place +caused by our sun’s motion. It is more like moving in a small steamer +at sea, among hundreds of other craft, each of which is going on its +own way, at the same time that all on either side seem to move backward +because we are moving forward. + +So each movement had to be noted, and the real motions had to be +separated from the seeming backward drift of stars to the right and +left of the sun’s pathway. The result of all this is that the sun, +with his planets, is found to be hastening towards a certain far-off +constellation named Hercules. + +It is a strange and unexpected fact, but absolutely true, that each sun +of space is carried along with a velocity so rapid that a cannon-ball +represents rest in comparison; it is at neither a hundred, nor three +hundred, nor five hundred yards per second that the earth, the sun, +Sirius, Vega, Arcturus, and all the systems of infinitude travel: it +is at ten, twenty, thirty, a hundred thousand yards a second; all run, +fly, fall, roll, rush through the void--and still, seen as a whole, all +seems in repose. + +The immense distance which isolates us from all the stars reduces +them to the state of motionless lights apparently fixed on the vault +of the firmament. All human eyes, since humanity freed its wings +from the animal chrysalis, all minds since minds have been, have +contemplated these distant stars lost in the ethereal depths; our +ancestors of Central Asia, the Chaldeans of Babylon, the Egyptians of +the Pyramids, the Argonauts of the Golden Fleece, the Hebrews sung by +Job, the Greeks sung by Homer, the Romans sung by Virgil,--all these +earthly eyes, for so long dull and closed, have been fixed, from age +to age, on these eyes of the sky, always open, animated, and living. +Terrestrial generations, nations and their glories, thrones and altars +have vanished: the sky of Homer is always there. Is it astonishing +that the heavens were contemplated, loved, venerated, questioned, and +admired, even before anything was known of their true beauties and +their unfathomable grandeur? + +Better than the spectacle of the sea, calm or agitated, grander than +the spectacle of mountains adorned with forests or crowned with +perpetual snow, the spectacle of the sky attracts us, envelops us, +speaks to us of the Infinite. “I have ascended into the heavens, which +receive most of His light, and I have seen things which he who descends +from on high knows not, neither can repeat,” wrote Dante in the first +canto of his poem on “Paradise.” Let us, like him, rise towards the +celestial heights, no longer on the trembling wings of faith, but +on the stronger wings of science. What the stars would teach us is +incomparably more beautiful, more marvelous, and more splendid than +anything we can dream of. + +How do such contemplations enlarge and transfigure the vulgar idea +which is generally entertained of the world! Should not the knowledge +of these truths form the first basis of all instruction which aims +at being serious? Is it not strange to see the immense majority of +human beings living and dying without suspecting these grandeurs, +without thinking of learning something of the magnificent reality which +surrounds them? + +Where the sun and his planets will journey in future ages no living man +can say. Indeed, though it is a question which does not lack interest +to a thoughtful mind, yet there are numberless other questions about +centuries near at hand which concern man far more nearly. The history +of the Universe, and the history of this Earth of ours, must have +advanced many broad stages before our sun and his attendant planets can +have traveled so far that any change will be apparent in the shape of +the star-constellations which spangle our sky. + + + + +CHAPTER XI. + +MORE ABOUT THE SOLAR SYSTEM. + + +We have now reached a point where it ought not to be difficult for +us to picture to ourselves, with something of vividness, the general +outlines of the Solar System. Awhile ago this Solar System was a very +simple matter in the eyes of astronomers. There was the great sun +fixed in the center, with seven planets circling round him--seven of +course, it was said, since seven was the perfect number--and a few +moons keeping pace with some of the planets, and an occasional comet, +and a vast amount of black, empty space. But astronomers now begin to +understand better the wonderful richness of the system as a whole; the +immense variety of the bodies contained in it; the perpetual rush and +stir and whirl of life in every part. Certainly there is no such thing +as dull stagnation throughout the family. + +First, we have the great, blazing, central sun; not a sun at rest, as +regards the stars, but practically at rest as regards his own system, +of which he is always head and center. Then come the four smaller +planets, rapidly whirling round him, all journeying in the same +direction, and all having their oval pathways lying on nearly the same +flat plane in space. Then the broad belt of busy little planetoids. +Then the four giant planets,--Jupiter nearly five times as far as our +earth from the sun; Saturn nearly twice as far as Jupiter; Uranus +nearly twice as far as Saturn; Neptune as far from Uranus as Uranus +from Saturn,--all keeping on very nearly the same level as the four +inner planets. + +[Illustration: POSITION OF PLANETS INFERIOR TO JUPITER--SHOWING THE +ZONE OF THE ASTEROIDS.] + +And between and about these principal members of the system, with their +accompanying moons, we have thousands of comets flashing hither and +thither, with long, radiant trains; and myriads of meteorites, gathered +often into dense, vast herds or families, but also scattered thickly +throughout every part of the system, each tiny ball reflecting the +sun’s rays with its little glimmer of light. + +Broad reaches of black and empty space! Where are they? Perhaps +nowhere. We are very apt, in our ignorance, to imagine that where we +see nothing, there must of necessity be nothing. But, for aught we +know, the whole Solar System, not to speak of sky-depths lying beyond, +may be bright with reflecting bodies great and small, from the mighty +Jupiter down to the fine diamond-dust of countless meteorites. In this +earth of ours we find no emptiness. Closer and closer examination with +the microscope only shows tinier and yet tinier wonders of form and +life, each perfect in finish. Not of form only, but of _life_. How +about that matter as regards the Solar System? Is our little world +the one only spot in God’s great universe which teems with life? Are +all other worlds mere barren, empty wastes? Surely not. We may safely +conclude that life of one kind or another has been, is, or will be, +upon our brother and sister worlds. + +The same reasoning may be used for the distant stars--those millions +of suns lying beyond reach of man’s unassisted eyes. Are they formed +in vain? Do their beams pour uselessly into space, carrying light, +warmth, and life-giving power to nothing? Surely around many of them, +as around our sun, must journey worlds; and not only worlds, but worlds +containing life. + +We shall have to speak of this matter again as we go on. Whether men +and women like ourselves could live on the other planets is another +question. In some cases it looks doubtful, in some it would seem to +be impossible. But the endless variety of life on this earth--life +on land, life in the air, life in water, life underground, life in +tropical heat, life in arctic cold--forbids us in anywise to be +positive as to what may or may not be. + +If no animals that we know could exist there, animals that we do not +know might be found instead. Any one of the planets may, and very +likely does, abound with life. Nay, the very meteorites themselves, +before they catch fire and burn in our air, _may_ be the homes of tiny +animalcula, altogether different from anything we see on earth. We can +not fancy life without air, but neither could we fancy life in water, +if we had not seen and known it to be possible. + +I have spoken of the probable _brightness_ of the Solar System as a +whole. We are so apt to think of things merely as we see them with our +short sight, that it is well sometimes to try to realize them as they +actually are. Picture to yourself the great central sun pouring out in +every direction his burning rays of light. A goodly abundance of them +fall on our earth, yet the whole amount of light and heat received over +the whole surface of this world is only the two-thousand-millionth +part of the enormous amount which he lavishly pours into space. How +much of that whole is wasted? None, though God gives his gifts with a +kingly profusion which knows no bounds. Each ray has its own work to +do. Millions of rays are needed for the lighting and nourishing and +warming of our companion-planets, while others are caught up by passing +comets, and myriads flash upon swift, tiny meteorites. Of the rays not +so used, many pass onwards into the vast depths beyond our system, and +dwindle down into dim, starlike shining till they reach the far-off +brother-stars of our sun. + +Have they work to do there? We can not tell. We do not know how far the +sun’s influence reaches. As head and center, he reigns only in his own +system. As a star among stars, a peer among his equals, he may, for +aught we can tell, have other work to do. + +In an early chapter, mention was made of the earth’s three motions, two +only being explained. First, she spins ceaselessly upon her axis. So +does the sun, and so do the planets. Secondly, she travels ceaselessly +round and round the sun in her fixed orbit. So does each one of the +planets. Thirdly, she journeys ceaselessly onward through space with +the sun. So also do the rest of the planets. These last two movements, +thought of together, make the earth’s pathway rather perplexing at +first sight. We talk of her orbit being an ellipse or oval; but how can +it be an ellipse, if she is always advancing in one direction? + +The truth is, the earth’s orbit is and is not an ellipse. As regards +her yearly journey round the sun, roughly speaking, we may call it +an ellipse. As regards her movement in space, it certainly is not an +ellipse. + +Think of the Solar System, with the orbits of all the planets, as lying +_nearly flat_--in the manner that hoops might be laid upon a table, +one within another. The asteroids, comets, and meteorites do not keep +to the same level; but their light weight makes the matter of small +importance. + +Having imagined the sun thus in the center of a large table--a small +ball, with several tiny balls traveling round him on the table at +different distances--suppose the sun to rise slowly upwards, not +directly up, but in a sharp slant, the whole body of planets continuing +to travel round, and at the same time rising steadily with him. + +By carefully considering this double movement, you will see that the +real motion of the earth--as also of each of the planets--is not a +going round on a flat surface to the same point from which she started, +but is a corkscrew-like winding round and round upwards through space. +Yet as regards the central sun, the shape of the orbit comes very near +being an ellipse, if calculated simply by the earth’s distance from him +at each point in turn of her pathway through the year. + +An illustration may help to explain this. On the deck of a moving +vessel, you see a little boy walking steadily round and round the mast. +Now is that child moving in a circle, or is he not? Yes, he is. No, he +is not. He walks in a circle as regards the position of the mast, which +remains always the center of his pathway. But his movement _in space_ +is never a circle, since he constantly advances, and does not once +return to his starting-point. You see how the two facts are possible +side by side. Being carried forward by the ship, with no effort of his +own, the forward motion does not interfere with the circling motion. +Each is performed independently of the other. + +It is the same with the earth and the planets. The sun, by force of +his mighty attraction, bears them along wherever he goes--no exertion +on their part, so to speak, being needed. That motion does not in the +least interfere with their steady circling round the sun. + +Just as--to use another illustration--the earth, turning on her axis, +bears through space a man standing on the Equator at the rate of one +thousand miles an hour. But this uniform movement, unfelt by himself, +does not prevent his walking backwards, or forwards, or in circles, as +much as he will. + +So, also, a bird in the air is unconsciously borne along with the +atmosphere, yet his freedom to wheel in circles for any length of time +is untouched. + +A few words about the orbits of the planets. I have more than once +remarked that these pathways are, in shape, not circles, but ellipses. +A circle is a line drawn in the shape of a ring, every part of which +is at exactly the same distance from the center-point or focus. But an +ellipse, instead of being, like a circle, perfectly round, is oval in +shape; and instead of having only one focus, it has two foci, neither +being exactly in the center. Foci is the plural word for focus. If +an ellipse is only slightly oval--or slightly _elliptical_--the two +foci are near together. The more oval or _eccentric_ the ellipse, the +farther apart are the two foci. + +You may draw a circle in this manner. Lay a sheet of white paper on a +board, and fix a nail through the paper into the board. Then pass a +loop of thread--say an inch or an inch and a half in length--round the +nail, and also round a pencil, which you hold. Trace a line with the +pencil, keeping the loop tight, so that the distance of your line from +the nail will be always equal, and when it joins you have a circle. The +nail in the center is the focus of the circle. + +To draw an ellipse, you must fix _two_ nails. Let them be about half an +inch apart; pass a loop over both of them, and again placing a pencil +point within the loop, again trace a line carefully all round, keeping +the thread drawn tight. This time an oval instead of a circle will +appear. By putting the nails nearer together or farther apart, you may +vary as you will the shape of the ellipse. + +In the orbits of the earth and the planets, all of which are ellipses +in shape, the sun is not placed in the exact center, but in one of +the two foci, the second being empty. So at one time of the year the +planet is nearer to the sun than at another time. Our earth is no +less than three millions of miles nearer in winter than she is in +summer--speaking of the winter and summer of the northern hemisphere. +Three millions of miles is so tiny a piece out of ninety-three millions +of miles, that it makes little or no difference in our feelings of heat +or cold. + +The orbits of the comets are ellipses also, but ellipses often so +enormously lengthened out, that the two foci are almost--if one may so +speak--at the two _ends_ of the oval. To draw a good comet orbit, you +must fix the two nails on your paper some five or six inches apart, +with a loop of thread just large enough to slip over them both, and to +allow the pencil to pass round them. When your ellipse is drawn, you +must picture the sun in the place of one of the two nails, and you will +see how, in their pathways, the comets at one time pass very near the +sun, and at another time travel very far away from him. + +[Illustration: COMPARATIVE SIZE OF THE PLANETARY WORLDS.] + +It is generally found in families, not only that the parent or head +of the family has great influence over all the members, but that each +member has influence over each other member. Brother influences +brother, and sister influences sister. + +This, too, we find in the Solar System. Not only does the sun, by his +powerful attraction, bind the whole family together, but each member +of the family attracts each other member. True, the force of the sun’s +attraction is overpowering in amount compared with others. The sun +attracts the planets, and the planets attract the sun; but their feeble +pulling is quite lost in the display of his tremendous strength. + +Among themselves we see the power more plainly. The earth attracts the +moon, keeping her in constant close attendance; and the moon attracts +the earth, causing a slight movement on her part, and also causing the +tides of the sea. Each planet has more or less power to hinder or help +forward his nearest brother-planet. For instance, when Jupiter on his +orbit draws near the slower Saturn on his orbit, Saturn’s attraction +pulls him on, and makes him move faster than usual; but as soon as he +gets ahead of Saturn then the same attraction pulls him back, and makes +him go more slowly than usual. Jupiter has the same influence over +Saturn; and so also have Saturn and Uranus over one another, or Uranus +and Neptune. + +In early days astronomers were often greatly puzzled by these quickened +and slackened movements, which could not be explained. Now the +“perturbations” of the planets, as they are called, are understood and +allowed for in all calculations. Indeed, it is by means of this very +attraction that Neptune was discovered, and the planets have actually +been weighed. What a wonderful difference we find in this picture of +the Solar System, as we now know it to be, from the old-world notion of +our earth as the center of the universe! + +When we think of all the planets, and of the magnificent sun; when we +pass onward in imagination through space, and find our sun himself +merely one twinkling star amid the myriads of twinkling stars scattered +broadcast through the heavens, while planets and comets have sunk to +nothing in the far distance,--then indeed we begin to realize the +unutterable might of God’s power! Why, our earth and all that it +contains may be regarded as but one grain of dust in the wide universe. + + + + +CHAPTER XII. + +MORE ABOUT THE SUN. + + +Not among the least of the wondrous things of creation are the +tremendous disturbances taking place upon the surface of the sun--that +raging, roaring sea of flame. + +A good many explanations have been from time to time offered as to the +dark spots seen to move across the face of the sun. Some one or more of +these explanations may be true; but we know little about the matter. +A sun-spot does not commonly consist of merely one black patch. There +is the dark center, called the _umbra_--plural, _umbræ_. There is the +grayish part surrounding the umbra, called the _penumbra_. Also, in +the center of the umbra there is sometimes observable an intensely +black spot, called the _nucleus_. Sometimes a spot is made up of +nucleus and umbra alone, without any penumbra. Sometimes it is made +of penumbra alone, without any umbra. Sometimes in one spot there are +several umbræ, with the gray penumbra round the whole, and gray bridges +dividing the umbræ. + +The enormous size of these spots has been already described in an +earlier chapter. Fifty thousand to one hundred thousand miles across +is nothing unusual. In the year 1839 a spot was seen which measured no +less than one hundred and eighty-six thousand miles in diameter. + +One explanation proposed was, that the sun might be a cool body, +covered over with different envelopes or dense layers of cloudy form, +one above another. The inside envelope--or, as some say, the inside +atmosphere--would then be thick and dull-colored, protecting the solid +globe within and reflecting light, but having none of its own. The next +envelope would be one mass of raging, burning gases--the _photosphere_, +in fact. The outer envelope would be a transparent, surrounding +atmosphere, lighted up by the sea of fire within. A sun-spot would then +consist of the tearing open of one or more of these envelopes, so as to +give glimpses of the gray, inner atmosphere, or even of the dark, cool +globe at the center. + +There may be some truth in this explanation; but the notion of a +cool and dark body within is now pretty well given up. The apparent +blackness of a spot-nucleus does not prove actual blackness or absence +of heat. A piece of white-hot iron, held up against the sun, looks +black; and it may be merely the contrast of the glowing photosphere +which makes the nucleus seem so dark. It is even believed that the +blackest parts may be the most intensely hot of all. + +Another proposed explanation was of dark clouds floating in the sun’s +atmosphere. There, again, are found difficulties, particularly in +the fact that, as the spots move across the sun, the changes which +regularly take place in their appearance make it pretty clear that +their shape is not flat, but hollow and cave-like. The changes here +spoken of are seeming changes of shape, caused by change of position. +There are also real changes constantly taking place. Although the spots +often keep their general outlines long enough to be watched across the +face of the sun, and even to be known again after spending nearly a +fortnight hidden on the other side, still they are far from being fixed +in form. + +[Illustration: A TYPICAL SUN-SPOT.] + +The alterations are at times not only very great, but very rapid. +Sometimes in a single hour of watching, an astronomer can see marked +movement going on--as you or I might in an hour observe movements +slowly taking place in a high layer of clouds. For movement to show at +all in one hour, at so immense a distance, proves that the actual rate +of motion must be very great. + +The first great fact which was got from the study of these spots was +this, that this great sun is very much like our own earth, in so far +as it rotates on an axis in exactly the same way that our earth does. +Not only do the spots change their position on the face of the sun, in +consequence of the sun’s rotation on its axis, but they change very +much from day to day, and even from hour to hour; so that we have +evidence not only that the sun is rotating like our earth, but that the +atmosphere of the sun is subjected to most tremendous storms--storms +so tremendous, in fact, that the fiercest cyclones on our own earth +are not for one moment to be compared with them. The fact that the +spots do really move with the sun, and are really indentations, +saucer-like hollows, in the photosphere, is shown by the appearance, +which is always presented by a spot when it is near the edge of the +sun. You know if you take a dinner-plate, and look it full in the face, +it is round; but if you look at it edgeways, it is not round. Take +two different views of the same spot: In one, you look the sun-spot +straight in the face, and you see into it and can learn all about it; +but in the other, when it has nearly gone round the corner, and is +disappearing on the sun’s edge, you see it in the same way that you +would see a plate looked at edgeways. + +These sun-cyclones must indeed be of terrific force and extent, +compared with anything we see on earth. It was calculated that the +speed of movement perceived in one spot was about three hundred and +sixty-three miles each second. + +And still all this is nothing, or almost nothing, in comparison with +the real power of the sun! The liquid state of the ocean; the gaseous +state of the atmosphere; the currents of the sea; the raising of the +clouds, the rains, storms, streams, rivers; the calorific value of +all the forests of the globe and all the coal-mines of the earth; the +motion of all living beings; the heat of all humanity; the stored-up +power in all human muscles, in all the manufactories, in all the +guns,--all that is almost nothing compared with that of which the +sun is capable. Do we think that we have measured the solar power +by enumerating the effects which it produces on the earth? Error! +profound, tremendous, foolish error! This would be to believe still +that this star has been created on purpose to illuminate terrestrial +humanity. In reality, what an infinitesimal fraction of the sun’s total +radiation the earth receives and utilizes! In order to appreciate +it, let us consider the distance of ninety-three millions of miles +which separates us from the central star, and at this distance let us +see what effect our little globe produces, what heat it intercepts. +Let us imagine an immense sphere _traced at this distance from the +sun_, and entirely surrounding it. Well, on this gigantic sphere, +the spot intercepted by our little earth is only equivalent to the +fraction 1/2,138,000,000; that is to say, that the dazzling solar +hearth radiates all round it through immensity a quantity of light +and heat two thousand one hundred and thirty-eight million times more +than that which we receive, and of which we have just now estimated +the stupendous effects. The earth only stops in its passage the _two +thousand millionth part of the total radiation_. + +Sometimes the storms or outbursts come in the shape of a bright spot +instead of a dark one. + +[Illustration: A SOLAR ERUPTION.] + +Two astronomers were one day watching the sun from two different +observatories, when they saw such an event take place. An intense +and dazzling spot of light burst out upon the surface of the sun--so +intense, so dazzling, as to stand quite apart from the radiant +photosphere. To one astronomer it looked like a single spot, while the +other saw two spots close together. In about a minute the light grew +more dim, and in five minutes all was over. But in those five minutes +the spot or spots had traveled a distance of thirty-five thousand +miles. + +It was a very remarkable thing that the _magnets_ on earth--those +delicate little needles which point so steadily yet perseveringly +towards the North Pole--seemed to be strongly agitated by the distant +solar outburst. This brings us to another interesting fact. + +The spots on the sun are not always the same in number. Sometimes they +are many, sometimes they are few. Long and close watching has made it +clear that they pass through a regular _order_ of changes: some years +of many spots being followed by other years of less and less spots; +then some years of very few spots being followed by other years of more +and more spots,--decrease and increase being seemingly regular and +alternate. + +This turn or _cycle_ of changes--from more to less, and then from less +to more again--is found to run its course about once in every eleven +years, with some variations. + +Now, it has long been known that the magnetic-needle goes through +curious variations. Though we speak of it as pointing always north, +yet it does not always so point exactly. Every day the needle is found +to make certain tiny, delicate motions, as if faintly struggling to +follow the daily movements of the sun--just a little towards the east, +or just a little towards the west. These tiny motions, having been +long watched and measured, were found to go through a regular course +of changes--some years more, and some years less, waxing and waning by +turns. It was discovered that the course of changes from more to less, +and from less to more again, took place in about eleven years. + +These two things, you see, were quite independent of one another. +Those who watched the sun-spots were not thinking of the magnets, and +those who watched the magnets were not thinking of the sun-spots. But +somebody did at last happen to think of both together. He was laughed +at, yet he took the trouble carefully to compare the two. And, strange +to say, he found that these two periods in the main agreed--the eleven +years of alternate changes in the number of sun-spots, and the eleven +years of alternate changes in the movements of the magnetic-needle. +When the spots are most, the needle moves most. When the spots are +least, the needle moves least. So much we know. But to explain the why +and the wherefore is beyond our power. + +This study of the magnetism of our wandering planet is very +interesting, and one which is still very little known. Here is a weak +needle, a slip of magnetic iron, which, with its restless and agitated +finger, incessantly seeks a region near the north. Carry this needle +in a balloon up to the higher aerial regions, where human life begins +to be extinguished; shut it up in a tomb closely separated from the +light of day; take it down into the pit of a mine, to more than a +thousand yards in depth,--and incessantly, day and night, without +fatigue and without rest, it watches, trembles, throbs, seeks the +point which attracts it across the sky, through the earth, and through +the night. Now--and here is a coincidence truly filled with notes of +interrogation--the years when the oscillation of this innocent little +steel wire is strongest are the years when there are more spots, more +eruptions, more tempests in the sun; and the years when its daily +fluctuations are weakest are those when we see in the day-star neither +spots, eruptions, nor storms. Does there exist, then, a magnetic bond +between the immense solar globe and our wandering abode? Is the sun +magnetic? But the magnetic currents disappear at the temperature of +red-hot iron, and the incandescent focus of light is at a temperature +incomparably higher still. Is it an electrical influx which is +transmitted from the sun to the earth across a space of ninety-three +millions of miles? On September 1, 1859, two astronomers--Carrington +and Hodgson--were observing the sun, independently of each other; +the first on a screen which received the image; the second directly +through a telescope,--when, in a moment, a dazzling flash blazed +out in the midst of a group of spots. This light sparkled for five +minutes above the spots without modifying their form, as if it were +completely independent, and yet it must have been the effect of a +terrible conflagration occurring in the solar atmosphere. Each observer +ascertained the fact separately, and was for an instant dazzled. Now, +here is a surprising coincidence: at the very moment when the sun +appeared inflamed in this region the magnetic instruments of the Kew +Observatory, near London, where they were observing, manifested a +strange agitation; the magnetic needle jumped for more than an hour +as if infatuated. Moreover, a part of the world was on that day and +the following one enveloped in the fires of an aurora borealis, in +Europe as well as in America. It was seen almost everywhere,--at Rome, +at Calcutta, in Cuba, in Australia, and in South America. Violent +magnetic perturbations were manifested, and at several points the +telegraph-lines ceased to act. Why should these two curious events not +be associated with each other? A similar coincidence was observed on +August 3, 1872, by Professor Charles A. Young, of Princeton, N. J.: a +paroxysm in the solar chromosphere, magnetic disturbances everywhere. + +There is a very singular appearance seen upon the sun which must not +be passed over without mention. Some astronomers speak of the whole +surface as being _mottled_ all over with a curious rough look when +examined through a powerful telescope. This “mottling” is described by +various observers in various ways. One speaks of “luminous spots shaped +like rice-grains.” Another, of “luminous spots resembling strokes +made with a camel’s-hair pencil.” Another, of “luminous objects or +granules.” Others, of “multitudes of leaves,” “nodules,” “crystalline +shapes,” “leaves or scales, crossing one another in all directions, +like what are called spills in the game of spillikens.” They have also +been pictured as “certain luminous objects of an exceedingly definite +shape and general uniformity of size, whose form is that of the oblong +leaves of a willow-tree.” These cover the whole disk of the sun, +excepting the space occupied by the spots, in countless millions, and +lie crossing each other in every imaginable direction. + +In size they are said to be about one thousand miles long, by two +or three hundred broad, but they vary a good deal. Where there is a +spot, the willow-leaves at its edge are said to point pretty regularly +towards the center. Whether they are, as they seem to be, solid in +form; whether they are, as some suppose, the chief source of the +sun’s light and heat; whether they lie on his surface or float in +his atmosphere; what is their real nature, and what is their real +use,--about these questions we are at present quite in the dark. + +We have next to think a little more about the edge or limb of the sun, +and the stormy flames and outburst there seen. Until quite lately +the only time for observing such appearances was during a total +eclipse of the sun. Lately, by means of the new instrument called the +“spectroscope,” it has been found possible to take observations when no +eclipse is going on. + +[Illustration: SUN-FLAMES, MAY 3, 1892.] + +A few words of explanation as to eclipses of the sun seem needful, +before going further. An eclipse of the sun is caused simply by the +round body of the moon passing exactly between the sun and the earth, +so as to hide the sun from us. + +Let there be a candle on the table, while you stand near. The rays of +light from the candle fall upon your face. Now move slowly, to and +fro, a round ball between you and the candle. So long as it is not +precisely in the line between--so long as it is a little higher, or +a little lower, or a little to one side--then you can still see the +flame. Once you let the ball come just between the light and your +eyes, and you see it no more. In other words the candle-flame is +eclipsed--hidden, veiled, cut off--by the ball. + +It may seem curious at first sight that the moon, which is very small +compared with the sun, should have power to cover the sun. But remember +the difference of the distance. The sun is very far, and the moon +is very near. Any small object very near will easily hide from your +sight a large object at a considerable distance. You may hold up a +shilling-piece at arm’s length, and make it cover from sight a man, or +even a house, if the latter be far enough away. The sun at a distance +of ninety-three millions of miles, and the moon at a distance of two +hundred and forty thousand miles, have to our vision the same seeming +size. So, when the moon glides between, her round face just about +covers the sun’s round face. + +If the moon were traveling exactly in the same plane as the plane of +the earth’s orbit, an eclipse would be a very common affair indeed. But +the plane of the moon’s orbit being not quite the same as the plane of +the earth’s orbit, she passes sometimes a little above, and sometimes a +little below, the exact spot where she would hide the sun’s rays from +us. Now and then, at certain intervals, she goes just between. And so +well is the moon’s path in the heavens understood that astronomers can +tell us, long years beforehand, the day and the hour an eclipse will +take place. + +An eclipse of the sun is sometimes partial, sometimes total, sometimes +annular. In a partial eclipse, the moon does indeed pass between, but +only so as to hide from us _part_ of the sun. She is a little too +low, or a little too high, to cover his face. In a total eclipse, the +moon covers the sun completely, so that for a few minutes the bright +photosphere seems blotted out from the heavens, a black round body, +surrounded by light, taking its place. In an annular eclipse, the moon +in like manner crosses the sun, but does not succeed in covering him +entirely, a rim of bright photosphere showing round the black moon. For +in an annular eclipse, the moon, being a little farther away from the +earth than at the time of a total eclipse, has too small a disk quite +to hide the sun’s disk. + +The blackness of the moon during an eclipse is caused by the fact that +her bright side is turned towards the sun, and her dark side toward us. +An eclipse of the sun can take place only at new moon, never at full +moon. At her full, the moon is outside the earth’s orbit, away from the +sun, and can not by any possibility pass between. + +Eclipses, like comets, have always been interpreted as the indication +of inevitable calamities. Human vanity sees the finger of God making +signs to us on the least pretext, as if we were the end and aim of +universal creation. Let us mention, for example, what passed even in +France, with reference to the announcement of an eclipse of the sun, on +August 21, 1560. For one, it presaged a great overthrow of States and +the ruin of Rome; for another, it implied another universal deluge; +for a third, nothing less would result than a conflagration of the +globe; finally, for the less excited, it would infect the air. The +belief in these terrible effects was so general that, by the express +order of the doctors, a multitude of frightened people shut themselves +up in very close cellars, well heated and perfumed, in order to shelter +themselves from these evil influences. Petit relates that the decisive +moment approached, that the consternation was at its height, and that +a parish priest of the country, being no longer able to confess his +parishioners, who believed their last hour had come, was obliged to +tell them in a sermon “not to be so much hurried, seeing that, on +account of the wealth of the penitents, the eclipse had been postponed +for a fortnight.” These good parishioners found no more difficulty in +believing in the postponement of the eclipse than they had in believing +in its unlucky influence. + +History relates a crowd of memorable acts on which eclipses have +had the greatest influence. Alexander, before the battle of Arbela, +expected to see his army routed by the appearance of a phenomenon of +this kind. The death of the Athenian general Nicias and the ruin of +his army in Sicily, with which the decline of the Athenians commenced, +had for their cause an eclipse of the moon. We know how Christopher +Columbus, with his little army, threatened with death by famine at +Jamaica, found means of procuring provisions from the natives by +depriving them in the evening of the light of the moon. The eclipse +had scarcely commenced when they supplied him with food. This was the +eclipse of March 1, 1504. We need not relate other facts of this +nature, in which history abounds, and which are known to every one. + +Eclipses no longer cause terror to any one, since we know that they +are a natural and inevitable consequence of the combined motions of +the three great celestial bodies--the sun, the earth, and the moon; +especially since we know that these motions are regular and permanent, +and that we can predict, by means of calculation, the eclipses which +will be produced in the future as well as recognize those which have +occurred in the past. + +The following description of the total eclipse of 1860 will be found +interesting. Mr. Lowe, who observed it at Santander, Spain, thus writes: + +“Before totality commenced, the colors in the sky and on the hills were +magnificent beyond all description. The clear sky in the north assumed +a deep indigo color, while in the west the horizon was first black +like night. In the east the clear sky was very pale blue, with orange +and red, like sunrise. On the shadow creeping across, the deep blue in +the north changed, like magic, to pale, sunrise tints of orange and +red, while the sunrise appearance in the east had changed to indigo. +The darkness was great; the countenances of men were of a livid pink. +The Spaniards lay down, and their children screamed with fear; fowls +hastened to roost, ducks clustered together, pigeons dashed against the +houses; flowers closed; many butterflies flew as if drunk, and at last +disappeared. The air became very humid, so much so that the grass felt +to one of the observers as if recently rained upon.” + + + + +CHAPTER XIII. + +YET MORE ABOUT THE SUN. + + +Having seen something of storms taking place on the sun’s photosphere, +we must next give our attention to storms taking place at his edge. But +it should be remembered that the said edge, far from being a mere rim +to a flat surface, is a kind of horizon-line--is, in fact, just that +part of the photosphere which is passing out of or coming under our +sight. The surface there is, in kind, the same as the surface of the +broad disk facing us. In watching outbursts at the edge of the sun, we +have a side view instead of a bird’s-eye view. + +In the year 1871, Professor Charles A. Young, of Princeton, was looking +at a large hydrogen cloud on the edge of the sun. When I speak of a +“cloud,” it must not be supposed that anything like a damp, foggy, +earthly cloud is meant. This solar cloud was a huge mass of red-hot +gas, about one hundred thousand miles long, rising to a height of fifty +thousand miles from the sun’s surface, and appearing to rest on glowing +pillars of fire. + +The professor, while watching, was called away for half an hour. He +came back, expecting to find things much as he had left them. Instead +of this, a startling change had taken place. The whole mass of glowing +fire seemed to have been actually “blown to shreds” by some tremendous +outburst from below. In place of the motionless cloud were masses of +scattered fire, each from about four thousand to fourteen thousand +miles long, and a thousand miles wide. + +As the professor gazed, these “bits” of broken cloud rose rapidly +upwards, away from the surface of the sun. When I say “rapidly,” I mean +that the real movement, which the professor could calculate, was rapid. +The seeming movements were of course slow, and over a small space. The +actual motions were not tardy, for in ten minutes these huge, fiery +cloud-pieces rushed upwards to a height of two hundred thousand miles +from the edge of the sun, moving at a rate of at least one hundred and +sixty-seven miles each second. Gradually they faded away. + +But what caused this sudden change? Just before the professor was +interrupted, he had noticed a curious little brilliant lump--a sort of +suspicious thunder-cloud appearance--below the quiet, bright cloud. And +after this tremendous shattering, the little bright lump rose upwards +into a huge mass of rolling flame, reaching like a pyramid to a height +of fifty thousand miles. In the course of a few minutes these enormous +flames could be seen to move and bend, and to curl over their gigantic +tips. But they did not last long. At half-past twelve the professor +had been called away; by half-past two the rolling flames completely +vanished. + +Now, whatever may be the full explanation of this sight, there is no +doubt that on that day was observed from earth a tremendous outburst, +compared with which our mightiest volcanoes are like the sputtering of +a farthing dip beside a roaring furnace. The awful force and greatness +of such a solar eruption are more than we can possibly picture to +ourselves. At our distance we may catch a faint glimpse of what is +going on, and calculate speed of movement. But vividly to realize the +actual terrific grandeur of what took place is past our power. + +Possibly this was much the same kind of outburst as that seen by the +two English astronomers; only theirs was a bird’s-eye view, as it +were, looking down on the top of the sight, while the professor had a +side-view, certainly much the best for observation. + +It does not follow from what he saw that the eruption must have taken +place exactly at the “edge” of the sun. Probably it happened near +the edge. All he could say, was that the flames rose fifty thousand +miles, and the pieces of cloud were carried two hundred thousand miles, +away from the edge. The eruption may have begun on the other side of +the sun, at any distance from the horizon-edge where it first became +visible to earthly eyes. + +Also, while the professor found that the shattered cloudlets moved at +a rate of about one hundred and sixty-seven miles each second, it is +calculated that the first fearful outburst must have caused movement, +near the surface of the sun, at a rate of at least three hundred miles +each second. Probably the hydrogen cloud was borne upwards along with +a vast mass of fragments flung out from the sun. We are here upon +doubtful ground; but this tremendous power of eruption in the sun, +and of driving matter out of and away from his surface, should not be +forgotten. + +Though such a sun-storm as that just described is not often to be seen, +yet there are at all times certain strange red prominences, or glowing +flames, rising up here and there from the sun’s “limb.” Doubtless they +rise also from other parts of the photosphere, though they are only +visible to us when near enough to the edge to stand out beyond it. + +Seen during an eclipse, these prominences have clear, sharp outlines, +and are usually bright rose-red in color. They are described as +sometimes wide and low, sometimes tall and slender; sometimes jagged, +sometimes regular; sometimes keeping long the same shape, sometimes +changing quickly in a few minutes. They are said to be like flames, +like mountains, like the teeth of a saw, like icebergs, like floating +cloudlets. + +As to their height, from fifty to eighty thousand miles is nothing +unusual. We must not speak of Mont Blanc or Mount Everest here. Jupiter +placed bodily on the surface of the sun, beside such a fire-mountain, +would not far overtop it. The earth, Venus, Mars, and Mercury, would +lie like little toy-balls at its foot. And these are common-sized +sun-flames. One was measured which reached to the enormous height +of two hundred thousand miles. The spectroscope shows these solar +prominences or jets to be made--at least in part--of burning hydrogen +gas. + +Beyond the sierra or chromatosphere--that border of rippling, crimson +flame-billows round the edge of the sun, with red flame-mountains +rising out of it here and there--beyond these, stretches the corona. +The corona, as seen from earth, is a bright, far-reaching glory of +light, shining round the sun in a total eclipse. The moon then comes +between the sun and the earth, her dark, round body creeping over the +face of the sun till the bright photosphere is completely covered. But +the sierra and the tall, red flames stand out from behind the black +moon, and the beautiful, soft corona-light stretches far beyond. + +[Illustration: SOLAR CORONA AND PROMINENCE.] + +It was long doubted whether the corona really belonged to the sun or to +the moon. There seems now no doubt that it is a part of the sun. + +Various descriptions of the corona have been given at different +times, as observed during different eclipses. It has been seen as a +steady, beamy, white cloud behind the moon, showing no flickering. +It has been seen marked with bright lines of light, and seeming to +move rapidly round and round. It has been seen silvery white, sending +off long streams of brightness. It has been seen in the form of +white light, with bluish rays running over it. It has been seen with +entangled jets of light, like “a hank of thread in disorder.” It has +been seen silvery-white again, with a faint tinge of greenish-violet +about the outer edge. It has been seen from a high mountain-top as a +mass of soft, bright light, “through which shot out, as if from the +circumference of the moon, straight, massive, silvery rays, seeming +distinct and separate from each other, to a distance of two or three +diameters of the lunar disk, the whole spectacle showing as upon a +background of diffused, rose-colored light.” + +Majestic, indeed, are the proportions of some of those mighty flames +which leap from the surface of the sun, yet these flames flicker, as +do our terrestrial flames, when we allow them time comparable to their +gigantic dimensions. Drawings of the same prominence often show great +changes in a few hours, or even less. The magnitude of the changes +could not be less than many thousands of miles, and the actual velocity +with which such masses move is often not less than one hundred miles +a second. Still more violent are the solar convulsions, which some +observers have been so fortunate as to behold, when from the sun’s +surface, as from a mighty furnace, vast incandescent masses are +projected upwards. All indications point to the surface of the sun as +the seat of the most frightful storms and tempests, in which the winds +sweep along incandescent vapors. + +The corona consists of two parts--the inner and brighter corona, the +outer and fainter corona. The shape of the whole seems to change much +at different times. The outer edge is usually blurred and indistinct, +fading gently away. + +Many explanations have been suggested. At one time the corona was +supposed to be a solar atmosphere, reflecting light like our own +atmosphere. Some have thought the light might be caused by countless +myriads of meteorite systems, revolving in the close neighborhood of +the sun. Some suppose it may be owing, in part at least, to solar +eruptions, and the pouring outward of burning gas and matter. But our +knowledge of the true nature of the corona is yet in its infancy. + +A few closing words as to the size and weight of the sun. In diameter, +eight hundred and fifty-eight thousand miles, and in bulk equal to +one million two hundred and eighty thousand earths, his weight is in +proportion less. Our earth is about four times as dense as the sun. If +her size were increased to the sun’s size, her density being the same +as now, she would be very much heavier than the sun, and would attract +much more strongly. Still, though the sun is of lighter materials than +the earth, his immense size gives him weight equal to seven hundred and +fifty times as much as all the planets put together. + +The attraction on the surface of the sun is also very great--so great +that we can hardly picture it to ourselves. If life exists there at +all--supposing it possible that any kind of life can be in such a +fiery atmosphere--it must be life very different from any known in +this world. A man who on earth weighs one hundred and sixty pounds, +and walks lightly erect, would, on the sun, lie helplessly bound to +the ground, crushed by his own overpowering weight. It is said that a +cannon-ball, reposing on the sun, if lifted one inch and allowed to +fall, would dash against the ground with a speed three times greater +than that of our fastest express-trains. For weight on earth is merely +caused by the amount of force with which the earth draws downward a +body towards herself--a force greater or less according to the density +of that body. So weight on the sun would be immensely increased by his +immensely greater power of attraction. + +[Illustration: COMPARATIVE SIZE OF THE EARTH AND SUN.] + +It is an interesting question how far the sun’s attractive influence +reaches effectually through space. The nearer a body is to the sun, +the greater the attraction which he exercises over it. At the distance +of the planet Mercury, a speed of twenty-nine miles each second is +needful to overcome or balance it sufficiently for the planet to remain +in his orbit. At the distance of the planet Neptune, about three miles +each second is enough. If a planet were journeying at four times the +distance of Neptune, the speed would need to be not over two miles each +second, lest the planet should break loose and wander away. But even +two miles a second is no mean speed--more than seven thousand miles an +hour. If we come to speak of that which we on earth call rapid motion, +we shall gain a clearer idea as to the extent of the sun’s power. + +Suppose a planet were traveling through space at the rate of one of our +fastest express-trains--sixty miles an hour. It has been calculated +that, unless the sun’s attraction were interfered with and overpowered +by some nearer sun, the said planet, though placed at a distance ten +or twelve times as great as that of the far-off star Alpha Centauri, +would still be forced by the sun’s attraction to journey round him in a +closed orbit. At such a speed it would not be free to wander off into +the depths of space. + + + + +CHAPTER XIV. + +MORE ABOUT THE MOON. + + +From a globe all fire, all energy, all action, we come to a globe +silent, voiceless, changeless, lifeless. So, at least, the moon seems +to us. But it will not do to speak too confidently. + +True, we can find no trace of an atmosphere in the moon. If there is +any atmosphere at all, it must be so thin as to be less than that which +we on earth count as actually none. We pump away the air from a glass +inclosure in an air-pump, and say the glass is empty. Only it is not +quite empty. There is always just a very little air remaining, though +so little that fire would not burn and animals could not live in it. +Some believe that air, up to that amount, may be found in the moon. But +this is much the same as to say there is none at all. For, of course, +with either no air or so very little air, life can not possibly exist +on the moon. We can not imagine such a thing for a moment. That is +just how the matter stands. We “can not imagine,” and therefore we +conclude it to be an impossibility. As if we knew a hundredth part of +the possibilities in any one corner of God’s great universe! As if our +being unable to picture a thing proves that thing not to exist! + +Suppose we had always lived in tropical heat, and had never seen, +known, or heard of such a fact as life in Arctic snows. Should we +consider it a thing possible? Suppose we had always lived on dry land, +with never a sight of sea or river or pond, and never a proof that +animal life could exist under water--aye, and that some living animals +may be suffocated by air, just as other living animals are suffocated +by water. Should we not, in our wisdom, reason out such a state of +affairs to be utterly impossible? + +There _may_ be no life on the moon. It _may_ be that she is now passing +through a dead, cold, blasted stage, either at the close of some past +history, or in preparation for some future history--or both. But, on +the other hand, it _may_ be that the moon is no less full of life than +the earth; only the life must be different in kind, must be something +which we do not know any thing at all about. + +The moon is very much smaller than the earth. Her diameter is about +two-sevenths of the earth’s diameter; her entire surface is about +two twenty-sevenths of the earth’s surface; her size is about two +ninety-ninths of the earth’s size; and her whole weight is about +one-eightieth of the earth’s weight. Attraction or gravitation on the +surface of the moon is very different from what it is on the earth. Her +much smaller bulk greatly lessens her power of attraction. While a man +from earth would, on the surface of the sun--supposing he could exist +there at all--lie helpless, motionless, and crushed by his own weight, +he would on the moon find himself astonishingly light and active. A +leap over a tall house would be nothing to him. + +[Illustration: THE MOON--AN EXPIRED PLANET.] + +The moon, unlike the sun, has no light or heat of her own to give out. +She shines merely by reflected light. Rays of sunlight falling upon +her, rebound thence, and find their way earthward. This giving of +reflected light is not a matter all on one side. We yield to the moon a +great deal more than she yields to us. Full earth, seen from the moon, +covers a space thirteen times as large as full moon seen from earth. + +Perhaps you may have noticed, soon after new moon, when a delicate +crescent of silver light shows in the sky, that within the said +crescent seems to lie the body of a round, dark moon, only not +perfectly dark. It shows a faint glimmer. That glimmer is called +earth-shine. The bright crescent shines with reflected sunlight. The +dim portion shines with reflected earth-light. What a journey those +rays have had! First, leaving the sun, flashing through ninety-three +millions of miles to earth, rebounding from earth and flashing over two +hundred and forty thousand miles to the dark shaded part of the moon, +then once more rebounding and coming back, much wasted and enfeebled, +across the same two hundred and forty thousand miles, to shine dimly in +your eyes and mine. The popular description of this particular view of +the moon is “the old moon in the arms of the new.” + +Now about the _phases_ of the moon; that is, her changes from “new” +to “full,” and back again to “new.” If the moon were a starlike body, +shining by her own light, she would always appear to be round. But as +she shines by reflected sunlight, and as part of her bright side is +often turned away from us, the size and shape of the bright part seem +to vary. For, of course, only that half of the moon which is turned +directly towards the sun is bright. The other half turned away is dark, +and can give out no light at all, unless it has a little earth-shine to +reflect. + +As the moon travels round the earth, she changes gradually from new to +full moon, and then back to new again. “New moon” is when the moon, in +her orbit, comes between the sun and the earth. The half of her upon +which the sun shines is turned away from us, and only her dark side is +towards us. So at new moon she is quite invisible. It is at new moon +that an eclipse of the sun takes place, when the moon’s orbit carries +her in a line precisely between sun and earth. + +Passing onwards round the earth, the moon, as we get a little glimpse +of her shining side, first shows a slender sickle of light, which +widens more and more till she reaches her first quarter. She is then +neither between earth and sun, nor outside the earth away from the sun, +but just at one side of us, passing over the earth’s own orbit. Still, +as before, half her body is lighted up by the sun. By this time _half_ +the bright part and _half_ the dark part are turned towards us; so +that, seeing the bright quarter, we name it the “first quarter.” + +On and on round us moves the moon, showing more light at every step. +Now she passes quite outside the earth’s orbit, away from the sun. Not +the slightest chance here of an eclipse of the sun, though an eclipse +of the moon herself is quite possible. But more of that presently. As +she reaches a point in a line with earth and sun--only generally a +little higher or lower than the plane of the earth’s orbit--her round, +bright face, shining in the sun’s rays, is turned exactly towards us. +Then we have “full moon.” + +Still she goes on. Once more her light narrows and wanes, as part of +her bright half turns away. Again at the “last quarter,” as at the +first, she occupies a “sideways” position, turning towards us half +her bright side and half her dark side. Then she journeys on, with +lessening rim of light, till it vanishes, and once more we have the +dark, invisible “new moon.” + +It was these phases and aspects of the moon which formerly gave birth +to the custom of measuring time by months, and by weeks of seven days, +on account of the return of the moon’s phases in a month, and because +the moon appears about every seven days, so to say, under a new form. +Such was the first measure of time; there was not in the sky any signal +of which the differences, the alternations, and the epochs were more +remarkable. Families met together at a time fixed by some lunar phase. + +The new moons served to regulate assemblies, sacrifices, and public +functions. The ancients counted the moon from the day they first +perceived it. In order to discover it easily, they assembled at evening +upon the heights. The first appearance of the lunar crescent was +watched with care, reported by the high priest, and announced to the +people by the sound of trumpets. The new moons which correspond with +the renewal of the four seasons were the most solemn; we find here the +origin of the “ember weeks” of the Church, as we find that of most of +our festivals in the ceremonies of the ancients. The Orientals, the +Chaldeans, Egyptians, and Jews religiously observed this custom. + +An eclipse of the sun has already been described. An eclipse of the +moon is an equally simple matter. An eclipse of the sun is caused by +the dark, solid body of the moon passing just between earth and sun, +hiding the sun from us, and casting its shadow upon the earth. An +eclipse of the moon is also caused by a shadow--the shadow of our own +earth--falling upon the moon. + +Here again, if the plane of the moon’s orbit were the same as ours, +eclipses of the moon would be very common. As it is, her orbit carries +her often just a little too high or too low to be eclipsed, and it is +only now and then, at regular intervals, that she passes through the +shadow of the earth. + +If a large, solid ball is hung up in the air, with bright sunlight +shining on it, the sunlight will cast a _cone of shadow_ behind the +ball. It will throw, in a direction just away from the sun, a long, +round shadow, the same as the ball at first, but tapering gradually off +to a point. If the ball is near the ground, a round shadow will rest +there, almost as large as the ball. The higher the ball is placed, the +smaller will be the round shadow, till at length, if the ball be taken +far enough upwards, the shadow will not reach the ground at all. Our +earth and all the planets cast just such tapering cones of dark shadow +behind them into space. The cone always lies in a direction away from +the sun. + +It is when the moon comes into this shadow that an “eclipse of the +moon” takes place. Sometimes she only dips half-way into it, or just +grazes along the edge of it, and that is called a “partial eclipse.” +Sometimes she goes in altogether, straight through the midst of the +shadow, so that the whole of her bright face for a short time grows +quite dark. Then we have a “total lunar eclipse.” + + + + +CHAPTER XV. + +YET MORE ABOUT THE MOON. + + +There are two ways of thinking about the moon. One way is to consider +her as merely the earth’s attendant satellite. The other way is to +consider her as our sister-planet, traveling with us round the central +sun. + +The first is the more common view; but the second is just as true as +the first. + +For the sun does actually pull the moon towards himself, with a very +much stronger pulling than that of the earth. The attraction of the sun +for the moon is more than double the attraction of the earth for the +moon. If it were not that he pulls the earth quite as hard as he pulls +the moon, he would soon overpower the earth’s attraction, and drag the +moon away from us altogether. + +People are often puzzled about the orbit or pathway of the moon through +the heavens. For in one sense they have to think of her as traveling +round and round in a fixed orbit, with the earth in the center. In +another sense they have to think of her as always journeying onwards +with the earth in her journey round the sun, and thus never returning +to the same point. + +There are two ways of meeting this difficulty. First of all, remember +that the one movement does not interfere with the other. Just as in the +case of the earth traveling round the sun, and also traveling onward +with him through space; just as in the case of a boy walking round and +round a mast, and also being borne onwards by the moving vessel,--so it +is here. The two movements are quite separate and independent of each +other. As regards the earth alone, the moon journeys round and round +perpetually, not in a circle, but in a pathway which comes near being +an ellipse. As regards the actual _line_ which the moon’s movements may +be supposed to draw in space, it has nothing elliptical about it, since +no one point of it is ever reached a second time by the moon. + +But according to this last view of the question, nobody ever can or +will walk in a circle or an oval. Take a walk round your grass-plot, +measuring your distance carefully at all points from the center. Is +that a circle? All the while you moved, the surface of the earth was +rushing along and bearing you with it, and the whole earth was hurrying +round the sun, and was being also carried by him in a third direction. +Whatever point in space you occupied when you started, you can _never +fill that particular part of space again_. The two ends of your +so-called circle can never be joined. + +But then you may come back to the same point _on the grass_, as +that from which you started. And this is all that really signifies. +Practically you have walked in a circle. Though not a circle as regards +space generally, it is a circle as regards the earth. So also the moon +comes back to the same point _in her orbit round the earth_. Letting +alone the question of space, and considering only the earth, the moon +has--roughly speaking--journeyed in an ellipse. You may, however, look +at this matter in quite another light. Forget about the moon being the +earth’s satellite, and think of earth and moon as two sister-planets +going round the sun in company. + +The earth, it is true, attracts the moon. So, also, the moon attracts +the earth; though the far greater weight of the earth makes her +attraction to be far greater. If earth and moon were of the same size, +they would pull each other with equal force. + +But though the pull of the earth upon the moon is strong, the pull of +the sun upon the moon is more than twice as strong. And greatly as the +earth influences the moon, yet the actual center of the moon’s orbit is +the sun, and not the earth. Just as the earth travels round the sun, so +also the moon travels round the sun. + +The earth travels steadily in her path, being only a little swayed and +disturbed by the attraction of the moon. The moon on the contrary, +while traveling in her orbit, is very much swayed and disturbed indeed +by the earth’s attraction. In fact, instead of being able to journey +straight onwards like the earth, her orbit is made up of a succession +of delicate curves or scallops, passing alternately backwards and +forwards over the orbit of the earth. Now she is behind the earth; now +in front of the earth; now between earth and sun; now outside the earth +away from the sun. The order of positions is not as here given, but +each is occupied by her in turn. Sometimes she moves quickly, sometimes +she moves slowly, just according to whether the earth is pulling her +on or holding her back. Two hundred and forty thousand miles sounds +a good deal. That is the distance between earth and moon. But it is, +after all, a mere nothing, compared with the ninety-three millions of +miles which separate the sun from the earth and moon. + +If we made a small model, with the sun in the center, and the earth and +moon traveling a few inches off, only one slender piece of wire would +be needed to represent the path of earth and moon together. For not +only would the earth and the moon be so small as to be quite invisible, +but the whole of the moon’s orbit would have disappeared into the +thickness of the single wire. This question of the moon’s motions is +in its nature intricate, and in its details quite beyond the grasp of +any beginner in astronomy. But so much at least may be understood, +that though the earth’s attraction powerfully affects the moon, and +causes in her motions _perturbations_, such as have been already spoken +about as taking place among the planets, yet that in reality the great +controlling power over the moon is the attraction of the sun. + +The tides of the ocean are chiefly brought about by the moon’s +attraction. The sun has something to do with the matter, but the moon +is the chief agent. This action of the moon can best be seen in the +southern hemisphere, where there is less land. As the moon travels +slowly round the earth, her attraction draws up the yielding waters +of the ocean in a vast wave which travels slowly along with her. The +same pulling which thus lifts a wave on the side of the earth towards +the moon, also pulls the earth gently _away from_ the water on the +opposite side, and causes a second wave there. The parts of the ocean +between these two huge waves are depressed, or lower in level. These +two waves on the opposite sides of the earth sweep steadily onwards, +following the moon’s movements,--not real, but seeming movements, +caused by the turning of the earth upon her axis. + +Once in every twenty-four hours these wide waves sweep round the whole +earth in the southern ocean. They can not do the same in the north, on +account of the large continents, but offshoots from the south waves +travel northwards, bringing high-tide into every sea and ocean inlet. +If there were only one wave, there would be only one tide in each +twenty-four hours. As there are two waves, there are two tides, one +twelve hours after the other. In the space between these two high-tides +we have low-tide. + +Twice every month we have very high and very low tides. Twice every +month we have tides not so high or so low. The highest are called +“spring-tides,” and the lowest “neap-tides.” When the moon is between +us and the sun, or when she is “new moon,” there are spring-tides; +for the pull or attraction of sun and moon upon the ocean act exactly +together. It is the same at full moon, when once more the moon is in a +straight line with earth and sun. But at the first and last quarters, +when the moon has her _sideways_ position, and when the sun pulls in +one direction and the moon pulls in another, each undoes a little of +the other’s work. Then we only have neap-tides; for the wave raised is +smaller, and the water does not flow so high upon our shores. + +In speaking of the surface of the moon, we are able only to speak +about one side. The other is entirely hidden from us. This is caused +by the curious fact that the moon turns on her axis and travels round +the earth in exactly the same length of time. One-half of the moon is +thus always turned towards us, though of that half we can only see so +much as is receiving the light of the sun. But the half turned in our +direction is always the same half. One part of the moon--not quite so +much as half, though always the same portion--is turned away from us. A +small border on each side of that part becomes now and then visible to +us, owing to certain movements of the earth and the moon. + +What sort of a landscape may lie in the unknown district, it is idle to +imagine. Many guesses have been made. Some have supposed it possible +that air _might_ be found there; that water _might_ exist there; that +something like earthly animals _might_ live there. It is difficult to +say what may not be, in a place about which we know nothing whatever. +But judging from our earthly experience, nothing seems more unlikely +than that air, water, clouds, should be entirely banished from over +one-half of a globe, and collected together in the space remaining. + +We are on safer ground when we speak about that part of the moon +which is turned towards us. For we can say with confidence that if +any atmosphere exist there, it must be in thickness less than the +two-thousandth part of our earthly atmosphere. It seems equally clear +that water also must be entirely wanting. The tremendous heat of the +long lunar day would raise clouds of vapor, which could not fail to +be visible. But no such mistiness ever disturbs the sharply-defined +outline of the moon, and no signs of water action are seen in the +craggy mountains and deep craters. + +[Illustration: THE LUNAR CRATER COPERNICUS.] + +The craters which honeycomb the surface of the moon are various in +size. Many of the larger ones are from fifty to a hundred miles in +diameter. These huge craters--or, as we may call them, deep circular +plains--are surrounded by mighty mountain ramparts, rising to the +height of thousands of feet. Usually they have in their center a +sugar-loaf or cone-shape mountain, or even two or more such mountains, +somewhat lower in height than the surrounding range. The sunset-lights +upon certain of these distant mountain-peaks were first watched by +Galileo through his telescope, and have since been seen by many an +observer--intense brightness contrasting with intense blackness of +shadow. + +In addition to her great craters, the moon seems to be thickly covered +with little ones, many of them being as small as can be seen at all +through a telescope. Whether these are all volcano-craters remains to +be discovered. It is not supposed that any of them are now active. From +time to time, signs of faint changes on the moon’s surface have been +noticed, which it was thought might be owing to volcanic outbursts. +Such an outburst as the worst eruptions of Mount Vesuvius would be +invisible at this distance. But the said changes may be quite as well +accounted for by the startling fortnightly variations of climate which +the moon has to endure. The general belief now inclines to the idea +that the moon-volcanoes are extinct, though no doubt there was in the +past great volcanic activity there. + +A description has been given earlier of the rain of meteorites +constantly falling to our earth, and only prevented by the atmosphere +from becoming serious. But the moon has no such protecting atmosphere, +and the amount of cannonading which she has to endure must be by no +means small. Perhaps in past times, when her slowly-cooling crust +was yet soft, these celestial missiles showering upon her may have +occasionally made deep round holes in her surface. + +This is another guess, which time may prove to be true. Guesses at +possible explanations of mysteries do no harm, so long as we do not +accept them for truth without ample reason. + +[Illustration: LUNAR ERUPTION--BRISK ACTION.] + +The origin of the lunar craters must be referred to some ancient epoch +in the moon’s history. How ancient that epoch is we have no means of +knowing; but in all probability the antiquity of the lunar craters is +enormously great. At the time when the moon was sufficiently heated +to have these vast volcanic eruptions, of which the mighty craters +are the survivals, the earth must have been very much hotter than it +is at present. It is not, indeed, at all unreasonable to believe that +when the moon was hot enough for its volcanoes to be active, the earth +was so hot that life was impossible on its surface. This supposition +would point to an antiquity for the moon’s craters far too great to +be estimated by the centuries and the thousands of years which are +adequate for the lapse of time as recognized by the history of human +events. It seems not unlikely that millions of years may have elapsed +since the mighty craters of Plato or of Copernicus consolidated into +their present form. + +[Illustration: LUNAR ERUPTION--FEEBLE ACTION.] + +It will now be possible for us to attempt to account for the formation +of the lunar craters. The most probable views on the subject are +certainly those adopted by Mr. Nasmyth, as represented in the cuts, +though it must be admitted that they are by no means free from +difficulty. We can explain the way in which the rampart around the +lunar crater is formed, and the great mountain which so often adorns +the center of the plain. The first of these cuts contains an imaginary +sketch of a volcanic vent on the moon in the days when the craters were +active. The eruption is here in the full flush of its energy, when the +internal forces are hurling forth a fountain of ashes or stones, which +fall at a considerable distance from the vent; and these accumulations +constitute the rampart surrounding the crater. The second cut depicts +the crater in a later stage of its history. The prodigious explosive +power has now been exhausted, and perhaps has been intermitted for some +time. A feeble jet issues from the vent, and deposits the materials +close around the orifice, and thus gradually raises a mountain in the +center. + +Besides the craters and their surrounding barriers, there are ranges of +mountains on the moon, and flat plains which were once named “seas,” +before it was found that water did not exist there. Astronomers also +see bright ridges, or lines, or cracks of light, hard to explain. + +One of the chief craters is called “Ptolemy,” and in size it is roughly +calculated to be no less than one hundred and fourteen miles across. +Another, “Copernicus,” is about fifty-six miles; and another, “Tycho,” +about fifty-four miles. The central cone-mountain of Tycho is five +thousand feet high. The crater of “Schickard” is supposed to be as much +as one hundred and thirty-three miles in diameter. + +Astronomers have agreed to name these craters after the great +discoverers who enlarged our knowledge of the solar and sidereal +systems. It is fitting that these great names are suggested every time +the moon is seen through a telescope. To Ptolemy we are indebted for +what is known as “The Ptolemaic System of the Universe,” which makes +the earth the center around which the sun, moon, planets, and stars all +revolve, and explains the apparently erratic movements of the planets +by supposing their orbits to be epicycles; that is, curves returning +upon themselves and forming loops. Tycho Brahe was willing to allow, +with Copernicus, that the planets all revolved around the sun; but he +taught that both sun and planets turned around the earth. + +The system known as “The Copernican” is now known to be the only true +one, and it is universally accepted. It is so called after Nicolaus +Copernicus, who was born in Thorn, Prussia, February 19, 1473. He was +educated for the Church, and studied medicine, but devoted himself +especially to astronomy. + +Without being precisely a great genius, this quiet and thoughtful monk +seems to have been wise far beyond the age in which he lived, and +remarkable for his independence of mind. He had a “profound sagacity,” +and a wide general grasp of scientific subjects. + +The extremely complicated and cumbrous nature of the Ptolemaic +system appeared to his judgment hardly compatible with the harmony +and simplicity elsewhere characteristic of nature. Moreover, he was +impressed and perplexed by the very marked changes in the brilliancy +of the planets at different seasons. These changes _now_ are no +difficulty at all. Venus, Mars, Jupiter, when on the same side of the +sun as ourselves, are comparatively near to us, and naturally look much +more bright in consequence of that nearness than when they are on +the opposite side of the sun from ourselves. But under the Ptolemaic +system, each planet was supposed to revolve round our earth, and to +be always at about the same distance from us; therefore, why such +variations in their brilliancy? + +[Illustration: NICOLAUS COPERNICUS.] + +During thirty-six long years he patiently worked out this theory, and +during part of those thirty-six years he wrote the one great book of +his lifetime, explaining the newer view of the Solar System which +had taken hold of his reason and imagination. This book, named _De +Revolutionibus Orbium Cœlestium_, or, “Concerning the Revolutions of +the Celestial Spheres,” which came out only a few hours before his +death, was dedicated to the Bishop of Rome--a little touch of worldly +wisdom which doubtless staved off for a while the opposition of the +Vatican. + +Copernicus was not the first who thought of interpreting the +celestial motions by the theory of the earth’s motion. That immortal +astronomer has taken care to give, with rare sincerity, the passages +in the ancient writers from which he derived the first idea of the +probability of this motion--especially Cicero, who attributed this +opinion to Nicetas of Syracuse; Plutarch, who puts forward the names +of Philolaus, Heraclides of Pontus, and Ecphantus the Pythagorean; +Martianus Capella, who adopted, with the Egyptians, the motion of +Mercury and Venus around the sun, etc. Even a hundred years before the +publication of the work of Copernicus, Cardinal Nicolas of Cusa, in +1444, in his great theological and scientific encyclopedia, had also +spoken in favor of the idea of the earth’s motion and the plurality +of worlds. From ancient times to the age of Copernicus, the system of +the earth’s immobility had been doubted by clear-sighted minds, and +that of the earth’s motion was proposed under different forms. But all +these attempts still leave to Copernicus the glory of establishing it +definitely. + +Not content with merely admitting the idea of the earth’s motion as a +simple arbitrary hypothesis, which several astronomers had done before +him, he wished--and this is his glory--to demonstrate it to himself +by acquiring the conviction by study, and wrote his book to prove it. +The true prophet of a creed, the apostle of a doctrine, the author of +a theory, is the man who, by his works, demonstrates the theory, makes +the creed believed in, and spreads the doctrine. He is not the creator. +“There is nothing new under the sun,” says an ancient proverb. We may +rather say, Nothing which succeeds is entirely new. The newborn is +unformed and incapable. The greatest things are born from a state of +germ, so to say, and increase unperceived. Ideas fertilize each other. +The sciences help each other; progress marches. Men often feel a truth, +sympathize with an opinion, touch a discovery, without knowing it. The +day arrives when a synthetical mind feels in some way an idea, almost +ripe, becoming incarnate in his brain. He becomes enamored of it, he +fondles it, he contemplates it. It grows as he regards it. He sees, +grouping round it, a multitude of elements which help to support it. +To him the idea becomes a doctrine. Then, like the apostles of good +tidings, he becomes an evangelist, announces the truth, proves it by +his works, and all recognize in him the author of the new contemplation +of nature, although all know perfectly well that he has not invented +the idea, and that many others before him have foreseen its grandeur. + +Such is the position of Copernicus in the history of astronomy. The +hypothesis of the earth’s motion had been suggested long before his +birth on this planet. This theory counted partisans in his time. +But he--he did his work. He examined it with the patience of an +astronomer, the rigor of a mathematician, the sincerity of a sage, and +the mind of a philosopher. He demonstrated it in his works. Then he +died without seeing it understood, and it was not till a century after +his death that astronomy adopted it, and popularized it by teaching +it. However, Copernicus is really the author of the true system of the +world, and his name will remain respected to the end of time. + +The so-called “seas” on the moon are those large dark spots to be seen +on its surface, in the shape of “eyes, nose, and mouth,” or of the +famous old man with his bundle of sticks. The brighter parts are the +more mountainous parts. + +The chief ranges of lunar mountains have been named by astronomers +after mountains on earth, such as the Apennines, the Alps, the +Caucasian range, the Carpathian and the Altai Mountains. + + + + +CHAPTER XVI. + +MERCURY, VENUS, AND MARS. + + +Once again we have to journey through the high-roads of the Solar +System, paying a brief visit to each in turn of our seven chief +brother-and-sister planets, and learning a few more leading facts about +them. Having gone the same way before, it will not now seem quite so +far. + +Busy, hurrying Mercury! we must meet him first in his wild rush through +space. If he were to slacken speed for a single instant, he would begin +to fall with fearful rapidity towards the sun. And if Mercury were to +drop into one of those huge black chasms of rent furnace-flame on the +sun’s surface, there would be a speedy end to his life as a planet. + +Mercury’s day is about the same length as our day, and his year is +about one quarter the length of our year. If Mercury has spring, +summer, autumn, and winter, each season must be extremely short; but +this depends upon whether Mercury’s axis slopes like the earth’s +axis--a matter difficult to find out. Mercury is always so near to the +sun, that it is by no means easy to observe him well. + +We know more about his orbit than his axis. The earth’s orbit, as +before explained, is not a circle, but an ellipse or oval. Mercury’s +orbit is an ellipse also, and a much longer--or, as it is called, a +more eccentric--ellipse. The earth is three millions of miles nearer +to the sun at one time of the year, than six months before or after. +Mercury is no less than fifteen millions of miles nearer at one time +than another, which must make a marked difference in the amount of heat +received. + +Even when the distance is greatest, the sun as seen from Mercury looks +four and a half times as large as the sun we see. What a blazing +splendor of light! It is not easy to imagine human beings living there, +in such heat and glare, and with either no changes of season at all, or +such very short seasons rapidly following one another. Mercury may, and +very likely does, abound with living creatures, as much as the earth +abounds with them; only one fancies they must be altogether a different +kind of living creatures from any ever seen on earth. And yet we do not +know. Man can so wonderfully adapt himself or be adapted to different +climates on earth, from extreme heat to extreme cold, that we can not +tell how far this adapting power may reach. + +Both Mercury and Venus seem to be enfolded in dense, cloud-laden +atmospheres, rarely parting so as to allow us to get even a glimpse +of the real planets within the thick, light-reflecting covering. Some +have thought that a heavy, moist, protecting atmosphere may help to +ward off the intense heat, and to make Mercury a more habitable place. +Our earthly atmosphere is rather of a kind to store up heat, and to +make us warmer than we should be without it; but there might be vapors +differently constituted which might act in some other way. At all +events, we know how easily God can have adapted either the planet to +the creatures he meant to place there, or the creatures to the climate. +“All things are possible” to him. The how and the what are interesting +questions for us, but we must often be content to wait for an answer. + +A thick, gray ring or belt has been noticed round the small, black disk +of Mercury, while it has passed between us and the sun. The edge of +Mercury, seen against the bright photosphere beyond, would, if there +were no atmosphere, be sharp and clear as the edge of the airless moon. +This surrounding haze seems to show that Mercury has an atmosphere. The +sunlight reflected from Mercury’s envelope of clouds shines at least as +brightly as if it were reflected from his solid body. + +The small size of Mercury makes attraction on his surface much less +than on earth. A lump of iron weighing on earth one pound, would weigh +on Mercury only about seven ounces, or less than half as much. So a +man would be a very light leaper indeed there, and an elephant might +be quite a frolicsome animal. If there are star-gazers in Mercury, and +if the cloud-laden atmosphere allows many clear views of the sky, the +earth and Venus must both be beautiful to look upon. Each of the two +would shine far more brightly than Jupiter, as seen at his best from +earth. + +Like Mercury, Venus, the next planet, has an orbit lying inside our +orbit. Mercury and Venus are always nearer to the sun than we are; +and if Mercury and Venus traveled round the sun in orbits, the planes +of which were exactly the same as the plane of the earth’s orbit, we +should very often see them creeping over the surface of the sun. Not +that they really “creep over” it; only, as they journey between the sun +and us, we can see them pass like little black dots across the sun’s +disk. This is the same thing as when the moon passes across the sun’s +disk and eclipses it. But Mercury and Venus are too far away from us to +cause any eclipse of the sun’s light. + +Mercury has given more trouble to astronomers than any other member of +the system; for, owing to his proximity to the sun, he is usually lost +in the solar glory, and is never seen in a dark part of the heavens, +even at the time of his greatest distance. This circumstance, together +with a small mass and an immense velocity, renders it difficult to +catch and watch him. In high latitudes, where the twilight is strong +and lengthened, while mists often overhang the horizon, the planet can +seldom be seen with the naked eye. Hence an old astro-meteorologist +contemptuously describes him as “a squirting lacquey of the sun, who +seldom shows his head in these parts, as if he was in debt.” Copernicus +lamented that he had never been able to obtain a sight of Mercury; and +the French astronomer Delambre saw him not more than twice with the +naked eye. + +The most favorable times for making observations are about an hour and +three-quarters before sunrise in autumn, and after sunset in spring; +but very clear weather and a good eye are required. At certain periods, +when between the earth and the sun, on a line joining the centers of +the two bodies, Mercury appears projected on the solar disk as a small, +round, dark spot. This is called a _transit_, and would occur during +every revolution if the plane of his orbit coincided with that of the +orbit of the earth. But as one-half of his orbit is a little above +that of the earth, and the other half a little below it, he passes +above or below the sun to the terrestrial spectator, except at those +intervals, when, being between us and the sun, he is also at one of the +two opposite points where the planes of the respective orbits intersect +each other. Then, stripped of all luster, the planet passes over +the face of the great luminary as a black circular speck, affording +evidence of his shining by reflected light, and of his spherical form. + +The first transit of Mercury recorded in history was predicted by +Kepler, and witnessed by Gassendi, at Paris, on the morning of a +cloudy day, the 7th of November, 1631. It was toward nine o’clock +when he saw the planet; but owing to its extreme smallness, he was +at first inclined to think it was a minute solar spot. It was then +going off the sun; and made its final egress toward half-past ten. The +observed time of the transit was nearly five hours in advance of the +computed time. This was a very satisfactory accordance for that age +between theory and observation; but it was the effect of a fortuitous +combination of circumstances, rather than of computations founded +upon well-established data. “The crafty god,” wrote Gassendi, in the +peculiar style of his day, “had sought to deceive astronomers by +passing over the sun a little earlier than was expected, and had drawn +a veil of dark clouds over the earth in order to make his escape more +effectual. But Apollo, knowing his knavish tricks from his infancy, +would not allow him to pass altogether unnoticed. To be brief, I have +been more fortunate than those hunters after Mercury who have sought +the cunning god in the sun. I found him out, and saw him where no one +else had hitherto seen him.” Since Gassendi’s time a number of transits +have been observed. + +These crossings of the sun’s face, or “transits,” as they are called, +have been important matters. The transit of Venus especially was once +eagerly looked for by astronomers, since, by close observations of +Venus’s movements and positions, the distance of the sun could at that +time be better calculated than in any other way. Other methods are now +coming into vogue. + +The transits of Venus are rare. Two come near together, separated by +only eight years, and then for more than one hundred years the little +dark body of Venus is never seen from earth to glide over the sun’s +photosphere. There was a transit of Venus in the year 1761, and another +in the year 1769. There was a transit of Venus in 1874, and another in +1882. At the last transits it was found that the sun, instead of being +ninety-five millions of miles away, as astronomers thought, was only +ninety-three millions of miles away. The reason why these transits +happen so seldom, is that the orbits of Mercury and Venus lie in rather +a different plane or level from the earth’s orbit. So, like the moon, +though often passing between us and the sun, they generally go just a +little higher or just a little lower than his bright face. + +Mercury and Venus show phases like the moon, although they do not +circle round the earth as the moon does. These “phases,” or changes of +shape, are probably never visible except through a telescope. It will +be easier to think about the phases of Venus alone, than to consider +both together. Her orbit lies within the earth’s orbit, and the earth +and Venus travel round the sun--as do all the planets--in the same +direction. But as Venus’s pathway is shorter than ours, and as her +speed is greater, she is much the quickest about her yearly journey, +and she overtakes us again and again at different points of our orbit +in turn. + +[Illustration: PHASES OF VENUS.] + +At one time she comes between us and the sun. That is her nearest +position to us, and she is then only about twenty-five millions of +miles distant. A beautiful sight she would be, but unfortunately her +bright side is entirely turned away, and only her dark side is turned +towards us. So then she is “new Venus,” and is invisible. + +At another time she is completely beyond the sun, and at her farthest +position away from us. Her shining is quite lost in the sun’s rays +coming between. And though we get a good view of her as “full Venus,” +at a little to one side or the other, yet so great is her distance--as +much as one hundred and fifty-seven millions of miles--that her size +and brightness are very much lessened. + +Between these two nearest and farthest points, she occupies two middle +distances, one on each side of the sun. Then, like the moon at her +“quarters,” she turns to us only half of her bright side. But this +is the best view of Venus that we have, as a brilliant, untwinkling, +starlike form,--the Evening Star of ancients and of poets. Between +these four leading positions Venus is always traveling gradually +from one to another--always either waxing or waning in size and in +brightness. Mercury passes through the same seeming changes. + +Inhabitants of Venus must have a glorious view of the earth, with her +attendant moon. For just at the time when the two planets are nearest +together, and when she is only “new Venus” to us, a dark and invisible +body, the earth is “full earth” to Venus. The very best sight we ever +have of Venus can not come near that sight. But if Mercury and Venus +really are so often covered with heavy clouds as astronomers believe, +this must greatly interfere with any habits of star-gazing. + +Venus and the earth have often been called twin-sister planets. There +are many points of likeness between them. In size they differ little, +and in length of day they are within an hour of being the same. Earth +certainly has a companion-moon, and Venus, it is believed, has not. At +one time several astronomers were pretty certain that they had caught +glimpses of a moon; but the supposed moon has of late quite vanished, +and nobody can say whether it ever really existed. Venus travels in +an ellipse which comes nearer to being a circle than the orbit of any +other planet. + +Mountain-shadows have been watched through the telescope, in Venus, +as in the moon. Some astronomers have believed that they saw signs of +very lofty mountains--as much as twenty-eight miles, or four times the +height of our highest earthly mountains, but this requires confirmation. + +There is a good deal of uncertainty about the climate of Venus. The +heat there must greatly surpass heat ever felt on earth--the sun being +about double the apparent size of our sun, and pouring out nearly +double the amount of light and heat that we receive. + +This difference may be met, as already stated, by a sheltering, cloudy +atmosphere, or the inhabitants may have frames and eyesight suited to +the increased glare and warmth. + +An atmosphere and water exist there as here. From what we have seen +above of the rapid and violent seasons of this planet, we might think +that the agitations of the winds, the rains, and the storms would +surpass everything which we see and experience here, and that its +atmosphere and its seas would be subject to a continual evaporation +and precipitation in torrential rains--an hypothesis confirmed by its +light, due, doubtless, to reflection from its upper clouds, and to the +multiplicity of the clouds themselves. To judge by our own impressions, +we should be much less pleased with this country than with our own, and +it is even very probable that our physical organization, accommodating +and complaisant as it is, could not become acclimatized to such +variations of temperature. But it is not necessary to conclude from +this that Venus is uninhabitable and uninhabited. We may even suppose, +without exaggeration, that its inhabitants, organized to live in the +midst of these conditions, find themselves at their ease, like a fish +in water, and think that our earth is too monotonous and too cold to +serve as an abode for active and intelligent beings. + +Of what nature are the inhabitants of Venus? Do they resemble us in +physical form? Are they endowed with an intelligence analogous to +ours? Do they pass their life in pleasure, as Bernardin de St. Pierre +said; or, rather, are they so tormented by the inclemency of their +seasons that they have no delicate perception, and are incapable of +any scientific or artistic attention? These are interesting questions, +to which we have no reply. All that we can say is, that organized +life on Venus must be little different from terrestrial life, and +that this world is one of those which resemble ours most. It should, +then, be inhabited by vegetable, animal, and human races but little +different from those which people our planet. As to imagining it desert +or sterile--this is an hypothesis which could not arise in the brain +of any naturalist. The action of the divine sun must be there, as in +Mercury, still more fertile than his terrestrial work, already so +wonderful. We may add that Venus and Mercury, having been formed after +the earth, are relatively younger than our planet. + +It is believed also that the axis of Venus, instead of being slanted +only as much as the earth’s axis, is tilted much more. Even if +the tilting is less than some have supposed, it is probably very +considerable. If Venus really does “lie over” in such a manner, +certain startling changes of climate on its surface--unpleasant +changes, according to our ideas--would take place. + +Like earth, Venus would have her two arctic regions, where a burning +summer’s day would succeed a bitter winter’s night, each half a year in +length. She would have also her tropical region--only in that region +intense cold would alternate with intense heat, brief seasons of each +in turn. And between the tropics and the arctic regions would lie wide +belts, by turns entirely tropical and entirely arctic. The rapidity and +severity of these changes, following one another in a year about as +long as eight of our months, would seem to be too much for any human +frame to endure. But it all rests upon an _if_. And we may be quite +sure that _if_ there are any manner of human beings in Venus, their +frames are well suited to the climate of their world. + +Though Mars is one of the inner group of four small planets, divided by +the zone of asteroids from the outer group of four great planets, yet +he belongs to the outside set of Superior Planets. His orbit surrounds +ours, being at all points farther off from the sun. Very slight +“phases” have been seen in Mars. He turns to us, from time to time, +just enough of his dark side to prove that he _has_ a dark side, and +that he does not shine like a star by his own light. But the phases on +that planet are by no means marked as they are with Venus. + +Until lately it was believed that Mars possessed no moons. Two very +small ones have, however, been lately found circling round him.[2] +They have been named Deimos and Phobos, after the “sons of Mars” in +Greek mythology. Deimos travels round Mars in thirty-nine hours, while +Phobos performs the same journey in the astonishingly short period of +seven hours and a half! + +[2] The discovery of the two moons is due to the agency of a woman. +Professor Asaph Hall, of Washington City, was searching by the aid of +the most powerful telescope which had yet been directed to Mars, and at +the very moment when the planet was in the most favorable condition for +observation. Having searched in vain during several evenings in August, +1877, he was about to give up, when Mrs. Hall begged him to search a +little more. He did so, and on the night of the 11th he discovered the +first of the satellites, and then on the 17th the second. + +[Illustration: MARS AND THE PATH OF ITS SATELLITES.] + +We have here, then, a system very different from that of the earth +and moon. But the most curious point is the rapidity with which the +inner satellite of Mars revolves round its planet. This revolution +is performed in seven hours, thirty-nine minutes, fifteen seconds, +although the world of Mars rotates on itself in twenty-four hours, +thirty-seven minutes--that is to say, this moon turns much more +quickly than the planet itself. This fact is inconsistent with all the +ideas we have had up to the present on the law of formation of the +celestial bodies. Thus, while the sun appears to revolve in the Martian +sky in a slow journey of more than twenty-four hours, the inner moon +performs its entire revolution in a third of a day. It follows that +_it rises in the west_ and _it sets in the east_! It passes the second +moon, eclipses it from time to time, and goes through all its phases +in eleven hours, each quarter not lasting even three hours. What a +singular world! + +These satellites are quite small--they are the smallest celestial +bodies we know. The brightness of the planet prevents us from measuring +them exactly. It seems, however, that the nearer is the larger, and +shows the brightness of a star of the tenth magnitude, and that the +second shines as a star of the twelfth magnitude. According to the +most trustworthy photometric measures, the first satellite may have a +diameter of 7.45 miles, and the second a diameter of 6.2 miles. _The +larger of these two worlds is scarcely larger than Paris._ Should we +honor them with the title of worlds? They are not even terrestrial +continents, nor empires, nor kingdoms, nor provinces, nor departments. +Alexander, Cæsar, Charlemagne, or Napoleon, might care but little to +receive the scepter of such worlds. Gulliver might juggle with them. +Who knows, however? The vanity of men being generally in the direct +ratio of their mediocrity, the microscopical reasoning mites which +doubtless swarm on their surface have also, perhaps, permanent armies, +which mutilate each other for the possession of a grain of sand. + +These two little moons received from their discoverer the names of +_Deimos_ (Terror) and _Phobos_ (Flight), suggested by the two verses of +Homer’s “Iliad” which represent Mars descending on the earth to avenge +the death of his son Ascalaphus: + + “He ordered Terror and Flight to yoke his steeds, + And he himself put on his glittering arms.” + +_Phobos_ is the name of the nearer satellite; _Deimos_, that of the +more distant. + +The existence of these little globes had already been suspected from +analogy, and thinkers had frequently suggested that, since the earth +has one satellite, Mars should have two, Jupiter four, Saturn eight; +and this is indeed the fact--though as Jupiter is now found to have +_five_ satellites, this arithmetical progression is upset. But as we +experience too often in practice the insufficiency of these reasonings +of purely human logic, we can not give them more value than they +really possess. We might suppose in the same way now that Uranus has +sixteen satellites, and Neptune thirty-two. This is possible; but +we know nothing of them, and have not even the right to consider +this proportion as probable. It is not the less curious to read the +following passage, written by Voltaire in 1750 in his masterpiece, the +“Micromégas:” + +“On leaving Jupiter, our travelers crossed a space of about a hundred +millions of leagues, and reached the planet Mars. They saw _two +moons_, which wait on this planet, and which have escaped the gaze +of astronomers. I know well that Father Castel wrote against the +existence of these two moons; but I agree with those who reason from +analogy. These good philosophers know how difficult it would be for +Mars, which is so far from the sun, to get on with less than two moons. +However this may be, our people found it so small that they feared they +might not find anything to lie upon, and went on their way.” + +Here we have unquestionably a very clear prophecy, a rare quality +in this kind of writing. The astronomico-philosophical romance of +“Micromégas” has been considered as an imitation of Gulliver. Let us +open the masterpiece of Swift himself, composed about 1720, and we +read, word for word, in Chapter III of the “Voyage to Laputa:” + +“Certain astronomers ... spend the greatest part of their lives in +observing the celestial bodies, which they do by the assistance of +glasses far excelling ours in goodness. For this advantage hath enabled +them to extend the discoveries much farther than our astronomers in +Europe; for they have made a catalogue of ten thousand fixed stars, +whereas the largest of ours do not contain above one-third part of that +number. They have likewise discovered two lesser stars, or satellites, +which revolve about Mars, whereof the innermost is distant from the +center of the primary planet exactly three of his diameters, and the +outermost five. The former revolves in the space of ten hours, and +the latter in twenty-one and a half; so that the squares of their +periodical times are very near in the same proportion with the cubes of +their distance from the center of Mars, which evidently shows them to +be governed by the same law of gravitation that influences the other +heavenly bodies.” + +What are we to think of this double prediction of the two satellites of +Mars? Indeed, the prophecies which have been made so much of in certain +doctrinal arguments have not always been as clear, nor the coincidences +so striking. However, it is evident that no one had ever seen these +satellites before 1877, and that there was in this hit merely the +capricious work of chance. We may even remark that both the English and +French authors have only spoken ironically against the mathematicians, +and that in 1610, Kepler, on receiving the news of the discovery of the +satellites of Jupiter, wrote to his friend Wachenfals that “not only +the existence of these satellites appeared to him probable, but that +doubtless there might yet be found two to Mars, six or eight to Saturn, +and perhaps one to Venus and Mercury.” We can not, assuredly, help +noticing that reasoning from analogy is here found on the right road. +However this may be, this discovery truly constitutes one of the most +interesting facts of contemporary astronomy. + +Mars is not only much smaller than the earth, but a good deal less +dense in his “make.” His material is only about three-quarters as heavy +as an equal amount of the earth’s material. A very heavy man on earth +would be a most light and active individual on Mars. Gold taken from +earth to Mars would weigh there no more than tin weighs upon earth. + +Mars has, it seems, an atmosphere, even as earth has. Of all the +planets Mars, is the only one whose actual surface is discernible in +the telescope. Mercury and Venus are so hidden by dense envelopes of +clouds that the real planets within are only now and then to be dimly +caught sight of. Jupiter and Saturn are so completely enwrapped in +mighty masses of vapor, that we can not even be certain whether there +are any solid bodies at all inside. + +But Mars can be studied. Here and there, it is true, clouds sweep over +the landscape, hiding from view for a little while one continent or +another, one sea or another, growing, changing, melting away, as do +the clouds of earth. Still, though these clouds come and go, there are +other markings on the surface of Mars which do not change. Or, rather, +they only change so much as the continents and oceans of earth would +seem to vary, if watched from another planet, as the daily movement of +earth carried them from west to east, or as they might be hidden for +a while by cloud-layers coming between. It has been curiously noted +that these clouds over Mars form often in the morning and evening, and +are afterwards dispersed by the heat of midday. Also there seems every +reason to believe that rainfalls take place in Mars as upon earth. + +The red color of Mars is well known. This does not vanish in the +telescope, but it is found that parts only have the red or orange +hue, while other parts are dark and greenish. These are the markings +which remain always the same, and they have been so closely examined +that more is known about the geography of Mars than of any other world +outside our own. + +Mars, at his nearest point, does not draw closer to us than forty +millions of miles. At such a distance one must not speak too +confidently. There are, however, many reasons for believing that the +red portions are continents and that the green portions are oceans. + +The spectroscope has lately shown us that water does really exist in +the atmosphere of Mars--unlike the dreary, waterless moon. So we no +longer doubt that the cloudlike appearances are clouds, and that rain +sometimes falls on Mars. If there is rain, and if there are clouds and +vapor, there are probably oceans also. + +Two singular white spots are to be seen at the north and south poles, +which we believe to be polar ice and snow. Somebody looking at our +earth in like manner from a distance, would doubtless perceive two +such white snow-spots. These two polar caps are seen to vary with the +seasons. When the north pole of Mars is turned towards the sun, the +white spot there grows smaller; and at the same time, the south pole of +Mars being turned away from the sun, the white spot there grows larger. +Again, when the south pole is towards the sun, and the north pole away +from the sun, the white spot at the south is seen to be the smallest, +and the white spot at the north is seen to be the largest. This is +exactly what takes place in the summers and winters of our north and +south poles. + +The markings of Mars have been so carefully studied, that at last a map +has been made of the planet--a map of a world, never less than forty +millions of miles away! Names have been given to the continents and +oceans--such as Dawes Continent, Herschel Continent, De La Rue Ocean, +Airy Sea, Huggins Inlet, and so on. + +Land and water seem to be very differently arranged on Mars from what +they are on earth. Here we have about three times as much water as +land, and to get from one continent to another without crossing the +sea is in some cases impossible. But a traveler there might go most +conveniently to and fro, hither and thither, to all parts of his world, +either on land or on water, without any change. If he preferred water, +he would never need to set foot on land; and if he preferred land, he +would never need to enter a boat. The two are so curiously mingled +together, narrow necks of land running side by side with long, narrow +sea-inlets, that Atlantic and Pacific Oceans are unknown. + +Some have wondered whether the reddish color of the land may be caused +by grass and trees being red instead of green. Very strange if so it +were. But in that case, no doubt the inhabitants of Mars would find +green just as trying to their eyesight, as we should find red trying to +ours. + + + + +CHAPTER XVII. + +JUPITER. + + +Passing at one leap over the belt of tiny asteroids, about which we +know little beyond their general movement, and the size and weight of +a few among them, we reach at once the giant planet Jupiter: Mighty +Jupiter, hurrying ever onward, with a speed, not indeed equal to that +of Mercury or of our earth, yet eighty times as rapid as the speed of +a cannon-ball! Think of a huge body, equal in bulk to twelve hundred +earths, equal in weight to three hundred earths, rushing ceaselessly +through space, at the rate of seven hundred thousand miles a day! + +Jupiter’s shape is greatly flattened at the poles. He spins rapidly on +his axis, once in nearly ten hours, and has therefore a five hours’ +day and a five hours’ night. As the slope of his axis is exceedingly +slight, he can boast little or no changes of season. The climate near +the poles has never much of the sun’s heat. In fact, all the year round +the sun must shine upon Jupiter much as he shines on the earth at the +equinoxes. + +But the amount of light and heat received by Jupiter from the sun is +only about one twenty-fifth part of that which we receive on earth; and +the sun, as seen from Jupiter, can have but a small, round surface, not +even one-quarter the diameter of the sun we see in the sky. + +When looked at with magnifying power, the bright, starlike Jupiter +grows into a broad, softly-shining disk or plate, with flattened top +and bottom, and five tiny, bright moons close at hand. Sometimes one +moon is on one side, and four are on the other; sometimes two are one +side and three on the other; sometimes one or more are either hidden +behind Jupiter or passing in front of him. Jupiter has also curious +markings on his surface, visible through a telescope. These markings +often undergo changes; for Jupiter is no chill, fixed, dead world, such +as the moon seems to be. + +[Illustration: GENERAL ASPECT OF JUPITER--SATELLITE AND ITS SHADOW.] + +There are dark belts and bright belts, usually running in a line with +the equator, from east to west. Across the regions of the equator lies +commonly a band of pearly white, with a dark band on either side of +“coppery, ruddy, or even purplish” hue. Light and dark belts follow one +after another, up to the north pole and down to the south pole. + +When we talk of “north and south poles” in the other planets, we merely +mean those poles which point towards those portions of the starry +heavens which we have chosen to call “northern” and “southern.” You +know that all the chief planets travel round the sun in very nearly the +same _plane_ or flat surface that we do ourselves. That plane is called +the “plane of the ecliptic.” Suppose that you had an enormous sheet of +cardboard, and that in the middle of this cardboard the sun were fixed, +half his body being above and half below. At a little distance, fixed +in like manner in the card, would be the small body of the earth, half +above and half below, her axis being in a slanting position. The piece +of cardboard represents what is called in the heavens the _plane of +the ecliptic_--an imaginary flat surface, cutting exactly through the +middle of the sun and of the earth. + +If the planets all traveled in the same precise plane, they would +all be fixed in the cardboard just like the earth, half the body of +each above and half below. As they do not so travel, some would have +to be placed a little higher, some a little lower, according to what +part of their orbits they were on. This supposed cardboard “plane of +the ecliptic” would divide the heavens into two halves. One half, +containing the constellations of the Great Bear, the Little Bear, +Cepheus, Draco, and others, would be called the Northern Heavens. One +end of the earth’s axis, pointing just now nearly to the Polar Star, +we name the North Pole; and all poles of planets pointing towards this +northern half of the heavens, are in like manner named by us their +north poles. + +With regard to west and east, lay in imagination upon this cardboard +plane a watch, with its face upwards; remembering that all the planets +and nearly all the moons of the Solar System are said both to spin on +their axes, and to travel in their orbits round the sun, _from west to +east_. Note how the hands of your watch would move in such a position. +The “west to east” motions of planets and moons would be in exactly the +opposite direction from what the motions of the watch-hands would be. + +To return to Jupiter. It is believed that these bands of color are +owing to a heavy, dense atmosphere, loaded with vast masses of cloudy +vapor. By the “size” of Jupiter, we really mean the size of this +outside envelope of clouds. How large the solid body within may be, +or whether there is any such solid body at all, we do not know. The +extreme lightness of Jupiter, as compared with his great size, has +caused strong doubts on this head. + +The white belts are supposed to be the outer side of cloud-masses +shining in the sunlight. Travelers in the Alps have seen such +cloud-masses, spreading over the whole country beneath their feet, +white as driven snow, and shining in the sunbeams which they were +hiding from villages below; or looking like soft masses of cotton-wool, +from which the mountain-peaks rose sharply here and there. + +The dark spaces between seem to be rifts or breaks in the clouds. +Whether, when we look at those dark spaces, we are looking at the +body of Jupiter, or only at lower layers of clouds, is not known. +But sometimes blacker spots show upon the dark cloud-belts, and this +seems rather as if they were only lower layers of clouds, the black +spots giving us peeps down into still lower and deeper layers, or else +perhaps to the planet itself. These appearances remind one strongly of +the sun-spots, each with its penumbra, umbra, and nucleus. Occasionally +bright white spots show, instead of dark ones. It is thought that they +may be caused by a violent upward rush of dense clouds of white vapor. +The white spots again recall the sun and his _faculæ_. + +Jupiter’s bands are not fixed. Great changes go on constantly among +them. Sometimes a white band will turn dark-colored, or a dark band +will turn white. Sometimes few and sometimes many belts are to be seen. +Sometimes a dark belt will lie slanting across the others, nearly from +north to south. Once, in a single hour, an entirely new belt was seen +to come into shape. Another time, two whole belts vanished in one day. +The bands, in which such rapid movements are seen, are often thousands +of miles in breadth. Sometimes these wide zones of clouds will remain +for weeks the same. At another time a break or rift in them will be +seen to journey swiftly over the surface of the planet. + +The winds on earth are often destructive. A hurricane, moving at the +rate of ninety miles an hour, will carry away whole buildings and level +entire plantations. Such hurricanes rarely, if ever, last more than +a few hours. But winds in Jupiter, judging from the movements of the +clouds, often travel at the rate of one hundred and fifty miles an +hour; and that, not for hours only, but for many weeks together. What +manner of living beings could stand such weather may well be questioned. + +Another difficulty which arises is as to the cause of these tremendous +disturbances on Jupiter. Our earthly storms are brought about by the +heat of the sun acting on our atmosphere. But the sun-heat which +reaches Jupiter seems very far from enough to raise such vast clouds of +vapor, and to bring about such prolonged and tremendous hurricanes of +wind. + +What if there is another cause? What if Jupiter is _not_ a cooled +body like our earth, but a liquid, seething, bubbling mass of fiery +heat--just as we believe our earth was once upon a time, in long past +ages, before her outside crust became cold enough for men and animals +to live thereon? _Then_, indeed, we could understand how, instead +of oceans lying on his surface, all the water of Jupiter would be +driven aloft to hang in masses of steam or be condensed into vast +cloud-layers. _Then_ we could understand why a perpetual stir of +rushing winds should disturb the planet’s atmosphere. + +In that case would Jupiter be a planet at all? Certainly--in the sense +of obeying the sun’s control. Our earth was once, we believe, a globe +of melted matter, glowing with heat--and farther back still, possibly, +a globe of gas. Some people are very positive about these past changes; +but it is wise not to be over-positive where we can not know to a +certainty what has taken place. However, Jupiter _may_ have cooled down +only to the liquid state, and if he goes on cooling he may, by and by, +gain a solid crust like the earth. + +This idea about Jupiter’s hot and molten state belongs quite to late +years. Certain other matters seem to bear it out, though of actual +proof we have none. It is thought, for instance, that the dull, coppery +red light, showing often in the dark bands, may be a red glow from the +heated body within. Also it has been calculated that Jupiter gives out +much more light than our earth would do, if increased to his size and +moved to his place--more, in fact, than we could reasonably expect him +to give out. If so, whence does he obtain the extra brightness? If he +does not shine by reflected light alone, he probably shines also in +some additional degree by his own light. + +But what about Jupiter being inhabited? Would it in such a case be +quite impossible? “Impossible” is not a word for us to use about +matters where we are ignorant. We can only say that it is impossible +for us to _imagine_ any kind of living creatures finding a home there, +if our present notions about the present state of Jupiter are correct. +Then is the chief planet of the Solar System a huge, useless monument +of God’s power to create? Not so fast. Even as merely such a monument, +he could not be useless. And even if he were put to no present use at +all, it might be merely because this is a time of preparation for the +future. God has his times of long and slow preparation, alike with +worlds, with nations, and with individuals. + +But now as to the five moons circling round Jupiter. There used to be +some very pretty ideas afloat about the wonderful beauty of the moons, +as seen from Jupiter, their united brilliancy so far surpassing the +shining of our one poor satellite, and making up for the dim light of +Jupiter’s sun. + +A certain little difficulty was not quite enough considered. If +anybody were living on the surface of Jupiter, he would have, one is +inclined to think, small chance of often seeing the moons through the +cloud-laden atmosphere. + +[Illustration: SATELLITES OF JUPITER COMPARED WITH THE EARTH AND MOON.] + +The nearest of the four larger moons to Jupiter would, it is true, +appear--when visible at all--rather bigger than ours does to us; while +the two next would be almost half as large, and the farthest about a +quarter as large--supposing inhabitants of Jupiter to have our powers +of vision. + +All taken together they would cover a considerably larger space in the +sky than does our moon. But it must be remembered that Jupiter’s moons, +like ours, shine merely by reflected sunlight. And so dim is the +sunshine at that distance compared with what it is at our distance, +that all the five moons together, even if full at the same time, could +only give about one-sixteenth part of the light which we obtain from +our one full moon. + +Besides, they never are full together, seen from any one part of +Jupiter. The four inner moons are never to be seen “full” at all; for +just when they might be so, they are eclipsed or shaded by Jupiter’s +shadow. The fourth sometimes escapes this eclipse, from being so much +farther away. + +A thought has been lately put forward, which may or may not have truth +in it. What if--instead of Jupiter being a world, inhabited by animals +and people, as is often supposed, with a small distant sun and five dim +moons to give them light--what if Jupiter is himself in some sort a +second sun to his moons, and what if those “moons” are really inhabited +planets? It may be so. That is all we can say. The idea is not an +impossible one. + +The so-called “moons” are certainly small. But they are by no means +too small for such a purpose. Jupiter would in that case, with his +five moons circling round him, enjoying his light and warmth, be a +small picture of the sun, with his four inner planets and the asteroids +circling round him, basking in a more lavish amount of the same. + +Picturing the moons as giving light to Jupiter, we find them seemingly +dim and weak for such a purpose--though, of course, we may here make a +grand mistake in supposing the eyesight of living creatures in Jupiter +to be no better than our own eyesight. Even upon earth a cat can see +plainly where a man has to grope his way in darkness. + +But by picturing the moons as inhabited, and Jupiter as giving out some +measure of heat and light to make up for the lessened amount of light +and heat received from the sun, the matter becomes more easy to our +understanding. + +[Illustration: THE SYSTEM OF JUPITER.] + +The nearest moon has indeed a magnificent view of Jupiter as a huge +bright disk in its sky, no less than three thousand times as large +as our moon appears to us, shining brightly with reflected sunlight, +and it may be glowing with a red light of his own in addition. Even +the farthest off of the five sees him with a face sixty-five times +the size of our moon. And the varying colors and stormy changes in +the cloud-belts, viewed thus near at hand, must afford marvelously +beautiful effects. + +Just as Mercury, Venus, Earth, and Mars travel round the sun, at +different distances, nearly in the same plane, so Jupiter’s five moons +travel round him, at different distances, nearly in the same plane. +Jupiter’s moons are always to be seen in a line, not one high and +another low, one near his pole and another near his equator. + +The moon nearest to Jupiter, discovered in September, 1892, by +Professor Barnard, now of the Yerkes Observatory of the Chicago +University, has a probable diameter of one hundred miles, and revolves +round its primary in about twelve hours. The second satellite, named +Io, is said to be over two thousand miles in diameter, travels round +Jupiter in less than two of our days, and is eclipsed by Jupiter’s +shadow once in every forty-two hours. + +The third moon, Europa, is rather smaller, takes over three days to its +journey, and suffers eclipse once in every eighty-five hours. + +The fourth moon, Ganymede, is believed to be considerably larger than +Mercury, journeys round Jupiter once a week, and is eclipsed once every +hundred and seventy-one hours. + +The fifth moon, Callisto, is also said to be slightly larger than +Mercury, performs its journey in something more than sixteen days, and +from its greater distance suffers eclipse less often than the other +four. + +The distance of the nearest is more than one hundred thousand miles +from Jupiter; that of the farthest, more than one million miles. + +The following table presents more minutely the results of the latest +discoveries concerning these satellites: + + +-----------------------+----------------+------------+-----------+ + | | DISTANCE FROM | | PERIOD OF | + | SATELLITES. | CENTER OF | DIAMETER. |REVOLUTION.| + | | JUPITER. | | | + +-----------------------+----------------+------------+-----------+ + | | | |D. H. M. S.| + |1. Barnard’s Satellite,| 112,500 miles.| 100 miles.| 11 57 23| + |2. Io, | 266,000 ” |2,356 ” | 1 18 27 33| + |3. Europa, | 424,000 ” |2,046 ” | 3 13 13 42| + |4. Ganymede, | 676,000 ” |3,596 ” | 7 3 42 33| + |5. Callisto, |1,189,000 ” |2,728 ” |16 15 32 11| + +-----------------------+----------------+------------+-----------+ + +The fact of these eclipses, and of the shadow thrown by Jupiter’s body, +shows plainly that though he may give out some measure of light, as has +been suggested, yet that light can not be strong, or it would prevent +any shadow from being thrown by the sunlight. Also, the dense masses +of cloud around him, though reflecting sunlight brightly, would shut +in much of his own light. Possibly it is chiefly as heat-giver and as +sunlight-reflector that Jupiter serves his five satellites. + +As with our own moon, so with Jupiter’s moons, the real center of +their orbit is the sun, and not Jupiter. They accompany Jupiter in his +journey, controlled by the sun, and immensely influenced by Jupiter. + +At night the spectacle of the sky seen from Jupiter is, with reference +to the constellations, the same as that which we see from the earth. +There, as here, shine Orion, the Great Bear, Pegasus, Andromeda, +Gemini, and all the other constellations, as well as the diamonds of +our sky: Sirius, Vega, Capella, Procyon, Rigel, and their rivals. The +390,000,000 of miles which separate us from Jupiter _in no way_ alter +the celestial perspectives. But the most curious character of this sky +is unquestionably the spectacle of the five moons, each of which shows +a different motion. The second moves in the firmament with an enormous +velocity, and Barnard’s satellite still faster, and produce almost +every day total eclipses of the sun in the equatorial regions. The four +inner moons are eclipsed at each revolution, just at the hours when +they are at their “full.” The fifth alone attains the full phase. + +Contrary to the generally received opinion, these bodies do not give to +Jupiter all the light which is supposed. We might think, in fact, as +has been so often stated, that these five moons illuminate the nights +five times better relatively than our single moon does in this respect, +and that they supplement in some measure the feebleness of the light +received from the sun. This result would be, assuredly, very agreeable, +but nature has not so arranged it. The five satellites cover, it is +true, an area of the sky greater than our moon, but they reflect the +light of a sun twenty-seven times smaller than ours; indeed, the total +light reflected is only equal to a sixteenth of that of our full moon, +even supposing the soil of these satellites to be as white as it +appears to be, especially the fifth satellite. + +Jupiter appears to be a world still in process of formation, which +lately--some thousands of centuries ago--served as a sun to his +own system of five or perhaps more worlds. If the central body is +not at present inhabited, his satellites may be. In this case, the +magnificence of the spectacle presented by Jupiter himself to the +inhabitants of the satellites is worthy of our attention. Seen from +Barnard’s satellite, Jupiter’s disk has a diameter of 47°, or more than +half the distance from the horizon to the zenith. Seen from the second +satellite, the Jovian globe presents an immense disk of twenty degrees +in diameter, or 1,400 times larger than the full moon! What a body! +What a picture, with its belts, its cloud motions, and its glowing +coloration, seen from so near! What a nocturnal sun!--still warm, +perhaps. Add to this the aspect of the satellites themselves seen from +each other, and you have a spectacle of which no terrestrial night can +give an idea. + +Such is the world of Jupiter from the double point of view of its vital +organization and of the spectacle of external nature, seen from this +immense observatory. + +The attraction of the planets has always played an important part +in the motion of comets and the form of their orbits. The enormous +size of Jupiter gives it more influence than any other planet, and we +are not surprised that it should have seriously interfered with some +of the comets that belong to the Solar System. We have already seen +that Biela’s comet was captured by Jupiter, and that it was probably +dissolved into meteoric dust. We show in the cut the orbits of eight +others that circle around the sun, but retreat no farther away than +Jupiter. These are the orbits as now determined, but they vary from +age to age on account of disturbances of other planets. But it is not +likely that the comets themselves will ever escape from the control of +Jupiter. + +[Illustration: ORBITS OF NINE COMETS CAPTURED BY JUPITER.] + + + + +CHAPTER XVIII. + +SATURN. + + +The system of Jupiter is a simple system compared with that of Saturn, +next in order. For whereas Jupiter has only five moons, Saturn has +eight, and, in addition to these, he has three wonderful rings. Neither +rings nor moons can be seen without a telescope, on account of Saturn’s +great distance from us--more than three thousand times the distance of +the moon, or upwards of eight hundred millions of miles. Saturn’s mean +distance from the sun is eight hundred and seventy-six million seven +hundred and sixty-seven thousand miles. + +Saturn does not equal his mighty brother Jupiter in size, though he +comes near enough in this respect to be called often his “twin”--just +as that small pair of worlds, Venus and Earth, are called “twins.” +While Jupiter is equal in size to over one thousand two hundred earths, +Saturn is equal to about seven hundred earths. And while Jupiter is +equal in weight to three hundred earths, Saturn is only equal in weight +to ninety earths. He appears to be made of very light materials--not +more than three-quarters as dense as water. This would show the present +state of Saturn to be very different from the present state of the +earth. We are under the same uncertainty in speaking of Saturn as in +speaking of Jupiter. Like Jupiter, Saturn is covered with dense masses +of varying clouds, occasionally opening and allowing the astronomer +peeps into lower cloud-levels; but rarely or never permitting the +actual body of the planet to be seen. + +The same perplexities also come in here, to be answered much in the +same manner. We should certainly expect that in a vast globe like +Saturn the strong force of attraction would bind the whole into a +dense solid mass; instead of which, Saturn is about the least solid of +all the planets. He seems to be made up of a light, watery substance, +surrounded by vapor. + +[Illustration: SATURN AND THE EARTH--COMPARATIVE SIZE.] + +One explanation can be offered. What if the globe of Saturn be still +in a red-hot, molten state, keeping such water as would otherwise lie +in oceans on his surface, floating aloft in masses of steam, the outer +parts of which condense into clouds? + +No one supposes that Jupiter and Saturn are in the same condition +of fierce and tempestuous heat as the sun. They may have been so +once, but they must now have cooled down very many stages from that +condition. Though no longer, however, a mass of far-reaching flames and +fiery cyclones, the body of each may have only so far cooled as to have +reached a stage of glowing molten red-heat, keeping all water in the +form of vapor, and sending up strong rushes of burning air to cause the +hurricanes which sweep to and fro the vast cloud-masses overhead. + +And if this be the case, then, with Saturn as with Jupiter, comes the +question, Can Saturn be inhabited? And if--though we may not say it is +impossible, yet we feel it to be utterly unlikely--then again follows +the question, What if Saturn’s _moons_ are inhabited? + +Telescopic observations tempt us to believe that there is on this +planet a quantity of heat greater than that which results from its +distance from the sun; for the day-star as seen from Saturn is, as we +have said, ninety times smaller in surface, and its heat and light +are reduced in the same proportion. Water could only exist in the +solid state of ice, and the vapor of water could not be produced so +as to form clouds similar to ours. Now, meteorological variations are +observed similar to those which we have noticed on Jupiter, but less +intense. Facts, then, combine with theory to show us that the world of +Saturn is at a temperature at least as high as ours, if not higher. + +But the strangest feature of the Saturnian calendar is, unquestionably, +its being complicated, not only with the fabulous number of 25,060 +days in a year, but, further, with eight different kinds of months, of +which the length varies from 22 hours to 79 days--that is to say, from +about two Saturnian days to 167. It is as if we had here _eight moons +revolving in eight different periods_. + +The inhabitants of such a world must assuredly differ strangely +from us from all points of view. The specific lightness of the +Saturnian substances and the density of the atmosphere will have +conducted the vital organization in an extra-terrestrial direction, +and the manifestations of life will be produced and developed under +unimaginable forms. To suppose that there is nothing fixed, that the +planet itself is but a skeleton, that the surface is liquid, that the +living beings are gelatinous--in a word, that all is unstable--would be +to surpass the limits of scientific induction. + +The diameter of the largest moon is about half the diameter of the +earth, or much larger than Mercury. The four inner satellites are +all nearer to Saturn than our moon to us, though the most distant of +the eight is ten times as far away. The inner moon takes less than +twenty-three hours to travel round Saturn, and the outer one over +seventy-nine days. + +A great many charming descriptions have been worked up, with Saturn +as with Jupiter, respecting the magnificent appearance of the eight +radiant moons, joined to the glorious shining of the rings, as quite +making up for the diminished light and heat of the sun. But here again +comes in the doubt, whether really it is the moons who make up to +Saturn for lack of light, or whether it is Saturn who makes up to the +moons for lack of light. + +Certainly, Saturn’s cloudy covering would a little interfere with +observations of the moons by any inhabitants of the solid body +within--supposing there be any solid body at all. And though it sounds +very wonderful to have eight moons instead of one moon, yet all the +eight together give Saturn only a very small part of the light which we +receive from our one full moon--so much more dimly does the sun light +them up at that enormous distance. + +The same thing has been noticed with Saturn as with Jupiter--that he +seems to shine more brightly than is to be expected in his position, +from mere reflection of the sun’s rays. A glowing body within, sending +a certain amount of added light through or between the masses of +clouds, would explain away this difficulty. + +One more possible proof of Saturn’s half-liquid state is to be found +in his occasional very odd changes of shape. Astronomers have been +startled by a peculiar bulging out on one side, taking off from his +roundness, and giving a square-shouldered aspect. We may not say it +is quite impossible that a solid globe should undergo such tremendous +upheavals and outbursts as to raise a great portion of its surface five +or six hundred miles above the usual level--the change being visible +at a distance of eight hundred millions of miles. But it would be +easier to understand the possibility of such an event, in the case of a +liquid, seething mass, than in the case of a solid ball. + +On the other hand this alteration of outline may be caused simply by +a great upheaval not of the planet’s surface, but of the overhanging +layers of clouds. Some such changes, only much slighter, have been +remarked in Jupiter. + +And now as to the rings. Nothing like them is to be seen elsewhere in +the Solar System. They are believed to be three in number; though some +would divide them into more than three. Passing completely round the +whole body of Saturn, they rise, one beyond another, to a height of +many thousands of miles. + +The inner edge of the inner ring--an edge perhaps one hundred miles in +thickness--is more than ten thousand miles from the surface of Saturn +or more strictly speaking, from the outer surface of Saturn’s cloudy +envelope. A man standing exactly on the equator and looking up, even if +no clouds came between, would scarcely be able to see such a slender +dark line at such a height. + +This dark, transparent ring, described sometimes as dusky, sometimes as +richly purple, rises upwards to a height or breadth of nine thousand +miles. Closely following it is a ring more brilliant than Saturn +himself, over eighteen thousand miles in breadth. When astronomers talk +of the “breadth” of these rings, it must be understood that they mean +the width of the band measured _upwards_, in a direction away from the +planet. + +Beyond the broad, bright ring is a gap of about one thousand seven +hundred miles. Then follows the third ring, ten thousand miles in +breadth; its outermost edge being at a height of more than forty-eight +thousand miles from Saturn. The color of the third ring is grayish, +much like the gray markings often seen on Saturn. + +What would not be our admiration, our astonishment, our stupor perhaps, +if it were granted us to be transported there alive, and, among all +these extra-terrestrial spectacles, to contemplate the strange aspect +of the rings, which stretch across the sky like a bridge suspended +in the heights of the firmament! Suppose we lived on the Saturnian +equator itself, these rings would appear to us as a thin line drawn +across the sky above our heads, and passing exactly through the zenith, +rising from the east and increasing in width, then descending to the +west and diminishing according to perspective. Only there have we +the rings precisely in the zenith. The traveler who journeys from +the equator towards either pole leaves the plane of the rings, and +these sink imperceptibly, at the same time that the two extremities +cease to appear diametrically opposite, and by degrees approach each +other. What an amazing effect would be produced by this gigantic +arch, which springs from the horizon and spans the sky! The celestial +arch diminishes in height as we approach the pole. When we reach the +sixty-third degree of latitude the summit of the arch has descended to +the level of our horizon and the marvelous system disappears from the +sky; so that the inhabitants of those regions know nothing of it, and +find themselves in a less favorable position to study their own world +than we, who are nearly 800,000,000 miles distant. + +During one-half of the Saturnian year the rings afford an admirable +moonlight on one hemisphere of the planet, and during the other half +they illuminate the other hemisphere; but there is always a half-year +without “ringlight,” since the sun illuminates but one face at a time. +Notwithstanding their volume and number, the satellites do not give +as much nocturnal light as might be supposed; for they receive, on an +equal surface, only the ninetieth part of the solar light which our +moon receives. All the Saturnian satellites which can be at the same +time above the horizon and as near as possible to the full phase do not +afford more than the hundredth part of our lunar light. But the result +may be nearly the same, for the optic nerve of the Saturnians may be +ninety times more sensitive than ours. + +But there are further strange features in this system. The rings are +so wide that their shadow extends over the greater part of the mean +latitudes. During fifteen years the sun is to the south of the rings, +and for fifteen years it is to the north. The countries of Saturn’s +world which have the latitude of Paris endure this shadow for more than +five years. At the equator the eclipse is shorter, and is only renewed +every fifteen years; but there are every night, so to say, eclipses of +the Saturnian moons by the rings and by themselves. In the circumpolar +regions the day-star is never eclipsed by the rings; but the satellites +revolve in a spiral, describing fantastic rounds, and the sun himself +disappears at the pole during a long night of fifteen years. + +At one time it was supposed that the rings were solid, but they are now +believed to consist of countless myriads of meteorites, each whirling +in its own appointed pathway round the monster planet. + +[Illustration: IDEAL VIEW OF SATURN’S RINGS AND SATELLITES FROM THE +PLANET.] + +As already said--leaving out of the question the cloudy atmosphere--a +man standing on the equator would see nothing of the rings. A man +standing at the north pole or the south pole of Saturn could see +nothing either, since the rings would all lie below his horizon. But +if he traveled southward from the north pole, or northward from the +south pole, towards the equator, he would in time see the ringed arch +appearing above the horizon, rising higher and growing wider with every +mile of his journey; and when he was in a position to view the whole +broad expanse, the transparent half-dark belt below, the wide radiant +band rising upwards over that, and the grayish border surmounting all, +he would truly have a magnificent spectacle before him. + +This magnificent spectacle is, however, by no means always visible, +even from those parts of Saturn where alone it ever can be seen. The +rings shine merely by reflected sunlight. Necessarily, therefore, while +the sunbeams make one side bright the other side is dark; and not only +this, but the rings throw broad and heavy shadows upon Saturn in the +direction away from the sunlight. + +In the daytime they probably give out a faint shining, something like +our own moon when seen in sunlight. During the summer nights they +shine, no doubt, very beautifully. During the winter nights it so +happens that their bright side is turned away; and not only that, but +during the winter days the rings, while giving no light themselves to +the wintry hemisphere of Saturn, completely hide the sun. + +When it is remembered that Saturn’s winter--that is, the winter of each +hemisphere in turn--lasts during fifteen of our years; and when we hear +of total eclipses of the sun lasting unbroken through eight years of +such a winter, with not even bright rings to make up for his absence, +we can not think of Saturn as a tempting residence. The sun gives +Saturn at his best only about one-ninetieth of the heat and light that +he gives to our earth; but to be deprived of even that little for eight +years at a time, does indeed sound somewhat melancholy. + +Looking now at the other side of the question, the possible inhabitants +of the moons, especially those near at hand, would have splendid views +of Saturn and his rings in all their varying phases. For Saturn is a +beautiful globe, wrapped in his changeful envelope of clouds, which, +seen through a telescope, are lit up often with rainbow tints of blue +and gold; a creamy white belt lying usually on the equator; while +around extend the purple and shining and gray rings, sometimes rivaling +in bright colors Saturn himself. + +We are compelled to assume that the continuous appearance of the rings +is not due to real continuity of substance, but that they are composed +of flights of disconnected satellites, so small and so closely packed +that, at the immense distance to which Saturn is removed, they appear +to form a continuous mass. There are analogous instances in the Solar +System. In the zone of asteroids we have an undoubted instance of a +flight of disconnected bodies traveling in a ring about a central +attracting mass. The existence of zones of meteorites traveling around +the sun has long been accepted as the only probable explanation of the +periodic returns of meteoric showers. Again, the singular phenomenon +called the Zodiacal Light is, in all probability, caused by a ring of +minute cosmical bodies surrounding the sun. In the Milky Way and in +the ring-nebulæ we have other illustrations of similar arrangements +in nature, belonging, however, to orders immeasurably vaster than any +within the Solar System. + +The moons of Saturn do not, like those of Jupiter, travel in one plane. + + + + +CHAPTER XIX. + +URANUS AND NEPTUNE. + + +Till the year 1781, Saturn was believed to be the outermost planet +of the Solar System, and nobody suspected the fact of two great, +lonely brother-planets wandering around the same sun at vast distances +beyond,--Uranus, nine hundred millions of miles from Saturn; Neptune, +nine hundred millions of miles from Uranus. No wonder they remained +long undiscovered. + +Uranus can sometimes be seen by the unaided eye as a dim star of the +sixth magnitude. And when he was known for a planet, it was found that +he _had_ been often so seen and noted. Again and again he had been +taken for a fixed star, and as he moved on, disappearing from that +particular spot, it was supposed that the star had vanished. + +One night, March 13, 1781, when William Herschel was busily exploring +the heavens with a powerful telescope, he noticed something which +he took for a comet without a tail. He saw it was no mere point of +light like the stars, but had a tiny round disk or face, which could +be magnified. So he watched it carefully, and found in the course of +a few nights that it moved--very slowly, certainly; but still it did +move. Further watching and calculation made it clear that, though the +newly-found heavenly body was at a very great distance from the sun, +yet it was moving slowly in an orbit _round_ the sun. Then it was +known to be a planet, and another member of the Solar System. + +From that day the reputation of Herschel rapidly increased. King George +III, who loved the sciences and patronized them, had the astronomer +presented to him; charmed with the simple and modest account of his +efforts and his labors, he secured him a life pension and a residence +at Slough, in the neighborhood of Windsor Castle. His sister Caroline +assisted him as secretary, copied all his observations, and made all +his calculations; the king gave him the title and salary of assistant +astronomer. Before long the observatory at Slough surpassed in +celebrity the principal observatories of Europe; we may say that, in +the whole world, this is the place where the most discoveries have been +made. + +Astronomers soon applied themselves to the observation of the new body. +They supposed that this “comet” would describe, as usually happens, +a very elongated ellipse, and that it would approach considerably +to the sun at its perihelion. But all the calculations made on this +supposition had to be constantly recommenced. They could never succeed +in representing all its positions, although the star moved very slowly: +the observations of one month would utterly upset the calculations of +the preceding month. + +Several months elapsed without a suspicion that a veritable planet +was under observation, and it was not till after recognizing that all +the imaginary orbits for the supposed comet were contradicted by the +observations, and that it had probably a circular orbit much farther +from the sun than Saturn, till then the frontier of the system, that +astronomers came to consider it as a planet. Still, this was at first +but a provisional consent. + +[Illustration: PROMINENT ASTRONOMERS OF FORMER TIMES. Tycho Brahe, +Hipparchos, Galilei, Newton, Kepler, Kant, Kopernikus, Laplace.] + +It was, in fact, more difficult than we may think to increase without +scruple the family of the sun. Indeed, for reasons of expediency this +idea was opposed. Ancient ideas are tyrannical. Men had so long been +accustomed to consider old Saturn as the guardian of the frontiers, +that it required a rare boldness of spirit to decide on extending these +frontiers and marking them by a new world. + +William Herschel proposed the name of _Georgium Sidus_ “the Star of +George,” just as Galileo had given the name of “Medicean stars” to +the satellites of Jupiter discovered by him, and as Horace had said +_Julium Sidus_. Others proposed the name of _Neptune_, in order to +maintain the mythological character, and to give to the new body the +trident of the English maritime power; others, _Uranus_, the most +ancient deity of all, and the father of Saturn, to whom reparation +was due for so many centuries of neglect. Lalande proposed the name +of _Herschel_, to immortalize the name of its discoverer. These last +two denominations prevailed. For a long time the planet bore the +name of Herschel; but custom has since declared for the mythological +appellation, and Jupiter, Saturn, and Uranus succeed each other in +order of descent--son, father, and grandfather. + +The discovery of Uranus extended the radius of the Solar System from +885,000,000 to 1,765,000,000 of miles. + +The apparent brightness of this planet is that of a star of the +sixth magnitude; observers whose sight is very piercing may succeed +in recognizing it with the naked eye when they know where to look for +it. Uranus moves slowly from west to east, and takes no less than +eighty-four years to make the complete circuit of the sky. In its +annual motion round the sun the earth passes between the sun and Uranus +every 369 days--that is to say, once in a year and four days. It is at +these times that this planet crosses the meridian at midnight. We can +observe it in the evening sky for about six months of every year. + +Everybody supposed that now, at least, the outermost member of all was +discovered. But a very strange and remarkable thing happened. + +Astronomers know with great exactness the paths of the planets in +the heavens. They can tell, years beforehand, precisely what spot in +space will be filled at any particular time by any particular planet. +I am speaking now of their movements round the sun and in the Solar +System--not of the movements of the whole family with the sun, about +which little is yet known. + +Each planet has its own particular pathway; its own particular distance +from the sun, varying at each part of its pathway; its own particular +speed in traveling round the sun, changing constantly from faster to +slower or slower to faster, according to its distance from the sun, and +according to the pull backwards or forwards of our neighboring planets +in front or in rear. For as the orbits of all the planets are ovals, +with the sun not in the middle, but somewhat to one side of the middle, +it follows that all the planets, in the course of their years, are +sometimes nearer to and sometimes farther from the sun. + +The astronomers of the present day understand this well, and can +describe with exactness the pathway of each planet. This knowledge +does not come merely from watching one year how the planets travel, +and remembering for another year, but is much more a matter of close +and difficult calculation. Many things have to be considered, such as +the planet’s distance from the sun, the sun’s power of attraction, the +planet’s speed, the nearness and weight of other neighboring planets. + +All these questions were gone into, and astronomers sketched out the +pathway in the heavens which they expected Uranus to follow. He would +move in such and such an orbit, at such and such distances from the +sun, and at such and such rates of speed. + +But Uranus would not keep to these rules. He quite discomfited the +astronomers. Sometimes he went fast, when, according to their notions, +he ought to have gone more slowly; and sometimes he went slowly, when +they would have looked for him to go more fast, and the line of his +orbit was quite outside the line of the orbit which they had laid +down. He was altogether a perplexing acquaintance, and difficult to +understand. However, astronomers felt sure of their rules and modes of +calculation, often before tested, and not found to fail. They made a +guess at an explanation. What if there were yet another planet beyond +Uranus, disturbing his motions--now drawing him on, now dragging him +back, now so far balancing the sun’s attraction by pulling in the +opposite direction as to increase the distance of Uranus from the sun? + +It might be so. But who could prove it? Hundreds of years might pass +before any astronomer, in his star-gazing, should happen to light upon +such a dim and distant world. Nay, the supposed planet might be, like +Uranus, actually seen, and only be mistaken for a “variable star,” +shining but to disappear. + +There the matter seemed likely to rest. There the matter probably would +have rested for a good while, had not two men set themselves to conquer +the difficulty. One was a young Englishman, a student of Cambridge, +John Couch Adams; the other, a young Frenchman, Urbain Jean Joseph +Leverrier,--both being astronomers. + +Each worked independently of the other, neither knowing of the other’s +toil. The task which they had undertaken was no light one--that of +reaching out into the unknown depths of space to find an unknown planet. + +Each of these silent searchers into the sky-depths calculated what the +orbit and speed of Uranus would be, without the presence of another +disturbing planet beyond. Each examined what the amount of disturbance +was, and considered the degree of attraction needful to produce that +disturbance, together with the direction from which it had come. Each, +in short, gradually worked his way through calculations far too deep +and difficult for ordinary minds to grasp, till he had found just that +spot in the heavens where a planet _ought_ to be, to cause, according +to known laws, just such an effect upon Uranus as had been observed. + +Adams finished his calculation first, and sent the result to two +different observatories. Unfortunately, his report was not eagerly +taken up. It was, in fact, hardly believed. Leverrier finished his +calculation also, and sent the result to the Berlin Observatory. The +planet was actually seen in England first, but the discovery was +actually made known from Berlin first. The young Englishman had been +beforehand, but the young Frenchman gained foremost honor. + +It was on the 23d of September, 1846, that Leverrier’s letter reached +the Berlin astronomers. The sky that night was clear, and we can easily +understand with what anxiety Dr. Galle directed his telescope to the +heavens. The instrument was pointed in accordance with Leverrier’s +instructions. The field of view showed, as does every part of the +heavens, a multitude of stars. One of these was really the planet. The +new chart--prepared by the Berlin Academy of Sciences, upon which the +place of every star, down even to those of the tenth magnitude, was +engraved--was unrolled, and, star by star, the heavens were compared +with the chart. As the process of identification went on, one object +after another was found in the heavens as engraved on the chart, and +was of course rejected. At length a star of the eighth magnitude--a +brilliant object--was brought into review. The map was examined, but +there was no star there. This object could not have been in its present +place when the map was formed. The object was therefore a wanderer--a +planet. Yet it is necessary to be excessively cautious in such a matter. + +Many possibilities had to be guarded against. It was, for instance, +possible that the object was really a star which, by some mischance, +eluded the careful eye of the astronomer who constructed the map. +It was even possible that the star might be one of the large class +of variables which alternate in brightness, and it might have been +conceivable that it was too faint to be seen when the chart was made. +Even if neither of these explanations would answer, it was still +necessary to show that the object was now moving, and moving with that +particular velocity and in that particular direction which the theory +of Leverrier indicated. The lapse of a single day was sufficient to +dissipate all doubts. The next night the object was again observed. +It had moved, and when its motion was measured it was found to +accord precisely with what Leverrier had foretold. Indeed, as if no +circumstance in the confirmation should be wanting, it was ascertained +that the diameter of the planet, as measured by the micrometers at +Berlin, was practically coincident with that anticipated by Leverrier. + +The world speedily rang with the news of this splendid achievement. +Instantly the name of Leverrier rose to a pinnacle hardly surpassed by +that of any astronomer of any age or country. For a moment it seemed +as if the French nation were to enjoy the undivided honor of this +splendid triumph. But in the midst of the pæans of triumph with which +the enthusiastic French nation hailed the discovery of Leverrier, +there appeared a letter from Sir John Herschel in the _Athenæum_ for +3d October, 1846, in which he announced the researches made by Adams, +and claimed for him a participation in the glory of the discovery. +Subsequent inquiry has shown that this claim was a just one, and it is +now universally admitted by all independent authorities. + +This, however, was of slight comparative importance. The truly +wonderful part of the matter was, that these two men could have so +reasoned that, from the movements of one lately-discovered planet, they +could point out the exact spot where a yet more distant planet ought to +be, and that close to this very spot the planet was found. For when, +both in England and in Germany, powerful telescopes were pointed in the +direction named--_there the planet was_. No doubt about the matter. Not +a star, but a real new planet in the far distance, wandering slowly +round the sun. + +Here we have the discovery of Neptune in its simple grandeur. This +discovery is splendid, and of the highest order from a philosophical +point of view, for it proves the security and the precision of the data +of modern astronomy. Considered from the point of view of practical +astronomy, it was but a simple exercise of calculation, and the most +eminent astronomers saw in it nothing else! It was only after its +verification, its public demonstration--it was only after the visual +discovery of Neptune--that they had their eyes opened, and felt for a +moment the dizziness of the infinite in view of the horizon revealed by +the Neptunian perspective. The author of the calculation himself, the +transcendent mathematician, did not even give himself the trouble to +take a telescope and look at the sky to see whether a planet was really +there! I even believe that he never saw it. For him, however, then +and always, to the end of his life, astronomy was entirely inclosed in +formulæ--the stars were but centers of force. + +Very often I submitted to him the doubts of an anxious mind on the +great problems of infinitude: I asked him if he thought that the other +planets might be inhabited like ours, what might be especially the +strange vital conditions of a world separated from the sun by the +distance of Neptune, what might be the retinue of innumerable suns +scattered in immensity, what astonishing colored lights the double +stars should shed on the unknown planets which gravitate in these +distant systems. His replies always showed me that these questions had +no interest for him, and that, in his opinion, the essential knowledge +of the universe consisted in equations, formulæ, and logarithmic series +having for their object the mathematical theory of velocities and +forces. + +But it is not the less surprising that he had not the _curiosity_ to +verify the position of his planet, which would have been easy, since +it shows a planetary disk; and, besides, he might have had the aid of +a chart, because he had only to ask for these charts from the Berlin +Observatory, where they had just been finished and _published_. It +is not the less surprising that Arago, who was more of a physicist +than a mathematician, more of a naturalist than a calculator, and +whose mind had so remarkable a synthetical character, had not himself +directed one of the telescopes of the observatory towards this point +of the sky, and that no other French astronomer had this idea. But +what surprises us still more is to know that _nearly a year before_, +in October, 1845, a young student of the University of Cambridge, Mr. +Adams, had sought the solution of the _same_ problem, obtained the +same results, and communicated these results to the director of the +Greenwich Observatory, and that the astronomer to whom these results +were confided had said nothing, and had not himself searched in the sky +for the optical verification of his compatriot’s solution! + +This was indeed a triumph of human intellect. Yet it is no matter +for human pride, but rather of thankfulness to God, who gave to man +this marvelous reasoning power. And the very delight we have in such +a success may humble us in the recollection of the vast amount lying +beyond of the utterly unknown. But while the rare mind of a Newton +could meekly realize the littleness of all he knew, lesser minds are +very apt to be puffed up with the thought of what the human intellect +can accomplish. + +Perhaps the chief feeling of lawful satisfaction in this particular +discovery arises from the fact that it gives marked and strong proof +of the truth of our present astronomical system and beliefs. Many +mistakes may be made, and much has often to be unlearned. Nevertheless, +if the general principles of modern astronomy were wrong, if the +commonly-received facts were a delusion, such complete success could +not have attended so delicate and difficult a calculation. + +We do not know much about these two outer planets, owing to their +enormous distance from us. Uranus is in size equal to seventy-four +earths, and Neptune is in size equal to one hundred and five earths. +Both these planets are formed of somewhat heavier materials than +Saturn, being about as dense as water. + +The size of the sun as seen from Uranus is about one +three-hundred-and-ninetieth part of the size of the sun we see. To +Neptune he shows a disk only one nine-hundredth part of the size +of that visible to us--no disk at all, in fact, but only starlike +brilliancy. + +The Uranian year lasts about eighty-four of our years; and this, with +a very sloping axis, must cause most long and dreary winters, the +tiny sun being hidden from parts of the planet during half an earthly +life-time. + +Uranus has at least four moons, traveling in very different planes from +the plane of the ecliptic. Once it was thought that he had eight, but +astronomers have since searched in vain for the other four, believed +for a while to exist. Neptune has one moon, and may possess others not +yet discovered. + +Sir Henry Holland, the celebrated physician, and a devoted student of +astronomy, has left on record an incident of his life connected with +the planet Neptune of singular interest. I give it here, and in his own +words, because it is scarcely likely otherwise to fall under the notice +of astronomical readers. After stating that his interest in astronomy +had led him to take advantage of all opportunities of visiting foreign +observatories, he says: + +“Some of these opportunities, indeed, arising out of my visits to +observatories both in Europe and America, have been remarkable enough +to warrant a more particular mention of them. That which most strongly +clings to my memory is an evening I passed with Encke and Galle in the +observatory at Berlin, some ten or twelve days after the discovery +of the planet Neptune on this very spot; and when every night’s +observations of its motions had still an especial value in denoting +the elements of its orbit. I had casually heard of the discovery +at Bremen, and lost no time in hurrying on to Berlin. The night in +question was one of floating clouds, gradually growing into cumuli; and +hour after hour passed away without sight of the planet which had just +come to our knowledge by so wonderful a method of predictive research. +Frustrated in this main point, it was some compensation to stay and +converse with Encke in his own observatory, one signalized by so many +discoveries, the stillness and darkness of the place broken only by +the solemn ticking of the astronomical clock, which, as the unfailing +interpreter of the celestial times and motions, has a sort of living +existence to the astronomer. Among other things discussed, while thus +sitting together in a sort of tremulous impatience, was the name to be +given to the new planet. Encke told me he had thought of ‘Vulcan,’ but +deemed it right to remit the choice to Leverrier, then supposed to be +the sole indicator of the planet and its place in the heavens; adding +that he expected Leverrier’s answer by the first post. Not an hour had +elapsed before a knock at the door of the observatory announced the +letter expected. Encke read it aloud; and, coming to the passage where +Leverrier proposed the name of ‘Neptune,’ exclaimed, ‘_So lass den +Namen Neptun sein._’ + +It was a midnight scene not easily to be forgotten. A royal baptism, +with its long array of titles, would ill compare with this simple +naming of the remote and solitary planet thus wonderfully discovered. +There is no place, indeed, where the grandeur and wild ambitions of the +world are so thoroughly rebuked and dwarfed into littleness as in the +astronomical observatory. As a practical illustration of this remark, +I would add that my own knowledge of astronomers--those who have +worked themselves with the telescope--has shown them to be generally +men of tranquil temperament, and less disturbed than others by worldly +affairs, or by the quarrels incident even to scientific research.” + +The same reasoning which has been used in reference to Jupiter and his +moons, and to Saturn and his moons, might perhaps be applied also to +Uranus and Neptune and their moons. + +We know too little yet of their condition to venture far in such +speculations. Still, taking the matter as a whole, there seem many +reasons to incline us to the idea that each of the four greater outside +planets may be a kind of secondary half-cooled sun to his satellites, +helping to make up to them for the small amount of light and heat which +they can obtain from the far-off sun. + + + + +CHAPTER XX. + +COMETS AND METEORITES. + + +A curious discovery has been lately made. It is that some sort of +mysterious tie seems to exist between comets and meteorites. For a long +while this was never suspected. How should it be? The comets, so large, +so airy, so light; the meteorites, so small, so solid, so heavy,--how +could it possibly be supposed that the one had anything to do with +the other? But supposings often have to give in to facts. Astronomers +are gradually becoming convinced that there certainly is a connection +between the two. + +Strange to say, comets and meteorites occupy--sometimes, at least--the +very same pathways in the heavens, the very same orbits round the +sun. A certain number of meteorite systems are now pretty well known +to astronomers as regularly met by our earth at certain points in +her yearly journey. Some of these systems or rings have each a comet +belonging to it--not merely journeying near, but actually in its midst, +on the same orbit. + +Perhaps it would be more correct to say that the meteorites belong to +the comet, than that the comet belongs to the meteorites. We tread here +on uncertain ground; for whether the meteorites spring from the comet, +or whether the comet springs from the meteorites, or whether each has +been brought into existence independently of the other, no one can at +present say. + +Though it is out of our power to explain the kind of connection, yet a +connection there plainly is. So many instances are now known of a comet +and a meteorite ring traveling together that it is doubtful whether any +such ring could be found without a comet in its midst. By and by the +doubt may spring up whether there ever exists a comet without a train +of meteorites following him. + +Among the many different meteorite rings which are known, two of the +most important are the so-called August and November systems. Of these +two, the November system must claim our chief attention. Not that we +are at all sure of these being the most important meteorite rings in +the Solar System. On the contrary, as regards the November ring, we +have some reason to think that matters may lie just the other way. + +The comet belonging to the November system is a small one--quite an +insignificant little comet--only visible through a telescope. We +do not, of course, know positively that larger comets and greater +meteorite systems generally go together, but, to say the least, it +seems likely. And if the greatness of a ring can at all be judged of by +the size of its comet, then the November system must be a third-rate +specimen of its kind. It is of particular importance to us, merely +because it happens to be the one into which our earth plunges most +deeply, and which we therefore see and know the best. The August ring +is, on the contrary, connected with a magnificent comet, and may be +a far grander system. But our pathway does not lead us into the midst +of the August meteors as into those of November. We pass, seemingly, +through its outskirts. + +The meteorites of the November system are very small. They are believed +to weigh commonly only a few grains each. If they were larger and +heavier, some of them would fall to earth as aerolites, not more than +half-burnt in their rush through the atmosphere. But this they are +never found to do. + +There are known meteorite systems, which our earth merely touches +or grazes in passing, from which drop aerolites of a very different +description--large, heavy, solid masses. It is well for us that we do +not plunge into the midst of any such ring, or we might find our air, +after all, a poor protection. + +The last grand display of the November system of meteorites took place +in the years 1866 to 1869, being continued more or less during three or +four Novembers following. The next grand display will occur in the year +1899. + +For this system--Leonides, as it is called, because the falling-stars +in this display seem all to shoot towards us from a spot in the +constellation Leo--seems to have a “time” or “year” of thirty-three and +a quarter earthly years. The shape of its orbit is a very long ellipse, +near one end of which is the sun, while the other end is believed to +reach farther away than the orbit of Uranus. + +A great deal of curiosity has been felt about the actual length and +breadth and depth of the stream of meteorites through which our +solid earth has so often plowed her way. During many hours at a +time, lookers-on have watched the magnificent display of heavenly +fireworks,--not a mere shooting-star here and there, as on common +nights, but radiant meteors, flashing and dying by thousands through +the sky. In 1866 no less than eight thousand meteors, in two hours and +a quarter, were counted from the Greenwich Observatory in England. A +natural wonder sprang up in many minds as to the extent of the ring +from which they fell. + +For not in one night only, but in several nights during three or four +years, and that not once only but once in every thirty-three years, +thousands and tens of thousands appear to have been stolen by our earth +from the meteorite-ring, never again to be restored. Yet each time we +touch the ring, we find the abundance of little meteorites in nowise +seemingly lessened. + +When speaking of a “ring” of meteorites, it must not be supposed that +necessarily the meteorites form a whole unbroken ring all round the +long oval orbit. There may be no breaks. There may be a more or less +thin scattering throughout the entire length of the pathway. But the +meteorites certainly seem to cluster far more densely in some parts of +the orbit than in other parts, and it was about the size of the densest +cluster that so much curiosity was felt. + +Little can be positively known, though it is very certain that the +cluster must be enormous in extent. Three or four years running, as our +earth, after journeying the whole way round the sun, came again to that +point in her orbit where she passes through the orbit of the Leonides, +she found the thick stream of meteorites still pouring on, though each +year lessening in amount. Taking into account this fact, and also the +numbers that were seen to fall night after night, and also the speed of +our earth, a “rough estimate” was formed. + +The length of this dense cluster is supposed to reach to many +hundreds of millions of miles. The thickness or depth of the stream +is calculated to be in parts over five hundred thousand miles, and +the breadth about ten times as much as the depth. Each meteorite is +probably at a considerable distance from his neighbor; but the whole +mass of them, when in the near neighborhood of the sun, must form a +magnificent sight. + +And if this be only a third-rate system, what must a first-rate system +be like? And how many such systems are there throughout the sun’s wide +domains? The most powerful telescope gives us no hint of the existence +of these rings till we find ourselves in their midst. + +It may be that they are numbered by thousands, even by millions. The +whole of the Solar System--nay, the very depths of space beyond--may, +for aught we know, be crowded with meteorite systems. Every comet may +have his stream of meteorites following him. But though the comet is +visible to us, the meteorites are not. Billions upon billions of them +may be ever rushing round our sun, entirely beyond our ken, till one +or another straggler touches our atmosphere to flash and die as a +“shooting star” in our sight. + +We have, and with our present powers we can have, no certainty as +to all this. But I may quote here the illustration of a well-known +astronomical writer on the subject. + +Suppose a blind man were walking out of doors along a high road, and +during the course of a few miles were to feel rain falling constantly +upon him. Would it be reasonable on his part, if he concluded that a +small shower of rain had accompanied him along the road as he moved, +but that fine weather certainly existed on either side of the road? On +the contrary, he might be sure that the drops which he felt, were but a +few among millions falling all together. + +Or, look at the raindrops on your window some dull day at home. Count +how many there are? Could you, with any show of common sense, decide +that those raindrops, and those alone, had fallen that day? So, when +we find these showers of meteorites falling to earth, we may safely +conclude that, for every one which touches our atmosphere, myriads rush +elsewhere in space, never coming near us. + + + + +CHAPTER XXI. + +MORE ABOUT COMETS AND METEORITES. + + +The three prominent features of comets--a head, nucleus, and tail--are +seen only in particular instances. The great majority appear as faint +globular masses of vapor, with little or no central condensation, and +without tails. On the other hand, some have a strongly-defined nucleus, +which shines with a light as vivacious as that of the planets, so as to +be even visible in the daytime. This was the case with one seen at Rome +soon after the assassination of Julius Cæsar, believed by the populace +to be the soul of the dictator translated to the skies. The first comet +of the year 1442 was also so brilliant, that the light of the sun at +noon, at the end of March, did not prevent it from being seen; and the +second, which appeared in the summer, was visible for a considerable +time before sunset. In 1532, the people of Milan were alarmed by the +appearance of a star in the broad daylight; and as Venus was not then +in a position to be visible, the object is inferred to have been a +comet. Tycho Brahe discovered the comet of 1577, from his observatory +in the isle of Huene, in the sound, before sunset; and Chizeaux saw the +comet of 1744, at one o’clock in the afternoon, without a telescope. + +The comet of 1843, already referred to in a previous chapter, was +distinctly seen at noon by many persons in the streets of Bologna +without the aid of glasses. The nucleus is generally of small size, +but the surrounding nebulosity, which forms the head, is often of +immense extent; and the hazy envelope, the “horrid hair” of poetry, is +sometimes seen separated from it by a dark space, encircling it like a +ring. This was the aspect of the comet of 1811. The entire diameter of +the head measured 1,250,000 miles, and hence its bulk was nearly three +times that of the sun, and four million times that of the earth. But +such extraordinary dimensions are quite exceptional. + +[Illustration: THE GREAT COMET OF 1811.] + +Popular impressions respecting the supposed terrestrial effects of +the comet of 1811--a fine object in the autumn of that year, long +remembered by many--are on record. It was gravely noted, that wasps +were very few in number; that flies became blind, and disappeared +early; and that twins were born more frequently than usual. The +season was remarkable for its bountiful harvest and abundant vintage. +Grapes, figs, melons, and other fruits, were not only produced in +extraordinary quantity, but of delicious flavor, so that “comet wines” +had distinct bins allotted to them in the cellars of merchants, and +were sold at high prices. There is, however, no fact better attested, +by a comparison of observations, than that comets have no influence +whatever in heightening or depressing the temperature of the seasons. +The fine fruits and ample harvest of the year in question were, +therefore, coincidences merely with the celestial phenomenon, without +the slightest physical connection with it. + +Though the advanced civilization of recent times has led to juster +views of cometary apparitions than to regard them as divinely-appointed +omens of terrestrial calamity, yet society is apt to be nervous +respecting these bodies, as likely to cause some great natural +convulsion by collision with our globe. + +The great comet, which in 1682 received first the name of Halley’s +comet, appeared last in 1835, his return having been foretold within +three days of its actually taking place. For Halley’s comet is a member +of the Solar System, having a yearly journey of seventy-six earthly +years. He journeys nearer the sun than Venus, and travels farther away +than Neptune. + +In the years 1858, 1861, and 1862, three more comets appeared, all +visible without the help of a telescope. Of these three, Donati’s +comet, in 1858, was far superior to the rest. This fine object was +first discovered on the 2d of June by Dr. Donati, at Florence. It +appeared at first as a faint nebulous patch of light, without any +remarkable condensation; and as its motion towards the sun at that +time was slow, it was not till the beginning of September that it +became visible to the naked eye. A short tail was then seen on the side +opposite to the sun. + +[Illustration: DONATI’S COMET, 1858.] + +The development was afterwards rapid, and the comet became equally +interesting to the professional astronomer and to the unlearned gazer. +In the first week of October the tail attained its greatest length, +36°. At this time the tail was sensibly curved, and had the appearance +of a large ostrich-feather when waved gently in the hand. At the latter +end of October the comet was lost in the evening twilight. Its nearest +approach to the earth was about equal to half the distance of the earth +from the sun, and the nearest approach to Venus was about one-ninth +part of that distance. An elliptical orbit, with a periodic time of +more than 2,000 years, has been assigned to our late visitor. + +It was a singular fact about this comet that at one time the star +Arcturus could be seen shining through the densest portion of the tail, +close to the nucleus. Now, although the faintest cloud-wreath of earth +would dim, if not hide, this star, yet the tail of the great comet was +of so transparent a nature that Arcturus shone undimmed, as if no veil +had come between. The exceedingly slight and airy texture of a comet’s +tail could hardly be more plainly shown. It was this gauzy appendage to +a little nucleus which men once thought could destroy our solid earth +at a single blow! + +These cometary trains generally appear straight, or at least, by the +effect of perspective, they seem to be directed along the arcs of great +circles of the celestial sphere. Some are recorded, however, which +presented a different appearance. Thus, in 1689, a comet was seen whose +tail, according to the historians, was curved like a Turkish saber. +This tail had a total length of 68°. It was the same with the beautiful +comet of Donati, which we admired in 1858, and of which the tail had a +very decided curvature. + +A comet can only be observed in the sky for a limited time. We +perceive it at first in a region where nothing was visible on preceding +days. The next day, the third day, we see it again; but it has changed +its place considerably among the constellations. We can thus follow it +in the sky for a certain number of days, often during several months; +then we cease to perceive it. Often the comet is lost to view because +it approaches the sun, and the vivid light of that body hides it +completely; but soon we observe it again on the other side of the sun, +and it is not till some time afterwards that it definitely disappears. +Some have been visible at noonday, quite near the sun, like that of +1882, on September 17th. + +Yet, while taking care not to overrate, we must not underrate. True, +the comets are delicate and slight in structure. One comet, in 1770, +wandered into the very midst of Jupiter’s moons, and so small was its +weight that it had no power whatever, so far as has been detected, to +disturb the said moons in their orbits. Jupiter and his moons did very +seriously disturb the comet, however; and when he came out from their +midst, though none the worse for his adventure, he was forced to travel +in an entirely new orbit, and never managed to get back to his old +pathway again. + +But there are comets _and_ comets, some being heavier than others. The +comet named after Donati, albeit too transparent to hide a star, was +yet so immense in size that his weight was calculated by one astronomer +to amount to as much as a mass of water forty thousand miles square and +one hundred and nine yards deep. + +When first noticed, Donati’s comet had, like all large comets, a +bright envelope of light round the nucleus. After a while the one +envelope grew into three envelopes, and a new tail formed beside the +principal tail, which for a time was seen to bend gracefully into a +curve, like a splendid plume. A third, but much fainter tail, also +made its appearance, and many angry-looking jets were poured out from +the nucleus. These changes took place while the comet was passing +through the great heat of near neighborhood to the sun. Afterwards, as +he passed away, he seemed gradually to cool down and grow quiet. The +singular changes in the appearance of Newton’s comet have been earlier +noticed. No marvel that he did undergo some alterations. The tremendous +glare and burning heat which that comet had to endure in his rush past +the sun, were more than twenty-five thousand times as much as the glare +and heat of the fiercest tropical noonday ever known upon earth. Can we +wonder that he should have shown “signs of great excitement,” that his +head should have grown larger and his tail longer? + +It certainly was amazing, and past comprehension, that the said tail, +over ninety millions of miles in length, should in four days have +seemingly swept round in a tremendous half-circle, so as first to point +in one direction, and then to point in just the opposite direction. + +We are much in the habit of speaking about comets as traveling through +the heavens with their tails streaming behind them. But though this is +sometimes the case, it is by no means always. + +The tails of comets always stream _away from the sun_--whether before +or behind the comet’s head seeming to be a matter of indifference. As +the comet comes hurrying along his orbit, with ever-increasing speed, +towards the sun, the head journeys first, and the long tail follows +after. But as the comet rounds the loop of his orbit near the sun--the +point nearest of all being called his _perihelion_--the head always +remains towards the sun, while the tail swings, or seems to swing, in +a magnificent sweep round, pointing always in the direction just away +from the sun. + +Then, as the comet journeys with slackening speed, on the other side of +his orbit, towards the distant _aphelion_, or farthest point from the +sun, he still keeps his head towards the sun. So, at this part of his +passage, in place of the head going first and the tail following after, +the tail goes first and the head follows after. The comet thus appears +to be moving backwards; or, like an engine pushing instead of drawing a +train, the head seems to be driving the tail before it. + +[Illustration: GREAT COMET OF 1744.] + +[Illustration: THE FIRST COMET OF 1888--JUNE 4.] + +The sun, then, acts on these bodies when they approach him, produces +in them important physical and chemical transformations, and exercises +on their developed atmosphere a repulsive force, the nature of which +is still unknown to us, but the effects of which coincide with the +formation and development of the tails. The tails are thus, in the +extension of the cometary atmosphere, driven back, either by the +solar heat, by the light, by electricity, or by other forces; and +this extension is rather a motion in the ether than a real transport +of matter, at least in the great comets which approach very near the +sun, and in their immense luminous appendages. The effects produced +and observed are not the same in all comets, which proves that they +differ from each other in several respects. The tails have sometimes +been seen to diminish before the perihelion passage, as in 1835. +Luminous envelopes have also been seen succeeding each other round the +head, concentrating themselves on the side opposite to the sun, and +leaving the central line of the tail darker than the two sides. This +is what happened in the Donati comet and in that of 1861. Sometimes a +secondary tail has been seen projected towards the sun, as in 1824, +1850, 1851, and 1880. Comets have been seen with the head enveloped in +phosphorescence, surrounding them with a sort of luminous atmosphere. +Comets have also been seen with three, four, five, and _six tails_, +like that of 1744, for example, which appeared like a splendid aurora +borealis rising majestically in the sky, until, the celestial fan being +raised to its full height, it was perceived that the six jets of light +all proceeded from the same point, which was nothing else but the +nucleus of a comet. On the other hand, the nuclei themselves show great +variations--some appear simply nebulous, and permit the faintest stars +to be visible through them; others seem to be formed of one or more +solid masses surrounded by an enormous atmosphere; in others, again, a +nucleus does not exist, as in the Southern comet of 1887. One of the +comets of 1888 showed a triple nucleus and a bristling coma, as may +be seen in the cut. We may, then, consider that the wandering bodies +collected under the name of comets are of several origins and _several +different species_. + +_Why_ the tails of comets should so persistently avoid the sun it is +impossible to say. We do not even know whether the cause lies actually +in the sun or in the comet. Astronomers speak of the “repulsive +energy” with which the sun “sweeps away” from his neighborhood the +light vapory matter of which the tails are made. But the how and the +wherefore of this strange seeming repulsion they can not explain. For +at the selfsame time the sun appears to be attracting the comet towards +himself, and driving the comet’s tail away from himself. + +A few of the more well-known comets have been mentioned; but a year +rarely passes in which at least one comet is not discovered, though +often only a small specimen, sometimes even tailless and hairless. No +doubt many others pass unseen. The large and grand ones only come to +view now and then. + +What are comets and meteorites made of? Respecting comets, a good +many ideas are put forth, and a good many guesses are made, as to +“burning gas,” “luminous vapor,” “beams of light,” and so on. But in +truth, little is known about the matter. Respecting meteorites, we can +speak more certainly. A good many meteorites have fallen to earth as +aerolites, and have been carefully examined. They are found to contain +nickel, cobalt, iron, phosphorus, and sometimes at least, a large +supply of hydrogen gas. + +Not only do solid aerolites fall half-burnt to the ground, but even +when the meteorites are quite consumed in the air, the fine dust +remaining still sinks earthward. This fine dust has been found upon +mountain-tops, and has been proved by close examination to be precisely +the same as the material of the solid aerolites. + +A luminous body of sensible dimensions rapidly traverses space, +diffusing on all sides a vivid light--like a globe of fire of which +the apparent size is often comparable with that of the moon. This +body usually leaves behind it a perceptible luminous train. On or +immediately after its appearance it often produces an explosion, and +sometimes even several successive explosions, which are heard at great +distances. These explosions are also often accompanied by the division +of the globe of fire into luminous fragments, more or less numerous, +which seem to be projected in different directions. This phenomenon +constitutes what is called a _meteor_, properly speaking, or a +_bolide_. It is produced during the day as well as the night. The light +which it causes in the former case is greatly enfeebled by the presence +of the solar light, and it is only when it is developed with sufficient +intensity that it can be perceived. + +In the British Museum there is a superb collection of meteorites. They +have been brought together from all parts of the earth, and vary in +size from bodies not much larger than a pin’s-head up to vast masses +weighing many hundred pounds. There are also many models of celebrated +meteorites, of which the originals are dispersed through various other +museums. + +Many of these objects have nothing very remarkable in their external +appearance. If they were met with on the sea-beach, they would be +passed by without more notice than would be given to any other stone. +Yet what a history such a stone might tell us if we could only manage +to obtain it! It fell; it was seen to fall from the sky; but what +was its course anterior to that movement? Where was it one hundred +years ago, one thousand years ago? Through what regions of space has +it wandered? Why did it never fall before? Why has it actually now +fallen? Such are some of the questions which crowd upon us as we +ponder over these most interesting bodies. Some of these objects are +composed of very characteristic materials. Take, for example, one of +the more recent meteorites, known as the Rowton siderite. This body +differs very much from the more ordinary kind of stony meteorite. It +is an object which even a casual passer-by would hardly pass without +notice. Its great weight would also attract attention, while if it be +scratched or rubbed with a file, it would be found that it was not in +any sense a stone, but that it was a mass of nearly pure iron. We know +the circumstances under which that piece of iron fell to the earth. +It was on the 20th of April, 1876, about 3.40 P. M., that a strange +rumbling noise, followed by a startling explosion, was heard over an +area of several miles in extent among the villages in Shropshire. About +an hour after this occurrence, a farmer noticed the ground in one of +his grass-fields to have been disturbed, and he probed the hole which +the meteorite had made, and found it, still warm, about eighteen inches +below the surface. Some men working at no great distance had actually +heard the noise of its descent, but without being able to indicate +the exact locality. This remarkable object weighs 7¾ pounds. It is an +irregular angular mass of iron, though all its edges seem to have been +rounded by fusion in its transit through the air, and it is covered +with a thick black film of the magnetic oxide of iron, except at the +point where it first struck the ground. + +This siderite is specially interesting on account of its distinctly +metallic character. Falls of the siderites, as they are called, are not +so common as those of the stony meteorites; in fact, there are only +a few known instances of meteoric irons having been actually seen to +fall, while the falls of stony meteorites are to be counted in scores +or in hundreds. The inference is that the iron meteorites are much less +frequent than the stony ones. + +It is a wonderful thought that we should really have these visitants +from the sky, solid metal or showers of dust, coming to us from distant +space. + +If the dust of thousands of meteorites is always thus falling +earthward, one would imagine that it must in time add something to the +weight of the earth. And this actually is the case. During the last +three thousand years, no less than one million tons of meteorite-dust +must, according to calculation, have fallen to earth out of the sky. A +million tons is of course a mere nothing compared with the size of the +world. Still, the fact is curious and interesting. + +It has been suggested that, _perhaps_ the flames of the sun are partly +fed by vast showers of falling meteorites. It has even been suggested +that _perhaps_, in long past ages, the earth and the planets grew to +their present size under a tremendous downpour of meteorites; the +numbers which now drop to earth being merely the thin remains of what +once existed. But for this guess there is no real foundation. + +Whether suns and worlds full-grown, created as in an instant; +whether tiny meteorites in countless myriads to be used as stones in +“building;” whether vast masses of flaming gas, to be gradually cooled +and “framed” into shape--which ever may have come first, and whichever +may have been the order of God’s working--still that “first” was made +by him; still he throughout was the Master-builder. + +[Illustration: GREAT COMET OF 1680.] + +A few words more about “comet-visitors.” Many comets, as already +stated, belong to our Solar System, though whether they have always so +belonged is another question. It is not impossible that they may once +upon a time have wandered hence from a vast distance, and, being caught +prisoner by the powerful attraction of Jupiter or one of his three +great brother-planets, have been compelled thenceforth to travel in a +closed pathway round the sun. + +[Illustration: GREAT COMET OF 1769.] + +There are also many comets which come once only to our system, flashing +round past the sun, and rushing away in quite another direction, never +to return. Where do these comets come from? And where do they go? From +other suns--brother suns to ours? It may be. One is almost disposed to +think that it must be so. + +Do we ever think what an immense voyage they must have made to come +from there to here? Do we imagine for how many years they must have +flown through the dark immensity to plunge themselves into the fires +of our sun? If we take into account the directions from which certain +comets come to us, and if we assign to the stars situated in that +region the least distances consistent with known facts, we find that +these comets certainly left their last star more than _twenty millions +of years ago_. + +In thus putting to us from the height of their celestial apparitions +so many notes of interrogation on the grandest problems of creation, +comets assume to our eyes an interest incomparably greater than that +with which superstition blindly surrounded them in past ages. When we +reflect for a moment that a certain comet which shines before us in +the sky came originally from the depths of the heavens, that it has +traveled during millions of years to arrive here, and that consequently +it is by millions of years that we must reckon its age if we wish to +form any idea of it, we can not refrain from respecting this strange +visitor as a witness of vanished eras, as an echo of the past, as +the most ancient testimony which we have of the existence of matter. +But what do we say? These bodies are neither old nor young. There +is nothing old, nothing new--all is present. The ages of the past +contemplate the ages of the future, which all work, all gravitate, all +circulate, in the eternal plan. Musing, you look at the river which +flows so gently at your feet, and you believe you see again the river +of your childhood; but the water of to-day is not that of yesterday, it +is not the same substance which you have before your eyes, and never, +never shall this union of molecules, which you behold at this moment, +come back there--never till the consummation of the ages! + +If the appearance of comets forebodes absolutely nothing as to the +microscopical events of our ephemeral human history, it is not the same +with the effects which might be produced by their encounter with our +wandering planet. In such an encounter there is nothing impossible. No +law of celestial mechanics forbids that two bodies should come into +collision in their course, be broken up, pulverized, and mutually +reduced to vapor. + +I have before described some of the tremendous outbursts seen on the +surface of our sun. It is believed that in these outbursts matter is +expelled, or driven forth, with such fearful violence as to send it +whirling through space, never to fall back to the sun. + +Some meteorites may have their births thus. So also may some comets. +And if all the stars are suns--huge fiery globes like our sun, and +subject like him to tremendous eruptions--they too, probably, send out +comets and meteorites to wander through space. Whether or no comets +come into existence in any such manner, one thing seems pretty certain. +Those comets which come to us from outside our system must come from +some other system. And the nearest systems known are those of the stars. + +The nearest star of all, whose distance has been measured, is Alpha +Centauri. It has been roughly calculated that a comet, passing direct +from Alpha Centauri to our sun, would take about twenty millions of +years for his journey. But here we tread upon very doubtful ground. +Many matters, at present unknown to us, might greatly affect the result +of such a calculation. Also it is by no means impossible that other +stars lie really much nearer to us than Alpha Centauri, whose distance +astronomers have not yet attempted to measure. + +[Illustration: BARON ALEXANDER VON HUMBOLDT.] + +“In order to complete our view,” says Alexander Von Humboldt, “of all +that we have learned to consider as appertaining to our Solar System, +which now, since the discovery of the small planets, of the interior +comets of short revolutions, and of the meteoric asteroids, is so rich +and complicated in its form, it remains for us to speak of the ring +of zodiacal light. Those who have lived for many years in the zone of +palms must retain a pleasing impression of the mild radiance with which +the zodiacal light, shooting pyramidally upward, illumines a part of +the uniform length of tropical nights. I have seen it shine with an +intensity of light equal to the Milky Way in Saggitarius, and that not +only in the rare and dry atmosphere of the summit of the Andes, at an +elevation of from thirteen to fifteen thousand feet, but even on the +boundless grassy plains of Venezuela, and on the seashore, beneath the +ever-clear sky of Cumana. This phenomenon was often rendered especially +beautiful by the passage of light, fleecy clouds, which stood out in +picturesque and bold relief from the luminous background. + +“This phenomenon, whose primordial antiquity can scarcely be doubted, +is not the luminous solar atmosphere itself, which can not be diffused +beyond nine-tenths of the distance of Mercury. With much probability we +may regard the existence of a very compressed ring of nebulous matter, +revolving freely in space around the sun between the orbits of Venus +and Mars, as the material cause of the zodiacal light. These nebulous +particles may either be self-luminous or receive their light from the +sun. + +“I have occasionally been astonished, in the tropical climates of +South America, to observe the variable intensity of the zodiacal +light. As I passed the nights, during many months, in the open air, +on the shores of rivers and on plains, I enjoyed ample opportunities +of carefully examining this phenomenon. When the zodiacal light had +been most intense, I have observed that it would be weakened for a +few minutes, until it again suddenly shone forth in full brilliancy. +In a few instances I have thought I could perceive, not exactly a +reddish coloration, nor the lower portion darkened in an arc-like +form, nor even a scintillation, but a kind of flickering and wavering +of the light. Must we suppose that changes are actually in progress +in the nebulous ring? Or is it not more probable that processes of +condensation may be going on in the uppermost strata of the air, +by means of which the transparency--or, rather, the reflection of +light--may be modified in some peculiar and unknown manner? An +assumption of the existence of such meteorological causes on the +confines of our atmosphere is strengthened by the sudden flash and +pulsations of light which have been observed to vibrate for several +seconds through the tail of a comet. During the continuation of these +pulsations it has been noticed that the comet’s tail was lengthened by +several degrees, and then again contracted.” + + + + +CHAPTER XXII. + +MANY SUNS. + + +Once more we have to wing our flight far, far away from the busy Solar +System where we live; away from whirling planets, moons, meteorites, +all shining with reflected sunlight; away from the great central +sun himself, our own particular bright star. Once more we have, in +imagination, to cross the vast, black, empty space--_is_ it black, and +_is_ it empty, had we sight to see things as they are?--separating +our sun from other suns, our star from other stars. For the sun is a +star--only a star. And stars are suns--big, blazing suns. One is near, +and the others are far away. That is the difference. + +We have no longer to do with bodies merely reflecting another’s +light--always dark on one side and bright on the other--but with +burning bodies, shining all round by their own light. We have no longer +to picture just one single star with his surrounding worlds, but we +have to fix our thoughts upon the great universe of stars or suns in +countless millions. + +The earth is forgotten, with its small and ephemeral history. The +sun himself, with all his immense system, has sunk in the infinite +night. On the wings of inter-sidereal comets we have taken our flight +towards the stars, the suns of space. Have we exactly measured, have +we worthily realized the road passed over by our thoughts? The nearest +star to us reigns at a distance of 275,000 times our distance from +the sun; out to that star an immense desert surrounds us, the most +profound, the darkest, and the most silent of solitudes. + +The solar system seems to us very vast; the abyss which separates our +world from Mars, Jupiter, Saturn, and Neptune, appears to us immense; +relatively to the fixed stars, however, our whole system represents but +an isolated family immediately surrounding us: a sphere as vast as the +whole solar system would be reduced to the size of a simple point if it +were transported to the distance of the nearest star. The space which +extends between the solar system and the stars, and which separates +the stars from each other, appears to be entirely void of visible +matter, with the exception of nebulous fragments, cometary or meteoric, +which circulate here and there in the immense voids. Nine thousand +two hundred and fifty systems like ours, bounded by Neptune, would be +contained in the space which isolates us from the nearest star! + +It is marvelous that we can perceive the stars at such a distance. +What an admirable transparency in these immense spaces to permit the +light to pass, without being wasted, to thousands of billions of +miles! Around us, in the thick air which envelops us, the mountains +are already darkened and difficult to see at seventy miles; the least +fog hides from us objects on the horizon. What must be the tenuity, +the rarefaction, the extreme transparency of the ethereal medium which +fills the celestial spaces! + +The sun is center and ruler and king in his own system. But as a star, +he is only one among many stars, some greater, some less than himself. +From the far siderial heavens he is hardly recognized even as a star +among the constellations, so faint is his light. + +Do the suns which surround us form a system with that which illuminates +us, as the planets form one round our solar focus, and does our sun +revolve round an attractive center? Does this center, the point of the +revolutions of many suns, itself revolve round a preponderating center? +In a word, is the visible universe organized in one or several systems? +No Divine revelation comes to instruct men on the mysteries which +interest them most--their personal or collective destinies. We have +now, as ever, but science and observation to answer us. + +A problem so vast as this is still far from receiving even an +approximate solution. From whatever point of view we consider it, +we find ourselves face to face with the infinite in space and time. +The present aspect of the universe immediately brings into question +its past and its future state, and then the whole of united human +learning supplies us in this great research with but a pale light, +scarcely illuminating the first steps of the dark and unknown road on +which we are traveling. However, such a problem is worthy of engaging +our attention, and positive science has already made sufficient +discoveries in the knowledge of the laws of nature to permit us to +attempt to penetrate these great mysteries. What is it that the general +observation of the heavens--what is it that sidereal synthesis teaches +us on our real situation in infinitude? + +[Illustration: A TELESCOPIC FIELD IN THE MILKY WAY.] + +In the calm and silent hours of beautiful evenings, what pensive gaze +is not lost in the vague windings of the Milky Way, in the soft and +celestial gleam of that cloudy arch, which seems supported on two +opposite points of the horizon, and elevated more or less in the sky +according to the place of the observer and the hour of the night? While +one-half appears above the horizon, the other sinks below it, and if we +removed the earth, or if it were rendered transparent, we should see +the complete Milky Way, under the form of a great circle, making the +whole circuit of the sky. The scientific study of this trail of light, +and its comparison with the starry population of the heavens, begins +for us the solution of the great problem. + +Let us point a telescope towards any point of this stupendous arch. +Suddenly hundreds, thousands of stars show themselves in the telescopic +field, like needle-points on the celestial vault. Let us wait for some +moments, that our eye may become accustomed to the darkness of the +background, and the little sparks shine out by thousands. Let us leave +the instrument pointed motionless towards the same region, and there +slowly passes before our dazzled vision the distant army of stars. In +a quarter of an hour we see them appear by thousands and thousands. +William Herschel counted three hundred and thirty-one thousand in a +width of 5° in the constellation Cygnus, so nebulous to the naked eye. +If we could see the whole of the Milky Way pass before us, we should +see eighteen millions of stars. + +This seed-plot of stars is formed of objects individually invisible +to the naked eye, below the sixth magnitude; but so crowded that they +appear to touch each other, and form a nebulous gleam which all human +eyes, directed to the sky for thousands of years, have contemplated and +admired. Since it is developed like a girdle round the whole circuit of +the sky, we ourselves must be in the Milky Way. The first fact which +impresses our mind is, that _our sun is a star of the Milky Way_. + +Thought travels fast--faster than a comet, faster than light. A rushing +comet would, it is believed, take twenty millions of years to cross the +chasm between the nearest known fixed star and us. Light, flashing +along at the rate of about one hundred and eighty-six thousand miles a +second, will perform the same journey in four years and a third. But +thought can overleap the boundary in less than a single moment. + +Each star that we see in the heavens is to our eyesight simply one +point of light. The brighter stars are said to be of greater magnitude, +and the fainter stars of lesser magnitude; yet, one and all, they have +no apparent size. The most powerful telescope, though it can increase +their brilliancy, can not add to their size. A planet, which to the +naked eye may look like a star, will, under a telescope, show a disk, +the breadth of which can be measured or divided; but no star has any +real, visible disk in the most powerful telescope yet constructed. The +reason of this is the enormous distance of the stars. Far off as many +of the planets lie, yet the farthest of them is as a member of our +household compared with the nearest star. + +I have already tried to make clear the fact of their vast distance. +Light, which comes to us from the sun in eight minutes and a half, +takes over four and a third years to reach us from Alpha Centauri. From +this four-years-and-a-third length of journey between Alpha Centauri +and earth, the numbers rise rapidly to twenty years, fifty years, +seventy years, even hundreds of years. The distance of most of the +stars is completely beyond our power to measure. The whole orbit of our +earth, nay, the whole wide orbit of the far-off Neptune, would dwindle +down to one single point, if seen from the greater number of the stars. + +It used to be believed that, taking the stars generally, there was +probably no very marked difference in their size, their kind, their +brightness. Some of course would be rather larger, and others rather +smaller; still it was supposed that they might be roughly classed as +formed much on the same scale and the same plan. But doubts are now +felt about this notion. For a very similar idea used to be held with +regard to the Solar System. The wonderful variety of form and richness +in numbers, now known to abound within its limits, are discoveries of +late years. May not the same variety in kind and size be found also +among the stars? The more we look into the heavens, the more we find +that dull, blank uniformity is not to be seen there. + +It is the same upon earth. Man builds his little rows of boxlike houses +side by side, each one exactly like all the rest, or dresses his +thousand soldiers in coats of the same cut and color, or repeats a neat +leaf-design hundreds of times on carpets or wall-papers; but God never +makes two leafs or two blades of grass alike. Wholesale turning out of +things after one pattern is quite a human idea, not divine. + +We know so much about the stars as that some are at least considerably +larger and some considerably smaller than others. When one star is +seen to shine brightly, and another beside it shines dimly, we are +apt to think that the brightest must be the nearest. Yet it is often +impossible for us to say how much of the difference is owing to the +greater distance of one or the other, to the greater size of one or +the other, or to the greater brilliancy of one or the other. In many +instances we do know enough to be quite sure that there is a great +difference, not only in the distance of the stars, but in their size, +their kind, their brightness. + +The stars have been lately classed by one or two astronomers into four +distinct orders or degrees--partly depending on their color. The first +class is that of the White Suns. These are said to be the grandest and +mightiest of all. The star Sirius belongs to the order of White Suns. +Secondly comes the class of Golden Suns. To these blazing furnaces of +yellow light, second only to the white-light stars, belongs our own +sun. Thirdly, there are numbers of stars called Variable Stars, the +light of which is constantly changing, now becoming more, now becoming +less. Fourthly, there is the class of small Red Suns, about which not +much is known. + +These four orders or divisions do not by any means include all the +stars, or even all the single stars. Roughly speaking, however, the +greater number of single stars, and many also of the double stars, +belong to one or another of the above classes. + +When we talk of the different sizes of the different stars, it should +be plainly understood that we have no means of directly measuring them. +A point of light showing no disk, no surface, no breadth, can not be +measured, for there is nothing to measure. + +In certain cases we are not entirely without the power of judging. The +distances of a few of the stars from us have been found out. Knowing +how far off any particular star is, astronomers are able to calculate +exactly how bright our own sun would look at that same distance. If +they find that our sun would shine just as the star in question +shines, there is some reason for supposing that our sun and the star +may be of the same size. If our sun would shine more brightly than the +star shines, there is some reason for supposing that the star may be +smaller than our sun. If our sun would shine more dimly than the star +shines, there is some reason for supposing that the star may be larger +than our sun. + +Other matters, however, have to be considered. Suppose we find a star +at a certain distance shining twice as brilliantly as our own sun would +shine at that same distance. Naturally, then, we say, That star must be +much larger than our sun. + +The reasoning may be mistaken. We do not know the fact. What if, +instead of being a much _larger_ sun, it is only a much _brighter_ +sun? This possibly must be allowed for. It has, indeed, been strongly +doubted by one astronomer, after close study of the sun, whether any +surface of any star _could_ exceed the surface of our sun in its power +of light and heat. + +But Sirius sheds actually forty-eight times as much light around +it as does our sun; we are not exactly entitled to say that Sirius +is forty-eight times as big as the sun, but we can say that Sirius +is forty-eight times as brilliant or as splendid. In making this +calculation we have taken a lower determination of the brightness of +Sirius relatively to the sun than some other careful observations would +have warranted. It will thus be seen that if there be any uncertainty +in our result it must only be as to whether Sirius is not really more +than forty-eight times as bright as the sun. + +When we picture to ourselves the star-depths, the boundless reaches of +heavenly space, with these countless blazing suns scattered broadcast +throughout, we have not to picture an universe in repose. On the +contrary, all is life, stir, energy. Just as in the busy whirl of our +Solar System no such thing as rest is to be found, so also it seems to +be in the wide universe. + +Every star is in motion. “Fixed,” as we call them, they are not fixed. +Invisible as their movements are to our eyes through immensity of +distance, yet all are moving. Those silent, placid, twinkling specks of +light are, in reality, huge, roaring, seething, tumultuous furnaces of +fire and flame, heat and radiance. + +Each, too, is hurrying along his appointed pathway in space. Some move +faster, some move more slowly. One mile per second; ten miles per +second; twenty, thirty, forty, fifty miles per second,--thus varying +are their rates of speed. But whether fast or whether slowly, still +onward and ever onward they press. Some are rushing towards us, some +are rushing away from us. Some are speeding to the right, some are +speeding to the left. + +The fine star Arcturus, which any one may admire every evening on the +prolongation of the tail of the Great Bear, is slowly withdrawing from +the fixed point where the celestial charts placed it two thousand years +ago, and is moving towards the southwest. It takes eight hundred years +to describe a space in the sky equal to the apparent diameter of the +moon; nevertheless, this displacement was sufficiently perceptible to +attract attention more than a century and a half ago, for Halley had +noticed it in 1718, as well as those of Sirius and Aldebaran. However +slow it may appear at the distance we are from Arcturus, this motion +is, at a minimum, 1,637 millions of miles a year. Sirius takes 1,338 +years to pass over the same angular space in the sky; at the distance +of that star this is, at a minimum, 397 millions of miles per annum. +The study of the proper motions of the stars has made the greatest +progress in the last half-century, and especially in recent years. All +the stars visible to the naked eye and a large number of telescopic +stars show displacements of this kind. + +Where are they going? Does any single star ever return to his +starting-point--wherever that starting-point may have been? Do they +journey in vast circles or ellipses, round some far-distant center? +What controls them all? Is it the mighty power of some such center, or +does each star, by his faint and distant attraction, help to control +all his brother-stars, to guide them on their appointed path, to +preserve the delicate balance of a universe? + +How little we know about the matter! Only so much we can tell--that +the controlling and restraining hand of God is over the whole. Whether +by the attraction of one great center or by the united influences of +a thousand fainter attractions, he steers each radiant sun upon its +heavenly path, “upholding all things by the words of his power.” There +is no blundering, no confusion, no entanglement. All is perfect order, +calm arrangement, restrained energy. + + + + +CHAPTER XXIII. + +SOME PARTICULAR SUNS. + + +In the constellation of the Swan there is a little, dim, +sixth-magnitude star, scarcely to be seen without a telescope. This +star, 61 Cygni by name, is the first whose distance from us it was +found possible to determine. + +We may think it strange that so faint a star was even attempted. +Would not astronomers have naturally supposed it to be one of the +farther-distant stars? No, they did not. For though 61 Cygni showed but +a dim light, yet his motion--not the daily apparent motion, but the +real motion as seen from earth--was found to be so much more rapid than +the motion of most other stars that they rightly guessed 61 Cygni to be +a rather near neighbor of ours. + +Do not misunderstand me, when I speak of a “more rapid motion,” and of +“rather near neighborhood.” The real rate of 61 Cygni’s rush through +space is believed to be about forty miles each second, or one thousand +four hundred and fifty millions of miles each year. All we can perceive +of this quick motion is that, in the course of three hundred and fifty +years, 61 Cygni travels over a space in the sky about as long as the +breadth of the full moon. Little enough, yet very far beyond what can +be detected in the greater number of even the brightest stars. + +Then, again, as to the near neighborhood of this star, 61 Cygni is +near enough to have his distance measured, and that is saying a good +deal. Alpha Centauri, the nearest star of which we know in the southern +heavens, is two hundred and seventy-five thousand times as far distant +as the sun. But 61 Cygni, the nearest star of which we know in the +northern heavens, is nearly twice as far away as Alpha Centauri. + +[Illustration: CYGNUS.] + +We call 61 Cygni a star, for so he appears to common observers. In +reality, instead of being only one star, the speck of light which +we call 61 Cygni consists of _two stars_. The two are separated by +a gap about half as wide again as the wide gap between the sun and +Neptune. Yet so great is their distance from us that to the naked eye +the two seem to be one. These two suns would together make a sun only +about one-third as large as our sun. They differ in size, the quicker +movements of one showing it to be the smaller; and it is by means of +their known distance from one another, and their known rate of motion, +that their size, or rather their weight, can be roughly calculated. Of +course neither of the two shows any actual measurable disk. So much and +so little is with tolerable certainty known about this particular pair +of suns. + +Next let us turn to Alpha Centauri--named _Alpha_, the first +letter of the Greek alphabet, because it is the brightest star in +the constellation of the Centaur. The second brightest star in a +constellation is generally called Beta, the third Gamma, the fourth +Delta, and so on; just as if we were to name them A, B, C, D, in order +of brightness. + +The constellation Centaur lies in the southern heavens, close to the +beautiful constellation called the Southern Cross, and is invisible in +the northern hemisphere. Of all the stars shining in the heavens round +our earth, two only--Sirius and Canopus--show greater brilliancy than +Alpha Centauri. + +As in the case of 61 Cygni, astronomers were led to attempt the +measurement of Alpha Centauri’s distance, by noticing how much more +distinct were his movements than the movements of other stars, though +less rapid both to the eye and in reality than those of 61 Cygni. Alpha +Centauri’s rate of motion is some thirteen miles each second. + +And this, so far as we yet know, is our sun’s nearest neighbor in the +heavens outside his own family circle. + +Strange to say, Alpha Centauri, like 61 Cygni, consists, not of a +single star, but of a pair of stars. It is a two-sun system--whether or +no surrounded by planets can not be told. We can only reason from what +we see to what we do not see. And as God did not form our earth “in +vain,” and did not form our sun “in vain,” so we firmly believe that he +did not form “in vain” any one of his myriads of suns scattered through +space. What is, has been, or will be the particular use of each one, +it would be rash to attempt to say. But that many among them have, +like our own sun, systems of worlds revolving round them, we may safely +consider very probable. + +[Illustration: STARS WHOSE DISTANCES ARE BEST KNOWN. (See Table.)] + +The two suns of the Alpha Centauri double-star are separated by a +distance about twenty-two times as great as the distance of the earth +from the sun, yet to the naked eye they show as a single star. Here +again one is much smaller than the other; and the smaller revolves +round the larger in about eighty-five years. + +It is believed that the two together would form a sun about twice as +large and heavy as our sun. This belief is strengthened by the great +brilliancy of Alpha Centauri. Our own sun, placed at that distance from +us, would shine only one-third as brightly as he does. + + +STARS WHOSE DISTANCES ARE BEST KNOWN. + + +--+--------------------+----------+------------------+ + | | NAME OF STAR. |MAGNITUDE.|DISTANCE IN MILES.| + +--+--------------------+----------+------------------+ + | 1| Alpha Centauri, | 1.0 | 25 trillions. | + | 2| 61 Cygni, | 5.1 | 43 ” | + | 3| 2,398, Draco, | 8.2 | 55 ” | + | 4| Sirius, | 1.0 | 58 ” | + | 5| 9,352, Lacaille, | 7.5 | 66 ” | + | 6| Procyon, | 1.3 | 71 ” | + | 7| Lalande, 21,258, | 8.5 | 74 ” | + | 8| Œltzen, 11,677, | 9.0 | 74 ” | + | 9| Sigma Draconis, | 4.7 | 78 ” | + |10| Aldebaran, | 1.5 | 81 ” | + |11| Epsilon Indi, | 5.2 | 87 ” | + |12| Œltzen, 17,415, | 9.0 | 94 ” | + |13| 1,516, Draco, | 7.0 | 101 ” | + |14| Omicron Eridani, | 4.4 | 101 ” | + |15| Altair, | 1.6 | 101 ” | + |16| Bradley, 3,077, | 5.5 | 101 ” | + |17| Eta Cassiopeiæ, | 3.6 | 118 ” | + |18| Vega, | 1.0 | 128 ” | + |19| Capella, | 1.2 | 174 ” | + |20| Arcturus, | 1.0 | 204 ” | + |21| Pole Star, | 2.1 | 215 ” | + |22| Mu Cassiopeiæ, | 5.2 | 320 ” | + |23| 1,830, Groombridge,| 6.5 | 426 ” | + +--+--------------------+----------+------------------+ + +This table presents the most trustworthy data which we have yet +obtained with reference to stellar distances. As a great number of +attempts have been made on stars which, by their brightness or by the +magnitude of their proper motion, would appear to be the nearest to us, +we may believe that the star now considered as the nearest is really +so, and that there is no other less distant. Thus our sun, a star +in the immensity, is isolated in infinitude, and _the nearest_ sun +reigns at twenty-five trillions of miles from our terrestrial abode. +Notwithstanding its unimaginable velocity of 186,400 miles a second, +light moves, flies, during four years and one hundred and twenty-eight +days to come from this sun to us. Sound would take more than three +millions of years to cross the same abyss. At the constant velocity of +thirty-seven miles an hour, _an express train starting from the sun +Alpha Centauri would not arrive here till after an uninterrupted course +of nearly seventy-five millions of years_. + +Here, then, are the nearest suns to us. These stars, twenty-three +in number, are almost the only ones which have shown a perceptible +parallax; still the result is very doubtful for the last four, of which +the parallax is less than a tenth of a second. Attempts have been made +to ascertain the parallax of all the stars of the first magnitude, +and the result has been negative for those which are not entered in +this list. Canopus, Rigel, Betelgeuse, Achernar, Alpha of the Cross, +Antares, Spica, and Fomalhaut, do not show a perceptible parallax. The +fine star Alpha Cygni, which shines near 61 Cygni, does not present to +the most accurate researches any trace of fluctuation: it is, then, +incomparably more distant than its modest neighbor--at least five +times, and perhaps twenty times, fifty times, one hundred times beyond +that. What must be the colossal size and amazing light of these suns, +of which the distance is greater than three hundred to four hundred +trillions of miles, and which nevertheless still shine with so splendid +a brightness! + +We did not know the distance of any stars till the year 1840. This +shows how recent this discovery is; indeed, we have hardly now begun +to form an approximate idea of the real distances which separate the +stars from each other. The parallax of 61 Cygni, the first which was +known, was determined by Bessel, and resulted from observations made at +Königsberg from 1837 to 1840. Since then, the first figure obtained has +been corrected by a series of more recent observations. + +Such distances are amazing and almost terrifying to the imagination. +The mind is bewildered and almost overwhelmed when attempting to form a +conception of such portions of immensity, and feels its own littleness, +the limited nature of its powers, and its utter incapacity for grasping +the amplitudes of creation. But though it were possible for us to wing +our flight to such a distant orb as 61 Cygni, we should still find +ourselves standing only on the verge of the starry firmament where ten +thousands of other orbs a thousand times more distant would meet our +view. We have reason to believe that a space equal to that which we are +now considering intervenes between most of the stars which diversify +our nocturnal sky. The stars appear of different magnitudes; but we +have the strongest reason to conclude that in the majority of instances +this is owing, not to the difference of their real magnitudes, but to +the different distances at which they are placed from our globe. + +If, then, the distance of a star of the first or second magnitude, or +those which are nearest to us, be so immensely great, what must be the +distance of stars of the sixteenth or twentieth magnitude, which can +be distinguished only by the most powerful telescopes? Some of these +must be many millions of times more distant than the nearest star whose +distance now appears to be determined. And what shall we think of the +distance of those which lie beyond the reach of any telescope that has +yet been constructed, stretching beyond the utmost limits of mortal +vision, within the unexplored regions of immensity? Here even the most +vigorous imagination drops its wing, and owns itself utterly unable to +penetrate this mysterious and boundless unknown. + +Turning now from the sun, whose distance was first measured, and from +the nearest star with which we are acquainted, let us think about the +most radiant star in the heavens--Sirius, “the blazing Dog-star of the +ancients;” named by one astronomer “the king of suns.” + +First, as to the color of Sirius. He belongs to the order of “White +Suns,” and among all the white suns known to us, Sirius ranks as +chief. There may be many at greater distances far surpassing him in +size, and weight, and brilliancy; but we can only speak so far as we +know. Strange to say, Sirius was not always a “white sun;” for ancient +writers describe him as being, in their days, a _red_ star. This change +is very singular, and difficult to understand. But Sirius is not the +only example of the kind. Many alterations in color have been noticed +as taking place, often in a much shorter space of time. For instance, +one star, which was a white sun in the days of Herschel, is now a +golden sun. + +Secondly, as to the distance of Sirius. Like a few other stars, Sirius +lies not quite so far away as to be beyond reach of measurement. +No base-line upon earth would cause the slightest seeming change of +position in him; but as our earth journeys round the sun, the line from +one side of her orbit to the other is found wide enough. A base-line +of one hundred and eighty-six millions of miles does cause just a tiny +seeming change. + +It is very little even with Alpha Centauri, and with Sirius it is much +less. The “displacement” of Sirius is so slight that to measure his +distance with exactness is impossible. Sirius lies more than twice as +far away from earth as Alpha Centauri. To reach Sirius, the straight +line between earth and sun must be repeated six hundred and twenty-six +thousand times. Light, which reaches us from the sun in eight minutes +and a half, and from Alpha Centauri in four years and a third, can not +reach us from Sirius in less than nine years. + +Thirdly, as to the size of Sirius. Here, of course, we are in +difficulties. Radiantly as Sirius shines on a clear night, and dazzling +as he looks through a powerful telescope, he shows no real disk or +round surface, but only appears as one point of brilliant light. +Some believe him to be much the same size as our sun, while others +believe him to be very much larger. But we have no certain ground to +rest upon. The only safe method of calculating the probable size--or, +rather, weight--of a star is through the discovery of a companion, +and a knowledge of its distance from the chief star, and its time of +revolution round the chief star. + +Fourthly, as to the motions of Sirius--not his nightly apparent +movement, caused by the earth’s turning on her axis, but his real +journey through space. For a long while it was only possible to observe +the movements of a star when the star was traveling _sideways_ to us +across the sky. A star coming straight towards us, or going straight +away from us, would seem to be at rest. Lately, however, by means +of that remarkable instrument, the spectroscope, it has been found +possible to measure the motions of stars coming towards or going away +from us. This is possible as yet only in a few scattered cases, but +among those few is the brilliant Sirius. + +The sideways motion of Sirius had been known before. It now appears +that he does not move exactly sideways to us, but is rushing away in a +slanting direction at the rate of thirty miles each second, or about +one thousand millions of miles a year. + +How many millions upon millions of miles Sirius must now be farther +from us than in the days of the ancients! Yet he shines still, the most +brilliant star in the sky. So small a matter are all those millions of +miles, compared with the whole of his vast distance from us, that we do +not perceive any lessening of light. + +It is an interesting fact that while Sirius is moving away from us, +we are also moving away from him. Our “first station ahead,” in the +constellation Hercules, lies exactly in the opposite direction from +Sirius. But the sun does not move so fast as Sirius. He is believed +to accomplish only about one hundred and fifty millions of miles each +year, drawing all his planets with him. + +Fifthly, has Sirius a family, or system, like that of our sun? +Why not? Common sense and reason alike answer with a “Probably, +yes”--not only about Sirius, but about other stars also. No doubt +the systems--the number, size, weight, speed, distance, and kind of +planets--differ very greatly. No doubt there are boundless varieties of +beauty and grandeur. + +But that our sun should be the head of so wonderful and complex a +system, that his rays should be the source of life and heat to so many +dependents, and that all the myriads of suns besides should be mere +solitary lamps shining into empty space, warming, lighting, controlling +_nothing_, is an idea scarcely to be looked in the face. + +Of course, there may be other and different uses for some of these +suns, beyond our understanding. We must not be positive in the matter. +It seems, however, pretty certain that Sirius at least is not a +solitary, unattended sun. + +Astronomers, carefully watching his movements, were somewhat perplexed. +As with Uranus, the attraction of a heavy body beyond was suspected +from the nature of the planet’s motions, so it happened again with the +far more distant Sirius. Astronomers could only explain his movements +by supposing the attraction of some large and near satellite. No one +knew anything about such a satellite, but it was felt that one must +exist. + +Nearly twenty years had elapsed after Bessel had predicted the +disturber of Sirius before the telescopic discovery which confirmed it +was made. The circumstances under which that discovery was made are +not, indeed, so dramatic as those which attended the discovery of +Neptune, but yet they have an interest of their own. In February, 1862, +Alvan Clark & Sons, the celebrated telescope-makers, of Cambridge, +Massachusetts, were completing a superb eighteen-inch object-glass for +the Chicago Observatory. Turning the instrument on Sirius, for the +purpose of trying it, the practiced eye of Alvan Graham Clark, the +son, soon detected something unusual, and he exclaimed, “Why, father, +the star has a companion!” The father looked, and there was a faint +companion due east from the bright star, and distant about ten seconds +of a degree. This was exactly the predicted direction of the companion +of Sirius, and yet the observers knew nothing of the prediction. As +the news of this discovery spread, many great telescopes were pointed +on Sirius; and it was found that when observers knew exactly where to +look for the object, many instruments would show it. The new companion +star to Sirius lay in the true direction, and it was now watched with +the keenest interest, to see whether it also was moving in the way +it should move,--if it were really the body whose existence had been +foretold. Four years of observation showed that this was the case, so +that hardly any doubt could remain that the telescopic discovery had +been made of the star which had caused the inequality in the motion of +Sirius. + +It is certainly a very remarkable fact that, out of the thousands of +stars with which the heavens are adorned, no single star has yet been +found which certainly shows an appreciable disk in the telescope. We +are aware that some skillful observers have thought that certain small +stars do show disks; but we may lay this aside, and appeal only to the +ordinary fact that our best telescopes turned on the brightest stars +show merely glittering points of light, so hopelessly small as to elude +our most delicate micrometers. The ideal astronomical telescope is, +indeed, one which will show Sirius, or any other bright star, as nearly +identical as possible with Euclid’s definition of a point, being that +which has no parts and no magnitude. + +Lastly, what is Sirius made of? The late discovery of spectrum +analysis, or of the instrument called the spectroscope, helps us here. +A little further explanation on this subject will be given later. It +may be observed in passing that before the said discovery, astronomers +can scarcely be asserted to have known with any certainty that stars +were suns. They could, indeed, be sure that at the vast distances of +the fixed stars no bodies, shining by merely reflected light, could +possibly be visible to us. But there knowledge stopped. + +Now we can say more. Now the spectroscope, by breaking up and dividing +for us the slender ray of light traveling from each star, has shown to +us something of the nature of the stars. Now we know that the stars, +like our sun, are burning bodies, surrounded by atmospheres full of +burning gas. + +It has even been found out that in Sirius there are large quantities of +sodium and magnesium, besides other metals, and an abundant supply of +hydrogen gas. + + + + +CHAPTER XXIV. + +DIFFERENT KINDS OF SUNS. + + +Various in kind, various in size, various in color, various in +position, various in motion, are the myriad suns scattered through +space. So far are they from being formed on the same plan, turned out +on the same model, that it may with reason be doubted whether any two +stars could be found exactly alike. Why should we expect to find them +so? No two oak-leaves, no two elm-leaves, precisely alike, are to be +found upon earth. + +So some stars are large, some are small. Some are rapid in movement, +some are slow. Some are yellow, some white, some red, green, blue, +purple, or gray. Some are single stars; others are arranged in pairs, +trios, quartets, or groups. Some appear only for a time, and then +disappear altogether. Others are changeful, with a light that regularly +waxes and wanes in brightness. + +We have now to give a little time and thought to variable stars and +temporary stars; afterwards to double stars and colored stars. There +are many stars which pass through gradual and steady changes--first +brightening, then lessening in light, then brightening again. One such +star is to be seen in the constellation of the Whale. It is named +“Mira,” or “The Marvelous,” and the time in which its changes take +place extends to eleven months. For about one fortnight it is a star +of the second magnitude. Through three months it grows slowly more and +more dim, till it becomes invisible, not only to the naked eye, but +through ordinary telescopes. About five months it remains thus. Then +again, during three months, it grows brighter and brighter, till it is +once more a second-magnitude star, and after a fortnight’s pause begins +anew to fade. + +At its maximum, this star is yellow; when it is faint, it is reddish. +Spectrum analysis shows in it a striped spectrum of the third type, +and when its light diminishes it preserves all the principal bright +rays reduced to very fine threads. The most plausible explanation +of this variability is to suppose that it periodically emits vapors +similar to the eruptions observed in the solar photosphere. Instead +of its periodicity being like that of the sun--eleven years and +hardly perceptible--this variation of the sun of the Whale is three +hundred and thirty-one days and very considerable. It is subject to +oscillations and irregularities similar to those which we remark in our +sun. Of all the variable stars, this is the easiest to observe, and it +has been known for nearly three hundred years. + +The most celebrated of all the variable stars is that known as Algol, +in the constellation of Perseus. This star is very conveniently placed +for observation, being visible every night in the Northern Hemisphere, +and its wondrous and regular changes can be observed without any +telescopic aid. Every one who desires to become acquainted with the +great truths of astronomy should be able to recognize this star, and +should have also followed it during one of its periods of change. +Algol is usually a star of the second magnitude; but in a period +between two or three days--or, more accurately, in an interval of two +days, twenty hours, forty-eight minutes, and fifty-five seconds--its +brilliancy goes through a most remarkable cycle of variations. The +series commences with a gradual decline of the star’s brightness, +which, in the course of three or four hours, falls from the second +magnitude down to the fourth. At this lowest stage of brightness, Algol +remains for about twenty minutes, and then begins to increase, until +in three or four hours it regains the second magnitude, at which it +continues for about two days, thirteen hours, when the same series +commences anew. It seems that the period required by Algol to go +through its changes is itself subject to a slow, but certain variation. + +Another variable star, Betelgeuse in Orion, undergoes its variations in +about two hundred days; while yet another, Delta Cephei, takes only six +days. Our own sun is believed to be in some slight degree a variable +star, passing through his changes in eleven years. When the sun-spots +are most numerous, he would probably appear, if seen from a great +distance, more dim than when there are few or none of them. + +Sometimes a star is not merely variable. Stars have appeared for a +brief space, and then utterly vanished. They are then named Temporary +Stars. Whether such a star really does go out of existence, or whether +it merely becomes too dim to be seen; whether the furnace-fires are +extinguished, and the glowing sun changes into a dark body, or whether +it merely turns a dark side towards us for a very long period,--these +are questions we can not answer. + +An extraordinary specimen of a temporary star was seen in 1572. It was +not a comet, for it had no coma or tail, and it never moved from its +place. The brightness of the star was so great as to surpass Sirius and +Jupiter, and to equal Venus at her greatest brilliancy. Nay, it must +have surpassed even Venus, for it was plainly visible at midday in a +clear sky. Gradually the light faded and grew more dim, till at length +it entirely disappeared. As it lessened in brilliancy, it also changed +in color, passing from white to yellow, and from yellow to red. This +curiously agrees with the three tints of the first, second, and fourth +orders of suns, as lately classified. + +This star was observed by Tycho Brahe, who gives the following curious +account: + +“One evening, when I was contemplating, as usual, the celestial +vault, whose aspect was so familiar to me, I saw, with inexpressible +astonishment, near the zenith, in Cassiopeia, a radiant star of +extraordinary magnitude. Struck with surprise, I could hardly believe +my eyes. To convince myself that it was not an illusion, and to obtain +the testimony of other persons, I called out the workmen employed in my +laboratory, and asked them, as well as all passers-by, if they could +see, as I did, the star, which had appeared all at once. I learned +later on that in Germany carriers and other people had anticipated the +astronomers in regard to a great apparition in the sky, which gave +occasion to renew the usual railleries against men of science (as with +comets whose coming had not been predicted). + +“The new star was destitute of a tail; no nebulosity surrounded it; +it resembled in every way other stars of the first magnitude. Its +brightness exceeded that of Sirius, of Lyra, and of Jupiter. It could +only be compared with that of Venus when it is at its nearest possible +to the earth. Persons gifted with good sight could distinguish this +star in daylight, even at noonday, when the sky was clear. At night, +with a cloudy sky, when other stars were veiled, the new star often +remained visible through tolerably thick clouds. The distance of +this star from the other stars of Cassiopeia, which I measured the +following year with the greatest care, has convinced me of its complete +immobility. From the month of December, 1572, its brightness began to +diminish; it was then equal to Jupiter. In January, 1573, it became +less brilliant than Jupiter; in February and March, equal to stars of +the first order; in April and May, of the brightness of stars of the +second order. The passage from the fifth to the sixth magnitude took +place between December, 1573, and February, 1574. The following month +the new star disappeared without leaving a trace visible to the naked +eye, having shone for seventeen months.” + +These circumstantial details permit us to imagine the influence +which such a phenomenon must have exercised on the minds of men. Few +historical events have caused so much excitement as this mysterious +envoy of the sky. It first appeared on November 11, 1572. General +uneasiness, popular superstition, the fear of comets, the dread of the +end of the world, long since announced by the astrologers, were an +excellent setting for such an apparition. It was soon announced that +the new star was the same which had led the wise men to Bethlehem, +and that its arrival foretold the return of the Messiah and the last +judgment. For the hundredth time, perhaps, this sort of prognostication +was recognized as absurd. It did not, however, prevent the astrologers +from being believed, twelve years later, when they announced anew the +end of the world for the year 1588; these predictions exercised the +same influence on the public mind. + +After the star of 1572 the most celebrated is that which appeared +in October, 1604, in Serpentarius, and which was observed by two +illustrious astronomers, Kepler and Galileo. As happened with the +preceding, its light imperceptibly faded. It remained visible for +fifteen months, and disappeared without leaving any traces. In 1670 +another temporary star, blazing out in the head of the Fox (Vulpecula), +showed the singular phenomenon of being extinguished and reviving +several times before it completely vanished. We know of _twenty-four_ +stars which, during the last two thousand years, have presented a +sudden increase of light; have been visible to the naked eye, often +brilliant; and have then again become invisible. The last apparitions +of this kind happened before our eyes in 1866, 1876, 1885, and 1892, +and spectrum analysis enabled us to ascertain, as we have seen, that +they were due to veritable combustion--a fire caused by a tremendous +expansion of incandescent hydrogen, and to phenomena analogous to +those which take place in the solar photosphere. A rather curious fact +about these stars is, that they do not blaze out indifferently in any +point of the sky, but in rather restricted regions, chiefly in the +neighborhood of the Milky Way. + +Many other instances have been known, beside those referred to, of +variable and temporary stars. + +There are two distinct kinds of double-stars. First, we have those +which merely seem to be double, because one lies almost directly behind +the other, though widely distant from it. Just as a church-tower, +two miles off, may appear to stand close side by side with another +church-tower two and a half miles off, though they are in fact +separated. Secondly, we have the real systems of two suns belonging to +one another; the smaller moving round the larger, or more correctly +both traveling round one central point called the center of gravity, +the smaller having the quicker rate of motion. + +[Illustration: LYRA] + +Alpha Centauri and 61 Cygni have been already described, as examples of +true double-stars. In the constellation Lyra a marked instance is to be +seen. The brightest star in the Lyre is Vega, and near Vega shines a +tiny star, which to people with particularly clear sight has sometimes +rather a longish look. If you examine this star through an opera-glass, +you find it to consist of two separate stars. But if you get a more +powerful telescope, and look again, you will find that _each star_ of +the couple actually consists of _two_ stars. The four are not at equal +distances. Two points of light seemingly close together are parted by +a wide gap from two other points equally close together. These four +stars are believed to have a double motion. Each of the separate pairs +revolves by itself, the two suns traveling round one center; and in +addition to this the two _couples_ of suns probably perform a long +journey round another center common to them all. + +Many thousands of double stars have been discovered; and a large number +of these are now known to be, not merely two distinct suns lying in the +same line of sight, but two brother-suns, each probably the center of +his own system of planets. + +We have not only to consider the number of suns, though of simple +numbers more yet remains to be said. Attention must also be given to +the varying colors of different stars; for all suns in the universe are +not made after the model of our sun. All suns are not yellow. + +So far as single stars are concerned, colors seem rather limited. White +stars, golden or orange stars, ruby-red stars, placed alone, are often +seen; but blue stars, green stars, gray stars, silver stars, purple +stars, are seldom if ever visible to the naked eye, or known to exist +as single stars. + +Take a powerful telescope and examine star-couples, and a very +different result you will find. Not white, yellow, and red alone, but +blue, purple, gray, green, fawn, buff, silvery white, and coppery hues, +will delight you in turn. As a rule, when the two stars of a couple +are alike in color, they are either white, or yellow, or red. Also in +the case of double-stars of different colors, the larger of the two is +almost invariably white or some shade of yellow or red. + +There are, however, exceptions to all such rules. Blue stars are almost +never seen alone, and as one of a pair the blue star is generally, if +not invariably, the smaller. But instances are known of double-stars, +both of which are blue; and one group in the southern heavens is +entirely made up of a multitude of bluish suns. + +It is when we come to consider double-stars of two colors that the +most striking effects are found. Now and then the two suns are nearly +the same in size; but more commonly one is a good deal larger than the +other. This is known by the brighter light of the largest, and the more +rapid movements of the smallest. The lesser star is often only small by +comparison, and may be in reality a very goodly and brilliant sun. + +Among nearly six hundred “doubles” examined by one astronomer, there +were three hundred and seventy-five in which the two stars were of one +color, generally white, yellow, orange, or red. The rest were different +in tint, the difference between the two suns in about one hundred and +twenty cases being very marked. + +For instance, a red “primary,” as the larger star is called, will +be seen with a small green satellite; or a white primary will have +a little brother-sun of purple, or of dark ruby, or of light red. +Sometimes the larger sun is orange, the companion being purple or +dark blue. Again, the chief star will be red with a blue satellite, +or yellow with a green satellite, or orange with an emerald satellite, +or golden with a reddish-green satellite. We hear of golden and lilac +couples, of cream and violet pairs, of white and green companions. But, +indeed, the variety is almost endless. + +[Illustration: CONSTELLATIONS IN THE NORTHERN HEMISPHERE.] + +There may be worlds circling around these suns--worlds, perhaps, with +living creatures on them. We know little about how such systems of suns +and worlds may be arranged. Probably each sun would have his own set +of planets, and both suns with their planets would travel round one +central point. Perhaps, where the second sun is much the smallest, it +might occasionally be like a big blazing satellite among the planets--a +kind of burning Jupiter-sun to the chief sun. + +Among colored stars, single and double, a few may be mentioned by name +as examples. Sirius, as already observed, is a brilliant white sun; and +brilliant white also are Vega, Altair, Regulus, Spica, and many others. +Capella, Procyon, the Pole-star, and our own sun, are examples of +yellow stars. Aldebaran, Betelgeuse, and Pollux, are ruby-red. Antares +is a red star, with a greenish “scintillation” or change of hue in its +twinkling. A tiny green sun belonging to this great and brilliant red +sun has been discovered. Some have called Antares “the Sirius of Red +Suns.” + +It is during the fine nights of winter that the constellation Taurus, +or The Bull, with the star Aldebaran marking its eye, shines in +the evening above our heads. No other season is so magnificently +constellated as the months of winter. While nature deprives us of +certain enjoyments in one way, it offers us in exchange others no less +precious. The marvels of the heavens present themselves from Taurus and +Orion in the east to Virgo and Boötes on the west. Of eighteen stars +of the first magnitude, which are counted in the whole extent of the +firmament, a dozen are visible from nine o’clock to midnight, not to +mention some fine stars of the second magnitude, remarkable nebulæ, +and celestial objects well worthy of the attention of mortals. It is +thus that nature establishes an harmonious compensation, and while it +darkens our short and frosty days of winter, it gives us long nights +enriched with the most opulent creations of the sky. The constellation +of Orion is not only the richest in brilliant stars, but it conceals +for the initiated treasures which no other is known to afford. We might +almost call it the California of the sky. + +To the southeast of Orion, on the line of the Three Kings, shines +the most magnificent of all the stars, _Sirius_, or _Alpha_ of the +constellation of the Great Dog. This constellation rises in the evening +at the end of November, passes the meridian at midnight at the end of +January, and sets at the end of March. It played the greatest part in +Egyptian astronomy, for it regulated the ancient calendar. It was the +famous Dog Star; it predicted the inundation of the Nile, the summer +solstice, great heats and fevers; but the precession of the equinoxes +has in three thousand years moved back the time of its appearance by +a month and a half; and now this fine star announces nothing, either +to the Egyptians who are dead or to their successors. But we shall see +farther on what it teaches us of the grandeur of the sidereal universe. + +The _Little Dog_, or Procyon, is found above the Great Dog and below +the Twins (Castor and Pollux), to the east of Orion. With the exception +of Alpha Procyon, no brilliant star distinguishes it. + +The two double-stars, 61 Cygni and Alpha Centauri, are formed each of +two orange suns. + +In the Southern Cross there is a wonderful group of stars, consisting +of about one hundred and ten suns, nearly all invisible to the naked +eye. Among the principal stars of this group, which Sir John Herschel +described as being, when viewed through a powerful telescope, like “a +casket of variously-colored precious stones,” are two red stars, two +bright green, three pale green, and one of a greenish blue. + +The splendor of these natural illuminations can hardly be conceived +by our terrestrial imagination. The tints which we admire in these +stars from here can give but a distant idea of the real value of their +colors. Already, in passing from our foggy latitudes to the limpid +regions of the tropics, the colors of the stars are accentuated, and +the sky becomes a veritable casket of brilliant gems. What would it be +if we could transport ourselves beyond the limits of our atmosphere? +Seen from the moon, these colors would be splendid. Antares, Alpha +Herculis, Pollux, Aldebaran, Betelgeuse, Mars, shine like rubies; the +Polar Star, Capella, Castor, Arcturus, Procyon, are veritable celestial +topazes; while Sirius, Vega, and Altair are diamonds, eclipsing all +by their dazzling whiteness. How would it be if we could approach the +stars so as to perceive their luminous disks, instead of merely seeing +brilliant points destitute of all diameter? + +Blue days, violet days, dazzling red days, livid green days! Could the +imagination of poets, could the caprice of painters, picture on the +palette of fancy a world of light more astounding than this? Could the +mad hand of the chimera, throwing on the receptive canvas the strange +lights of its fancy, erect by chance a more astonishing edifice? + + + + +CHAPTER XXV. + +GROUPS AND CLUSTERS OF SUNS. + + +We have been thinking a good deal about single stars and double stars, +as seen from earth. Now we have to turn our attention to groups, +clusters, _masses_ of stars, in the far regions of space. + +Have you ever noticed on a winter night, when the sky was clear and +dotted with twinkling stars, a band of faintly-glimmering light +stretching across the heavens from one horizon to the other? The band +is irregular in shape, sometimes broader, sometimes narrower; here more +bright, there more dim. If you were in the Southern Hemisphere you +would see the same soft belt of light passing all across the southern +heavens. This band or belt is called the Milky Way. + +But what is the Milky Way? It is made up of stars. So much we know. +As the astronomer turns his telescope to the zone of faintly-gleaming +light, he finds stars appearing behind stars in countless multitudes; +and the stronger his telescope, the more the white light changes into +distant stars. + +Our sun we believe to be one of the stars of the Milky Way; merely +one star among millions of stars; merely one golden grain among the +millions of sparkling gold-dust grains scattered lavishly through +creation. Scattered, not recklessly, not by chance, but placed, +arranged, and guided each by its Maker’s upholding hand. + +The Milky Way, or the Galaxy, as it has been called, has great interest +for astronomers. Many have been the attempts made to discover its +actual size, its real shape, how many stars it contains, how far +it extends; but to all such questions the only safe answers to be +returned are fenced around with “perhaps” and “may be.” There are many +very remarkable clusters of stars to be seen in the heavens--some +few visible as faint spots of light to the naked eye, though the +greater number are only to be seen through a telescope. Either with +the naked eye, or in telescopes of varying power, they show first as +mere glimmers of light, which, viewed with a more powerful telescope, +separate into clusters of distant stars. + +[Illustration: A CLUSTER OF STARS IN CENTAURUS.] + +The most common shape of these clusters is globular--to the eye +appearing simply round. Stars gather densely near the center, and +gradually open out to a thin scattering about the edge. Thousands of +suns are often thus collected into one cluster. + +The clusters are to be seen in all parts of the sky; but the greater +number seem to be gathered into the space covered by the Milky Way and +by the famous south Magellanic Clouds. + +Some of them are beautifully colored; as, for instance, a cluster in +Toucan, not visible from England, the center of which is rose-colored, +bordered with white. No doubt it contains a large number of bright red +suns, surrounded by a scattering of white suns. + +It used to be supposed that many of these clusters were other vast +gatherings or galaxies of stars, like the Milky Way, lying at enormous +distances from us. This now seems unlikely. The present idea rather is, +that each cluster, in place of being another “Milky Way” of millions of +widely-scattered suns, is one great _star-system_, consisting indeed +of thousands of suns, but all moving round one center. Probably most +of these clusters are themselves a part of the collection of stars to +which our sun belongs. + +If this be so, and if worlds are traveling among the suns--as may well +be, since they are doubtless quite far enough apart for each sun to +have his own little or great system of planets--what sights must be +seen by the inhabitants of such planets! + +We do not indeed know the distance between the separate suns of +a cluster, which may be far greater than appears to us. But if +astronomers calculate rightly, they are near enough together to shed +bright light on all sides of a planet revolving in their midst. The +said planet might perhaps not have within view a single sun equal in +apparent size to our sun as seen from earth; yet thousands of lesser +suns, shining brightly in the firmament night and day, would cause a +radiance which we never enjoy. + +No, not _night_. In such a world there could be no night. Worlds in the +midst of a star-cluster must be regions of perpetual day. No night, no +starry heaven, no sunrise lights or sunset glories, no shadow mingling +with sunshine, but one continual, ceaseless blaze of brightness. We can +hardly picture, even in imagination, such a condition of things. + +[Illustration: THE GREAT NEBULA IN ANDROMEDA, COMPARED WITH SIZE OF THE +SOLAR SYSTEM.] + +Besides star-clusters there are also nebulæ. The word _nebula_ comes +from the Latin word for “cloud,” and the nebulæ are so named from their +cloudlike appearance. + +It is not easy to draw a line of clear division between nebulæ and +distant star-clusters; for both have at first sight the same dim, +white, cloudy look. In past days the star-clusters were included +by astronomers under the general class of nebulæ. And as with the +star-clusters, so with many of the nebulæ, the more powerful telescopes +of modern days have shown them to be great clusters, or systems, or +galaxies of stars, at vast distances from us. + +It was supposed with the nebulæ, as with some of the star-clusters, +that they were other “Milky Ways” of countless stars, far beyond the +outside boundaries of our Milky Way. This may still be true of some or +many nebulæ, but certainly not of all. + +For there are different kinds of nebulæ. Some may, as just said, be +vast gatherings of stars lying at distances beyond calculation, almost +beyond imagination. Others appear rather to be clusters of stars, like +those already described, probably situated in our own galaxy of stars. +There is also a third kind of nebula. Many nebulæ, once supposed to +be clusters of stars, having been lately examined by means of the +spectroscope, are found to be enormous masses of glowing gas, and not +solid bodies at all. + +The number of nebulæ known amounts to many thousands. They are +commonly divided into classes, according to their seeming shape. There +are nebulæ of regular form, and nebulæ of irregular form. There are +circular nebulæ, oval nebulæ, annular nebulæ, conical nebulæ, cometary +nebulæ, spiral nebulæ, and nebulæ of every imaginable description. +These shapes would no doubt entirely change, if we could see them +nearer; and indeed, even in more powerful telescopes, they are often +found to look quite different. While on the subject of clusters and +nebulæ, mention should be made of the famous Magellanic Clouds in the +southern heavens. Sometimes they are called the Cape Clouds. They +differ from other nebulæ in many points, and more particularly in their +apparent size. The Great Cloud is about two hundred times the size of +the full moon, while the Small Cloud is about one-quarter as large. In +appearance they are not unlike two patches of the Milky Way, separated +and moved to a distance from the main stream. + +These clouds are surrounded by a very barren portion of the heavens, +containing few stars; but in themselves they are peculiarly rich. +Seen through a powerful telescope, they are found to abound with +stars. The Greater Cloud alone contains over six hundred from the +seventh to the tenth magnitudes, countless tiny star-points of lesser +magnitudes, star-clusters of all descriptions, and nearly three hundred +nebulæ,--all crowded into this seemingly limited space. + +Among many famous nebulæ, the one in Orion and the one in Andromeda may +be particularly mentioned. The size of the latter, as compared with the +size of our Solar System, is shown in the cut of this nebula. On the +hypothesis of a complete resolvability into stars, the mind is lost in +numbering the myriads of suns, the agglomerated individual lights of +which produce these nebulous fringes of such different intensities. +What must be the extent of this universe, of which each sun is no more +than a grain of luminous dust! + + + + +CHAPTER XXVI. + +THE PROBLEM OF SUN AND STAR DISTANCES. + + +One question had long occupied the minds of scientific men without the +finding of any satisfactory answer, and this was the distance of the +sun from our earth. + +At length the sun had fully gained his rightful position in the minds +of men as center and controller of the Solar System, and earth was +fully dethroned from her old false position. In point of fact, the sun +had gained _more_ than his rightful position; since he was now looked +upon very much as the earth had been formerly looked upon; since he +was regarded practically as the motionless Universe-Center. The earth +might and did move--people had grown used to that idea--but the sun, +at all events, was fixed. The sun, beyond turning upon his axis, was +motionless. + +Still, as to the true distance of the sun from ourselves, ignorance +reigned. Tycho Brahe had made a great advance on earlier notions by +placing the light-giver 4,000,000 miles away in imagination. Kepler, +a quarter of a century later, increased this to 14,000,000. Galileo +afterwards reverted to the 4,000,000. All this, however, was sheer +guesswork. + +Not till well on in the seventeenth century did Cassini make a +definite attempt at actual measurement of the sun’s distance, and this +attempt gave as a result some 82,000,000 miles--not far removed from +the truth. But at the same period other observers gave results of +41,000,000 and 136,000,000; so for years the question still remained +swathed in mist. Better modes and better instruments were required +before it could receive settlement. + +The measurement of the distance of objects a good way off is by means +of their “parallax,” or the apparent change in their position when +viewed from two different points at some distance from each other. To +this method of calculating distance we have already referred. + +This kind of measurement of distances is not confined to our earth’s +surface alone. The distances of bright bodies in the heavens may be +calculated after just the same method, provided only that the heavenly +body is not too far distant to be made to change its seeming position +in the sky. + +Suppose you wished to find out how far off the moon is. You would have +to make your observation of the moon’s exact position in the sky--of +just that spot precisely where she is to be seen among heavenly scenery +at a particular moment; and you would have to get somebody else to make +a similar observation, at the same time, from some other part of earth, +at a good distance from your post. + +There are no hills or woods in the sky for the moon to be seen against; +but there are plenty of stars, bright points of light far beyond the +moon. If you look at her from one place, and your friend looks at her +from another place a good way off, there will be a difference in your +two “views.” You will see her very close to certain stars; and your +friend will see her not quite so close to those stars, but closer to +others. This difference of view would give the moon’s parallax. + +If your observation were very careful, very exact, and if you had +the precise distance between the spot where you stood, and the spot +where your friend stood,--then, from that base-line, and from the two +angles formed by its junction with the lines from the two ends of it +straight to the moon, you might reckon how many miles away the moon is. +The greater the distance between the two places of observation, the +better,--as, for instance, at Greenwich and the Cape of Good Hope. + +Practically, this is not nearly so simple a matter as it may sound, +because our earth is always on the move, and the moon herself is +perpetually journeying onward. All such motions have to be most +scrupulously allowed for. So the actual measurement of moon-distance +requires a great deal of knowledge and of study. Many other +difficulties and complications besides these enter into the question, +and have to be overcome. + +Now, the sun is very much farther away than the moon, and the +stumbling-blocks in the way of finding out his distance become +proportionately greater and more numerous. To observe him from two +parts of England, or from two parts of Europe, would give him no +parallax. That is to say, there would be no change of position on his +part apparent to us. + +I do not say that there would be no change at all; but only that it +would be so minute as to be quite unseen by human eyes, even with the +help of most careful and accurate measurement. A very long base-line +is needed to make the sun distinctly appear to change his position +ever so little. Only the very longest base-line which can be found +on earth will do for this,--nothing less than the earth’s whole +diameter of nearly eight thousand miles. And I think you will see that +the success of the calculation would then depend, not alone on most +careful observation from two posts at the opposite sides of earth; not +alone on mathematical gifts and powers of close reckoning; but also, +essentially, on a true knowledge of our earth’s diameter; that is, of +_the exact length of the base-line_ from which the whole calculation +would have to be made, and upon which the answer would largely depend. + +For a long while the earth’s diameter was not well known. As time +went on, fresh measurements were again and again made of different +portions of earth’s surface, fresh calculations following therefrom; +and gradually clear conclusions were reached. A very important matter +it was that they should be reached; for the semi-diameter of our earth +has been adopted as a “standard measure” for the whole universe; and +the slightest error in that standard measure would affect all after +calculations. + +When actual observations of sun-distance came to be made, innumerable +difficulties arose. Foremost stood the huge amount of that distance. +This made precise observations more difficult; and at the same time it +made every mistake in observation so much the worse. A little mistake +in observing the moon might mean only a hundred miles or so wrong in +the answer; but a mistake equally small in observing the sun would lead +to an error of many millions of miles. + +Again, to observe the sun’s exact position among the stars, as with the +moon, was not possible; because when the sun is visible, the stars are +not visible. Then, too, the dazzling brightness of the sun balked the +needed exactitude. + +Halley had a brilliant thought before he died. He could not carry +it out himself, but he left it to others as a legacy; that was, by +observing the transit of Venus from two different points on the earth’s +surface. At his suggestion, on the first opportunity--which was not +till after his death--the above mode was tried of measuring the sun’s +distance. + +A certain observer, stationed on one part of earth, saw the tiny dark +body of Venus take one particular line across the sun’s bright face. +Another observer, standing on quite another and a far-off part of +earth, saw the little dark body take quite another line across the +sun’s bright face. Not that there were two little dark bodies, but that +the one body was seen by different men in different places. + +From these separate views of the path of Venus across the face of the +sun, in connection with what was already known of the earth’s diameter, +and therefore of the length of base-line between the two places, the +distance of the sun was reckoned to be about 95,000,000 miles. + +Since that date many fresh attempts have been made, and errors have +been set right. Mercury as well as Venus has been used in this matter, +and other newer modes of measurement have also been successfully tried. +We know now, with tolerable accuracy, that the sun’s greater distance +from earth is between 92,000,000 and 93,000,000 miles. A curious +illustration of sun-distance has been offered by one writer. Sound and +light, heat and sensation, all require _time_ for journeying. When a +child puts his finger into a candle-flame, he immediately shrieks with +pain. Yet, quickly as the cry follows the action, his brain is not +really aware of the burn until a certain interval has elapsed. True, +the interval is extremely minute; still it is a real interval. News of +the burn has to be telegraphed from the finger, through the nerves of +the arm, up to the brain; and it occupies time in transmission, though +so small a fraction of a second that we can not be conscious of it. + +Now, try to imagine a child on earth with an arm long enough to reach +the sun. His fingers might be scorched by the raging fires there, while +yet his brain on earth would remain quite unaware of the fact for +about one hundred and thirty years. All through those years, sensation +would be darting along the arm exactly as fast as it darts from the +finger-tips of an ordinary child on earth to that child’s brain. + +If the scorching began before he was one year old, he would have become +a very aged man, one hundred and thirty years old, before he could know +in his mind what was happening in the region of his hand. Moreover, if, +on receiving the intimation, he should decide to withdraw his hand from +that unpleasantly-hot neighborhood, another hundred and thirty years +would elapse before the fingers could receive and act upon the message, +telegraphed from the brain, through the nerves of the arm. So much for +the distance of the sun from our earth! + +But the stars! How far off are the stars? + +The distance of the moon is a mere nothing. The distances of the +planets have been found out. The distance of the sun has been measured. +But the stars--those wondrous points of light, twinkling on, night +after night, century after century, unchanged in position save by the +seeming nightly pilgrimage of them all across the sky in company, +caused only by our earth’s restless, continual whirl,-- + +What about the distances of the stars? Can we measure their distance +by means of their parallax? This mode of measurement was tried +successfully on the moon, on the planets, and on the sun. But when it +was tried upon the stars, from two stations as far apart as any two +stations on earth could be, the attempt was a failure. Not a ghost of +parallax could be detected with any one star. Not the faintest sign +of displacement was seen in the position of a single star when most +critically and carefully examined. + +Then arose a brilliant thought! What of earth’s yearly journey round +the sun? If a base-line of 8,000 miles were not enough, compared with +the great distance of the stars, this at least remained. Our earth at +midsummer is somewhere about 185,000,000 miles away from where she +is at midwinter, comparing her position with that of the sun, and +reckoning him to be at rest. + +In reality, the sun is not at rest, but is in ceaseless motion, +carrying with him, wherever he goes, the whole Solar System with as +much ease as a train carries its passengers. Those passengers are truly +in motion, yet, with regard merely to the train, they are at rest. So +each member of the Solar System--attached to the sun, not by Ptolemaic +bars, but by the bond of gravity--is borne along by him through space; +yet, with respect to each member of that system, the central sun is +always and absolutely at rest. + +At one time of the year, our earth is on one side of the sun, over +92,000,000 miles distant. Six months later, the earth is on the other +side of the sun, not quite 93,000,000 miles away from him in that +opposite direction. Twice 93,000,000 comes to 186,000,000. This line, +therefore--the diameter of the earth’s whole yearly orbit, may be +roughly stated as about 185,000,000 of miles in length. + +Here surely was a base-line fit to give parallax to any star--or, +rather, to make parallax visible in the case of any star. For it is, +after all, a question, not of fact, but of visibility; not of whether +the thing _is_, but of whether we are able to _see_ it. + +As the earth journeys on her annual tour round the sun, following a +slightly elliptic pathway, the diameter of which is about 185,000,000 +miles, each star in the sky must of necessity undergo a change of +position, however minute, performing a tiny apparent annual journey in +exact correspondence with the earth’s great annual journey. + +The question is not, Does the star do this? but, Can we _see_ the star +do this? Its apparent change of position may be so infinitesimal, +through enormous distance, that no telescopes or instruments yet made +by man can possibly show it to us. + +The star-motion of which I am now speaking is purely a seeming +movement, not real. Be very clear on this point in your mind. +_Real_ star-movements, though suspected earlier, were not definitely +surmised--one may even say “discovered”--until the year 1718, by +Halley. And though Cassini in 1728 referred to this discovery of +Halley’s, yet very little was heard about the matter until the days of +Herschel. Only _apparent_ star-motions were generally understood and +accepted. + +The first and simplest of such seeming star-motions is one which we can +all see--the nightly journey of the whole host of stars, caused by our +earth’s whirl upon her axis. + +The second is also simple, but by no means also easily seen. +Astronomers reasoned out the logical necessity for such an apparent +motion long before it could be perceived. As far back as the days of +Copernicus it was felt that if the Copernican System were true, if the +earth in very deed traveled round the sun, then the stars ought to +change their positions in the sky when viewed from different parts of +earth’s annual journey. Observations were taken, divided by six months +of time and by one hundred and eighty-five millions of miles of space. +And the stars stirred not! + +Stupendous as was this base-line, it proved insufficient. So much +_more_ stupendous was the distance of the stars that the base-line sank +to nothing, and once again parallax could not be detected. Not that the +seeming change of position in the star did not take place, but that +human eyes were unable to see it, human instruments were unable to +register it. + +There lies the gist of the matter. If the change of position can be +observed, well and good! The length of the base-line being known, the +distance of the star may be mathematically calculated. For the size of +the tiny apparent path, followed in a year by the star, is and must be +exactly proportioned to the distance of the star from that base-line. +If the tiny oval be so much larger, then the star is known to be so +much nearer. If the tiny oval be so much smaller, then the star is +known to be so much farther away. + +But when not the minutest token could be discovered of a star’s +position in the sky being in the least degree affected by the earth’s +great annual change of position, astronomers were at a loss. There was +absolutely nothing to calculate from. The star was a motionless point +to earth. The whole yearly orbit of earth was a motionless point to the +star. One slender beam of light united the two. Reckoners had nothing +to stand upon. + +It is interesting to know that Copernicus had actually, long +before, suggested this as a possible explanation of the absence of +star-parallax. He thought that astronomers might fail altogether +to find it, because the stars might be “at a practically infinite +distance” from our earth. + + + + +CHAPTER XXVII. + +MEASUREMENT OF STAR DISTANCES. + + +Until the days of Sir William Herschel, little attention was bestowed +upon the universe of distant stars. Before his advent the interest +of astronomers had been mainly centered in the sun and his revolving +worlds. The “fixed stars” were indeed studied, as such, with a certain +amount of care, and numberless efforts were made to discover their +distances from earth; but the thought of a vast Starry System, in which +our little Solar System should sink to a mere point by comparison with +its immensity, had not yet dawned. + +With larger and yet larger telescopes of his own making, Herschel +studied the whole Solar System, and especially the nature of sun-spots, +the rings of Saturn, the various motions of attendant moons, together +with countless other details. He enlarged the system by the discovery +of another planet outside Saturn--the planet Uranus, till then unknown. + +These were only first steps. The work which he did in respect of the +Solar System was as nothing compared with the work which he did among +the stars. His work in our system was supplementary to other men’s +labors; his work among the stars was the beginning of a new era. Like +many before him, he, too, sought eagerly to find star-parallax, and he, +too, failed. Not yet had instruments reached a degree of finish which +should permit measuring operations of so delicate a nature. + +Although he might not detect star-parallax, he sprang a mine upon the +older notions of star-fixity. He shook to its very foundations the +sidereal astronomy of the day,--the theory, long held, of a motionless +universe, motionless stars, and a rotating but otherwise motionless +sun. He did away with the mental picture, then widely believed in, +of vast interminable fixity and stillness, extending through space, +varied only by a few little wandering worlds. As he swept the skies, +and endeavored to gauge the fathomless depths, and vainly pursued the +search for the parallax of one star after another, he made a great and +unlooked-for discovery. This was in connection with double-stars. + +Double-stars had long been known, and were generally recognized. But +whether the doubleness were purely accidental, due merely to the fact +of two stars happening to lie almost in the same line of sight, as +viewed from earth, or whether any real connection existed between +the two, no man living could say. Indeed, so long as all stars were +regarded as utter fixtures, the question was of no very great interest. + +But light dawned as Herschel watched. He found the separate stars in a +certain pair to be moving. Each from time to time had slightly, very +slightly, changed its place. Then, at least, if all other stars in +the universe were fixed, those two were not fixed. He watched on, and +gradually he made out that their motions were steady, were systematic, +and were connected the one with the other. That was one of the first +steps towards breaking down the olden notion, so widely held, of a +fixed and unchanging universe. + +Another double-star, and yet another, responded to Herschel’s intense +and careful searching. These other couples, too, were revolving, not +separately, but in company; journeying together round one center; bound +together apparently by bonds of gravitation, even as our sun and his +planets are bound together. + +Other stars besides binary stars are found to move with a real and +not merely a seeming movement. Viewed carelessly, the stars do indeed +appear to remain fixed in changeless groups; fixed even through +centuries. But, to exceedingly close watching and accurate measurement, +many among them are distinctly _not_ fixed; many among them can be +actually seen to move. + +Of course the observed motions are very small and slow. One may be +found to creep over a space as wide as the whole full moon in the +course of three hundred or four hundred years; and this is rapid +traveling for a star in earth’s sky! Another will perhaps cross a space +one-tenth or one-twentieth or one-fiftieth of the moon’s width in one +hundred years. + +Such motions had never been carefully noted or examined, until Herschel +came to do away with the old received notions of star-fixity. Happily, +Herschel was no slave to “received ideas.” Like Galileo in earlier +times, he wished to “prove all things” personally, anxious only to find +out what was the truth. And he found that the stars were _not_ fixed! +He found that numbers of them were moving. He conjectured that probably +all the rest were moving also; that in place of a fixed universe of +changeless stars we have a whirling universe of rushing suns. + +Herschel could not, of course, watch any one star for a hundred years, +much less for several centuries. But in a very few years he could, by +exceedingly close measurement, detect sufficient motion to be able to +calculate how long it would take a certain star to creep across a space +as wide as the full moon. + +From step to step he passed on, never weary of his toil. He sought to +gauge the Milky Way, and to form some notion of its shape. He noted +a general drift of stars to right and to left, which seemed to speak +of a possible journey of our sun through space, with all the planets +of the Solar System. He flung himself with ardor into the study of +star-clusters and of nebulæ. He saw, with an almost prophetic eye, the +wondrous picture of a developing universe--of nebulæ growing slowly +into suns, and of suns cooling gradually into worlds--so far as to +liken the heavens to a piece of ground, containing trees and plants in +every separate stage of growth. + +And still the search for star parallax went on, so long pursued in +vain. No longer base-line than that of the diameter of earth’s yearly +orbit lay within man’s reach. But again and yet again the attempt was +made. Instruments were improved, and measurements became ever more +delicate; and at length some small success crowned these persistent +endeavors. The tiny sounding-line of earth, lowered so often into the +mysterious depths of space, did at last “touch bottom.” + +Herschel died, full of years and honors, in 1822; and some ten years +later three different attempts proved, all to some extent, and almost +at the same date, successful. Bessel, however, was actually the first +in point of time; and his attempt was upon the double-star, 61 Cygni; +not at all a bright star, but only just visible to the naked eye. + +There are stars and stars, enough to choose from. The difficulty +always was, which to select as a subject for trial with any reasonable +prospect of a good result. Some astronomers held that the brightest +stars were the most hopeful, since they were probably the nearest; and +of course the nearer stars would show parallax more readily, because +their parallax would be the greater. But certain very bright stars +indeed are now known to be far more distant than certain very dim stars. + +Again, some astronomers thought that such stars as could be perceived +to move most rapidly in the course of years would be the most hopeful +objects to attack, since the more rapid movement might be supposed to +mean greater nearness, and so greater ease of measurement. But some +stars, seen to move rapidly, are now known to be more distant than +others which are seen to move more sluggishly. So neither of these two +rules could altogether be depended on; yet both were, on the whole, the +best that could be followed, either separately or together. + +The star 61 Cygni is not one of the brighter stars, but it is one of +those stars which can be seen to travel most quickly across the sky in +the course of a century. Therefore it was selected for a trial; and +that trial was the first to meet with success. + +For 61 Cygni was found to have an apparent parallax; in other words, +its tiny seeming journey through the year, caused by our earth’s great +journey round the sun, could be detected. Small as the star-motion +was, it might, through careful measurement, be perceived. And, in +consequence, the distance of the star from earth could be measured. +Not measured with anything like such exactitude as the measurements +of sun-distance, but with enough to give a fair general notion of +star-distance. + +One success was speedily followed by others. By a few others,--not by +many. Among the thousands of stars which can be seen by the naked eye, +one here and one there responded faintly to the efforts made. One here +and one there was found to stir slightly in the sky, when viewed from +earth’s summer and winter positions, or from her spring and autumn +positions, in her yearly pathway round the sun. + +It was a very, very delicate stir on the part of the star. Somewhat +like the difference in position which you might see in a penny a +few miles off, if you looked at it first out of one window and then +out of another window in the same house. You may picture the penny +as radiantly bright, shining through pitch darkness; and you may +picture yourself as looking at it through a telescope. But even so, +the apparent change of position in the penny, viewed thus, would be +exceedingly minute, and exceedingly difficult to see. + +There are two ways of noting this little seeming movement on the part +of a star in the sky. + +Either its precise place in the sky may be observed--its exact +position, as in a map of the heavens--or else its place may be noted +as compared with another more distant star, near to it in the sky, +though really far beyond. Parallax, if visible, would make it alter its +precise place in the sky. Parallax, if visible, would bring it nearer +to or farther from any other star more distant than itself from earth. +The more distant star would have a much smaller parallax--probably +so small as to be invisible to us--and so it would do nicely for a +“comparison star.” + +The first of these methods was the first tried; and the second was the +first successful. + +To find star-distance through star-parallax sounds quite simple, +when one thinks of the general principle of it. Just merely the +question of a base-line, accurately measured; and of two angles, +accurately observed; and of another angle, a good way off, accurately +calculated,--all resting on the slight seeming change of position in +a certain distant object, watched from two different positions, about +185,000,000 miles apart. + +Quite simple, is it not? Only, when one comes to realize that the +“change of position” is about equal to the change of position in a +penny piece, miles away, looked at from two windows in one house,--then +the difficulty grows. + +Besides this, one has to remember all the “corrections” necessary, +before any true result can be reached. + +A penny piece, miles away, seen from two windows, would be difficult +enough as a subject for measurement. But, at least, the penny would +be at rest; and you yourself would be at rest; and light would pass +instantaneously from it to you; and there would be no wobbling and +nodding motions of everything around to add to your perplexities. + +In the measurement of star-parallax, all these things have to be +considered and allowed for; all have to be put out of the question, as +it were, before any correct answer is obtained. + +The refraction of light must be considered; because that displaces the +star, and makes it seem to us to be where it is not. And the aberration +of light must be considered; because, in a different way, that does the +same thing, making the star seem to take a little journey in the course +of the year. And the precession, or forward motion, of the equinoxes, +and nutation, or vibratory motion, have both to be separately +considered; because they, too, affect the apparent position of every +star in the sky. + +To watch the star in comparison with another star is easier than +merely to note its exact position in the sky; for the other star--the +“companion-star”--is equally with itself affected by refraction of +light and by aberration of light. But, then, another question comes in +seriously: whether or no the companion-star shows any parallax also; +since, if it does, that parallax must be carefully calculated and +allowed for. + +So the measurement of star-distance, even when parallax can be +detected, is by no means a light or easy matter. On the contrary, it +bristles with difficulties. It is a most complicated operation, needing +profound knowledge, accurate observation, trained powers of reasoning +and calculation. + +Nothing short of what has been termed “the terrific accuracy” of the +present day could grapple with the truly tremendous difficulties of +this problem of star-distance. It has, however, been grappled with, +and grappled with successfully. We now know, not indeed with anything +like exactitude, yet with reasonable certainty, the distances of a good +many stars, as expressed roughly in round number of “about” so many +trillions of miles.[3] We have at least learned enough to gain some +notion of the immeasurable distances of countless other stars, lying +far beyond reach of earth’s longest measuring-line. + +[3] The diameter of the moon as seen from the earth is equal to +one thousand eight hundred and sixty eight seconds of space. When +the parallax of a star is ascertained, it is a simple matter to +calculate the distance of the star by the use of the following table. +If the star shows a displacement of one second in space, or one +eighteen-hundred-and-sixty-eighth part of the width of the moon, that +star is distant two hundred and six thousand two hundred and sixty-five +times the distance of the earth from the sun. + + An angle of 1″ is equivalent to 206,265 times 93,000,000 of miles. + “ “ “ 0″.9 “ “ “ 229,183 “ “ “ “ + “ “ “ 0″.8 “ “ “ 257,830 “ “ “ “ + “ “ “ 0″.7 “ “ “ 294,664 “ “ “ “ + “ “ “ 0″.6 “ “ “ 343,750 “ “ “ “ + “ “ “ 0″.5 “ “ “ 412,530 “ “ “ “ + “ “ “ 0″.4 “ “ “ 515,660 “ “ “ “ + “ “ “ 0″.3 “ “ “ 687,500 “ “ “ “ + “ “ “ 0″.2 “ “ “ 1,031,320 “ “ “ “ + “ “ “ 0″.1 “ “ “ 2,062,650 “ “ “ “ + “ “ “ 0″.0 “ “ “ Immeasurable. + +The nearest star, Alpha Centauri, shows a parallax of less than one +second (0″.75). The farthest star, the distance of which has been +ascertained, is 1830 Groombridge, which shows a parallax of only +0″.045, and is distant 4,583,000 times earth’s distance from the sun, +or 426 trillions of miles. + +The very thought of such unimaginable depths of space, of suns beyond +suns “in endless range,” toned down by simple distance to mere +quivering specks of light, is well-nigh overwhelming. + + + + +CHAPTER XXVIII. + +THE MILKY WAY. + + +The Milky Way forms a soft band of light round the whole heavens. In +the Southern Hemisphere, as in the Northern Hemisphere, it is to be +seen. In some parts the band narrows; in some parts it widens. Here +it divides into two branches; there we find dark spaces in its midst. +One such space in the south is so black and almost starless as to have +been named the Coal-sack. All along, over the background of soft, dim +light, lies a scattering of brighter stars shining on its surface. +Much interest and curiosity have long been felt about this mysterious +Milky Way. That it consists of innumerable suns, and that our sun is +one among them, has been believed for a considerable time. But other +questions arise. How many stars does the Milky Way contain? What is its +shape? How far does it reach? + +No harm in asking the questions, only we have to be satisfied in +astronomy to ask many questions which can not yet receive answers. No +harm for man to learn that the utmost reach of his intellect must fall +short in any attempt to sound the depths of God’s universe, even as the +arm of a child would fall short in seeking to sound the depths of the +ocean over the side of a little boat. For the attempt has been made to +sound the depths of our star-galaxy out of this little earth-boat. + +The idea first occurred to the great Herschel, as we have already +mentioned, and a grand idea it was--only a hopeless one. He turned +his powerful telescope north, south, east, west. He counted the stars +visible at one time in this, in that, in the other directions. He found +a marked difference in the numbers. The portion of sky seen through +his telescope was about one quarter the size of that covered by the +moon. Sometimes he could merely perceive two or three bright points +on a black background. At other times the field of his telescope was +crowded. In the fuller portions of the Milky Way, he had four or five +hundred stars under view at once. In one place he saw about one hundred +and sixteen thousand stars pass before him in a single quarter of an +hour. + +Herschel took it for granted that the stars of the Milky Way, +uncountable in numbers, are, as a rule, much the same in size--so that +brightest stars would, as a rule, be nearest, and dimmest stars would, +as a rule, be farthest off. Where he found stars clustering thickly, +beyond his power to penetrate, he believed that the Milky Way reached +very far in that direction. Where he found black space, unlighted by +stars or lighted by few stars, he decided that he had found the borders +of our galaxy in that direction. + +Following these rules which he had laid down, he made a sort of rough +sketch of what he supposed might be the shape of the Milky Way. He +thought it was somewhat flat, extending to a good distance breadthways +and a much greater distance lengthways, and he placed our sun not far +from the middle. This imagined shape of the Milky Way is called “The +Cloven-disk Theory.” To explain the appearance of the Milky Way in the +sky, Herschel supposed it to be cloven or split through half of its +length, with a black space between the two split parts. + +It seems that Herschel did not hold strongly to this idea in later +years, and doubts are now felt whether the rules on which he formed it +have sufficient foundation. + +For how do we know that the stars of the Milky Way are, as a rule, +much the same in size? Certainly the planets of the Solar System are +very far from being uniform, and the few stars whose weight can with +any certainty be measured, seem to vary considerably. There is a +great difference also between the large and small suns in many of the +double-stars! + +Again, how do we know that the bright stars are, as a rule, the +nearest, and the dim stars the farthest off? Here, also, late +discoveries make us doubtful. Look at Sirius and 61 Cygni--Sirius the +most radiant star in the heavens, and 61 Cygni almost invisible to the +naked eye. According to this rule, 61 Cygni ought to lie at an enormous +distance beyond Sirius. Yet in actual fact, Sirius is the farthest away +of the two. + +The illustrious Herschel believed that he had penetrated, on one +occasion, into the star-cluster on the sword-hand in the constellation +of Perseus until he found himself among sidereal depths, from which the +light could not have reached him in less than four thousand years. + +The distance of those stars had not, and has not, been mathematically +measured. Herschel judged of it by their dimness, by the strong power +needed to make them visible, and by the rules which he had adopted as +most likely true. + +Again, when Herschel found black spaces in the heavens almost void of +stars, and believed that he had reached the outside borders of the +Milky Way, he may have been in the right, or he may have been mistaken. +The limit might lie there, or thousands more of small stars might +extend in that very direction, too far off for their little glimmer to +be seen through the most powerful telescope. + +[Illustration: A CLUSTER OF STARS IN PERSEUS.] + +If this latter idea about the Milky Way being formed of a great many +brilliant suns, and of vast numbers of lesser suns also, be true, +astronomers will, in time, be able to prove its truth. For in that +case, many faint telescopic stars being much nearer to us than bright +stars of the greater magnitudes, it will be found possible to measure +their distance. The journey of our earth round the sun must cause a +seeming change in their position between summer and winter. + +The theory also that some of the nebulæ are other outlying Milky Ways, +or galaxies of stars, separated by tremendous distances from our own, +is interesting, and was long held as almost certain, yet we have no +distinct proof either one way or the other. Many of the nebulæ may be +such gatherings of countless stars outside our own, or every nebula +visible may be actually part and parcel of our galaxy. + +Much attention has of late been paid to the arrangement of stars in the +sky. The more the matter is looked into, the more plainly it is seen +that stars are neither regular in size nor regular in distribution. +They are not merely scattered carelessly, as it were, here, there, and +anywhere, but certain laws and plans of arrangement seem to have been +followed which astronomers are only now beginning dimly to perceive. + +Stars are not flung broadcast through the heavens, each one alone and +independent of the rest. They are placed often, as we have already +seen, in pairs, in triplets, in quartets, in clusters. Also, the great +masses of them in the heavens seem to be more or less arranged in +streams, and sprays, and spirals. So remarkable are the numbers and +forms of many of these streams that the idea has been suggested, with +regard to the Milky Way, whether it also may not be a vast stream of +stars, like a mighty river, collecting into itself hundreds of lesser +streams. + +The contemplation of the heavens affords no spectacle so grand and so +eloquent as that of a cluster of stars. Most of them lie at such a +distance that the most powerful telescopes still show them to us like +star-dust. “Their distance from us is such that they are beyond, not +only all our means of measurement,” says Newcomb, “but beyond all our +powers of estimation. Minute as they appear, there is nothing that +we know of to prevent our supposing each of them to be the center of +a group of planets as extensive as our own, and each planet to be as +full of inhabitants as this one. We may thus think of them as little +colonies on the outskirts of creation itself, and as we see all the +suns which give them light condensed into one little speck, we might +be led to think of the inhabitants of the various systems as holding +intercourse with each other. Yet, were we transported to one of these +distant clusters, and stationed on a planet circling one of the suns +which compose it, instead of finding the neighboring suns in close +proximity, we should see a firmament of stars around us, such as we see +from the earth. Probably it would be a brighter firmament, in which +so many stars would glow, with more than the splendor of Sirius, as +to make the night far brighter than ours; but the inhabitants of the +neighboring worlds would as completely elude telescopic vision as the +inhabitants of Mars do here. Consequently, to the inhabitants of every +planet in the cluster, the question of the plurality of worlds might be +as insolvable as it is to us.” + +These are clusters of stars of regular form in which attraction appears +to mark its secular stamp. Our mind, accustomed to order in the cosmos, +anxious for harmony in the organization of things, is satisfied with +these agglomerations of suns, with these distant universes, which +realize in their entirety an aspect approaching the spherical form. +More extraordinary, more marvelous still, are the clusters of stars +which appear organized in spirals. + +In considering stars of the first six magnitudes only--stars visible +to the naked eye--a somewhat larger number is found in the Southern +Hemisphere than in the Northern Hemisphere. In both hemispheres there +are regions densely crowded with stars, and regions by comparison +almost empty. + +It has been long questioned whether the number of bright stars is or is +not greater in the Milky Way than in other parts of the sky. Careful +calculations have at length been made. It appears that the whole of the +Milky Way--that zone of soft light passing round the earth--covers, if +we leave out the Coal-sack and other such gaps, between one-tenth and +one-eleventh of the whole heavens. + +The entire number of naked-eye stars, or stars of the first six +magnitudes, does not exceed six thousand; and of these, eleven hundred +and fifteen lie scattered along the bed of the Milky Way stream. If the +brighter stars were scattered over all the sky as thickly as throughout +the Milky Way, their number would amount to twelve thousand instead of +only six thousand. This shows us that the higher-magnitude stars really +are collected along the Milky Way in greater numbers than elsewhere, +and is an argument used by those who believe the Milky Way to be a +mighty stream of streams of stars. + +In the dark spaces of the Milky Way, on the contrary, bright stars are +so few that if they were scattered in the same manner over all the sky, +their present number of six thousand would come down to twelve hundred +and forty. This would be a serious loss. + +We know in the sky 1,034 clusters of stars and more than 11,000 +nebulæ. The former are composed of associated stars; the latter may +be divided into two classes: First, nebulæ which the ever-increasing +progress of optics will one day resolve into stars, or which in any +case are composed of stars, although their distances may be too great +to enable us to prove it; second, nebulæ properly so called, of which +spectrum analysis demonstrates their gaseous constitution. Here is +an instructive fact. The clusters of stars present the same general +distribution as the telescopic stars--they are more numerous in the +plane of the Milky Way, while it is the contrary which is presented +by the nebulæ properly so called; they are rare, thinly spread in the +Milky Way, and thickly scattered to the north as well as to the south +of this zone up to its poles. The constitution of the Milky Way--not +nebulous, but stellar--is a very significant fact. The nebulæ properly +so called are distributed, in a sense, contrary to the stars, being +more numerous towards the poles of the Milky Way and in regions poor +in stars, as if they had absorbed the matter of which the stars are +formed. + + + + +CHAPTER XXIX. + +A WHIRLING UNIVERSE. + + +No rest, no quiet, no repose, in that great universe, which to our dim +eyesight looks so fixed and still, but one perpetual rush of moving +suns and worlds. For every star has its own particular motion, every +sun is pressing forward in its own appointed path. And among the +myriads of stars--bright, blazing furnaces of white or golden, red, +blue, or green flame--sweeping with steady rush through space, our sun +also hastens onwards. + +The rate of his speed is not very certain, but it is generally believed +to be about one hundred and fifty million miles each year. Possibly he +moves in reality much faster. + +When I speak of the sun’s movement, it must of course be understood +that the earth and planets all travel with him, much as a great steamer +on the sea might drag in his wake a number of little boats. From one +of the little boats you could judge of the steamer’s motion quite as +well as if you were on the steamer itself. Astronomers can only judge +of the sun’s motion by watching the seeming backward drift of stars to +the right and left of him; and the watching can be as well accomplished +from earth as from the sun himself. + +After all, this mode of judging is, and must be, very uncertain. Among +the millions of stars visible, we only know the real distances of +about twenty-five; and every star has its own real motion, which has to +be separated from the apparent change of position caused by the sun’s +advance. + +It seems now pretty clear that the sun’s course is directed towards a +certain point in the constellation Hercules. If the sun’s path were +straight, he might be expected by and by, after long ages, to enter +that constellation. But if orbits of suns, like orbits of planets, are +ellipses, he will curve away sideways long before he reaches Hercules. + +[Illustration: HERCULES] + +One German astronomer thought he had found the center of the sun’s +orbit. He believed the sun and the stars of the Milky Way to be +traveling round the chief star in the Pleiades, Alcyone. This is +not impossible; but it is now felt that much stronger proof will be +required before the idea can be accepted. + +In the last chapter mention was made of star-streams as a late +discovery. Though a discovery still in its infancy, it is one of no +small importance. Briefly stated, the old theory as to the plan of +the Milky Way was as follows: Our sun was a single star among millions +of stars forming the galaxy, some comparatively near, some lying at +distances past human powers of calculation, and all formed upon much +the same model as to size and brightness. Where the band of milky +light showed, stars were believed to extend in countless thousands to +measureless distances. Where dark spaces showed, it was believed that +we looked beyond the limits of our universe into black space. Stars +scattered in other parts of the sky were supposed generally to be +outlying members of the same great Milky Way. Many of the nebulæ and +star-clusters were believed to be vast and distant gatherings of stars, +like the Milky Way itself, but separated by unutterably wide reaches of +space. Some of these views may yet be found to contain truth, though at +the present moment a different theory is afloat. + +It is still thought probable that our sun is one among many millions +of suns, forming a vast system or collection of stars, called by +some a universe. It is also thought possible that other such mighty +collections of stars may exist outside and separate from our own at +immense distances. It is thought not impossible or improbable that some +among the nebulæ may be such far-off galaxies of stars; though, on the +other hand, it is felt that every star-cluster and nebula within reach +of man’s sight may form a part of our own “universe.” + +According to this view of the question, the Milky Way, instead of +being an enormous universe of countless suns reaching to incalculable +distances, may rather be a vast and mighty star-stream, consisting +of hundreds of brilliant leading suns, intermixed with thousands or +even millions of lesser shining orbs. If this be the true view, the +lesser suns would often be nearer than the greater suns, although more +dim; and the Milky Way would not be itself a universe, though a very +wonderful and beautiful portion of our universe. + +Which of these two different theories or opinions contains the most +truth remains to be found out. But respecting the arrangement of +stars into streams, interesting facts have lately been discovered. We +certainly see in the Solar System a tendency of heavenly bodies to +travel in the same lines and in companies. Not to speak of Jupiter and +his moons, or Saturn and his moons, we see it more remarkably in the +hundreds of asteroids pursuing one path, the millions of meteorites +whirling in herds. Would there be anything startling in the same +tendency appearing on a mightier scale? Should we be greatly astonished +to find streams of stars, as well as streams of planets? + +For such, indeed, appears to be the case. Separated by abysses of +space, brother suns are plainly to be seen journeying side by side +through the heavens, towards the same goal. + +The question of star-drift is too complex and difficult to be gone +into closely in a book of this kind. One example, however, may be +given. Almost everybody knows by sight the constellation of the Great +Bear--the seven principal stars of which are called also Charles’s +Wain, a corruption of the old Gothic _Karl Wagen_, the churl’s or +peasant’s wagon. It is also called the Great Dipper. Four bright stars +form a rough sort of oblong, and from one of the corners three more +bright stars stretch away in a curve, representing the Bear’s tail. +Many smaller stars are intermixed. + +[Illustration: THE GREAT BEAR.] + +These seven bright stars have always been bound together in men’s +minds, as if they belonged to one another. But who, through the +centuries past, since aught was known of the real distances of the +stars from ourselves and from one another, ever supposed that any among +the seven were _really_ connected together? + +One of these seven stars, the middle one in the tail, has a tiny +companion-star, close to it, visible to the naked eye. For a good +while it was uncertain whether the two were a “real double,” or only +a seeming double. In time it became clear that the two did actually +belong to one another. + +Mizar is the name of the chief star, and Alcor of the companion. Alcor +is believed to be about three thousand times as far away from Mizar, +as our earth from the sun. Now, if this be the width of space between +those two bright points, lying seemingly so close together as almost to +look to the naked eye like one, what must be the distance between the +seven leading stars of the Great Bear, separated by broad sky-spaces? +Who could imagine that one of these suns had aught to do with the rest? + +Yet among other amazing discoveries of late years it has been found by +means of the new instrument, the spectroscope, that _five_ out of these +seven suns are traveling the same journey, with the same speed. Two of +the seven appear to be moving in another direction, but three of the +body-stars and two of the tail-stars are hastening in the direction +away from us, all in the same line of march, all rushing through space +at the rate of twenty miles each second. Some smaller stars close to +them are also moving in the same path. Is not this wonderful? We see +here a vast system of suns, all moving towards one goal, and each +probably bearing with him his own family of worlds. + +Many such streams have been noticed, and many more will doubtless be +found. For aught we know, our own sun may be one among such a company +of brother-suns, traveling in company. + +It is difficult to give any clear idea of the immensity of the +universe--even of that portion of the universe which lies within reach +of our most powerful telescopes. How far beyond such limits it may +reach, we lose ourselves in imagining. + +Earlier in the book we have supposed possible models of the Solar +System, bringing down the sun and worlds to a small size, yet keeping +due proportions. What if we were to attempt to make a reduced model of +the universe; that is of just so much of it as comes within our ken? + +Suppose a man were to set himself to form such a model, including +every star which has ever been seen. Let him have one tiny ball for +the sun, and another tiny ball for Alpha Centauri; and let him, as a +beginning, set the two _one yard apart_. That single yard represents +ninety-three millions of miles, two hundred and seventy-five thousand +times repeated. Then let him arrange countless multitudes of other tiny +balls, at due distances--some five times, ten times, twenty times, +fifty times, as far away from the sun as Alpha Centauri. + +It is said that the known universe, made upon a model of these +proportions, would be many miles in length and breadth. But the model +would appear fixed as marble. The sizes and distances of the stars +being so enormously reduced, their rates of motion would be lessened +in proportion. Long intervals of time would need to pass before the +faintest motion in one of the millions of tiny balls could become +visible to a human eye. + + + + +CHAPTER XXX. + +READING THE LIGHT. + + +[Illustration: THE PRISM AND SPECTRUM.] + +Several times, in the course of this book, mention has been made of a +wonderful new instrument called the spectroscope. We now proceed to +give a brief account of the origin and achievements of this newest of +scientific appliances. The first step towards its formation was made +by Sir Isaac Newton, when he discovered the power of the prism to +decompose light. This consists in the fact that a ray of light, after +passing through a transparent prism, becomes expanded into an elongated +spectrum, no longer white, but presenting an invariable succession of +colors from red to violet. These are called the seven primary colors; +namely, red, orange, yellow, green, blue, indigo, and violet. The +rainbow is a familiar illustration of this spectrum with its various +colors; and the raindrops are the prisms which reflect and decompose +the light. + +[Illustration: THE SPECTROSCOPE.] + +Optical science was long satisfied with this glance into the interior +constitution of light, occupying itself with the phenomena of the +prismatic colors, and theorizing on the nature of white light. In +1802, Dr. W. H. Wollaston, in closely examining a spectrum, found it +to be crossed by at least four fine dark lines. It is only when an +extremely narrow slit is employed in admitting the sunlight that they +become visible. Dr. Wollaston, supposing them to be merely “natural +boundaries” of the different color-bands, inquired no further; and +there for a while the matter rested. Not many years later, in 1815, +the matter was taken up by a German optician and scientist of Munich, +Joseph von Fraunhofer. Applying more delicate means of observation, he +was surprised to find very numerous dark lines crossing the spectrum. + +With patience he went into the question, using the telescope as well +as a very narrow slit, and soon he discovered that the dark lines were +to be numbered, not by units or by tens, but by hundreds--or, as we +now know, by thousands. Some were in the red, some were in the violet, +some were in the intermediate bands; but each one had, and has, its own +invariable position on the solar spectrum. For, be it understood, these +dark lines are constant, not variable. Where a line is seen, there it +remains. Whenever a ray of sunlight is properly examined, with slit and +with prism, that line will be found always occupying precisely the same +spot in the spectrum. + +Some of the chief and more distinct lines were named by Fraunhofer +after certain letters of the alphabet, and by those letter-names they +are still known. He began with A in the red and went on to H in the +violet. Fraunhofer made a great many experiments connected with these +mysterious lines, anxious to discover, if possible, their meaning. For +although he now saw the lines, which had scarcely so much as been seen +before, he could not understand them--he could not read what they said. +They spoke to him, indeed, about the sun; but they spoke in a foreign +language, the key to which he did not possess. He tried making use of +prisms of different materials, thinking that perhaps the lines might be +due to something in the nature of the prism employed. But let the prism +be what it might, he found the lines still there. Then he examined +the light which shines from bright clouds, instead of capturing a ray +direct from the sun. And he found the lines still there. For cloudlight +is merely reflected sunlight. + +Then he examined the light of the moon, to see if perchance the +spectrum might be clear of breaks. And he found the lines still +there. For moonlight is only reflected sunlight. Next he set himself +to examine the light which travels to us from some of the planets, +imagining that a different result might follow. And he found the lines +still there. For planet-light again is no more than reflected sunlight. + +[Illustration: SPECTRA, SHOWING THE DARK LINES.] + +Lastly, he turned his attention to some of the brighter stars, +examining, one by one, the ray which came from each. And, behold! he +found the lines _not_ there. For starlight is not reflected sunlight. +That is to say, the identical lines which distinguish sunlight were +not there. Each star had a spectrum as the sun has a spectrum, and +each star-spectrum was crossed by faint dark lines, more or less in +number. But the spectra of the stars differed from the spectrum of the +sun. Each particular star had its own particular spectrum of light, +different from that of the sun, and different from that of every other +star. For now, Fraunhofer was examining, not sunlight, but starlight; +not the light of our sun, either direct from himself or reflected from +some other body, such as planet or moon or cloud, but the light of +other suns very far distant, each one varying to some extent from the +rest in its make. The fact of the stars showing numerous sets of black +lines, all unlike those of our sun, showed conclusively that those +lines could not possibly be due to anything in our earthly atmosphere. +Sunlight and starlight travel equally through the air, and are equally +affected by it. If our atmosphere were the cause of the black lines in +sunlight, it would cause the _same_ lines in starlight. But the sun and +each individual star has its own individual lines, quite irrespective +of changeful states of the air. + +So, also, the light from any metal sufficiently heated will give +a spectrum, just as sunlight gives a spectrum, under the needful +conditions. That is to say, there must be slit and prism, or slit and +diffraction-grating, for the light to pass through. But the kind of +spectrum is by no means always the same. + +Putting aside for a few minutes the thought of sunlight and starlight, +let us look at the kind of rays or beams which are given forth by +heated earthly substances. Any very much heated substance sends forth +its light in rays or beams, and any such rays or beams may be passed +through a prism, and broken up or “analyzed,” just as easily as +sunlight may be “analyzed.” + +Suppose that we have a solid substance first--a piece of iron or of +steel wire. If it is heated so far as to give out, not only heat, +but also light, and if that light is made to travel through the slit +and prism of a spectroscope, the ray will then be broken up into its +sub-rays. They, like the sub-rays of a sunbeam, will form a continuous +row of soft color-bands, one melting into another. This is the +characteristic spectrum of the light which is given forth by a burning +or glowing _solid_. + +Next, suppose we take a liquid--some molten iron or some molten glass, +for instance. If you have ever been to a great plate-glass manufactory, +like that at St. Helens, not far from Manchester, you will have seen +streams of liquid glass pouring about, carried to and fro in huge +caldrons, bright with a living light of fire from its intensity of +heat. If a ray of _that_ light had been passed through slit and prism, +what do you think would have been the result? A continuous spectrum +once more, the same as with the glowing iron or steel. The light-ray +from a heated and radiant _liquid_, when broken up by a prism, lies in +soft bands of color, side by side. + +Both of them a good deal like the solar spectrum, you will say. Only +here are no mysterious dark lines crossing the bright bands of color. +But how about gases? Suppose we have a substance in the state of gas +or vapor, as almost every known substance might be under the requisite +conditions, and suppose that substance to be heated to a glowing +brilliance. Then let its light be passed through the slit and prism of +a spectroscope. What result shall we find this time? Entirely different +from anything seen before. Instead of soft, continuous bands of color, +there are _bright lines_, well separated and sharply defined. + +How many bright lines? Ah, that depends upon which particular gas +is having its ray analyzed. Try sodium first--one of the commonest +of earthly substances. Enormous quantities of it are distributed +broadcast in earth and air and water. More than two-thirds of the +surface of our globe lies under an enfolding vesture of water saturated +with salt, which is a compound of sodium. That is to say, sodium enters +largely into the make of salt. Every breeze which sweeps over the ocean +carries salt inland, to float through the atmosphere. Sir H. E. Roscoe +writes: “There is not a speck of dust, or a mote seen dancing in the +sunbeam, which does not contain chloride of sodium”--otherwise salt. +The very air which surrounds us is full of compounds of sodium, and +we can not breathe without taking some of it into our bodies. Sodium +is an “elementary substance.” By which I mean that it is one of a +number of substances called by us “simple,” because chemists have never +yet succeeded in breaking up those substances, by any means at their +command, into other and different materials. + +Iron is, so far as we know, a simple substance. It is found as iron +in the earth. No chemist has ever been able to make iron by combining +other materials together. No chemist has ever managed to separate iron +into other materials unlike itself. Iron it is, and iron it remains, +whether as a solid, as a liquid, or as a gas. Gold is another simple +substance, and so is silver. Sodium is another. All these we know best +in the solid form. Mercury, another simple substance, we know best as a +liquid. + +Water is not a simple substance; for it can be separated into +two different gases. Glass is not a simple substance; for it is +manufactured out of other substances combined together. + +We can speak quite positively as to such substances as are not simple; +but with regard to so-called “elements,” we may only venture to assert +that, thus far, nobody has succeeded in breaking them up. Therefore, at +least for the present, they are to us “elementary.” + +All the simple substances, and very many of the combinations of them, +though often known to us only in the solid form, may, under particular +conditions, be rendered liquid, and even gaseous. Every metal may be +either in the solid form, or the liquid form, or the vapor form. Iron, +as we commonly see it, is solid--in other words, it is frozen, like +ice. Just as increase of warmth will turn ice into water, so a certain +amount of heat will make solid iron become liquid iron. And just as yet +greater warmth will turn water into steam, so a very much increased +amount of heat will turn liquid iron into vapor of iron. A little heat +will do for ice what very great heat will do for iron. + +Whether iron and other metals exist in the sun, as on earth, in a +hard and solid form, it is impossible to say. It is only in the form +of gas that man can become aware of their presence at that distance. +The intense, glowing, furnace-heat of the sun causes many metals to +be present in large quantities in the sun’s atmosphere in the form of +vapor. + +Not only have we learned about some of the metals in the sun, but +this strange spectrum analysis has taught us about some of the metals +and gases in the stars as well. It is found that in Sirius, sodium +and magnesium, iron and hydrogen, exist. In Vega and Pollux there are +sodium, magnesium, and iron. In Aldebaran, these substances and many +others, including mercury, seem to abound. These are merely a few +examples among many stars, each being in some degree different from the +rest. + +But how can we know all this? How could the wildest guessing reveal to +us the fact of iron in the sun, not to speak of the stars? We know it +by means of the spectrum analysis--or, as we may say, by means of the +spectroscope. This instrument may be looked upon as the twin-sister to +the telescope. The telescope gathers together the scattered rays of +light into a small spot or focus. The spectroscope tears up these rays +of light into ribbons, sorts them, sifts them, and enables us to read +in them hidden meanings. + +When a ray of light reaches us from the sun, that ray is _white_; but +in the white ray there are bright colors concealed. Newton was the +first to discover that a ray of white light is really a bundle of +colored rays, so mixed up together as to appear white. If a ray of +sunlight is allowed to pass through a small round hole in a wall, it +will fall upon the opposite wall in a small round patch of white light. +But if a _prism_--a piece of glass cut in a particular shape--is put in +the path of the ray, it has power to do two curious things. First, it +bends the ray out of a straight course, causing the light to fall upon +a different part of the wall. Secondly, it breaks up or divides the +ray of white light into the several rays of colored light of which the +white ray is really composed. This breaking up, or dividing, is called +“analyzing.” + +If in place of a round hole the ray of light is made to pass through +a very narrow slit, it is proved that the bright bands of color do not +overlap. Instead of this, dark lines, or gaps, show here and there. +Now, these lines or gaps are always to be seen in the spectrum or image +of bright colors formed by a broken-up ray of _sunlight_. There is +always a certain number of dark lines in each colored band--some near +together, some far apart; here one or two, there a great many. Where a +simple ray of sunlight is concerned, the exact arrangement of the lines +never changes. + +When the stars were examined--when the rays of light coming from +various stars were split up and analyzed--it was found that they too, +like the sun, gave a spectrum of bright colors with dark lines. But +the lines were different in number and different in arrangement from +the sun’s lines. Each star has his own particular number and his own +particular arrangement, and that arrangement and number do not change. + +If a white-hot metal is burnt, and the light of it as it burns is +allowed to pass through a prism, a row of bright colors appears as in +the sun’s spectrum, only there are no dark lines. If a gas is burnt, +and the light is allowed to pass through a prism, no bright color-bands +appear, and no dark lines either; but instead of this, there are +_bright lines_. Each gas or vapor has its own number of lines and its +own arrangement. Sodium shows two bright lines, side by side. Iron +shows sixty bright lines, arranged in a particular way. + +Now you see how a row of bright colors without bands of color may +appear. But what about color-bands and dark lines together? That +discovery came latest. It was found that if a white-hot metal were +burned, and if its light were allowed before touching the prism to +shine through the flame of a burning gas, _then_ there were dark lines +showing in the colored bands. These dark lines changed in position and +number and arrangement with each different kind of gas, just as the +bright lines changed if the gases were burned alone. If the light of +the burning metal passed through a flame colored with gas of sodium, +two dark lines showed on one part of the spectrum; but if it passed +through a flame colored with vapor of iron, sixty dark lines showed on +another part of the spectrum. + +So now, by means of this spectrum analysis, we know with all but +certainty that the sun and stars are solid, burning bodies, sending +their light through burning, gas-laden atmospheres. By examining the +little black lines which appear in the spectrum of one or another, it +is possible to say the names of many metals existing as gas in those +far-off heavenly bodies. Is not this a wonderful way of reading light? + +The split-up rays tell us much more than the kinds of metals in +different stars. When a nebula is examined, and is found to give no +spectrum of bright bands and dark lines, but only a certain number of +bright lines, we know it to be formed of gas, unlike stars and other +nebulæ. Also, it is by means of the spectroscope that so much has +lately been discovered about the motions and speed of the stars coming +towards or going from us. + + + + +CHAPTER XXXI. + +STELLAR PHOTOGRAPHY. + + +Photography is not only a useful handmaid to astronomy as a whole, but +also it is so, peculiarly, to that division of astronomy with which we +are now chiefly concerned--to spectroscopy. A few pages may therefore +with advantage be given to the subject of celestial photography. + +Photography is, indeed, the greatest possible help to the astronomer. +It pictures for him those stars which his eyes can see but dimly, or +even can not see at all; it paints for him those light-rays of which he +would obtain but a passing glance, and which he could not accurately +remember in all their details; it maps out for him the wide heavens, +which he, unaided, could never do with anything like equal completeness +by eye and hand alone. + +Only recently a vast photographic map of the whole sky was undertaken. +About eighteen different observatories, in divers parts of the world, +divided the task among them, stars down to the sixteenth magnitude +being most carefully registered in a complete series of something like +fifteen hundred separate photographs. The whole result, when finally +completed, will be a grand achievement of the present century. Each +individual star, in the entire heavens all around our earth, from the +first to the sixteenth magnitudes, will have its exact position in +the sky accurately known, and the smallest change in the position of +anyone of those stars may then be detected. + +Even in the delicate and abstruse operation earlier described, the +measurement of star-distances through annual parallax, photography +again steps in. Dr. Pritchard, Savilian professor of Astronomy at +Oxford, pressed photography into the service of this task also. +Measurements for parallax were made under his direction upon +photographic plates--a work of no small interest. Here, as elsewhere, +peculiar advantages belong to the photographic method when it can be +followed. Its records are lasting, the limited number of hours which +are fully suitable for direct astronomical work may be employed in +obtaining those records, and in broad daylight the examination of them +can be carried on. + +One very curious use is made of star-photographs, more especially of +the photographs of unseen stars--that is, of stars too distant or too +dim to be detected by the eye. These photographs, when taken, may +be afterwards looked into further with a microscope. So, first, the +far-off, invisible suns of the universe are photographed on a prepared +plate, with the help of a powerful telescope, this being needful to +secure sufficient starlight; and then the tiny picture of those suns is +examined more closely with the help of a powerful microscope. + +Spectroscopy has much to say to us. It tells us about the positions +of the different stars. It tells us about the structure of the stars. +It tells us about the various classes to which the various stars +belong. And also it tells us about the motions of the stars--not mere +apparent motions, caused by movements of our own earth, but true onward +journeyings of the stars themselves through the depths of space. + +For by means of photography we do not obtain simple pictures of +the stars themselves _only_, but pictures also of the _spectra_ of +the stars. An instrument is made uniting the spectroscope with the +photographic apparatus, and this is called a spectrograph. By its +means the disintegrated or broken-up star-ray is photographed in its +broken-up condition, so that an exact picture is obtained of the bands +and lines characteristic of any particular star. + +No easy matter, as may be imagined, are these spectroscopic +observations and these spectroscopic photographings of the stars. To +bring the image of a star exactly opposite a slender opening or slit, +perhaps only about the _three-hundredth part of an inch in width_, +and to keep it there, is a task which might well be looked upon as +practically impossible. + +No sooner is a star found in the field of a telescope than it vanishes +again. As the astronomer gazes, the ground beneath him is ever whirling +onward, leaving the star behind; and although clockwork apparatus in +all observatories of any importance is made to counteract this motion +of the earth, and to keep the heavenly object, whether star or moon, or +comet, within view by following its apparent motion, yet, as can easily +be imagined, to follow thus the seeming motion of a dim star through an +opening so minute, demands exceeding care and delicacy of adjustment. + +It is not indeed, for purposes of analysis, _always_ needful to pass +the light of a star through a narrow slit. In the case of a nearer +body, such as the sun or moon or one of the planets, light flows +from all parts of the body, one ray crossing another; and for the +examination of such light, a slit is imperatively needed, all side-rays +having to be cut off. But the whole of the brightest star in the sky +is only one point of light to us, and a slitless telescope may be +used with no confused results. Where, however, direct comparison is +required, the star-lines being made to appear, side by side or above +and below, with the solar spectrum, or with the lines of earthly +metals, then the slit becomes unavoidable. + +By such comparison of the two, side by side--the light from an +intensely-heated earthly substance and the light from a star, the rays +of both being broken up in the spectroscope--the oneness or difference +of lines in the rays can be easily made out. + +One main difficulty in such observations arises from the diminution +of starlight, caused by its passage through a prism. If a rope of a +dozen strands is untwisted, each of those strands is far weaker than +the whole rope was; and each strand of color in the twisted rope of +light is of necessity much more feeble, seen by itself, than the whole +white ray seen in one. Another difficulty in our country generally +is the climate, which gives so few days or hours in the year for +effective work. Yet the full amount accomplished by seizing upon every +possible opportunity is, in the aggregate, astonishing. A third and +very pressing difficulty attendant upon examination of star-spectra is +caused by the incessant motion of our air, through which, as through +a veil, all observations have to be made. The astronomer can never +get away from the atmosphere; and unless the air be very still--that +is to say, as still as it ever can remain--the spectrum-lines are +so uncertainly seen as to make satisfactory results impossible. Dr. +Huggins has sometimes passed hours in the examination of a single line, +unable to determine whether or no it precisely coincided with the +comparison-line of some earthly substance. In _this_ matter, no leaping +at conclusions is admissible. + +The photography of stars would be easy enough if one could just +expose a plate to the shining of the star, and there leave it to be +impressed--there leave the star-ray to sketch slowly its own image. But +this is hardly possible. The unceasing motion of the earth, causing +the star perpetually to pass away from the telescopic field, and the +exceeding narrowness of the slit opposite to which the star has to +be kept in a stationary position, make the most accurate adjustment +needful. + +Clockwork alone can not be trusted. If it could, the star and the +photographic apparatus might be comfortably “fixed,” and left to do +their own work. Instead of which, while a photograph is proceeding, +it is desirable that an observer should sit gazing patiently at +the telescope-tube, where the image of the star is seen, ready at +any moment to correct by a touch the slightest irregularity in the +clockwork motion of the telescope, and so to prevent a blurred and +spoilt reproduction of the star, or of its spectrum. + +One hour, two hours, three hours, at a stretch, this unceasing +watchfulness may have to be kept up, and no small amount of enthusiasm +in the cause of science is requisite for so monotonous and wearying a +vigil. + +As noted earlier, it has been found possible, if the photograph of a +star or nebula is not completed in one night, to renew the work and +carry it on the next night, or even for many nights in succession. This +is especially practicable in spectroscopic photography. + +From four to five hours, sometimes from eight to ten hours, may +be needful before the clear image of the star or of its spectrum +appears--a dim little star probably to us, yet perhaps in reality a +splendid sun, shedding warmth and light and life upon any number of +such worlds as ours. + +Eight or ten hours of photography at one stretch with a star are +impossible; for the stars, ever seemingly on the move, do not remain +long enough in a good position. For three to six hours, a telescope may +be made, by means of its clockwork machinery, to keep a star steadily +in sight, and all that while the photograph is progressing. If further +exposure is needed, the process has to be resumed the next night. + +The more one considers the matter, the more plainly one perceives how +enormously our powers of sky-observation are increased by photography. +It is not only that one photographer, with his apparatus, may +accomplish in a single night the work of many astronomers who have +to depend upon the power of the eye alone. It is not only that, with +the help of photography, as much can now be done in a lifetime as +formerly must have occupied many generations. It is not only that the +photograph, once taken, remains a permanent possession, instead of a +record, more or less imperfect, in which otherwise the astronomer would +have to trust. + +It is not even only that in the photograph details come out which could +not be detected by the eye, and that stars are actually brought to our +knowledge which no man has ever seen, which perhaps no man ever will +see from this earth with the assistance of the most powerful telescope. +For the weak shining, which can by no possibility make itself felt by +the retina of a man’s eye, _can_ slowly impress its picture on the +photographic plate. Hundreds of stars, thousands of stars, utterly +invisible to man, have had their photographs taken as truly as you have +had your photograph taken, and by the same process, only it has been a +longer business. + +But in addition to all this, we see reproduced upon the plate those +ultra-violet and infra-red portions of the spectrum of light which but +for the handmaid, photography, would still be to us as things which +have no existence. And by means of photography we can observe and study +in those same unseen portions of the spectra, when looking into a ray +from sun or star, the innumerable dark lines, every one of which has +its own tale to tell. To these tales we must have remained blind and +deaf, but for photographic aid to our limited powers. + +Look at some dim star in the sky, and try how long you can gaze without +blinking. You will very soon find that you have done your best, and +that to gaze longer only means a sense of fatigue in your eyes, a +growing dimness in the star. How different with the photographic plate! +There, no exertion is wasted, no weariness is felt. Faint though the +light may be, which travels earthward and falls upon the plate, it is +all collected, all used. + +It is easy to photograph the sun, and this has been done. When we come +to the moon the operation is more difficult on account of the feeble +intensity of its light, and the difference of tint of the various parts +of its surface. Skill and perseverance have, however, surmounted the +greatest difficulties, and now we have photographs of the moon enlarged +to more than a yard in diameter, which show the smallest details with a +truly admirable clearness. + +In the first second of time, your eye receives as much light from the +star as does the photographic plate in the same time. But during the +course of one hour, the plate receives and stores up about thirty-six +hundred times as much light as it or you received in the first instant. +There is the secret of the matter. The photographic plate does not only +receive, it can also keep and treasure up the light, and that our eyes +are not able to do. + +If you magnify the amount received in one hour by five or ten, and +remember that it is all retained, then you will begin to understand +how feeble stars, unseen by man, should become known to us through +photography. + + + + +CHAPTER XXXII. + +THE DAWN OF ASTRONOMY. + + +The beginnings of astronomy lie in the distance of earliest historical +ages. It is no easy matter to say when first, in all probability, this +science grew into existence. Astronomy was alive before the British +nation was heard of; before Saxons or Franks had sprung into being; +before the Roman Empire extended its iron rule; before the Grecian +Empire began to flourish; before the Persian Empire gained power; +before the yet earlier Assyrian Empire held sway. + +Among the ancient Chaldeans were devoted star-gazers--much more devoted +than the ordinary run of educated Anglo-Saxons in this present century. +They earnestly sought, in the dim light of those ages, to decipher the +meaning of heaven’s countless lamps. We have better instruments, and +more practiced modes of reasoning; also, we have the collected piles +of knowledge built up by our forefathers through tens of centuries. +Yet our search is in essence the same as was theirs, to know the truth +about the stars: not merely to start some attractive theory, and then +to prove that our theory must be right, because we have been so clever +as to start it; but to discover that which is in those regions of +space. No lower aim than this is worthy to be called scientific. + +Mistakes, of course, are made; how should it be otherwise? A man +finding his way at night, for the first time, through a wild and +unknown country, will almost certainly take some wrong turns before +he discovers the right road. In astronomy, as in all other natural +sciences, blunders are a necessity if advance is to be made. We have +to grope our way to knowledge through observation and conjecture; in +simpler terms, through gazing and guessing. Observation of facts leads +to conjecture as to the possible causes for those facts; and each +conjecture is proved by later observation to be either right or wrong. +If proved to be right, it takes its place among accepted truths; if +proved to be wrong, it is flung aside. Some pet delusions die hard, +because of people’s love for them. + +Astronomy, as an infant science, mixed up with astrology, existed +in the days when the Pyramids were juvenile, and when the Assyrian +sculptures were modern. How much farther back who shall say? By +astrology, those who studied the heavens endeavored to determine +the fate of men and of nations, to predict events, and to interpret +results. They paid particular attention to the aspect of the planets, +and the general appearance of the firmament. + +These observations were at first simple remarks made by the shepherds +of the Himalayas after sunset and before sunrise: The phases of the +moon, and diurnal retrograde motion of that body with reference to +the sun and stars; the apparent motion of the starry sky accomplished +silently above our heads; the movements of the beautiful planets +through the constellations; the shooting star, which seems to fall +from the heavens; eclipses of the sun and moon, mysterious subjects +of terror; curious comets, which appear with disheveled hair in +the heights of heaven,--such were the first subjects of these old +observations made during thousands of years. + +The ancient Chaldean star-gazers had rivals among the early Egyptians; +and the Chinese profess to have kept actual record of eclipses during +between three and four thousand years. The earlier records are not +trustworthy; but of thirty-six eclipses reckoned by the Chinese sage, +Confucius, no less than thirty-one have been proved true by modern +astronomers. + +We can not name with certainty those people whose shepherds first gazed +with intelligent eyes upon the midnight sky, and noted the steady sweep +of stars across the firmament--intelligent eyes, that is to say, so +far as man then knew how to use his eyes intelligently; so far as man +had begun to note anything in nature, to watch, to compare, and to +conjecture causes. + +In those times, and indeed for long afterwards, men thought much +more about the “influences” of stars upon their own lives, and about +supposed prophecies of the future to be read in the sky, than about the +actual physical condition of the stars themselves, or the causes and +meanings of the various phenomena observed in the heavens. + +The desire to know, for the pure delight of knowing, had perhaps hardly +begun to dawn upon the mind of man. What people did want to know was +what might be going to happen to themselves; whether _they_ would be +happy or unhappy; and the stars were chiefly of interest as appearing +to tell beforehand of troubles or joys to come. + +The wisest of men in those times knew less of the outspread heavens +than many a child now knows in our public schools. Earth and sky were +one vast bewildering puzzle. They had to discover everything for +themselves--how the sun rose each morning and set each evening; how the +seasons changed in steady sequence through the year; how the moon and +stars journeyed in the night; how the ocean-tides went and came; how +numberless every-day phenomena took place. + +In olden days the daily rising and setting of the sun was a mystery, +accounted for by divers theories, none of which were right; and the +march of stars across the midnight sky was a complete puzzle; and an +eclipse of sun or moon was a fearful perplexity; and the tides of +ocean were a great bewilderment. These things are mysteries still to +barbarous nations; but they perplex us no longer, because we have found +out the mode in which such movements, or appearances of movement, are +brought about through the action of quite natural causes. + +As a first step, in earliest times, the journey of the sun by day, +the journeys of moon and stars by night, across the sky, could hardly +fail to arrest attention. Very early, too, the stars were grouped into +constellations, definite figures and names being attached to each. Many +of the constellations are now known to us by names which belong to the +earliest historic ages. + +The stars were known as “fixed,” because they continued unchangeably in +their relative positions--that is, in the position held by each star +with respect to its neighbor stars--although the whole array of them +moved nightly in company; constellations rising and setting at night, +as the sun rose and set in the day. + +Ages may well have passed before the planets were recognized as +distinct from the fixed stars; ages more before any definite plan +was noted in their wanderings. In the course of time men’s attention +was directed to these matters; and one fact after another, of daily +or monthly or yearly occurrence, was observed, and commented upon, +and became familiar to the minds of people. Very slowly the first +beginnings of systematized knowledge took shape and grew, one discovery +being made after another, one explanation being offered after another, +one theory being started after another. + +But an essential difference existed between the infantine science of +those primitive days and the matured astronomy of these later days. +The whole ancient science was built upon a huge mistake. Men held, +as a fact of absolutely unquestionable certainty, that this earth +of ours--this small whirling globe, less than eight thousand miles +in diameter--was the center, around which sun, moon, and stars all +revolved. + +The Greek philosopher Thales, who lived about six hundred years before +Christ, is said to have laid the foundations of the Grecian astronomy; +and Pythagoras is stated to have been one of his disciples. Though, in +many respects, Thales wandered wide of the truth, he yet taught many +correct ideas; as, for instance, that the stars were made of fire; that +the moon had all her light from the sun; that the earth was a sphere +in shape, besides other facts respecting the earth’s zones and the +sun’s apparent path in the sky. He was also one of the three ancient +astronomers who were able to calculate and foretell eclipses. + +After him came numerous astronomers, of greater or less merit, in the +Grecian and in other schools. They watched carefully; they discovered +many things of interest; they held divers theories. But one truth never +took firm root among them, although several of them dimly apprehended +it; and this was the very foundation-truth, for lack of which they were +all going hopelessly astray--the simple truth that our earth is _not_ +the center of the universe, and that our earth _does_ move. Yet it is +not surprising. No wonder they were slow to grasp such a possibility. + +Anything more bewildering to the mind of ancient man than the thought +of a solid, substantial world floating in empty space, supported upon +nothing, upheld by nothing, can hardly be imagined. As yet little was +known of the controlling laws or forces of nature, and that little was +with reference only to our earth. The very suspicion of gravitation +as a universal law lay in the far-distant future, waiting for the +intellect of a Newton to call it out of apparent chaos; and the +delicate balance of forces, by means of which the Solar System may +almost be said to exist, could not be so much as guessed at. + +So men still clung to the thought of earth as the center of all things, +and still believed in a little sun, busily circling round her once in +every twenty-four hours. + +Perhaps the greatest of all ancient astronomers was Hipparchus, about +150 B. C., who did more than any other in those early times to gather +together the scattered facts of astronomy, and to arrange them into +one united and orderly whole. He it was who discovered the precession +of the equinoxes. He studied eclipses and the motions of the various +planets. He made elaborate and valuable astronomical tables and +star-catalogues; but he, like others, failed to discover the gigantic +error which lay at the root of the whole ancient science. + +Despite this great mistake, still persistently believed in, and despite +the crude notions of early astronomers on many points, it is marvelous +how much they did manage to observe and to learn for themselves,--as +to the sun and his apparent path, as to the moon and her path, as to +the five then known planets and their paths, as to eclipses and other +phenomena. + +By all such careful watching, although they to some extent missed their +aim and fell into mistakes, yet they paved a way to later discoveries +and to fuller knowledge. Their work was not thrown away, their trouble +was not lost; for out of their very errors grew the fair form of truth. + +Nearly three hundred years after the time of Hipparchus came the famous +Ptolemy--famous, not, like certain other astronomers, for stupendous +genius, or for the brilliancy and accuracy of his observations, but +rather noted for the ingenuity of his explanations, and for the adroit +manner in which he systematized such knowledge, on the subject of the +heavenly bodies, as was then in the possession of mankind. + +Ptolemy’s name is best known in connection with what is commonly called +“The Ptolemaic System of the Universe,” and his greatest astronomical +work is best known as the _Almagest_. + +A great many of Ptolemy’s leading notions, as well as the principal +mass of facts upon which he worked, were doubtless borrowed from +Hipparchus. The latter is said to have explained the movements of the +sun and of the moon by means of small epicycles, traveling round the +earth on circular orbits; and even Hipparchus did not originate this +fundamental idea of the so-called “Ptolemaic System,” which had indeed +been held by the ancients in much earlier days. Hipparchus worked it +out to some extent, and Ptolemy carried on the process much farther, +giving forth the system to the world in such wise that ever since it +has gone by his name. + +The theory of cycles and epicycles lasted long--lasted from the time +of Ptolemy in the second century to the time of Copernicus in the +sixteenth century, of whom we have already spoken. + +[For about two thousand years, astronomers observed attentively the +apparent revolutions of the heavenly bodies, and this attentive study +gradually showed them a large number of irregularities and inexplicable +complications, until at last they recognized that they were deceived as +to the earth’s position, in the same way that they had been deceived +as to its stability. The immortal Copernicus, in particular, discussed +with perseverance the earth’s motion, already previously suspected for +two thousand years, but always rejected by man’s self-love; and when +this learned Polish canon bid adieu to our world in the year 1543, he +bequeathed to science his great work, which demonstrated clearly the +long-standing error of mankind.--_F._] + +The new theory of Copernicus had to make its way slowly against +the dead weight of unreasoning public opinion, and against +wrongly-reasoning hierarchical opposition. In time, gradually, despite +all resistance, the truth made its way, and was generally received, +though not till Galileo had been forced by ecclesiastical authority to +recant his opinions. All the same, Copernicus, Kepler, Galileo, were +right; public sentiment and the Church were wrong,--the earth did move, +and was not the fixed universe center, and, by and by, those who lived +on earth had to acknowledge the same. + +The succession of these great men is interesting to note. Between the +two shining lights, Hipparchus and Ptolemy, nearly three hundred years +intervened. But as the history of the world advances, we find brilliant +scientific minds appearing more quickly, one following close upon +another, instead of their being divided by long intervals of blankness. + +Within thirty years from the death of Copernicus, were born two mighty +men of Science: Kepler, who lived till 1630; and Galileo, who lived +till 1642, when England was plunged in civil strife. + +Between Copernicus and Kepler came Tycho Brahe. Copernicus was a +Roman ecclesiastic, born in Poland. Tycho Brahe was a wealthy Danish +nobleman, an ardent lover of astronomy, and a most patient and accurate +observer. But Tycho held fast by the old astronomy. He was not +convinced by the arguments of Copernicus. To him, earth was still the +motionless center of all things. He was willing to allow that the rest +of the planets circled round the sun, as an explanation of things which +he could not help seeing; but the sun itself had still, in Tycho’s +imagination, to revolve daily, with planets and stars and the whole +sky, round our earth. + +As an explainer of causes, therefore, Tycho rose to no lofty heights. +The real good which he did was in watching and noting actual phenomena, +not in trying to explain how those phenomena were brought about. This +was left for one of his young pupils, a sickly German lad, named John +Kepler. + +In later years, Kepler made a grand use of his master’s mass of careful +and thoroughly dependable observations. These had really been gathered +together by Tycho, with a view of disproving the Copernican theory, and +of establishing the main features of the olden astronomy, with certain +improvements. But Kepler used the accumulated information to disprove +the old astronomy, and to establish the truth of the new Copernican +system which Tycho had rejected. He found a vast advantage, ready to +his hand, in the collection of careful observations systematically +worked out by Tycho in his observatory during many a long year. And +Kepler did not fail to use his advantage. + +The planets still refused, as they always had refused, to keep to the +paths marked out for them by astronomers. Kepler grappled with the +difficulty. He particularly turned his attention to Mars, that near +neighbor of ours, in which we are all now so much interested. A long +series of close observations of Mars’s movements, made by Tycho in the +course of many years, lay before him; and he knew that he could depend +upon the absolute honesty and accuracy of Tycho’s work. + +With immense labor and immense patience, he went into the matter, still +clinging to the old idea of a circular pathway round the sun. He tried +things this way and that way. He placed his orbit in imagination after +one mode and another mode; he conjectured various arrangements; he +tested and proved them in turn, comparing each plan with observations +made,--and still Mars defied all his efforts; still the little world +went persistently wrong, traveling contrary to every theory. + +Thus far, nobody had ever thought of an orbit of any other shape than +a circle. When a straightforward journey round a circle was found +impossible, then epicycles were introduced to explain the planet’s +perplexing motions. No one had dreamt of an elliptic pathway. But +suddenly a gleam of daylight came upon this groping in the dark. What +if Mars traveled round the sun--_not_ in a circle, but in an oval? + +Kepler tried this oval and that oval, comparing observations +past--testing, examining, proving or disproving, with unwearied +patience. And at length he found, beyond dispute, that Mars actually +did travel round the sun in a yearly pathway, which was shaped, not as +a circle, but as the kind of oval known as an _ellipse_; and, further, +that the sun was not in the exact center of this ellipse, but to one +side of the center, in one of the foci. Kepler’s success in detecting +the true shape of a planetary orbit is doubtless owing to the fact +that the orbit of Mars makes a wider departure from the circular form +than any of the other important planets. + +One step further would have led Kepler to the knowledge that comets +also travel in elliptic orbits--only in very long and narrow ones +generally. But he had quite made up his mind that all comets merely +paid our sun one visit, and never by any chance returned; so he did not +trouble himself to enter into calculations with respect to them. This +taking for granted of ideas long held was a very common practice in +those days. + +The above wonderful discovery of elliptic orbits, in place of +circular orbits, was only one among many made by the illustrious +Kepler--discoveries not carelessly hit upon, as one might pick up in +the street a valuable stone which somebody had dropped, but earnestly +sought for, and found with toil and diligence, as gems are first +found in foreign lands, after much seeking and long patience. Casual +discoveries in science are rare. Attainment is far more usually made +through intense study, through hard work, through profound thought, +through a gradual groping upward out of darkness to the point where +daylight breaks forth. + +The three well-known “Laws of Kepler” still lie at the very foundation +of the modern system of astronomy. They are: First, every planet moves +in an elliptical orbit, in one focus of which the sun is situated; +second, the line drawn from the sun to a planet moves over equal areas +in equal times; and, third, the square of the periodic times of the +planets varies inversely as the cubes of their distances. + + + + +CHAPTER XXXIII. + +MODERN ASTRONOMY. + + +Still, however, the world was not convinced of the truth of the +Copernican system. One man here or there saw and acknowledged its +reality. The mass of mankind continued firmly to believe that they +dwelt at the universe center, and utterly to scout the idea of a moving +earth. Indeed, it may be very much doubted whether, not merely the +mass of mankind, but even the most civilized and cultivated portion of +that mass, had as yet, to any wide extent, heard a whisper of the new +theories. Knowledge, in those days, traveled from place to place with +exceeding deliberation. + +Another great man arose, contemporary with Kepler--a man whose story +seizes more strongly upon our imagination than that of the severe and +successful studies of Kepler. From an ordinary worldly point of view, +Kepler would hardly be looked upon as altogether a successful man. He +was poor, and in sickly health. His chief book was promptly prohibited +by Rome--then a power in the whole reading world of Europe to an extent +which can hardly be realized in these days of freedom. Kepler’s book +was placed in the forbidden category, side by side with the dying +publication of Copernicus. This checked all hope of literary gains, and +life with Kepler was one long struggle. But if he could have looked +ahead two or three hundred years; if he could have foreseen the time +when not a few wise men of science alone, but all the civilized world, +including the very Church which condemned him, should meekly have +accepted and indorsed his discoveries,--then he would have been able to +gauge the measure of his own real success. + +Moreover, with all his troubles, Kepler was so happy as to escape +absolute persecution. He lived in a country which knew something of +liberty as an ideal; he was left to write and work freely; and, at +least, no public recantation of what he held to be truth was forced +from him. + +Galileo’s was a sadder tale. A Florentine of noble birth, he turned his +attention early to science as the needle turns to the north, and before +the age of twenty-seven he already occupied a foremost position as +mathematical lecturer at Pisa. There it was that he direfully offended +the philosophers of the day by proving Aristotle to be in the wrong. +For Aristotle was the great master of the schoolmen. His philosophy +and theories were accepted as final, and whatsoever could not be +proved in accordance with them was regarded as untrue. Aristotle had +declared that if two weights--the one being ten times as heavy as the +other--were dropped together from a height, the heavier weight would +reach the ground ten times as quickly as the lighter. + +Everybody believed this, and nobody had ever thought of putting it to +the test of actual trial. Aristotle had said so, and Aristotle was +indorsed as a whole by all the schools of Europe; and what more could +possibly be wanted by any reasonable human being? But Galileo was not +so easily satisfied. He looked into the matter independently, bent upon +finding out, not what Aristotle had thought or what the Church might +support, but simply what actually _was_. + +[Illustration: PROMINENT ASTRONOMERS OF THE NINETEENTH CENTURY.] + +Then, in view of many observers, called together for the occasion, he +dropped, at the same instant, from the top of the leaning tower of +Pisa, a shot weighing one pound and another shot weighing a hundred +pounds. And, behold! both reached the ground simultaneously. There was +not a fraction of difference between the two. To prove Aristotle wrong +was to prove everybody wrong, the authorities of the Church included. +Men calmly declined to believe their own eyes, and Galileo was in very +evil odor. + +From falling bodies he went on to subjects of yet wider interest to +people in general. He read about and eagerly embraced the Copernican +system. Not only did he accept it himself, but he vigorously set +to work to teach and convince others also. This, as might only be +expected, aroused vehement opposition. But Galileo was still in the +heyday of his powers, and he was not to be easily silenced. In those +days he could afford to press onward in the teeth of resistance, and to +laugh at men who would not listen. + +When at Venice, a report reached him of a certain optician in Holland +who had happened to hit upon a curious “combination of lenses,” through +which objects afar off could be actually seen as if they were near. +Galileo promptly seized upon the notion, and within twenty-four hours +he had rigged up a small, rough telescope out of an old organ-pipe and +two spectacle-glasses. + +Thus the first telescope was made--a very elementary affair, formed of +two lenses, convex and concave, and capable of magnifying some three +times--a mere child’s toy compared with telescopes of the present day, +but of exceeding value and interest, because it was the very first; +because in all the history of the world no telescope had ever been +manufactured before. + +This earliest effort was speedily improved upon. The next trial +produced a tube which could magnify seven or eight times; and in a +little while, Galileo had a telescope magnifying as much as thirty-two +times. Even thirty-two times does not sound very startling to us; but +in those days the revelations of such an instrument came upon men like +a thunderclap. + +Through it could be seen clearly the broken nature of the moon’s +surface--the craters, the shadows, the mountains. Through it could be +seen the phases of Venus, which no man had ever yet detected, but which +Copernicus had declared must certainly exist, if indeed his system +were a reality. Through it could be seen four of the moons of Jupiter, +and their ceaseless journeyings. Through it could be seen spots upon +the face of the sun, the movements of which showed the rotation of the +sun upon his axis. Through it could be seen the very curious shape of +Saturn, caused by his rings, though a much stronger power was needed to +separate the rings from the body of the planet. + +Of all these discoveries, and many others also made by Galileo, none +seemed worse to the bigoted schoolmen of his day than the preposterous +notion of black spots upon the sun’s face. + +Rather curiously, no human being seems ever before then to have noticed +such spots, though often they are quite large enough to be detected by +the naked eye. A general belief had been held that the sun was and must +be perfect--an absolutely spotless and unblemished being, the purest +symbol of celestial incorruptibility--and the said discovery went right +in the teeth of deductions drawn from, and lessons founded upon, this +belief. Therefore the schoolmen held out and determinedly resisted, and +would have nought to do with Galileo or his telescopes, shutting their +eyes to marvels newly revealed. + +But Kepler was a true scientist, a man who earnestly pursued truth, +and sought to discover it at any hazard. He and Galileo were +contemporaries, and they held communication on these subjects. Some +of Galileo’s discoveries went quite as much in the teeth of some of +Kepler’s most dearly-loved theories as they did in the teeth of the +schoolmen’s most dearly-loved doctrines. Yet, none the less, Kepler +welcomed them with great delight and eagerness, showing thereby his +true greatness of character. + +Till after the age of fifty, Galileo was allowed to go on undisturbed, +or at least not materially disturbed, by opposition in his career of +success--observing, learning, theorizing, calculating, explaining, +teaching--a prominent figure indeed. Not only did he take a large share +in establishing firmly the Copernican system of astronomy, but some of +the principal laws of motion were discovered by him. He first found +the uses of a pendulum, and there is strong reason for believing that +the first microscope, as well as the first telescope, was from his +hands. + +But after the age of fifty, reverses came, and one blow succeeded +another. Rome had been gradually waking up to the true sense of all +that was implied by his discoveries and his teaching, and at length she +let loose her thunders--impotent thunders enough, so far as regarded +any permanent checking of the progress of truth, but by no means +impotent to crush one defenseless victim, the champion of scientific +truth in that country and age. + +Years of greater or less opposition, amounting often to persecution, +were followed by an imperious order commanding him to Rome. There he +was examined and severely “questioned,” and recantation was forced from +him, worth as much as such forced recantations commonly are worth. + +Even then he did not cease from the work that he loved; even in prison +he carried it on; even when he might not write, nothing could stop him +from thinking. But his health was broken; his liberty was taken away; +illness followed illness; his favorite daughter died; his eyesight +gradually failed; the last book that he wrote might not for a long +while be printed; and at last he passed away, mercifully set free from +those who, in an essentially bigoted and intolerant age, were incapable +of appreciating his greatness. + +They would fain _then_ have denied him even a respectable grave. Now, +all the civilized world unites to honor the name of Galileo. + + + + +CHAPTER XXXIII. + +ISAAC NEWTON. + + +Even the great fame of Galileo must be relegated to a second place in +comparison with that of the philosopher who first saw the light in a +Lincolnshire farmhouse on the 25th of December, 1642, the very same +year of Galileo’s death. His father, Isaac Newton, had died before his +birth. The little Isaac was at first so frail and weakly that his life +was despaired of. The watchful mother, however, tended her delicate +child with such success that he ultimately acquired a frame strong +enough to outlast the ordinary span of human life. + +In due time the boy was sent to the public school at Grantham. That +he might be near his work, he was boarded at the house of Mr. Clark, +an apothecary. He had at first a very low place in the class. His +first incentive to diligent study seems to have been derived from the +circumstance that he was severely kicked by one of the boys above +him in the class. This indignity had the effect of stimulating young +Newton’s activity to such an extent that he not only attained the +desired object of passing over the head of the boy who had maltreated +him, but continued to rise until he became the head of the school. + +The play-hours of the great philosopher were devoted to pursuits very +different from those of most schoolboys. His chief amusement was +found in making mechanical toys, and various ingenious contrivances. +He watched, day by day, with great interest, the workmen engaged in +constructing a windmill in the neighborhood of the school, the result, +of which was that the boy made a working model of the windmill and of +its machinery, which seems to have been much admired as indicating his +aptitude for mechanics. We are told that he also indulged in somewhat +higher flights of mechanical enterprise. The first philosophical +instrument he made was a clock, which was actuated by water. He also +devoted much attention to the construction of paper kites, and his +skill in this respect was highly appreciated by his schoolfellows. Like +a true philosopher, even at this stage, he experimented on the best +methods of attaching the string, and on the proportions which the tail +ought to have. + +When the schoolboy at Grantham was fourteen years of age, it was +thought necessary to recall him from the school. His recently-born +industry had been such that he had already made good progress in his +studies, and his mother hoped that he would now lay aside his books, +and those silent meditations to which, even at this early age, he had +become addicted. It was hoped that instead of such pursuits, which were +deemed quite useless, the boy would enter busily into the duties of +the farm and the details of a country life. But before long it became +manifest that the study of nature and the pursuit of knowledge had such +a fascination for the youth that he could give little attention to +aught else. It was plain that he would make but an indifferent farmer. +He greatly preferred experimenting on water-wheels, and working at +mathematics in the shadow of a hedge. + +Fortunately for humanity, his mother, like a wise woman, determined +to let her boy’s genius have the scope which it required. He was +accordingly sent back to Grantham school, with the object of being +trained in the knowledge which would fit him for entering the +University of Cambridge. + +It was the 5th of June, 1660, when Isaac Newton, a youth of eighteen, +was enrolled as an undergraduate of Trinity College, Cambridge. Little +did those who sent him there dream that this boy was destined to be the +most illustrious student who ever entered the portals of that great +seat of learning. Little could the youth himself have foreseen that the +rooms near the gateway which he occupied would acquire a celebrity from +the fact that he dwelt in them, or that the antechapel of his college +was in good time to be adorned by that noble statue of himself which +is regarded as the chief art treasure of Cambridge University, both +on account of its intrinsic beauty and the fact that it commemorates +the fame of her most distinguished alumnus, Isaac Newton, the immortal +astronomer. His advent at the university seemed to have been by +no means auspicious or brilliant. His birth was, as we have seen, +comparatively obscure, and though he had already given indication of +his capacity for reflecting on philosophical matters, yet he seems to +have been but ill-equipped with the routine knowledge which youths are +generally expected to take with them to the universities. + +From the outset of his college career, Newton’s attention seems to have +been mainly directed to mathematics. Here he began to give evidence of +that marvelous insight into the deep secrets of nature which, more than +a century later, led so dispassionate a judge as Laplace to pronounce +Newton’s immortal work as pre-eminent above all the productions of +the human intellect. But though Newton was one of the very greatest +mathematicians that ever lived, he was never a mathematician for the +mere sake of mathematics. He employed his mathematics as an instrument +for discovering the laws of nature. + +His industry and genius soon brought him under the notice of the +university authorities. It is stated in the university records that +he obtained a scholarship in 1664. Two years later we find that +Newton, as well as many residents in the university, had to leave +Cambridge temporarily on account of the breaking out of the plague. The +philosopher retired for a season to his old home at Woolsthorpe, and +there he remained until he was appointed a Fellow of Trinity College, +Cambridge, in 1667. From this time onwards, Newton’s reputation as a +mathematician and as a natural philosopher steadily advanced, so that +in 1669, while still but twenty-seven years of age, he was appointed to +the distinguished position of professor of Mathematics at Cambridge. +Here he found the opportunity to continue and develop that marvelous +career of discovery which formed his life’s work. + +The earliest of Newton’s great achievements in natural philosophy was +his detection of the composite character of light. That a beam of +ordinary sunlight is, in fact, a mixture of a very great number of +different colored lights, is a doctrine now familiar to every one who +has the slightest education in physical science. We must, however, +remember that this discovery was really a tremendous advance in +knowledge at the time when Newton announced it. + +[Illustration: SIR ISAAC NEWTON.] + +A certain story is often told about Newton. It is said that as he +sat in a garden an apple fell from a tree, and that its fall set him +thinking, and that, in consequence of this train of thought, he found +out all about the law of attraction or gravitation. + +But the fall of an apple could not possibly have set Newton thinking, +because he had already been thinking long and hard upon these +difficult questions. Indeed, it was _because_ he had been so thinking, +_because_ his mind was in a watchful and receptive condition, that so +slight a matter as a falling apple should, perhaps, have suggested to +him a useful train of ideas. + +Newton was a man who really did think, and who really did think +intensely. He was not, like the ordinary run of people, one who merely +had a good many notions walking loosely through his brain. He would +bend his mind to a subject and be absolutely absorbed in it; later in +life so absorbed that he would forget to finish his dressing, and would +be unable to say whether or no he had dined. This sort of forgetfulness +does sometimes spring from vacancy of mind; but with Newton it arose +from fullness of thought. + +An apple falls, of course, as a stone or any other body falls, because +the earth attracts it. Otherwise, it might as easily rise and float +away into the sky. But this was known perfectly well long before +Newton’s days. It was clearly understood that the earth had a curious +power of drawing all things towards herself. People could not explain +why or how it was so; neither can we explain now; but they were fully +aware of the fact. + +So men knew something of the force called gravity; but they knew it +mainly, almost exclusively, as having to do with our earth, and with +the things upon our earth. They had not begun definitely to think of +gravity as having to do with bodies in the heavens; as being a chief +controlling force in the whole Solar System; much less as reigning +throughout the vast universe of stars. It had not come into their +minds with any distinctness that, just as the earth pulls towards her +own center a mountain, a horse, a man, so the sun pulls toward his +center the earth, the moon, and all the planets. + +Certain glimmerings of the notion had, indeed, begun to dawn on the +horizon of learning. Horrocks, Borelli, Robert Hook, Wren, Halley, and +others had _glimpses_ of universal gravitation; but only glimpses. A +gifted English philosopher, late in the sixteenth century, Gilbert +by name, went so far as to speak of earth and moon acting one upon +the other “like two magnets.” He also saw the effect of the moon’s +attraction in bringing about ocean tides, though he oddly explained +that the said attraction was not so much exerted upon ocean waters as +upon “subterranean spirits and humors”--whatever he may have meant by +such an expression. + +Kepler, not long after Gilbert, made further advance. He gained some +definite notions as to the nature of gravity; and he saw distinctly +that the moon’s attraction was the main cause of the tides. The +following remarkable statement is found in his writings: “If the earth +ceased to attract its waters, the whole sea would mount up and unite +itself with the moon. The sphere of the attracting force of the moon +extends even to the earth, and draws the waters towards the torrid +zone, so that they rise to the point which has the moon in the zenith.” +Here is a distinct enough grasp of the fact that gravity can and does +act through distance, between worlds separated by thousands of miles. + +Yet, though both Gilbert and Kepler saw so much, they failed to go +farther. Neither of the two had any clear knowledge of the modes in +which gravitation acts, or of the laws which govern its working. +Gilbert and Kepler alike, while dimly recognizing, not only the moon’s +attraction for earth’s oceans, but the mutual attraction of earth and +moon each for the other, were utterly perplexed as to what force could +possibly hold the two bodies asunder. Gilbert could seriously talk of +“subterranean spirits and humors.” Kepler could soberly write of an +“animal force” or some tantamount power in the moon, which prevented +her nearer approach to earth. + +Galileo was equally vague on the subject. With all his brilliant gifts, +and while acknowledging the earth’s attractive power over the moon, he +would not even admit the existence of _mutual_ attraction, and talked +of the moon as being compelled to “follow the earth.” Unquestionably +there are times when the moon does follow the earth, and that is when +the earth happens to go before. But quite as often it happens that the +moon goes before, and the earth follows after. + +All these great men were groping near the truth, yet none managed to +find the clue that was wanted. They left the unfinished process of +thought to be carried on by the master-mind of Newton. And Newton set +himself to think the question out. He used Kepler’s observations. +He sought to penetrate the secrets of a Solar System in mysterious +and inviolable order. Some reason or cause for that order he knew +must exist--if only it might be grasped! He pondered deeply; lost in +profound cogitation, through stormy days of civil strife, of plague and +loss and suffering. The object of his life was to discover, if so he +might, what power or what forces retained the different worlds in their +respective pathways; in short, what manner of celestial guidance was +vouchsafed to the planets. + +For although men had now learned the shape of the planet-orbits, and +even knew certain laws which helped to govern the planet-motions, they +had not discovered one supreme controlling law. They did not dream of +gravity in the heavens as a prevailing force. There was absolutely no +reason, with which men were acquainted, why each planet should preserve +its own particular distance from the sun; why Mars should not wander +as far away as Jupiter; why Mercury should not flee to the position of +Saturn; why our own earth should be always about as near as she always +is. + +The resources of Newton’s genius seemed equal to almost any demand +that could be made upon it. He saw that each planet must disturb the +other, and in that way he was able to render a satisfactory account of +certain phenomena which had perplexed all preceding investigators. That +mysterious movement by which the pole of the earth sways about among +the stars, had been long an unsolved enigma; but Newton showed that the +moon grasped with its attraction the protuberant mass at the equatorial +regions of the earth, and thus tilted the earth’s axis in a way that +accounted for the phenomenon which had been known, but had never been +explained, for two thousand years. All these discoveries were brought +together in that immortal work, Newton’s “Principia,” the greatest work +on science that the world had yet seen. + +It may well be that, as Newton pondered this perplexing question +while seated in the garden, an apple dropping to the ground might +have sufficed to turn his wide-awake and ready mind in the direction +of that familiar force, gravity, which draws all loose bodies towards +earth’s surface. The apple fell because of gravity. Quite naturally the +question might have arisen in Newton’s mind--“Why not this same gravity +in the heavens also? If the earth draws an apple towards herself, why +should not the earth draw the moon? Why should not the sun draw the +earth? Nay, more, why should not the sun draw all the planets?” Newton +set himself to work out this problem, allowing for the distance of the +moon from earth, and for the bulk and weight of both earth and moon. + +And because the answer was _not_ precisely what he had looked for, +he put the calculation aside, and waited for years. It seems that he +mentioned his conjecture to no living person. After many years he took +it up again, and worked it out afresh. By this time new measurements of +earth’s surface, and new calculations of earth’s size had been made, +and Newton had fresh figures to go upon. This time the answer came +just as he had originally hoped, and the truth of his surmise was thus +proved. + +Gravity held the moon near the earth, preventing her from wandering +off into unknown distances. Gravity held earth and moon, Mars, Venus, +Jupiter, each planet, in its own pathway, within a certain distance of +the sun. Gravity held many of the comets as permanent members of the +Solar System. So strong, indeed, was the drawing of gravity found to +be, that only the resisting force of each bright world’s rapid rush +round the sun could keep the sun and his planets apart. + +Newton had discovered the long-sought secret. He had found that “every +particle of matter in the universe attracts every other particle?” +He had found also the main laws which govern the working of that +attraction--that it depends, first, upon the mass or amount of “matter” +in each body; that it depends, secondly, upon the distance of one body +from another. He found, too, how far attraction increases with greater +nearness, and decreases with greater distance. All these and countless +other questions he worked out in the course of years. But first he had +grasped the great leading principle, after which men had until then +groped in vain, that by the force of gravity the sun and his worlds +and their moons are all bound together into one large united family or +system. + +Though Newton lived long enough to receive the honor that his +astonishing discoveries so justly merited, and though for many years +of his life his renown was much greater than that of any of his +contemporaries, yet it is not too much to say that, in the years which +have since elapsed, Newton’s fame has been ever steadily advancing. + +We hardly know whether to admire more the sublime discoveries at +which he arrived, or the extraordinary character of the intellectual +processes by which those discoveries were reached. He died on Monday, +March 20, 1727, in the eighty-fifth year of his age. + + + + +CHAPTER XXXV. + +LATER ASTRONOMY. + + +Sir William Herschel was born in the city of Hanover, November 15, +1738. He was the second son of Isaac Herschel, a musician, who brought +him up, with his four other sons, to his own profession. + +A faithful chronicler has given us an interesting account of the way in +which Isaac Herschel educated his boys; the narrative is taken from the +recollections of one who, at the time, was a little girl of five or six +years old. She writes: + +“My brothers were often introduced as solo performers and assistants +in the orchestra at the court, and I remember that I was frequently +prevented from going to sleep by the lively criticisms on music +on coming from a concert. Often I would keep myself awake that I +might listen to their animated remarks, for it made me happy to see +them so happy. But generally their conversation would branch out on +philosophical subjects, when my brother William and my father often +argued with such warmth that my mother’s interference became necessary +when the names Euler, Leibnitz, and Newton sounded rather too loud for +the repose of her little ones, who had to be at school by seven in the +morning.” + +The child, whose reminiscences are here given, became afterwards +the famous Caroline Herschel. The narrative of her life is a most +interesting book, not only for the account it contains of the +remarkable woman herself, but also because it presents the best picture +we have of the great astronomer, to whom Caroline devoted her life. + +This modest family circle was, in a measure, dispersed at the outbreak +of the Seven Years’ War in 1756. The French proceeded to invade +Hanover, which, it will be remembered, belonged at this time to +the British dominions. Young William Herschel had already obtained +the position of a regular performer in the regimental band of the +Hanoverian Guards, and it was his fortune to obtain some experience +of actual warfare in the disastrous battle of Hastenbeck. He was not +wounded, but he had to spend the night after the battle in a ditch, and +his meditations on the occasion convinced him that soldiering was not +the profession exactly suited to his tastes. He left his regiment by +the very simple, but somewhat risky, process of desertion. He had, it +would seem, to adopt disguises in order to effect his escape. By some +means he succeeded in eluding detection, and reached England in safety. + +The young musician must have had some difficulty in providing for his +maintenance during the first few years of his abode in England. + +It was not until he had reached the age of twenty-two that he succeeded +in obtaining any regular appointment. He was then made instructor of +music to the Durham Militia. Shortly afterwards, his talents being more +widely recognized, he was appointed as organist of the parish Church at +Halifax. + +In 1766 we find that Herschel had received the further promotion of +organist in the Octagon Chapel, at Bath. Bath was then, as now, a +highly fashionable resort, and many notable personages patronized the +rising musician. Herschel had other points in his favor besides his +professional skill; his appearance was striking, his address superb, +and his conversation animated, interesting, and instructive; and +even his nationality was a distinct advantage, inasmuch as he was a +Hanoverian in the reign of King George the Third. From his earliest +youth, Herschel had been endowed with that invaluable characteristic, +an intense desire for knowledge. He naturally wished to perfect himself +in the theory of music, and thus he was led to study mathematics. When +he had once tasted the charms of mathematics, he saw vast regions of +knowledge unfolded before him, and in this way he was induced to direct +his attention to astronomy. More and more this pursuit engrossed his +attention until, at last, it had become an absorbing passion. + +It was with quite a small telescope, which had been lent him by a +friend, that Herschel commenced his career as an observer. However, he +speedily discovered that to see all he wanted to see, a telescope of +far greater power would be necessary. + +He commissioned a friend to procure for him in London a telescope with +high magnifying power. Fortunately for science the price was so great +that it precluded the purchase, and he set himself at work to construct +one. After many trials he succeeded in making a reflecting instrument +of five feet focal length, with which he was able to observe the rings +of Saturn and the satellites of Jupiter. + +It was in 1774, when the astronomer was thirty-six years old, that he +obtained his first glimpse of the stars with an instrument of his own +construction. Night after night, as soon as his musical labors were +ended, his telescopes were brought out. + +His sister Caroline, who occupies such a distinct place in scientific +history, the same little girl to whom we have already referred, was +his able assistant, and when mathematical work had to be done, she +was ready for it. She had taught herself sufficiently to enable her +to perform the kind of calculations--not, perhaps, very difficult +ones--that Herschel’s work required; indeed, it is not much to say that +the mighty life-work which this man was enabled to perform could never +have been accomplished had it not been for the self-sacrifice of this +ever-loving and faithful sister. + +It was not until 1782 that the great achievement took place by which +Herschel at once sprang into fame. He appears to have formed a project +for making a close examination of all the stars above a certain +magnitude for the purpose of discovering, if possible, a parallax among +them. Star after star was brought to the center of the field of view of +his telescope, and after being carefully examined, was then displaced, +while another star was brought forward to be submitted to the same +process. + +In the great review which Herschel undertook, he doubtless examined +hundreds, or perhaps thousands of stars, allowing them to pass away +without note or comment. But on an ever-memorable night in March, +1782, it happened that he was pursuing his task among the stars in the +constellation of Gemini. One star was noticed which, to Herschel’s +acute vision, seemed different from the stars which in so many +thousands are strewn over the sky. There was something in the starlike +object that immediately arrested his attention, and made him apply to +it a higher magnifying power. This at once disclosed the fact that the +object possessed a disk--that is, a definite, measurable size--and +that it was thus totally different from any of the hundreds and +thousands of stars which exist elsewhere in space. The organist at the +Octagon Chapel at Bath had discovered a new planet with his home-made +telescope. Great was the astonishment of the scientific world when the +Bath organist announced that the five planets, which had been known +from all antiquity, must now admit the company of a sixth. + +The now great astronomer was invited to Windsor, and to bring his +famous telescope in order to exhibit the planet to George III, and +to tell his majesty all about it. The king took so great a fancy to +Herschel that he proposed to confer on him the title of “his majesty’s +own astronomer,” to assign him a residence near Windsor, to provide him +with a salary, and to furnish such funds as might be required for the +erection of great telescopes, and for the conduct of that mighty scheme +of celestial observation on which Herschel was so eager to enter. + +No single discovery of Herschel’s later years was, however, of the same +momentous description as that which first brought him to fame. There +is no separate collection of his writings, and very scanty accounts of +his life have been published; but he who has written his name among the +stars needs no other testimonial to his fame. Prior to his time the +number of bodies known as belonging to the Solar System was eighteen, +including secondary planets and Halley’s comet. To these he added nine; +namely, Uranus and six satellites, and two satellites of Saturn. + +Though no additional honors could add to his fame, Dr. Herschel, in +1816, received the decoration of the Guelphic Order of Knighthood. +In 1820 he was elected president of the Astronomical Society, and +among their Transactions, the next year, he published an interesting +memoir on the places of one hundred and forty-five double-stars. This +paper was the last which he lived to publish. His health had begun to +decline, and on the 24th of August, 1822, he sank under the infirmities +of age, having completed his eighty-fourth year. He was survived by his +widow, Lady Herschel, an only son, Sir John F. W. Herschel, and his +sister Caroline, who died in 1847, in her ninety-eighth year. + + +LAPLACE. + +The author of “Celestial Mechanics” was born at Beaumont-en-Auge in +1749, just thirteen years later than his renowned friend Lagrange. +His father was a farmer, but appears to have been in a position to +provide a good education for a son who seemed promising. The subject +which first claimed his attention was theology. He was, however, soon +introduced to the study of mathematics, in which he presently became so +proficient that, while he was still no more than eighteen years old, he +obtained employment as a mathematical teacher in his native town. + +Desiring wider opportunities for study, young Laplace started for +Paris, being provided with letters of introduction to D’Alembert, +who then occupied the most prominent positions as a mathematician in +France, if not in Europe. On presenting these letters, he seems to have +had no reply; whereupon, Laplace wrote to D’Alembert, submitting a +discussion of some point in dynamics. + +This letter instantly produced the desired effect. D’Alembert thought +that such mathematical talent as the young man displayed was in itself +the best of introductions to his favor. It could not be overlooked, and +accordingly he invited Laplace to come and see him. Laplace, of course, +presented himself, and erelong D’Alembert obtained for the rising +philosopher a professorship of Mathematics in the military school in +Paris. This gave the brilliant young mathematician the opening for +which he sought, and he quickly availed himself of it. + +Laplace’s most famous work is “Celestial Mechanics,” in which he +essayed a comprehensive attempt to carry out, in much greater detail, +the principles which Newton had laid down. The fact was that Newton +had not only to construct the theory of gravitation, but he had to +invent the mathematical processes by which his theory could be applied +to the explanation of the movements of the heavenly bodies. In the +course of the century which had elapsed between the time of Newton and +the time of Laplace, mathematics had been extensively developed. The +disturbances which one planet exercises upon the rest can only be fully +ascertained by the aid of long calculations, and for these calculations +analytical methods are required. + +With an armament of mathematical methods which had been perfected +since the days of Newton by the labors of two or three generations of +mathematical inventors, Laplace essayed in his “Celestial Mechanics” +to unravel the mysteries of the heavens. It will hardly be disputed +that the book which he has produced is one of the most difficult +books to understand that has ever been written. The investigations of +Laplace are, generally speaking, of too technical a character to make +it possible to set forth any account of them in such a work as the +present. He did, however, publish one treatise, called the “System of +the Universe,” in which, without introducing mathematical symbols, he +was able to give a general account of the theories of the celestial +movements, and of the discoveries to which he and others had been led. +In this work Laplace laid down the principles of the nebular theory, +which, in modern days, has been generally accepted. + +The nebular theory gives a physical account of the origin of the +Solar System, and has already been explained in this volume. Bach +advance in science seems to make it more certain that this hypothesis +substantially represents the way in which our Solar System has grown to +its present form. + +Not satisfied with a career which was merely scientific, Laplace sought +to connect himself with public affairs. Napoleon appreciated his +genius, and desired to enlist him in the service of the state. Laplace +was appointed to the office of minister of the interior. The experiment +was not successful, for he was not by nature a statesman. In despair +of Laplace’s capacity as an administrator, Napoleon declared that he +carried the spirit of his infinitesimal calculus into the management +of business. Indeed, Laplace’s political conduct hardly admits of much +defense. While he accepted the honors which Napoleon showered on him in +the time of his prosperity, he seems to have forgotten all this when +Napoleon could no longer render him service. Laplace was made a marquis +by Louis XVIII. During the latter part of his life the philosopher +lived in a retired country-place at Arcueile. Here he pursued his +studies, and, by strict abstemiousness, preserved himself from many of +the infirmities of old age. + +He was endowed with remarkable scientific sagacity; but above all +his powers his wonderful memory shone pre-eminent. His “Celestial +Mechanics” is, next to Newton’s “Principia,” the greatest of +astronomical works. + +He died on March 5, 1827, in his seventy-eighth year, his last words +being, “What we know is but little, what we do not know is immense.” + + +LEVERRIER. + +We are apt to identify the idea of an astronomer with that of a man +who looks through a telescope at the stars; but the word astronomer +has really a much wider significance. No man who ever lived has been +more entitled to be designated an astronomer than Urbain Jean Joseph +Leverrier, and yet it is certain that he never made a telescopic +discovery of any kind. In mathematics, however, he excelled, and +he simply used the observations of others as the basis of his +calculations. + +These observations form, as it were, the raw material on which the +mathematician exercises his skill. It is for him to elicit from the +observed places the true laws which govern the movements of the +heavenly bodies. Here is indeed a task in which the highest powers of +the human intellect may be worthily employed. To Leverrier it has been +given to provide a superb illustration of the success with which the +mind of man can penetrate the deep things of nature. + +The illustrious Frenchman was born on the 11th of March, 1811, at +Saint-Lô, in the department of Manche. In the famous polytechnic +school for education in the higher branches of science he acquired +considerable fame as a mathematician. His labors at school had revealed +to Leverrier that he was endowed with the powers requisite for dealing +with the subtlest instruments of mathematical analysis. When he was +twenty-eight years old his first great astronomical investigation was +brought forth. This was the profound calculation of the disturbances of +the planet Uranus and the causes of them. + +The talent which his researches displayed brought Leverrier into +notice. At that time the Paris Observatory was presided over by +Arago, a savant who occupies a distinguished position in French +scientific annals. Arago at once perceived that Leverrier possessed the +qualifications suitable for undertaking a problem of great importance +and difficulty that had begun to force itself on the attention of +astronomers. What this great problem was, and how astonishing was the +solution it received, must now be considered. + +Ever since Herschel brought himself into fame by the discovery of +Uranus, the movements of this new addition to the Solar System had been +scrutinized with care and attention. The position of Uranus was thus +accurately determined from time to time. When due allowance was made +for whatever influence the attraction of Jupiter and Saturn and all +the other planets could possibly produce, the movements of Uranus were +still inexplicable. It was perfectly obvious that there must be some +other influence at work besides that which could be attributed to the +planets already known. + +Astronomers could only recognize one solution of such a difficulty. +It was impossible to doubt that there must be some other planet in +addition to the bodies at that time known, and that the perturbations +of Uranus, hitherto unaccounted for, were due to the disturbances +caused by the action of this unknown planet. Arago urged Leverrier +to undertake the great problem of searching for this body. But the +conditions of the search were such that it must be conducted on +principles wholly different from any search which had ever before been +undertaken for a celestial object. For this was not a case in which +mere survey with a telescope might be expected to lead to the discovery. + +There are in the heavens many millions of stars, and the problem of +identifying the planet, if indeed it should lie among these stars, +seemed a very complex matter. Of course, it is the abundant presence of +the stars which causes the difficulty. + +The materials available to the mathematician for the solution of +this problem were to be derived solely from the discrepancies between +the calculated places in which Uranus should be found, taking into +account the known causes of disturbances, and the actual places in +which observation had shown the planet to exist. Here was, indeed, an +unprecedented problem, and one of extraordinary difficulty. Leverrier, +however, faced it, and, to the astonishment of the world, succeeded in +carrying it through to a brilliant solution. + +After many trials, Leverrier ascertained that, by assuming a certain +size, shape, and position for the unknown planet’s orbit, and a certain +value for the mass of the hypothetical body, it would be possible +to account for the observed disturbances of Uranus. Gradually it +became clear to his perception, not only that the difficulties in +the movements of Uranus could be thus explained, but that no other +explanation need be sought for. And now for an episode in this history +which will be celebrated so long as science shall endure. It is nothing +less than the telescopic confirmation of the existence of this new +planet, which had previously been indicated only by mathematical +calculation. + +Great indeed was the admiration of the scientific world at this superb +triumph. Here was a mighty planet, whose very existence was revealed by +the indications afforded by refined mathematical calculation. At once +the name of Leverrier, already known to those conversant with the more +profound branches of astronomy, became everywhere celebrated. + +When, in 1854, Arago’s place had to be filled at the head of the great +Paris Observatory, it was universally felt that the discoverer of +Neptune was the suitable man to assume the office. Leverrier died on +Sunday, September 23, 1877, in his sixty-seventh year. + + * * * * * + +FREDERICK WILLIAM BESSEL was born at Minden in 1784, and early turned +his attention to mathematical subjects. He devoted himself with +ardor to astronomy, and in 1804 he undertook the reduction of the +observations made on the comet of 1607. His results were communicated +to Olbers, who warmly praised the young astronomer, and in 1806 +recommended him to Schroeter as an assistant in the observatory of +Lilienthal. In 1810 he was appointed director of the new observatory +then being founded by the king at Königsberg. He was admirably fitted +for this post, and is distinguished mainly for his discovery of the +parallax of the star 61 Cygni, which he accomplished by methods of +extreme ingenuity and delicacy. + +Two kinds of telescopes are commonly used, the refractor and the +reflector. The first telescopes made were all refractors, and the very +first of them was made, as you know, by Galileo. The first reflector +was made in later days by Sir Isaac Newton. + +In a refractor the rays of light, from a star or any other bright +body, reach first a large object-glass, through which they pass, and +by which, as they pass, they are caused to converge, narrowing to a +focus or point. From this point they widen slightly on their way to the +eye-piece. After passing through the eye-piece, by which they are once +more straightened into parallel rays, they arrive at the eye. + +Speaking broadly, the eye receives--actually sees--nearly as much of +the starlight as if its pupil were the full size of the object-glass +of that telescope, and the power of such an instrument depends upon +the size of the object-glass. A refractor has been made with an +object-glass forty inches across, and this, for the observer, means +looking at a star with an eye pupil more than three feet in diameter. +This refractor is now in the Yerkes Observatory at Williams Bay, Lake +Geneva, Wisconsin. + +There are several forms of reflectors. With one form, when it is +pointed at a star, the rays of starlight fall direct through the +telescope-tube upon a highly-polished mirror, so shaped that rays of +light reflected thence are caused to fall converging upon a small +plane-mirror in the center of the tube, from which they are thrown, +parallel to the side of the tube, to the eye-piece, which converges +them to the eye. + +The mirror of a reflector can be made very much larger than the +object-glass of a refractor. The famous Lord Rosse telescope, which +has a tube sixty feet long, contains a mirror no less than six feet in +diameter. This, to an observer, is tantamount to looking at the stars +with an eye so huge that its pupil alone would be nearly equal in size +to the six-foot wheel of a steam-engine. It will readily be perceived +how much more starlight can be grasped by such a fishing-net than by +the tiny pupil of your eye or mine. + +A main difference between the two kinds of telescope thus resides in +the fact that the star-rays--or any other kind of light-rays--when +first captured, pass, in one case, _through_ the glass on which they +fall, and, in the other case, are thrown off _from_ the mirror. In both +cases, the whole amount of light so captured is gathered into a small +compass, so as to be available for human sight. + +[Illustration: EYE-PIECE OF THE LICK TELESCOPE.] + +Once more, let me remind you, it should be always kept clearly in +mind that every object that is seen by us--from a mote of dust to a +sun, from a coal-scuttle to a star--is perceived purely and solely by +the light which it gives out, either intrinsic or reflected light. +Countless myriads of rays pass from the surface of the thing seen to +our eyes, picturing there, on the sensitive retina, a fleeting vision +of its form. + +All the leading Governments in Europe have observatories for the study +of the heavens, which are furnished with the best instruments of modern +construction. The principal observatories are those at Paris, Berlin, +Vienna, Nice; Dorpat, the seat of a celebrated university founded by +Gustavus Adolphus, of Sweden, in 1630; Pulkowa, near St. Petersburg; +Lisbon, and at Greenwich in England. In America, though only in recent +years has astronomy been cultivated with ardor, there are observatories +of more or less importance,--the National Observatory at Washington, +D. C.; the Cincinnati Observatory, projected by the late General O. M. +Mitchel; the Dudley Observatory, founded by Mrs. Blandina Dudley in +honor of her husband, at Albany, N. Y.; the Lick Observatory, founded +by James Lick, on Mount Hamilton, Cal.; and the Yerkes Observatory, +connected with the Chicago University, founded by Charles T. Yerkes. +Besides these, there are observatories connected with some of our other +leading universities and colleges, as those of Harvard, at Cambridge, +Mass.; Yale University; Williams College; West Point Military Academy; +Amherst College; Princeton; Dartmouth; Michigan University; Hamilton +College, N. Y., and several others. + +[Illustration: LICK OBSERVATORY IN WINTER, FROM THE EAST.] + +The largest and best refracting telescopes in the world are those +at Lick Observatory and at Yerkes Observatory, now in charge +of Professor E. E. Barnard, who, while at the head of the Lick +Observatory, discovered the fifth satellite of Jupiter, and determined +the character of the inner ring of Saturn. The best reflecting +telescope is that of Lord Rosse, at Birr Castle, in Kings County, +Ireland. + +[Illustration: E. E. BARNARD.] + +In reviewing the path which we have traversed in this volume, though we +have penetrated the sidereal depths and wandered at will through space, +we feel that we have not yet reached the outskirts of creation. We +have never left the center. Beyond us still lies the circumference. We +see opened before us the infinite, of which the study is not yet begun! +We have seen nothing; we recoil in terror; we fall back astounded. +Indeed, we might fall into the yawning abyss--fall forever, during a +whole eternity; never, never should we reach the bottom, any more than +we have attained the summit. There is no east nor west, neither right +nor left. There is no up nor down; there is neither a zenith nor a +nadir. In whatever way we look, it is infinite in all directions. + +In this infinitude of space, the associations of suns and of worlds +which constitute our visible universe form but an island, a vast +archipelago; and in the eternity of duration, the life of our proud +humanity, with all its concerns, its aspirations, and its achievements, +the whole life of our entire planet, is but the shadow of a dream! Well +might the Hebrew poet, as he looked forth upon nature, exclaim in his +amazement: “When I consider thy heavens, the work of thy fingers, the +moon and the stars which thou hast ordained, what is man that thou art +mindful of him, and the son of man that thou visitest him?” + +The constellations, the charts of the sky; the catalogues of curious +stars--variable, double or multiple, and colored; the description of +instruments accessible to the observer of the heavens, and useful +tables to consult, are only touched upon in this volume. The reader +whose scientific desires are satisfied by the elements of astronomy, +may stop here. Few have time to pursue the subject further; but it is +sweet to live in the sphere of the mind; it is sweet to contemn the +rough noises of a vulgar world; it is sweet to soar in the ethereal +heights, and to devote the best moments of our life to the study of the +true, the infinite, and the eternal! + + + + +PUBLISHERS’ NOTE. + + +We have now reached the conclusion of “The Story of the Sun, Moon, +and Stars.” Miss Giberne’s work has been supplemented with a large +amount of matter from other sources. The value of the book has thus +been increased without diminishing its popular character. In most +admirable form it tells the story of the heavenly world, which is the +work of God’s hands, the moon and the stars which he has made. The +reverent reader, to whom the Word of God is “sweeter than honey and +the honey-comb,” may here find that “the heavens declare the glory of +God, and the firmament showeth his handiwork.” We confidently present +it to the reader as the best and completest work in print on the great +subject of which it treats. + + + + +INDEX + + + Adams, John Couch, 231, 236 + + Aërolites, 84 + Size of, 86 + + Aldebaran, Movement of, 277 + + Alexander at Arbela, 146 + + Alpha Centauri, Distance of, 99 + Duration of light journey, 102 + Position, 279 + + Alps, Lunar Mountains, 179 + + Altai, Lunar Mountains, 179 + + Andromeda, Constellation of, 112 + + Apennines, Lunar Mountains, 179 + + Arago, 235, 402 + + Arcturus, Motion of, 114 + Position, 276 + + Aristotle, 376 + + Asteroids, 53 + + Astronomy, The dawn of, 363 + + Attraction, 34 + + Aurora Borealis, where seen, 141 + + Axis of earth slanting, 44 + + + Barnard, E. E., 53, 410 + + Bessel, F. W., 284 + Discovery of star parallax, 324 + Discovers star parallax, 405 + + Bolides, 87, 257 + + Borelli, 388 + + + Capella, Duration of light journey, 103 + Velocity of motion, 114 + + Caucasian Range, Lunar Mountains, 179 + + Carpathian, Lunar Mountains, 179 + + Carrington, 141 + + Cassini, Measurement of sun’s distance, 310 + + Cassiopeia, Constellation of, 112 + + Ceres, size of, 53 + + Chaldean star-gazers, 365 + + Chinese records of eclipses, 365 + + Cicero, 177 + + Clark, Alvan Graham, 289 + + Cloven-disk theory, 331 + + Coal sack, 329 + + Columbus in Jamaica, 146 + + Comet, Biela’s, 90, 93 + Halley’s, 78, 248 + Of 1843, 80 + Newton’s, 78 + With two tails, 77 + Encke’s, 78 + Heat endured by, 81 + Length of tail, 81 + Collision with, 82 + Split in two, 91 + + Comets, 73, 240, 246 + Number of, 75 + Nature of, 74 + Captured by Jupiter, 213 + Composition of, 256 + Composition of tails, 253 + Orbits of, 129 + With closed orbits, 76 + + Confucius as an astronomer, 365 + + Constellations, Grouping, 366 + When named, 366 + + Copernicus, Author of “Celestial Spheres,” 177, 183, 370, 371, 375 + Star parallax, 319 + + Copernican system of the universe, 175 + + Corona, Description of, 153 + + + D’Alembert, 399 + + Dante, 121 + + Demos, Satellite of Mars, 191 + + Donati’s Comet, 248, 250 + + Draco, Constellation of, 112 + + + Earth, Globular, 17 + How formed, 21 + Member of the Solar System, 14 + In motion, 16 + Motions, 18, 41, 126 + One of a family, 14 + Size of, 26 + What is it? 13 + + Ecliptic, 43 + + Eclipses omens of evil, 145 + + Egyptian astronomers, 365 + + Encke, 238 + + Epicycles, 373 + + Equinox, 44 + + + Fire-balls, Speed of, 88 + + Fabricius discovers sun-spots, 27 + + Fraunhofer, Joseph von, 345 + + + Galle, 232, 238 + + Galileo, 28, 276, 371, 376, 378, 380 + + Gassendi, 184 + + George III, 226 + + Gilbert, 388 + + Great Bear, Constellation of, 108, 340 + + + Halley, 388 + Transit of Venus, 314 + Star motions, 318 + + Hercules, Constellation of, 112 + + Herschel, Caroline, 226, 393 + + Herschel, Sir John, 81, 233, 303, 398 + + Herschel, William, 96, 119, 225, 271, 393 + + Hipparchus, 368, 371 + + Hodgson, 141 + + Holland, Sir Henry, 237 + + Hook, Robert, 388 + + Horrocks, 388 + + Huggins, Dr., 359 + + Humboldt, Alexander von, 265 + + + Jupiter, 55 + Comparative size, 56 + Distance of, 122 + His satellites, 56, 206, 210 + Velocity, 199 + Wind storms, 204 + + + Kepler, 75, 296 + Laws of, 371, 374, 380, 388 + + Kew Observatory, 141 + + + Lacaille, Catalogue of, 105 + + Lalande, Catalogue of, 105 + + Laplace, 385, 398 + + Later astronomy, 393 + + Leverrier, Urbain J. J., 231, 401 + Discovers Neptune, 321 + + Light, Rapidity of, 101 + Time, Duration of, 331 + + Lowe at Santander, 147 + + Lunar craters, Antiquity of, 172 + How formed, 173 + Plato and Copernicus, 173 + Ptolemy, 174 + Schickard, 174 + Tycho, 174 + + Lunar Mountains, How formed, 174 + + Lyra, Constellation, 297 + + + Magellanic clouds, 309 + + Magnetism, 140, 141 + + Mars, 52, 373, 374 + Moons of, 191 + Continents of, 197 + Distance from earth, 197 + + Maury, Lieutenant, 80 + + Mercury, Atmosphere, 181 + Distance from sun, 49 + Length of year, 180 + Is it inhabited? 181 + Orbit of, 180 + Phases, 50 + Size of, 49 + Transit of, 184 + + Meteor, 84, 257 + + Meteorites, 240, 257 + Around the sun, 94 + August system, 90, 242 + In Saturn’s rings, 94 + November system, 90, 94, 241 + Number of, 86 + Protection from, 86 + Shower of 1872, 92 + Shower of 1885, 93 + + Milky Way, 270, 329 + + Mizar, 342 + + Modern Astronomy, 375 + + Moon, 62 + Appearance at its full, 63 + Atmosphere, 157, 169 + Phases of, 160 + Condition of, 65 + Craters, 68, 170 + Earth’s satellite, 164 + Earth-shine, 160 + Eclipse, 163 + Influence on tides, 167 + Landscape of, 68 + Mountains, 67 + Orbit of, 166 + Temperature on, 72 + Revolution, 64 + Size of, 64 + Surface, 67 + + + Nasmyth, 173 + + Nebulæ, Number of, 336 + + Neptune, 59 + Discovery of, 232, 234 + Distance of, 123 + Length of year, 59 + + Newton analyzes light, 385 + Birth and childhood, 382 + + Nicetos of Syracuse, 177 + + Nicias, Athenian General, 146 + + Nicolas, Cardinal, 177 + + + Observatories, 408 + + Orbits, Planetary, 47 + + Orion, Constellation of, 112 + + + Parallax, 311 + + Phobos, Satellite of Mars, 191 + + Photography, Stellar, 355 + + Pius IX, 93 + + Pisa, Leaning Tower of, 378 + + Plane of the Ecliptic, 201 + + Planets, Distance from the sun, 123 + First group, 48 + How formed, 22 + Length of years, 49 + Orbits, 47 + Order of formation, 23 + Second group, 48,55 + + Plutarch, 177 + + Pole star, Duration of light journey, 103 + Position, 108 + Rate of motion, 115 + + Prism, 344 + + Pritchard, C., 356 + + Ptolemaic system of the universe, 175, 369 + + Ptolemy, 371, 369 + + Pythagoras, Grecian astronomer, 367 + + + Rosse, Lord, Telescope, 406 + + Rowton siderite, 258 + + + Saturn, 57 + Composition of rings, 221 + Distance of, 122 + Distance from sun, 214 + Length of year, 57 + Moons, 217 + Rings, 219 + Satellites, 58 + Size, 214 + Weight, 214 + + Shickard, Crater on the moon, 174 + + Scheiner, 28 + + Secchi, 92 + + Shooting stars, 84 + + Sirius, Brightness of, 275, 285 + Changing color, 285 + Distance of, 100 + Duration of light journey, 103 + Movement of, 277 + + Solar cloud, 148 + + Solar System, 60, 122 + Model of, 60 + + Spectroscope, 143, 345 + + Spectroscopic photography, 360 + + Spectrum analysis, 346, 354 + + Star clusters, 304, 336 + Parallax, 284, 316 + Spectroscopy, 356 + + Stars, Apparent motion, 107 + Attraction, 21 + Distance of, 99, 310, 320 + Distance, 281, 282 + Fixed, Why so called, 20 + Fixed, Why, 366 + Golden, 274 + Magnitude of, 97 + How many visible, 95 + Measurement, 278 + Red, 274 + Variable, 274, 291 + White, 274 + + Sun, 24 + Attraction of, 156 + Attraction of gravitation, 34 + Chromatosphere, 32 + Cyclones of 30, 136 + Density, 26 + Destination, 119 + Distance of, 25 + Eclipse of, 143 + Flames, Their height, 31, 151 + Flames, Their velocity, 138 + Forces and influences, 39 + Head of our family, 24 + Magnetic power of, 139 + Its mottled appearance, 142 + Rate of motion, 119 + Penumbra, 133 + Photosphere, 31, 134 + Power of, 39, 137 + Rapidity of motion, 26 + Revolution on axis, 28 + Size, 26, 154 + Solar prominence, 32 + Spots, 27, 30, 133 + Symbol of purity, 380 + Umbra, 133 + Weight, 27, 154 + + Swift, Voyage to Laputa, 194 + + + Telescopes, 378, 379, 405 + Refractors and reflectors, 405, 408, 410 + + Tides, 168 + + Thales, founder of Grecian Astronomy, 367 + + Toucan, 306 + + Tycho Brahe, 175, 371, 372, 373 + + + Universe, Definition of, 19 + + Uranus, 58 + Discovery of, 225 + Distance of, 123 + + + Venus, Orbit of 51 + Is it inhabited? 189 + Distance from earth, 186 + Phases of, 51, 379 + Transits of, 185 + + Vesta, Size of, 53 + + Voltaire, Prophecy of, 193 + + + Wilson, 30 + + Wollaston, Dr. W. H., 345 + + Wren, 388 + + + Yerkes Observatory, 406 + + Young, Chas. A., 142, 148 + + + Zodiacal Light, 94, 224, 265 + + + + + Transcriber's Notes: + + In the original a link to Sir Isaac Newton was omitted from the + List of Illustrations. The transcriber has inserted one. + + Italics are shown thus: _sloping_. + + Variations in spelling and hyphenation are retained. + + Perceived typographical errors have been changed. + + + +*** END OF THE PROJECT GUTENBERG EBOOK 77004 *** |