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diff --git a/old/64577-0.txt b/old/64577-0.txt deleted file mode 100644 index 017229f..0000000 --- a/old/64577-0.txt +++ /dev/null @@ -1,7747 +0,0 @@ -The Project Gutenberg eBook of The New Astronomy, by Samuel Pierpont -Langley - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: The New Astronomy - -Author: Samuel Pierpont Langley - -Release Date: February 16, 2021 [eBook #64577] - -Language: English - -Character set encoding: UTF-8 - -Produced by: Tim Lindell, Charlie Howard, and the Online Distributed - Proofreading Team at https://www.pgdp.net (This file was - produced from images generously made available by The Internet - Archive/American Libraries.) - -*** START OF THE PROJECT GUTENBERG EBOOK THE NEW ASTRONOMY *** - - - - -THE NEW ASTRONOMY - - - - - THE NEW ASTRONOMY - - - BY - - SAMUEL PIERPONT LANGLEY, PH.D., LL.D. - - DIRECTOR OF THE ALLEGHENY OBSERVATORY, MEMBER NATIONAL ACADEMY, - FELLOW ROYAL ASTRONOMICAL SOCIETY, ETC., ETC. - - - Illustrated - - - [Illustration] - - - BOSTON. - TICKNOR AND COMPANY - 211 Tremont Street - 1888 - - - - - COPYRIGHT, 1884, 1885, 1886, AND 1887, BY THE CENTURY CO.; - AND 1887, BY S. P. LANGLEY. - - _All rights reserved._ - - University Press: - JOHN WILSON AND SON, CAMBRIDGE. - - - - -PREFACE. - - -I have written these pages, not for the professional reader, but with -the hope of reaching a part of that educated public on whose support -he is so often dependent for the means of extending the boundaries of -knowledge. - -It is not generally understood that among us not only the support -of the Government, but with scarcely an exception every new private -benefaction, is devoted to “the Old” Astronomy, which is relatively -munificently endowed already; while that which I have here called “the -New,” so fruitful in results of interest and importance, struggles -almost unaided. - -We are all glad to know that Urania, who was in the beginning but a -poor Chaldean shepherdess, has long since become well-to-do, and dwells -now in state. It is far less known than it should be that she has a -younger sister now among us, bearing every mark of her celestial birth, -but all unendowed and portionless. It is for the reader’s interest in -the latter that this book is a plea. - - - - -CONTENTS. - - - CHAPTER PAGE - - I. SPOTS ON THE SUN 1 - - II. THE SUN’S SURROUNDINGS 35 - - III. THE SUN’S ENERGY 70 - - IV. THE SUN’S ENERGY (_Continued_) 91 - - V. THE PLANETS AND THE MOON 117 - - VI. METEORS 175 - - VII. COMETS 199 - - VIII. THE STARS 221 - - - INDEX 253 - - - - -LIST OF ILLUSTRATIONS. - - - FIGURE PAGE - - 1. THE SUN’S SURROUNDINGS 4 - - 2. VIEW OF THE SUN ON SEPT. 20, 1870 6 - - 3. THE SUN ON SEPT. 22, 1870 6 - - 4. THE SUN ON SEPT. 26, 1870 7 - - 5. THE SUN ON SEPT. 19, 1870 8 - - 6. THE SUN ON SEPT. 20, 1870 8 - - 7. THE SUN ON SEPT. 21, 1870 9 - - 8. THE SUN ON SEPT. 22, 1870 9 - - 9. THE SUN ON SEPT. 23, 1870 10 - - 10. THE SUN ON SEPT. 26, 1870 10 - - 11. NASMYTH’S WILLOW LEAVES 11 - - 12. THE CACTUS TYPE 12 - - 13. EQUATORIAL TELESCOPE AND PROJECTION 13 - - 14. POLARIZING EYE-PIECE 14 - - 15. SPOT OF SEPT. 21, 1870 15 - - 16. SPOT OF MARCH 5, 1873 15 - - 17. SUN ON MARCH 5, 1873 18 - - 18. “THE PLUME” SPOT OF MARCH 5 AND 6, 1873 19 - - 19. TYPICAL SUN-SPOT OF DECEMBER, 1873 21 - - 20. FROST CRYSTAL 23 - - 21. CYCLONE SPOT 24 - - 22. SPOT OF MARCH 31, 1875 25 - - 23. CIRROUS CLOUD 27 - - 24. SPOT OF MARCH 31, 1875 28 - - 25. TYPICAL ILLUSTRATION OF FAYE’S THEORY 29 - - 26. SPOT OF OCT. 13, 1876 30 - - 27. PHOTOGRAPH OF EDGE OF SUN 31 - - 28. FACULA 33 - - 29. LUNAR CONE SHADOW 36 - - 30. TRACK OF LUNAR SHADOW 39 - - 31. INNER CORONA ECLIPSE OF 1869 40 - - 32. SKETCH OF OUTER CORONA, 1869 41 - - 33. TACCHINI’S DRAWING OF CORONA OF 1870 43 - - 34. WATSON’S NAKED-EYE DRAWING OF CORONA OF 1870 44 - - 35. PHOTOGRAPH SHOWING COMMENCEMENT OF OUTER CORONA 45 - - 36. ECLIPSE OF 1857, DRAWING BY LIAIS 48 - - 37. ENLARGEMENT OF PART OF FIG. 38 49 - - 38. FAC-SIMILE OF PHOTOGRAPH OF CORONA OF 1871 51 - - 39. “SPECTRES” 54 - - 40. OUTER CORONA OF 1878 57 - - 41. SPECTROSCOPE SLIT AND SOLAR IMAGE 59 - - 42. SLIT AND PROMINENCES 59 - - 43. TACCHINI’S CHROMOSPHERIC CLOUDS 62 - - 44. TACCHINI’S CHROMOSPHERIC CLOUDS 62 - - 45. VOGEL’S CHROMOSPHERIC FORMS 64 - - 46. TACCHINI’S CHROMOSPHERIC FORMS 66 - - 47. ERUPTIVE PROMINENCES 67 - - 48. SUN-SPOTS AND PRICE OF GRAIN 77 - - 49. SUN-SPOT OF NOV. 16, 1882, AND EARTH 80 - - 50. GREENWICH RECORD OF DISTURBANCE OF MAGNETIC NEEDLE, - NOV. 16 AND 17, 1882 81 - - 51. SUN-SPOTS AND MAGNETIC VARIATIONS 87 - - 52. GREENWICH MAGNETIC OBSERVATIONS, AUG. 3 AND 5, 1872 89 - - 53. ONE CUBIC CENTIMETRE 93 - - 54. POUILLET’S PYRHELIOMETER 93 - - 55. BERNIÈRES’S GREAT BURNING-GLASS 103 - - 56. A “POUR” FROM THE BESSEMER CONVERTER 105 - - 57. PHOTOMETER-BOX 108 - - 58. MOUCHOT’S SOLAR ENGINE 109 - - 59. ERICSSON’S NEW SOLAR ENGINE, NOW IN PRACTICAL USE IN NEW - YORK 113 - - 60. SATURN 119 - - 61. THE EQUATORIAL TELESCOPE AT WASHINGTON 122 - - 62. JUPITER, MOON, AND SHADOW 125 - - 63. THREE VIEWS OF MARS 129 - - 64. MAP OF MARS 129 - - 65. THE MOON 137 - - 66. THE FULL MOON 141 - - 67. GLASS GLOBE, CRACKED 145 - - 68. PLATO AND THE LUNAR ALPS 149 - - 69. THE LUNAR APENNINES: ARCHIMEDES 153 - - 70. VESUVIUS AND NEIGHBORHOOD OF NAPLES 157 - - 71. PTOLEMY AND ARZACHEL 161 - - 72. MERCATOR AND CAMPANUS 165 - - 73. WITHERED HAND 168 - - 74. IDEAL LUNAR LANDSCAPE AND EARTH-SHINE 169 - - 75. WITHERED APPLE 171 - - 76. GASSENDI. NOV. 7, 1867 173 - - 77. THE CAMP AT MOUNT WHITNEY 177 - - 78. VESUVIUS DURING AN ERUPTION 183 - - 79. METEORS OBSERVED NOV. 13 AND 14, 1868, BETWEEN MIDNIGHT - AND FIVE O’CLOCK, A. M. 189 - - 80. COMET OF DONATI, SEPT. 16, 1858 201 - - 81. “A PART OF A COMET” 203 - - 82. COMET OF DONATI, SEPT. 24, 1858 205 - - 83. COMET OF DONATI, OCT. 3, 1858 209 - - 84. COMET OF DONATI, OCT. 9, 1858 213 - - 85. COMET OF DONATI, OCT. 5, 1858 217 - - 86. TYPES OF STELLAR SPECTRA 222 - - 87. THE MILKY WAY 225 - - 88. SPECTRA OF STARS IN PLEIADES 231 - - 89. SPECTRUM OF ALDEBARAN 235 - - 90. SPECTRUM OF VEGA 235 - - 91. GREAT NEBULA IN ORION 239 - - 92. A FALLING MAN 243 - - 93. A FLASH OF LIGHTNING 245 - - - - -THE NEW ASTRONOMY. - - - - -I. - -SPOTS ON THE SUN. - - -The visitor to Salisbury Plain sees around him a lonely waste, -utterly barren except for a few recently planted trees, and otherwise -as desolate as it could have been when Hengist and Horsa landed in -Britain; for its monotony is still unbroken except by the funeral -mounds of ancient chiefs, which dot it to its horizon, and contrast -strangely with the crowded life and fertile soil which everywhere -surround its borders. In the midst of this loneliness rise the rude, -enormous monoliths of Stonehenge,--circles of gray stones, which seem -as old as time, and were there, as we now are told, the temple of a -people which had already passed away, and whose worship was forgotten, -when our Saxon forefathers first saw the place. - -In the centre of the inner circle is a stone which is believed once -to have been the altar; while beyond the outmost ring, quite away to -the northeast upon the open plain, still stands a solitary stone, -set up there evidently with some special object by the same unknown -builders. Seen under ordinary circumstances, it is difficult to divine -its connection with the others; but we are told that once in each -year, upon the morning of the longest day, the level shadow of this -distant, isolated stone is projected at sunrise to the very centre of -the ancient sanctuary, and falls just upon the altar. The primitive -man who devised this was both astronomer and priest, for he not only -adored the risen god whose first beams brought him light and warmth, -but he could mark its place, and though utterly ignorant of its nature, -had evidently learned enough of its motions to embody his simple -astronomical knowledge in a record so exact and so enduring that though -his very memory has gone, common men are still interested in it; for, -as I learned when viewing the scene, people are accustomed to come from -all the surrounding country, and pass in this desolate spot the short -night preceding the longest day of the year, to see the shadow touch -the altar at the moment of sunrise. - -Most great national observatories, like Greenwich or Washington, -are the perfected development of that kind of astronomy of which -the builders of Stonehenge represent the infancy. Those primitive -men could know where the sun would rise on a certain day, and make -their observation of its place, as we see, very well, without knowing -anything of its physical nature. At Greenwich the moon has been -observed with scarcely an intermission for one hundred and fifty -years, but we should mistake greatly did we suppose that it was for -the purpose of seeing what it was made of, or of making discoveries in -it. This immense mass of Greenwich observations is for quite another -purpose,--for the very practical purpose of forming the lunar tables, -which, by means of the moon’s place among the stars, will tell the -navigator in distant oceans where he is, and conduct the fleets of -England safely home. - -In the observatory at Washington one may see a wonderfully exact -instrument, in which circles of brass have replaced circles of stone, -all so bolted between massive piers that the sun can be observed by -it but once daily, as it crosses the meridian. This instrument is the -completed attainment along that long line of progress in one direction, -of which the solitary stone at Stonehenge marks the initial step,--the -attainment, that is, purely of precision of measurement; for the -astronomer of to-day can still use his circles for the special purpose -of fixing the sun’s place in the heavens, without any more knowledge of -that body’s chemical constitution than had the man who built Stonehenge. - -Yet the object of both is, in fact, the same. It is true that the -functions of astronomer and priest have become divided in the advance -of our modern civilization, which has committed the special cultivation -of the religious aspect of these problems to a distinct profession; -while the modern observer has possibly exchanged the emotions of awe -and wonder for a more exact knowledge of the equinox than was possessed -by his primitive brother, who both observed and adored. Still, both -aim at the common end, not of learning what the sun is made of, but -of where it will be at a certain moment; for the prime object of -astronomy, until very lately indeed, has still been to say _where_ -any heavenly body is, and not _what_ it is. It is this precision of -measurement, then, which has always--and justly--been a paramount -object of this oldest of the sciences, not only as a good in itself, -but as leading to great ends; and it is this which the poet of Urania -has chosen rightly to note as its characteristic, when he says,-- - - “That little Vernier, on whose slender lines - The midnight taper trembles as it shines, - Tells through the mist where dazzled Mercury burns, - And marks the point where Uranus returns.” - -But within a comparatively few years a new branch of astronomy has -arisen, which studies sun, moon, and stars for what they are in -themselves, and in relation to ourselves. Its study of the sun, -beginning with its external features (and full of novelty and interest, -even, as regards those), led to the further inquiry as to what it was -made of, and then to finding the unexpected relations which it bore to -the earth and our own daily lives on it, the conclusion being that, in -a physical sense, it made us and re-creates us, as it were, daily, and -that the knowledge of the intimate ties which unite man with it brings -results of the most practical and important kind, which a generation -ago were unguessed at. - -This new branch of inquiry is sometimes called Celestial Physics, -sometimes Solar Physics, and is sometimes more rarely referred to as -the New Astronomy. I will call it here by this title, and try to tell -the reader something about it which may interest him, beginning with -the sun. - -[Illustration: FIG. 1.--THE SUN’S SURROUNDINGS.] - -The whole of what we have to say about the sun and stars presupposes a -knowledge of their size and distance, and we may take it for granted -that the reader has at some time or another heard such statements as -that the moon’s distance is two hundred and forty thousand miles, and -the sun’s ninety-three million (and very probably has forgotten them -again as of no practical concern). He will not be offered here the -kind of statistics which he would expect in a college text-book; but -we must linger a moment on the threshold of our subject--the nature of -these bodies--to insist on the real meaning of such figures as those -just quoted. We are accustomed to look on the sun and moon as far off -together in the sky; and though we know the sun is greater, we are apt -to think of them vaguely as things of a common order of largeness, -away among the stars. It would be safe to say that though nine out of -ten readers have learned that the sun is larger than the moon, and, in -fact, larger than the earth itself, most of them do not at all realize -that the difference is so enormous that if we could hollow out the -sun’s globe and place the earth in the centre, there would still be so -much room that the moon might go on moving in her present orbit at two -hundred and forty thousand miles from the earth,--_all within the globe -of the sun itself_,--and have plenty of room to spare. - -As to the distance of ninety-three million miles, a cannon-ball would -travel it in about fifteen years. It may help us to remember that at -the speed attained by the Limited Express on our railroads a train -which had left the sun for the earth when the “Mayflower” sailed from -Delftshaven with the Pilgrim Fathers, and which ran at that rate day -and night, would in 1887 still be a journey of some years away from -its terrestrial station. The fare at the customary rates, it may be -remarked, would be rather over two million five hundred thousand -dollars, so that it is clear that we should need both money and leisure -for the journey. - -Perhaps the most striking illustration of the sun’s distance is -given by expressing it in terms of what the physiologists would call -velocity of nerve transmission. It has been found that sensation is not -absolutely instantaneous, but that it occupies a very minute time in -travelling along the nerves; so that if a child puts its finger into -the candle, there is a certain almost inconceivably small space of -time, say the one-hundredth of a second, before he feels the heat. In -case, then, a child’s arm were long enough to touch the sun, it can be -calculated from this known rate of transmission that the infant would -have to live to be a man of over a hundred before it knew that its -fingers were burned. - -Trying with the help of these still inadequate images, we may get some -idea of the real size and distance of the sun. I could wish not to have -to dwell upon such figures, that seem, however, indispensable; but we -are now done with these, and are ready to turn to the telescope and see -what the sun itself looks like. - -[Illustration: FIG. 2.--VIEW OF THE SUN ON SEPT. 20, 1870.] - -[Illustration: FIG. 3.--THE SUN ON SEPT. 22, 1870. - -(FROM A PHOTOGRAPH)] - -The sun, as we shall learn later, is a star, and not a particularly -large star. It is, as has been said, “only a private in the host of -heaven,” but it is one of that host; it is one of those glittering -points to which we have been brought near. Let us keep in mind, then, -from the first, what we shall see confirmed later, that there is an -essentially similar constitution in them all, and not forget that when -we study the sun, as we now begin to do, we are studying the stars also. - -If we were called on to give a description of the earth and all that -is on it, it would be easily understood that the task was impossibly -great, and that even an account of its most striking general features -might fill volumes. So it is with the sun; and we shall find that -in the description of the general character of its immediate surface -alone, there is a great deal to be told. First, let us look at a little -conventional representation (Fig. 1), as at a kind of outline of the -unknown regions we are about to explore. The circle represents the -Photosphere, which is simply what the word implies, that “sphere” of -“light” which we have daily before our eyes, or which we can study -with the telescope. Outside this there is a thin envelope, which rises -here and there into irregular prominences, some orange-scarlet, some -rose-pink. This is the Chromosphere, a thin shell, mainly of crimson -and scarlet tints, invisible even to the telescope except at the time -of a total eclipse, when alone its true colors are discernible, but -seen as to its form at all times by the spectroscope. It is always -there, not hidden in any way, and yet not seen, only because it is -overpowered by the intenser brilliancy of the Photosphere, as a -glow-worm’s shine would be if it were put beside an electric light. -Outside all is the strange shape, which represents the mysterious -Corona, seen by the naked eye in a total eclipse, but at all other -times invisible even to telescope and spectroscope, and of whose true -nature we are nearly ignorant from lack of opportunity to study it. - -[Illustration: FIG. 4.--THE SUN ON SEPT. 26, 1870.] - -Disregarding other details, let us carry in our minds the three main -divisions,--the Photosphere, or daily visible surface of the sun, which -contains nearly all its mass or substance; the Chromosphere; and the -unsubstantial Corona, which is nevertheless larger than all the rest. -We begin our examination with the Photosphere. - -There are records of spots having been seen with the naked eye before -the invention of the telescope, but they were supposed to be planets -passing between us and the surface; and the idea that the sun was pure -fire, necessarily immaculate, was taught by the professors of the -Aristotelian philosophy in mediæval schools, and regarded almost as -an article of religious faith. We can hardly conceive, now, the shock -of the first announcement that spots were to be found on the sun, but -the notion partook in contemporary minds at once of the absurd and the -impious; and we notice here, what we shall have occasion to notice -again, that these physical discoveries from the first affect men’s -thoughts in unexpected ways, and modify their scheme of the moral -universe as well as of the physical one. - -[Illustration: FIG. 5.--SEPT. 19, 1870.] - -[Illustration: FIG. 6.--SEPT. 20, 1870. - -(ENGRAVED FROM A PHOTOGRAPH BY RUTHERFURD.)] - -Very little indeed was added to the early observations of Fabricius and -Galileo until a time within the remembrance of many of us; for it is -since the advent of the generation now on the stage that nine-tenths of -the knowledge of the subject has been reached. - -Let us first take a general view of the sun, and afterward study it -in detail. What we see with a good telescope in this general view is -something like this. Opposite are three successive views (Figs. 2, 3, -4) taken on three successive days,--quite authentic portraits, since -the sun himself made them; they being, in fact, projected telescopic -images which have been fixed for us by photography, and then exactly -reproduced by the engraver. The first was taken (by Mr. Rutherfurd, of -New York) on the 20th of September, 1870, when a remarkably large spot -had come into view. It is seen here not far from the eastern edge (the -left hand in the engraving), and numerous other spots are also visible. -The reader should notice the position of these, and then on turning to -the next view (Fig. 3, taken on September 22d) he will see that they -have all shifted their places, by a common motion toward the west. The -great spot on the left has now got well into view, and we can see its -separate parts; the group which was on the left of the centre has got -a little to the right of it, and so on. From the common motion of them -all, we might suspect that the sun was turning round on an axis like -the earth, carrying the spots with it; and as we continue to observe, -this suspicion becomes certainty. In the third view (Fig. 4), taken on -September 26th, the spot we first saw on the left has travelled more -than half across the disk, while others we saw on September 20th have -approached to the right-hand edge or passed wholly out of sight behind -it. The sun does rotate, then, but in twenty-five or twenty-six of -our days,--I say twenty-five _or_ twenty-six, because (what is very -extraordinary) it does not turn all-of-a-piece like the earth, but some -parts revolve faster than others,--not only faster in feet and inches, -but in the number of turns,--just as though the rim of a carriage wheel -were to make more revolutions in a mile than the spokes, and the spokes -more than the hub. Of course no solid wheel could so turn without -wrenching itself in pieces, but that the great solar wheel does, is -incontestable; and this alone is a convincing proof that the sun’s -surface is not solid, but liquid or gaseous. - -[Illustration: FIG. 7.--SEPT. 21, 1870.] - -[Illustration: FIG. 8.--SEPT. 22, 1870.] - -But let us return to the great spot which we saw coming round the -eastern edge. Possibly the word “great” may seem misapplied to what was -but the size of a pin-head in the first engraving, but we must remember -that the disk of the sun there shown is in reality over 800,000 miles -in diameter. We shall soon see whether this spot deserves to be called -“great” or not. - -[Illustration: FIG. 9.--SEPT. 23, 1870.] - -[Illustration: FIG. 10.--SEPT. 26, 1870.] - -Next we have six enlarged views of it on the 19th, 20th, 21st, 22d, -23d, and 26th. On the 19th it is seen very near the eastern limb, -showing like a great hole in the sun, and foreshortened as it comes -into view around the dark edge; for the edge of the sun is really -darker than the central parts, as it is shown here, or as one may see -even through a smoked glass by careful attention. On the 20th we have -the edge still visible, but on the 21st the spot has advanced so far -that the edge cannot be shown for want of room. We see distinctly -the division of the spot into the outer shades which constitute the -penumbra, and the inner darker ones which form the umbra and nucleus. -We notice particularly in this enlarged view, by comparing the -appearances on the 21st, 22d, and 23d, that the spot not only turns -with the sun (as we have already learned), but moves and changes within -itself in the most surprising way, like a terrestrial cloud, which -not only revolves with the rest of the globe, but varies its shape -from hour to hour. This is seen still more plainly when we compare -the appearance on the 23d with that on the 26th, only three days -later, where the process has begun by which the spot finally breaks -up and forever disappears. On looking at all this, the tremendous -scale on which the action occurs must be borne in mind. On the 21st, -for instance, the umbra, or dark central hole, alone was large enough -to let the whole globe of our own earth drop in without touching -the sides! We shall have occasion to recur to this view of the 21st -September again. - -[Illustration: FIG. 11.--NASMYTH’S WILLOW LEAVES. (FROM HERSCHEL’S -“OUTLINES OF ASTRONOMY.”)] - -In looking at this spot and its striking changes, the reader must not -omit to notice, also, a much less obvious feature,--the vaguely seen -mottlings which show all over the sun’s surface, both quite away from -the spots and also close to them, and which seem to merge into them. - -[Illustration: FIG. 12.--THE CACTUS TYPE. (FROM SECCHI’S “LE SOLEIL.”)] - -I think if we assign one year rather than another for the birth of the -youthful science of solar physics, it should be 1861, when Kirchhoff -and Bunsen published their memorable research on Spectrum Analysis, -and when Nasmyth observed what he called the “willow-leaf” structure -of the solar surface (see Fig. 11). Mr. Nasmyth, with a very powerful -reflecting telescope, thought he had succeeded in finding what these -faint mottlings really are composed of, and believed that he had -discovered in them some most extraordinary things. This is what he -thought he saw: The whole sun is, according to him, covered with huge -bodies of most definite shape, that of the oblong willow leaf, and of -enormous but uniform size; and the faint mottlings the reader has just -noticed are, according to him, made up of these. “These,” he says, -“cover the whole disk of the sun (except in the space occupied by the -spots) in countless millions, and lie crossing each other in every -imaginable direction.” Sir John Herschel took a particular interest -in the supposed discovery, and, treating it as a matter of established -fact, proceeded to make one of the most amazing suggestions in -explanation that ever came from a scientific man of deserved eminence. -We must remember how much there is unknown in the sun still, and what -a great mystery even yet overhangs many of our relations to that body -which maintains our own vital action, when we read the following words, -which are Herschel’s own. Speaking of these supposed spindle-shaped -monsters, he says: - - “The exceedingly definite shape of these objects, their exact - similarity to one another, and the way in which they lie across - and athwart each other,--all these characters seem quite - repugnant to the notion of their being of a vaporous, a cloudy, - or a fluid nature. Nothing remains but to consider them as - separate and independent sheets, flakes, or scales, having some - sort of solidity. And these ... are evidently _the immediate - sources of the solar light and heat_, by whatever mechanism or - whatever processes they may be enabled to develop, and as it were - elaborate, these elements from the bosom of the non-luminous - fluid in which they appear to float. Looked at in this point of - view, we cannot refuse to regard them as _organisms_ of some - peculiar and amazing kind; and though it would be too daring to - speak of such organization as partaking of the nature of life, - yet we do know that vital action is competent to develop at once - heat and light and electricity.” - -[Illustration: FIG. 13.--EQUATORIAL TELESCOPE AND PROJECTION.] - -Such are his words; and when we consider that each of these solar -inhabitants was supposed to extend about two hundred by one thousand -miles upon the surface of the fiery ocean, we may subscribe to Mr. -Proctor’s comment, that “Milton’s picture of him who on the fires of -hell ‘lay floating many a rood,’ seems tame and commonplace compared -with Herschel’s conception of these floating monsters, the least -covering a greater space than the British Islands.” - -[Illustration: FIG. 14.--POLARIZING EYE-PIECE.] - -I hope I may not appear wanting in respect for Sir John Herschel--a man -whose memory I reverence--in thus citing views which, if his honored -life could have been prolonged, he would have abandoned. I do so -because nothing else can so forcibly illustrate the field for wonder -and wild conjecture solar physics presented even a few years ago; and -its supposed connection with that “Vital Force,” which was till so -lately accepted by physiology, serves as a kind of landmark on the way -we have come. - -This new science of ours, then, youthful as it is, has already had its -age of fable. - -After a time Nasmyth’s observation was attributed to imperfect -definition, but was not fairly disproved. He had, indeed, a basis of -fact for his statement, and to him belongs the credit of first pointing -out the existence of this minute structure, though he mistook its true -character. It will be seen later how the real forms might be mistaken -for leaves, and _in certain particular cases_ they certainly do take on -a very leaf-like appearance. Here is a drawing (Fig. 12) which Father -Secchi gives of some of them in the spot of April 14, 1867, and which -he compares to a branch of cactus. He remarks somewhere else that they -resemble a crystallization of sal-ammoniac, and calls them veils of -most intricate structure. This was the state of our knowledge in 1870, -and it may seem surprising that such wonderful statements had not been -proved or disproved, when they referred to mere matters of observation. -But direct observation is here very difficult on account of the -incessant tremor and vibration of our own atmosphere. - -[Illustration: FIG. 15.--SPOT OF SEPT. 21, 1870. (REDUCED FROM AN -ORIGINAL DRAWING BY S. P. LANGLEY.)] - -[Illustration: FIG. 16.--SPOT OF MARCH 5, 1873. (REDUCED FROM AN -ORIGINAL DRAWING BY S. P. LANGLEY.)] - -The surface of the sun may be compared to an elaborate engraving, -filled with the closest and most delicate lines and hatchings, but an -engraving which during ninety-nine hundredths of the time can only be -seen across such a quivering mass of heated air as makes everything -confused and liable to be mistaken, causing what is definite to look -like a vaguely seen mottling. It is literally true that the more -delicate features we are about to show, are only distinctly visible -even by the best telescope during less than one-hundredth of the -time, coming out as they do in brief instants when our dancing air is -momentarily still, so that one who has sat at a powerful telescope all -day is exceptionally lucky if he has secured enough glimpses of the -true structure to aggregate five minutes of clear seeing, while at all -other times the attempt to magnify only produces a blurring of the -image. This study, then, demands not only fine telescopes and special -optical aids, but endless patience. - -[Illustration: FIG. 17.--SUN ON MARCH 5, 1873. (FROM A DRAWING BY S. P. -LANGLEY.)] - -My attention was first particularly directed to the subject in 1870 -(shortly after the regular study of the Photosphere was begun at the -Allegheny Observatory by means of its equatorial telescope of thirteen -inches’ aperture), with the view of finding out what this vaguely seen -structure really is. Nearly three years of constant watching were given -to obtain the results which follow. The method I have used for it is -indicated in the drawing (Fig. 13), which shows the preliminary step -of projecting the image of the sun directly upon a sheet of paper, -divided into squares and attached to the eye-end of a great equatorial -telescope. When this is directed to the sun in a darkened dome, the -solar picture is formed upon the paper as in a camera obscura, and this -picture can be made as large or as small as we please by varying the -lenses which project it. As the sun moves along in the sky, its image -moves across the paper; and as we can observe how long the whole sun -(whose diameter in miles is known) takes to cross, we can find how many -miles correspond to the time it is in crossing one of the squares, and -so get the scale of the future drawing, and the true size in miles of -the spot we are about to study. Then a piece of clock-work attached to -the telescope is put in motion, and it begins to follow the sun in the -sky, and the spot appears fixed on the paper. A tracing of the spot’s -outline is next made, but the finer details are not to be observed by -this method, which is purely preliminary, and only for the purpose -of fixing the scale and the points of the compass (so to speak) on -the sun’s face. The projecting apparatus is next removed and replaced -by the polarizing eye-piece. Sir William Herschel used to avoid the -blinding effects of the concentrated solar light by passing the rays -through ink and water, but the phenomena of “polarization” have been -used to better advantage in modern apparatus. This instrument, one -of the first of its kind ever constructed, and in which the light is -polarized with three successive reflections through the three tubes -seen in the drawing (Fig. 14), was made in Pittsburgh as a part of the -gift of apparatus by one of its citizens to the Observatory, and has -been most useful. By its aid the eye can be safely placed where the -concentrated heat would otherwise melt iron. In practice I have often -gazed through it at the sun’s face without intermission from four to -five hours, with no more fatigue or harm to the eye than in reading a -book. By its aid the observer fills in the outline already projected on -the paper. - -[Illustration: FIG. 18.--“THE PLUME” SPOT OF MARCH 5 AND 6, 1873. (FROM -AN ORIGINAL DRAWING BY S. P. LANGLEY.)] - -The photograph has transported us already so near the sun’s surface -that we have seen details there invisible to the naked eye. We have -seen that what we have called “spots” are indeed regions whose actual -vastness surpasses the vague immensity of a dream, and it will not -cause surprise that in them is a temperature which also surpasses -greatly that of the hottest furnace. We shall see later, in fact, that -the whole surface is composed largely of metals turned into vapor in -this heat, and that if we could indeed drop our great globe itself upon -the sun, it would be dissipated as a snow-flake. Now, we cannot suppose -this great space is fully described when we have divided it into the -penumbra, umbra, and nucleus, or that the little photograph has shown -us all there is, and we rather anticipate that these great spaces must -be filled with curious things, if we could get near enough to see them. -We cannot advantageously enlarge our photograph further; but if we -could really come closer, we should have the nearer view that the work -at Allegheny, I have just alluded to, now affords. The drawing (Fig. -15) of the central part of the same great spot, already cited, was made -on the 21st of September, 1870, and may be compared with the photograph -of that day. We have now a greatly more magnified view than before, but -it is not blurred by the magnifying, and is full of detail. We have -been brought within two hundred thousand miles of the sun, or rather -less than the actual distance of the moon, and are seeing for ourselves -what was a few years since thought out of the reach of any observer. -See how full of intricate forms that void, black, umbral space in -the photograph has become! The penumbra is filled with detail of the -strangest kind, and there are two great “bridges,” as they are called, -which are almost wholly invisible in the photograph. Notice the line -in one of the bridges which follows its sinuosities through its whole -length of twelve thousand miles, making us suspect that it is made up -of smaller parts as a rope is made up of cords (as, in fact, it is); -and look at the end, where the cords themselves are unravelled into -threads fine as threads of silk, and these again resolved into finer -fibres, till in more and more web-like fineness it passes beyond the -reach of sight! I am speaking, however, here rather of the wonderful -original, as I so well remember it, than of what my sketch or even the -engraver’s skill can render. - -[Illustration: FIG. 19.--TYPICAL SUN SPOT OF DECEMBER, 1873. - -(REDUCED FROM AN ORIGINAL DRAWING BY S. P. LANGLEY.)] - -[Illustration: FIG. 20.--FROST CRYSTAL.] - -Next we have quite another “spot” belonging to another year (1873). -First, there is a view (Fig. 17) of the sun’s disk with the spot on -it (as it would appear in a small telescope), to show its relative -size, and then a larger drawing of the spot itself (Fig. 16), on a -scale of twelve thousand miles to the inch, so that the region shown -to the reader’s eyes, though but a “spot” on the sun, covers an area -of over one billion square miles, or more than five times the entire -surface of the earth, land, and water. To help us to conceive its -vastness, I have drawn in one corner the continents of North and South -America on the same scale as the “spot.” Notice the evidence of -solar whirlwinds and the extraordinary “plume” (Fig. 16), which is a -something we have no terrestrial simile for. The appearance of the -original would have been described most correctly by such incongruous -images as “leaf-like” and “crystalline” and “flame-like;” and even in -this inadequate sketch there may remain some faint suggestion of the -appearance of its wonderful archetype, which was indeed that of a great -flame leaping into spires and viewed through a window covered with -frost crystals. Neither “frost” nor “flame” is really there, but we -cannot avoid this seemingly unnatural union of images, which was fully -justified by the marvellous thing itself. The reader must bear in mind -that the whole of this was actually in motion, not merely turning with -the sun’s rotation, but whirling and shifting within itself, and that -the motion was in parts occasionally probably as high as fifty miles -per second,--per _second_, remember, not per hour,--so that it changed -under the gazer’s eyes. The hook-shaped prominence in the lower part -(actually larger than the United States) broke up and disappeared in -about twenty minutes, or while the writer was engaged in drawing it. -The imagination is confounded in an attempt to realize to itself the -true character of such a phenomenon. - -[Illustration: FIG. 21.--CYCLONE SPOT. (DRAWN BY FATHER SECCHI.)] - -On page 19 is a separate view of the plume (Fig. 18), a fac-simile of -the original sketch, which was made with the eye at the telescope. The -pointed or flame-like tips are not a very common form, the terminals -being more commonly clubbed, like those in Father Secchi’s “branch -of cactus” type given on page 12. It must be borne in mind, too, if -the drawing does not seem to contain all that the text implies, that -there were but a few minutes in which to attempt to draw, where even a -skilled draughtsman might have spent hours on the details momentarily -visible, and that much must be left to memory. The writer’s note-book -at the time contains an expression of despair at his utter inability to -render most of what he saw. - -Let us now look at another and even more wonderful example. Fig. 19 -shows part of a great spot which the writer drew in December, 1873, -when the rare coincidence happened of a fine spot and fine terrestrial -weather to observe it in. In this, as well as in the preceding drawing, -the pores which cover the sun’s surface by millions may be noted. The -luminous dots which divide them are what Nasmyth imperfectly saw, but -we are hardly more able than he to say what they really are. Each of -these countless “dots” is larger than England, Scotland, and Ireland -together! The wonderful “crystalline” structure in the centre cannot -be a real crystal, for it is ten times the area of Europe, and changed -slowly while I drew it; but the reader may be sure that its resemblance -to some crystallizations has not been in the least exaggerated. I have -sought to study various actual crystals for comparison, but found none -quite satisfactory. That of sal-ammoniac in some remote way resembles -it, as Secchi says; but perhaps the frost crystals on a window-pane -are better. Fig. 20 shows one selected among several windows I had -photographed in a preceding winter, which has some suggestions of the -so-called crystalline spot-forms in it, but which lacks the filamentary -thread-like components presently described. Of course the reader will -understand that it is given as a suggestion of the appearance merely, -and that no similarity of nature is meant to be indicated. - -[Illustration: FIG. 22.--SPOT OF MARCH 31, 1875. (FROM AN ORIGINAL -DRAWING BY S. P. LANGLEY.)] - -There were wonderful fern-like forms in this spot, too, and an -appearance like that of pine-boughs covered with snow; for, strangely -enough, the intense whiteness of the solar surface in the best -telescopes constantly suggests cold. I have had the same impression -vividly in looking at the immense masses of molten-white iron in a -great puddling-furnace. The salient feature here is one very difficult -to see, even in good telescopes, but one which is of great interest. It -has been shown in the previous drawings, but we have not enlarged on -it. Everywhere in the spot are long white threads, or filaments, lying -upon one another, tending in a general sense toward the centre, and -each of which grows brighter toward its inner extremity. These make up, -in fact, as we now see, the penumbra, or outer shade, and the so-called -“crystal” is really affiliated to them. Besides this, on closer looking -we see that the inner shade, or umbra, and the very deepest shades, or -nuclei, are really made of them too. We can look into the dark centre, -as into a funnel, to the depth of probably over five thousand miles; -but as far as we may go down we come to no liquid or solid floor, and -see only volumes of whirling vapor, disposed not vaguely like our -clouds, but in the singularly definite, fern-like, flower-like forms -which are themselves made of these “filaments,” each of which is from -three to five thousand miles long, and from fifty to two hundred miles -thick, and each of which (as we saw in the first spot) appears to be -made up like a rope of still finer and finer strands, looking in the -rare instants when irradiation makes an isolated one visible, like a -thread of gossamer or the finest of cobweb. These suggest the fine -threads of spun glass; and here there is something more than a mere -resemblance of form, for both appear to have one causal feature in -common, due to a viscous or “sticky” fluid; for there is much reason to -believe that the solar atmosphere, even where thinner than our own air, -is rendered viscous by the enormous heat, and owes to this its tendency -to pull out in strings in common with such otherwise dissimilar things -as honey, or melted sugar, or melted glass. - -We may compare those mysterious things, the filaments, to long grasses -growing in the bed of a stream, which show us the direction and the -eddies of the current. The likeness holds in more ways than one. They -are not lying, as it were, flat upon the surface of the water, but -_within_ the medium; and they do not stretch along in any one plane, -but they bend down and up. Moreover, they are, as we see, apparently -rooted at one end, and their tips rise above the turbid fluid and grow -brighter as they are lifted out of it. But perhaps the most significant -use of the comparison is made if we ask whether the stream is moving in -an eddy like a whirlpool or boiling up from the ground. The question -in other words is, “Are these spots themselves the sign of a mere -chaotic disturbance, or do they show us by the disposition of these -filaments that each is a great solar maelstrom, carrying the surface -matter of the sun down into its body? or, finally, are they just the -opposite,--something comparable to fiery fountains or volcanoes on the -earth, throwing up to the surface the contents of the unknown solar -interior?” - -[Illustration: FIG. 23.--CIRROUS CLOUD. (FROM A PHOTOGRAPH.)] - -Before we try to answer this question, let us remember that the -astonishing rapidity with which these forms change, and still more the -fact that they do not by any means always change by a bodily removal -of one part from another, but by a dissolving away and a fading out -into invisibility, like the melting of a cloud into thin air,--let us -remember that all this assimilates them to something cloud-like and -vaporous, rather than crystalline, and that, as we have here seen, -we can ourselves pronounce from such results of recent observation -that these are not lumps of scoriæ floating on the solar furnace (as -some have thought them), and still less, literal crystals. We can see -for ourselves, I believe, that so far there is no evidence here of -any solid, or even liquid, but that the surface of the sun is purely -vaporous. Fig. 23 shows a cirrous cloud in our own atmosphere, caught -for us by photography, and which the reader will find it interesting to -compare with the apparently analogous solar cloud-forms. - -[Illustration: FIG. 24.--SPOT OF MARCH 31, 1875. (FROM AN ORIGINAL -DRAWING BY S. P. LANGLEY.)] - -“Vaporous,” we call them, for want of a better word, but without -meaning that it is like the vapor of our clouds. There is no exact -terrestrial analogy for these extraordinary forms, which are in fact, -as we shall see later, composed of iron and other metals--not of solid -iron nor even of liquid, but iron heated beyond even the liquid state -to that of iron-steam or vapor. - -With all this in mind, let us return to the question, “Are the spots, -these gigantic areas of disturbance, comparable to whirlpools or to -volcanoes?” It may seem unphilosophical to assume that they are one -or the other, and in fact they may possibly be neither; but it is -certain that the surface of the sun would soon cool from its enormous -temperature, if it were not supplied with fresh heat, and it is almost -certain that this heat is drawn from the interior. As M. Faye has -pointed out,[1] there _must_ be a circulation up and down, the cooled -products being carried within, heated and brought out again, or the -sun would, however hot, grow cold outside; and, what is of interest -to us, the earth would grow cold also, and we should all die. No one, -I believe, who has studied the subject, will contradict the statement -that if the sun’s surface were absolutely cut off from any heat supply -from the interior, organic life in general upon the earth (and our -own life in particular) would cease much within a month. This solar -circulation, then, is of nearly as much consequence to us as that of -our own bodies, if we but knew it; and now let us look at the spots -again with this in mind. - - [1] To Mr. Herbert Spencer must be assigned the earliest - suggestion of the necessity of such a circulation. - -[Illustration: FIG. 25.--TYPICAL ILLUSTRATION OF FAYE’S THEORY.] - -Fig. 21 shows a drawing by Father Secchi of a spot in 1854; and it is, -if unexaggerated, quite the most remarkable case of distinct cyclonic -action recorded. I say “if unexaggerated” because there is a strong -tendency in most designers to select what is striking in a spot, and -to emphasize that unduly, even when there is no conscious disposition -to alter. Every one who sketches may see a similar unconscious -tendency in himself or herself, shown in a disposition to draw all the -mountains and hills too high,--a tendency on which Ruskin, I think, -has remarked. In drawings of the sun there is a strong temptation to -exaggerate these circular forms, and we must not forget this in making -up the evidence. There is great need of caution, then, in receiving -such representations; but there certainly are forms which seem to be -clearly due to cyclonic action. They are usually scattered, however, -through larger spots, and I have never, in all my study of the sun, -seen one such complete type of the cyclone spot as that first given -from Secchi. Instances where spots break up into numerous subdivisions -by a process of “segmentation” under the apparent action of separate -whirlwinds are much more common. I have noticed, as an apparent effect -of this segmentation, what I may call the “honeycomb structure” from -its appearance with low powers, but which with higher ones turns out to -be made up of filamentary masses disposed in circular and ovoid curves, -often apparently overlying one another, and frequently presenting a -most curious resemblance to vegetable forms, though we appear to see -the real agency of whirlwinds in making them. I add some transcripts -of my original pencil memoranda themselves, made with the eye at the -telescope, which, though not at all finished drawings, may be trusted -the more as being quite literal transcripts at first hand. - -[Illustration: FIG. 26.--SPOT OF OCT. 13, 1876. (FROM ORIGINAL DRAWING -BY S. P. LANGLEY.)] - -Figs. 22 and 24, for instance, are two sketches of a little spot, -showing what, with low powers, gives the appearance I have called the -honeycomb structure, but which we see here to be due to whirls which -have disposed the filaments in these remarkable forms. The first was -drawn at eleven in the forenoon of March 31, 1875, the second at -three in the afternoon of the same day. The scale of the drawing is -fifteen thousand miles to the inch, and the changes in this little -spot in these few hours imply a cataclysm compared with which the -disappearance of the American continent from the earth’s surface would -be a trifle. - -The very act of the solar whirlwind’s motion seemed to pass before my -eyes in some of these sketches; for while drawing them as rapidly as -possible, a new hole would be formed where there was none before, as if -by a gigantic invisible auger boring downward. - -[Illustration: FIG. 27.--PHOTOGRAPH OF EDGE OF SUN. (BY PERMISSION OF -WARREN DE LA RUE, LONDON.)] - -M. Faye, the distinguished French astronomer, believes that, owing to -the fact that different zones of the sun rotate faster than others, -whirlwinds analogous to our terrestrial cyclones, but on a vaster -scale, are set in motion, and suck down the cooled vapors of the solar -surface into its interior, to be heated and returned again, thus -establishing a circulation which keeps the surface from cooling down. -He points out that we should not conclude that these whirlwinds are not -acting everywhere, merely because our bird’s-eye view does not always -show them. We see that the spinning action of a whirlpool in water -becomes more marked as we go below the surface, which is comparatively -undisturbed, and we often see one whirl break up into several minor -ones, but all sucking downward and never upward. According to M. Faye, -something very like this takes place on the sun, and in Fig. 25 he -gives this section to show what he believes to occur in the case of a -spot which has “segmented,” or divided into two, like the one whose -(imaginary) section is shown above it. This theory is to be considered -in connection with such drawings as we have just shown, which are -themselves, however, no way dependent on theory, but transcripts from -Nature. - -I do not here either espouse or oppose the “cyclonic” theory, but it is -hardly possible for any one who has been an eyewitness of such things -to refuse to regard some such disturbance as a real and efficient cause -in such instances as this. - -Fig. 26, on nearly the same scale as the last, shows a spot which was -seen on Oct. 13, 1876. It looked at first, in the telescope, like two -spots without any connection; then, as vision improved and higher -powers were employed, the two were seen to have a subtle bond of union, -and each to be filled with the most curious foliage-forms, which I -could only indicate in the few moments that the good definition lasted. -The reader may be sure, I think, that there is no exaggeration of the -curious shapes of the original; for I have been so anxious to avoid the -overstatement of curvature that the error is more likely to be in the -opposite direction. - -We must conclude that the question as to the cyclonic hypothesis cannot -yet be decided, though the probabilities from telescopic evidence -at present seem to me on the whole in favor of M. Faye’s remarkable -theory, which has the great additional attraction to the student that -it unites and explains numerous other quite disconnected facts. - -Turning now to the other solar features, let us once more consider -the sun as a whole. Fig. 27 is a photograph taken from a part of the -sun near its edge. We notice on it, what we see on every careful -delineation of the sun, that its general surface is not uniformly -bright, but that it grows darker as we approach the edge, where it -is marked by whiter mottlings called faculæ, “something in the sun -brighter than the sun itself,” and looking in the enlarged view which -we present of one of them (Fig. 28), as if the surface of partly -cooled metal in a caldron had been broken into fissures showing the -brighter glow beneath. These “faculæ,” however, are really above the -solar surface, not below it, and what we wish to direct particular -attention to is that darkening toward the edge which makes them visible. - -[Illustration: FIG. 28.--FACULA. (FROM A DRAWING BY CHACORNAC.)] - -This is very significant, but its full meaning may not at first be -clear. It is owing to an atmosphere which surrounds the sun, as the -air does the earth. When we look horizontally through our own air, as -at sunrise and sunset, we gaze through greater thicknesses of it than -when we turn our eyes to the zenith. So when we look at the edge of -the sun, the line of sight passes through greater depths of this solar -atmosphere, and it dims the light shining behind it more than at the -centre, where it is thin. - -This darkening toward the edge, then, means that the sun has an -atmosphere which tempers its heat to us. Whatever the sun’s heat -supply is within its globe, if this atmosphere grow thicker, the -heat is more confined within, and our earth will grow colder; if the -solar atmosphere grow thinner, the sun’s energy will be expended more -rapidly, and our earth will grow hotter. This atmosphere, then, is in -considerable part, at least, the subject of the action of the spots; -this is what they are supposed to carry down or to spout up. - -We shall return to the study of it again; but what I want to point out -now is that the temperature of the earth, and even the existence of man -upon it, depends very much upon this, at first sight, insignificant -phenomenon. What, then, is the solar atmosphere? Is it a permanent -thing? Not at all. It is more light and unsubstantial than our own -air, and is being whirled about by solar winds as ours toss the dust -of the streets. It is being sucked down within the body of the sun by -some action we do not clearly understand, and returned to the surface -by some counter effect which we comprehend no better; and upon this -imperfectly understood exchange depends in some way our own safety. - -There used to be recorded in medical books the case of a boy who, to -represent Phœbus in a Roman mask, was gilded all over to produce the -effect of the golden-rayed god, but who died in a few hours because, -all the pores of the skin being closed by the gold-leaf, the natural -circulation was arrested. We can count with the telescope millions of -pores upon the sun’s surface, which are in some way connected with the -interchange which has just been spoken of; and if this, his own natural -circulation, were arrested or notably diminished, we should see his -face grow cold, and know that our own health, with the life of all the -human race, was waiting on his recovery. - - - - -II. - -THE SUN’S SURROUNDINGS. - - -As I write this, the fields glitter with snow-crystals in the winter -noon, and the eye is dazzled with a reflection of the splendor which -the sun pours so fully into every nook that by it alone we appear to -see everything. - -Yet, as the day declines, and the glow of the sunset spreads up to the -zenith, there comes out in it the white-shining evening star, which -not the light, but the darkness, makes visible; and as the last ruddy -twilight fades, not only this neighbor-world, whose light is fed from -the sunken sun, but other stars appear, themselves self-shining suns, -which were above us all through the day, unseen because of the very -light. - -As night draws on, we may see the occasional flash of a shooting-star, -or perhaps the auroral streamers spreading over the heavens; and -remembering that these will fade as the sun rises, and that the nearer -they are to it the more completely they will be blotted out, we infer -that if the sun were surrounded by a halo of only similar brightness, -this would remain forever invisible,--unless, indeed, there were -some way of cutting off the light from the sun without obscuring its -surroundings. But if we try the experiment of holding up a screen which -just conceals the sun, nothing new is seen in its vicinity, for we are -also lighted by the neighboring sky, which is so dazzlingly bright with -reflected light as effectually to hide anything which may be behind it, -so that to get rid of this glare we should need to hang up a screen -_outside_ the earth’s atmosphere altogether. - -[Illustration: FIG. 29.--LUNAR CONE SHADOW.] - -Nature hangs such a screen in front of the earth when the moon passes -between it and the sun; but as the moon is far too small to screen -all the earth completely, and as so limited a portion of its surface -is in complete shadow that the chances are much against any given -individual’s being on the single spot covered by it, many centuries -usually elapse before such a _total_ eclipse occurs at any given point; -while yet almost every year there may be a partial eclipse, when, over -a great portion of the earth at once, people may be able to look round -the moon’s edge and see the sunlight but partly cut off. Nearly every -one, then, has seen a partial eclipse of the sun, but comparatively few -a total one, which is quite another thing, and worth a journey round -the world to behold; for such a nimbus, or glory, as we have suggested -the possibility of, does actually exist about the sun, and becomes -visible to the naked eye on the rare occasions when it is visible at -all, accompanied by phenomena which are unique among celestial wonders. - -The “corona,” as this solar crown is called, is seen during a total -eclipse to consist of a bright inner light next the invisible sun, -which melts into a fainter and immensely extended radiance (the writer -has followed the latter to the distance of about ten million miles), -and all this inner corona is filled with curious detail. All this is -to be distinguished from another remarkable feature seen at the same -time; for close to the black body of the moon are prominences of a -vivid crimson and scarlet, rising up like mountains from the hidden -solar disk, and these, which will be considered later, are quite -distinct from the corona, though seen on the background of its pearly -light. - -To understand what the lunar screen is doing for us, we may imagine -ourselves at some station outside the earth, whence we should behold -the moon’s shadow somewhat as in Fig. 29, where we must remember that -since the lunar orbit is not a circle, but nearly an ellipse, the -moon is at some times farther from the earth than at others. Here the -extremity of its shadow is represented as just touching the surface of -the globe, while it is evident that if the moon were at its greatest -distance, its shadow might come to a point before reaching the earth at -all. We speak, of course, only of the central cone of shade; for there -is an outer one, indicated by the faint dotted lines, within whose much -more extended limits the eclipse is partial, but with the latter we -have at present nothing to do. The figure however, for want of room, -is made to represent the proportions incorrectly, the real ones of the -shadow being actually something like those of a sewing-needle,--this -very long attenuated shadow sometimes, as we have just said, not -reaching the earth at all, and when it does reach it, covering at the -most a very small region indeed. Where this point touches, and wherever -it rests, we should, in looking down from our celestial station, see -that part of the earth in complete shadow, appearing like a minute dark -spot, whose lesser diameter is seldom over a hundred and fifty miles. - -The eclipse is total only to those inhabitants of the earth within -the track of this dark spot, though the spot itself travels across -the earth with the speed of the moon in the sky; so that if it could -leave a mark, it would in a few hours trace a dark line across the -globe, looking like a narrow black tape curving across the side of the -world next the sun. In Fig. 30, for instance, is the central track of -the eclipse of July 29, 1878, as it would be visible to our celestial -observer, beginning in Alaska in the forenoon, and ending in the Gulf -of Mexico, which it reached in the afternoon. To those on the earth’s -surface within this shadow it covered everything in view, and, for -anything those involved in it could see, it was all-embracing and -terrible, and worthily described in such lines as Milton’s,-- - - “As when the sun ... - In dim eclipse, disastrous twilight sheds - On half the nations, and with fear of change - Perplexes monarchs.” - -We may enjoy the poet’s vision; but here, while we look down on -the whole earth at once, we must admit that the actual area of the -“twilight” is very small indeed. Within this area, however, the -spectacle is one of which, though the man of science may prosaically -state the facts, perhaps only the poet could render the impression. - -We can faintly picture, perhaps, how it would seem, from a station -near the lunar orbit, to see the moon--a moving world--rush by with a -velocity greater than that of the cannon-ball in its swiftest flight; -but with equal speed its shadow actually travels along the earth. And -now, if we return from our imaginary station to a real one here below, -we are better prepared to see why this flying shadow is such a unique -spectacle; for, small as it may be when seen in relation to the whole -globe, it is immense to the observer, whose entire horizon is filled -with it, and who sees the actual velocity of one of the heavenly -bodies, as it were, brought down to him. - -The reader who has ever ascended to the Superga, at Turin, will recall -the magnificent view, and be able to understand the good fortune of -an observer (Forbes) who once had the opportunity to witness thence -this phenomenon, and under a nearly cloudless sky. “I perceived,” he -says, “in the southwest a black shadow like that of a storm about to -break, which obscured the Alps. It was the lunar shadow coming toward -us.” And he speaks of the “stupefaction”--it is his word--caused by -the spectacle. “I confess,” he continues, “it was the most terrifying -sight I ever saw. As always happens in the cases of sudden, silent, -unexpected movements, the spectator confounds real and relative motion. -I felt almost giddy for a moment, as though the massive building under -me bowed on the side of the coming eclipse.” Another witness, who had -been looking at some bright clouds just before, says: “The bright cloud -I saw distinctly put out like a candle. The rapidity of the shadow, and -the intensity, produced a feeling that something material was sweeping -over the earth at a speed perfectly frightful. I involuntarily listened -for the rushing noise of a mighty wind.” - -[Illustration: FIG. 30--TRACK OF LUNAR SHADOW.] - -Each one notes something different from another at such a time; and -though the reader will find minute descriptions of the phenomena -already in print, it will perhaps be more interesting if, instead of -citations from books, I invite him to view them with me, since each can -tell best what he has personally seen. - -[Illustration: FIG. 31.--INNER CORONA ECLIPSE OF 1869. FROM SHELBYVILLE -PHOTOGRAPH. (ROYAL ASTRONOMICAL SOCIETY’S MEMOIRS.)] - -I have witnessed three total eclipses, but I do not find that -repetition dulls the interest. The first was that of 1869, which -passed across the United States and was nearly central over Louisville. -My station was on the southern border of the eclipse track, not very -far from the Mammoth Cave in Kentucky, and I well remember that -early experience. The special observations of precision in which I -was engaged would not interest the reader; but while trying to give -my undivided attention to these, a mental photograph of the whole -spectacle seemed to be taking without my volition. First, the black -body of the moon advanced slowly on the sun, as we have all seen it do -in partial eclipses, without anything noticeable appearing; nor till -the sun was very nearly covered did the light of day about us seem -much diminished. But when the sun’s face was reduced to a very narrow -crescent, the change was sudden and startling, for the light which fell -on us not only dwindled rapidly, but became of a kind unknown before, -so that a pallid appearance overspread the face of the earth with an -ugly livid hue; and as this strange wanness increased, a cold seemed to -come with it. The impression was of something _unnatural_; but there -was only a moment to note it, for the sun went out as suddenly as a -blown-out gas-jet, and I became as suddenly aware that all around, -where it had been, there had been growing into vision a kind of ghostly -radiance, composed of separate pearly beams, looking distinct each from -each, as though the black circle where the sun once was, bristled with -pale streamers, stretching far away from it in a sort of crown. - -This was the mysterious corona, only seen during the brief moments -while the shadow is flying overhead; but as I am undertaking to recall -faithfully the impressions of the instant, I may admit that I was at -the time equally struck with a circumstance that may appear trivial -in description,--the extraordinary globular appearance of the moon -herself. We all know well enough that the moon is a solid sphere, but -it commonly _looks_ like a bright, flat circle fastened to the concave -of the starry vault; and now, owing to its unwonted illumination, the -actual rotundity was seen for the first time, and the result was to -show it as it really is,--a monstrous, solid globe, suspended by some -invisible support above the earth, with nothing apparent to keep it -from tumbling on us, looking at the moment very near, and more than -anything else like a gigantic black cannon-ball, hung by some miracle -in the air above the neighboring cornfield. But in a few seconds all -was over; the sunlight flashed from one point of the moon’s edge and -then another, almost simultaneously, like suddenly kindled electric -lights, which as instantly flowed into one, and it was day again. - -[Illustration: FIG. 32.--SKETCH OF OUTER CORONA, 1869. (U. S. COAST -SURVEY REPORT.)] - -I have spoken of the “unnatural” appearance of the light just before -totality. This is not due to excited fancy, for there is something -so essentially different from the natural darkness of twilight, that -the brute creation shares the feeling with us. Arago, for instance, -mentions that in the eclipse of 1842, at Perpignan, where he was -stationed, a dog which had been kept from food twenty-four hours was, -to test this, thrown some bread just before “totality” began. The -dog seized the loaf, began to devour it ravenously, and then, as the -appearance already described came on, he dropped it. The darkness -lasted some minutes, but not till the sun came forth again did the poor -creature return to the food. It is no wonder, then, that men also, -whether educated or ignorant, do not escape the impression. A party of -the courtiers of Louis XV. is said to have gathered round Cassini to -witness an eclipse from the terrace of the Paris observatory, and to -have been laughing at the populace, whose cries were heard as the light -began to fade; when, as the unnatural gloom came quickly on, a sudden -silence fell on them too, the panic terror striking through their -laughter. Something common to man and the brute speaks at such times, -if never before or again; something which is not altogether physical -apprehension, but more like the moral dismay when the shock of an -earthquake is felt for the first time, and we first know that startling -doubt, superior to reason, whether the solid frame of earth is real, -and not “baseless as the fabric of a vision.” - -But this is appealing for illustration to an experience which most -readers have doubtless been spared,[2] and I would rather cite the -lighter one of our central party that day, a few miles north of me, -at Shelbyville. In this part of Kentucky the colored population was -large, and (in those days) ignorant of everything outside the life of -the plantation, from which they had only lately been emancipated. On -that eventful 8th of August they came in great numbers to view the -enclosure and the tents of the observing party, and to inquire the -price of the show. On learning that they might see it without charge -from the outside, a most unfavorable opinion was created among them as -to the probable merits of so cheap a spectacle, and they crowded the -trees about the camp, shouting to each other sarcastic comments on the -inferior interest of the entertainment. “Those trees there,” said one -of the observers to me the next day, “were black with them, and they -kept up their noise till near the last, when they suddenly stopped, and -all at once, and as ‘totality’ came, we heard a wail and a noise of -tumbling, as though the trees had been shaken of their fruit, and then -the boldest did not feel safe till he was under his own bed in his own -cabin.” - - [2] This was written before the “Charleston earthquake” - occurred. - -[Illustration: FIG. 33.--TACCHINI’S DRAWING OF CORONA OF 1870. - -(SECCHI’S “LE SOLEIL.”)] - -It is impossible to give an exact view of what our friends at -Shelbyville saw, for no drawings made there appear to have been -preserved, and photography at that time could only indicate feebly -the portion of the corona near the sun where it is brightest. Fig. -31 is a fac-simile of one of the photographs taken on the occasion, -which is interesting perhaps as one of the early attempts in this -direction, for comparison with later ones; but as a picture it is very -disappointing, for the whole structure of the outer corona we have -alluded to is missed altogether, the plate having taken no impression -of it. - -A drawing (Fig. 32) made by another observer, Mr. M’Leod, at -Springfield, represents more of the outer structure; but the reader -must remember that all drawings must, in the nature of the case (since -there are but two or three minutes to sketch in), be incomplete, -whatever the artist’s skill. - -[Illustration: FIG. 34.--WATSON’S NAKED-EYE DRAWING OF CORONA OF 1870. -(U. S. COAST SURVEY REPORT.)] - -Up to this time it was still doubtful, not only what the corona -was, but where it was; whether it was a something about the sun or -moon, or whether, indeed, it might not be in our own atmosphere. The -spectroscopic observations of Professors Young and Harkness at this -same eclipse of a green line in its spectrum, due to some glowing -gas, showed conclusively that it was largely, at any rate, a solar -appendage, and partly, at least, self-luminous; and these and other -results having awakened general discussion among astronomers in Europe -as well as at home, the United States Government sent an expedition, -under the direction of the late Professor Pierce, to observe an eclipse -which in the next year, on Dec. 8, 1870, was total in the south of -Spain. There were three parties; and of the most western of these, -which was at Xeres under the charge of Professor Winlock, I was a -member. - -[Illustration: FIG. 35.--PHOTOGRAPH SHOWING COMMENCEMENT OF OUTER -CORONA. - -(ROYAL ASTRONOMICAL SOCIETY’S MEMOIRS.)] - -The duration of totality was known beforehand. It would last two -minutes and ten seconds, and to secure what could be seen in this brief -interval we crossed the ocean. Our station was in the midst of the -sherry district, and a part of the instruments were in an orange-grove, -where the ground was covered with the ripe fallen fruit, while the -olive and vine about us in December reminded us of the distance we had -come to gather the results of so brief an opportunity. - -To prepare for it, we had all arrived on the ground some weeks -beforehand, and had been assiduously busy in installing the -apparatus in the observing camp, which suggested that of a small -army, the numerous instruments, some of them of considerable -size,--equatorials, photographic apparatus, polariscopes, photometers, -and spectroscopes,--being under tents, the fronts of which could be -lifted when the time came for action. - -To the equatorial telescopes photographic cameras are attached instead -of the eye-pieces, in the hope that the corona may be made to impress -itself on the plate instead of on the eye. The eye is an admirable -instrument itself, no doubt; but behind it is a brain, perhaps -overwrought with excitement, and responding too completely to the -nervous tension which most of us experience when those critical moments -are passing so rapidly. The camera can see far less of the corona than -the man, _but it has no nerves_, and what it sets down we may rely on. - -At such a time each observer has some particular task assigned to -him, on which, if wise, he has drilled himself for weeks beforehand, -so that no hesitation or doubt may arise in the moment of action; and -his attention is expected to be devoted to this duty alone, which may -keep him from noting any of the features which make the occasion so -impressive as a spectacle. Most of my own particular work was again of -a kind which would not interest the reader. - -Apart from this, I can recall little but the sort of pain of -expectation, as the moment approached, till within a minute before -totality the hum of voices around ceased, and an utter and most -impressive silence succeeded, broken only by a low “Ah!” from the group -without the camp, when the moment came. I remember that the clouds, -which had hung over the sun while the moon was first advancing on its -body, cleared away before the instant of totality, so that the last -thing I saw was a range of mountains to the eastward still bright -in the light; then, the next moment, the shadow rushed overhead and -blotted out the distant hills, almost before I could turn my face to -the instrument before me. - -[Illustration: FIG. 36.--ECLIPSE OF 1857, DRAWING BY LIAIS. (ROYAL -ASTRONOMICAL SOCIETY’S MEMOIRS.)] - -The corona appeared to me a different thing from what it did the year -before. It was apparently confined to a pearly light of a roughly -quadrangular shape, close to the limb of the sun, broken by dark rifts -(one of which was a conspicuous object); while within, and close to -the limb, was what looked like a mountain rising from the hidden sun, -of the color of the richest tint we should see in a rose-leaf held up -against the light, while others were visible of an orange-scarlet. -After a short scrutiny I turned to my task of analyzing the nature of -the white light. - -The seconds fled, the light broke out again, and so did the hubbub -of voices,--it was all over, and what had been missed then could not -be recovered. The sense of self-reproach for wasted opportunity is -a common enough feeling at this time, though one may have done his -best, so little it seems to each he has accomplished; but when all the -results had been brought together, we found that the spectroscopes, -cameras, and polariscopes had each done their work, and the journey had -not been taken in vain. In one point only we all differed, and this -was about the direct ocular evidence, for each seemed to have seen a -different corona, and the drawings of it were singularly unlike. Here -are two (Figs. 33 and 34) taken at this eclipse at the same time, -and from neighboring stations, by two most experienced astronomers, -Tacchini and Watson. No one could guess that they represented the same -object, and a similar discrepancy was common. - -[Illustration: FIG. 37.--ENLARGEMENT OF PART OF FIG. 38.] - -Considering that these were trained experts, whose special task it -was, in this case, to draw the corona, which therefore claimed their -undivided attention, I hardly know a more striking instance of the -fallibility of human testimony. The evidence of several observers, -however, pointed to the fact that the light really was more nearly -confined to the part next the sun than the year before, so that the -corona had probably changed during that interval, and grown smaller, -which was remarkable enough. The evidence of the polariscope, on the -whole, showed it to be partly due to reflected sunlight, while the -spectroscope in the hands of Professor Young confirmed the last year’s -observation, that it was also, and largely, self-luminous. Finally, -the photographs, taken at very distant stations, showed the same dark -rifts in the same place, and thus brought confirmatory evidence that -it was not a local phenomenon in our own atmosphere. A photograph of -it, taken by Mr. Brothers in Sicily, is the subject of the annexed -illustration (Fig. 35), in which the very bright lights which, owing to -“photographic irradiation,” seem to indent the moon, are chiefly due to -the colored flames I have spoken of, which will be described later. - -It may be observed that the photographs taken in the next year (1871) -were still more successful, and began to show still more of the -structure, whose curious forms, resembling large petals, had already -been figured by Liais. His drawing (Fig. 36), made in 1857, was -supposed to be rather a fanciful sketch than a trustworthy one; but, as -it will be seen, the photograph goes far to justify it. - -Figures 37 and 38 are copies published by Mr. Ranyard of the excellent -photographs obtained in 1871, which are perhaps as good as anything -done since, though even these do not show the outer corona. The first -is an enlargement of a small portion of the detail in the second. It is -scarcely possible for wood-engraving to reproduce the delicate texture -of the original. - -[Illustration: FIG. 38.--FAC-SIMILE OF PHOTOGRAPH OF CORONA OF 1871. - -(ROYAL ASTRONOMICAL SOCIETY’S MEMOIRS.)] - -The years brought round the eclipse of 1878, which was again in United -States territory, the central track (as Fig. 30 has already shown) -running directly over one of the loftiest mountains of the country, -Pike’s Peak, in Colorado. Pike’s Peak, though over fourteen thousand -feet high, is often ascended by pleasure tourists; but it is one thing -to stay there for an hour or two, and another to take up one’s abode -there and get acclimated,--for to do the latter we must first pass -through the horrors (not too strong a word) of mountain-sickness. -This reaches its height usually on the second or third day, and is -something like violent sea-sickness, complicated with the sensations -a mouse may be supposed to have under the bell of an air-pump. After -a week the strong begin to get over it, but none but the very robust -should take its chances, as we did, without preparation; for on the -night before the eclipse the life of one of our little party was -pronounced in danger, and he was carried down in a litter to a cabin at -an altitude of about ten thousand feet, where he recovered so speedily -as to be able to do good service on the following day. The summit -of the “Peak” is covered with great angular bowlders of splintered -granite, among which we laid logs brought up for firewood, and on -these, sacks of damp hay, then stretching a little tent over all and -tying it down with wire to the rocks, we were fain to turn in under -damp blankets, and to lie awake with incessant headache, drawing long, -struggling breaths in the vain attempt to get air, and wondering how -long the tent would last, as the canvas flapped and roared with a noise -like that of a loose sail in a gale at sea, with occasional intervals -of a dead silence, usually followed by a gust that shoved against the -tent with the push of a solid body, and if a sleepers shoulders touched -the canvas, shouldered him over in his bed. The stout canvas held, but -the snow entered with the wind and lay in a deep drift on the pillow, -when I woke after a brief sleep toward morning, and, looking out on the -gray dawn, found that the snow had turned to hail, which was rattling -sharply on the rocks with an accompaniment of thunder, which seemed to -roll from all parts of the horizon. The snow lay thick, and the sheets -of hail were like a wall, shutting out the sight of everything a few -rods off, and this was in July! I thought of my December station in -sunny Andalusia. - -[Illustration: FIG. 39.--“SPECTRES.”] - -Hail, rain, sleet, snow, fog, and every form of bad weather continued -for a week on the summit, while it was almost always clear below. -It was often a remarkable sight to go to the edge and look down. The -expanse of “the plains,” which stretched eastward to a horizon line -over a hundred miles distant, would be in bright sunshine beneath, -while the hail was all around and above us; and the light coming _up_ -instead of down gave singular effects when the clouds parted below, the -plains seeming at such times to be opalescent with luminous yellow and -green, as though the lower world were translucent, and the sun were -beneath it and shining up through. Fig. 39 is a picture of three of us -on the mountain-top, who saw a rarer spectacle; for directly opposite -the setting sun, and on the mist over the gulf beyond us, was a bright -ring, in whose centre were three phantom images of our three selves, -which moved as we moved, and then faded as the sun sank. It was “the -spectre of the Brocken.” These ghostly presentments were tolerably -defined, as in the sketch, but did not seem to be gigantic, as some -have described them. We rather thought them close at hand; but before -we could determine, the vision faded. - -The clouds, to our good fortune, rolled away on the 29th; and a -number of pleasure-seekers, who came up to view the eclipse and the -unwonted bright sunshine, made a scene which it was hard to identify -with the usual one. This time my business was to draw the corona; and -the extreme altitude and the clearness of the air, with perhaps some -greater extension than usual in the object itself, enabled it to be -followed to an unprecedented distance. During totality the sun was -surrounded by a narrow ring--hardly more than a line--of vivid light, -presenting no structure to the naked eye (but a remarkable one in -the telescope); and this faded with great suddenness into a circular -nebulous luminosity between two and three diameters of the sun wide, -but without such marked plumes, or filaments, as I had seen in 1869. -The most extraordinary thing, however, was a beam of light, inclined -at an angle of about forty-five degrees, about as wide as the sun, -and extending to the distance of nearly six of its diameters on one -side and over twelve on the other; on one side alone, that is, to the -amazing distance of over ten million miles from its body. Substantially -the same observation was made, as it appeared later, by Professor -Newcomb, at a lower level. The direction, when more carefully measured, -it was interesting to note, coincided closely with that of the Zodiacal -light, and a faint central rib added to its resemblance to that body. -It is noteworthy, in illustration of what has already been said as -to the conflict of ocular testimony, that though I, with the great -majority of observers below, saw only this beam, two witnesses whose -evidence is unimpeachable, Professors Young and Abbe, saw a pale beam -at right angles to it; and that one observer did not see the beam in -question at all. Fig. 40 is a sketch made from my own, but necessarily -on a scale which can show only its general features. - -With the telescope, the whole of the bright inner light close to the -sun was found to be made up of filaments, more definite even than those -described in a previous chapter as seen in sun-spots, and bristling in -all directions from the edge; not concealing each other, as we might -expect such things to do, upon a sphere, but fringing the sun’s edge in -definite outline, as though it were really but a disk. - -[Illustration: FIG. 40.--OUTER CORONA OF 1878. (U. S. NAVAL -OBSERVATORY.)] - -Those who were at leisure to watch the coming shadow of the moon -described its curved outline as distinctly visible on the plains. “A -rounded ball of darkness with an orange-yellow border,” one called -it. Those, again, who looked down on the bright clouds below say the -shadow was preceded by a yellow fringe, casting a bright light over -the clouds and passing into orange, pink, rose-red, and dark-red, in -about twenty seconds. This beautiful effect was noticed by nearly all -the amateur observers present, who had their attention at liberty, and -was generally unseen by the professional ones, who were shut up in dark -tents with photometers, or engaged otherwise than in admiring the glory -of the spectacle as a spectacle merely. This strange light, forming a -band of color about the shadow as seen from above, must have really -covered ten miles or more in width, and have occupied a considerable -fraction of a minute in passing over the heads of those below, to whom -it probably constituted that lurid light on their landscape I have -spoken of as so peculiar and “unnatural.” It seems to be due to the -colored flames round the sun, which shine out when its brighter light -is extinguished. I should add that on the summit of Pike’s Peak the -corona did not entirely disappear at the instant the sun broke forth -again, but that its outlying portions first went and then its brighter -and inner ones, till our eager gaze, trying to follow it as long as -possible, only after the lapse of some minutes saw the last of the -wonderful thing disappear and “fade into the light of common day.” - -[Illustration: FIG. 41.--SPECTROMETER SLIT AND SOLAR IMAGE. (FROM “THE -SUN,” BY YOUNG.)] - -There have been other eclipses since; but, in spite of all, our -knowledge of the corona remains very incomplete, and if the most -learned in such matters were asked what it was, he could probably -answer truthfully, “I don’t know.” - -[Illustration: FIG. 42.--SLIT AND PROMINENCES. - -(“THE SUN,” BY YOUNG.)] - -This will not be wondered at when it is considered that as total -eclipses come, about every other year, and continue, one with another, -hardly three minutes, an astronomer who should devote thirty years -exclusively to the subject, never missing an eclipse in whatever -quarter of the globe it occurred, would in that time have secured, -in all, something like three-quarters of an hour for observation. -Accordingly, what we know best about the corona is how it looks, what -it _is_ being still largely conjecture; and it is for this reason that -I have thought the space devoted to it would be best used by giving the -unscientific reader some idea of the visible phenomena as they present -themselves to an eyewitness. Treatises like Lockyer’s “Solar Physics,” -Proctor’s “The Sun,” Secchi’s “Le Soleil,” and Young’s “The Sun” (the -latter is most recent), will give the reader who desires to learn more -of the little that is known, the fuller information which this is not -the place for; but it may be said very briefly that it is certain that -the corona is at times of enormous extent (the whole length of the -longer beam seen on Pike’s Peak must have been over fourteen million -miles), that it almost certainly changes in its shape and dimensions -from year to year (possibly much oftener, but this we cannot yet -know), and that it shines partly by its own and partly by reflected -light. When we come to ask whether it is a gas or not, the evidence -is conflicting. The appearance of the green coronal line, and other -testimony we have not alluded to, would make it seem almost certain -that there must be a gas here of extreme tenuity, reaching the height -of some hundred thousand miles, at the least; while yet the fact that -such light bodies as comets have been known to pass through it, close -to the sun, without suffering any visible retardation, such as would -come even from a gas far lighter than hydrogen, appears to throw doubt -on evidence otherwise strong. It is possible to conceive of the corona, -and especially of the outer portion, as very largely made up of minute -particles such as form the scattered dust of meteoric trains, and this -seems to be the most probable constitution of its outlying parts. It -is even possible to conceive that it is in some degree a subjective -phenomenon, caused, as Professor Hastings has suggested, by diffraction -upon the edge of the moon,--the moon, that is, not merely serving as a -screen to the sun to reveal the corona, but partly _making_ the corona -by diffracting the light, somewhat as we see that the edge of any very -distant object screening the sun is gilded by its beams. This effect -may be seen when the sun rises or sets unusually clear, for objects on -the horizon partly hiding it are then fringed for a moment with a line -of light,--an appearance which has not escaped Shakspeare, where he -says,-- - - “But when from under this terrestrial ball - He fires the tall tops of the eastern pines.” - -Still, in admitting the possibility of some such contributory effect on -the part of the moon, we must not, of course, be understood as meaning -that the corona as a whole does not have a real existence, quite -independent of the changes which the presence of the moon may bring; -and in leaving the wonderful thing we must remember that it is, after -all, a reality, and not a phantasm. - -[Illustration: FIG. 43.--TACCHINI’S CHROMOSPHERIC CLOUDS. (“MEMORIE -DEGLI SPETTROSCOPISTI ITALIANI.”)] - -[Illustration: FIG. 44.--TACCHINI’S CHROMOSPHERIC CLOUDS. (“MEMORIE -DEGLI SPETTROSCOPISTI ITALIANI.”)] - -I have already described how, at the eclipse of 1870, I (with others) -saw within the corona what seemed like rose and scarlet-colored -mountains rising from the sun’s edge, an appearance which had first -been particularly studied in the eclipse of 1868, two years before, and -which, it might be added, Messrs. Lockyer and Janssen had succeeded in -observing without an eclipse by the spectroscope. Besides the corona, -it may be said, then, that the sun is surrounded by a thin envelope, -rising here and there into prominences of a rose and scarlet color, -invisible in the telescope, except at a total eclipse, but always -visible through the spectroscope. It is within and quite distinct -from the corona, and is usually called the “chromosphere,” being a -sort of sphere of colored fire surrounding the sun, but which we can -usually see only on the edge. “The appearance,” says Young, “is as if -countless jets of heated gas were issuing through vents and spiracles -over the whole surface, thus clothing it with flame, which heaves and -tosses like the blaze of a conflagration.” Out of this, then, somewhat -like greater waves or larger swellings of the colored fires, rise the -prominences, whose place, close to the sun’s edge, has been indicated -in many of the drawings and photographs just given of the corona, on -whose background they are seen during eclipses; but as they can be -studied at our leisure with the spectroscope, we have reserved a more -particular description of them till now. They are at all times directly -before us, as well as the corona; but while both are yet invisible from -the overpowering brightness of the sunlight reflected from the earth’s -atmosphere in front of them, these red flames are so far brighter than -the coronal background, that if we could only weaken this “glare” a -little, they at least might become visible, even if the corona were -not. The difficulty is evidently to find some contrivance which will -weaken the “glare” without enfeebling the prominences too; and this the -spectroscope does by diffusing the white sunlight, while it lets the -color pass nearly unimpaired. For the full understanding of its action -the reader must be referred to such works as those on the sun already -mentioned; but a general idea of it may be gathered, if we reflect -that white light is composed of every possible variety of colors, and -that the spectroscope, which consists essentially of a prism behind a -very narrow slit through which the light enters, lets any single color -pass freely, without weakening it or altering it in anything but its -direction, but gives a different direction to each, and hence sorts out -the tints, distributing them side by side, every one in its own place, -upon the long colored band called the spectrum. If this distribution -has spread the colors along a space a thousand times as wide as the -original beam, the average light must be just so much weaker than the -white light was, because this originally consisted of a thousand (let -us say a thousand, but it is really an infinite number) mingled tints -of blue, green, yellow, orange, and red, which have now been thus -distributed. If, however, we look through the prism at a rose-leaf, and -it has no blue, green, yellow, or orange in it, and nothing but pure -red, as each single color passes unchanged, this red will, according -to what has been said, be as bright after it has passed as before. All -depends, then, on the fact that these prominences do consist mainly -of light of one color, like the rose-leaf, so that this monochromatic -light will be seen through the spectroscope just as it is, while the -luminous veil of glaring white before it will seem to be brushed away. - -If a large telescope be directed toward the sun, the glass at the -farther end will, if we remove the eye-piece, form a little picture -of the sun, as a picture is formed in a camera-obscura; and now, if -we also fasten the spectroscope to this eye-end, where the observer’s -head would be were he looking through, the edge of the solar image may -be made to fall just _off_ the slit, so that only the light from the -prominences (and the white glare about them) shall pass in. To see -this more clearly, let us turn our backs to the sun and the telescope, -and look at the place where the image falls by the spectroscope slit, -which in Fig. 41 is drawn of its full size. This is a brass plate, -having a minute rectangular window, the “slit,” in it. The width of -this slit is regulated by a screw, and any rays falling into the -narrow aperture pass through the prism within, and finally fall on the -observer’s eye, but not till they have been sorted by the prism in -the manner described. Formed on the brass plate, just as it would be -formed on a sheet of paper, or anything else held in the focus, we see -the bright solar image, a circle of light perhaps an inch and a half -in diameter,--a miniature of the sun with its spots. The whole of the -sun (the photosphere) then is hidden to an observer who is looking up -through the slit from the other side, for, as the sun’s edge does not -quite touch the slit, none of its rays can enter it; but if there be -also the image here of a prominence, projecting beyond the edge, and -really overhanging the slit (though to us invisible on account of the -glare about it), these rays will fall into the slit and pass down to -the prism, which will dispose of it in the way already stated. - -[Illustration: FIG. 45.--VOGEL’S CHROMOSPHERIC FORMS. (“BEOBACHTUNGEN,” -DR. H. C. VOGEL.)] - -And now let us get to the other side, and, looking up through the prism -with the aid of a magnifying-glass, see what it has done for us (Fig. -42). The large rectangular opening here is the same as the small one -which was visible from the outside, only that it is now magnified, and -what was before invisible is seen; the edge of the sun itself is just -hidden, but the scarlet flames of the chromosphere have become visible, -with a cloudy prominence rising above them. The “flames” are flame-like -only in form, for their light is probably due not to any combustion, -but to the glow of intensely heated matter; and as its light is not -quite pure red, we can, by going to another part of the spectrum, see -the same thing repeated in orange, the effect being as though we had a -number of long narrow windows, some glazed with red, some with orange, -and some with other colors, through which we could look out at the -same clouds. I have looked at these prominences often in this way; but -I prefer, in the reader’s interest, to borrow from the description by -Professor Young, who has made these most interesting and wonderful -forms a special study. - -Let us premise that the depth of the crimson shell out of which they -rise is usually less than five thousand miles, and that though the -prominences vary greatly, the majority reach a height of nearly twenty -thousand miles, while in exceptional cases this is immensely exceeded. -Professor Young has seen one which grew to a height of three hundred -and fifty thousand miles in an hour and a half, and in half an hour -more had faded away. - -These forms fall into two main classes,--that of the quiet and -cloud-like, and that of the eruptive,--the first being almost exactly -in form like the clouds of our own sky, sometimes appearing to lie on -the limb of the sun like a bank of clouds on the horizon, sometimes -floating entirely free; while sometimes “the whole under surface is -fringed with down-hanging filaments, which remind one of a summer -shower hanging from a heavy thunder-cloud.” - -Here are some of the typical forms of the quieter ones:-- - -Fig. 43, by Tacchini, the Director of the Roman Observatory, represents -an ordinary prominence, or cloud-group in the chromosphere, whose -height is about twenty-five thousand miles. The little spires of flame -which rise, thick as grass-blades, everywhere from the surface, are -seen on its right and left. - -[Illustration: FIG. 46.--TACCHINI’S CHROMOSPHERIC FORMS. (“MEMORIE -DEGLI SPETTROSCOPISTI ITALIANI.”)] - -Fig. 44 (Tacchini) is one where the agitation is greater and the -“filamentary” type is more marked. Besides the curiously thread-like -forms (so suggestive of what we have already seen in the photosphere), -we have here what looks like an extended cloudy mass, drawn out by a -horizontally moving wind. - -Fig. 45 (by Vogel, at Bothkamp) represents another of these numerous -types. - -The extraordinary Fig. 46 is from another drawing, by Tacchini, of a -protuberance seen in 1871 (a time of great solar disturbance), and it -belongs to the more energetic of its class. - -[Illustration: FIG. 47.--ERUPTIVE PROMINENCES. (“THE SUN,” BY YOUNG.)] - -This fantastic cloud-shape, “if shape it might be called that shape had -none,” looking like some nightmare vision, was about fifty thousand -miles long and sixty thousand high above the surface. The reader will -notice also the fiery rain, like the drops from a falling rocket, and -may add to it all, in imagination, the actual color, which is of a deep -scarlet. - -It may add to the-interest such things excite, to know that they -have some mysterious connection with a terrestrial phenomenon,--the -aurora,--for the northern lights have been again and again noticed to -dance in company with these solar displays. - -The eruptive prominences are very different in appearance, as will be -seen by the next illustration, for which we are indebted to Professor -Young. - -In Fig. 47 we have a group of most interesting views by him (drawn -here on the common scale of seventy-five thousand miles to an inch), -illustrating the more eruptive types, of which we will let him speak -directly. The first shows a case of the vertical filaments, like those -rocket-drops we saw just, now in Tacchini’s drawing, but here more -marked; while the second (on the left side) is a cyclone-form, where -the twisted stems suggest what we have seen before in the “bridges” of -sun-spots, and below this is another example of filamentary forms. - -The upper one, on the right, is the view of a cloud prominence as it -appeared at _half-past twelve_ o’clock, on Sept. 7, 1871. Below it is -the same prominence at _one_ o’clock (half an hour later), when it -has been shattered by some inconceivable explosion, blowing it into -fragments, and driving the hydrogen to a height of two hundred thousand -miles. The lowest figure on the right shows another case where inclined -jets (of hydrogen) were seen to rise to a height of fifty thousand -miles. - -Professor Young says of these:-- - - “Their form and appearance change with great rapidity, so that - the motion can almost be seen with the eye. Sometimes they - consist of pointed rays, diverging in all directions, like - hedgehog-spines. Sometimes they look like flames; sometimes like - sheaves of grain; sometimes like whirling water-spouts, capped - with a great cloud; occasionally they present most exactly the - appearance of jets of liquid fire, rising and falling in graceful - parabolas; frequently they carry on their edges spirals like the - volutes of an Ionic column; and continually they detach filaments - which rise to a great elevation, gradually expanding and growing - fainter as they ascend, until the eye loses them. There is no end - to the number of curious and interesting appearances which they - exhibit under varying circumstances. The velocity of the motions - often exceeds a hundred miles a second, and sometimes, though - very rarely, reaches two hundred miles.” - -In the case of the particular phenomenon recorded by Professor Young in -the last illustration, Mr. Proctor, however, has calculated that the -initial velocity probably exceeded five hundred miles a second, which, -except for the resistance experienced by the sun’s own atmosphere, -would have hurled the ejected matter into space entirely clear of the -sun’s power to recall it, so that it would never return. - -It adds to our interest in these flames to know that they at least are -connected with that up-rush of heated matter from the sun’s interior, -forming a part of the circulation which maintains both the temperature -of its surface and that radiation on which all terrestrial life -depends. The flames, indeed, add of themselves little to the heat the -sun sends us, but they are in this way the outward and visible signs of -a constant process within, by which we live; and so far they seem to -have a more immediate interest to us, though invisible, than the corona -which surrounds them. But we must remember when we lift our eyes to the -sun that this latter wonder is really there, whether man sees it or -not, and that the cause of its existence is still unknown. - -We ask for its “object” perhaps with an unconscious assumption that the -whole must have been in some way provided to subserve _our_ wants; but -there is not as yet the slightest evidence connecting its existence -with any human need or purpose, and as yet we have no knowledge that, -in this sense, it exists to any “end” at all. “As the thought of man is -widened with the process of the suns,” let us hope that we shall one -day know more. - - - - -III. - -THE SUN’S ENERGY. - - -“It is indeed,” says good Bishop Berkeley, “an opinion strangely -prevailing amongst men that ... all sensible objects have an existence -... distinct from their being perceived by the understanding. But -... some truths there are, so near and obvious to the mind, that a -man need only open his eyes to see them. Such I take this important -one to be, namely, that all the choir of heaven and furniture of the -earth--in a word, all those bodies which compose the mighty frame of -the world--have not any subsistence without a mind.” - -We are not going to take the reader along “the high priori road” of -metaphysics, but only to speak of certain accepted conclusions of -modern experimental physics, which do not themselves, indeed, justify -all of Berkeley’s language, but to which these words of the author of -“A New Theory of Vision” seem to be a not unfit prelude. - -When we see a rose-leaf, we see with it what we call a color, and we -are apt to think it is in the rose. But the color is in _us_, for it is -a sensation which something coming from the sun excites in the eye; so -that if the rose-leaf were still there, there would be no color unless -there were an eye to receive and a brain to interpret the sensation. -Every color that is lovely in the rainbow or the flower, every hue -that is vivid in a ribbon or sombre in the grave harmonies of some -old Persian rug, the metallic lustre of the humming-bird or the sober -imperial yellow of precious china,--all these have no existence as -color apart from the seeing eye, and all have their fount and origin in -the sun itself. - -“Color” and “light,” then, are not, properly speaking, external things, -but names given to the sensations caused by an uncomprehended something -radiated from the sun, when this falls on our eyes. If this very same -something falls on our face, it produces another kind of sensation, -which we call “heat,” or if it falls on a thermometer it makes it rise; -while if it rests long on the face it will produce yet another effect, -“chemical action,” for it will _tan_ the cheek, producing a chemical -change there; or it will do the like work more promptly if it meet a -photographic plate. If we bear in mind that it is the identically same -thing (whatever that is) which produces all these diverse effects, we -see, some of us perhaps for the first time, that “color,” “light,” -“radiant heat,” “actinism,” etc., are only names given to the diverse -effects of some thing, not things themselves; so that, for instance, -all the splendor of color in the visible world _exists only in the -eye that sees it_. The reader must not suppose that he is here being -asked to entertain any metaphysical subtlety. We are considering a fact -almost universally accepted within the last few years by physicists, -who now generally admit the existence of a something coming from the -sun, which is not itself light, heat, or chemical action, but of which -these are effects. When we give this unknown thing a name, we call it -“radiant energy.” - -How it crosses the void of space we cannot be properly said to know, -but all the phenomena lead us to think it is in the form of motion -in some medium,--somewhat (to use an imperfect analogy) like the -transmission through the air of the vibrations which will cause sound -when they reach an ear. This, at any rate, is certain, that there is an -action of some sort incessantly going on between us and the sun, which -enables us to experience the effects of light and heat. We assume -it to be a particular mode of vibration; but whatever it is, it is -repeated with incomprehensible rapidity. Experiments recently made by -the writer show that the _slower_ heat vibrations which reach us from -the sun succeed each other nearly 100,000,000,000,000 times in a single -second, while those which make us see, have long been known to be more -rapid still. These pass outward from the sun in every direction, in -ever-widening spheres; and in them, so far as we know, lies the potency -of life for the planet upon whose surface they fall. - -Did the reader ever consider that next to the mystery of gravitation, -which draws all things on the earth’s surface down, comes that -mystery--not seen to be one because so familiar--of the occult force -in the sunbeams which lifts things _up_? The incomprehensible energy -of the sunbeam brought the carbon out of the air, put it together in -the weed or the plant, and lifted each tree-trunk above the soil. The -soil did not lift it, any more than the soil in Broadway lifted the -spire of Trinity. Men brought stones there in wagons to build the -church, and the sun brought the materials in its own way, and built up -alike the slender shaft that sustains the grass blade and the column -of the pine. If the tree or the spire fell, it would require a certain -amount of work of men or horses or engines to set it up again. So much -actual work, at least, the sun did in the original building; and if we -consider the number of trees in the forest, we see that this alone is -something great. But besides this, the sun locked up in each tree a -store of energy thousands of times greater than that which was spent in -merely lifting the trunk from the ground, as we may see by unlocking -it again, when we burn the tree under the boiler of an engine; for it -will develop a power equal to the lifting of thousands of its kind, -if we choose to employ it in this way. This is so true, that the tree -may fall, and turn to coal in the soil, and still keep this energy -imprisoned in it,--keep it for millions of years, till the black lump -under the furnace gives out, in the whirling spindles of the factory or -the turning wheel of the steamboat, the energy gathered in the sunshine -of the primeval world. - -The most active rays in building up plant-life are said to be the -yellow and orange, though Nature’s fondness for green everywhere is -probably justified by some special utility. At any rate, the action -of these solar rays is to decompose the products of combustion, to -set free the oxygen, and to fix the carbon in the plant. Perhaps -these words do not convey a definite meaning to the reader, but it -is to be hoped they will, for the statement they imply is wonderful -enough. Swift’s philosopher at Laputa, who had a project for extracting -sunbeams out of cucumbers, was wiser than his author knew; for -cucumbers, like other vegetables, are now found to be really in large -part put together by sunbeams, and sunbeams, or what is scarcely -distinguishable from such, could with our present scientific knowledge -be extracted from cucumbers again, only the process would be too -expensive to pay. The sunbeam, however, does what our wisest chemistry -cannot do: it takes the burned out ashes and makes them anew into green -wood; it takes the close and breathed out air, and makes it sweet and -fit to breathe by means of the plant, whose food is the same as our -poison. With the aid of sunlight a lily would thrive on the deadly -atmosphere of the “black hole of Calcutta;” for this bane to us, we -repeat, is vital air to the plant, which breathes it in through all its -pores, bringing it into contact with the chlorophyl, its green blood, -which is to it what the red blood is to us; doing almost everything, -however, by means of the sun ray, for if this be lacking, the oxygen is -no longer set free or the carbon retained, and the plant dies. This too -brief statement must answer instead of a fuller description of how the -sun’s energy builds up the vegetable world. - -But the ox, the sheep, and the lamb feed on the vegetable, and we in -turn on them (and on vegetables too); so that, though we might eat -our own meals in darkness and still live, the meals themselves are -provided literally at the sun’s expense, virtue having gone out of him -to furnish each morsel we put in our mouths. But while he thus prepares -the material for our own bodies, and while it is plain that without him -we could not exist any more than the plant, the processes by which he -acts grow more intricate and more obscure in our own higher organism, -so that science as yet only half guesses how the sun makes us. But the -making is done in some way by the sun, and so almost exclusively is -every process of life. - -It is not generally understood, I think, how literally true this is -of every object in the organic world. In a subsequent illustration -we shall see a newspaper being printed by power directly and visibly -derived from the sunbeam. But all the power derived from coal, and all -the power derived from human muscles, comes originally from the sun, -in just as literal a sense; for the paper on which the reader’s eye -rests was not only made primarily from material grown by the sun, but -was stitched together by derived sun-power, and by this, also, each -page was printed, so that the amount of this solar radiation expended -for printing each chapter of this book could be stated with approximate -accuracy in figures. To make even the reader’s hand which holds this -page, or the eye which sees it, energy again went out from the sun; and -in saying this I am to be understood in the plain and common meaning of -the words. - -Did the reader ever happen to be in a great cotton-mill, where many -hundreds of operatives watched many thousands of spindles? Nothing is -visible to cause the multiplied movement, the engine being perhaps away -in altogether another building. Wandering from room to room, where -everything is in motion derived from some unseen source, he may be -arrested in his walk by a sudden cessation of the hum and bustle,--at -once on the floor below, and on that above, and all around him. The -simultaneousness of this stoppage at points far apart when the steam -is turned off, strikes one with a sense of the intimate dependence of -every complex process going on upon some remote invisible motor. The -cessation is not, however, absolutely instantaneous; for the great -fly-wheel, in which a trifling part of the motor power is stored, makes -one or two turns more, till the energy in this also is exhausted, -and all is still. The coal-beds and the forests are to the sun what -the fly-wheel is to the engine: all their power comes from him; they -retain a little of it in store, but very little by comparison with the -original; and were the change we have already spoken of to come over -the sun’s circulation,--were the solar engine disconnected from us,--we -could go on perhaps a short time at the cost of this store, but when -this was over it would be over with us, and all would be still here too. - -Is there not a special interest for us in that New Astronomy which -considers these things, and studies the sun, not only in the heavens as -a star, but in its workings here, and so largely in its relations to -man? - - * * * * * - -Since, then, we are the children of the sun, and our bodies a product -of its rays, as much as the ephemeral insects that its heat hatches -from the soil, it is a worthy problem to learn how things earthly -depend upon this material ruler of our days. But although we know it -does nearly all things done on the earth, and have learned a little of -the way it builds up the plant, we know so little of the way it does -many other things here that we are still often only able to connect the -terrestrial effect with the solar cause by noting what events happen -together. We are in this respect in the position of our forefathers, -who had not yet learned the science of electricity, but who noted -that when a flash of lightning came a clap of thunder followed, and -concluded as justly as Franklin or Faraday could have done that there -was a physical relation between them. Quite in this way, we who are in -a like position with regard to the New Astronomy, which we hope will -one day explain to us what is at present mysterious in our connection -with the sun, can as yet often only infer that when certain phenomena -there are followed or accompanied by others here, all are really -connected as products of one cause, however dissimilar they may look, -and however little we know what the real connection may be. - -There is no more common inquiry than as to the influence of sun-spots -on the weather; but as we do not yet know the real nature of the -connection, if there be any, we can only try to find out by assembling -independent records of sun-spots and of the weather here, and noticing -if any changes in the one are accompanied by changes in the other; to -see, for instance, if when sun-spots are plenty the weather the world -over is rainy or not, or to see if when an unusual disturbance breaks -out in a sun-spot any terrestrial disturbance is simultaneously noted. - -[Illustration: FIG. 48.--SUN-SPOTS AND PRICE OF GRAIN. (FROM -“OBSERVATIONS OF SOLAR SPOTS.”)] - -When we remember how our lives depend on a certain circulation in -the sun, of which the spots appear to be special examples, it is of -interest not only to study the forms within them, as we have already -been doing here, but to ask whether the spots themselves are present -as much one year as another. The sun sometimes has numerous spots on -it, and sometimes none at all; but it does not seem to have occurred to -any one to see whether they had any regular period for coming or going, -till Schwabe, a magistrate in a little German town, who happened to -have a small telescope and a good deal of leisure, began for his own -amusement to note their number every day. He commenced in 1826, and -with German patience observed daily for forty years. He first found -that the spots grew more numerous in 1830, when there was no single -day without one; then the number declined very rapidly, till in 1833 -they were about gone; then they increased in number again till 1838, -then again declined; and so on, till it became evident that sun-spots -do not come and go by chance, but run through a cycle of growth and -disappearance, on the average about once in every eleven years. While -amusing himself with his telescope, an important sequence in Nature had -thus been added to our knowledge by the obscure Hofrath Schwabe, who -indeed compares himself to Saul, going out to seek his father’s asses -and finding a kingdom. Old records made before Schwabe’s time have -since been hunted up, so that we have a fairly connected history of the -sun’s surface for nearly a hundred and fifty years; and the years when -spots will be plentiful or rare can now be often predicted from seeing -what has been in the past. Thus I may venture to say that the spots, so -frequent in 1885, will have probably nearly disappeared in 1888, and -will be probably very plentiful in 1894. I do not know at all why this -is likely to happen; I only know that it has repeatedly happened at -corresponding periods in the past. - -“Now,” it may be asked, “have these things any connection with weather -changes, and is it of any practical advantage to know if they have?” - -Would it be, it may be answered, of any practical interest to a -merchant in bread-stuffs to have private information of a reliable -character that crops the world over would be fine in 1888 and fail in -1894? The exclusive possession of such knowledge might plainly bring -“wealth beyond the dreams of avarice” to the user; or, to ascend -from the lower ground of personal interest to the higher aims of -philanthropy and science, could we predict the harvests, we should -be armed with a knowledge that might provide against coming years of -famine, and make life distinctly happier and easier to hundreds of -millions of toilers on the earth’s surface. - -“But can we predict?” We certainly cannot till we have, at any rate, -first shown that there is a connection between sun-spots and the -weather. Since we know nothing of the ultimate causes involved, we can -only at present, as I say, collect records of the changes there, and -compare them with others of the changes here, to see if there is any -significant coincidence. To avoid columns of figures, and yet to enable -the reader to judge for himself in some degree of the evidence, I will -give the results of some of these records represented graphically by -curves, like those which he may perhaps remember to have seen used to -show the fluctuations in the value of gold and grain, or of stocks in -the stock-market. It is only fair to say that mathematicians used this -method long before it was ever heard of by business men, and that the -stockbrokers borrowed it from the astronomers, and not the astronomers -from them. - -In Fig. 48, from Carrington’s work, each horizontal space represents -ten years of time, and the figures in the upper part represent the -fluctuations of the sun-spot curve. In the middle curve, variations -in vertical distances correspond to differences in the distance from -the sun of the planet Jupiter, the possibility of whose influence -on sun-spot periods can thus be examined. In the third and lowest, -suggested by Sir William Herschel, the figures at the side are -proportional to the price of wheat in the English market, rising when -wheat ruled high, falling when it was cheap. In all three curves -one-tenth of a horizontal spacing along the top or bottom corresponds -to one year; and in this way we have at a glance the condensed result -of observations and statistics for sixty years, which otherwise stated -would fill volumes. The result is instructive in more ways than one. -The variations of Jupiter’s distance certainly do present a striking -coincidence with the changes in spot frequency, and this may indicate -a real connection between the phenomena; but before we decide that -it does so, we must remember that the number of cycles of change -presented by the possible combination of planetary periods is all but -infinite. Thus we might safely undertake, with study enough, to find a -curve, depending solely on certain planetary configurations, which yet -would represent with quite striking agreement for a time the rise and -fall in any given railroad stock, the relative numbers of Democratic -and Republican congressmen from year to year, or anything else with -which the heavenly bodies have in reality as little to do. The third -curve (meant by the price of wheat to test the possible influence of -sun-spots on years of good or bad harvests) is not open to the last -objection, but involves a fallacy of another kind. In fact the price -of wheat depends on many things quite apart from the operations of -Nature,--on wars and legislation, for instance; and here the great -rise in the first years of the century is as clearly connected with the -great continental wars of the first Napoleon, which shut up foreign -ports, as the sudden fall about 1815, the year of Waterloo, is with -the subsequent peace. Meanwhile an immense amount of labor has been -spent in making tables of the weather, and of almost every conceivable -earthly phenomenon which may be supposed to have a similar periodic -character, with very doubtful success, nearly every one having brought -out some result which might be plausible if it stood alone, but which -is apt to be contradicted by the others. For instance, Mr. Stone, -at the Cape of Good Hope, and Dr. Gould, in South America, consider -that the observations taken at those places show a little diminution -of the earth’s temperature (amounting to one or two degrees) at a -sun-spot maximum. Mr. Chambers concludes, from twenty-eight years’ -observations, that the hottest are those of most sun-spots. So each of -these contradicts the other. Then we have Gelinck, who, from a study of -numerous observations, concludes that all are wrong together, and that -there is really no change in either way. - -[Illustration: FIG. 49.--SUN-SPOT OF NOV. 16, 1882, AND EARTH.] - -I might go on citing names with no better result. One observer -tabulates observations of terrestrial temperature, or rain-fall, or -barometer, or ozone; another, the visitations of Asiatic cholera; while -still another (the late Professor Jevons) tabulates commercial crises -with the serious attempt to find a connection between the sun-spots and -business panics. Of making such cycles there is no end, and much study -of them would be a weariness I will not inflict. - -[Illustration: FIG. 50.--GREENWICH RECORD OF DISTURBANCE OF MAGNETIC -NEEDLE, NOV. 16 AND 17, 1882.] - -Our own conclusion is, that from such investigations of terrestrial -changes nothing is yet certainly known with regard to the influence -of sun-spots on the weather. There is, however, quite another way; -that is, to measure their effect at the origin in the sun itself. -The sun-spot is cooler than the rest of the surface, and it might be -thought that when there are many the sun would give less heat. As far -as the spots themselves are concerned, this is so, but in a very small -degree. I have been able to ascertain how much this deprivation of heat -amounts to, and find it is a real but a most insignificant quantity, -rising to about two-thirds of one degree Fahrenheit every eleven -years. This, it will be remembered, is the direct effect of the spots -considered merely as so many cool patches on the surface, and it does -not imply that when there are most spots the sun will necessarily give -less heat. In fact there may be a compensating action accompanying them -which makes the radiation greater than when they are absent. I will not -enter on a detailed explanation, but only say that in the best judgment -I can form by a good deal of study and direct experiment, there is no -certain evidence that the sun is hotter at one time than at another. - -If we investigate, however, the connection between spots and -terrestrial magnetic disturbances, we shall find altogether more -satisfactory testimony. This evidence is of all degrees of strength, -from probability up to what may be called certainty, and it is always -obtained, not by _a priori_ reasoning, but by the comparison of -independent observations of something which has happened on the sun and -on the earth. We will first take an instance of what we consider the -weakest degree of evidence (weak, that is, when any such single case -is considered), and we do so by simply quoting textually three records -which were made at nearly the same time in different parts of the world -in 1882. - -A certain spot had been visible on the sun at intervals for some weeks; -but when on the 16th of November a glimpse was caught of it after -previous days of cloudy weather, the observer, it will be seen, is -struck by the great activity going on in it, and, though familiar with -such sights, describes this one as “magnificent.” - -1. From the daily record at the Allegheny Observatory, November 16, -1882:-- - - “Very large spot on the sun; ... great variety of forms; inrush - from S. E. to S. W.; tendency to cyclonic action at several - points. The spot is apparently near its period of greatest - activity. A magnificent sight.” - -At the same time a sketch was commenced which was interrupted by the -cloudy weather of this and following days. The outline of the main spot -only is here given (Fig. 49). Its area, as measured at Allegheny, was -2,200,000,000 square miles; at Greenwich its area, inclusive of some -outlying portions, was estimated on the same day to be 2,600,000,000 -square miles. The earth is shown of its relative size upon it, to give -a proper idea of the scale. - -2. From the “New York Tribune” of November 18th (describing what took -place in the night preceding the 17th):-- - - - AN ELECTRIC STORM. - - TELEGRAPH WIRES GREATLY AFFECTED. - - THE DISTURBANCE WIDE-SPREAD. - - ... At the Mutual Union office the manager said, “Our wires are - all running, but very slowly. There is often an intermission of - from one to five minutes between the words of a sentence. The - electric storm is general as far as our wires are concerned.”... - The cable messages were also delayed, in some cases as much as an - hour. - - The telephone service was practically useless during the day. - - WASHINGTON, _Nov. 17_.--A magnetic storm of more than usual - intensity began here at an early hour this morning, and has - continued with occasional interruptions during the day, - seriously interfering with telegraphic communication.... As - an experiment one of the wires of the Western Union Telegraph - Company was worked between Washington and Baltimore this - afternoon with the terrestrial current alone, the batteries - having been entirely detached. - - CHICAGO, _Nov. 17_.--An electric storm of the greatest violence - raged in all the territory to points beyond Omaha.... The - switch-board here has been on fire a dozen times during the - forenoon. At noon only a single wire out of fifteen between this - city and New York was in operation. - -And so on through a column. - -3. In Fig. 50 we give a portion of the automatic trace of the magnetic -needles at Greenwich.[3] These needles are mounted on massive piers in -the cellars of the observatory, far removed from every visible source -of disturbance, and each carries a small mirror, whence a spot of light -is reflected upon a strip of photographic paper, kept continually -rolling before it by clock-work. If the needle is still, the moving -strip of paper will have a straight line on it, traced by the point of -light, which is in this case motionless. If the needle swings to the -right or left, the light-spot vibrates with it, and the line it traces -becomes sinuous, or more and more sharply zigzagged as the needle -shivers under the unknown forces which control it. - - [3] It appears here through the kindness of the Astronomer - Royal. We regret to say that American observers are - dependent on the courtesy of foreign ones in such matters, - the United States having no observatory where such records - of sun-spots and magnetic variation are systematically kept. - -The upper part of Fig. 50 gives a little portion of this automatic -trace on November 16th before the disturbance began, to show the -ordinary daily record, which should be compared with the violent -perturbation occurring simultaneously with the telegraphic disturbance -in the United States. We may, for the reader’s convenience, remark -that as the astronomical day begins twelve hours later than the civil -day, the approximate Washington mean times, corresponding to the -Greenwich hours after twelve, are found by adding one to the days and -subtracting seventeen from the hours. Thus “November 16th, twenty-two -hours” corresponds in the eastern United States nearly to five o’clock -in the morning of November 17th. - -The Allegheny observer, it will be remembered, in his glimpse of the -spot on November 16th, was struck with the great activity of the -internal motions then going on in it. The Astronomer Royal states that -a portion of the spot became detached on November 17th or 18th, and -that several small spots which broke out in the immediate neighborhood -were seen for the first time on the photographs taken November 17th, -twenty-two hours. - -“Are we to conclude from this,” it may be asked, “that what went on -in the sun was the cause of the trouble on the telegraph wires?” I -think we are not at all entitled to conclude so from this instance -_alone_; but though in one such case, taken by itself, there is nothing -conclusive, yet when such a degree of coincidence occurs again and -again, the habitual observer of solar phenomena learns to look with -some confidence for evidence of electrical disturbance here following -certain kinds of disturbance there, and the weight of this part of the -evidence is not to be sought so much in the strength of a single case, -as in the multitude of such coincidences. - -We have, however, not only the means of comparing sun-spot _years_ with -years of terrestrial electric disturbance, but individual instances, -particular _minutes_ of sun-spot changes, with particular minutes of -terrestrial change; and both comparisons are of the most convincing -character. - -First, let us observe that the compass needle, in its regular and -ordinary behavior, does not point constantly in any one direction -through the day, but moves a very little one way in the morning, and -back in the afternoon. This same movement, which can be noticed even -in a good surveyor’s compass, is called the “diurnal oscillation,” -and has long been known. It has been known, too, that its amount -altered from one year to another; but since Schwabe’s observations it -has been found that the changes in this variation and in the number -of the spots went on together. The coincidences which we failed to -note in the comparison of the spots with the prices of grain are here -made out with convincing clearness, as the reader will see by a simple -inspection of this chart (Fig. 51, taken from Professor Young’s work), -where the horizontal divisions still denote years, and the height of -the continuous curve the relative number of spots, while the height of -the dotted curve is the amount of the magnetic variation. Though we -have given but a part of the curve, the presumption from the agreement -in the forty years alone would be a strong one that the two effects, -apparently so widely remote in their nature, are really due to a common -cause. - -[Illustration: FIG. 51.--SUN-SPOTS AND MAGNETIC VARIATIONS.] - -Here we have compared years with years; let us next compare minutes -with minutes. Thus, to cite (from Mr. Proctor’s work) a well-known -instance: On Sept. 1, 1869, at eighteen minutes past eleven, Mr. -Carrington, an experienced solar observer, suddenly saw in the sun -something brighter than the sun,--two patches of light, breaking out so -instantly and so intensely that his first thought was that daylight -was entering through a hole in the darkening screen he used. It was -immediately, however, made certain that something unusual was occurring -in the sun itself, across which the brilliant spots were moving, -travelling thirty-five thousand miles in five minutes, at the end of -which time (at twenty-three minutes past eleven) they disappeared from -sight. By good fortune, another observer a few miles distant saw and -independently described the same phenomenon; and as the minute had been -noted, it was immediately afterward found that recording instruments -registered a magnetic disturbance at the same time,--“at the very -moment,” says Dr. Stewart, the director of the observatory at Kew. - -“By degrees,” says Sir John Herschel, “accounts began to pour in of -... great electro-magnetic disturbances in every part of the world.... -At Washington and Philadelphia, in America, the telegraphic signal men -received severe electric shocks. At Boston, in North America, a flame -of fire followed the pen of Bain’s electric telegraph.” (Such electric -disturbances, it may be mentioned, are called “electric storms,” though -when they occur the weather may be perfectly serene to the eye. They -are shown also by rapid vibrations of the magnetic needle, like those -we have illustrated.) - -On Aug. 3, 1872, Professor Young, who was observing at Sherman in the -Rocky Mountains, saw three notable paroxysms in the sun’s chromosphere, -jets of luminous matter of intense brilliance being projected at 8h. -45m., 10h. 30m., and 11h. 50m. of the local time. “At dinner,” he -says, “the photographer of the party, who was making our magnetic -observations, told me, before knowing anything about what I had been -observing, that he had been obliged to give up work, his magnet having -swung clear off the limb.” Similar phenomena were observed August 5th. -Professor Young wrote to England, and received from Greenwich and -Stonyhurst copies of the automatic record, which he gives, and which -we give in Fig. 52. After allowing for difference of longitude, the -reader who will take the pains to compare them may see for himself that -both show a jump of the needles in the cellars at Greenwich at the same -_minute_ in each of the four cases of outburst in the Rocky Mountains. - -[Illustration: FIG. 52.--GREENWICH MAGNETIC OBSERVATIONS, AUG. 3 AND 5, -1872.] - -While we admit that the evidence in any single case is rarely so -conclusive as in these; while we agree that the spot is not so much -the cause of the change as the index of some other solar action which -does cause it; and while we fully concede our present ignorance of -the nature of this cause,--we cannot refuse to accept the cumulative -evidence, of which a little has been submitted. - -It is only in rare cases that we can feel quite sure; and yet, in -regard even to one of the more common and less conclusive ones, we -may at least feel warranted in saying that if the reader forfeited -a business engagement or missed an invitation to dinner through the -failure of the telegraph or telephone on such an occasion as that of -the 17th of November, 1882, the far-off sun-spot was not improbably -connected with the cause. - -Probably we should all like to hear some at least equally positive -conclusion about the weather also, and to learn that there was a -likelihood of our being able to predict it for the next year, as the -Signal Service now does for the next day; but there is at present -no such likelihood. The study of the possible connection between -sun-spots and the weather is, nevertheless, one that will always have -great interest to many; for even if we set its scientific aim aside -and consider it in its purely utilitarian aspect, it is evident that -the knowledge how to predict whether coming harvests would be good or -bad, would enable us to do for the whole world what Joseph’s prophetic -vision of the seven good and seven barren years did for the land of -Egypt, and confer a greater power on its discoverer than any sovereign -now possesses. There is something to be said, then, for the cyclists; -for if their zeal does sometimes outrun knowledge, their object is a -worthy one, and their aims such as we can sympathize with, and of which -none of us can say that there is any inherent impossibility in them, -or that they may not conceivably yet lead to something. Let us not, -then, treat the inquirer who tries to connect panics on ‘Change with -sun-spots as a mere lunatic; for there is this amount of reason in his -theory, that the panics, together with the general state of business, -are connected in some obscure way with the good or bad harvests, and -these again in some still obscurer way with changes in our sun. - -We may leave, then, this vision of forecasting the harvests and the -markets of the world from a study of the sun, as one of the fair dreams -for the future of our science. Perhaps the dream will one day be -realized. Who knows? - - - - -IV. - -THE SUN’S ENERGY (_Continued_). - - -If we paused on the words with which our last chapter closed, the -reader might perhaps so far gather an impression that the whole -all-important subject of the solar energy was involved in mystery and -doubt. But if it be indeed a mystery when considered in its essence, so -are all things; while regarded separately in any one of its terrestrial -effects of magnetic or chemical action, or of light or heat, it may -seem less so. Since there is not room to consider all these aspects, -let us choose the last, and look at this energy in its familiar form of -the _heat_ by which we live. - -We, the human race, are warming ourselves at this great fire which -called our bodies into being, and when it goes out we shall go too. -What is it? How long has it been? How long will it last? How shall we -use it? - -To look across the space of over ninety million miles, and to try to -learn from that distance the nature of the solar heat, and how it is -kept up, seemed to the astronomers of the last century a hopeless task. -The difficulty was avoided rather than met by the doctrine that the sun -was pure fire, and shone because “it was its nature to.” In the Middle -Ages such an idea was universal; and along with it, and as a logical -sequence of it, the belief was long prevalent that it was possible -to make another such flame here, in the form of a lamp which should -burn forever and radiate light endlessly without exhaustion. With -the philosopher’s stone, which was to transmute lead into gold, this -perpetual lamp formed a prime object of research for the alchemist and -student of magic. - -We recall the use which Scott has made of the belief in this product -of “gramarye” in the “Lay of the Last Minstrel,” where it is sought to -open the grave of the great wizard in Melrose Abbey. It is midnight -when the stone which covers it is heaved away, and Michael’s undying -lamp, buried with him long ago, shines out from the open tomb and -illuminates the darkness of the chancel. - - “I would you had been there to see - The light break forth so gloriously; - That lamp shall burn unquenchably - Until the eternal doom shall be,” - -says the poet. Now we are at liberty to enjoy the fiction as a fiction; -but if we admit that the art which could make such a lamp would indeed -be a black art, which did not work under Nature’s laws, but against -them, then we ought to see that as the whole conception is derived from -the early notion of a miraculous constitution of the sun, the idea of -an eternal self-sustained sun is no more permitted to us than that of -an eternal self-sustained lamp. We must look for the cause of the sun’s -heat in Nature’s laws, and we know those laws chiefly by what we see -here. - -Before examining the source of the sun’s heat, let us look a little -more into its amount. To find the exact amount of heat which it sends -out is a very difficult problem, especially if we are to use all the -refinements of the latest methods in determining it. The underlying -principle, however, is embodied in an old method, which gives, it is -true, rather crude results, but by so simple a treatment that the -reader can follow it readily, especially if unembarrassed with details, -in which most of the actual trouble lies. We must warn him in advance -that he is going to be confronted with a kind of enormous sum in -multiplication, for whose general accuracy he may, however, trust to us -if he pleases. We have not attempted exact accuracy, because it is more -convenient for him that we should deal with round numbers. - -[Illustration: FIG. 53.--ONE CUBIC CENTIMETRE.] - -[Illustration: FIG. 54.--POUILLET’S PYRHELIOMETER.] - -The apparatus which we shall need for the attack of this great problem -is surprisingly simple, and moderate in size. Let us begin by finding -how much sun-heat falls in a small known area. To do this we take a -flat, shallow vessel, which is to be filled with water. The amount it -contains is usually a hundred cubic centimetres (a centimetre being -nearly four-tenths of an inch), so that if we imagine a tiny cubical -box about as large as a backgammon die, or, more exactly, having each -side just the size of this (Fig. 53), to be filled and emptied into the -vessel one hundred times, we shall have a precise idea of its limited -capacity. Into this vessel we dip a thermometer, so as to read the -temperature of the water, seal all up so that the water shall not run -out, and expose it so that the heat at noon falls perpendicularly on -it. The apparatus is shown in Fig. 54, attached to a tree. The stem -of the instrument holds the thermometer, which is upside down, its -bulb being in the water-vessel. Now, all the sun’s rays do not reach -this vessel, for some are absorbed by our atmosphere; and all the heat -which falls on it does not stay there, as the water loses part of it -by the contact of the air with the box outside, and in other ways. -When allowance is made for these losses, we find that the sun’s heat, -if all retained, would have raised the temperature of the few drops of -water which would fill a box the size of our little cube (according -to these latest observations) nearly three degrees of the centigrade -thermometer in one minute,--a most insignificant result, apparently, -as a measure of what we have been told is the almost infinite heat of -the sun! But if we think so, we are forgetting the power of numbers, of -which we are about to have an illustration as striking in its way as -that which Archimedes once gave with the grains of sand. - -There is a treatise of his extant, in which he remarks (I cite from -memory) that as some people believe it possible for numbers to express -a quantity as great as that of the grains of sand upon the sea-shore, -while others deny this, he will show that they can express one even -larger. To prove this beyond dispute, he begins by taking a small -seed, beside which he ranges single grains of sand in a line, till he -can give the number of these latter which equal its length. Next he -ranges seeds beside each other till their number makes up the length -of a span; then he counts the spans in a stadium, and the stadia in -the whole world as known to the ancients, at each step expressing his -results in a number certainly _greater_ than the number of sand-grains -which the seed, or the span, or the stadium, or finally the whole -world, is thus successively shown to contain. He has then already got -a number before his reader’s eyes demonstrably larger than that of all -the grains of sand on the sea-shore; yet he does not stop, but steps -off the earth into space, to calculate and express a number _greater_ -than that of all the grains of sand which would fill a sphere embracing -the earth and the sun! - -We are going to use our little unit of heat in the same way, for -(to calculate in round figures and in English measure) we find that -we can set over nine hundred of these small cubes side by side in a -square foot, and, as there are 28,000,000 feet in a square mile, that -the latter would contain 25,000,000,000 of the cubes, placed side by -side, touching each other, like a mosaic pavement. We find also, by -weighing our little cup, that we should need to fill and empty it -almost exactly a million times to exhaust a tank containing a ton of -water. The sun-heat falling on one square mile corresponds, then, to -over seven hundred and fifty tons of water raised _every minute_ from -the freezing-point to boiling, which already is becoming a respectable -amount! - -But there are 49,000,000 square miles in the cross-section of the -earth exposed to the sun’s rays, which it would therefore need -1,225,000,000,000,000,000 of our little dies to cover one deep; and -therefore in each _minute_ the sun’s heat falling on the earth would -raise to boiling 37,000,000,000 tons of water. - -We may express this in other ways, as by the quantity of ice it would -melt; and as the heat required to melt a given weight of ice is 79/100 -of that required to bring as much water from the freezing to the -boiling point, and as the whole surface of the earth, including the -night side, is four times the cross-section exposed to the sun, we -find, by taking 526,000 minutes to a year, that the sun’s rays would -melt in the year a coating of ice over the whole earth more than one -hundred and sixty feet thick. - -We have ascended already from our small starting-point to numbers which -express the heat that falls upon the whole planet, and enable us to -deal, if we wish, with questions relating to the glacial epochs and -other changes in its history. We have done this by referring at each -step to the little cube which we have carried along with us, and which -is the foundation of all the rest; and we now see why such exactness -in the first determination is needed, since any error is multiplied -by enormous numbers. But now we too are going to step off the earth -and to deal with numbers which we can still express in the same way -if we choose, but which grow so large thus stated that we will seek -some greater term of comparison for them. We have just seen the almost -incomprehensible amount of heat which the sun must send the earth in -order to warm its oceans and make green its continents; but how little -this is to what passes us by! The earth as it moves on in its annual -path continually comes into new regions, where it finds the same amount -of heat already pouring forth; and this same amount still continues to -fall into the empty space we have just quitted, where there is no one -left to note it, and where it goes on in what seems to us utter waste. -If, then, the whole annual orbit were set close with globes like ours, -and strung with worlds like beads upon a ring, each would receive the -same enormous amount the earth does now. But this is not all; for not -only along the orbit, but above and below it, the sun sends its heat in -seemingly incredible wastefulness, the final amount being expressible -in the number of _worlds_ like ours that it could warm like ours, which -is 2,200,000,000. - -We have possibly given a surfeit of such numbers, but we cannot escape -or altogether avoid them when dealing with this stupendous outflow of -the solar heat. They are too great, perhaps, to convey a clear idea to -the mind, but let us before leaving them try to give an illustration of -their significance. - -Let us suppose that we could sweep up from the earth all the ice and -snow on its surface, and, gathering in the accumulations which lie -on its Arctic and Antarctic poles, commence building with it a tower -greater than that of Babel, fifteen miles in diameter, and so high as -to exhaust our store. Imagine that it could be preserved untouched by -the sun’s rays, while we built on with the accumulations of successive -winters, until it stretched out 240,000 miles into space, and formed an -ice-bridge to the moon, and that then we concentrated on it the sun’s -whole radiation, neither more nor less than that which goes on every -moment. In _one_ second the whole would be gone, melted, boiled, and -dissipated in vapor. And this is the rate at which the solar heat is -being (to human apprehension) _wasted_! - -Nature, we are told, always accomplishes her purpose with the least -possible expenditure of energy. Is her purpose here, then, something -quite independent of man’s comfort and happiness? Of the whole solar -heat, we have just seen that less than 1/2,000,000,--less, that is, -than the one twenty-thousandth part of one per cent,--is made useful -to us. “But may there not be other planets on which intelligent life -exists, and where this heat, which passes us by, serves other beings -than ourselves?” There _may_ be; but if we could suppose all the other -planets of the solar system to be inhabited, it would help the matter -very little; for the whole together intercept so little of the great -sum, that all of it which Nature bestows on man is still as nothing to -what she bestows on some end--if end there be--which is to us as yet -inscrutable. - -How is this heat maintained? Not by the miracle of a perpetual -self-sustained flame, we may be sure. But, then, by what fuel is such a -fire fed? There can be no question of simple burning, like that of coal -in the grate, for there is no source of supply adequate to the demand. -The State of Pennsylvania, for instance, is underlaid by one of the -richest coal-fields of the world, capable of supplying the consumption -of the whole country at its present rate for more than a thousand -years to come. If the source of the solar heat (whatever that is) were -withdrawn, and we were enabled to carry this coal there, and shoot it -into the solar furnace fast enough to keep up the known heat-supply, -so that the solar radiation would go on at just its actual rate, the -time which this coal would last is easily calculable. It would not last -days or hours, but the whole of these coal-beds would demonstrably be -used up in rather less than one one-thousandth of a second! We find by -a similar calculation that if the sun were itself one solid block of -coal, it would have burned out to the last cinder in less time than man -has certainly been on the earth. But during historic times there has as -surely been no noticeable diminution of the sun’s heat, for the olive -and the vine grow just as they did three thousand years ago, and the -hypothesis of an actual burning becomes untenable. It has been supposed -by some that meteors striking the solar surface might generate heat by -their impact, just as a cannon-ball fired against an armor-plate causes -a flash of light, and a heat so sudden and intense as to partly melt -the ball at the instant of concussion. This is probably a real source -of heat-supply so far as it goes, but it cannot go very far; and, -indeed, if our whole world should fall upon the solar surface like an -immense projectile, gathering speed as it fell, and finally striking -(as it would) with the force due to a rate of over three hundred miles -a second, the heat developed would supply the sun for but little more -than sixty years.[4] - - [4] These estimates differ somewhat from those of Helmholtz and - Tyndall, as they rest on later measures. - -It is not necessary, however, that a body should be moving rapidly to -develop heat, for arrested motion always generates it, whether the -motion be fast or slow, though in the latter case the mass arrested -must be larger to produce the same result. It is in the slow settlement -of the sun’s own substance toward its centre, as it contracts in -cooling, that we find a sufficient cause for the heat developed. - -This explanation is often unsatisfactory to those who have not studied -the subject, because the fact that heat is so generated is not made -familiar to most of us by observation. - -Perhaps the following illustration will make the matter plainer. When -we are carried up in a lift, or elevator, we know well enough that heat -has been expended under the boiler of some engine to drag us up against -the power of gravity. When the elevator is at the top of its course, it -is ready to give out in descending just the same amount of power needed -to raise it, as we see by its drawing up a nearly equal counterpoise -in the descent. It can and must give out in coming down the power that -was spent in raising it up; and though there is no practical occasion -to do so, a large part of this power could, if we wished, be actually -recovered in the form of heat again. In the case of a larger body, -such as the pyramid of Ghizeh, which weighs between six and seven -million tons, all the furnaces in the world, burning coal under all its -engines, would have to supply their heat for a measurable time to lift -it a mile high; and then, if it were allowed to come down, whether it -tell at once or were made to descend with imperceptible slowness, by -the time it touched the earth the same heat would be given out again. - -Perhaps the fact that the sun is gaseous rather than solid makes it -less easy to realize the enormous weight which is consistent with this -vaporous constitution. A cubic mile of hydrogen gas (the lightest -substance known) would weigh much more at the sun’s surface than the -Great Pyramid does here, and the number of these cubic miles in a -stratum one mile deep below its surface is over 2,000,000,000,000! This -alone is enough to show that as they settle downward as the solar globe -shrinks, here is a _possible_ source of supply for all the heat the sun -sends out. More exact calculation shows that it _is_ sufficient, and -that a contraction of three hundred feet a year (which in ten thousand -years would make a shrinkage hardly visible in the most powerful -telescope) would give all the immense outflow of heat which we see. - -There is an ultimate limit, however, to the sun’s shrinking, and -there must have been some bounds to the heat he can already have thus -acquired; for--though the greater the original diameter of his sphere, -the greater the gain of heat by shrinking to its present size--if the -original diameter be supposed as great as possible, there is still a -finite limit to the heat gained. - -Suppose, in other words, the sun itself and all the planets ground to -powder, and distributed on the surface of a sphere whose radius is -infinite, and that this matter (the same in amount as that constituting -the present solar system) is allowed to fall together at the centre. -The actual shrinkage cannot possibly be greater than in this extreme -case; but even in this practically impossible instance, it is easy -to calculate that the heat given out would not support the _present_ -radiation over eighteen million years, and thus we are enabled to look -back over past time, and fix an approximate limit to the age of the sun -and earth. - -We say “present” rate of radiation, because, so long as the sun is -purely gaseous, its temperature rises as it contracts, and the heat -is spent faster; so that in early ages before this temperature was as -high as it is now, the heat was spent more slowly, and what could have -lasted “only” eighteen million years at the present rate might have -actually spread over an indefinitely greater time in the past; possibly -covering more than all the æons geologists ask for. - -If we would look into the future, also, we find that at the present -rate we may say that the sun’s heat-supply is enough to last for some -such term as four or five million years before it sensibly fails. It -is certainly remarkable that by the aid of our science man can look -out from this “bank and shoal of time,” where his fleeting existence -is spent, not only back on the almost infinite lapse of ages past, but -that he can forecast with some sort of assurance what is to happen -in an almost infinitely distant future, long after the human race -itself will have disappeared from its present home. But so it is, and -we may say--with something like awe at the meaning to which science -points--that the whole future radiation cannot last so long as ten -million years. Its probable life in its present condition is covered -by about thirty million years. No reasonable allowance for the fall -of meteors or for all other known causes of supply could possibly at -the present rate of radiation raise the whole term of its existence to -sixty million years. - -This is substantially Professor Young’s view, and he adds:-- - - “At the same time it is, of course, impossible to assert that - there has been no catastrophe in the past, no collision with - some wandering star ... producing a shock which might in a few - hours, or moments even, restore the wasted energy of ages. - Neither is it wholly safe to assume that there may not be ways, - of which we as yet have no conception, by which the energy - apparently lost in space may be returned. But the whole course - and tendency of Nature, so far as science now makes out, points - backward to a beginning and forward to an end. The present order - of things seems to be bounded both in the past and in the future - by terminal catastrophes which are veiled in clouds as yet - inscrutable.” - -There is another matter of interest to us as dwellers on this planet, -connected not with the amount of the sun’s heat so much as with the -degree of its temperature; for it is almost certain that a very -little fall in the temperature will cause an immense and wholly -disproportionate diminution of the heat-supply. The same principle may -be observed in more familiar things. We can, for instance, warm quite -a large house by a very small furnace, if we urge this (by a wasteful -use of coal) to a dazzling white heat. If we now let the furnace cool -to half this white-heat temperature, we shall be sure to find that -the heat radiated has not diminished in proportion, but out of all -proportion,--has sunk, for instance, not only to one-half what it was -(as we might think it would do), but to perhaps a twentieth or even -less, so that the furnace which heated the house can no longer warm a -single room. - -The human race, as we have said, is warming itself at the great solar -furnace, which we have just seen contains an internal source for -generating heat enough for millions of years to come; but we have -also learned that if the sun’s internal circulation were stopped, -the surface would cool and shut up the heat inside, where it would -do us no good. The _temperature_ of the surface, then, on which the -rate of heat-emission depends, concerns us very much; and if we had -a thermometer so long that we could dip its bulb into the sun and -read the degrees on the stem here, we should find out what observers -would very much like to know, and at present are disposed to quarrel -about. The difficulty is not in measuring the heat,--for that we have -just seen how to do,--but in telling what temperature corresponds to -it, since there is no known rule by which to find one from the other. -One certain thing is this--that we cannot by any contrivance raise -the temperature in the focus of any lens or mirror beyond that of -its source (practically we cannot do even so much); we cannot, for -instance, by any burning-lens make the image of a candle as hot as the -original flame. Whatever a thermometer may read when the candle-heat is -concentrated on its bulb by a lens, it would read yet more if the bulb -were dipped in the candle-flame itself; and one obvious application of -this fact is that though we cannot dip our thermometer in the sun, we -know that if we could do so, the temperature would at least be greater -than any we get by the largest burning-glass. We need have no fear of -making the burning-glass too big; the temperature at its solar focus is -_always_ and necessarily lower than that of the sun itself. - -For some reason no very great burning-lens or mirror has been -constructed for a long time, and we have to go back to the eighteenth -century to see what can be done in this way. The annexed figure (Fig. -55) is from a wood-cut of the last century, describing the largest -burning-lens then or since constructed in France, whose size and -mode of use the drawing clearly shows. All the heat falling on the -great lens was concentrated on a smaller one, and the smaller one -concentrated it in turn, till at the very focus we are assured that -iron, gold, and other metals ran like melted butter. In England, the -largest burning-lens on record was made about the same time by an -optician named Parker for the English Government, who designed it as -a present to be taken by Lord Macartney’s embassy to the Emperor of -China. Parker’s lens was three feet in diameter and very massive, being -seven inches thick at the centre. In its focus the most refractory -substances were fused, and even the diamond was reduced to vapor, so -that the temperature of the sun’s surface is at any rate higher than -_this_. - -[Illustration: FIG. 55.--BERNIÈRES’S GREAT BURNING-GLASS. (AFTER AN OLD -FRENCH PRINT.)] - -(What became of the French lens shown, it would be interesting to know. -If it is still above ground, its fate has been better than that of the -English one. It is said that the Emperor of China, when he got his -lens, was much alarmed by it, as being possibly sent him by the English -with some covert design for his injury. By way of a test, a smith was -ordered to strike it with his hammer; but the hammer rebounded from -the solid glass, and this was taken to be conclusive evidence of magic -in the thing, which was immediately buried, and probably is still -reposing under the soil of the Celestial Flowery Kingdom.) - -We can confirm the evidence of such burning-lenses as to the sun’s -high temperature by another class of experiment, which rests on an -analogous principle. We can make the comparison between the heat from -some artificially heated object and that which would be given out -from an equal area of the sun’s face. Now, supposing like emissive -powers, if the latter be found the hotter, though we cannot tell what -its temperature absolutely is, we can at least say that it is greater -than that of the thing with which it is compared; so that we choose -for comparison the hottest thing we can find, on a scale large enough -for the experiment. One observation of my own in this direction I will -permit myself to cite in illustration. - -Perhaps the highest temperature we can get on a large scale in the arts -is that of molten steel in the Bessemer converter. As many may be as -ignorant of what this is as I was before I tried the experiment, I will -try to describe it. - -[Illustration: FIG. 56.--A “POUR” FROM THE BESSEMER CONVERTER.] - -The “converter” is an enormous iron pot, lined with fire-brick, and -capable of holding thirty or forty thousand pounds of melted metal; -and it is swung on trunnions, so that it can be raised by an engine -to a vertical position, or lowered by machinery so as to pour its -contents out into a caldron. First the empty converter is inclined, -and fifteen thousand pounds of fluid iron streams down into the mouth -from an adjacent furnace where it has been melted. Then the engine -lifts the converter into an erect position, while an air-blast from -a blowing-engine is forced in at the bottom and through the liquid -iron, which has combined with it nearly half a ton of silicon and -carbon,--materials which, with the oxygen of the blast, create a heat -which leaves that of the already molten iron far behind. After some -time the converter is tipped forward, and fifteen hundred pounds more -of melted iron is added to that already in it. What the temperature -of this last is, may be judged from the fact that though ordinary -melted iron is dazzlingly bright, the melted metal in the converter -is so much brighter still, that the entering stream is dark brown by -comparison, presenting a contrast like that of chocolate poured into -a white cup. The contents are now no longer iron, but liquid steel, -ready for pouring into the caldron; and, looking from the front down -into the inclined vessel, we see the almost blindingly bright interior -dripping with the drainage of the metal running down its side, so that -the circular mouth, which is twenty-four inches in diameter, presents -the effect of a disk of molten metal of that size (were it possible to -maintain such a disk in a vertical position). In addition, we have the -actual stream of falling metal, which continues nearly a minute, and -presents an area of some square feet. The shower of scintillations from -this cataract of what seems at first “sunlike” brilliancy, and the area -whence such intense heat and light are for a brief time radiated, make -the spectacle a most striking one. (See Fig. 56.) - -The “pour” is preceded by a shower of sparks, consisting of little -particles of molten steel which are projected fully a hundred feet in -the direction of the open mouth of the converter. In the line of this -my apparatus was stationed in an open window, at a point where its view -could be directed down into the converter on one side, and up at the -sun on the other. This apparatus consisted of a long photometer-box -with a _porte-lumière_ at one end. The mirror of this reflected the -sun’s rays through the box and then on to the pouring metal, tracing -their way to it by a beam visible in the dusty air (Fig. 57). In the -path of this beam was placed the measuring apparatus, both for heat -and light. As the best point of observation was in the line of the -blast, a shower of sparks was driven over the instrument and observer -at every “pour;” and the rain of wet soot from chimneys without, the -bombardment from within, and the moving masses of red-hot iron around, -made the experiment an altogether peculiar one. The apparatus was -arranged in such a way that the effect (except for the absorption of -its beams on the way) was independent of the size or distance of the -sun, and depended on the absolute radiation there, and was equivalent, -in fact, to taking a sample piece of the sun’s face _of equal size_ -with the fluid metal, bringing them face to face, and seeing which -was the hotter and brighter. The comparison, however, was unfair to -the sun, because its rays were in reality partly absorbed by the -atmosphere on the way, while those of the furnace were not. Under these -circumstances the heat from any single square foot of the sun’s surface -was found to be _at least_ eighty-seven times that from a square foot -of the melted metal, while the light from the sun was proved to be, -foot for foot, over five thousand times that from the molten steel, -though the latter, separately considered, seemed to be itself, as I -have said, of quite sunlike brilliancy. - -[Illustration: FIG. 57.--PHOTOMETER-BOX.] - -We must not conclude from this that the _temperature_ of the sun was -five thousand times that of the steel, but we may be certain that it -was at any rate a great deal the higher of the two. It is probable, -from all experiments made up to this date, that the solar effective -temperature is not less than 3,000 nor more than 30,000 degrees of -the centigrade thermometer. Sir William Siemens, whose opinion on any -question as to heat is entitled to great respect, thought the lower -value nearer the truth, but this is doubtful. - -[Illustration: FIG. 58.--MOUCHOT’S SOLAR ENGINE. (FROM A FRENCH -PRINT.)] - - * * * * * - -We have, in all that has preceded, been speaking of the sun’s -constitution and appearance, and have hardly entered on the question -of its industrial relations to man. It must be evident, however, that -if we derive, as it is asserted we do, almost all our mechanical power -from this solar heat,--if our water-wheel is driven by rivers which -the sun feeds by the rain he sucks up for them into the clouds, if -the coal is stored sun-power, and if, as Stevenson said, it really is -the sun which drives our engines, though at second hand,--there is an -immense fund of possible mechanical power still coming to us from him -which might be economically utilized. Leaving out of sight all our -more important relations to him (for, as has been already said, he -is in a physical sense our creator, and he keeps us alive from hour -to hour), and considering him only as a possible servant to grind -our corn and spin our flax, we find that even in this light there -are startling possibilities of profit in the study of our subject. -From recent measures it appears that from every square yard of the -earth exposed perpendicularly to the sun’s rays, in the absence of an -absorbing atmosphere, there could be derived more than one horse-power, -if the heat were all converted into this use, and that even on such a -little area as the island of Manhattan, or that occupied by the city -of London, the noontide heat is enough, could it all be utilized, to -drive all the steam-engines in the world. It will not be surprising, -then, to hear that many practical men are turning their attention to -this as a source of power, and that, though it has hitherto cost more -to utilize the power than it is worth, there is reason to believe -that some of the greatest changes which civilization has to bring -may yet be due to such investigations. The visitor to the last Paris -Exposition may remember an extraordinary machine on the grounds of -the Trocadéro, looking like a gigantic inverted umbrella pointed -sunward. This was the sun-machine of M. Mouchot, consisting of a great -parabolic reflector, which concentrated the heat on a boiler in the -focus and drove a steam-engine with it, which was employed in turn to -work a printing-press, as our engraving shows (Fig. 58). Because these -constructions have been hitherto little more than playthings, we are -not to think of them as useless. If toys, they are the toys of the -childhood of a science which is destined to grow, and in its maturity -to apply this solar energy to the use of all mankind. - -Even now they are beginning to pass into the region of practical -utility, and in the form of the latest achievement of Mr. Ericsson’s -ever-young genius are ready for actual work on an economical scale. -We present in Fig. 59 his new actually working solar engine, which -there is every reason to believe is more efficient than Mouchot’s, -and probably capable of being used with economical advantage in -pumping water in desert regions of our own country. It is pregnant -with suggestion of the future, if we consider the growing demand for -power in the world, and the fact that its stock of coal, though vast, -is strictly limited, in the sense that when it _is_ gone we can get -absolutely no more. The sun has been making a little every day for -millions of years,--so little and for so long, that it is as though -time had daily dropped a single penny into the bank to our credit for -untold ages, until an enormous fund had been thus slowly accumulated in -our favor. We are drawing on this fund like a prodigal who thinks his -means endless, but the day will come when our check will no longer be -honored, and what shall we do then? - -[Illustration: FIG. 59.--ERICSSON’S NEW SOLAR ENGINE, NOW IN PRACTICAL -USE IN NEW YORK.] - -The exhaustion of some of the coal-beds is an affair of the immediate -future, by comparison with the vast period of time we have been -speaking of. The English coal-beds, it is asserted, will, from present -indications, be quite used up in about three hundred years more. - -Three hundred years ago, the sun, looking down on the England of our -forefathers, saw a fair land of green woods and quiet waters, a land -unvexed with noisier machinery than the spinning-wheel, or the needles -of the “free maids that weave their threads with bones.” Because of the -coal which has been dug from its soil, he sees it now soot-blackened, -furrowed with railway-cuttings, covered with noisy manufactories, -filled with grimy operatives, while the island shakes with the throb -of coal-driven engines, and its once quiet waters are churned by the -wheels of steamships. Many generations of the lives of men have passed -to make the England of Elizabeth into the England of Victoria; but what -a moment this time is, compared with the vast lapse of ages during -which the coal was being stored! What a moment in the life of the -“all-beholding sun,” who in a few hundred years--his gift exhausted -and the last furnace-fire out--may send his beams through rents in the -ivy-grown walls of deserted factories, upon silent engines brown with -rust, while the mill-hand has gone to other lands, the rivers are clean -again, the harbors show only white sails, and England’s “black country” -is green once more! To America, too, such a time may come, though at a -greatly longer distance. - -Does this all seem but the idlest fancy? That something like it will -come to pass sooner or later, is a most certain fact--as certain as any -process of Nature--if we do not find a new source of power; for of the -coal which has supplied us, after a certain time we can get no more. - -Future ages may see the seat of empire transferred to regions of the -earth now barren and desolated under intense solar heat,--countries -which, for that very cause, will not improbably become the seat of -mechanical and thence of political power. Whoever finds the way to -make industrially useful the vast sun-power now wasted on the deserts -of North Africa or the shores of the Red Sea, will effect a greater -change in men’s affairs than any conqueror in history has done; for he -will once more people those waste places with the life that swarmed -there in the best days of Carthage and of old Egypt, but under another -civilization, where man no longer shall worship the sun as a god, but -shall have learned to make it his servant. - - - - -V. - -THE PLANETS AND THE MOON. - - -When we look up at the heavens, we see, if we watch through the night, -the host of stars rising in the east and passing above us to sink -in the west, always at the same distance and in unchanging order, -each seeming a point of light as feeble as the glow-worm’s shine in -the meadow over which they are rising, each flickering as though the -evening wind would blow it out. The infant stretches out its hand to -grasp the Pleiades; but when the child has become an old man the “seven -stars” are still there unchanged, dim only in his aged sight, and -proving themselves the enduring substance, while it is his own life -which has gone, as the shine of the glow-worm in the night. They were -there just the same a hundred generations ago, before the Pyramids were -built; and they will tremble there still, when the Pyramids have been -worn down to dust with the blowing of the desert sand against their -granite sides. They watched the earth grow fit for man long before man -came, and they will doubtless be shining on when our poor human race -itself has disappeared from the surface of this planet. - -Probably there is no one of us who has not felt this solemn sense of -their almost infinite duration as compared with his own little portion -of time, and it would be a worthy subject for our thought if we could -study them in the light that the New Astronomy sheds for us on their -nature. But I must here confine myself to the description of but a few -of their number, and speak, not of the infinite multitude and variety -of stars, each a self-shining sun, but only of those which move close -at hand; for it is not true of quite all that they keep at the same -distance and order. - -Of the whole celestial army which the naked eye watches, there are five -stars which do change their places in the ranks, and these change in -an irregular and capricious manner, going about among the others, now -forward and now back, as if lost and wandering through the sky. These -wanderers were long since known by distinct names, as Mercury, Venus, -Mars, Jupiter, and Saturn, and believed to be nearer than the others; -and they are, in fact, companions to the earth and fed like it by the -warmth of our sun, and like the moon are visible by the sunlight which -they reflect to us. With the earliest use of the telescope, it was -found that while the other stars remained in it mere points of light -as before, these became magnified into disks on which markings were -visible, and the markings have been found with our modern instruments, -in one case at least, to take the appearance of oceans and snow-capped -continents and islands. These, then, are not uninhabitable self-shining -suns, but worlds, vivified from the same fount of energy that supplies -us, and the possible abode of creatures like ourselves. - -[Illustration: FIG. 60.--SATURN. (FROM A DRAWING BY TROUVELOT).] - -“Properly speaking,” it is said, “man is the only subject of interest -to man;” and if we have cared to study the uninhabitable sun because -all that goes on there is found to be so intimately related to us, -it is surely a reasonable curiosity which prompts the question so -often heard as to the presence of life on these neighbor worlds, -where it seems at least not impossible that life should exist. Even -the very little we can say in answer to this question will always be -interesting; but we must regretfully admit at the outset that it is -but little, and that with some planets, like Mercury and Venus, the -great telescopes of modern times cannot do much more than those of -Galileo, with which our New Astronomy had its beginning. - -Let us leave these, then, and pass out to the confines of the planetary -system, where we may employ our telescopes to better advantage. - -The outer planets, Neptune and Uranus, remain pale disks in the most -powerful instruments, the first attended by a single moon, the second -by four, barely visible; and there is so very little yet known about -their physical features, that we shall do better to give our attention -to one of the most interesting objects in the whole heavens,--the -planet Saturn, on which we can at any rate see enough to arouse a -lively curiosity to know more. - -When Galileo first turned his glass on Saturn, he saw, as he thought, -that it consisted of three spheres close together, the middle one -being the largest. He was not quite sure of the fact, and was in a -dilemma between his desire to wait longer for further observation, and -his fear that some other observer might announce the discovery if he -hesitated. To combine these incompatibilities--to announce it so as to -secure the priority, and yet not announce it till he was ready--might -seem to present as great a difficulty as the discovery itself; but -Galileo solved this, as we may remember, by writing it in the sentence, -“Altissimum planetam tergeminum observavi” (“I have observed the -highest planet to be triple”), and then throwing it (in the printer’s -phrase) “into pi,” or jumbling the letters, which made the sentence -into the monstrous word - - SMAJSMRMJLMEBOETALEVMJPVNENVGTTAVJRAS, - -and publishing _this_, which contained his discovery, but under lock -and key. He had reason to congratulate himself on his prudence, for -within two years two of the supposed bodies disappeared, leaving only -one. This was in 1612; and for nearly fifty years Saturn continued to -all astronomers the enigma which it was to Galileo, till in 1656 it -was finally made clear that it was surrounded by a thin flat ring, -which when seen fully gave rise to the first appearance in Galileo’s -small telescope, and when seen edgewise disappeared from its view -altogether. Everything in this part of our work depends on the power -of the telescope we employ, and in describing the modern means of -observation we pass over two centuries of slow advance, each decade -of which has marked some progress in the instrument, to one of its -completest types, in the great equatorial at Washington, shown in Fig. -61. - -[Illustration: FIG. 61.--THE EQUATORIAL TELESCOPE AT WASHINGTON.] - -The revolving dome above, the great tube beneath, its massive piers, -and all its accessories are only means to carry and direct the great -lens at the further end, which acts the part of the lens in our own -eye, and forms the image of the thing to be looked at. Galileo’s -original lens was a single piece of glass, rather smaller than that of -our common spectacles; but the lens here is composed of two pieces, -each twenty-six inches in diameter, and collects as much light as a -human eye would do if over two feet across. But this is useless if the -lens is not shaped with such precision as to send every ray to its -proper place at the eye-piece, nearly thirty-five feet away; and, in -fact, the shape given its surface by the skilful hands of the Messrs. -Clark, who made it, is so exquisitely exact that all the light of a -star gathered by this great surface is packed at the distant focus into -a circle very much smaller than that made by the dot on this _i_, and -the same statement may be made of the great Lick glass, which is three -feet in diameter,--an accuracy we might call incredible were it not -certain. It is with instruments of such accuracy that astronomy now -works, and it is with this particular one that some of the observations -we are going to describe have been made. - -In all the heavens there is no more wonderful object than Saturn, for -it preserves to us an apparent type of the plan on which all the worlds -were originally made. Let us look at it in this study by Trouvelot -(Fig. 60). The planet, we must remember, is a globe nearly seventy -thousand miles in diameter, and the outermost ring is over one hundred -and fifty thousand miles across, so that the proportionate size of our -earth would be over-represented here by a pea laid on the engraving. -The belts on the globe show delicate tints of brown and blue, and parts -of the ring are, as a whole, brighter than the planet; but this ring, -as the reader may see, consists of at least three main divisions, each -itself containing separate features. First is the gray outer ring, then -the middle one, and next the curious “crape” ring, very much darker -than the others, looking like a belt where it crosses the planet, -and apparently feebly transparent, for the outline of the globe has -been seen (though not very distinctly) _through_ it. The whole system -of rings is of the most amazing thinness, for it is probably thinner -in proportion to its size than the paper on which this is printed is -to the width of the page; and when it is turned edgewise to us, it -disappears to all but the most powerful telescopes, in which it looks -then like the thinnest conceivable line of light, on which the moons -have been seen projected, appearing like beads sliding along a golden -wire. The globe of the planet casts on the ring a shadow, which is -here shown as a broken line, as though the level of the rings were -suddenly disturbed. At other times (as in a beautiful drawing made with -the same instrument by Professor Holden) the line seems continuous, -though curved as though the middle of the ring system were thicker -than the edge. The rotation of the ring has been made out by direct -observations; and the whole is in motion about the globe,--a motion -so smooth and steady that there is no flickering in the shadow “where -Saturn’s steadfast shade sleeps on its luminous ring.” - -[Illustration: FIG. 62.--JUPITER, MOON, AND SHADOW. (BY PERMISSION OF -WARREN DE LA RUE.)] - -What is it? No solid could hold together under such conditions; we can -hardly admit the possibility of its being a liquid film extended in -space; and there are difficulties in admitting it to be gaseous. But if -not a solid, a liquid, or a gas, again what can it be? It was suggested -nearly two centuries ago that the ring might be composed of innumerable -little bodies like meteorites, circling round the globe so close -together as to give the appearance we see, much as a swarm of bees at -a distance looks like a continuous cloud; and this remains the most -plausible solution of what is still in some degree a mystery. Whatever -it be, we see in the ring the condition of things which, according -to the nebular hypothesis, once pertained to all the planets at a -certain stage of their formation; and this, with the extraordinary -lightness of the globe (for the whole planet would float on water), -makes us look on it as still in the formative stage of uncondensed -matter, where the solid land as yet is not, and the foot could find -no resting-place. Astrology figured Saturn as “spiteful and cold,--an -old man melancholy;” but if we may indulge such a speculation, modern -astronomy rather leads us to think of it as in the infancy of its -life, with every process of planetary growth still in its future, and -separated by an almost unlimited stretch of years from the time when -life under the conditions in which we know it can even begin to exist. - - * * * * * - -Like this appears also the condition of Jupiter (Fig. 62), the -greatest of the planets, whose globe, eighty-eight thousand miles in -diameter, turns so rapidly that the centrifugal force causes a visible -flattening. The belts which stretch across its disk are of all delicate -tints--some pale blue, some of a crimson lake; a sea-green patch has -been seen, and at intervals of late years there has been a great oval -red spot, which has now nearly gone, and which our engraving does not -show. The belts are largely, if not wholly, formed of rolling clouds, -drifting and changing under our eyes, though more rarely a feature -like the oval spot just mentioned will last for years, an enduring -enigma. The most recent observations tend to make us believe that the -equatorial regions of Jupiter, like those of the sun, make more turns -in a year than the polar ones; while the darkening toward the edge is -another sunlike feature, though perhaps due to a distinct cause, and -this is beautifully brought out when any one of the four moons which -circle the planet passes between us and its face, an occurrence also -represented in our figure. The moon, as it steals on the comparatively -dark edge, shows us a little circle of an almost lemon-yellow, but the -effect of contrast grows less as it approaches the centre. Next (or -sometimes before), the disk is invaded by a small and intensely black -spot, the shadow of the moon, which slides across the planet’s face, -the transit lasting long enough for us to see that the whole great -globe, serving as a background for the spectacle, has visibly revolved -on its axis since we began to gaze. Photography, in the skilful hands -of the late Professor Henry Draper, gave us reason to suspect the -possibility that a dull light is sent to us from parts of the planet’s -surface besides what it reflects, as though it were still feebly -glowing like a nearly extinguished sun; and, on the whole, a main -interest of these features to us lies in the presumption they create -that the giant planet is not yet fit to be the abode of life, but is -more probably in a condition like that of our earth millions of years -since, in a past so remote that geology only infers its existence, and -long before our own race began to be. That science, indeed, itself -teaches us that such all but infinite periods are needed to prepare a -planet for man’s abode, that the entire duration of his race upon it is -probably brief in comparison. - - * * * * * - -We pass by the belt of asteroids, and over a distance many times -greater than that which separates the earth from the sun, till we -approach our own world. Here, close beside it as it were, in comparison -with the enormous spaces which intervene between it and Saturn and -Jupiter, we find a planet whose size and features are in striking -contrast to those of the great globe we have just quitted. It is Mars, -which shines so red and looks so large in the sky because it is so -near, but whose diameter is only about half that of our earth. This is -indeed properly to be called a neighbor world, but the planetary spaces -are so immense that this neighbor is at closest still about thirty-four -million miles away. - -[Illustration: FIG 63.--THREE VIEWS OF MARS.] - -[Illustration: FIG 64.--MAP OF MARS.] - -Looking across that great gulf, we see in our engraving (Fig. -63)--where we have three successive views taken at intervals of a few -hours--a globe not marked by the belts of Jupiter or Saturn, but with -outlines as of continents and islands, which pass in turn before our -eyes as it revolves in a little over twenty-four and a half of our -hours, while at either pole is a white spot. Sir William Herschel was -the first to notice that this spot increased in size when it was turned -away from the sun, and diminished when the solar heat fell on it; so -that we have what is almost proof that here is ice (and consequently -water) on another world. Then, as we study more, we discern forms which -move from day to day on the globe apart from its rotation, and we -recognize in them clouds sweeping over the surface,--not a surface of -still other clouds below, but of what we have good reason to believe to -be land and water. - -By the industry of numerous astronomers, seizing every favorable -opportunity when Mars comes near, so many of these features have been -gathered that we have been enabled to make fairly complete maps of the -planet, one of which by Mr. Green is here given (Fig. 64). - -Here we see the surface more diversified than that of our earth, -while the oceans are long, narrow, canal-like seas, which everywhere -invade the land, so that on Mars one could travel almost everywhere by -water. These canals seem also in some cases to exist in pairs or to be -remarkably duplicated. The spectroscope indicates water-vapor in the -Martial atmosphere, and some of the continents, like “Lockyer Land,” -are sometimes seen white, as though covered with ice: while one island -(marked on our map as Hall Island) has been seen so frequently thus, -that it is very probable that here some mountain or tableland rises -into the region of perpetual snow. - -The cause of the red color of Mars has never been satisfactorily -ascertained. Its atmosphere does not appear to be dark enough to -produce such an effect, and perhaps as probable an explanation as any -is one the suggestion of which is a little startling at first. It is -that vegetation on Mars may be _red_ instead of green! There is no -intrinsic improbability in the idea, for we are even to-day unprepared -to say with any certainty why vegetation is green here, and it is quite -easy to conceive of atmospheric conditions which would make red the -best absorber of the solar heat. Here, then, we find a planet on which -we obtain many of the conditions of life which we know ourselves, and -here, if anywhere in the system, we may allowably inquire for evidence -of the presence of something like our own race; but though we may -indulge in supposition, there is unfortunately no prospect that with -any conceivable improvement in our telescopes we shall ever obtain -anything like certainty. We cannot assert that there are any bounds to -man’s invention, or that science may not, by some means as unknown to -us as the spectroscope was to our grandfathers, achieve what now seems -impossible; but to our present knowledge no such means exist, though we -are not forbidden to look at the ruddy planet with the feeling that it -may hold possibilities more interesting to our humanity than all the -wonders of the sun, and all the uninhabitable immensities of his other -worlds. - -Before we leave Mars, we may recall to the reader’s memory the -extraordinary verification of a statement made about it more than a -hundred years ago. We shall have for a moment to leave the paths of -science for those of pure fiction, for the words we are going to quote -are those of no less a person than our old friend Captain Gulliver, -who, after his adventures with the Lilliputians, went to a flying -island inhabited largely by astronomers. If the reader will take down -his copy of Swift, he will find in this voyage of Gulliver’s to Laputa -the following imaginary description of what its imaginary astronomers -saw:-- - - “They have likewise discovered two lesser stars or satellites - which revolve about Mars, whereof the innermost is distant from - the centre of the primary planet exactly three of its diameters, - and the outermost five; the former revolves in the space of ten - hours, and the latter in twenty-one and a half.” - -Now, compare this passage, which was published in the year 1727, with -the announcement in the scientific journals of August, 1877 (a hundred -and fifty years after), that two moons did exist, and had just been -discovered by Professor Hall, of Washington, with the great telescope -of which a drawing has been already given. The resemblance does not end -even here, for Swift was right also in describing them as very near the -planet and with very short periods, the actual distances being about -one and a half and seven diameters, and the actual times about eight -and thirty hours respectively,--distances and periods which, if not -exactly those of Swift’s description, agree with it in being less than -any before known in the solar system. It is certain that there could -not have been the smallest ground for a suspicion of their existence -when “Gulliver’s Travels” was written, and the coincidence--which is -a pure coincidence--certainly approaches the miraculous. We can no -longer, then, properly speak of “the snowy poles of moonless Mars,” -though it does still remain moonless to all but the most powerful -telescopes in the world, for these bodies are the very smallest known -in the system. They present no visible disks to measure, but look -like the faintest of points of light, and their size is only to be -guessed at from their brightness. Professor Pickering has carried on -an interesting investigation of them. His method depended in part on -getting holes of such smallness made in a plate of metal that the light -coming through them would be comparable with that of the Martial moons -in the telescope. It was found almost impossible to command the skill -to make these holes small enough, though one of the artists employed -had already distinguished himself by drilling a hole through a fine -cambric needle _lengthwise_, so as to make a tiny steel tube of it. -When the difficulty was at last overcome, the satellites were found to -be less than ten miles in diameter, and a just impression both of their -apparent size and light may be gathered from the statement that either -roughly corresponds to that which would be given by a human hand held -up at Washington, and viewed from Boston, Massachusetts, a distance of -four hundred miles. - -We approach now the only planet in which man is certainly known to -exist, and which ought to have an interest for us superior to any which -we have yet seen, for it is our own. We are voyagers on it through -space, it has been said, as passengers on a ship, and many of us have -never thought of any part of the vessel but the cabin where we are -quartered. Some curious passengers (these are the geographers) have -visited the steerage, and some (the geologists) have looked under the -hatches, and yet it remains true that those in one part of our vessel -know little, even now, of their fellow-voyagers in another. How much -less, then, do most of us know of the ship itself, for we were all born -on it, and have never once been off it to view it from the outside! - -No world comes so near us in the aerial ocean as the moon; and if we -desire to view our own earth as a planet, we may put ourselves in fancy -in the place of a lunar observer. “Is it inhabited?” would probably -be one of the first questions which he would ask, if he had the same -interest in us that we have in him; and the answer to this would call -out all the powers of the best telescopes such as we possess. - -An old author, Fontenelle, has put in the mouth of an imaginary -spectator a lively description of what would be visible in twenty-four -hours to one looking down on the earth as it turned round beneath him. -“I see passing under my eyes,” he says, “all sorts of faces,--white and -black and olive and brown. Now it’s hats, and now turbans, now long -locks and then shaven crowns; now come cities with steeples, next more -with tall, crescent-capped minarets, then others with porcelain towers; -now great desolate lands, now great oceans, then dreadful deserts,--in -short, all the infinite variety the earth’s surface bears.” The truth -is, however, that, looking at the earth from the moon, the largest -moving animal, the whale or the elephant, would be utterly beyond our -ken; and it is questionable whether the largest ship on the ocean -would be visible, for the popular idea as to the magnifying power -of great telescopes is exaggerated. It is probable that under any -but extraordinary circumstances our lunar observer, with our best -telescopes, could not bring the earth within less than an apparent -distance of five hundred miles; and the reader may judge how large a -moving object must be to be seen, much less recognized, by the naked -eye at such a distance. - -Of course, a chief interest of the supposition we are making lies in -the fact that it will give us a measure of our own ability to discover -evidences of life in the moon, if there are any such as exist here; and -in this point of view it is worth while to repeat, that scarcely any -temporary phenomenon due to human action could be even telescopically -visible from the moon under the most favoring circumstances. An army -such as Napoleon led to Russia might conceivably be visible if it moved -in a dark solid column across the snow. It is barely possible that such -a vessel as one of the largest ocean steamships might be seen, under -very favorable circumstances, as a moving dot; and it is even quite -probable that such a conflagration as the great fire of Chicago would -be visible in the lunar telescope, as something like a reddish star on -the night side of our planet; but this is all in this sort that could -be discerned. - -By making minute maps, or, still better, photographs, and comparing -one year with another, much however might have been done by our lunar -observer during this century. In its beginning, in comparison to the -vast forests which then covered the North American continent, the -cultivated fields along its eastern seaboard would have looked to him -like a golden fringe bordering a broad mantle of green; but now he -would see that the golden fringe has encroached upon the green farther -back than the Mississippi, and he would gather his best evidence of -change from the fact (surely a noteworthy one) that the people of -the United States have altered the features of the world during the -present century to a degree visible in another planet! - -Our observer would probably be struck by the moving panorama of -forests, lakes, continents, islands, and oceans, successively gliding -through the field of view of his telescope as the earth revolved; -but, travelling along beside it on his lunar station, he would hardly -appreciate its actual flight through space, which is an easy thing to -describe in figures, and a hard one to conceive. If we look up at the -clock, and as we watch the pendulum recall that we have moved about -nineteen miles at every beat, or in less than three minutes, over a -distance greater than that which divides New York from Liverpool, we -still probably but very imperfectly realize the fact that (dropping -all metaphor) the earth is really a great projectile, heavier than the -heaviest of her surface rocks, and traversing space with a velocity of -over sixty times that of the cannon-ball. Even the firing of a great -gun with a ball weighing one or two hundred pounds is, to the novice at -least, a striking spectacle. The massive iron sphere is hoisted into -the gun, the discharge comes, the ground trembles, and, as it seems, -almost in the same instant, a jet rises where the ball has touched the -water far away. The impression of immense velocity and of a resistless -capacity of destruction in that flying mass is irresistible, and -justifiable too: but what is this ball to that of the earth, which is -a globe counting eight thousand miles in diameter, and weighing about -six thousand millions of millions of millions of tons; which, if our -cannon-ball were flying ahead a mile in advance of its track, would -overtake it in less than the tenth part of a second; and which carries -such a potency of latent destruction and death in this motion, that if -it were possible instantly to arrest it, then, in that instant, “earth -and all which it inherits would dissolve” and pass away in vapor? - -Our turning sphere is moving through what seems to be all but an -infinite void, peopled only by wandering meteorites, and where warmth -from any other source than the sun can scarcely be said to exist; for -it is important to observe that whether the interior be molten or -not, we get next to no heat from it. The cold of outer space can only -be estimated in view of recent observations as at least four hundred -degrees Fahrenheit below zero (mercury freezes at thirty-nine degrees -below), and it is the sun which makes up the difference of all these -lacking hundreds of degrees to us, but indirectly, and not in the way -that we might naturally think, and have till very lately thought; for -our atmosphere has a great deal to do with it beside the direct solar -rays, allowing more to come in than to go out, until the temperature -rises very much higher than it would were there no air here. Thus, -since it is this power in the atmosphere of storing the heat which -makes us live, no less than the sun’s rays themselves, we see how the -temperature of a planet may depend on considerations quite beside its -distance from the sun; and when we discuss the possibility of life in -other worlds, we shall do well to remember that Saturn may be possibly -a warm world, and Mercury conceivably a cold one. - -We used to be told that this atmosphere extended forty-five miles above -us, but later observation proves its existence at a height of many -times this; and a remarkable speculation, which Dr. Hunt strengthens -with the great name of Newton, even contemplates it as extending in -ever-increasing tenuity until it touches and merges in the atmosphere -of other worlds. - -[Illustration: FIG. 65.--THE MOON. - -(FROM A PHOTOGRAPH BY L. M. RUTHERFURD, 1873, PUBLISHED BY O. G. -MASON.)] - -But if we begin to talk of things new and old which interest us in our -earth as a planet, it is hard to make an end. Still we may observe -that it is the very familiarity of some of these which hinders us from -seeing them as the wonders they really are. How has this familiarity, -for instance, made commonplace to us not only the wonderful fact that -the fields and forests, and the apparently endless plain of earth and -ocean, are really parts of a great globe which is turning round -(for this rotation we all are familiar with), but the less appreciated -miracle that we are all being hurled through space with an immensely -greater speed than that of the rotation itself. It needs the vision -of a poet to see this daily miracle with new eyes; and a great poet -has described it for us, in words which may vivify our scientific -conception. Let us recall the prologue to “Faust,” where the archangels -are praising the works of the Lord, and looking at the earth, not as we -see it, but down on it, from heaven, as it passes by, and notice that -it is precisely this miraculous swiftness, so insensible to us, which -calls out an angel’s wonder. - - “And swift and swift beyond conceiving - The splendor of the world goes round, - Day’s Eden-brightness still relieving - The awful Night’s intense profound. - The ocean tides in foam are breaking, - Against the rocks’ deep bases hurled, - And both, the spheric race partaking, - Eternal, swift, are onward whirled.”[5] - - [5] Bayard Taylor’s translation. - -So, indeed, might an angel see it and describe it! - - * * * * * - -We may have been already led to infer that there is a kind of evolution -in the planets’ life, which we may compare, by a not wholly fanciful -analogy, to ours; for we have seen worlds growing into conditions -which may fit them for habitability, and again other worlds where we -may surmise, or may know, that life has come. To learn of at least one -which has completed the analogy, by passing beyond this term to that -where all life has ceased, we need only look on the moon. - - * * * * * - -The study of the moon’s surface has been continued now from the time -of Galileo, and of late years a whole class of competent observers has -been devoted to it, so that astronomers engaged in other branches have -oftener looked on this as a field for occasional hours of recreation -with the telescope than made it a constant study. I can recall one or -two such hours in earlier observing days, when, seated alone under -the overarching iron dome, the world below shut out, and the world -above opened, the silence disturbed by no sound but the beating of the -equatorial clock, and the great telescope itself directed to some hill -or valley of the moon, I have been so lost in gazing that it seemed as -though a look through this, the real magic tube, had indeed transported -me to the surface of that strange alien world. Fortunately for us, the -same spectacle has impressed others with more time to devote to it and -more ability to render it, so that we not only have most elaborate -maps of the moon for the professional astronomer, but abundance of -paintings, drawings, and models, which reproduce the appearance of -its surface as seen in powerful telescopes. None of the latter class -deserves more attention than the beautiful studies of Messrs. Nasmyth -and Carpenter, who prepared at great labor very elaborate and, in -general, very faithful models of parts of its surface, and then had -them photographed under the same illumination which fell on the -original; and I wish to acknowledge here the special indebtedness of -this part of what I have to lay before the reader to their work, from -which the following illustrations are chiefly taken. - -Let us remember that the moon is a little over twenty-one hundred miles -in diameter; that it weighs, bulk for bulk, about two-thirds what the -earth does, so that, in consequence of this and its smaller size, its -total weight is only about one-eightieth of that of our globe; and -that, the force of gravity at its surface being only one-sixth what it -is here, eruptive explosions can send their products higher than in our -volcanoes. Its area is between four and five times that of the United -States, and its average distance is a little less than two hundred and -forty thousand miles. - -[Illustration: FIG. 66.--THE FULL MOON.] - -This is very little in comparison with the great spaces we have been -traversing in imagination; but it is absolutely very large, and across -it the valleys and mountains of this our nearest neighbor disappear, -and present to the naked eye only the vague lights and shades known to -us from childhood as “the man in the moon,” and which were the puzzle -of the ancient philosophers, who often explained them as reflections -of the earth itself, sent back to us from the moon as from a mirror. -It, at any rate, shows that the moon always turns the same face toward -us, since we always see the same “man,” and that there must be a back -to the moon which we never behold at all; and, in fact, nearly half of -this planet does remain forever hidden from human observation. - -The “man in the moon” disappears when we are looking in a telescope, -because we are then brought so near to details that the general -features are lost; but he can be seen in any photograph of the full -moon by viewing it at a sufficient distance, and making allowance for -the fact that the contrasts of light and shade appear stronger in the -photograph than they are in reality. If the small full moon given in -Fig. 66, for instance, be looked at from across a room, the naked-eye -view will be recovered, and its connection with the telescopic ones -better made out. The best time for viewing the moon, however, is not -at the full, but at the close of the first quarter; for then we see, -as in this beautiful photograph (Fig. 65) by Mr. Rutherfurd, that the -sunlight, falling slantingly on it, casts shadows which bring out all -the details so that we can distinguish many of them even here,--this -photograph, though much reduced, giving the reader a better view than -Galileo obtained with his most powerful telescope. The large gray -expanse in the lower part is the Mare Serenitatis, that on the left the -Mare Crisium, and so on; these “seas,” as they were called by the old -observers, being no seas at all in reality, but extended plains which -reflect less light than other portions, and which with higher powers -show an irregular surface. Most of the names of the main features of -the lunar surface were bestowed by the earlier observers in the infancy -of the telescope, when her orb - - “Through optic glass the Tuscan artist ‘viewed’ - At evening from the top of Fiesole - Or in Valdarno, to descry new lands, - Rivers, or mountains in her spotty globe.” - -Mountains there are, like the chain of the lunar Apennines, which the -reader sees a little below the middle of the moon, and to the right -of the Mare Serenitatis, and where a good telescope will show several -thousand distinct summits. Apart from the mountain chains, however, the -whole surface is visibly pitted with shallow, crater-like cavities, -which vary from over a hundred miles in diameter to a few hundred yards -or less, and which, we shall see later, are smaller sunken plains -walled about with mountains or hills. - -One of the most remarkable, of these is Tycho, here seen on the -photograph of the full moon (Fig. 66), from which radiating streaks go -in all directions over the lunar surface. These streaks are a feature -peculiar to the moon (at least we know of nothing to which they can be -compared on the earth), for they run through mountain and valley for -hundreds of miles without any apparent reference to the obstacles in -their way, and it is clear that the cause is a deep-seated one. This -cause is believed by our authors to be the fact that the moon was once -a liquid sphere over which a hard crust formed, and that in subsequent -time the expansion of the interior before solidification cracked the -shell as we see. The annexed figure (Fig. 67) is furnished by them to -illustrate their theory, and to show the effects of what they believe -to be an analogous experiment, _in minimis_, to what Nature has -performed on the grandest scale; for the photograph shows a glass globe -actually cracked by the expansion of an enclosed fluid (in this case -water), and the resemblance of the model to the photograph of the full -moon on page 141 is certainly a very interesting one. - -[Illustration: FIG. 67.--GLASS GLOBE, CRACKED.] - -We are able to see from this, and from the multitude of craters shown -even on the general view, where the whole face of our satellite is -pit-marked, that eruptive action has been more prominent on the moon in -ages past than on our own planet, and we are partly prepared for what -we see when we begin to study it in detail. - -We may select almost any part of the moon’s surface for this nearer -view, with the certainty of finding something interesting. Let us -choose, for instance, on the photograph of the half-full moon (Fig. -65), the point near the lower part of the Terminator (as the line -dividing light from darkness is called) where a minute sickle of light -seems to invade the darkness, and let us apply in imagination the power -of a large telescope to it. We are brought at once considerably within -a thousand miles of the surface, over which we seem to be suspended, -everything lying directly beneath us as in a bird’s-eye view, and what -we see is the remarkable scene shown in Fig. 68. - -We have before us such a wealth of detail that the only trouble is -to choose what to speak of where every point has something to demand -attention, and we can only give here the briefest reference to the -principal features. The most prominent of these is the great crater -“Plato,” which lies in the lower right-hand part of the cut. It will -give the reader an idea of the scale of things to state that the -diameter of its ring is about seventy miles; so that he will readily -understand that the mountains surrounding it may average five to six -thousand feet in height, as they do. The sun is shining from the left, -and, being low, casts long shadows, so that the real forms of the -mountains on one side are beautifully indicated by these shadows, where -they fall on the floor of the crater. In the lower part of the mountain -wall there has been a land-slide, as we see by the fragments that have -rolled down into the plain, and of which a trace can be observed in our -engraving. The whole is quite unlike most terrestrial craters, however, -not only in its enormous size, but in its proportions; for the floor -is not precipitous, but flat, or partaking of the general curvature of -the lunar surface, which it sinks but little below. I have watched with -interest in the telescope streaks and shades on the floor of Plato, not -shown in our cut; for here some have suspected evidences of change, -and fancied a faint greenish tint, as if due to vegetation, but it is -probably fancy only. Notice the number of small craters around the -big one, and everywhere on the plate, and then look at the amazingly -rugged and tumbled mountain heaps on the left (the lunar Alps), cut -directly through by a great valley (the valley of the Alps), which is -at the bottom about six miles wide and extraordinarily flat,--flatter -and smoother even than our engraving shows it, and looking as though -a great engineering work, rather than an operation of Nature, were in -question. Above this the mountain shadows are cast upon a wide plain, -in which are both depressed pits with little mountain (or rather hill) -rings about them, and extraordinary peaks, one of which, Pico (above -the great crater), starts up abruptly to the height of eight thousand -feet, a lunar Matterhorn. - -If Mars were as near as the moon, we should see with the naked eye -clouds passing over its face; and that we never do see these on the -moon, even with the telescope, is itself a proof that none exist there. -Now, this absence of clouds, or indeed of any evidence of moisture, -is confirmed by every one of the nearer views like those we are here -getting. We might return to this region with the telescope every month -of our lives without finding one indication of vapor, of moisture, or -even of air; and from a summit like Pico, could we ascend it, we should -look out on a scene of such absolute desolation as probably no -earthly view could parallel. If, as is conceivable, these plains were -once covered with verdure, and the abode of living creatures, verdure -and life exist here no longer, and over all must be the silence of -universal death. But we must leave it for another scene. - -[Illustration: FIG. 68.--PLATO AND THE LUNAR ALPS.] - -South of Plato extends for many hundred miles a great plain, which -from its smoothness was thought by the ancient observers to be water, -and was named by them the “Imbrian Sea,” and this is bounded on the -south and west by a range of mountains--the “lunar Apennines” (Fig. -69)--which are the most striking on our satellite. They are visible -even with a spy-glass, looking then like bread-crumbs ranged upon a -cloth, while with a greater power they grow larger and at the same -time more chaotic. As we approach nearer, we see that they rise -with a comparatively gradual slope, to fall abruptly, in a chain of -precipices that may well be called tremendous, down to the plain below, -across which their shadows are cast. Near their bases are some great -craters of a somewhat different type from Plato, and our illustration -represents an enlarged view of a part of this Apennine chain, of the -great crater Archimedes, and of its companions Aristillus and Autolycus. - -Our engraving will tell, more than any description, of the contrast -of the tumbled mountain peaks with the level plain from which they -spring,--a contrast for which we have scarcely a terrestrial parallel, -though the rise of the Alps from the plains of Lombardy may suggest an -inadequate one. The Sierra Nevadas of California climb slowly up from -the coast side, to descend in great precipices on the east, somewhat -like this; but the country at their feet is irregular and broken, and -their highest summits do not equal those before us, which rise to -seventeen or eighteen thousand feet, and from one of which we should -look out over such a scene of desolation as we can only imperfectly -picture to ourselves from any experience of a terrestrial desert. The -curvature of the moon’s surface is so much greater than ours, that it -would hide the spurs of hills which buttress the southern slopes of -Archimedes, leaving only the walls of the great mountain ring visible -in the extremest horizon, while between us and them would extend what -some still maintain to have been the bed of an ancient lunar ocean, -though assuredly no water exists there now. - -Among the many fanciful theories to account for the forms of the -ringed plains, one (and this is from a man of science whose ideas are -always original) invokes the presence of water. According to it, these -great plains were once ocean beds, and in them worked a coral insect, -building up lunar “atolls” and ring-shaped submarine mountains, as the -coral polyp does here. The highest summits of the great rings thus -formed were then low islands, just “a-wash” with the waves of the -ancient lunar sea, and, for aught we know, green with feathery palms. -Then came (in the supposition in question) a time when the ocean dried -up, and the mountains were left standing, as we see, in rings, after -the cause of their formation was gone. If it be asked where the water -went to, the answer is not very obvious on the old theories; but those -who believe in them point to the extraordinary cracks in the soil, like -those our engraving shows, as chasms and rents, by which the vanished -seas, and perhaps also the vanished air, have been absorbed into the -interior. - -[Illustration: FIG. 69.--THE LUNAR APENNINES: ARCHIMEDES.] - -If there was indeed such an ancient ocean, it would have washed the -very feet of the precipices on whose summits we are in imagination -standing, and below us their recesses would have formed harbors which -fancy might fill with commerce, and cities in which we might picture -life and movement where all is now dead. It need hardly be said that -no telescope has ever revealed their existence (if such ruins, indeed, -there are), and it may be added that the opinion of geologists is, as -a whole, unfavorable to the presence of water on the moon, even in -the past, from the absence of any clear evidence of erosive action; -but perhaps we are not yet entitled to speak on these points with -certainty, and are not forbidden to believe that water may have existed -here in the past by any absolute testimony to the contrary. The views -of those who hold the larger portion of the lunar craters to have -been volcanic in their formation are far more probable; and perhaps -as simple an evidence of the presumption in their favor as we can -give is directly to compare such a lunar region as this, the picture -of which was made for us from a model, with a similar model made from -some terrestrial volcanic region. Here (Fig. 70) is a photograph of -such a modelled plan of the country round the Bay of Naples, showing -the ancient crater of Vesuvius and its central cone, with other and -smaller craters along the sea. Here, of course, we _know_ that the -forms originated in volcanic action, and a comparison of them with our -moon-drawing is most interesting. To return to our Apennine region -(Fig. 69), we must admit, however, when we consider the vast size of -these things (Archimedes is fifty miles in diameter), that they are -very different in proportion from our terrestrial craters, and that -numbers of them present no central cone whatever; so that if some of -them seem clearly eruptive, there are others to which we have great -difficulties in making these volcanic theories apply. Let us look, for -instance, at still another region (Fig. 71). It lies rather above the -centre of the full moon, and may be recognized also on the Rutherfurd -photograph; and it consists of the group of great ring-plains, three of -which form prominent figures in our cut. - -Ptolemy (the lower of these in the drawing) is an example of such a -plain, whose diameter reaches to about one hundred and fifteen miles, -so that it encloses an area of nearly eight thousand square miles -(or about that of the State of Massachusetts), within which there is -no central cone or point from which eruptive forces appear to have -acted, except the smaller craters it encloses. On the south we see -a pass in the mountain wall opening into the neighboring ring-plain -of Alphonsus, which is only less in size; and south of this again is -Arzachel, sixty-six miles in diameter, surrounded with terraced walls, -rising in one place to a height greater than that of Mont Blanc, while -the central cone is far lower. The whole of the region round about, -though not the roughest on the moon, is rough and broken in a way -beyond any parallel here, and which may speak for itself; but perhaps -the most striking of the many curious features--at least the only one -we can pause to examine--is what is called “The Railway,” an almost -perfectly straight line, on one side of which the ground has abruptly -sunk, leaving the undisturbed part standing like a wall, and forming a -“fault,” as geologists call it. This is the most conspicuous example of -its kind in the moon, but it is only one of many evidences that we are -looking at a world whose geological history has been not wholly unlike -our own. But the moon contains, as has been said, but the one-eightieth -part of the mass of our globe, and has therefore cooled with much -greater rapidity, so that it has not only gone through the epochs -of our own past time, but has in all probability already undergone -experiences which for us lie far in the future; and it is hardly less -than justifiable language to say that we are beholding here in some -respects what the face of our world may be when ages have passed away. - -[Illustration: FIG. 70.--VESUVIUS AND NEIGHBORHOOD OF NAPLES.] - -To see this more clearly, we may consider that in general we find that -the early stages of cosmical life are characterized by great heat; a -remark of the truth of which the sun itself furnishes the first and -most obvious illustration. Then come periods which we appear to have -seen exemplified in Jupiter, where the planet is surrounded by volumes -of steam-like vapor, through which we may almost believe we recognize -the dull glow of not yet extinguished fires; then times like those -which our earth passed through before it became the abode of man; -and then the times in which human history begins. But if this process -of the gradual loss of heat go on indefinitely, we must yet come to -still another era, when the planet has grown too cold to support life, -as it was before too hot; and this condition, in the light of some very -recent investigations, it seems probable we have now before us on the -moon. - -We have, it is true, been taught until very lately that the side of the -moon turned sunward would grow hotter and hotter in the long lunar day, -till it reached a temperature of two hundred to three hundred degrees -Fahrenheit, and that in the equally long lunar night it would fall as -much as this below zero. But the evidence which was supposed to support -this conclusion as to the heat of the lunar day is not supported by -recent experiments of the writer; and if these be trustworthy, certain -facts appear to him to show that the temperature of the moon’s surface, -even under full perpetual sunshine, must be low,--and this because -of the absence of air there to keep the stored sun-heat from being -radiated away again into space. - -As we ascend the highest terrestrial mountains, and get partly above -our own protecting blanket of air, things do not grow hotter and -hotter, but colder and colder; and it seems contrary to the teachings -of common sense to believe that if we could ascend higher yet, where -the air ceases altogether, we should not find that it grew colder -still. But this last condition (of airlessness) is the one which does -prevail beyond a doubt in the moon, on whose whole surface, then, there -must be (unless there are sources of internal heat of which we know -nothing) conditions of temperature which are an exaggeration of those -we experience on the summit of a very lofty mountain, where we have the -curious result that the skin may be burned under the solar rays, while -we are shivering at the same time in what the thermometer shows is an -arctic cold. - -We have heard of this often; but a personal experience so impressed the -fact on me that I will relate it for the benefit of the reader, who -may wish to realize to himself the actual conditions which probably -exist in the airless lunar mountains and plains we are looking at. -He cannot go there; but he may go if he pleases, as I have done, to -the waterless, shadeless waste which stretches at the eastern slope -of the Sierra Nevadas (a chain almost as high and steep as the lunar -Apennines), and live some part of July and August in this desert, where -the thermometer rises occasionally to one hundred and ten degrees in -the shade, and his face is tanned till it can tan no more, and he -appears to himself to have experienced the utmost in this way that the -sun can do. - -The sky is cloudless, and the air so clear that all idea of the real -distance and size of things is lost. The mountains, which rise in -tremendous precipices above him, seem like moss-covered rocks close -at hand, on the tops of which, here and there, a white cloth has been -dropped; but the “moss” is great primeval forests, and the white cloths -large isolated snow-fields, tantalizing the dweller in the burning -desert with their delusive nearness. When I climbed the mountains, -at an altitude of ten thousand feet I already found the coolness -delicious, but at the same time (by the strange effect I have been -speaking of) the skin began to burn, as though the seasoning in the -desert counted for nothing at all; and as the air grew thinner and -thinner while I mounted still higher and higher, though the thermometer -fell, every part of the person exposed to the solar rays presented the -appearance of a recent severe burn from an actual fire,--and a really -severe burn it was, as I can testify,--and yet all the while around us, -under this burning sun and cloudless sky, reigned a perpetual winter -which made it hard to believe that torrid summer still lay below. The -thinner the air, then, the colder it grows, even where we are exposed -to the sun, and the lower becomes the reading of the thermometer. -Now, by means of suitable apparatus, it was sought by the writer to -determine, while at this elevation of fifteen thousand feet, _how_ -great the fall of temperature would be if the thin air there could be -removed altogether; and the result was that the thermometer would under -such circumstances fall, at any rate, below zero in the full sunshine. - -[Illustration: FIG. 71.--PTOLEMY AND ARZACHEL.] - -Of course, all this applies indirectly to the moon, above whose -surface (if these inferences be correct) the mercury in the bulb of a -thermometer would probably freeze and never melt again during the lunar -day (and still less during the lunar night),--a conclusion which has -been reached through other means by Mr. Ericsson,--and whose surface -itself cannot be very greatly warmer. Other and direct measures of the -lunar heat are still in progress while this is being written, but their -probable result seems to be already indicated: it is that the moon’s -surface, even in perpetual sunshine, must be forever cold. Just how -cold, is still doubtful; and it is not yet certain whether ice, if once -formed there, could ever melt. - -Here (Fig. 72) is one more scene from the almost unlimited field the -lunar surface affords. - -The most prominent things in the landscape before us are two fine -craters (Mercator and Campanus), each over thirty miles in diameter; -but we have chosen this scene for remark rather on account of the great -crack or rift which is seen in the upper part, and which cuts through -plain and mountain for a length of sixty miles. Such cracks are counted -by hundreds on the moon, where they are to be seen almost everywhere; -and other varieties, in fact, are visible on this same plate, but -we will not stop to describe them. This one varies in width from an -eighth of a mile to a mile; and though we cannot see to the bottom -of it, others are known to be at least eight miles deep, and may be -indefinitely deeper. - -The edge of a cliff on the earth commonly gets weather-worn and -rounded; but here the edge is sharp, so that a traveller along the -lunar plains would come to the very brink of this tremendous chasm -before he had any warning of its existence. It is usually thus with all -such rifts; and the straightness and sharpness of the edge in these -cases suggest the appearance of an ice-crack to the observer. I do -not mean to assert that there is more than a superficial resemblance. -I do not write as a geologist; but in view of what we have just been -reading of the lunar cold, we may ask ourselves whether, if water -ever did exist here, we should not expect to find perpetual ice, not -necessarily glittering, but covered, perhaps, with the deposits of an -air laden with the dust-products of later volcanic eruptions, or even -covered in after ages, when the air has ceased from the moon, with the -slow deposit of meteoric dust during millions of years of windless -calm. What else can we think will become of the water on our own earth -if it be destined to pass through such an experience as we seem to see -prophesied in the condition of our dead satellite? - -The reader must not understand me as saying that there is ice on the -moon,--only that there is not improbably perpetual ice there now _if_ -there ever was water in past time; and he is not to suppose that to -say this is in any way to deny what seems the strong evidence of the -existence of volcanic action everywhere, for the two things may well -have existed in successive ages of our satellite’s past, or even have -both existed together, like Hecla, within our own arctic snows; and -if no sign of any still active lunar volcano has been discovered, we -appear to read the traces of their presence in the past none the less -clearly. - -I remember that at one time, when living on the lonely upper -lava-wastes of Mount Etna, which are pitted with little craters, I grew -acquainted with so many a chasm and rent filled with these, that the -dreary landscape appeared from above as if a bit of the surface of -the moon I looked up at through the telescope had been brought down -beside me. - -[Illustration: FIG. 72.--MERCATOR AND CAMPANUS.] - -I remember, too, that as I studied the sun there, and watched the -volcanic outbursts on its surface, I felt that I possibly embraced in a -threefold picture as many stages in the history of planetary existence, -through all of which this eruptive action was an agent,--above in the -primal energies of the sun; all around me in the great volcano, black -and torn with the fires that still burn below, and whose smoke rose -over me in the plume that floated high up from the central cone; and -finally in this last stage in the moon, which hung there pale in the -daylight sky, and across whose face the vapors of the great terrestrial -volcano drifted, but on whose own surface the last fire was extinct. - -We shall not get an adequate idea of it all, unless we add to our -bird’s-eye views one showing a chain of lunar mountains as they would -appear to us if we saw them, as we do our own Alps or Apennines, from -about their feet; and such a view Fig. 74 affords us. In the barren -plain on the foreground are great rifts such as we have been looking -at from above, and smaller craters, with their extinct cones; while -beyond rise the mountains, ghastly white in the cold sunshine, their -precipices crowned by no mountain fir or cedar, and softened by no -intervening air to veil their nakedness. - -If the reader has ever climbed one of the highest Alpine peaks, like -those about Monte Rosa or the Matterhorn, and there waited for the -dawn, he cannot but remember the sense of desolation and strangeness -due to the utter absence of everything belonging to man or his works -or his customary abode, above all which he is lifted into an upper -world, so novel and, as it were, so unhuman in its features, that he -is not likely to have forgotten his first impression of it; and this -impression gives the nearest but still a feeble idea of what we see -with the telescope in looking down on such a colorless scene, where -too no water bubbles, no tree can sigh in the breeze, no bird can -sing,--the home of silence. - -[Illustration: FIG. 73.--WITHERED HAND.] - -But here, above it, hangs a world in the sky, which we should need to -call in color to depict, for it is green and yellow with the forests -and the harvest-fields that overspread its continents, with emerald -islands studding its gray oceans, over all of which sweep the clouds -that bring the life-giving rain. It is our own world, which lights up -the dreary lunar night, as the moon does ours. - -[Illustration: FIG. 74.--IDEAL LUNAR LANDSCAPE AND EARTH-SHINE.] - -The signs of age are on the moon. It seems pitted, torn, and rent by -the past action of long-dead fires, till its surface is like a piece -of porous cinder under the magnifying-glass,--a burnt-out cinder of a -planet, which rolls through the void like a ruin of what has been; and, -more significant still, this surface is wrinkled everywhere, till the -analogy with an old and shrivelled face or hand or fruit (Figs. 73 and -75), where the puckered skin is folded about a shrunken centre, forces -itself on our attention, and suggests a common cause,--a something -underlying the analogy, and making it more than a mere resemblance. - -[Illustration: FIG. 75.--WITHERED APPLE.] - -The moon, then, is dead; and if it ever was the home of a race like -ours, that race is dead too. I have said that our New Astronomy -modifies our view of the moral universe as well as of the physical one; -nor do we need a more pregnant instance than in this before us. In -these days of decay of old creeds of the eternal, it has been sought -to satisfy man’s yearning toward it by founding a new religion whose -god is Humanity, and whose hope lies in the future existence of our own -race, in whose collective being the individual who must die may fancy -his aims and purpose perpetuated in an endless progress. But, alas for -hopes looking to this alone! we are here brought to face the solemn -thought that, like the individual, though at a little further date, -Humanity itself may die! - -Before we leave this dead world, let us take a last glance at one of -its fairest scenes,--that which we obtain when looking at a portion -on which the sun is rising, as in this view of Gassendi (Fig. 76), -in which the dark part on our right is still the body of the moon, -on which the sun has not yet risen. Its nearly level rays stretch -elsewhere over a surface that is, in places, of a strangely smooth -texture, contrasting with the ruggedness of the ordinary soil, which is -here gathered into low plaits, that, with the texture we have spoken -of, look - - “Like marrowy crapes of China silk, - Or wrinkled skin on scalded milk,” - -as they lie, soft and almost beautiful, in the growing light. - -Where its first beams are kindling, the summits cast their shadows -illimitedly over the darkening plains away on the right, until they -melt away into the night,--a night which is not utterly black, for even -here a subdued radiance comes from the earth-shine of our own world in -the sky. - -Let us leave here the desolation about us, happy that we can come back -at will to that world, our own familiar dwelling, where the meadows -are still green and the birds still sing, and where, better yet, still -dwells our own kind,--surely the world, of all we have found in our -wanderings, which we should ourselves have chosen to be our home. - -[Illustration: FIG. 76.--GASSENDI. NOV. 7, 1867.] - - - - -VI. - -METEORS. - - -What is truth? What is fact, and what is fancy, even with regard to -solid visible things that we may see and handle? - -Among the many superstitions of the early world and credulous fancies -of the Middle Ages, was the belief that great stones sometimes fell -down out of heaven onto the earth. - -Pliny has a story of such a black stone, big enough to load a chariot; -the Mussulman still adores one at Mecca; and a mediæval emperor of -Germany had a sword which was said to have been forced from one of -these bolts shot out of the blue. But with the revival of learning, -people came to know better! That stones should fall down from the sky -was clearly, they thought, an absurdity; indeed, according to the -learned opinion of that time, one would hardly ask a better instance -of the difference between the realities which science recognized and -the absurdities which it condemned than the fancy that such a thing -could be. So at least the matter looked to the philosophers of the -last century, who treated it much as they might treat certain alleged -mental phenomena, for instance, if they were alive to-day, and at first -refused to take any notice of these stories, when from time to time -they still came to hand. When induced to give the matter consideration, -they observed that all the conditions for scientific observation were -violated by these bodies, since the wonder always happened at some -far-off place or at some past time, and (suspicious circumstance!) -the stones only fell in the presence of ignorant and unscientific -witnesses, and never when scientific men were at hand to examine the -facts. That there were many worthy, if ignorant, men who asserted that -they had seen such stones fall, seen them with their very eyes, and -held them in their own hands, was accounted for by the general love of -the marvellous and by the ignorance of the common mind, unlearned in -the conditions of scientific observation, and unguided by the great -principle of the uniformity of the Laws of Nature. - -Such a tone, of course, cannot be heard among us, who never hastily -pronounce anything a departure from the “Laws of Nature,” while -uncertain that these can be separated from the laws of the fallible -human mind, in which alone Nature is seen. But in the last century -philosophers had not yet become humble, or scientific men diffident -of the absoluteness of their own knowledge, and so it seemed that no -amount of evidence was enough to gain an impartial hearing in the face -of the settled belief that the atmosphere extended only a few miles -above the earth’s surface, and that the region beyond, whence alone -such things could come, was an absolute void extending to the nearest -planet. - -[Illustration: FIG. 77.--THE CAMP AT MOUNT WHITNEY. - -(FROM “PROFESSIONAL PAPERS OF THE SIGNAL SERVICE,” VOL. XV.)] - -It used to be supposed that we were absolutely isolated, not only from -the stars but from other planets, by vast empty spaces extending from -world to world,--regions altogether vacant except for some vagrant -comet; but of late years we are growing to have new ideas on this -subject, and not only to consider space as far from void or tenantless, -but to admit, as a possibility at least, that there is a sort of -continuity between our very earth’s surface, the air above it, and -all which lies beyond the blue overarching dome of our own sky. Our -knowledge of the physical nature of the universe without has chiefly -come from what the spectroscope, overleaping the space between us -and the stars, has taught us of them; as a telegram might report to -us the existence of a race across the ocean, without telling anything -of what lay between. It would be a novel path to the stars, and to the -intermediate regions whence these once mythical stones are now actually -believed to come, if we could take the reader to them by a route which -enabled us to note each step of a continuous journey from the earth’s -surface out into the unknown; but if we undertake to start upon it, he -will understand that we must almost at the outset leave the ground of -comparative certainty on which we have hitherto rested, and need to -speak of things on this road which are still but probabilities, and -even some which are little more than conjectures, before we get to the -region of comparative certainty again,--a region which, strange to say, -exists far away from us, while that of doubt lies close at hand, for we -may be said without exaggeration to know more about Sirius than about -the atmosphere a thousand miles above the earth’s surface; indeed, it -would be more just to say that we are sure not only of the existence -but of the elements that compose a star, though a million of times as -far off as the sun, while at the near point named we are not sure of so -much as that the atmosphere exists at all. - -To begin our outward journey in a literal sense, we might rise from -the earth’s surface some miles in a balloon, when we should find our -progress stayed by the rarity of the air. Below us would be a gray -cloud-ocean, through which we could see here and there the green -earth beneath, while above us there would still be something in the -apparently empty air, for if the sun has just set it will still be -_light_ all round us. Something then, in a cloudless sky, still exists -to reflect the rays towards us, and this something is made up of -separately invisible specks of dust and vapor, but very largely of -actual dust, which probably forms the nucleus of each mist-particle. -That discrete matter of some kind exists here has long been recognized -from the phenomena of twilight; but it is, I think, only recently that -we are coming to admit that a shell of actual solid particles in the -form of dust probably encloses the whole globe, up to far above the -highest clouds. - -In 1881 the writer had occasion to conduct a scientific expedition to -the highest point in the territories of the United States, on one of -the summits of the Sierra Nevadas of Southern California, which rise -even above the Rocky Mountains. - -The illustration on page 177 represents the camp occupied by this party -below the summit, where the tents, which look as if in the bottom of a -valley, are yet really above the highest zone of vegetation, and at an -altitude of nearly twelve thousand feet. - -Still above these rise the precipices of barren rock seen in -the background, their very bases far above the highest visible -dust-clouds, which overspread like a sea the deserts at the mountain’s -foot,--precipices which when scaled lift the observer into what is, -perhaps, the clearest and purest air to be found in the world. It will -be seen from the mere looks of the landscape that we are far away here -from ordinary sources of contamination in the atmosphere. Yet even -above here on the highest peak, where we felt as if standing on the -roof of the continent and elevated into the great aerial currents of -the globe, the telescope showed particles of dust in the air, which the -geologists deemed to have probably formed part of the soil of China -and to have been borne across the Pacific, but which also, as we shall -see later, may owe something to the mysterious source of the phenomena -already alluded to. - -It is far from being indifferent to us that the dust is there; for, to -mention nothing else, without it, it would be night till the sunrise, -and black night again as soon as the sun’s edge disappeared below -the horizon. The morning and the evening twilight, which in northern -latitudes increase our average time of light by some hours, and add -very materially to the actual days of man’s life, are probably due -almost wholly to particles scarcely visible in the microscope, and to -the presence of such atoms, smaller than the very motes ordinarily -seen in the sunbeam, which, as Mr. Aitken has shown, fill the air we -breathe,--so minute and remote are the causes on which the habits of -life depend. - -Before we can see that a part of this impalpable, invisible dust is -also perhaps a link between our world and other members of the solar -system, we must ask how it gets into the atmosphere. Is it blown up -from the earth, or does it fall down out of the miscalled “void” of -space? - -If we cast a handful of dust into the air, it will not mount far above -the hand unless we set the air in motion with it, as in ascending -smoke-currents; and the greatest explosions we can artificially -produce, hurl their finer products but a few hundred feet at most from -the soil. Utterly different are the forces of Nature. We have on page -183 a reproduction from a photograph of an eruption of Vesuvius,--a -mere toy-volcano compared to Etna or Hecla. But observe the smoke-cloud -which rises high in the sunshine, looking solid as the rounded snows of -an Alp, while the cities and the sea below are in the shadow. The smoke -that mounts from the foreground, where the burning lava-streams are -pouring over the surface and firing the woods, is of another kind from -that rolling high above. _This_ comes from within the mountain, and -is composed of clouds of steam mingled with myriads of dust-particles -from the comminuted products of the earth’s interior; and we can see -ourselves that it is borne away on a level, miles high in the upper air. - -But what is this to the eruption of Sumbawa or Krakatao? The latter -occurred in 1883, and it will be remembered that the air-wave started -by the explosion was felt around the globe, and that, probably owing -to the dust and water-vapor blown into the atmosphere, the sunsets -even in America became of that extraordinary crimson we all remember -three years ago; and coincidently, that dim reddish halo made its -appearance about the sun, the world over, which is hardly yet gone.[6] -Very careful estimates of the amount of ashes ejected have been made; -and though most of the heavier particles are known to have fallen -into the sea within a few miles, a certain portion--the lightest--was -probably carried by the explosion far above the lower strata of the -atmosphere, to descend so slowly that some of it may still be there. -Of this lighter class the most careful estimates must be vague; but -according to the report of the official investigation by the Dutch -Government, that which remained floating is something enormous. An idea -of its amount may be gained by supposing these impalpable and invisible -particles to condense again from the upper sky, and to pour down on -the highest edifice in the world, the Washington Monument. If the dust -were allowed to spread out on all sides, till the pyramidal slope was -so flat as to be permanent, the capstone of the monument would not only -be buried before the supply was exhausted, but buried as far below the -surface as that pinnacle is now above it. - - [6] In January, 1887. - -Of the explosive suddenness with which the mass was hurled, we can -judge something (comparing small things with great) by the explosion of -dynamite. - -It happened once that the writer was standing by a car in which some -railway porters were lifting boxes. At that moment came an almost -indescribable sound, for it was literally stunning, though close and -sharp as the crack of a whip in one’s hand, and yet louder than the -nearest thunder-clap. The men leaped from the car, thinking that one of -the boxes had exploded between them; but the boxes were intact, and we -saw what seemed a pillar of dust rising above the roof of the station, -hundreds of yards away. When we hurried through the building, we -found nothing on the other side but a bare plain, extending over a -mile, and beyond this the actual scene of the explosion that had -seemed to be at our feet. There had been there, a few minutes before, -extensive buildings and shops belonging to the railroad, and sidings -on which cars were standing, two of which, loaded with dynamite, had -exploded. - -[Illustration: FIG. 78.--VESUVIUS DURING AN ERUPTION.] - -Where they _had_ been was a crater-like depression in the earth, some -rods in diameter; the nearest buildings, great solid structures of -brick and stone, had vanished, and the more distant wooden ones and the -remoter lines of freight-cars on the side-tracks presented a curious -sight, for they were not shattered so much as bent and leaning every -way, as though they had been built of pasteboard, like card-houses, -and had half yielded to some gigantic puff of breath. All that the -explosion had shot skyward had settled to earth or blown away before -we got in sight of the scene, which was just as quiet as it had been a -minute before. It was like one of the changes of a dream. - -Now, it is of some concern to us to know that the earth holds within -itself similar forces, on an incomparably greater scale. For instance, -the explosion which occurred at Krakatao, at five minutes past ten, on -the 27th of August, 1883, according to official evidence, was heard -at a distance of eighteen hundred miles, and the puff of its air-wave -injured dwellings two hundred miles distant, and, we repeat, carried -into the highest regions of the atmosphere and around the world matter -which it is at least possible still affects the aspect of the sun -to-day from New York or Chicago. - -Do not the great flames which we have seen shot out from the sun -at the rate of hundreds of miles a second, the immense and sudden -perturbations in the atmosphere of Jupiter, and the scarred surface of -the moon, seem to be evidences of analogous phenomena, common to the -whole solar system, not wholly unconnected with those of earthquakes, -and which we can still study in the active volcanoes of the earth? - -If the explosion of gunpowder can hurl a cannon-shot three or four -miles into the air, how far might the explosion of Krakatao cast its -fragments? At first we might think there must be some proportionality -between the volume of the explosion and the distance, but this is not -necessarily so. Apart from the resistance of the air, it is a question -of the velocity with which the thing is shot upward, rather than the -size of the gun, or the size of the thing itself, and with a sufficient -velocity the projectile would never fall back again. “What goes up -must come down,” is, like most popular maxims, true only within the -limits of ordinary experience; and even were there nothing else in the -universe to attract it, and though the earth’s attraction extend to -infinity, so that the body would never escape from it, it is yet quite -certain that it would, with a certain initial velocity (very moderate -in comparison with that of the planet itself), go up and _never_ come -back; while under other and possible conditions it might voyage out -into space on a comet-like orbit, and be brought back to the earth, -perhaps in after ages, when the original explosion had passed out of -memory or tradition. But because all this is possible, it does not -follow that it is necessarily true; and if the reader ask why he should -then be invited to consider such suppositions at all, we repeat that -in our journey outward, before we come to the stars, of which we know -something, we pass through a region of which we know almost nothing; -and this region, which is peopled by the subjects of conjecture, is -the scene, if not the source, of the marvel of the falling stones, -concerning which the last century was so incredulous, but for which -we can, aided by what has just been said, now see at least a possible -cause, and to which we now return. - -Stories of falling stones, then, kept arising from time to time during -the last century as they had always done, and philosophers kept on -disbelieving them as they had always done, till an event occurred which -suddenly changed scientific opinion to compulsory belief. - -On the 26th of April, 1803, there fell, not in some far-off part of the -world, but in France, not one alone, but many thousand stones, over -an area of some miles, accompanied with noises like the discharge of -artillery. A committee of scientific men visited the spot on the part -of the French Institute, and brought back not only the testimony of -scores of witnesses or auditors, but the stones themselves. Soon after -stones fell in Connecticut, and here and elsewhere, as soon as men were -prepared to believe, they found evidence multiplied; and such falls, -it is now admitted, though rare in any single district, are of what -may be called frequent occurrence as regards the world at large,--for, -taking land and sea together, the annual stone-falls are probably to be -counted by hundreds. - -It was early noticed that these stones consisted either of a peculiar -alloy of iron, or of minerals of volcanic origin, or both; and the -first hypothesis was that they had just been shot out from terrestrial -volcanoes. As they were however found, as in the case of the -Connecticut meteorite, thousands of miles from any active volcanoes, -and were seen to fall, not vertically down, but as if shot horizontally -overhead, this view was abandoned. Next the idea was suggested that -they were coming from volcanoes in the moon; and though this had -little to recommend it, it was adopted in default of a better, and -entertained down to a comparatively very recent period. These stones -are now collected in museums, where any one may see them, and are to be -had of the dealers in such articles by any who wish to buy them. They -are coming to have such a considerable money value that, in one case -at least, a lawsuit has been instituted for their possession between -the finder, who had picked the stones up on ground leased to him, and -claimed them under the tenant’s right to wild game, and his landlord, -who thought they were his as part of the real estate. - -Leaving the decision of this novel law-point to the lawyers, let us -notice some facts now well established. - -The fall is usually preceded by a thundering sound, sometimes followed -or accompanied by a peculiar noise described as like that of a flock -of ducks rising from the water. The principal sound is often, however, -far louder than any thunder, and sometimes of stunning violence. At -night this is accompanied by a blaze of lightning-like suddenness and -whiteness, and the stones commonly do not fall vertically, but as if -shot from a cannon at long range. They are usually burning hot, but -in at least one authenticated instance one was so intensely cold that -it could not be handled. They are of all sizes, from tons to ounces, -comparatively few, however, exceeding a hundred-weight, and they -are oftenest of a rounded form, or looking like pieces of what was -originally round, and usually wholly or partly covered with a glaze -formed of the fused substance itself. If we slowly heat a lump of loaf -sugar all through, it will form a pasty mass, while we may also hold it -without inconvenience in our fingers to the gas-flame a few seconds, -when it will be melted only on the side next the sudden heat, and -rounded by the melting. The sharp contrast of the melted and the rough -side is something like that of the meteorites; and just as the sugar -does not burn the hand, though close to where it is brought suddenly -to a melting heat, a mass of ironstone may be suddenly heated on the -surface, while it remains cold on the inside. But, however it got -there, the stone undoubtedly comes from the intensely cold spaces above -the upper air; and what is the source of such a heat that it is melted -in the cold air, and in a few seconds? - -[Illustration: FIG. 79.--METEORS OBSERVED NOV. 13 AND 14, 1868, BETWEEN -MIDNIGHT AND FIVE O’CLOCK, A. M.] - -Everybody has noticed that if we move a fan gently, the air parts -before it with little effort, while, when we try to fan violently, -the same air is felt to react; yet if we go on to say that if the -motion is still more violent the atmosphere will resist like a solid, -against which the fan, if made of iron, would break in pieces, this may -seem to some an unexpected property of the “nimble” air through which -we move daily. Yet this is the case; and if the motion is only so quick -that the air cannot get out of the way, a body hurled against it will -rise in temperature like a shot striking an armor-plate. It is all a -question of speed, and that of the meteorite is known to be immense. -One has been seen to fly over this country from the Mississippi to -the Atlantic in an inappreciably short time, probably in less than -two minutes; and though at a presumable height of over fifty miles, -the velocity with which it shot by gave every one the impression that -it went just above his head, and some witnesses of the unexpected -apparition looked the next day to see if it had struck their chimneys. -The heat developed by arrested motion in the case of a mass of iron -moving twenty miles a second can be calculated, and is found to be -much more than enough, not only to melt it, but to turn it into vapor; -though what probably does happen is, according to Professor Newton, -that the melted surface-portions are wiped away by the pressure of the -air and volatilized to form the luminous train, the interior remaining -cold, until the difference of temperature causes a fracture, when the -stone breaks and pieces fall,--some of them at red-hot heat, some of -them possibly at the temperature of outer space, or far below that of -freezing mercury. - -Where do these stones come from? What made them? The answer is not yet -complete; but if a part of the riddle is already yielding to patience, -it is worthy of note, as an instance of the connection of the sciences, -that the first help to the solution of this astronomical enigma came -from the chemists and the geologists. - -The earliest step in the study, which has now been going on for many -years, was to analyze the meteorite, and the first result was that it -contained no elements not found on this planet. The next was that, -though none of these elements were unknown, they were not combined -as we see them in the minerals we dig from the earth. Next it was -found that the combinations, if unfamiliar at the earth’s surface and -nowhere reproduced exactly, were at least very like such as existed -down beneath it, in lower strata, as far as we can judge by specimens -of the earth’s interior cast up from volcanoes. Later, a resemblance -was recognized in the elements of the meteorites to those found by the -spectroscope in shooting stars, though the spectroscopic observation -of the latter is too difficult to have even yet proceeded very far. -And now, within the last few years, we seem to be coming near to a -surprising solution. - -It has now been shown that meteoric stones sometimes contain pieces -of essentially different rocks fused together, and pieces of -detritus,--the wearing down of older rocks. Thus, as we know that -sandstone is made of compacted sand, and sand itself was in some -still earlier time part of rocks worn down by friction,--when it is -shown, as it has been by M. Meunier, that a sandstone penetrated by -metallic threads (like some of our terrestrial formations) has come -to us in a meteorite, the conclusion that these stones may be part -of some old world is one that, however startling, we cannot refuse -at least to consider. According to this view, there may have been a -considerable planet near the earth, which, having reached the last -stage of planetary existence shown in the case of our present moon, -went one step further,--went, that is, out of existence altogether, by -literal breaking up and final disappearance. We have seen the actual -moon scarred and torn in every direction, and are asked to admit the -possibility that a continuance of the process on a similar body has -broken it up into the fragments that come to us. We do not say that -this is the case, but that (as regards the origin of some of the -meteorites at least) we cannot at present disprove it. We may, at any -rate, present to the novelist seeking a new _motif_ that of a meteorite -bringing to us the story of a lost race, in some fragment of art or -architecture of its lost world! - -We are not driven to this world-shattering hypothesis by the absence -of others, for we may admit these to be fragments of a larger body -without necessarily concluding that it was a world like ours, or, even -if it were, that the world which sent them to us is destroyed. In view -of what we have been learning of the tremendous explosive forces we -see in action on the sun and probably on other planets, and even in -terrestrial volcanoes to-day, it is certainly conceivable that some -of these stones may have been ejected by some such process from any -sun, or star, or world we see. The reader is already prepared for -the suggestion that part of them may be the product of terrestrial -volcanoes in early epochs, when our planet was yet glowing sunlike with -its proper heat, and the forces of Nature were more active; and that -these errant children of mother earth’s youth, after circulating in -lengthened orbits, are coming back to her in her age. - -Do not let us, however, forget that these are mostly speculations only, -and perhaps the part of wisdom is not to speculate at all till we learn -more facts; but are not the facts themselves as extraordinary as any -invention of fancy? - -Although it is true that the existence of the connection between -shooting stars and meteorites lacks some links in the chain of proof, -we may very safely consider them together; and if we wish to know what -the New Astronomy has done for us in this field, we should take up -some treatise on astronomy of the last century. We turn in one to the -subject of falling stars, and find that “this species of Star is only -a light Exhalation, almost wholly sulphurous, which is inflamed in -the free Air much after the same manner as Thunder in a Cloud by the -blowing of the Winds.” That the present opinion is different, we shall -shortly notice. - -All of us have seen shooting stars, and they are indeed something -probably as old as this world, and have left their record in mythology -as well as in history. According to Moslem tradition, the evil genii -are accustomed to fly at night up to the confines of heaven in order to -overhear the conversation of the angels, and the shooting stars are the -fiery arrows hurled by the latter at their lurking foes, with so good -an aim that we are told that for every falling star we may be sure that -there is one spirit of evil the less in the world. The scientific view -of them, however, if not so consolatory, is perhaps more instructive, -and we shall here give most attention to the latter. - -To begin with, there have been observed in history certain times when -shooting stars were unusually numerous. The night when King Ibrahim Ben -Ahmed died, in October, 902, was noted by the Arabians as remarkable in -this way; and it has frequently been observed since, that, though we -can always see some of these meteors nightly, there are at intervals -very special displays of them. The most notable modern one was on -Nov. 13, 1833, and this was visible over much of the North American -continent, forming a spectacle of terrifying grandeur. An eyewitness in -South Carolina wrote:-- - - “I was suddenly awakened by the most distressing cries that ever - fell on my ears. Shrieks of horror and cries for mercy I could - hear from most of the negroes of the three plantations, amounting - in all to about six hundred or eight hundred. While earnestly - listening for the cause I heard a faint voice near the door, - calling my name. I arose, and, taking my sword, stood at the - door. At this moment I heard the same voice still beseeching me - to rise, and saying, ‘O my God, the world is on fire!’ I then - opened the door, and it is difficult to say which excited me - the most--the awfulness of the scene, or the distressed cries - of the negroes. Upwards of one hundred lay prostrate on the - ground,--some speechless and some with the bitterest cries, but - with their hands raised, imploring God to save the world and - them. ‘The scene was truly awful; for never did rain fall much - thicker than the meteors fell toward the earth; east, west, - north, and south, it was the same.” - -The illustration on page 189 does not exaggerate the number of the -fiery flashes at such a time, though the zigzag course which is -observed in some is hardly so common as it here appears. - -When it was noted that the same date, November 13th, had been -distinguished by star-showers in 1831 and 1832, and that the great -shower observed by Humboldt in 1799 was on this day, the phenomenon was -traced back and found to present itself about every thirty-three years, -the tendency being to a little delay on each return; so that Professor -Newton and others have found it possible with this clew to discover -in early Arabic and other mediæval chronicles, and in later writers, -descriptions which, fitted together, make a tolerably continuous record -of this thirty-three-year shower, beginning with that of King Ibrahim -already alluded to. The shower appeared again in November, 1867 and -1868, with less display, but with sufficient brilliance to make the -writer well remember the watch through the night, and the count of the -flying stars, his most lively recollection being of their occasional -colors, which in exceptional cases ranged from full crimson to a vivid -green. The count on this night was very great, but the number which -enter the earth’s atmosphere even ordinarily is most surprising; for, -though any single observer may note only a few in his own horizon, -yet, taking the world over, at least ten millions appear every night, -and on these special occasions very many more. This November shower -comes always from a particular quarter of the sky, that occupied by the -constellation Leo, but there are others, such as that of August 10th -(which is annual), in which the “stars” seem to be shot at us from the -constellation Perseus; and each of the numerous groups of star-showers -is now known by the name of the constellation whence it seems to come, -so that we have _Perseids_ on August 10th, _Geminids_ on December 12th, -_Lyrids_, April 20th, and so on. - -The great November shower, which is coming once more in this century, -and which every reader may hope to see toward 1899, is of particular -interest to us as the first whose movements were subjected to analysis; -for it has been shown by the labors of Professor Newton, of Yale, and -Adams, of Cambridge, that these shooting stars are bodies moving around -the sun in an orbit which is completed in about thirty-three years. It -is quite certain, too, that they are not exhalations from the earth’s -atmosphere, but little solids, invisible till they shine out by the -light produced by their own fusion. Each, then, moves on its own track, -but the general direction of all the tracks concurs; and though some -of them may conceivably be solidified gases, we should think of them -not as gaseous in form, but as solid shot, of the average size of -something like a cherry, or perhaps even of a cherry-stone, yet each -an independent planetoid, flying with a hundred times the speed of a -rifle-bullet on its separate way as far out as the orbit of Uranus; -coming back three times in a century to about the earth’s distance from -the sun, and repeating this march forever, unless it happen to strike -the atmosphere of the earth itself, when there comes a sudden flash of -fire from the contact, and the distinct existence of the little body, -which may have lasted for hundreds of thousands of years, is ended in a -second. - -If the reader will admit so rough a simile, we may compare such a -flight of these bodies to a thin swarm of swift-flying birds--thin, but -yet immensely long, so as to be, in spite of the rapid motion, several -years in passing a given point, and whose line of flight is cut across -by us on the 13th of November, when the earth passes through it. We -are only there on that day, and can only see it then; but the swarm is -years in all getting by, and so we may pass into successive portions -of it on the anniversary of the same day for years to come. The stars -appear to shoot from Leo, only because that constellation is in the -line of their flight when we look up to it, just as an interminable -train of parallel flying birds would appear to come from some definite -point on the horizon. - -We can often see the flashes of meteors at over a hundred miles, and -though at times they may seem to come thick as Hakes of falling snow, -it is probable, according to Professor Newton, that even in a “shower” -each tiny planetoid is more than ten miles from its nearest neighbor, -while on the average it is reckoned that we may consider that each -little body, though possibly no larger than a pea, is over two hundred -miles from its neighbor, or that to each such grain there is nearly -ten million cubic miles of void space. Their velocity as compounded -with that of the earth is enormous, sometimes forty to fifty miles per -second (according to a recent but unproved theory of Mr. Denning, it -would be much greater), and it is this enormous rate of progress that -affords the semblance of an abundant fall of rain, notwithstanding the -distance at which one drop follows another. It is only from their light -that we are able to form a rough estimate of their average size, which -is, as we have seen, extremely small; but, from their great number, -the total weight they add to the earth daily may possibly be a hundred -tons, probably not very much more. As they are as a rule entirely -dissipated in the upper air, often at a height of from fifty to seventy -miles, it follows that many tons of the finest pulverized and gaseous -matter are shot into the earth’s atmosphere every twenty-four hours -from outer space, so that here is an independent and constant supply -of dust, which we may expect to find coming down from far above the -highest clouds. - -Now, when the reader sees the flash of a shooting star, he may, if he -please, think of the way the imagination of the East accounts for it, -or he may look at what science has given him instead. In the latter -case he will know that a light which flashed and faded almost together -came from some strange little entity which had been traversing cold -and vacant space for untold years, to perish in a moment of more than -fiery heat; an enigma whose whole secret is unknown, but of which, -during that instant flash, the spectroscope caught a part, and found -evidence of the identity of some of its constituents with those of the -observer’s own body. - - - - -VII. - -COMETS. - - -Of comets, the Old Astronomy knew that they came to the sun from great -distances in all directions, and in calculable orbits; but as to -_what_ they were, this, even in the childhood of those of us who are -middle-aged, was as little known as to the centuries during which they -still from their horrid heads shook pestilence and war. We do not know -even now by any means exactly what they are, for enough yet remains to -be learned about them still to give their whole study the attraction -which belongs to the unknown; and yet we learn so much, and in a way -which to our grandfathers would have been so unexpected, connecting -together the comet, the shooting star, and the meteorite, that the -astronomer who perhaps speaks with most authority about these to-day -was able, not long ago, in beginning a lecture, to state that he held -in his hand what had been a part of a comet; and what he held was, -not something half vaporous or gaseous, as we might suppose from our -old associations, but a curious stone like this on page 203, which, -with others, had fallen from the sky in Iowa, a flashing prodigy, to -the terror of barking dogs, shying horses, and fearful men, followed -by clouds of smoke and vapor, and explosions that shook the houses -like an earthquake, and “hollow bellowings and rattling sounds mingled -with clang and clash and roar,” as an auditor described it. It is only -a fragment of a larger stone which may have weighed tons. It looks -inoffensive enough now, and its appearance affords no hint of the -commotion it caused in a peaceable neighborhood only ten years ago. But -what, it may be asked, is the connection between such things and comets? - -To answer this, let us recall the statement that the orbit of the -November meteor swarm has been computed; which means that those flying -bodies have been found to come only from one particular quarter out -of all possible quarters, at one particular angle out of all possible -angles, at one particular velocity out of all possible velocities, and -so on; so that the chances are endless against mere accident producing -another body which agreed in all these particulars, and others besides. -Now, in 1867 the remarkable fact was established that a comet seen in -the previous year (Comet 1, 1866) had the same orbit as the meteoroids, -which implies, as we have just seen, that the comet and the meteors -were in some way closely related. - -The paths of the August meteors and of the Lyrids also have both been -found to agree closely with those of known comets, and there is other -evidence which not only connects the comets and the shooting stars, and -makes it probable that the latter are due to some disintegration of the -former, but even looks as though the process were still going on. And -now with this in mind we may, perhaps, look at these drawings with more -interest. - -[Illustration: FIG. 80.--COMET OF DONATI, SEPT. 16, 1858.[7]] - - [7] The five engravings of the Comet of Donati are from “Annals - of the Astronomical Observatory of Harvard College.” - -We have all seen a comet, and we have all felt, perhaps, something of -the awe which is called up by the thought of its immensity and its rush -through space like a runaway star. Its head is commonly like a small -luminous point, from which usually grows as it approaches the sun a -relatively enormous brush or tail of pale light, which has sometimes -been seen to stretch across the whole sky from zenith to horizon. It -is useless to look only along the ecliptic road for a comet’s coming; -rather may we expect to see it rushing down from above, or up from -below, sometimes with a speed which is possibly greater than it -could get from any fall--not so much, that is, the speed of a body -merely dropping toward the sun by its weight, as that of a missile -hurled into the orderly solar system from some unknown source without, -and also associated with some unknown power; for while it is doubtful -whether gravity is sufficient to account for the velocity of all -comets, it seems certain that gravity can in no way explain some of the -phenomena of their tails. - -[Illustration: FIG. 81.--“A PART OF A COMET.”] - -Thousands of comets have been seen since the Christian era, and the -orbits of hundreds have been calculated since the time of Newton. -Though they may describe any conic section, and though most orbits -are spoken of as parabolas, this is rather a device for the analyst’s -convenience than the exact representation of fact. Without introducing -more technical language, it will be enough to say here that we learn -in other cases from the form of the orbit whether the body is drawn -essentially by the sun’s gravity, or whether it has been thrown into -the system by some power beyond the sun’s control, to pass away again, -out of that control, never to return. It must be admitted, however, -that though several orbits are so classed, there is not any one known -to be beyond doubt of this latter kind, while we are certain that many -comets, if not all, are erratic members of the solar family, coming -back again after their excursions, at regular, though perhaps enormous, -intervals. - -But what we have just been saying belongs rather to the province of -the Old Astronomy than the New, which concerns itself more with the -nature and appearance of the heavenly bodies than the paths they travel -on. Perhaps the best way for us to look at comets will be to confine -our attention at first to some single one, and to follow it from its -earliest appearance to its last, by the aid of pictures, and thus -to study, as it were, the species in the individual. The difficulty -will be one which arises from the exquisitely faint and diaphanous -appearance of the original, which no ordinary care can possibly render, -though here the reader has had done for him all that the wood-engraver -can do. - -We will take as the subject of our illustration the beautiful comet -which those of us who are middle-aged can remember seeing in 1858, -and which is called Donati’s from the name of its discoverer. We -choose this one because it is the subject of an admirable monograph -by Professor Bond of the Harvard College Observatory, from which our -engravings have, by permission, been made. - -Let us take the history of this comet, then, as a general type of -others; and to begin at the beginning, we must make the very essential -admission that the origin of the comet’s life is unknown to us. Where -it was born, or how it was launched on its eccentric path, we can only -guess, but do not know; and how long it has been traversing it we can -only tell later. On the 2d of June, 1858, this one was discovered -in the way most comets are found, that is, by a _comet-hunter_, who -detected it as a telescopic speck long before it became visible to the -naked eye, or put forth the tail which was destined to grow into the -beautiful object many of us can remember seeing. For over a century now -there has been probably no year in which the heavens have not been thus -searched by a class of observers who make comet-hunting a specialty. - -[Illustration: FIG. 82.--COMET OF DONATI, SEPT. 24, 1858. (TELESCOPIC -VIEW OF HEAD.)] - -The father of this very valuable class of observers appears to have -been Messier, a Frenchman of the last century and of the purest type of -the comet-hunters, endowed by Nature with the instinct for their search -that a terrier has for rats. In that grave book, Delambre’s “History of -Astronomy,” as we plod along its dry statements and through its long -equations, we find, unexpected as a joke in a table of logarithms, the -following piece of human nature (quoted from Messier’s contemporary, La -Harpe):-- - - “He [Messier] has passed his life in nosing out the tracks - of comets. He is a very worthy man, with the simplicity of a - baby. Some years ago he lost his wife, and his attention to her - prevented him from discovering a comet he was on the search for, - and which Montaigne of Limoges got away from him. He was in - despair. When he was condoled with on the loss he had met, he - replied, with his head full of the comet, ‘Oh, dear! to think - that when I had discovered twelve, this Montaigne should have got - my thirteenth.’ And his eyes filled with tears, till, remembering - what it was he ought to be weeping for, he moaned, ‘Oh, my poor - wife!’ but went on crying for his comet.” - -Messier’s scientific posterity has greatly multiplied, and it is rare -now for a comet to be seen by the naked eye before it has been caught -by the telescope of one of these assiduous searchers. Donati had, as -we see, observed his some months before it became generally visible, -and accordingly the engraving on page 201 shows it as it appeared on -the evening of September 16, 1858, when the tail was already formed, -and, though small, was distinct to the naked eye, near the stars of the -Great Bear. The reader will easily recognize in the plate the familiar -“dipper,” as the American child calls it, where the leading stars are -put down with care, so that he may, if he please, identify them by -comparison with the originals in the sky, even to the little companion -to Mizar (the second in the handle of the “dipper,” and which the -Arabs say is the lost Pleiad). We would suggest that he should note -both the length of the tail on this evening as compared with the space -between any two stars of the “dipper” (for instance, the two right-hand -ones, called the “pointers”) and its distance from them, and then turn -to page 209, where we have the same comet as seen a little over a -fortnight later, on October 3d. Look first at its new place among the -stars. The “dipper” is still in view, but the comet has drifted away -from it toward the left and into other constellations. The large star -close to the left margin of the plate, with three little stars below -and to the right, is Arcturus; and the western stars of the Northern -Crown are just seen higher up. Fortunately the “pointers,” with which -we compared the comet on September 16th, are still here, and we can see -for ourselves how it has not only shifted but grown. The tail is three -times as long as before. It is rimmed with light on its upper edge, -and fades away so gradually below that one can hardly say where it -ends. But,--wonderful and incomprehensible feature!--shot out from the -head, almost as straight as a ray of light itself, but fainter than the -moonbeam, now appears an extraordinary addition, a sort of spur, which -we can hardly call a new tail, it is so unlike the old one, but which -appears to have been darted out into space as if by some mysterious -force acting through the head itself. What the spur is, what the tail -is, even what the nucleus is, we cannot be said really to know even -to-day; but of the tail and of the nucleus or speck in the very head of -the comet (too small to be visible in the engraving), we may say that -the hairy tail (_comes_) gives the comet its name, and _is_ the comet -to popular apprehension, but that it is probably the smallest part of -the whole mass, while the little shining head, which to the telescope -presents a still smaller speck called the nucleus, contains, it now -seems probable, the only element of possible danger to the earth. - -While admitting our lack of absolute knowledge, we may, if we agree -that meteorites were once part of a comet, say that it now seems -probable that the nucleus is a hard, stone-like mass, or collection -of such masses, which comes from “space” (that is, from we don’t know -how far) to the vicinity of the sun, and there is broken by the heat -as a stone in a hot fire. (Sir Isaac Newton calculates, in an often -quoted passage of the Principia, that the heat which the comet of 1680 -was subjected to in its passage by the sun was two thousand times -that of red-hot iron.) We have seen the way in which meteoric stones -actually do crack in pieces with heat in our own atmosphere, partly, -perhaps, from the expansion of the gases the stone contains, and it -seems entirely reasonable to suppose that they may do so from the heat -of the sun, and that the escaped gases may contribute something toward -the formation of the tail, which is always turned away from the sun, -and which always grows larger as that is approached, and smaller as -it is receded from. However this may be, there is no doubt that the -original solid which we here suppose may form the nucleus is capable -of mischief, for it is asserted that it often passes the earth’s orbit -with a velocity of as much as one hundred times that of a cannon-ball; -that is, with ten thousand times the destructive capacity of a ball of -the same weight shot from a cannon. - -[Illustration: FIG. 83.--COMET OF DONATI, OCT. 3, 1858.] - -One week later, October 9th, the comet had passed over Arcturus -with a motion toward our left into a new region of the sky, leaving -Arcturus, which we can recognize with the upper one of its three little -companions, on the right. Above it is the whole sickle of the Northern -Crown, and over these stars the extremity of the now lengthened tail -was seen to spread, but with so thin a veil that no art of the engraver -can here adequately represent its faintness. The tail then, as seen in -the sky, was now nearly twice its former size, though for the reason -mentioned it may not appear so in our picture. It should be understood, -too, that even the brightest parts of the original were far fainter -than they seem here in comparison with the stars, which in the sky -are brilliant points of light, which the engraver can only represent -by dots of the whiteness of the paper. This being observed, it will -be better understood that in the sky itself the faintest stars were -viewed apparently undimmed through the brighter parts of the comet, -while we can but faintly trace here another most faint but curious -feature, a division of the tail into faint cross-bands like auroral -streamers, giving a look as if it were yielding to a wind, which folded -it into faint ridges like those which may be seen in the smoke of a -steamer as it lags far behind the vessel. In fact, when we speak of -“the” tail, it must be understood, as M. Faye reminds us, to be in -the same sense that we speak of the plume of smoke that accompanies -an ocean steamer, without meaning that it is the same thing which -we are watching from night to night, more than we do that the same -smoke-particles accompany the steamer as it moves across the Atlantic. -In both cases the form alone probably remains; the thing itself is -being incessantly dissipated and renewed. There is no air here, and yet -some of these appearances in the original almost suggest the idea of -medium inappreciably thin as compared with the head of the comet, but -whose resistance is seen in the more unsubstantial tail, as that is -drawn through it and bent backward, as if by a wind blowing toward the -celestial pole. - -The most notable feature, however, is the development of a second ray -or spur, which has been apparently darted through millions of miles in -the interval since we looked at it, and an almost imperceptible bending -backward in both, as if they too felt the resistance of something in -what we are accustomed to think of as an absolute and perfect void. -These tails are a peculiarly mysterious feature. They are apparently -shot out in a direction opposite to the sun (and consequently opposed -to the direction of gravity) at the rate of millions of miles a day. - -[Illustration: FIG. 84.--COMET OF DONATI, OCT. 9, 1858.] - -Beyond the fact that the existence of some _repulsive_ force in the -sun, a “negative gravity” actually existent, not in fancy, but in fact, -seems pointed at, astronomers can offer little but conjecture here; -and while some conceive this force as of an electrical nature, others -strenuously deny it. We ought to admit that up to the present time we -really know nothing about it, except that it exists. - -At this date (October 9th) the comet had made nearly its closest -approach to the earth, and the general outline has been compared to -that of the wing of some bird, while the actual size was so vast that -even at the distance from which it was seen it filled an angle more -than half of that from the zenith to the horizon. - -All the preceding drawings have been from naked-eye views; but if -the reader would like to look more closely, he can see on page 217 -one taken on the night of October 5th through the great telescope -at Cambridge, Mass. We will leave this to tell its own story, only -remarking that it is not possible to reproduce the phantom-like -faintness of the original spur, here also distinctly seen, or indeed -to indicate fairly the infinite tenuity of the tail itself. Though -millions of miles thick, the faintest star is yet perceptibly undimmed -by it, and in estimating the character and quantity of matter it -contains, after noting that it is not self-luminous, but shines -only like the moon by reflected sunlight, we may recall the acute -observation of Sir Isaac Newton where he compares the brightness of a -comet’s tail with that of the light reflected from the particles in a -sunbeam an inch or two thick, in a darkened room, and, after observing -that if a little sphere of common air one inch in diameter were -rarified to the degree which must obtain at only four thousand miles -from the earth’s surface it would fill all the regions of the planets -to far beyond the orbit of Saturn, suggests the excessively small -quantity of vapor that is really requisite to create this prodigious -phantom. - -The writer has had occasion for many years to make a special study of -the reflection of light from the sky; and if such studies may authorize -him to express any opinion of his own, he would give his adhesion to -the remark of Sir John Herschel, that the actual weight of matter in -such a cometary tail may be conceivably only an affair of pounds or -even ounces. But if this is true of the tail, it does not follow of -the nucleus, just seen in this picture, but of which the engraving on -page 205 gives a much more magnified view. It is a sketch of the head -alone, taken from a telescopic view on the 24th of September. Here the -direction of the comet is still toward the sun (which must be supposed -to be some indefinite distance beyond the upper part of the drawing), -and we see that the lucid matter appears to be first jetted up, and -then forced backward on either side, as if by a wind _from_ the sun, -to form the tail, presenting successive crescent-shaped envelopes of -decreasing brightness, which are not symmetrical, but one-sided, while -sometimes the appearance is that of spurts of luminous smoke, wavering -as if thrown out of particular parts of the internal nucleus “like a -squib not held fast.” Down the centre of the tail runs a wonderfully -straight black line, like a shadow cast from the nucleus. Only the -nucleus itself still evades us, and even in this, the most magnified -view which the most powerful telescope till lately in existence could -give, remains a point. - -Considering the distance of the comet and the other optical conditions, -this is still perfectly consistent with the possibility that it may -have an actual diameter of a hundred miles or more. It “may” have, -observe, not it “has,” for in fact we know nothing about it; but that -it is at any rate less than some few hundred miles in diameter, and it -may, for anything we can positively say, not be more than a very large -stone, in which case our atmosphere would probably act as an efficient -buffer if it struck us; or it may have a mass which, coupled with its -terrible speed, would cause the shock of its contact not so much to -pulverize the region it struck, as dissipate it and everything on it -instantly into vapor. - -[Illustration: FIG. 85.--COMET OF DONATI, OCT. 5, 1858. (TELESCOPIC -VIEW.)] - -Of the remarkable investigations of the spectroscope on comets, we -have only room left to say that they inform us that the most prominent -cometary element seems to be carbon,--carbon, which Newton two hundred -years before the spectroscope, and before the term “carbonic-acid gas” -was coined, by some guess or divination had described in other words -as possibly brought to us by comets to keep up the carbonic-acid-gas -supply in our air,--carbon, which we find in our own bodies, and of -which, according to this view, the comets are original sources. - -That _we_ may be partly made of old and used-up comets,--surely it -might seem that a madder fancy never came from the brain of a lunatic -at the full of the moon! - -Science may easily be pardoned for not giving instant reception to such -an idea, but let us also remember, first, that it is a consequence of -that of Sir Isaac Newton, and that in the case of such a man as he -we should not be hasty to think we understand his ignorance, when we -may be “ignorant of his understanding;” and, second, that it has been -rendered at least debatable by Dr. Hunt’s recent researches whether -it is possible to account for the perennial supply of carbon from the -earth’s atmosphere, without looking to some means of renewal external -to the planet. - -The old dread of comets is passing away, and all that science has -to tell us of them indicates that, though still fruitful sources of -curiosity and indeed of wonder, they need no longer be objects of -terror. Though there be, as Kepler said, more comets in the sky than -fish in the ocean, the encounter of the earth with a comet’s tail would -be like the encounter with a shadow, and the chance of a collision -with the nucleus is remote indeed. We may sleep undisturbed even if -a new comet is announced every month, though it is true that here as -elsewhere lie remote possibilities of evil. - -The consideration of the unfamiliar powers certainly latent in Nature, -such as belong to a little tremor of the planet’s surface or such -as was shown in that scene I have described, when the comparatively -insignificant effect of the few tons of dynamite was to make solid -buildings unrealities, which vanished away as quickly as magic-lantern -pictures from a screen, may help us to understand that the words of -the great poet are but the possible expression of a physical fact, -and that “the cloud-capped towers, the gorgeous palaces, the solemn -temples,”--and we with them,--may indeed conceivably some day vanish -as the airy nothings at the touch of Prospero’s wand, and without the -warning to us of a single instant that the security of our ordinary -lives is about to be broken. We concede this, however, in the present -case only as an abstract possibility; for the advance of astronomical -knowledge is much more likely to show that the kernel of the comet -is but of the bigness of some large meteorite, against which our air -is an efficient shield, and the chance of evil is in any case most -remote,--in any case only such as may come in any hour of our lives -from any quarter, not alone from the earthquake or the comet, but -from “the pestilence that walketh in darkness;” from the infinitely -little below and within us, as well as from the infinite powers of the -universe without. - - - - -VIII. - -THE STARS. - - -In the South Kensington Museum there is, as everybody knows, an immense -collection of objects, appealing to all tastes and all classes, and -we find there at the same time people belonging to the wealthy and -cultivated part of society lingering over the Louis Seize cabinets or -the old majolica, and the artisan and his wife studying the statements -as to the relative economy of baking-powders, or admiring Tippoo Saib’s -wooden tiger. - -There is one shelf, however, which seems to have some attraction common -to all social grades, for its contents appear to be of equal interest -to the peer and the costermonger. It is the representation of a _man_ -resolved into his chemical elements, or rather an exhibition of the -materials of which the human body is composed. There is a definite -amount of water, for instance, in our blood and tissues, and there on -the shelf are just so many gallons of water in a large vessel. Another -jar shows the exact quantity of carbon in us; smaller bottles contain -our iron and our phosphorus in just proportion, while others exhibit -still other constituents of the body, and the whole reposes on the -shelf as if ready for the coming of a new Frankenstein to re-create -the original man and make him walk about again as we do. The little -vials that contain the different elements which we all bear about in -small proportions are more numerous, and they suggest, not merely the -complexity of our constitutions, but the identity of our elements with -those we have found by the spectroscope, not alone in the sun, but even -in the distant stars and nebulæ; for this wonderful instrument of the -New Astronomy can find the traces of poison in a stomach or analyze -a star, and its conclusions lead us to think that the ancients were -nearly right when they called man a microcosm, or little universe. We -have literally within our own bodies samples of the most important -elements of which the great universe without is composed; and you and I -are not only like each other, and brothers in humanity, but children of -the sun and stars in a more literal sense, having bodies actually made -in large part of the same things that make Sirius and Aldebaran. They -and we are near relatives. - -[Illustration: FIG. 86.--TYPES OF STELLAR SPECTRA.] - -But if near in kind, we are distant relatives in another way, for the -sun, whose remoteness we have elsewhere tried to give an idea of, is -comparatively close at hand; quite at hand, one may say, for if his -distance, which we have found so enormous, be represented by that -of a man standing so close beside us that our hand may rest on his -shoulder, to obtain the proportionate distance of one of the _nearest_ -stars, like Sirius, for instance, we should need to send the man over -a hundred miles away. It is probably impossible to give to any one an -adequate idea of the extent of the sidereal universe; but it certainly -is especially hard for the reader who has just realized with difficulty -the actual immensity of the distance of the sun, and who is next told -that this distance is literally a physical point as seen from the -nearest star. The jaded imagination can be spurred to no higher flight, -and the facts and the enormous numbers that convey them will not be -comprehended. - -Look down at one of the nests of those smallest ants, which are made -in our paths. To these little people, we may suppose, the other side -of the gravel walk is the other side of the world, and the ant who -has been as far as the gate, a greater traveller than a man who comes -back from the Indies. It is very hard to think not only of ourselves -as relatively far smaller than such insects, but that, less than such -an ant-hill is to the whole landscape, is our solar system itself in -comparison with the new prospect before us; yet so it is. - -All greatness and littleness are relative. When the traveller from the -great star Sirius (where, according to the author of “Micromegas,” -all the inhabitants are proportionately tall and proportionately -long-lived), discovered our own little solar system, and lighted on -what we call the majestic planet Saturn, he was naturally astonished at -the pettiness of everything compared with the world he had left. That -the Saturnian inhabitants were in his eyes a race of mere dwarfs (they -were only a mile high, instead of twenty-four miles like himself) did -not make them contemptible to his philosophic mind, for he reflected -that such little creatures might still think and reason; but when he -learned that these puny beings were also correspondingly short-lived, -and passed but fifteen thousand years between the cradle and the -grave, he could not but agree that this was like dying as soon as one -was born, that their life was but a span, and their globe an atom. Yet -it seems that when one of these very Saturnian dwarfs came afterward -with him to our own little ball, and by the aid of a microscope -discovered certain animalculæ on its surface, and even held converse -with two of them, he could not in turn make up his own mind that -intelligence could inhere in such invisible insects, till one of them -(it was an astronomer with his sextant) measured his height to an inch, -and the other, a divine, expounded to him the theology of some of these -mites, according to which all the heavenly host, including Saturn and -Sirius itself, were created for _them_. - -Do not let us hold this parable as out of place here, for what use is -it to write down a long series of figures expressing the magnitude of -other worlds, if it leave us with the old sense of the importance to -creation of our own; and what use to describe their infinite number to -a human mite who reads, and remains of the opinion that _he_ is the -object they were all created for? - -Above us are millions of suns like ours. The Milky Way (shown on page -225) spreads among them, vague and all-surrounding, as a type of the -infinities yet unexplored, and of the world of nebulæ of which we -still know so little. Let us say at once that it is impossible here to -undertake the description of the discoveries of the New Astronomy in -this region, for we can scarcely indicate the headings of the chapters -which would need to be written to describe what is most important. - -[Illustration: FIG. 87.--THE MILKY WAY. (FROM A STUDY BY E. L. -TROUVELOT).] - -The first of these chapters (if we treated our subjects in the order of -distance) would be one on space itself, and our changed ideas of the -void which separates us from the stars. Of this we will only say in -passing, that the old term “the temperature of space” has been nearly -abrogated; for while it used to be supposed that more than half of -the heat which warmed the earth came from this mysterious “space” -or from the stars, it is now recognized that the earth is principally -warmed only by the sun. Of the contents of the region between the -earth and the stars, we have, it must be admitted, still little but -conjecture; though perhaps that conjecture turns more than formerly to -the idea that the void is not a real void, but that it is occupied by -something which, if highly attenuated, is none the less matter, and -something other and more than the mere metaphysical conception of a -vehicle to transmit light to us. - -Of the stars themselves, we should need another chapter to tell what -has been newly learned as to their color and light, even by the old -methods, that is, by the eye and the telescope alone; but if we -cannot dwell on this, we must at least refer, however inadequately, -to what American astronomers are doing in this department of the New -Astronomy, and first in the photometry of the stars, which has assumed -a new importance of late years, owing to the labors carried on in this -department at Cambridge. - -That one star differs from another star in glory we have long heard, -but our knowledge of physical things depends largely on our ability -to answer the question, “how much?” and the value of this new work -lies in the accuracy and fulness of its measures; for in this case the -whole heavens visible from Cambridge to near the southern horizon have -been surveyed, and the brightness of every naked-eye star repeatedly -measured, so that all future changes can be noted. This great work has -taxed the resources of a great observatory, and its results are only to -be adequately valued by other astronomers; but Professor Pickering’s -own investigations on variable stars have a more popular interest. It -is surely an amazing fact that suns as large or larger than our own -should seem to dwindle almost to extinction, and regain their light -within a few days or even hours; yet the fact has long been known, -while the cause has remained a mystery. A mystery, in most cases, it -remains still; but in some we have begun to get knowledge, as in the -well-known instance of Algol, the star in the head of Medusa. Here it -has always been thought probable that the change was due to something -coming between us and the star; but it is on this very account that -the new investigation is more interesting, as showing how much can be -done on an old subject by fresh reasoning alone, and how much valuable -ore may lie in material which has already been sifted. The discussion -of the subject by Professor Pickering, apart from its elevated aim, -has if, in its acute analysis only, the interest belonging to a story -where the reader first sees a number of possible clews to some mystery, -and then the gradual setting aside, one by one, of those which are -only loose ends, and the recognition of the real ones which lead to -the successful solution. The skill of the novelist, however, is more -apparent than real, since the riddle he solves for us is one he has -himself constructed, while here the enigma is of Nature’s propounding; -and if the solution alone were given us, the means by which it is -reached would indeed seem to be inexplicable. - -This is especially so when we remember what a point there is to work -on, for the whole system reasoned about, though it may be larger than -our own, is at such a distance that it appears, literally and exactly, -far smaller to the eye than the point of the finest sewing-needle; -and it is a course of accurate reasoning, and reasoning alone, on -the character of the observed changing brightness of this point, -which has not only shown the existence of some great dark satellite, -but indicated its size, its distance from its sun, its time of -revolution, the inclination of its orbit, and still more. The existence -of dark invisible bodies in space, then, is in one case at least -demonstrated, and in this instance the dark body is of enormous size; -for, to illustrate by our own solar system, we should probably have -to represent it in imagination by a planet or swarm of planetoids -hundreds of times the size of Jupiter, and (it may be added) whirling -around the sun at less than a tenth the distance of Mercury. - -Of a wholly different class of variables are those which have till -lately only been known at intervals of centuries, like that new star -Tycho saw in 1572. I infer from numerous inquiries that there is such a -prevalent popular notion that the “Star of Bethlehem” may be expected -to show itself again at about the present time, that perhaps I may be -excused for answering these questions in the present connection. - -In the first place, the idea is not a new, but a very old one, going -back to the time of Tycho himself, who disputed the alleged identity -of his star with that which appeared to the shepherds at the Nativity. -The evidence relied on is, that bright stars are said to have appeared -in this constellation repeatedly at intervals of from three hundred -and eight to three hundred and nineteen years (though even this is -uncertain); and as the mean of these numbers is about three hundred and -fourteen, which again is about one-fifth of 1572 (the then number of -years from the birth of Christ), it has been suggested, in support of -the old notion, that the Star of Bethlehem might have been a variable, -shining out every three hundred and fourteen or three hundred and -fifteen years, whose fifth return would fall in with the appearance -that Tycho saw, and whose _sixth_ return would come in 1886 or 1887. -This is all there is about it, and there is nothing like evidence, -either that this was the star seen by the Wise Men, or that it is to -be seen again by us. On the other hand, nothing in our knowledge, or -rather in our ignorance, authorizes us to say positively it cannot -come again; and it may be stated for the benefit of those who like to -believe in its speedy return, that if it does come, it will make its -appearance some night in the northern constellation of Cassiopeia’s -chair, the position originally determined by Tycho at its last -appearance, being twenty-eight degrees and thirteen minutes from the -pole, and twenty-six minutes in right ascension. - -We were speaking of these new stars as having till lately only appeared -at intervals of centuries; but it is not to be inferred that if they -now appear oftener it is because there are more of them. The reason -is, that there are more persons looking for them; and the fact is -recognized that, if we have observers enough and look closely enough, -the appearance of “new stars” is not so very rare a phenomenon. Every -one at all interested in such matters remembers that in 1866 a new -star broke out in the Northern Crown so suddenly that it was shining -as bright as the Polar Star, where six hours before there had been -nothing visible to the eve. Now all stars are not as large as our sun, -though some are much larger; but there are circumstances which make -it improbable that this was a small or near object, and it is well -remembered how the spectroscope showed the presence of abnormal amounts -of incandescent hydrogen, the material which is perhaps the most -widely diffused in the universe (and which is plentiful, too, in our -own bodies), so that there was some countenance to the popular notion -that this was a world in flames. We were, at any rate, witnessing a -catastrophe which no earthly experience can give us a notion of, in a -field of action so remote that the flash of light which brought the -news was unknown years on the way, so that all this--strange but now -familiar thought--occurred long before we _saw_ it happen. The star -faded in a few days to invisibility to the naked eye, though not to the -telescope; and, in fact, all these phenomena at present appear rather -to be enormous and sudden enlargements of the light of existing bodies -than the creation of absolutely new ones; while of these “new stars” -the examples may almost be said to be now growing numerous, two having -appeared in the last two years. - -Not to enlarge, then, on this chapter of photometry, let us add, in -reference to another department of stellar astronomical work, that the -recognized master in the study of double stars the world over is not an -astronomer by profession, at the head of some national observatory in -Berlin or Paris, but a stenographer in the Chicago law-courts, Mr. W. -S. Burnham, who, after his day’s duties, by nightly labor, prolonged -for years with the small means at an amateur’s command, has perhaps -added more to our knowledge of his special subject in ten years than -all other living astronomers. - -[Illustration: FIG. 88.--SPECTRA OF STARS IN PLEIADES.] - -We have here only alluded to the spectroscope in its application to -stellar research, and we cannot now do more than to note the mere -headlines of the chapters that should be written on it. - -First, there is the memorable fact that, after reaching across the -immeasurable distances, we find that the stars are like _us_,--like in -their ultimate elements to those found in our own sun, our own earth, -our own bodies. Any fuller view of the subject than that which we here -only indicate, would begin with the evidence of this truth, which is -perhaps on the whole the most momentous our science has brought us, and -with which no familiarity should lessen our wonder, or our sense of its -deep and permanent significance. - -Next, perhaps, we should understand that, invading the province of the -Old Astronomy, the spectroscope now tells us of the motions of these -stars, which we cannot see move,--motions in what we have always called -the “fixed” stars, to signify a state of fixity to the human eye, which -is such, that to it at the close of the nineteenth century they remain -in the same relative positions that they occupied when that eye first -looked on them, in some period long before the count of centuries began. - -In perhaps the earliest and most enduring work of man’s hands, the -great pyramid of Egypt, is a long straight shaft, cut slopingly through -the solid stone, and pointing, like a telescope, to the heavens near -the pole. If we look through it now we see--nothing; but when it was -set up it pointed to a particular star which is no longer there. That -pyramid was built when the savages of Britain saw the Southern Cross -at night; and the same slow change in the direction of the earth’s -axis, that in thousands of years has borne that constellation to -southern skies, has carried the stone tube away from the star that it -once pointed at. The actual motion of the star itself, relatively to -our system, is slower yet,--so inconceivably slow that we can hardly -realize it by comparison with the duration of the longest periods -of human history. The stone tube was pointed at the star by the old -Egyptians, but “Egypt itself is now become the land of obliviousness, -and doteth. Her ancient civility is gone, and her glory hath vanished -as a phantasma. She poreth not upon the heavens, astronomy is dead unto -her, and knowledge maketh other cycles. Canopus is afar off, Memnon -resoundeth not to the Sun, and Nilus heareth strange voices.” In all -this lapse of ages, the star’s own motion could not have so much as -carried it across the mouth of the narrow tube. Yet a motion to or -from us of this degree, so slow that the unaided eve could not see it -in thousands of years of watching, the spectroscope, first efficiently -in the hands of the English astronomer, Dr. Huggins, and later in -those of Professor Young of Princeton, not only reveals at a look, but -tells us the amount and direction of it, in a way that is as strange -and unexpected, in the view of our knowledge a generation ago, as its -revelation of the essential composition of the bodies themselves. - -[Illustration: FIG. 89.--SPECTRUM OF ALDEBARAN.] - -[Illustration: FIG. 90.--SPECTRUM OF VEGA.] - -Again, in showing us this composition, it has also shown us more, for -it has enabled us to form a conjecture as to the relative ages of the -stars and suns; and this work of classifying them, not only according -to their brightness, but each after his kind, we may observe was -begun by a countryman of our own, Mr. Rutherfurd, who seems to have -been among the first after Fraunhofer to apply the newly-invented -instrument to the stars, and quite the first to recognize that these -were, broadly speaking, divisible into a few leading types, depending -not on their size but on their essential nature. After him Secchi -(to whom the first conception is often wrongly attributed) developed -it, and gave four main classes into which the stars are in this way -divisible, a classification which has been much extended by others; -while the first carefully delineated spectra were those of Dr. Huggins, -who has done so much for all departments of our science that in a -fuller account his name would reappear in every chapter of this New -Astronomy, and than whom there is no more eminent living example of -its study. Owing to their feeble light, years were needed when he -began his work to depict completely so full a single spectrum as that -he gives of Aldebaran, though he has lived to see stellar spectrum -photography, whose use he first made familiar, producing in its -newest development, which we give here, the same result in almost as -many minutes. Before we present this latest achievement of celestial -photography, let us employ the old method of an engraving made from -eye-drawings, once more, to illustrate on page 222 the distinct -character of these spectra, and their meaning. In the telespectroscope, -the star is drawn out into a band of colored light, but here we note -only in black and white the lines which are seen crossing it, the -red end in these drawings being at the left, and the violet at the -right; and we may observe of this illustration, that though it may -be criticised by the professional student, and though it lack to the -general reader the attraction of color, or of beautiful form, it is -yet full of interest to any one who wishes to learn the meaning of the -message the star’s light can be made to yield through the spectroscope, -and to know how significant the differences are it indicates between -one star and another, where all look so alike to the eye. First is -the spectrum of a typical white or blue-white star, Sirius,--the very -brightest star in the sky, and which we all know. The brighter part -of the spectrum is a nearly continuous ribbon of color, crossed by -conspicuous, broad, dark lines, exactly corresponding in place to -narrower ones in our sun, and due principally to hydrogen. Iron and -magnesium are also indicated in this class, but by too fine lines to be -here shown. - -Sirius, as will be presently seen, belongs to the division of stars -whose spectrum indicates a very high temperature, and in this case, as -in what follows, we may remark (to use in part Mr. Lockyer’s words) -that one of the most important distinctions between the stars in the -heavens is one not depending upon their mass or upon anything of that -kind, but upon conditions which make their spectra differ, just in the -way that in our laboratories the spectrum of one and the same body will -differ at different temperatures. - -What these absolutely are in the case of the stars, we may not -know; but placing them in their most probable relative order, we -have taken as an instance of the second class, or lower-temperature -stage, our own sun. The impossibility of giving a just notion of its -real complexity may be understood, when we state that in the recent -magnificent photographs by Professor Rowland, a part alone of this -spectrum occupies something like fifty times the space here given to -the whole, so that, crowded with lines as this appears, scarcely one -in fifty of those actually visible can be given in it. Without trying -to understand all these now, let us notice only the identity of two -or three of its principal elements with those found in other stars, -as shown by the corresponding identity of some leading lines. Thus, C -and F (with others) are known to be caused by hydrogen; D, by sodium; -_b_, by magnesium; while fainter lines are given by iron and by other -substances. These elements can be traced by their lines in most of -the different star-spectra on this plate, and all those named are -constituents of our own frames. - -The hydrogen lines are not quite accurately shown in the plate from -which our engraving is made, those in Sirius, for instance, being -really wider by comparison than they are here given; and we may observe -in this connection, that by the particular appearance such lines wear -in the spectrum itself we can obtain some notion of the _mass_ of a -star, as well as of its chemical constitution. We can compare the -essential characteristics of such bodies, then, without reference -to their apparent size, or as though they were all equally remote; -and it is a striking thought, that when we thus rise to an impartial -contemplation of the whole stellar universe, our sun, whose least ray -makes the whole host of stars disappear, is found to be not only -itself a star, but by comparison a small one,--one at least which is -more probably below than above the average individual of its class, -while some, such as Sirius, are not impossibly hundreds of times its -size. - -Then comes a third class, such as is shown in the spectrum of the -brightest star in Orion, looking still a little like that of our sun; -but yet more distinctively in that of the brightest star in Hercules, -looking like a columnar or fluted structure, and concerning which the -observations of Lockyer and others create the strong presumption, not -to say certainty, that we have here a lower temperature still. Antares -and other reddish stars belong to this division, which in the very -red stars passes into the fourth type, and there are more classes and -subclasses without end; but we invite here attention particularly to -the first three, much as we might present a child, an adult, and an -old man, as types of the stages of human existence, without meaning to -deny that there are any number of ages between. We can even say that -this may be something more than a mere figure of speech, and that a -succession in age is not improbably pointed at in these types. - -[Illustration: FIG. 91.--GREAT NEBULA IN ORION. (FROM A PHOTOGRAPH BY -A. A. COMMON, F. R. S.)] - -We may have considered--perhaps not without a sort of awe at the -vastness of the retrospect--the past life of the worlds of our own -system, from our own globe of fluid fire as we see it by analogy in -the past, through the stages of planetary life to the actual condition -of our present green earth, and on to the stillness of the moon. Yet -the life history of our sun, we can hardly but admit, is indefinitely -longer than this. We feel, rather than comprehend, the vastness of -the period that separates our civilization from the early life of the -world; but what is this to the age of the sun, which has looked on and -seen its planetary children grow? Yet if we admit this temperature -classification of the stars, we are not far from admitting that the -spectroscope is now pointing out the stages in the life of suns -themselves; suns just beginning their life of almost infinite years; -suns in the middle of their course; suns which are growing old and -casting feebler beams,--all these and many more it brings before us. - -Another division of our subject would, with more space, include a -fuller account of that strange and most interesting development of -photography which is going on even while we write; and this is so new -and so important, that we must try to give some hint of it even in -this brief summary, for even since the first numbers of this series -were written, great advances have taken place in its application to -celestial objects. - -Most of us have vague ideas about small portions of time; so much so, -that it is rather surprising to find to how many intelligent people, a -second, as seen on the clock face, is its least conceivable interval. -Yet a second has not only a beginning, middle, and end, as much as a -year has, but can, in thought at least, be divided into just as many -numbered parts as a year can. Without entering on a disquisition about -this, let us try to show by some familiar thing that we can at any rate -not only divide a second in imagination into, let us say, a hundred -parts, but that we can observe distinctly what is happening in such a -short time, and make a picture of it,--a picture which shall be begun -and completed while this hundredth of a second lasts. - -Every one has fallen through at least some such a little distance as -comes in jumping from a chair to the floor, and most of us, it is safe -to say, have a familiar impression of the fact that it takes, at any -rate, less than a second in such a case from the time the foot leaves -its first support till it touches the ground. Plainly, however large or -small the fall may be, each fraction of an inch of it must be passed -through in succession, and if we suppose the space to be divided, -for instance, into a hundred parts, we must divide in thought the -second into at least as many, since each little successive space was -traversed in its own little interval of time, and the whole together -did not make a second. We can even, as a matter of fact, very easily -calculate the time that it will take anything which has already fallen, -let us say one foot, to fall an inch more; and we find this, in the -supposed instance, to be almost exactly one one-hundredth of a second. -On page 243 is a reproduction of a photograph from Nature, of a man -falling freely through the air. He has dropped from the grasp of the -man above him, and has already fallen through some small distance,--a -foot or so. If we suppose it to be a foot, since we can see that the -man’s features are not blurred, as they would undoubtedly have been -had he moved even much less than an inch while this picture was being -taken, it follows, from what has been said, that the making of the -whole picture--landscape, spectators, and all--occupied not _over_ one -one-hundredth of a second. - -We have given this view of “the falling man” because, rightly -understood, it thus carries internal evidence of the limit of time in -which it could have been made; and this will serve as an introduction -to another picture, where probably no one will dispute that the time -was still shorter, but where we cannot give the same kind of evidence -of the fact. - -“Quick as lightning” is our common simile for anything occupying, -to ordinary sense, no time at all. Exact measurements show that the -electric spark does occupy a time, which is almost inconceivably small, -and of which we can only say here that the one one-hundredth of a -second we have just been considering is a long period by comparison -with the duration of the brightest portion of the light. - -[Illustration: FIG. 92.--A FALLING MAN.] - -On page 245 we have the photograph of a flash of lightning (which -proves to be several simultaneous flashes), taken last July from a -point on the Connecticut coast, and showing not only the vivid zigzag -streaks of the lightning itself, but something of the distant sea -view, and the masts of the coast survey schooner “Palinurus” in the -foreground, relieved against the sky. We are here concerned with this -interesting autograph of the lightning, only as an illustration of our -subject, and as proving the almost infinite sensitiveness of the recent -photographic processes; for there seems to be no limit to the briefness -of time in which, these can so act in some degree, whether the light be -bright or faint, and no known limit to the briefness of time required -for them to act _effectively_ if the light be bright enough. - -What has just preceded will now help us to understand how it is that -photography also succeeds so well in the incomparably fainter objects -we are about to consider, and which have been produced not by short but -by long exposures. We have just seen how sensitive the modern plate -is, and we are next to notice a new and very important point in which -photographic action in general differs remarkably from that of the eye. -Seeing may be described, not wholly inaptly, as the recognition of a -series of brief successive photographs, taken by the optic lens on the -retina; but the important difference between seeing and photographing, -which we now ask attention to, is this: When the eye looks at a faint -object, such as the spectrum of a star, or at the still fainter nebula, -this, as we know, appears no brighter at the end of half an hour than -at the end of the first half-second. In other words, after a brief -fraction of a second, the visual effect does not sensibly accumulate. -But in the action of the photograph, on the contrary, the effect _does_ -accumulate, and in the case of a weak light accumulates indefinitely. -It is owing to this precious property, that supposing (for illustration -merely) the lightning flash to have occupied the one-thousandth part -of a second in impressing itself on the plate, to get a nearly similar -effect from a continuous light one thousand times weaker, we have only -to expose the ¡date a thousand times as long, that is, for one second; -while from a light a million times weaker we should get the same -result by exposing it a million times as long, that is, for a thousand -seconds. - -And now that we come to the stars, whose spectra occupy minutes in -taking, what we just considered will help us to understand how we can -advantageously thus pass from a thousandth of a second or less, to -one thousand seconds or even more, and how we can even,--given time -enough,--conceivably, be able to photograph what the eye _cannot see at -all_. - -[Illustration: FIG. 93.--A FLASH OF LIGHTNING. (FROM A PHOTOGRAPH BY -DR. H. G. PIFFARD.)] - -We have on page 231 a photograph quite recently taken at Cambridge from -a group of stars (the Pleiades) passing by the telescope. Every star -is caught as it goes, and presented, not in its ordinary appearance to -the eye, but by its spectrum. There is a general resemblance in these -spectra from the same cluster; while in other cases the spectra are -of all types and kinds, the essential distinction between individuals -alike to the eve, being more strikingly shown, as stars apparently -far away from one another are seen to have a common nature, and stars -looking close together (but which may be merely in line, and really far -apart) have often no resemblance; and so the whole procession passes -through the field of view, each individual leaving its own description. -This self-description will be better seen in the remarkable photographs -of the spectra of Vega and Aldebaran, which are reproduced on page 235 -from the originals by a process independent of the graver. They were -obtained on the night of November 9, 1886, at Cambridge, as a part of -the work pursued by Professor Pickering, with means which have been -given from fitting hands, thus to form a memorial of the late Dr. Henry -Draper. We are obliged to the source indicated, then, for the ability -to show the reader here the latest, and as yet inedited, results in -this direction; and they are such as fully to justify the remark made -above, that minutes, by this new process, take the place of years of -work by the most skilful astronomer’s eye and hand. - -The spectrum of Vega (Alpha Lyræ) is marked only by a few strong lines, -due chiefly to hydrogen, because these are all there are to be seen -in a star of its class. Aldebaran (the bright star in Taurus), on the -contrary, here announces itself as belonging to the family of our own -sun, a probably later type, and distinguished by solar-like lines in -its spectrum, which may be counted in the original photograph to the -number of over two hundred. There is necessarily some loss in the -printed reproduction; but is it not a wonderful thing, to be able to -look up, as the reader may do, to Aldebaran in the sky, and then down -upon the page before us, knowing that that remote, trembling speck of -light has by one of the latest developments of the New Astronomy been -made, without the intervention of the graver’s hand, to write its own -autograph record on the page before him? - -In the department of nebular astronomy, photography has worked an equal -change. The writer well remembers the weeks he has himself spent in -drawing or attempting to draw nebulæ,--things often so ghost-like as -to disappear from view every time the eye turned from the white paper, -and only to be seen again when it had recovered its sensitiveness by -gazing into the darkness. The labors of weeks were, literally, only -represented by what looked like a stain on the paper; and no two -observers, however careful, could be sure that the change between -two drawings of a nebula at different dates was due to an alteration -in the thing itself, or in the eye or hand of the observer, though -unfortunately for the same reason it is impossible fully to render the -nebulous effect of the photograph in engraving. We cannot with our -best efforts, then, do full justice to the admirable one of Orion, on -page 239, which we owe to the particular kindness of Mr. Common, of -Ealing, England, whose work in this field is as yet unequalled. The -original enlargement measures nearly two square feet in area, with -fine definition. It is taken by thirty-nine minutes’ exposure, and its -character can only be indicated here; for it is not too much to say -here of this original also, that as many years of the life of the most -skilled artist could not produce so trustworthy a record of this wonder. - -The writer remembers the interest with which he heard Dr. Draper, -not long before his lamented death, speak of the almost incredible -sensitiveness of these most recent photographic processes, and his -belief that we were fast approaching the time when we should photograph -what we could not even see. That time has now arrived. At Cambridge, -in Massachusetts, and at the Paris Observatory, by taking advantage -of the cumulative action we have referred to, and by long exposures, -photographs have recently been taken showing stars absolutely invisible -to the telescope, and enabling us to discover faint nebulæ whose -previous existence had not been suspected; and when we consider that an -hour’s exposure of a plate, now not only secures a fuller star-chart -than years of an astronomer’s labor, but a more exact one, that the -art is every month advancing perceptibly over the last, and that it is -already, as we may say, not only making pictures of what we see, but -of what we cannot see even with the telescope,--we have before us a -prospect whose possibilities no further words are needed to suggest. - -We have now, not described, but only mentioned, some division of the -labors of the New Astronomy in its photometric, spectroscopic, and -photographic stellar researches, on each of which as many books, rather -than chapters, might be written, to give only what is novel and of -current interest. But these are themselves but a part of the modern -work that has overturned or modified almost every conception about the -stellar universe which was familiar to the last generation, or which -perhaps we were taught in our own youth. - - * * * * * - -In considering the results to be drawn from this glance we have taken -at some facts of modern observation, if it be asked, not only what -the facts are, but what lessons the facts themselves have to teach, -there is more than one answer, for the moral of a story depends on -the one who draws it, and we may look on our story of the heavens -from the point of view either of our own importance or of our own -insignificance. In the one case we behold the universe as a sort of -reflex of our own selves, mirroring in vast proportions of time and -space our own destiny; and even from this standpoint, one of the -lessons of our subject is surely that there is no permanence in any -created thing. When primitive man learned that with lapsing years the -oak withered and the very rock decayed, more slowly but as surely as -himself, he looked up to the stars as the types of contrast to the -change he shared, and fondly deemed them eternal; but now we have found -change there, and that probably the star clusters and the nebulæ, even -if clouds of suns and worlds, are fixed only by comparison with our own -brief years, and, tried by the terms of their own long existence, are -fleeting like ourselves. - - “We have often witnessed the formation of a cloud in a serene - sky. A hazy point barely perceptible--a little wreath of mist - increases in volume and becomes darker and denser, until it - obscures a large portion of the heavens. It throws itself into - fantastic shapes, it gathers a glory from the sun, is borne - onward by the wind, and as it gradually came, so, perhaps, it - gradually disappears, melting away in the untroubled air. But the - universe is nothing more than such a cloud,--a cloud of suns and - worlds. Supremely grand though it may seem to us, to the infinite - and eternal intellect it is no more than a fleeting mist. If - there be a succession of worlds in infinite space, there is also - a succession of worlds in infinite time. As one after another - cloud replaces clouds in the skies, so this starry system, the - universe, is the successor of countless others that have preceded - it,--the predecessor of countless others that will follow.” - -These impressions are strengthened rather than weakened when we come -back from the outer universe to our own little solar system; for -every process which we know, tends to the dissipation, or rather the -degradation, of heat, and seems to point, in our present knowledge, to -the final decay and extinction of the light of the world. In the words -of one of the most eminent living students of our subject, “The candle -of the sun is burning down, and, as far as we can see, must at last -reach the socket. Then will begin a total eclipse which will have no -end. - - ‘Dies iræ, dies illa, - Solvet sæclum in favilla.’” - -Yet though it may well be that the fact itself here is true, -it is possible that we draw the moral to it, unawares, from an -unacknowledged satisfaction in the idea of the vastness of the funeral -pyre provided for such beings as ourselves, and that it is pride, -after all, which suggests the thought that when the sun of the human -race sets, the universe will be left tenantless, as a body from which -the soul has fled. Can we not bring ourselves to admit that there may -be something higher than man and more enduring than frail humanity, -in some sphere in which _our_ universe, conditioned as it is in space -and time, is itself embraced; and so distrust the conclusions of man’s -reason where they seem to flatter his pride? - -May we not receive even the teachings of science, as to the “Laws of -Nature,” with the constant memory that all we know, even from science -itself, depends on our very limited sensations, our very limited -experience, and our still more limited power of conceiving anything for -which this experience has not prepared us? - - * * * * * - -I have read somewhere a story about a race of ephemeral insects who -live but an hour. To those who are born in the early morning the -sunrise is the time of youth. They die of old age while his beams are -yet gathering force, and only their descendants live on to midday; -while it is another race which sees the sun decline, from that which -saw him rise. Imagine the sun about to set, and the whole nation of -mites gathered under the shadow of some mushroom (to them ancient -as the sun itself) to hear what their wisest philosopher has to say -of the gloomy prospect. If I remember aright, he first told them -that, incredible as it might seem, there was not only a time in the -world’s youth when the mushroom itself was young, but that the sun in -those early ages was in the eastern, not in the western, sky. Since -then, he explained, the eyes of scientific ephemera had followed it, -and established by induction from vast experience the great “Law of -Nature,” that it moved only westward; and he showed that since it -was now nearing the western horizon, science herself pointed to the -conclusion that it was about to disappear forever, together with the -great race of ephemera for whom it was created. - -What his hearers thought of this discourse I do not remember, but I -have heard that the sun rose again the next morning. - - - - -INDEX. - - - Abbe, Professor, 56. - - Actinism, 71. - - Adams, Professor, 195. - - Africa, 116. - - Ages, stellar, 238. - - Air: - dancing, 17; - a medium, 33; - continuous, 176; - rarefied, 179; - motes, 181; - nimble, 191. - (See _Atmosphere_.) - - Airless Mountains, 160. - - Air-wave, 185. - - Aitken’s Researches, 181. - - Alaska, 38. - - Aldebaran, 222, 235, 236, 246. - - Algot, 228. - - Allegheny Observatory, 17, 19, 84, 86. - (See _Langley_.) - - Alphonsus Ring-plain, 156. - - Alps, 39, 148, 151, 167, 181. - (See _Apennines, Lunar_.) - - American Astronomers, 227. - - American Continents, 20, 21, 31. - (See _South_.) - - Andalusia, 53. - - Animalculæ, 224. - - Animals: - food, 74; - fright, 42. - (See _Dog_.) - - Antares, 238. - - Ants, 223. - (See _Insects_.) - - Apennines, 151, 153, 155, 160, 167. - (See _Alps, Lunar_.) - - Apples, 171. - - Arab Traditions, 194. - (See _Moslem_.) - - Arago, quoted, 41, 42. - - Archimedes, 94. - - Archimedes Crater, 151–153, 155. - - Arctic Cold, 159. - - Arctic Pole, 96. - - Arcturus, 208, 211. - - Aristillus Crater, 151. - - Aristotelian Philosophy, 8. - - Arzachel, 156, 161. - - Asteroids, 128. - - Astrology, 127. - - Astronomers and Priests, 1–3. - (See _American, New_, _Old_.) - - Astronomical Day, 85, 86. - - Atmosphere, 136, 180; - as a shield, 216, 220. - (See _Air_.) - - Atolls, 152. - - Auger, simile, 31. - - Aurora Borealis, 35, 67, 212. - - Autolycus Crater, 151. - - Axis, 9, 10. - - - Babel, 96. - - Bain Telegraph, 88. - - Balloons, 176. - - Bees, 124. - (See _Insects_.) - - Berkeley’s Theory, 70. - - Berlin Observatory, 233. - - Bernières’s Lens, 103. - - Bessemer Steel, 104–108. - - Birds, 172, 196, 197. - (See _Animals_.) - - Black Hole, 73. - - Bond, Professor, 204. - - Boston, Mass., 88, 132. - - Bothkamp, observations at, 66. - - Breadstuffs, 78, 79. - (See _Grain_, _Sun-spots_, _Wheat_.) - - Bridges, 20, 68. - - Britain, Ancient, 1, 234. - (See _England_.) - - British Isles, 14, 25. - - Brocken Spectre, 55. - - Brothers, Mr., 50. - - Bubbles, 168. - - Buffer, the air as a, 216, 220. - - Bunsen’s Researches, 12. - - Burnham, W. S., 233. - - Burning-glasses, 102–104. - - Burning Heat, 160, 163. - - - Cactus, 14, 24. - - Calcutta, 73. - - California, 151, 180. - - Cambric Needle (_q. v._), experiment, 132. - - Cambridge Observations, 227, 245–247. - - Camera Obscura, 63. - - Campanus Crater, 163, 165. - - Candle, simile, 39. - - Cannon-ball, 5, 38, 41, 98, 135, 186, 211. - - Canopus, 234. - - Carbon, 72, 73, 107, 221. - - Carbonic-acid Gas, 219. - - Carpenter’s Studio, 140. - - Carrington’s Work, 79, 87. - - Carthage, 116. - - Cassini, 42. - - Cassiopeia, 229. - - Cataclysm, 30. - - Centimetres, 93. - - Chacornac’s Drawing, 33. - - Chambers, on sun-spots, 80. - - Charleston Earthquake (_q. v._), 42. - - Chemical Elements, 221, 223. - - Cherry-stone, comparison, 196. - - Chicago: - great fire, 134; - astronomer, 233. - - China: - lens, 103, 104; - soil, 180. - - Chlorophyl, 73. - - Chocolate, simile, 107. - - Cholera, 80. - - Chromosphere, 7; - clouds, 62; - forms, 64–68. - - Cinders, 171. - - Clark’s Glasses, 123. - - Cliffs, 164. - - Clock, 135. - - Cloud-ocean, 179. - - Clouds: - cirrous, 27, 28; - beautiful, 54; - and rain, 111; - formed, 249. - - Coal-beds, 115. - - Coal: - energy, 73–75, 111; - destroyed, 97; - wasted, 101; - stock, 112. - - Cobweb, simile, 26. - - Cold: - and eclipses, 40; - in planets, 136. - - Colorado, 50. - - Colors: - in eclipses (_q. v._), 65; - mental, 70, 71; - in Jupiter (_q. v._), 127; - in moon (_q. v._), 168; - in stars (_q. v._), 227; - spectrum (_q. v._), 236. - - Comet-hunters, 204, 207. - - Comets: - chapter, 199–220; - Donati’s, 201, 204, 205, 207, 209, 217; - one part, 203; - parts and name, 208; - tail (_q. v._), 208, 211; - diameter and parts, 216; - spectroscope, elements, dread, 219; - numerous, stone, 219, 220; - kernel, 220; - (1858), 213–216; - (1866), 200. - - Common, A. A., 239, 247. - - Compass, 86. - - Connecticut Observations, 186, 242. - - Converter, 104–108. - - Coral, 151. - - Corn, 111. - (See _Grain_.) - - Corona, 7, 36, 37, 40, 41, 43, 45–52, 55, 56, 59, 60–62. - - Cotton-mill, 74. - - Counting, 94. - - Cracks, celestial, 163. - - Craters, 164. - (See special names.) - - Crystalline Structure, 4, 23–27. - - Cyclones, 24, 31, 32, 68. - - - Decay, 248, 249. - - Delambre’s History, 207. - - De la Rue’s Engraving, 125. - - Delfthaven, 5. - - Denning’s Theory, 197. - - Diamonds, melted, 103. - - Dies Iræ, 249. - - Dipper, 207, 208. - (See _Great Bear_, _Polar_.) - - Diurnal Oscillation, 87. - - Dog, anecdote of, 42. - (See _Animals_.) - - Donati, 201, 204, 205, 207, 209, 213, 217. - (See _Comets_.) - - Double Stars, 233. - - Draper, Professor Henry, 128, 246, 247. - - Ducks, noise, 188. - - Dust, 34, 100, 101, 102, 105, 197. - - Dynamite, 182, 185, 220. - - - Earth: - relations, 3, 4; - description difficult, 6; - temperature (_q. v._), 34, 101; - a string of earths, 96; - stars like, 118; - seen from outside, 133–135; - craters, 148. - - Earthquakes, 220. - (See _Charleston_.) - - Earth-shine, 167, 172. - - Eclipses: - total, 7, 37; - screen, 36; - three, 39, 55; - partial, 40; - singular gloom, 39–43; - causing fright, 43; - colors (_q. v._), 48, 56, 61, 65, 66; - (1842), 41; - (1857), 48; - (1869), 39, 40; - (1870), 44, 61; - (1871), 50, 66, 68; - (1878), 38, 50, 57, 58. - (See _Total_.) - - Egypt, 116, 234. - (See _Pyramids_.) - - Electricity, 13, 75, 76. - - Electric Light, 7. - - Electric Spark, 242. - (See _Lightning_.) - - Electric Storm, 84, 85, 88. - - Elizabeth, Queen, 115. - - Engine-power, 98, 111. - - England: - fleets, 2; - coal, 115. - (See _Britain_, _London_.) - - Engraving, 17. - - Enigma, 228. - - Ephemera, 250, 251. - - Equatorial Landscape, 13, 17, 18, 47. - - Equatorial Telescope, 122. - - Ericsson: - engravings, 112, 113; - discoveries, 163. - - Eruptive Promontories, 66–68. - - Etna, 164, 181. - - Europe, size, 25. - - Evolution, planetary, 139. - - Explosive Forces, 182–194. - - Eye, 71, 227. - - Eye-pieces, 47, 63. - - - Fabricius’s Observations, 8. - - Fact and Fancy, 175. - - Factory, 73. - - Faculæ, 32, 33. - - Falling, 242, 243. - - Falling Stars, 193. - (See _Meteors_, _Shooting_.) - - Faraday, Michael, 76. - - Fault, technical term, 156. - - Faust, 139. - - Faye: - theory, 29–32; - on Comets’ Tails, 212. - - Fern-like Forms, 25, 26. - - Filaments, 25–27, 30, 55, 56, 65, 66, 68. - - Fire, in sun (_q. v._), 92. - (See _Flames_, _Heat_.) - - Fixed Stars, 233. - - Flame-like Appearances, 23, 24. - - Flames, 65, 66, 69, 185. - - Flashes, 189, 195. - - Flax, 111. - - Flowers, color (_q. v._), 70. - (See _Rose_, _Plants_.) - - Foliage-forms, 32. - - Fontenelle’s Story, 133. - - Forbes’s Observations, 38, 39. - - Frankenstein, 221. - - Franklin’s Discoveries, 76. - - Fraunhofer Studies, 235. - - French Institute, 186. - - Frost-crystals (_q. v._), 23. - - Furnaces, 101. - - - Galileo, 8, 121–123, 139, 140. - - Gas: - glowing, 44; - in sun, 60. - - Gas-jets, 40, 61, 68, 88. - - Gassendi’s View, 172, 173. - - Gelinck’s Observations, 80. - - Geminids, 196. - - Genii, 193. - - Geographers and Geologists, 133. - - Glare, 14, 18, 62–64. - - Glass: - spun, 26; - globe, 145. - - Glow-worms, 7, 117. - - Good Hope Observations, 80. - - Gould’s Researches, 80. - - Grain, prices, 77, 80, 87. - (See _Corn_, _Sun-spots_, _Wheat_.) - - Gramarye, 92. - - Grass-blades, 66, 72. - - Grasses, 26. - - Gravitation, 72, 203; - negative, 215. - - Great Bear, 207. - (See _Dipper_, _Polar_.) - - Green’s Maps, 130. - - Greenwich Observatory, 2, 81, 82, 84, 85, 88, 89. - - Gulliver’s Travels, 131, 132. - (See _Swift_.) - - Gunpowder, 186. - - Guns, 135. - (See _Cannon-ball_.) - - - Hall Island, 130. - - Hall, Professor, 131. - - Hand, illustration, 168. - - Harkness’s Observations, 44. - - Harvests, 90. - - Hastings, Professor, 60. - - Heat: - development, 13; - concentration, 19; - loss, 29; - confinement, 33; - sensation, 71; - vibrations, 72; - energy, 91; - amount, 92, 97; - computation, 94–96; - diminution, 101; - emission, 102; - storage, 111; - in sugar, 188. - (See _Flames_, _Sun_.) - - Hecla, 164, 181. - - Hedgehog-spines, simile, 68. - - Helmholtz’s Estimates, 98. - - Hengist and Horsa, 1. - (See _Britain_.) - - Hercules, 238. - - Herschel, Sir John: - sun-spots, 12–14; - electric storms, 88; - comet’s tail, 216. - - Herschel, Sir William: - avoidance of light, 18; - prices, 79; - sun-spots (_q. v._), 129. - - Herschel’s Outlines, 11. - - Holden, Professor, 124. - - Honeycomb Structure, 30. - - Huggins’s Experiment, 234, 235. - - Humanity, deified, 172. - - Human Race, 250. - - Humboldt, 195. - - Humming-bird, 70. - - Hunt, Professor, 136, 219. - - Hydrogen, 68, 99, 237. - - - Ibrahim, King, story, 194, 195. - - Ice: - melted, 95, 96; - never melted, 163, 164. - - Imbrian Sea, 151. - - Insects, 224, 250. - (See _Ants_, _Bees_.) - - Iron: - melting, 19, 107; - appearance of cold, 25; - in sun, 28; - in man, 221; - in stars, 236, 237. - (See _Steel_.) - - Ironstone, 188. - - Ivy, 115. - - - Janssen’s Observations, 61. - - Jevons, Professor, 80. - - Joseph in Egypt, 90. - - Jumping, 241, 242. - - Jupiter, 79, 118, 124, 127–129, 156, 185, 229. - - - Kensington Museum, 221. - - Kepler, on Comets, 219. - - Kernels, 220. - - Kew, 88. - - Kirchoff’s Researches, 12. - - Krakatao, 181, 185, 186. - - - La Harpe, quoted, 207. - - Landscape, 169. - - Langley, Prof. S. P.: - drawings, 15, 16, 18, 19, 21, 22, 25, 28, 30; - note-book, 24; - expedition, 180; - study of Reflection, 216. - (See _Allegheny_, _Pittsburg_.) - - Latent Power, 220. - - Laws of Nature, 250, 251. - - Leaf-like Appearances, 23. - (See _Willow_.) - - Lenses, 102, 103; - Galileo’s, 123. - - Leo, 195, 197. - - Liais’s Drawing, 48, 50. - - Lick Glass, 123. - - Light: - development, 13; - day and night, 35; - white (_q. v._), 48; - mental (see _Eye_), 71; - from balloon, 179; - transmitted, 227. - (See _Sun_.) - - Lightning, 75, 76, 242, 244, 245. - (See _Electric_.) - - Lily, 73. - (See _Flowers_.) - - Limited Express Train, 5. - - Loaf-sugar, experiment, 188. - - Lockyer’s Land, 130. - - Lockyer’s Solar Physics, 59, 61, 236, 238. - - Lombardy, 151. - - London, 111. - - Lost Pleiad (_q. v._), 207. - - Louis XV., 42. - - Louis XVI., 221. - - Lunar Alps (_q. v._), 148, 149. - (See _Moon_.) - - Lunar Apennines (_q. v._), 153. - - Lunar Shadows, 36, 37, 39, 56. - - Lyrids, 196, 200. - - - Macartney’s Lens, 103. - - Maelstrom, 27. - - Magic Lantern, simile, 220. - - Magnesium, 236, 237. - - Magnetic Needle, 81, 82, 84, 85, 87, 89. - - Mammoth Cave, 40. - - Man, chemistry of, 221, 233. - (See _Humanity_.) - - Manhattan Island, 111. - - Mare Crisium, 143. - - Mare Serenitatis, 143, 144. - - Mars, 118, 128–132, 148. - - Mason’s Publication, 137. - - Matterhorn, 148, 167. - - Mayflower, 5. - - Meadows, 172. - - Mecca, 175. - - Medusa, 228. - - Memnon, 234. - - Mercator, 163, 165. - - Mercury, 3, 118, 136, 229. - - Messier, anecdote, 207. - - Metals, melted, 103. - (See _Iron_.) - - Metaphysics, 70, 71. - - Meteorites: - around Saturn, 124; - recent, 187; - lawsuit, 187, 188; - analyzed, 191, 192; - in Iowa, 199, 200; - swarm, 200; - cracking, 211. - - Meteors, 98, 175–198; - (1868), 189. - (See _Falling_, _Shooting_.) - - Meunier’s Investigations, 192. - - Mexican Gulf, 38. - - Microcosm, 222. - - Micromegas, 223. - - Microscope, 224. - - Middle Ages, 91, 175. - - Milky Way, 224, 225. - - Milton, quoted, 14, 38. - - Mind-causation, 70, 71. - - Mirror, 102, 107. - - Mississippi, 134. - - Mites, 224. - - Mizar, 207. - - M’Leod’s Drawing, 44. - - Monochromatic Light (_q. v._), 63. - - Montaigne of Limoges, 207. - - Mont Blanc, 156. - - Monte Rosa, 167. - - Moon: - practical observations, 2; - newly studied, 3; - distance, 4–6; - size, 5, 6, 140, 156; - shadows (_q. v._), 36, 125; - in sun-eclipse, 41; - planetary relations, 117–174; - and Jupiter, 127; - photograph, 137; - full, 141, 144, 147; - Man in the, 143; - mountains, 144; - craters, 147, 148; - temperature, 159; - airless, 160; - landscape (_q. v._), 169; - age, 171; - broken up, 192; - like comet, 215. - (See _Lunar_.) - - Moslem Traditions, 175, 194. - (See _Arab_.) - - Moss, 160. - - Mouchot’s Engravings, 109, 112. - - Mountain Sickness, 50, 53. - - - Naples, 155, 157. - (See _Vesuvius_.) - - Napoleon, 80, 134. - - Nasmyth’s Researches, 11, 12, 14, 24, 25, 140. - - Nativity of Jesus, 229. - - Nature’s Laws (_q. v._), 176. - - Nebulæ, 247. - - Needle, 228. - (See _Cambric_.) - - Neptune, 121. - - Nerves, none in camera, 47. - - Nerve Transmission, 5, 6. - - New Astronomy, 4, 75, 76, 117, 121, 171, 193, 222, 224, 227, 235, - 246, 248. - (See _Old_.) - - Newcomb, Professor, 55. - - Newspapers, printed by the sun, 74. - - Newton, Professor, 191, 195–197. - - Newton, Sir Isaac, 136, 203, 211; - on Comets, 215, 219. - - Nightmare, 67. - - Northern Crown, 208, 211, 230. - - Novelists, theme for, 193, 228. - - Nucleus, 11, 19, 216. - (See _Comets_, _Corona_.) - - - Oceans, 179. - - Old Astronomy, 199, 203, 233. - (See _New_.) - - Organisms in sun (_q. v._), 13. - - Orion, 238, 239, 247. - - Oxygen, 73. - - - Pacific Ocean, 180. - - Palinurus, 243. - - Parable, 224. - - Paris: - Observatory, 42, 233, 247; - Exposition, 112. - - Parker’s Lens, 103. - - Peirce, Professor, 44. - - Pennsylvania Coal, 97. - - Penumbra, 11, 19, 20. - - Perpignan, France, 42. - - Perseus, 196. - - Persian Rugs, 70. - - Philadelphia, 88. - - Philosopher’s Stone, 92. - - Phœbus, 34. - - Phosphorus, 221. - - Photographic Plate, 71. - - Photography, 9, 19, 128, 236, 237, 241, 244, 247, 248; - rapid, 242. - - Photometer, 56, 108. - - Photometry, 230. - - Photosphere, 7, 17, 64. - - Pickering, Professor, 132, 227, 228, 246. - - Pico Summit, 148. - - Piffard, Dr. H. G., 245. - - Pike’s Peak, 50, 53–57, 60. - - Pilgrim Fathers, 5. - - Pine-boughs, 25. - - Pine-trees, 60, 72. - - Pittsburg Observations, 18, 19. - (See _Allegheny_, _Langley_.) - - Planetoids, 196, 197, 229. - - Planets: - condition, 97; - pulverized, 100; - and moon, 117–174; - isolated, 176. - (See _Jupiter_, _Mars_, _Mercury_, _Saturn_, _Sirius_, _Stars_.) - - Plants, 72, 73. - (See _Flowers_.) - - Plato Crater, 147, 148, 151, 152. - - Pleiades, 17, 231, 245. - (See _Lost_.) - - Plume, The, 19, 23, 24, 55. - - Pointers, 208. - (See _Dipper_.) - - Poison, 222. - - Polariscope, 49. - - Polarization, 18. - - Polarizing Eye-piece, 14, 18. - - Polar Star, 230. - (See _Great Bear_.) - - Polyp, 152. - - Pores, 24. - - Pouillet’s Invention, 93. - - Printing, indebtedness to the sun, 74. - - Prism, 63, 64. - (See _Colors_, _Scarlet_.) - - Proctor’s Observations, 14, 59, 69, 87. - - Prospero’s Wand, 221. - - Ptolemy, 155, 161. - - Pyramids, 99, 117, 233, 234. - (See _Egypt_.) - - Pyrheliometer, 93. - - - Race, simile, 179. - - Radiant Energy, 71, 74; - rate, 104. - - Radiation, 101, 108. - - Railway Explosion, 182, 183. - - Railway, The, 156. - - Rain, 111. - - Rainbow, 70. - - Ranyard’s Photographs, 50. - - Red Sea, 116. - - Reflection, 216. - - Repulsive Force, 215. - - Ribbons, 70, 236. - - Rifts, 163, 164. - - Rings, 123, 124, 152, 155. - (See _Saturn_.) - - Rockets, 67, 68. - - Rocky Mountains, 88, 89, 180. - - Roman Boy, 34. - - Rope, 20, 26. - - Rose-leaf, 63, 70. - (See _Leaves_.) - - Rowland’s Photographs, 237. - - Ruskin, quoted, 29. - - Russia, 134. - - Rutherfurd Photographs, 8, 9, 137, 143, 155, 234. - - - Sal-ammoniac, 14, 25. - - Salisbury Plain, 1, 2. - - Sandstone, 192. - - Saturn, 118, 119, 121, 123, 124, 127–129, 136, 215. - - Saturnian Dwarfs, 223, 224. - - Saul, comparison, 77. - - Saxon Forefathers, 1, 2. - (See _Britain_.) - - Scarlet, 67. - (See _Colors_.) - - Schwabe, Hofrath, 76, 77, 87. - - Scott, Sir Walter, quoted, 92. - - Screen, 10, 35–37. - - Seas, lunar (_q. v._), 143. - - Secchi, Father, 14, 15, 24, 25, 29, 30, 43, 59, 235. - - Segmentations, 30, 31. - - Self-luminosity, 215. - - Sextant, 224. - - Shadows. (See _Lunar_.) - - Shakspeare, quoted, 60, 220. - - Sheaves, 68. - - Shelbyville, 42, 43. - - Sherman, observations at, 88. - - Ship, comparison, 133. - (See _Steamer_.) - - Shooting-stars, 35, 193, 196, 198, 199. - (See _Falling_, _Meteors_.) - - Sicily, 50. - (See _Etna_.) - - Siemens, Sir William, 111. - - Sierra Nevada, 151, 160, 180. - - Signal Service, 90. - - Silicon, 107. - - Sirius, 179, 222–224, 236–238. - - Slits, 59, 63, 64. - - Smoked Glass, 11. - - Snow-flakes, 19, 35. - - Snow-like Forms, 25. - - Sodium, 237. - - Solar Engine, 75, 109. - - Solar Light (_q. v._), 13. - - Solar Physics, 4, 12, 14. - (See _Sun_.) - - Solar System, 228, 229. - - South America (_q. v._), 80. - - South Carolina, meteors, 194, 195. - (See _Charleston_.) - - Southern Cross, 234. - - Space, 181, 211, 224, 227, 229. - - Spain, expedition, 44. - - Sparks, 107, 108. - - Spectra, 231, 237. - - Spectres, 54, 55. - (See _Brocken_.) - - Spectroscope, 7, 50, 59, 61, 63, 64, 130, 176, 198, 219, 222, - 233–235, 240. - - Spectrum, 65, 235. - - Spectrum Analysis, 12. - - Speculations, 193. - - Spinning-wheel, 115. - - Springfield Observations, 44. - - Spurs, 208, 212, 215. - - Star of Bethlehem, 229. - (See _Tycho_.) - - Stars: - new study, 3; - location, 4; - size, 4, 230; - seen in darkness, 35; - self-shining suns, 35, 118; - host, 117; - variety, 118; - five, 118; - elements, atmosphere, 179; - showers (see _Meteors_), 195; - seen through comet, 212, 215; - chapter, 221–250; - analysis, children, 222; - distances, 223; - intervals, 224, 227, 229; - colors (_q. v._), glory, 227; - new, fading, 230; - double, 233; - relation to man (_q. v._), 233; - fixed, 233; - changing place, 234; - mass, 237; - ages, 238; - photographed, 244, 247; - chart, 247; - death, 248. - (See _Falling_, _Planets_, _Shooting_.) - - Steam, 74, 75. - - Steamers, 21, 73, 115. - - Steel, melted, 104–108. - (See _Iron_.) - - Stellar Spectra (_q. v._), 222, 236, 237, 244, 245. - - Stevenson, George, 111. - - Stewart’s Observations, 88. - - Stonehenge, 1–3. - - Stones: - from heaven, 175, 176, 186, 187, 191, 193; - Iowa, 199, 200. - (See _Meteorites_.) - - Stonyhurst Records, 88. - - Sumbawa Observations, 181. - - Sunbeams: - lifting power, 72; - Laputa, 73; - printing, 74; - motes, 215. - (See _Light_.) - - Sun: - practical observations in Washington, 2, 3; - new study, 3; - surroundings, 4, 35–69; - distance, 4–6; - size, 5, 6; - a private, 6; - views, 6–12, 15, 16, 20; - details, 7; - fire, 8, 91, 92; - telescopic view, 8; - axis, 9; - revolutions, 10; - surface, 17; - paper record, 18; - heat (_q. v._) and eye, 19; - drawings exaggerated, 29, 30; - something brighter, 32; - atmosphere, 33, 34; - slits, 59; - miniature, 64; - flames (_q. v._), 69; - energy, 70–116 (see _Heat_); - versatile aid, 74; - children, 75, 222; - shrinkage, 99; - ground up, 100; - emissive power, 104; - constitution and appearance, 111; - god, 116; - self-shining, 118; - studied from mountains, 167; - affected by dust (_q. v._), 185; - and comet, 216; - elements, 233; - a star, 237; - life, 238; - candle, 249; - anecdote, 250. - (See _Solar_.) - - Sunrise, 234. - - Sunset, 181, 182. - (See _Twilight_.) - - Suns: - millions, 224; - dwindling, 227; - periods, 241. - - Sun-spots, 1–34 _passim_; - ancient, 8; - early observations, 8; - changing, 9; - great, 10, 20, 24; - individuality, darker, 11; - leaves (_q. v._), 11, 12; - how observed, 18, 19; - typical, 21, 22; - relative size, 20; - hook-shaped (see _Plume_), 24; - signs of chaos, 27; - double, 32; - weather, 76, 90; - periodicity, 76–78; - temperature, 83; - records, 85; - variations, 87; - (1870), 9, 15, 16, 20; - (1873), 20–24; - (1875), 25, 28, 30; - (1876), 30, 32; - (1882), 80, 83–86, 90. - - Superga, 38. - - Swift, Dean, 73, 131, 132. - (See _Gulliver_.) - - Sword Meteor (_q. v._), 175. - - - Tacchini’s Investigations, 43, 49, 62, 66, 68. - - Tail, 215, 216. - (See _Comets_.) - - Tan, 71. - - Taylor, Bayard, 139. - - Telephone, 84, 89. - - Telescopes: - many, 17; - best, 134; - alone, 227, 230; - use, 233, 234. - - Temperature, 101, 102, 108; - of space, 224, 227. - - Terminator, 147. - - Thermometer, 71, 93, 102; - low, 160, 163. - - Time, small divisions, 241. - - Tippoo Saib, 221. - - Total Eclipse (_q. v._), 39–48 _passim_, 55, 59. - - Trees, lacking, 168. - - Tribune, The New York, 84. - - Trinity Church, 72. - - Trocadéro, 112. - - Trouvelot, E. L., 119, 123, 225. - - Turin, 38. - - Twilight, small, 38. - - Tycho, 144, 229. - (See _Star_.) - - Tyndall, 98. - - - Umbra, 11, 12, 19, 20. - - United States, comparison, 24. - - Uranus, 3, 196. - - Vapor, 28. - - Vega, 235, 246. - - Vegetables, 74. - - Veils, 14, 17. - - Venus, 118. - - Vernier, 3. - - Vesuvius: - crater, 155, 157; - eruption, 181, 183. - (See _Naples_.) - - Vibrations, 72. - - Victoria, 115. - - Viscous Fluid, 26. - - Vital Force, 14. - - Vogel, H. C., 64, 66. - - Voids, 181, 227. - - Volcanoes, 27, 28; - in moon, 167, 193. - - - Wandering Star, 101. - (See _Comets_, _Falling_.) - - Washington: - Observatory, 2, 86–88; - telescope, 122; - Monument, 182. - - Water, 152; - in man, 221. - - Waterloo, 80. - - Water-wheel, 111. - - Watson’s Observations, 49. - - Wheat, prices, 79. - (See _Breadstuffs_, _Corn_, _Grain_, _Sun-spots_.) - - Wheel, comparison, 10. - - Whirlpools, 28, 31. - - Whirlwinds, 23, 31. - - White Light (_q. v._), 48, 62, 63. - - Whitney, Mount, 177. - - Willow-leaves (_q. v._), 11, 12, 14. - - Wing, simile, 215. - - Winlock, Professor, 44. - - Withered Surfaces, 168, 171. - - Wood-engraving, 50. - - Worlds and Clouds, 249. - - Wrinkles, 172. - - - Xeres, Spain (_q. v._), 44, 53. - - - Young, Professor: - spectroscope, 44, 50, 65, 234; - observations, 56, 59, 61, 68, 69; - magnetism, 87, 88; - radiation, 101. - - - Zodiacal Light, 55. - - -University Press: John Wilson & Son, Cambridge. - - - - -Transcriber’s Notes - - -Punctuation, hyphenation, and spelling were made consistent when a -predominant preference was found in the original book; otherwise they -were not changed. - -Simple typographical errors were corrected; unbalanced quotation -marks were remedied when the change was obvious, and otherwise left -unbalanced. - -Illustrations in this eBook have been positioned between paragraphs -and outside quotations. 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