[Illustration: Paul Renaud. CONTEMPLATION] ASTRONOMY FOR AMATEURS BY CAMILLE FLAMMARION AUTHOR OF POPULAR ASTRONOMY _AUTHORIZED TRANSLATION BY_ FRANCES A. WELBY _ILLUSTRATED_ [Illustration] NEW YORK AND LONDON D. APPLETON AND COMPANY 1910 COPYRIGHT, 1904, BY D. APPLETON AND COMPANY _Published October, 1904_ TO MADAME C. R. CAVARÉ ORIGINAL MEMBER OF THE ASTRONOMICAL SOCIETY OF FRANCE CHÂTEAU DE MAUPERTHUIS MADAME: I have dedicated none of my works, save Stella--offered to theliberal-minded, the free and generous friend of progress, and patron ofthe sciences, James Gordon Bennett, editor of the New York Herald. Inthis volume, Madame, I make another exception, and ask your permissionto offer it to the first woman who consented to be enrolled in the listof members of the Astronomical Society of France, as foundress of thissplendid work, from the very beginning of our vast association (1887);and who also desired to take part in the permanent organization of theObservatory at Juvisy, a task of private enterprise, emancipated fromadministrative routine. An Astronomy for Women[1] can not be betterplaced than upon the table of a lady whose erudition is equal to hervirtues, and who has consecrated her long career to the pursuit andservice of the Beautiful, the Good, and the True. CAMILLE FLAMMARION. OBSERVATORY OF JUVISY, _November, 1903_. CONTENTS CHAPTER PAGE INTRODUCTION 1 I. THE CONTEMPLATION OF THE HEAVENS 10 II. THE CONSTELLATIONS 28 III. THE STARS, SUNS OF THE INFINITE. A JOURNEY THROUGH SPACE 56 IV. OUR STAR THE SUN 88 V. THE PLANETS. A. MERCURY, VENUS, THE EARTH, MARS 113 VI. THE PLANETS. B. JUPITER, SATURN, URANUS, NEPTUNE 146 VII. THE COMETS 172 VIII. THE EARTH 205 IX. THE MOON 232 X. THE ECLIPSES 259 XI. ON METHODS. HOW CELESTIAL DISTANCES ARE DETERMINED, AND HOW THE SUN IS WEIGHED 287 XII. LIFE, UNIVERSAL AND ETERNAL 317 INDEX 341 LIST OF ILLUSTRATIONS Contemplation _Frontispiece_ From a painting by Paul Renaud FIG. PAGE 1. The great Book of the Heavens is open to all eyes 15 2. The earth in space. June solstice, midday 20 3. The Great Bear (or Dipper) and the Pole Star 34 4. To find the Pole Star 35 5. To find Cassiopeia 37 6. To find Pegasus and Andromeda 37 7. Perseus, the Pleiades, Capella 38 8. To find Arcturus, the Herdsman, and the Northern Crown 40 9. The Swan, Vega, the Eagle 41 10. The Constellations of the Zodiac: summer and autumn; Capricorn, Archer, Scorpion, Balance, Virgin, Lion 46 11. The Constellations of the Zodiac: winter and spring; Crab, Twins, Bull, Ram, Fishes, Water-Carrier 47 12. Orion and his celestial companions 48 13. Winter Constellations 51 14. Spring Constellations 52 15. Summer Constellations 53 16. Autumn Constellations 54 17. The double star Mizar 69 18. Triple star [xi] in Cancer 72 19. Quadruple star [epsilon] of the Lyre 73 20. Sextuple star [theta] in the Nebula of Orion 74 21. The Star-Cluster in Hercules 79 22. The Star-Cluster in the Centaur 80 23. The Nebula in Andromeda 81 24. Nebula in the Greyhounds 82 25. The Pleiades 83 26. Occultation of the Pleiades by the Moon 85 27. Stellar dial of the double star [gamma] of the Virgin 86 28. Comparative sizes of the Sun and Earth 93 29. Direct photograph of the Sun 96 30. Telescopic aspect of a Sun-Spot 97 31. Rose-colored solar flames 228, 000 kilometers (141, 500 miles) in height, _i. E. _, 18 times the diameter of the Earth 103 32. Orbits of the four Planets nearest to the Sun 115 33. Orbits of the four Planets farthest from the Sun 116 34. Mercury near quadrature 117 35. The Earth viewed from Mercury 119 36. The Evening Star 123 37. Successive phases of Venus 124 38. Venus at greatest brilliancy 126 39. The Earth viewed from Venus 130 40. Diminution of the polar snows of Mars during the summer 136 41. Telescopic aspect of the planet Mars (Feb. , 1901) 137 42. Telescopic aspect of the planet Mars (Feb. , 1901) 138 43. Chart of Mars 140 44. The Earth viewed from Mars 144 45. Telescopic aspect of Jupiter 150 46. Jupiter and his four principal satellites 155 47. Saturn 159 48. Varying perspective of Saturn's Rings, as seen from the Earth 161 49. The Great Comet of 1858 174 50. What our Ancestors saw in a Comet 177 After Ambroise Paré (1858) 51. Prodigies seen in the Heavens by our Forefathers 178 52. The orbit of a Periodic Comet 182 53. The tails of Comets are opposed to the Sun 185 54. A Meteor 191 55. Shooting Stars of November 12, 1799 196 From a contemporary drawing 56. Fire-Ball seen from the Observatory at Juvisy, August 10, 1899 199 57. Explosion of a Fire-Ball above Madrid, February 10, 1896 200 58. Raphael's Fire-Ball (_The Madonna of Foligno_) 202 59. A Uranolith 203 60. Motion of the Earth round the Sun 222 61. Inclination of the Earth 224 62. The divisions of the globe. Longitudes and latitudes 226 63. To find the long and short months 230 64. The Full Moon slowly rises 234 65. The Moon viewed with the unaided eye 236 66. The Man's head in the Moon 237 67. Woman's head in the Moon 238 68. The kiss in the Moon 239 69. Photograph of the Moon 240 70. The Moon's Phases 241 71. Map of the Moon 247 72. The Lunar Apennines 251 73. Flammarion's Lunar Ring 253 74. Lunar landscape with the Earth in the sky 254 75. Battle between the Medes and Lydians arrested by an Eclipse of the Sun 266 76. Eclipse of the Moon at Laos (February 27, 1877) 269 77. The path of the Eclipse of May 28, 1900 273 78. Total eclipse of the Sun, May 28, 1900, as observed from Elche (Spain) 281 79. The Eclipse of May 28, 1900, as photographed by King Alfonso XIII, at Madrid 285 80. Measurement of Angles 289 81. Division of the Circumference into 360 degrees 291 82. Measurement of the distance of the Moon 292 83. Measurement of the distance of the Sun 297 84. Small apparent ellipses described by the stars as a result of the annual displacement of the Earth 306 INTRODUCTION The Science of Astronomy is sublime and beautiful. Noble, elevating, consoling, divine, it gives us wings, and bears us through Infinitude. In these ethereal regions all is pure, luminous, and splendid. Dreams ofthe Ideal, even of the Inaccessible, weave their subtle spells upon us. The imagination soars aloft, and aspires to the sources of EternalBeauty. What greater delight can be conceived, on a fine spring evening, at thehour when the crescent moon is shining in the West amid the last glimmerof twilight, than the contemplation of that grand and silent spectacleof the stars stepping forth in sequence in the vast Heavens? All soundsof life die out upon the earth, the last notes of the sleepy birds havesunk away, the Angelus of the church hard by has rung the close of day. But if life is arrested around us, we may seek it in the Heavens. Theseincandescing orbs are so many points of interrogation suspended aboveour heads in the inaccessible depths of space. . . . Gradually theymultiply. There is Venus, the white star of the shepherd. There Mars, the little celestial world so near our own. There the giant Jupiter. The seven stars of the Great Bear seem to point out the pole, while theyslowly revolve around it. . . . What is this nebulous light that blanchesthe darkness of the heavens, and traverses the constellations like acelestial path? It is the Galaxy, the Milky Way, composed of millions onmillions of suns!. . . The darkness is profound, the abyss immense. . . . See! Yonder a shooting star glides silently across the sky, anddisappears!. . . Who can remain insensible to this magic spectacle of the starry Heavens?Where is the mind that is not attracted to these enigmas? Theintelligence of the amateur, the feminine, no less than the morematerial and prosaic masculine mind, is well adapted to theconsideration of astronomical problems. Women, indeed, are naturallypredisposed to these contemplative studies. And the part they are calledto play in the education of our children is so vast, and so important, that the elements of Astronomy might well be taught by the young motherherself to the budding minds that are curious about every issue--whosefirst impressions are so keen and so enduring. Throughout the ages women have occupied themselves successfully withAstronomy, not merely in its contemplative and descriptive, but also inits mathematical aspects. Of such, the most illustrious was thebeautiful and learned Hypatia of Alexandria, born in the year 375 of ourera, public lecturer on geometry, algebra, and astronomy, and author ofthree works of great importance. Then, in that age of ignorance andfanaticism, she fell a victim to human stupidity and malice, was draggedfrom her chariot while crossing the Cathedral Square, in March, 415, stripped of her garments, stoned to death, and burned as a dishonoredwitch! Among the women inspired with a passion for the Heavens may be cited St. Catherine of Alexandria, admired for her learning, her beauty and hervirtue. She was martyred in the reign of Maximinus Daza, about the year312, and has given her name to one of the lunar rings. Another celebrated female mathematician was Madame Hortense Lepaute, born in 1723, who collaborated with Clairaut in the immense calculationsby which he predicted the return of Halley's Comet. "Madame Lepaute, "wrote Lalande, "gave us such immense assistance that, without her, weshould never have ventured to undertake this enormous labor, in which itwas necessary to calculate for every degree, and for a hundred and fiftyyears, the distances and forces of the planets acting by theirattraction on the comet. During more than six months, we calculated frommorning to night, sometimes even at table, and as the result of thisforced labor I contracted an illness that has changed my constitutionfor life; but it was important to publish the result before the arrivalof the comet. " This extract will suffice for the appreciation of the scientific ardorof Madame Lepaute. We are indebted to her for some considerable works. Her husband was clock-maker to the King. "To her intellectual talents, "says one of her biographers, "were joined all the qualities of theheart. She was charming to a degree, with an elegant figure, a daintyfoot, and such a beautiful hand that Voiriot, the King's painter, whohad made a portrait of her, asked permission to copy it, in order topreserve a model of the best in Nature. " And then we are told thatlearned women can not be good-looking!. . . The Marquise du Châtelet was no less renowned. She was predestined toher career, if the following anecdote be credible. Gabrielle-Émilie deBreteuil, born in 1706 (who, in 1725, was to marry the Marquis duChâtelet, becoming, in 1733, the most celebrated friend of Voltaire), was four or five years old when she was given an old compass, dressed upas a doll, for a plaything. After examining this object for some time, the child began angrily and impatiently to strip off the silly draperiesthe toy was wrapped in, and after turning it over several times in herlittle hands, she divined its uses, and traced a circle with it on asheet of paper. To her, among other things, we owe a precious, andindeed the only French, translation of Newton's great work on universalgravitation, the famous Principia, and she was, with Voltaire, aneloquent propagator of the theory of attraction, rejected at that timeby the Académie des Sciences. Numbers of other women astronomers might be cited, all showing howaccessible this highly abstract science is to the feminine intellect. President des Brosses, in his charming Voyage en Italie, tells of thevisit he paid in Milan to the young Italian, Marie Agnesi, who deliveredharangues in Latin, and was acquainted with seven languages, and forwhom mathematics held no secrets. She was devoted to algebra andgeometry, which, she said, "are the only provinces of thought whereinpeace reigns. " Madame de Charrière expressed herself in an aphorism ofthe same order: "An hour or two of mathematics sets my mind at liberty, and puts me in good spirits; I feel that I can eat and sleep better whenI have seen obvious and indisputable truths. This consoles me for theobscurities of religion and metaphysics, or rather makes me forget them;I am thankful there is something positive in this world. " And did notMadame de Blocqueville, last surviving daughter of Marshal Davout, whodied in 1892, exclaim in her turn: "Astronomy, science of sciences! bywhich I am attracted, and terrified, and which I adore! By it my soul isdetached from the things of this world, for it draws me to those unknownspheres that evoked from Newton the triumphant cry: '_Coeli enarrantgloriam Dei!_'" Nor must we omit Miss Caroline Herschel, sister of the greatest observerof the Heavens, the grandest discoverer of the stars, that has everlived. Astronomy gave her a long career; she discovered no less thanseven comets herself, and her patient labors preserved her to the age ofninety-eight. --And Mrs. Somerville, to whom we owe the Englishtranslation of Laplace's Mécanique céleste, of whom Humboldt said, "Inpure mathematics, Mrs. Somerville is absolutely superior. " Like CarolineHerschel, she was almost a centenarian, appearing always much youngerthan her years: she died at Naples, in 1872, at the age ofninety-two. --So, too, the Russian Sophie Kovalevsky, descendant ofMathias Corvinus, King of Hungary, who, an accomplished mathematician atsixteen, married at eighteen, in order to follow the curriculum at theUniversity (then forbidden to unmarried women); arranging with her younghusband to live as brother and sister until their studies should becompleted. In 1888 the Prix Bordin of the Institut was conferred onher. --And Maria Mitchell of the United States, for whom Le Verrier gavea _fête_ at the Observatory of Paris, and who was exceptionallyauthorized by Pope Pius IX to visit the Observatory of the RomanCollege, at that time an ecclesiastical establishment, closed towomen. --And Madame Scarpellini, the Roman astronomer, renowned for herworks on shooting stars, whom the author had the honor of visiting, incompany with Father Secchi, Director of the Observatory mentioned above. At the present time, Astronomy is proud to reckon among its most famousworkers Miss Agnes Clerke, the learned Irishwoman, to whom we owe, _inter alia_, an excellent History of Astronomy in the NineteenthCentury;--Mrs. Isaac Roberts, who, under the familiar name of MissKlumpke, sat on the Council of the Astronomical Society of France, andis D. Sc. Of the Faculty of Paris and head of the Bureau for measuringstar photographs at the Observatory of Paris (an American who becameEnglish by her marriage with the astronomer Roberts, but is notforgotten in France);--Mrs. Fleming, one of the astronomers of theObservatory at Harvard College, U. S. A. , to whom we owe the discovery ofa great number of variable stars by the examination of photographicrecords, and by spectral photography;--Lady Huggins, who in England isthe learned collaborator of her illustrious husband;--and many others. * * * * * The following chapters, which aim at summing up the essentials ofAstronomy in twelve lessons for amateurs, will not make astronomers ormathematicians of my readers--much less prigs or pedants. They aredesigned to show the constitution of the Universe, in its grandeur andits beauty, so that, inhabiting this world, we may know where we areliving, may realize our position in the Cosmos, appreciate Creation asit is, and enjoy it to better advantage. This sun by which we live, thissuccession of months and years, of days and nights, the apparent motionsof the heavens, these starry skies, the divine rays of the moon, thewhole totality of things, constitutes in some sort the tissue of ourexistence, and it is indeed extraordinary that the inhabitants of ourplanet should almost all have lived till now without knowing where theyare, without suspecting the marvels of the Universe. * * * * * For the rest, my little book is dedicated to a woman, muse andgoddess--the charming enchantress Urania, fit companion of Venus, ranking even above her in the choir of celestial beauties, as purer andmore noble, dominating with her clear glance the immensities of theuniverse. Urania, be it noted, is feminine, and never would the poetryof the ancients have imagined a masculine symbol to personify thepageant of the heavens. Not Uranus, nor Saturn, nor Jupiter can comparewith the ideal beauty of Urania. Moreover, I have before me two delightful books, in breviary binding, dated the one from the year 1686, the other from a century later, 1786. The first was written by Fontenelle for a Marquise, and is entitledEntretiens sur la Pluralité des Mondes. In this, banter is pleasantlymarried with science, the author declaring that he only demands from hisfair readers the amount of application they would concede to a novel. The second is written by Lalande, and is called Astronomie des Dames. Inaddressing myself to both sexes, I am in honorable company with thesetwo sponsors and esteem myself the better for it. CHAPTER I THE CONTEMPLATION OF THE HEAVENS The crimson disk of the Sun has plunged beneath the Ocean. The sea hasdecked itself with the burning colors of the orb, reflected from theHeavens in a mirror of turquoise and emerald. The rolling waves are goldand silver, and break noisily on a shore already darkened by thedisappearance of the celestial luminary. We gaze regretfully after the star of day, that poured its cheerful raysanon so generously over many who were intoxicated with gaiety andhappiness. We dream, contemplating the magnificent spectacle, and indreaming forget the moments that are rapidly flying by. Yet the darknessgradually increases, and twilight gives way to night. The most indifferent spectator of the setting Sun as it descends beneaththe waves at the far horizon, could hardly be unmoved by the pageant ofNature at such an impressive moment. The light of the Crescent Moon, like some fairy boat suspended in thesky, is bright enough to cast changing and dancing sparkles of silverupon the ocean. The Evening Star declines slowly in its turn toward thewestern horizon. Our gaze is held by a shining world that dominates thewhole of the occidental heavens. This is the "Shepherd's Star, " Venus ofrays translucent. Little by little, one by one, the more brilliant stars shine out. Hereare the white Vega of the Lyre, the burning Arcturus, the seven stars ofthe Great Bear, a whole sidereal population catching fire, likeinnumerable eyes that open on the Infinite. It is a new life that isrevealed to our imagination, inviting us to soar into these mysteriousregions. O Night, diapered with fires innumerable! hast thou not written inflaming letters on these Constellations the syllables of the greatenigma of Eternity? The contemplation of thee is a wonder and a charm. How rapidly canst thou efface the regrets we suffered on the departureof our beloved Sun! What wealth, what beauty hast thou not reserved forour enraptured souls! Where is the man that can remain blind to such apageant and deaf to its language! To whatever quarter of the Heavens we look, the splendors of the nightare revealed to our astonished gaze. These celestial eyes seem in theirturn to gaze at, and to question us. Thus indeed have they questionedevery thinking soul, so long as Humanity has existed on our Earth. Homersaw and sung these self-same stars. They shone upon the slow successionof civilizations that have disappeared, from Egypt of the period of thePyramids, Greece at the time of the Trojan War, Rome and Carthage, Constantine and Charlemagne, down to the Twentieth Century. Thegenerations are buried with the dust of their ancient temples. The Starsare still there, symbols of Eternity. The silence of the vast and starry Heavens may terrify us; its immensitymay seem to overwhelm us. But our inquiring thought flies curiously onthe wings of dream, toward the remotest regions of the visible. It restson one star and another, like the butterfly on the flower. It seeks whatwill best respond to its aspirations: and thus a kind of communicationis established, and, as it were, protected by all Nature in these silentappeals. Our sense of solitude has disappeared. We feel that, if only asinfinitesimal atoms, we form part of that immense universe, and thisdumb language of the starry night is more eloquent than any speech. Eachstar becomes a friend, a discreet confidant, often indeed a preciouscounsellor, for all the thoughts it suggests to us are pure and holy. Is any poem finer than the book written in letters of fire upon thetablets of the firmament? Nothing could be more ideal. And yet, thepoetic sentiment that the beauty of Heaven awakens in our soul oughtnot to veil its reality from us. That is no less marvelous than themystery by which we were enchanted. And here we may ask ourselves how many there are, even among thinkinghuman beings, who ever raise their eyes to the starry heavens? How manymen and women are sincerely, and with unfeigned curiosity, interested inthese shining specks, and inaccessible luminaries, and really desirousof a better acquaintance with them? Seek, talk, ask in the intercourse of daily life. You, who read thesepages, who already love the Heavens, and comprehend them, who desire toaccount for our existence in this world, who seek to know what the Earthis, and what Heaven--you shall witness that the number of thoseinquiring after truth is so limited that no one dares to speak of it, sodisgraceful is it to the so-called intelligence of our race. And yet!the great Book of the Heavens is open to all eyes. What pleasures awaitus in the study of the Universe! Nothing could speak more eloquently toour heart and intellect! Astronomy is the science _par excellence_. It is the most beautiful andmost ancient of all, inasmuch as it dates back to the indeterminatetimes of highest antiquity. Its mission is not only to make usacquainted with the innumerable orbs by which our nights areilluminated, but it is, moreover, thanks to it that we know where andwhat we are. Without it we should live as the blind, in eternalignorance of the very conditions of our terrestrial existence. Withoutit we should still be penetrated with the naïve error that reduced theentire Universe to our minute globule, making our Humanity the goal ofthe Creation, and should have no exact notion of the immense reality. To-day, thanks to the intellectual labor of so many centuries, thanksalso to the immortal genius of the men of science who have devoted theirlives to searching after Truth--men such as Copernicus, Galileo, Kepler, Newton--the veil of ignorance has been rent, and glimpses of the marvelsof creation are perceptible in their splendid truth to the dazzled eyeof the thinker. The study of Astronomy is not, as many suppose, the sacrifice of oneselfin a cerebral torture that obliterates all the beauty, the fascination, and the grandeur of the pageant of Nature. Figures, and naught butfigures, would not be entertaining, even to those most desirous ofinstruction. Let the reader take courage! We do not propose that heshall decipher the hieroglyphics of algebra and geometry. Perish thethought! For the rest, figures are but the scaffolding, the method, anddo not exist in Nature. [Illustration: FIG. 1. --The great Book of the Heavens is open to alleyes. ] We simply beg of you to open your eyes, to see where you are, so thatyou may not stray from the path of truth, which is also the path ofhappiness. Once you have entered upon it, no persuasion will be neededto make you persevere. And you will have the profound satisfaction ofknowing that you are thinking correctly, and that it is infinitelybetter to be educated than to be ignorant. The reality is far beyond alldreams, beyond the most fantastic imagination. The most fairy-liketransformations of our theaters, the most resplendent pageants of ourmilitary reviews, the most sumptuous marvels on which the human race canpride itself--all that we admire, all that we envy on the Earth--is asnothing compared with the unheard-of wonders scattered throughInfinitude. There are so many that one does not know how to see them. The fascinated eye would fain grasp all at once. If you will yield yourselves to the pleasure of gazing upon thesparkling fires of Space, you will never regret the moments passed alltoo rapidly in the contemplation of the Heavens. Diamonds, turquoises, rubies, emeralds, all the precious stones withwhich women love to deck themselves, are to be found in greaterperfection, more beautiful, and more splendid, set in the immensity ofHeaven! In the telescopic field, we may watch the progress of armies ofmajestic and powerful suns, from whose attacks there is naught to fear. And these vagabond comets and shooting stars and stellar nebulæ, do theynot make up a prodigious panorama? What are our romances in comparisonwith the History of Nature? Soaring toward the Infinite, we purify oursouls from all the baseness of this world, we strive to become betterand more intelligent. * * * * * But in the first place, you ask, what are the Heavens? This vaultoppresses us. We can not venture to investigate it. Heaven, we reply, is no vault, it is a limitless immensity, inconceivable, unfathomable, that surrounds us on all sides, and in themidst of which our globe is floating. THE HEAVENS ARE ALL THAT EXISTS, all that we see, and all that we do not see: the Earth on which we are, that bears us onward in her rapid flight; the Moon that accompanies us, and sheds her soft beams upon our silent nights; the good Sun to whichwe owe our existence; the Stars, suns of Infinitude; in a word--thewhole of Creation. Yes, our Earth is an orb of the Heavens: the sky is her domain, and ourSun, shining above our heads, and fertilizing our seasons, is as much astar as the pretty sparkling points that scintillate up there, in thefar distance, and embellish the calm of our nights with theirbrilliancy. All are in the Heavens, you as well as I, for the Earth, inher course through Space, bears us with herself into the depths ofInfinitude. In the Heavens there is neither "above" nor "below. " These words do notexist in celestial speech, because their significance is relative to thesurface of this planet only. In reality, for the inhabitants of theEarth, "low" is the inside, the center of the globe, and "high" is whatis above our heads, all round the Earth. The Heavens are what surroundus on all sides, to Infinity. The Earth is, like her fellows, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, one of the planets of the great solar family. The Sun, her father, protects her, and directs all her actions. She, asthe grateful daughter, obeys him blindly. All float in perfect harmonyover the celestial ocean. But, you may say, on what does the Earth rest in her etherealnavigation? On nothing. The Earth turns round the colossal Sun, a little globe ofrelatively light weight, isolated on all sides in Space, like asoap-bubble blown by some careless child. Above, below, on all sides, millions of similar globes are grouped intofamilies, and form other systems of worlds revolving round the numerousand distant stars that people Infinitude; suns more or less analogous tothat by which we are illuminated, and generally speaking of larger bulk, although our Sun is a million times larger than our planet. Among the ancients, before the isolation of our globe in Space and themotions that incessantly alter its position were recognized, the Earthwas supposed to be the immobile lower half of the Universe. The sky wasregarded as the upper half. The ancients supplied our world withfantastic supports that penetrated to the Infernal Regions. They couldnot admit the notion of the Earth's isolation, because they had a falseidea of its weight. To-day, however, we know positively that the Earthis based on nothing. The innumerable journeys accomplished round it inall directions give definite proof of this. It is attached to nothing. As we said before, there is neither "above" nor "below" in the Universe. What we call "below" is the center of the Earth. For the rest the Earthturns upon its own axis in twenty-four hours. Night is only a partialphenomenon, due to the rotary motion of the planet, a motion that couldnot exist under conditions other than that of the absolute isolation ofour globe in space. [Illustration: FIG. 2. --The earth in space. June solstice, midday. ] Since the Sun can only illuminate one side of our globe at one moment, that is to say one hemisphere, it follows that Night is nothing but thestate of the part that is not illuminated. As the Earth revolves uponitself, all the parts successively exposed to the Sun are in the day, while the parts situated opposite to the Sun, in the cone of shadowproduced by the Earth itself, are in night. But whether it be noon ormidnight, the stars always occupy the same position in the Heavens, even when, dazzled by the ardent light of the orb of day, we can nolonger see them; and when we are plunged into the darkness of the night, the god Phoebus still continues to pour his beneficent rays upon thecountries turned toward him. The sequence of day and night is a phenomenon belonging, properlyspeaking, to the Earth, in which the rest of the Universe does notparticipate. The same occurs for every world that is illuminated by asun, and endowed with a rotary movement. In absolute space, there is nosuccession of nights and days. Upheld in space by forces that will be explained at a later point, ourplanet glides in the open heavens round our Sun. Imagine a magnificent aerostat, lightly and rapidly cleaving space. Surround it with eight little balloons of different sizes, the smallestlike those sold on the streets for children to play with, the larger, such as are distributed for a bonus in large stores. Imagine this groupsailing through the air, and you have the system of our worlds inminiature. Still, this is only an image, a comparison. The balloons are held up bythe atmosphere, in which they float at equilibrium. The Earth issustained by nothing material. What maintains her in equilibrium is theethereal void; an immaterial force; gravitation. The Sun attracts her, and if she did not revolve, she would drop into him; but rotating roundhim, at a speed of 107, 000 kilometers[2] (about 66, 000 miles) per hour, she produces a centrifugal force, like that of a stone in a sling, thatis precisely equivalent, and of contrary sign, to its gravitation towardthe central orb, and these two equilibrated forces keep her at the samemedium distance. This solar and planetary group does not exist solitary in the immensevoid that extends indefinitely around us. As we said above, each starthat we admire in the depths of the sky, and to which we lift up oureyes and thoughts during the charmed hours of the night, is another sunburning with its own light, the chief of a more or less numerous family, such as are multiplied through all space to infinity. Notwithstandingthe immense distances between the sun-stars, Space is so vast, and thenumber of these so great, that by an effect of perspective due solely tothe distance, appearances would lead us to believe that the stars weretouching. And under certain telescopic aspects, and in some of theastral photographs, they really do appear to be contiguous. The Universe is infinite. Space is limitless. If our love for theHeavens should incite in us the impulse, and provide us with the meansof undertaking a journey directed to the ends of Heaven as its goal, weshould be astonished, on arriving at the confines of the Milky Way, tosee the grandiose and phenomenal spectacle of a new Universe unfoldbefore our dazzled eyes; and if in our mad career we crossed this newarchipelago of worlds to seek the barriers of Heaven beyond them, weshould still find universe eternally succeeding to universe before us. Millions of suns roll on in the immensities of Space. Everywhere, on allsides, Creation renews itself in an infinite variety. According to all the probabilities, universal life is distributed thereas well as here, and has sown the germ of intelligence upon thosedistant worlds that we divine in the vicinity of the innumerable sunsthat plow the ether, for everything upon the Earth tends to show thatLife is the goal of Nature. Burning foci, inextinguishable sources ofwarmth and light, these various, multi-colored suns shed their rays uponthe worlds that belong to them and which they fertilize. Our globe is no exception in the Universe. As we have seen, it is one ofthe celestial orbs, nourished, warmed, lighted, quickened by the Sun, which in its turn again is but a star. Innumerable Worlds! We dream of them. Who can say that their unknowninhabitants do not think of us in their turn, and that Space may not betraversed by waves of thought, as it is by the vibrations of light anduniversal gravitation? May not an immense solidarity, hardly guessed atby our imperfect senses, exist between the Celestial Humanities, ourEarth being only a modest planet. Let us meditate on this Infinity! Let us lose no opportunity ofemploying the best of our hours, those of the silence and peace of thebewitching nights, in contemplating, admiring, spelling out the words ofthe Great Book of the Heavens. Let our freed souls fly swift and rapttoward those marvelous countries where indescribable joys are preparedfor us, and let us do homage to the first and most splendid of thesciences, to Astronomy, which diffuses the light of Truth within us. To poetical souls, the contemplation of the Heavens carries thought awayto higher regions than it attains in any other meditation. Who does notremember the beautiful lines of Victor Hugo in the Orientales? Who hasnot heard or read them? The poem is called "Ecstasy, " and it is afitting title. The words are sometimes set to music, and the melodyseems to complete their pure beauty: J'étais seul près des flots par une nuit d'étoiles. Pas un nuage aux cieux, sur les mers pas de voiles; Mes yeux plongeaient plus loin que le monde réel, Et les bois et les monts et toute la nature Semblaient interroger, dans un confus murmure, Les flots des mers, les feux du ciel. Et les étoiles d'or, légions infinies, A voix haute, à voix basse, avec mille harmonies Disaient, en inclinant leurs couronnes de feu; Et les flots bleus, que rien ne gouverne et n'arrête, Disaient en recourbant l'écume de leur crête: . . . C'est le Seigneur, le Seigneur Dieu! _Note: Free Translation_ I was alone on the waves, on a starry night, Not a cloud in the sky, not a sail in sight, My eyes pierced beyond the natural world. . . And the woods, and the hills, and the voice of Nature Seemed to question in a confused murmur, The waves of the Sea, and Heaven's fires. And the golden stars in infinite legion, Sang loudly, and softly, in glad recognition, Inclining their crowns of fire;. . . And the waves that naught can check nor arrest Sang, bowing the foam of their haughty crest. . . Behold the Lord God--Jehovah! The immortal poet of France was an astronomer. The author more thanonce had the honor of conversing with him on the problems of the starrysky--and reflected that astronomers might well be poets. It is indeed difficult to resist a sense of profound emotion before theabysses of infinite Space, when we behold the innumerable multitude ofworlds suspended above our heads. We feel in this solitary contemplationof the Heavens that there is more in the Universe than tangible andvisible matter: that there are forces, laws, destinies. Our ants' brainsmay know themselves microscopic, and yet recognize that there issomething greater than the Earth, the Heavens;--more absolute than theVisible, the Invisible;--beyond the more or less vulgar affairs of life, the sense of the True, the Good, the Beautiful. We feel that an immensemystery broods over Nature, --over Being, over created things. And it ishere again that Astronomy surpasses all the other sciences, that itbecomes our sovereign teacher, that it is the _pharos_ of modernphilosophy. O Night, mysterious, sublime, and infinite! withdrawing from our eyesthe veil spread above us by the light of day, giving back transparencyto the Heavens, showing us the prodigious reality, the shining casket ofthe celestial diamonds, the innumerable stars that succeed each otherinterminably in immeasurable space! Without Night we should knownothing. Without it our eyes would never have divined the siderealpopulation, our intellects would never have pierced the harmony of theHeavens, and we should have remained the blind, deaf parasites of aworld isolated from the rest of the universe. O Sacred Night! If on theone hand it rests upon the heights of Truth beyond the day's illusions, on the other its invisible urns pour down a silent and tranquil peace, apenetrating calm, upon our souls that weary of Life's fever. It makes usforget the struggles, perfidies, intrigues, the miseries of the hours oftoil and noisy activity, all the conventionalities of civilization. Itsdomain is that of rest and dreams. We love it for its peace and calmtranquillity. We love it because it is true. We love it because itplaces us in communication with the other worlds, because it gives usthe presage of Life, Universal and Eternal, because it brings us Hope, because it proclaims us citizens of Heaven. CHAPTER II THE CONSTELLATIONS In Chapter I we saw the Earth hanging in space, like a globe isolated onall sides, and surrounded at vast distances by a multitude of stars. These fiery orbs are suns like that which illuminates ourselves. Theyshine by their own light. We know this for a fact, because they are sofar off that they could neither be illuminated by the Sun, nor, stillmore, reflect his rays back upon us: and because, on the other hand, wehave been able to measure and analyze their light. Many of these distantsuns are simple and isolated; others are double, triple, or multiple;others appear to be the centers of systems analogous to that whichgravitates round our own Sun, and of which we form part. But thesecelestial tribes are situated at such remote distances from us that itis impossible to distinguish all the individuals of each particularfamily. The most delicate observations have only revealed a few of them. We must content ourselves here with admiring the principals, --thesun-stars, --prodigious globes, flaming torches, scattered profuselythrough the firmament. How, then, is one to distinguish them? How can they be readily found andnamed? There are so many of them! Do not fear; it is quite a simple matter. In studying the surface of theEarth we make use of geographical maps on which the continents and seasof which it consists are drawn with the utmost care. Each country of ourplanet is subdivided into states, each of which has its proper name. Weshall pursue the same plan in regard to the Heavens, and it will be allthe easier since the Great Book of the Firmament is constantly open toour gaze. Our globe, moreover, actually revolves upon itself so that weread the whole in due sequence. Given a clear atmosphere, and a littlestimulus to the will from our love of truth and science, and thegeography of the Heavens, or "uranography, " will soon be as familiar tous as the geography of our terrestrial atom. On a beautiful summer's night, when we look toward the starry sky, weare at first aware only of a number of shining specks. The stars seem tobe scattered almost accidentally through Space; they are so numerous andso close to one another that it would appear rash to attempt to namethem separately. Yet some of the brighter ones particularly attract andexcite our attention. After a little observation we notice a certainregularity in the arrangement of these distant suns, and take pleasurein drawing imaginary figures round the celestial groups. That is what the ancients did from a practical point of view. In orderto guide themselves across the trackless ocean, the earliest Pheniciannavigators noted certain fixed bearings in the sky, by which they mappedout their routes. In this way they discovered the position of theimmovable Pole, and acquired empire over the sea. The Chaldean pastors, too, the nomad people of the East, invoked the Heavens to assist intheir migrations. They grouped the more brilliant of the stars intoConstellations with simple outlines, and gave to each of these celestialprovinces a name derived from mythology, history, or from the naturalkingdoms. It is impossible to determine the exact epoch of thisprimitive celestial geography. The Centaur Chiron, Jason's tutor, wasreputed the first to divide the Heavens upon the sphere of theArgonauts. But this origin is a little mythical! In the Bible we havethe Prophet Job, who names Orion, the Pleiades, and the Hyades, 3, 300years ago. The Babylonian Tables, and the hieroglyphs of Egypt, witnessto an astronomy that had made considerable advance even in those remoteepochs. Our actual constellations, which are doubtless of Babylonianorigin, appear to have been arranged in their present form by thelearned philosopher Eudoxus of Cnidus, about the year 360 B. C. Aratussang of them in a didactic poem toward 270. Hipparchus of Rhodes was thefirst to note the astronomical positions with any precision, one hundredand thirty years before our era. He classified the stars in order ofmagnitude, according to their apparent brightness; and his catalogue, preserved in the Almagest of Ptolemy, contains 1, 122 stars distributedinto forty-eight Constellations. The figures of the constellations, taken almost entirely from fable, arevisible only to the eyes of the imagination, and where the ancientsplaced such and such a person or animal, we may see, with a littlegood-will, anything we choose to fancy. There is nothing real aboutthese figures. And yet it is indispensable to be able to recognize theconstellations in order to find our way among the innumerable army ofthe stars, and we shall commence this study with the description of themost popular and best known of them all, the one that circles everynight through our Northern Heavens. Needless to name it; it is familiarto every one. You have already exclaimed--the Great Bear! This vast and splendid association of suns, which is also known as theChariot of David, the Plow or Charles's Wain, and the Dipper, is one ofthe finest constellations in the Heavens, and one of the oldest--seeingthat the Chinese hailed it as the divinity of the North, over threethousand years ago. If any of my readers should happen to forget its position in the sky, the following is a very simple expedient for finding it. Turn to theNorth--that is, opposite to the point where the sun is to be found atmidday. Whatever the season of the year, day of the month, or hour ofthe night, you will always see, high up in the firmament, sevenmagnificent stars, arranged in a quadrilateral, followed by a tail, orhandle, of three stars. This magnificent constellation never sinks belowour horizon. Night and day it watches above us, turning in twenty-fourhours round a very famous star that we shall shortly become acquaintedwith. In the figure of the Great Bear, the four stars of thequadrilateral are found in the body, and the three at the extremity makethe tail. As David's Chariot, the four stars represent the wheels, andthe three others the horses. Sometimes our ancestors called them the Seven Oxen, the "oxen of thecelestial pastures, " from which the word septentrion (_septem triones_, seven oxen of labor) is derived. Some see a Plowshare; others morefamiliarly call this figure the Dipper. As it rotates round the pole, its outline varies with the different positions. It is not easy to guess why this constellation should have been calledthe Bear. Yet the name has had a certain influence. From the Greek word_arctos_ (bear) has come arctic, and for its antithesis, antarctic. Fromthe Latin word _trio_ (ox of labor) has come septentrion, the sevenoxen. Etymology is not always logical. Is not the word "venerate"derived from Venus? In order to distinguish one star from another, the convention ofdenoting them by the letters of the Greek Alphabet has been adopted, forit would be impossible to give a name to each, so considerable is theirnumber. [3] [alpha] and [beta] denote the front wheels of the Chariot generallyknown as the "pointers;" [gamma] and [delta] the hind wheels; [epsilon], [zeta], [eta] the three horses. All these stars are of the second orderof magnitude (the specific meaning of this expression will be explainedin the next chapter), except the last ([delta]) of the quadrilateral, which is of the third order. [Illustration: FIG. 3. --The Great Bear (or Dipper), and the Pole-Star. ] Figure 3 gives the outline of this primitive constellation. In revolvingin twenty-four hours round the Pole, which is situated at theprolongation of a line drawn from [beta] to [alpha], it occupies everyconceivable position, --as if this page were turned in all directions. But the relative arrangement of the seven stars remains unaltered. Incontemplating these seven stars it must never be forgotten that each isa dazzling sun, a center of force and life. One of them is especiallyremarkable: [zeta], known as Mizar to the Arabs. Those who have goodsight will distinguish near it a minute star, Alcor, or the Cavalier, also called Saidak by the Arabs--that is, the Test, because it can beused as a test of vision. But further, if you have a small telescope atyour disposal, direct it upon the fine star Mizar: you will beastonished at discovering two of the finest diamonds you could wish tosee, with which no brilliant is comparable. There are several doublestars; these we shall become acquainted with later on. Meantime, we must not forget our celestial geography. The Great Bearwill help us to find all the adjacent constellations. [Illustration: FIG. 4. --To find the Pole-Star. ] If a straight line is drawn (Fig. 4) from [beta] through [alpha], whichforms the extremity of the square, and is prolonged by a quantity equalto the distance of [alpha] from the tip of the handle, we come on a starof second magnitude, which marks the extremity of a figure perfectlycomparable with the Great Bear, but smaller, less brilliant, andpointing in the contrary direction. This is the Little Bear, composed, like its big brother, of seven stars; the one situated at the end of theline by which we have found it is the Pole-Star. Immovable in the region of the North Pole, the Pole-Star has captivatedall eyes by its position in the firmament. It is the providence ofmariners who have gone astray on the ocean, for it points them to theNorth, while it is the pivot of the immense rotation accomplished roundit by all the stars in twenty-four hours. Hence it is a very importantfactor, and we must hasten to find it, and render it due homage. Itshould be added that its special immobility, in the prolongation of theEarth's axis, is merely an effect caused by the diurnal movements of ourplanet. Our readers are of course aware that it is the earth that turnsand not the sky. But evidence of this will be given later on. In lookingat the Pole-Star, the South is behind one, the East to the right, andthe West to the left. Between the Great and the Little Bear, we can distinguish a windingprocession of smaller stars. These constitute the Dragon. We will continue our journey by way of Cassiopeia, a fine constellationplaced on the opposite side of the Pole-Star in relation to the GreatBear, and shaped somewhat like the open limbs of the letter W. It isalso called the Chair. And, in fact, when the figure is represented withthe line [alpha] [beta] below, the line [chi] [gamma] forms the seat, and [gamma] [delta] [epsilon] its back. If a straight line is drawn from [delta] of the Great Bear, andprolonged beyond the Pole-Star in a quantity equal to the distance whichseparates these two stars, it is easy to find this constellation (Fig. 5). This group, like the preceding, never sets, and is always visible, opposite to the Great Bear. It revolves in twenty-four hours round thePole-Star, and is to be seen, now above, now below, now to the right, now to the left. [Illustration: FIG. 5. --To find Cassiopeia. ] [Illustration: FIG. 6. --To Find Pegasus and Andromeda. ] If in the next place, starting from the stars [alpha] and [delta] in theGreat Bear, we draw two lines which join at Polaris and are prolongedbeyond Cassiopeia, we arrive at the Square of Pegasus (Fig. 6), a vastconstellation that terminates on one side in a prolongation formed ofthree stars. These three last stars belong to Andromeda, and themselves abut onPerseus. The last star in the Square of Pegasus is also the first inAndromeda. [gamma] of Andromeda is a magnificent double orb, to which we shallreturn in the next chapter, _i. E. _, the telescope resolves it into twomarvelous suns, one of which is topaz-yellow, and the otheremerald-green. Three stars, indeed, are visible with more powerfulinstruments. [Illustration: FIG. 7. --Perseus, the Pleiades, Capella. ] Above [beta] and near a small star, is visible a faint, whitish, luminous trail: this is the oblong nebula of Andromeda, the firstmentioned in the history of astronomy, and one of the most beautiful inthe Heavens, perceptible to the unaided eye on very clear nights. The stars [alpha], [beta] and [gamma] of Perseus form a concave bowwhich will serve in a new orientation. If it is prolonged in thedirection of [delta], we find a very brilliant star of the firstmagnitude. This is Capella, the Goat, in the constellation of theCharioteer (Fig. 7). If coming back to [delta] in Perseus, a line is drawn toward the South, we reach the Pleiades, a gorgeous cluster of stars, scintillating likethe finest dust of diamonds, on the shoulder of the Bull, to which weshall come shortly, in studying the Constellations of the Zodiac. Not far off is a very curious star, [beta] of Perseus, or Algol, whichforms a little triangle with two others smaller than itself. This staris peculiar in that, instead of shining with a fixed light, it varies inintensity, and is sometimes pale, sometimes brilliant. It belongs to thecategory of variable stars which we shall study later on. All theobservations made on it for more than two hundred years go to prove thata dark star revolves round this sun, almost in the plane of our line ofsight, producing as it passes in front of it a partial eclipse thatreduces it from the second to the fourth magnitude, every other twodays, twenty hours, and forty-nine minutes. And now, let us return to the Great Bear, which aided us so beneficentlyto start for these distant shores, and whence we shall set out afresh insearch of other constellations. If we produce the curved line of the tail, or handle, we encounter amagnificent golden-yellow star, a splendid sun of dazzling brilliancy:let us make our bow to Arcturus, [alpha] of the Herdsman, which is atthe extremity of this pentagonal constellation. The principal stars ofthis asterism are of the third magnitude, with the exception of [alpha], which is of the first. Alongside of the Herdsman is a circle consistingof five stars of the third and fourth magnitude, save the third, [alpha], or the Pearl, which is of the second magnitude. This is theCorona Borealis. It is very easily recognized (Fig. 8). [Illustration: FIG. 8. --To find Arcturus, the Herdsman, and the NorthernCrown. ] A line drawn from the Pole-Star to Arcturus forms the base of anequilateral triangle, the apex of which, situated opposite the GreatBear, is occupied by Vega, or [alpha] of the Lyre, a splendid diamond ofideal purity scintillating through the ether. This magnificent star, offirst magnitude, is, with Arcturus, the most luminous in our Heavens. Itburns with a white light, in the proximity of the Milky Way, not farfrom a constellation that is very easily recognized by the arrangementof its principal stars in the form of a cross. It is named Cygnus, theBird, or the Swan (Fig. 9), and is easy to find by the Square ofPegasus, and the Milky Way. This figure, the brilliancy of whoseconstituents (of the third and fourth magnitudes) contrasts stronglywith the pallor of the Milky Way, includes at its extremity at the footof the Cross, a superb double star, [beta] or Albirio: [alpha] of Cygnusis also called Deneb. The first star of which the distance wascalculated is in this constellation. This little orb of fifth magnitude, which hangs 69, 000, 000, 000, 000 kilometers (42, 000, 000, 000, 000 miles)above our Earth, is the nearest of all the stars to the skies of Europe. [Illustration: FIG. 9. --The Swan, Vega, the Eagle. ] Not far off is the fine Eagle, which spreads its wings in the Milky Way, and in which the star Altaïr, [alpha], of first magnitude, is situatedbetween its two satellites, [beta] and [gamma]. The Constellation of Hercules, toward which the motions of the Sun areimpelling us, with all the planets of its system, is near the Lyre. Itsprincipal stars can be recognized inside the triangle formed by thePole-Star, Arcturus, and Vega. All the Constellations described above belong to the NorthernHemisphere. Those nearest the pole are called circumpolar. They revolveround the pole in twenty-four hours. Having now learned the Northern Heavens, we must come back to the Sun, which we have left behind us. The Earth revolves round him in a year, and in consequence he seems to revolve round us, sweeping through a vastcircle of the celestial sphere. In each year, at the same period, hepasses the same points of the Heavens, in front of the sameconstellations, which are rendered invisible by his light. We know thatthe stars are at a fixed position from the Earth, whatever theirdistance, and that if we do not see them at noon as at midnight, it issimply because they are extinguished by the dazzling light of the orb ofday. With the aid of a telescope it is always possible to see the morebrilliant of them. The Zodiac is the zone of stars traversed by the Sun in the course of ayear. This word is derived from the Greek _Zodiakos_, which signifies"animal, " and this etymology arose because most of the figures tracedon this belt of stars represent animals. The belt is divided into twelveparts that are called the twelve Signs of the Zodiac, also named by theancients the "Houses of the Sun, " since the Sun visits one of them ineach month. These are the signs, with the primitive characters thatdistinguish them: the Ram [Aries], the Bull [Taurus], the Twins[Gemini], the Crab [Cancer], the Lion [Leo], the Virgin [Virgo], theBalance [Libra], the Scorpion [Scorpio], the Archer [Sagittarius], theGoat [Capricorn], the Water-Carrier [Aquarius], the Fishes [Pisces]. Thesign [Aries] represents the horns of the Ram, [Taurus] the head of theBull, and so on. If you will now follow me into the Houses of the Sun you will readilyrecognize them again, provided you have a clear picture of the principalstars of the Northern Heavens. First, you see the Ram, the initial signof the Zodiac; because at the epoch at which the actual Zodiac wasfixed, the Sun entered this sign at the vernal equinox, and the equatorcrossed the ecliptic at this point. This constellation, in which thehorns of the Ram (third magnitude) are the brightest, is situatedbetween Andromeda and the Pleiades. Two thousand years ago, the Ram wasregarded as the symbol of spring; but owing to the secular movement ofthe precession of the equinoxes, the Sun is no longer there on March 21:he is in the Fishes. To the left, or east of the Ram, we find the Bull, the head of whichforms a triangle in which burns Aldebaran, of first magnitude, amagnificent red star that marks the right eye; and the Hyades, scintillating pale and trembling, on its forehead. The timid Pleiades, as we have seen, veil themselves on the shoulder of the Bull--acaptivating cluster, of which six stars can be counted with the unaidedeye, while several hundred are discovered with the telescope. Next the Twins. They are easily recognized by the two fine stars, [alpha] and [beta], of first magnitude, which mark their heads, andimmortalize Castor and Pollux, the sons of Jupiter, celebrated for theirindissoluble friendship. Cancer, the Crab, is the least important sign of the Zodiac. It isdistinguished only by five stars of fourth and fifth magnitudes, situated below the line of Castor and Pollux, and by a pale clustercalled Præsepe, the Beehive. The Lion next approaches, superb in his majesty. At his heart is agorgeous star of first magnitude, [alpha] or Regulus. This figure formsa grand trapezium of four stars on the celestial sphere. The Virgin exhibits a splendid star of first magnitude; this is Spica, which with Regulus and Arcturus, form a triangle by which thisconstellation can be recognized. The Balance follows the Virgin. Its scales, marked by two stars ofsecond magnitude, are situated a little to the East of Spica. We next come to the eighth constellation of the Zodiac, which is one ofthe most beautiful of this belt of stars. Antares, a red star of firstmagnitude, occupies the heart of the venomous and accursed Scorpion. Itis situated on the prolongation of a line joining Regulus to Spica, andforms with Vega of the Lyre, and Arcturus of the Herdsman, a greatisosceles triangle, of which this latter star is the apex. The Scorpion, held to be a sign of ill luck, has been prejudicial to theArcher, which follows it, and traces an oblique trapezium in the sky, alittle to the east of Antares. These two southernmost constellationsnever rise much above the horizon for France and England. In fable, theArcher is Chiron, the preceptor of Jason, Achilles and Æsculapius. Capricorn lies to the south of Altaïr, on the prolongation of a linefrom the Lyre to the Eagle. It is hardly noticeable save for the stars[alpha] and [beta] of third magnitude, which scintillate on itsforehead. The Water-Carrier pours his streams toward the horizon. He is not richin stars, exhibiting only three of third magnitude that form a veryflattened triangle. Lastly the Fishes, concluding sign of the Zodiac, are found to thesouth of Andromeda and Pegasus. Save for [alpha], of third magnitude, this constellation consists of small stars that are hardly visible. These twelve zodiacal constellations will be recognized on examining thechart (Figs. 10-11). We must now visit the stars of the Southern Heavens, some of which areequally deserving of admiration. [Illustration: FIG. 10. --The Constellations of the Zodiac: summer andautumn; Capricorn, Archer, Scorpion, Balance, Virgin, Lion. ] It should in the first place be noted that the signs of the Zodiac andthe Southern Constellations are not, like those which are circumpolar, perpetually visible at all periods of the year. Their visibility dependson the time of year and the hour of the night. [4] In order to admire the fine constellations of the North, as describedabove, we have only to open our windows on a clear summer's evening, orwalk round the garden in the mysterious light of these inaccessiblesuns, while we look up at the immense fields in which each star is likethe head of a celestial spear. But the summer is over, autumn is upon us, and then, too soon, comeswinter clothed in hoar-frost. The days are short and cold, dark anddreary; but as a compensation the night is much longer, and adornsherself with her most beautiful jewels, offering us the contemplation ofher inexhaustible treasures. [Illustration: FIG. 11. --The Constellations of the Zodiac: winter andspring; Crab, Twins, Bull, Ram, Fishes, Water-Carrier. ] First, let us do homage to the magnificent Orion, most splendid of allthe constellations: he advances like a colossal giant, and confronts theBull. This constellation appears about midnight in November, in thesouth-eastern Heavens; toward eleven o'clock in December and January, due south; about ten in February, in the south-east; about nine inMarch, and about eight in April, in the west; and then sets below ourhorizon. [Illustration: FIG. 12. --Orion and his celestial companions. ] It is indisputably the most striking figure in the sky, and with theGreat Bear, the most ancient in history, the first that was noticed:both are referred to in the ancient texts of China, Chaldea, and Egypt. Eight principal stars delineate its outline; two are of the firstmagnitude, five of the second, and one of the third (Fig. 12). The mostbrilliant are Betelgeuse ([alpha]) and Rigel ([beta]): the formermarking the right shoulder of the Colossus as it faces us; the secondthe left foot. The star on the left shoulder is [gamma] or Bellatrix, ofsecond magnitude; that of the right foot, [chi], is almost of the third. Three stars of second magnitude placed obliquely at equal distances fromeach other, the first or highest of which marks the position of theequatorial line, indicate the Belt or Girdle. These stars, known as theThree Kings, and by country people as the Rake, assist greatly in therecognition of this fine constellation. A little below the second star of the Belt, a large white patch, like aband of fog, the apparent dimensions of which are equal to that of thelunar disk, is visible to the unaided eye: this is the Nebula of Orion, one of the most magnificent in the entire Heavens. It was discovered in1656 by Huyghens, who counted twelve stars in the pale cloud. Since thatdate it has been constantly studied and photographed by its manyadmirers, while the giant eye of the telescope discovers in it to-day aninnumerable multitude of little stars which reveal the existence of anentire universe in this region. Orion is not merely the most imposing of the celestial figures; it isalso the richest in sidereal wonders. Among these, it exhibits the mostcomplex of all the multiple systems known to us: that of the star[theta] situated in the celebrated nebula just mentioned. This marvelousstar, viewed through a powerful telescope, breaks up into six suns, forming a most remarkable stellar group. This region is altogether one of the most brilliant in the entirefirmament. We must no longer postpone our homage to the brightest starin the sky, the magnificent Sirius, which shines on the left belowOrion: it returns every year toward the end of November. This marvelousstar, of dazzling brilliancy, is the first, [alpha], in theconstellation of the Great Dog, which forms a quadrilateral, the base ofwhich is adjacent to a triangle erected from the horizon. When astronomers first endeavored to determine the distance of thestars, Sirius, which attracted all eyes to its burning fires, was theparticular object of attention. After long observation, they succeededin determining its distance as 92 trillion kilometers (57 trillionmiles). Light, that radiates through space at a velocity of 300, 000kilometers (186, 000 miles) per second, takes no less than ten years toreach us from this sun, which, nevertheless, is one of our neighbors. The Little Dog, in which Procyon ([alpha], of first magnitude) shinesout, is above its big brother. With the exception of [alpha], it has nobright stars. [Illustration: FIG. 13. --Winter Constellations. ] Lastly, toward the southern horizon, we must notice the Hydra, Eridanus, the Whale, the Southern Fish, the Ship, and the Centaur. This lastconstellation, while invisible to our latitudes, contains the star thatis nearest to the Earth, [alpha], of first magnitude, the distance ofwhich is 40 trillion kilometers (25 trillion miles). [Illustration: FIG. 14. --Spring Constellations. ] The feet of the Centaur touch the Southern Cross, which is alwaysinvisible to us, and a little farther down the Southern Pole reignsover the icy desert of the antarctic regions. [Illustration: FIG. 15. --Summer Constellations. ] [Illustration: FIG. 16. --Autumn Constellations. ] In order to complete the preceding descriptions, we subjoin four chartsrepresenting the aspect of the starry heavens during the evenings ofwinter, spring, summer, and autumn. To make use of these, we mustsuppose them to be placed above our heads, the center marking thezenith, and the sky descending all round to the horizon. The horizon, therefore, bounds these panoramas. Turning the chart in any direction, and looking at it from north, south, east, or west, we find all theprincipal stars. The first map (Fig. 13) represents the sky in winter(January) at 8 P. M. ; the second, in spring (April) at 9 P. M. ; the third, in summer (July) at the same hour; the fourth, the sky in autumn(October) at the same time. And so, at little cost, we have made one of the grandest and mostbeautiful journeys conceivable. We now have a new country, or, better, have learned to see and know our own country, for since the Earth is aplanet we must all be citizens of the Heavens before we can belong tosuch or such a nation of our lilliputian world. We must now study this sublime spectacle of the Heavens in detail. CHAPTER III THE STARS, SUNS OF THE INFINITE A JOURNEY THROUGH SPACE We have seen from the foregoing summary of the principal Constellationsthat there is great diversity in the brightness of the stars, and thatwhile our eyes are dazzled with the brilliancy of certain orbs, others, on the contrary, sparkle modestly in the azure depths of the night, andare hardly perceptible to the eye that seeks to plumb the abysses ofImmensity. We have appended the word "magnitude" to the names of certain stars, andthe reader might imagine this to bear some relation to the volume of theorb. But this is not the case. To facilitate the observation of stars of varying brilliancy, they havebeen classified in order of magnitude, according to their apparentbrightness, and since the dimensions of these distant suns are almostwholly unknown to us, the most luminous stars were naturally denoted asof first magnitude, those which were a little less bright of the second, and so on. But in reality this word "magnitude" is quite erroneous, forit bears no relation to the mass of the stars, divided thus at an epochwhen it was supposed that the most brilliant must be the largest. Itsimply indicates the apparent brightness of a star, the real brilliancydepending on its dimensions, its intrinsic light, and its distance fromour planet. And now to make some comparison between the different orders. Throughoutthe entire firmament, only nineteen stars of first magnitude arediscoverable. And, strictly speaking, the last of this series might justas well be noted of "second magnitude, " while the first of the secondseries might be added to the list of stars of the "first order. " But inorder to form classes distinct from one another, some limit has to beadopted, and it was determined that the first series should include onlythe following stars, the most luminous in the Heavens, which aresubjoined in order of decreasing brilliancy. STARS OF THE FIRST MAGNITUDE 1. Sirius, or [alpha] of the Great Dog. 2. Canopus, or [alpha] of the Ship. 3. Capella, or [alpha] of the Charioteer. 4. Arcturus, or [alpha] of the Herdsman. 5. Vega, or [alpha] of the Lyre. 6. Proxima, or [alpha] of the Centaur. 7. Rigel, or [beta] of Orion. 8. Achernar, or [alpha] of Eridanus. 9. Procyon, or [alpha] of the Little Dog. 10. [beta] of the Centaur. 11. Betelgeuse, or [alpha] of Orion. 12. Altaïr, or [alpha] of the Eagle. 13. [alpha] of the Southern Cross. 14. Aldebaran, or [alpha] of the Bull. 15. Spica, or [alpha] of the Virgin. 16. Antares, or [alpha] of the Scorpion. 17. Pollux, or [beta] of the Twins. 18. Regulus, or [alpha] of the Lion. 19. Fomalhaut, or [alpha] of the Southern Fish. THE STARS OF THE SECOND MAGNITUDE Then come the stars of the second magnitude, of which there arefifty-nine. The stars of the Great Bear (with the exception of [delta], which is of third magnitude), the Pole-Star, the chief stars in Orion(after Rigel and Betelgeuse), of the Lion, of Pegasus, of Andromeda, ofCassiopeia, are of this order. These, with the former, constitute theprincipal outlines of the constellations visible to us. Then follow the third and fourth magnitudes, and so on. * * * * * The following table gives a summary of the series, down to the sixthmagnitude, which is the limit of visibility for the unaided human eye: 19 stars of first magnitude. 59 of second magnitude. 182 of third magnitude. 530 of fourth magnitude. 1, 600 of fifth magnitude. 4, 800 of sixth magnitude. This makes a total of some seven thousand stars visible to the unaidedeye. It will be seen that each series is, roughly speaking, three timesas populated as that preceding it; consequently, if we multiply thenumber of any class by three, we obtain the approximate number of starsthat make up the class succeeding it. Seven thousand stars! It is an imposing figure, when one reflects thatall these lucid points are suns, as enormous as they are potent, asincandescent as our own (which exceeds the volume of the Earth by morethan a million times), distant centers of light and heat, exerting theirattraction on unknown systems. And yet it is generally imagined thatmillions of stars are visible in the firmament. This is an illusion;even the best vision is unable to distinguish stars below the sixthmagnitude, and ordinary sight is far from discovering all of these. Again, seven thousand stars for the whole Heavens makes only threethousand five hundred for half the sky. And we can only see onecelestial hemisphere at a time. Moreover, toward the horizon, the vaporof the atmosphere veils the little stars of sixth magnitude. In reality, we never see at a given moment more than three thousand stars. Thisnumber is below that of the population of a small town. * * * * * But celestial space is unlimited, and we must not suppose that theseseven thousand stars that fascinate our eyes and enrich our Heavens, without which our nights would be black, dark, and empty, [5] comprisethe whole of Creation. They only represent the vestibule of the temple. Where our vision is arrested, a larger, more powerful eye, that isdeveloping from century to century, plunges its analyzing gaze into theabysses, and reflects back to the insatiable curiosity of science thelight of the innumerable suns that it discovers. This eye is the lens ofthe optical instruments. Even opera-glasses disclose stars of theseventh magnitude. A small astronomical objective penetrates to theeighth and ninth orders. More powerful instruments attain the tenth. The Heavens are progressively transformed to the eye of the astronomer, and soon he is able to reckon hundreds of thousands of orbs in thenight. The evolution continues, the power of the instrument isdeveloped; and the stars of the eleventh and twelfth magnitudes arediscovered successively, and together number four millions. Then followthe thirteenth, fourteenth, and fifteenth magnitudes. This is thesequence: 7th magnitude 13, 000. 8th " 40, 000. 9th " 120, 000. 10th " 380, 000. 11th " 1, 000, 000. 12th " 3, 000, 000. 13th " 9, 000, 000. 14th " 27, 000, 000. 15th " 80, 000, 000. Accordingly, the most powerful telescopes of the day, reenforced bycelestial photography, can bring a stream of more than 120 millions ofstars into the scope of our vision. The photographic map of the Heavens now being executed comprises thefirst fourteen magnitudes, and will give the precise position of some40, 000, 000 stars, distributed over 22, 054 sheets, forming a sphere 3meters 44 centimeters in diameter. The boldest imagination is overwhelmed by these figures, and fails topicture such millions of suns--formidable and burning globes that rollthrough space, sweeping their systems along with them. What furnaces arethere! what unknown lives! what vast immensities! And again, what enormous distances must separate the stars, to admit oftheir free revolution in the ether! In what abysses, at what a distancefrom our terrestrial atom, must these magnificent and dazzling Sunspursue the paths traced for them by Destiny! * * * * * If all the stars radiated an equal light, their distances might becalculated on the principle that an object appears smaller in proportionto its distance. But this equality does not exist. The suns were not allcast in the same mold. Indeed, the stars differ widely in size and brightness, and thedistances that have been measured show that the most brilliant are notthe nearest. They are scattered through Space at all distances. Among the nearer stars of which it has been found possible to calculatethe distance, some are found to be of the fourth, fifth, sixth, seventh, eighth, and even ninth magnitudes, proving that the most brilliant arenot always the least distant. For the rest, among the beautiful and shining stars with which we madeacquaintance in the last chapter may be cited Sirius, which at adistance of 92 trillion kilometers (57 trillion miles) from here stilldazzles us with its burning fires; Procyon or [alpha] of the Little Dog, as remote as 112 trillion kilometers (69-1/2 trillion miles); Altaïr ofthe Eagle, at 160 trillion kilometers (99 trillion miles); the whiteVega, at 204 trillion kilometers (126-1/2 trillion miles); Capella, at276 trillion kilometers (171 trillion miles); and the Pole-Star at 344trillion kilometers (213-1/2 trillion miles). The light that fliesthrough Space at a velocity of 300, 000 kilometers (186, 000 miles) persecond, takes thirty-six years and a half to reach us from this distantsun: _i. E. _, the luminous ray we are now receiving from Polaris has beentraveling for more than the third of a century. When you, gentle reader, were born, the ray that arrives to-day from the Pole-Star was alreadyspeeding on its way. In the first second after it had started ittraveled 300, 000 kilometers; in the second it added another 300, 000which at once makes 600, 000 kilometers; add another 300, 000 kilometersfor the third second, and so on during the thirty-six years and a half. If we tried to arrange the number 300, 000 (which represents the distanceaccomplished in one second) in superposed rows, as if for an additionsum, as many times as is necessary to obtain the distance thatseparates the Pole-Star from our Earth, the necessary operation wouldcomprise 1, 151, 064, 000 rows, and the sheet of paper required for thesetting out of such a sum would measure approximately 11, 510 kilometers(about 7, 000 miles), _i. E. _, almost the diameter of our terrestrialglobe, or about four times the distance from Paris to Moscow! Is it not impossible to realize that our Sun, with its entire system, islost in the Heavens at such a distance from his peers in Space? At thedistance of the least remote of the stars he would appear as one of thesmallest. * * * * * The nearest star to us is [alpha] of the Centaur, of first magnitude, aneighbor of the South Pole, invisible in our latitudes. Its distance is275, 000 radii of the terrestrial orbit, _i. E. _, 275, 000 times 149million kilometers, which gives 41 trillions, or 41, 000 milliards ofkilometers (= 25-1/2 trillion miles). [A milliard = 1, 000 millions, theFrench billion. A trillion = 1, 000 milliards, or a million millions, theEnglish billion. The _French_ nomenclature has been retained by thetranslator. ] At a speed of 300, 000 kilometers (186, 000 miles) per secondthe light takes four years to come from thence. It is a fine doublestar. The next nearest star after this is a little orb invisible to theunaided eye. It has no name, and stands as No. 21, 185 in the Catalogueof Lalande. It almost attains the seventh magnitude (6. 8). Its distanceis 64 trillion kilometers (39-1/2 trillion miles). The third of which the distance has been measured is the small star inCygnus, already referred to in Chapter II, in describing theConstellations. Its distance is 69 trillion kilometers (42-1/2 trillionmiles). This, too, is a double star. The light takes seven years toreach us. As we have seen, the fine stars Sirius, Procyon, Aldebaran, Altaïr, Vega, and Capella are more remote. Our solar system is thus very isolated in the vastness of Infinitude. The latest known planet of our system, Neptune, performs its revolutionsin space at 4 milliards, 470 million kilometers (2, 771, 400, 000 miles)from our Sun. Even this is a respectable distance! But beyond thisworld, an immense gulf, almost a void abyss, extends to the neareststar, [alpha] of the Centaur. Between Neptune and Centauris there is nostar to cheer the black and cold solitude of the immense vacuum. One ortwo unknown planets, some wandering comets, and swarms of meteors, doubtless traverse those unknown spaces, but all invisible to us. Later on we will discuss the methods that have been employed inmeasuring these distances. Let us now continue our description. * * * * * Now that we have some notion of the distance of the stars we mustapproach them with the telescope, and compare them one with another. Let us, for example, get close to Sirius: in this star we admire a sunthat is several times heavier than our own, and of much greater mass, accompanied by a second sun that revolves round it in fifty years. Itslight is exceedingly white, and it notably burns with hydrogen flames, like Vega and Altaïr. Now let us approach Arcturus, Capella, Aldebaran: these are yellow starswith golden rays, like our Sun, and the vapor of iron, of sodium, and ofmany other metals can be identified in their spectrum. These stars areolder than the first, and the ruddy ones, such as Antares, Betelgeuse, [alpha] of Hercules, are still older; several of them are variable, andare on their way to final extinction. The Heavens afford us a perennial store of treasure, wherein thethinker, poet or artist can find inexhaustible subjects ofcontemplation. You have heard of the celestial jewels, the diamonds, rubies, emeralds, sapphires, topazes, and other precious stones of the sidereal casket. These marvels are met with especially among the double stars. Our Sun, white and solitary, gives no idea of the real aspect of some ofits brothers in Infinitude. There are as many different types as thereare suns! Stars, you will think, are like individuals: each has its distinctcharacteristics: no two are comparable. And indeed this reflection isjustified. While human vanity does homage to Phoebus, divine King ofthe Heavens, other suns of still greater magnificence form groups of twoor three splendid orbs, which roll the prodigious combinations of theirdouble, triple, or multiple systems through space, pouring on to theworlds that accompany them a flood of changing light, now blue, now red, now violet, etc. In the inexhaustible variety of Creation there exist Suns that areunited in pairs, bound by a common destiny, cradled in the sameattraction, and often colored in the most delicate and entrancing shadesconceivable. Here will be a dazzling ruby, its glowing color sheddingjoy; there a deep blue sapphire of tender tone; beyond, the finestemeralds, hue of hope. Diamonds of translucent purity and whitenesssparkle from the abyss, and shed their penetrating light into the vastspace. What splendors are scattered broadcast over the sky! whatprofusion! To the naked eye, the groups appear like ordinary stars, mere luminouspoints of greater or less brilliancy; but the telescope soon discoversthe beauty of these systems; the star is duplicated into two distinctsuns, in close proximity. These groups of two or several suns are notmerely due to an effect of perspective--_i. E. _, the presence of two ormore stars in our line of sight; as a rule they constitute real physicalsystems, and these suns, associated in a common lot, rotate round oneanother in a more or less rapid period, that varies for each system. One of the most splendid of these _double stars_, and at the same timeone of the easiest to perceive, is [zeta] in the Great Bear, or Mizar, mentioned above in describing this constellation. It has no contrastingcolors, but exactly resembles twin diamonds of the finest water, whichfascinate the gaze, even through a small objective. Its components are of the second and fourth magnitudes, their distance =14"[6]. Some idea of their appearance in a small telescope may beobtained from the subjoined figure (Fig. 17). Another very brilliant pair is Castor. Magnitudes second and third. Distance 5. 6"". Very easy to observe. [gamma] in the Virgin resolvesinto two splendid diamonds of third magnitude. Distance, 5. 0". Anotherdouble star is [gamma] of the Ram, of fourth magnitude. Distance, 8. 9". [Illustration: FIG. 17. --The double star Mizar. ] And here are two that are even more curious by reason of their coloring:[gamma] in Andromeda, composed of a fine orange star, and oneemerald-green, which again is accompanied by a tiny comrade of thedeepest blue. This group in a good telescope is most attractive. Magnitudes, second and fifth. Distance, 10". [beta] of the Swan, or Albireo, referred to in the last chapter, hasbeen analyzed into two stars: one golden-yellow, the other sapphire. Magnitudes, third and fifth. Distance, 34". [alpha] of the Greyhounds, known also as the Heart of Charles II, is golden-yellow and lilac. Magnitudes, third and fifth. Distance 20". [7] [alpha] of Hercules revolves a splendid emerald and a ruby in the skies;[zeta] of the Lyre exhibits a yellow and a green star; Rigel, anelectric sun, and a small sapphire; Antares is ruddy and emerald-green;[eta] of Perseus resolves into a burning red star, and one smaller thatis deep blue, and so on. * * * * * These exquisite double stars revolve in gracious and splendid couplesaround one another, as in some majestic valse, marrying theirmulti-colored fires in the midst of the starry firmament. Here, we constantly receive a pure and dazzling white light from ourburning luminary. Its ray, indeed, contains the potentiality of everyconceivable color, but picture the fantastic illumination of the worldsthat gravitate round these multiple and colored suns as they shed floodsof blue and roseate, red, or orange light around them! What a fairyspectacle must life present upon these distant universes! Let us suppose that we inhabit a planet illuminated by two suns, oneblue, the other red. It is morning. The sapphire sun climbs slowly up the Heavens, coloringthe atmosphere with a somber and almost melancholy hue. The blue diskattains the zenith, and is beginning its descent toward the West, whenthe East lights up with the flames of a scarlet sun, which in its turnascends the heights of the firmament. The West is plunged in thepenumbra of the rays of the blue sun, while the East is illuminated withthe purple and burning rays of the ruby orb. The first sun is setting when the second noon shines for the inhabitantsof this strange world. But the red sun, too, accomplishes the law of itsdestiny. Hardly has it disappeared in the conflagration of its lastrays, with which the West is flushed, when the blue orb reappears on theopposite side, shedding a pale azure light upon the world itilluminates, which knows no night. And thus these two suns fraternize inthe Heavens over the common task of renewing a thousand effects ofextra-terrestrial light for the globes that are subject to theirvariations. Scarlet, indigo, green, and golden suns; pearly and multi-colored Moons;are these not fairy visions, dazzling to our poor sight, condemned whilehere below to see and know but one white Sun? As we have learned, there are not only double, but triple, and alsomultiple stars. One of the finest ternary systems is that of [gamma] inAndromeda, above mentioned. Its large star is orange, its second green, its third blue, but the two last are in close juxtaposition, and apowerful telescope is needed to separate them. A triple star more easyto observe is [zeta] of Cancer, composed of three orbs of fifthmagnitude, at a distance of 1" and 5"; the first two revolve round theircommon center of gravity in fifty-nine years, the third takes over threehundred years. The preceding figure shows this system in a fairlypowerful objective (Fig. 18). [Illustration: FIG. 18. --Triple star [zeta] in Cancer. ] In the Lyre, a little above the dazzling Vega, [epsilon] is of fourthmagnitude, which seems a little elongated to the unaided eye, and caneven be analyzed into two contiguous stars by very sharp sight. But onexamining this attractive pair with a small glass, it is further obviousthat each of these stars is double; so that they form a splendidquadruple system of two couples (Fig. 19): one of fifth and a half andsixth magnitudes, at a distance of 2. 4", the other of sixth andseventh, 3. 2" distant. The distance between the two pairs is 207". [Illustration: FIG. 19. --Quadruple star [epsilon] of the Lyre. ] In speaking of Orion, we referred to the marvelous star [theta] situatedin the no less famous Nebula, below the Belt; this star forms adazzling sextuple system, in the very heart of the nebula (Fig. 20). Howdifferent to our Sun, sailing through Space in modest isolation! Be it noted that all these stars are animated by prodigious motions thatimpel them in every direction. [Illustration: FIG. 20. --Sextuple star [theta] in the Nebula of Orion. ] There are no fixed stars. On every side throughout Infinity, the burningsuns--enormous globes, blazing centers of light and heat--are flying atgiddy speed toward an unknown goal, traversing millions of miles eachday, crossing century by century such vast spaces as are inconceivableto the human intellect. If the stars appear motionless to us, it is because they are so remote, their secular movements being only manifested on the celestial sphere byimperceptible displacements. But in reality these suns are in perpetualcommotion in the abysses of the Heavens, which they quicken with anextraordinary animation. These perpetual and cumulative motions must eventually modify the aspectof the Constellations: but these changes will only take effect veryslowly; and for thousands and thousands of years longer the heroes andheroines of mythology will keep their respective places in the Heavens, and reign undisturbed beneath the starry vault. Examination of these star motions reveals the fact that our Sun isplunging with all his system (the Earth included) toward theConstellation of Hercules. We are changing our position every moment: inan hour we shall be 70, 000 kilometers (43, 500 miles) farther than we areat present. The Sun and the Earth will never again traverse the spacethey have just left, and which they have deserted forever. And here let us pause for an instant to consider the _variable stars_. Our Sun, which is constant and uniform in its light, does not set thetype of all the stars. A great number of them are variable--eitherperiodically, in regular cycles--or irregularly. We are already acquainted with the variations of Algol, in Perseus, dueto its partial eclipse by a dark globe gravitating in the line of ourvision. There are several others of the same type: these are not, properly speaking, variable stars. But there are many others theintrinsic light of which undergoes actual variations. In order to realize this, let us imagine that our Earth belongs to sucha sun, for example, to a star in the southern constellation of theWhale, indicated by the letter [omicron], which has been named the"wonderful" (Mira Ceti). Our new sun is shining to-day with a dazzlinglight, shedding the gladness of his joyous beams upon nature and in ourhearts. For two months we admire the superb orb, sparkling in the azureilluminated with its radiance. Then of a sudden, its light fades, anddiminishes in intensity, though the sky remains clear. Imperceptibly, our fine sun darkens; the atmosphere becomes sad and dull, there is ananticipation of universal death. For five long months our world isplunged in a kind of penumbra; all nature is saddened in the generalwoe. But while we are bewailing the cruelty of our lot, our cherishedluminary revives. The intensity of its light increases slowly. Itsbrilliancy augments, and finally, at the end of three months, it hasrecovered its former splendors, and showers its bright beams upon ourworld, flooding it with joy. But--we must not rejoice too quickly! Thissplendid blaze will not endure. The flaming star will pale once more;fade back to its minimum; and then again revive. Such is the nature ofthis capricious sun. It varies in three hundred and thirty-one days, andfrom yellow at the maximum, turns red at the minimum. This star, MiraCeti, which is one of the most curious of its type, varies from thesecond to the ninth magnitudes: we cite it as one example; hundreds ofothers might be instanced. Thus the sky is no black curtain dotted with brilliant points, no emptydesert, silent and monotonous. It is a prodigious theater on which themost fantastic plays are continually being acted. Only--there are nospectators. Again, we must note the _temporary stars_, which shine for a certaintime, and then die out rapidly. Such was the star in Cassiopeia, in1572, the light of which exceeded Sirius in its visibility in fulldaylight, burning for five months with unparalleled splendor, dominatingall other stars of first magnitude; after which it died out gradually, disappearing at the end of seventeen months, to the terror of thepeoples, who saw in it the harbinger of the world's end: that of 1604, in the Constellation of the Serpent, which shone for a year; of 1866, ofsecond magnitude, in the Northern Crown, which appeared for a few weeksonly; of 1876, in the Swan; of 1885, in the Nebula of Andromeda; of1891, in the Charioteer; and quite recently, of 1901, in Perseus. These temporary stars, which appear spontaneously to the observers onthe Earth, and quickly vanish again, are doubtless due to collisions, conflagrations, or celestial cataclysms. But we only see them long afterthe epoch at which the phenomena occurred, years upon years, andcenturies ago. For instance, the conflagration photographed by theauthor in 1901, in Perseus, must have occurred in the time of QueenElizabeth. It has taken all this time for the rays of light to reach us. * * * * * The Heavens are full of surprises, on which we can bestow but a fleetingglance within these limits. They present a field of infinite variety. Who has not noticed the Milky Way, the pale belt that traverses theentire firmament and is so luminous on clear evenings in theConstellations of the Swan and the Lyre? It is indeed a swarm of stars. Each is individually too small to excite our retina, but as a whole, curiously enough, they are perfectly visible. With opera-glasses wedivine the starry constitution: a small telescope shows us marvels. Eighteen millions of stars were counted there with the gauges of WilliamHerschel. Now this Milky Way is a symbol, not of the Universe, but of theUniverses that succeed each other through the vast spaces to Infinity. Our Sun is a star of the Milky Way. It surrounds us like a great circle, and if the Earth were transparent, we should see it pass beneath ourfeet as well as over our heads. It consists of a very considerable massof star-clusters, varying greatly in extent and number, some projectedin front of others, while the whole forms an agglomeration. [Illustration: FIG. 21. --The Star-Cluster in Hercules. ] Among this mass of star-groups, several thousands of which are alreadyknown to us, we will select one of the most curious, the Cluster inHercules, which can be distinguished with the unaided eye, between thestars [eta] and [zeta] of that constellation. Many photographs of ithave been taken in the author's observatory at Juvisy, showing somethousands of stars; and one of these is reproduced in the accompanyingfigure (Fig. 21). Is it not a veritable universe? [Illustration: FIG. 22. --The Star-Cluster in the Centaur. ] Another of the most beautiful, on account of its regularity, is that ofthe Centaur (Fig. 22). These groups often assume the most extraordinary shapes in thetelescope, such as crowns, fishes, crabs, open mouths, birds withoutspread wings, etc. We must also note the _gaseous nebulæ_, universes in the making, _e. G. _, the famous Nebula in Orion, of which we obtained some notion awhile ago in connection with its sextuple star: and also that inAndromeda (Fig. 23). [Illustration: FIG. 23. --The Nebula in Andromeda. ] [Illustration: FIG. 24. --Nebula in the Greyhounds. ] Perhaps the most marvelous of all is that of the Greyhounds, whichevolves in gigantic spirals round a dazzling focus, and then losesitself far off in the recesses of space. Fig. 24 gives a picture of it. [Illustration: FIG. 25. --The Pleiades. ] Without going thus far, and penetrating into telescopic depths, myreaders can get some notion of these star-clusters with the help of asmall telescope or opera-glasses, or even with the unaided eye, bylooking at the beautiful group of the Pleiades, already familiar to uson another page, and using it as a test of vision. The little mapsubjoined (Fig. 25) will be an assistance in recognizing them, and inestimating their magnitudes, which are in the following order: Alcyone 3. 0. Electra 4. 5. Atlas 4. 6. Maia 5. 0. Merope 5. 5. Taygeta 5. 8. Pleione 6. 3. Celæno 6. 5. Asterope 6. 8. Good eyes distinguish the first six, sharp sight detects the threeothers. In the times of the ancient Greeks, seven were accounted of equalbrilliancy, and the poets related that the seventh star had fled at thetime of the Trojan War. Ovid adds that she was mortified at not beingembraced by a god, as were her six sisters. It is probable that only thebest sight could then distinguish Pleione, as in our own day. Theangular distance from Atlas to Pleione is 5'. The length of this republic, from Atlas and Pleione to Celæno, is 4'/23"of time, or 1°6' of arc; the breadth, from Merope to Asterope, is36'. [8] In the quadrilateral, the length from Alcyone to Electra is 36', and thebreadth from Merope to Maia 25'. To us it appears as though, if the FullMoon were placed in front of this group of nine stars, she would coverit entirely, for to the naked eye she appears much larger than all thePleiades together. But this is not so. She only measures 31', less thanhalf the distance from Atlas to Celæno; she is hardly broader than thedistance from Alcyone to Atlas, and could pass between Merope andTaygeta without touching either of these stars. This is a perennial andvery curious optical illusion. When the Moon passes in front of thePleiades, and occults them successively, it is hard to believe one'seyes. The fact occurred, _e. G. _, on July 23, 1897, during a fineoccultation observed at the author's laboratory of Juvisy (Fig. 26). [Illustration: FIG. 26. --Occultation of the Pleiades by the Moon. ] Photography here discovers to us, not 6, 9, 12, 15, or 20 stars, buthundreds and millions. These are the most brilliant flowers of the celestial garden. [Illustration: FIG. 27. --Stellar dial of the double star [gamma] of theVirgin. ] We, alas, can but glance at them rapidly. In contemplating them we aretransported into immensities both of space and time, for the stellarperiods measured by these distant universes often overpower in theirmagnitude the rapid years in which our terrestrial days are estimated. For instance, one of the double stars we spoke of above, [gamma] of theVirgin, sees its two components, translucent diamonds, revolve aroundtheir common center of gravity, in one hundred and eighty years. Howmany events took place in France, let us say, in a single year of thisstar!--The Regency, Louis XV, Louis XVI, the Revolution, Napoleon, LouisXVIII, Louis Philippe, the Second Republic, Napoleon III, theFranco-German War, the Third Republic. . . . What revolutions here, duringa single year of this radiant pair! (Fig. 27. ) But the pageant of the Heavens is too vast, too overwhelming. We mustend our survey. Our Milky Way, with its millions of stars, represents for us only aportion of the Creation. The illimitable abysses of Infinitude arepeopled by other universes as vast, as imposing, as our own, which arerenewed in all directions through the depths of Space to endlessdistance. Where is our little Earth? Where our Solar System? We are fainto fold our wings, and return from the Immense and Infinite to ourfloating island. CHAPTER IV OUR STAR THE SUN In the incessant agitation of daily life in which we are involved by thethousand superfluous wants of modern "civilization, " one is prone toassume that existence is complete only when it reckons to the good anincalculable number of petty incidents, each more insignificant than thelast. Why lose time in thinking or dreaming? We must live at fever heat, must agitate, and be infatuated for inanities, must create imaginarydesires and torments. The thoughtful mind, prone to contemplation and admiration of thebeauties of Nature, is ill at ease in this perpetual vortex thatswallows everything--satisfaction, in a life that one has not time torelish; love of the beautiful, that one views with indifference; it is awhirlpool that perpetually hides Truth from us, forgotten forever at thebottom of her well. And why are our lives thus absorbed in merely material interests? Tosatisfy our pride and vanity! To make ourselves slaves to chimeras! Ifthe Moon were inhabited, and if her denizens could see us plainlyenough to note and analyze the details of human existence on the surfaceof our planet, it would be curious and perhaps a little humiliating forus, to see their statistics. What! we should say, is this the sum of ourlives? Is it for this that we struggle, and suffer, and die? Truly it isfutile to give ourselves such trouble. And yet the remedy is simple, within the power of every one; but onedoes not think of it just because it is too easy, although it has theimmense advantage of lifting us out of the miseries of this weary worldtoward the inexpressible happiness that must always awaken in us withthe knowledge of the Truth: we need only open our eyes to see, and tolook out. Only--one hardly ever thinks of it, and it is easier to letone's self be blinded by the illusion and false glamor of appearances. Think what it would be to consecrate an hour each day to voluntaryparticipation in the harmonious Choir of Nature, to raise one's eyestoward the Heavens, to share the lessons taught by the Pageant of theUniverse! But, no: there is no time, no time for the intellectual life, no time to become attached to real interests, no time to pursue them. Among the objects marshaled for us in the immense spectacle of Nature, nothing without exception has struck the admiration and attention ofman as much as the Sun, the God of Light, the fecundating orb, withoutwhich our planet and its life would never have issued from nonentity, _the visible image of the invisible god_, as said Cicero, and the poetsof antiquity. And yet how many beyond the circle of those likely to readthese pages know that this Sun is a star in the Milky Way, and thatevery star is a sun? How many take any account of the reality andgrandeur of the Universe? Inquire, and you will find that the number ofpeople who have any notion, however rudimentary, of its construction, issingularly restricted. Humanity is content to vegetate, much after thefashion of a race of moles. Henceforward, you will know that you are living in the rays of a star, which, from its proximity, we term a sun. To the inhabitants of othersystems of worlds, our splendid Sun is only a more or less brilliant, luminous point, according as the spot from which it is observed isnearer or farther off. But to us its "terrestrial" importance renders itparticularly precious; we forget all the sister stars on its account, and even the most ignorant hail it with enthusiasm without exactlyknowing what its rôle in the universe may be, simply because they feelthat they depend on it, and that without it life would become extinct onthis globe. Yes, it is the beneficent rays of the Sun that shed uponour Earth the floods of light and heat to which Life owes its existenceand its perpetual propagation. Hail, vast Sun! a little star in Infinitude, but for us a colossal andportentous luminary. Hail, divine Benefactor! How should we not adore, when we owe him the glow of the warm and cheery days of summer, thegentle caresses by which his rays touch the undulating ears, and gildthem with the touch? The Sun sustains our globe in Space, and keeps itwithin his rays by the mysteriously powerful and delicate cords ofattraction. It is the Sun that we inhale from the embalmed corollas ofthe flowers that uplift their gracious heads toward his light, andreflect his splendors back to us. It is the Sun that sparkles in thefoam of the merry wine; that charms our gaze in those first days ofspring, when the home of the human race is adorned with all the charmsof verdant and flowering youth. Everywhere we find the Sun; everywherewe recognize his work, extending from the infinitely great to theinfinitely little. We bow to his might, and admire his power. When inthe sad winter day he disappears behind the snowy eaves, we think hisfiery globe will never rise to mitigate the short December days whichare alleviated with his languid beams. April restores him to superb majesty, and our hearts are filled withhope in the illumination of those beauteous, sunny hours. * * * * * Our celestial journey carried us far indeed from our own Solar System. Guided by the penetrating eye of the telescope, we reached such distantcreations that we lost sight of our cherished luminary. But we remember that he burns yonder, in the midst of the pale cosmiccloud we term the Milky Way. Let us approach him, now that we havevisited the Isles of Light in the Celestial Ocean; let us traverse thevast plains strewn with the burning gold of the Suns of the Infinite. We embark upon a ray of light, and glide rapidly to the portals of ourUniverse. Soon we perceive a tiny speck, scintillating feebly in thedepths of Space, and recognize it as our own celestial quarters. Thislittle star shines like the head of a gold pin, and increases in size aswe advance toward it. We traverse a few more trillion miles in our rapidcourse, and it shines out like a fine star of the first magnitude. Itgrows larger and larger. Soon we divine that it is our humble Earth thatis shining before us, and gladly alight upon her. In future we shall notquit our own province of the Celestial Kingdom, but will enter intorelations with this solar family, which interests us the more in that itaffects us so closely. [Illustration: FIG. 28. --Comparative sizes of the Sun and Earth. ] The Sun, which is manifested to us as a fine white disk at noon, whileit is fiery red in the evening, at its setting, is an immense globe, whose colossal dimensions surpass those of our terrestrial atom beyondall conceivable proportion. In diameter, it is, in effect, 108-1/2 times as large as the Earth; thatis to say, if our planet be represented by a globe 1 meter in diameter, the Sun would figure as a sphere 108-1/2 meters across. This is shown onthe accompanying figure (Fig. 28), which is in exact proportion. If our world were set down upon the Sun, with all its magnificence, allits wealth, its mountains, its seas, its monuments, and its inhabitants, it would only be an imperceptible speck. It would occupy less space inthe central orb than one grain in a grenade. If the Earth were placed inthe center of the Sun, with the Moon still revolving round it at herproper distance of 384, 000 kilometers (238, 500 miles), only half thesolar surface would be covered. In volume the Sun is 1, 280, 000 times vaster than our abode, and 324, 000times heavier in mass. That the giant only appears to us as a smallthough very brilliant disk, is solely on account of its distance. Itsapparent dimensions by no means reveal its majestic proportions to us. When observed with astronomical instruments, or photographed, wediscover that its surface is not smooth, as might be supposed, butgranulated, presenting a number of luminous points dispersed over amore somber background. These granulations are somewhat like the poresof a fruit, _e. G. _, a fine orange, the color of which recalls the hue ofthe Sun when it sinks in the evening, and prepares to plunge us intodarkness. At times these pores open under the influence of disturbancesthat arise upon the solar surface, and give birth to a Sun-Spot. Forcenturies scientists and lay people alike refused to admit the existenceof these spots, regarding them as so many blemishes upon the King of theHeavens. Was not the Sun the emblem of inviolable purity? To find anydefect in him were to do him grievous injury. Since the orb of day wasincorruptible, those who threw doubt on his immaculate splendor werefools and idiots. And so when Scheiner, one of the first who studied thesolar spots with the telescope, published the result of his experimentsin 1610, no one would believe his statements. Yet, from the observations of Galileo and other astronomers, it becamenecessary to accept the evidence, and stranger still to recognize thatit is by these very spots that we are enabled to study the physicalconstitution of the Sun. They are generally rounded or oval in shape, and exhibit two distinctparts; first, the central portion, which is black, and is called the_nucleus_, or _umbra_; second, a clearer region, half shaded, which hasreceived the name of _penumbra_. These parts are sharply defined inoutline; the penumbra is gray, the nucleus looks black in relation tothe dazzling brilliancy of the solar surface; but as a matter of fact itradiates a light 2, 000 times superior in intensity to that of the fullmoon. [Illustration: FIG. 29. --Direct photograph of the Sun. ] Some idea of the aspect of these spots may be obtained from theaccompanying reproduction of a photograph of the Sun (taken September 8, 1898, at the author's observatory at Juvisy), and from the detaileddrawing of the large spot that broke out some days later (September 13), crossed by a bridge, and furrowed with flames. As a rule, the spotsundergo rapid transformations. [Illustration: FIG. 30. --Telescopic aspect of a Sun-Spot. ] These spots, which appear of insignificant dimensions to the observerson the Earth, are in reality absolutely gigantic. Some that have beenmeasured are ten times as large as the Earth's diameter, _i. E. _, 120, 000kilometers (74, 500 miles). Sometimes the spots are so large that they can be seen with the unaidedeye (protected with black or dark-blue glasses). They are not formedinstantaneously, but are heralded by a vast commotion on the solarsurface, exhibiting, as it were, luminous waves or _faculæ_. Out of thisagitation arises a little spot, that is usually round, and enlargesprogressively to reach a maximum, after which it diminishes, withfrequent segmentation and shrinkage. Some are visible only for a fewdays; others last for months. Some appear, only to be instantlyswallowed in the boiling turmoil of the flaming orb. Sometimes, again, white incandescent waves emerge, and seem to throw luminous bridgesacross the central umbra. As a rule the spots are not very profound. They are funnel-shaped depressions, inferior in depth to the diameter ofthe Earth, which, as we have seen, is 108 times smaller than that of theSun. * * * * * The Sun-Spots are not devoid of motion, and from their movements welearn that the radiant orb revolves upon itself in about twenty-fivedays. This rotation was determined in 1611, by Galileo, who, whileobserving the spots, saw that they traversed the solar disk from eastto west, following lines that are oblique to the plane of the ecliptic, and that they disappear at the western border fourteen days after theirarrival at the eastern edge. Sometimes the same spot, after beinginvisible for fourteen days, reappears upon the eastern edge, where itwas observed twenty-eight days previously. It progresses toward thecenter of the Sun, which is reached in seven days, disappears anew inthe west, and continues its journey on the hemisphere opposed to us, toreappear under observation two weeks later, if it has not meantime beenextinguished. This observation proves that the Sun revolves upon itself. The reappearance of the spots occurs in about twenty-seven days, becausethe Earth is not stationary, and in its movement round the burningfocus, a motion effected in the same direction as the solar rotation, the spots are still visible two and a half days after they disappearedfrom the point at which they had been twenty-five days previously. Inreality, the rotation of the Sun occupies twenty-five and a half days, but strangely enough this globe _does not rotate in one uniform period_, like the Earth; the rotation periods, or movements of the differentparts of the solar surface, diminish from the Sun's equator toward itspoles. The period is twenty-five days at the equator, twenty-six at thetwenty-fourth degree of latitude, north or south, twenty-seven at thethirty-seventh degree, twenty-eight at the forty-eighth. The spots areusually formed between the equator and this latitude, more especiallybetween the tenth and thirtieth degrees. They have never been seen roundthe poles. Toward the edges of the Sun, again, are very brilliant and highlyluminous regions, which generally surround the spots, and have beentermed _faculæ_ (_facula_, a little torch). These faculæ, whichfrequently occupy a very extensive surface, seem to be the seat offormidable commotions that incessantly revolutionize the face of ourmonarch, often, as we said, preceding the spots. They can be detectedright up to the poles. Our Sun, that appears so calm and majestic, is in reality the seat offierce conflagrations. Volcanic eruptions, the most appalling storms, the worst cataclysms that sometimes disturb our little world, are gentlezephyrs compared with the solar tempests that engender clouds of firecapable at one burst of engulfing globes of the dimensions of ourplanet. To compare terrestrial volcanoes with solar eruptions is like comparingthe modest night-light that consumes a midge with the flames of the firethat destroys a town. The solar spots vary in a fairly regular period of eleven to twelveyears. In certain years, _e. G. _, 1893, they are vast, numerous andfrequent; in other years, _e. G. _, 1901, they are few and insignificant. The statistics are very carefully preserved. Here, for instance, is thesurface showing sun-spots expressed in millionths of the extent of thevisible solar surface: 1889 78 1890 99 1891 569 1892 1, 214 1893 1, 464 1895 974 1896 543 1897 514 1898 375 1899 111 1900 75 1901 29 1902 62 The years 1889 and 1901 were _minima_; the year 1893 a _maximum_. It is a curious fact that terrestrial magnetism and the boreal aurorasexhibit an oscillation parallel to that of the solar spots, andapparently the same occurs with regard to temperature. We must regard our sun as a globe of gas in a state of combustion, burning at high temperature, and giving off a prodigious amount of heatand light. The dazzling surface of this globe is called a _photosphere_(light sphere). It is in perpetual motion, like the waves of an ocean offire, whose roseate and transparent flames measure some 15, 000kilometers (9, 300 miles) in height. This stratum of rose-colored flameshas received the name of _chromosphere_ (color sphere). It istransparent; it is not directly visible, but is seen only during thetotal eclipses of the Sun, when the dazzling disk of that luminary isentirely concealed by the Moon; or with the aid of the spectroscope. Thepart of the Sun that we see is its luminous surface, or photosphere. From this agitated surface there is a constant ejection of giganticeruptions, immense jets of flame, geysers of fire, projected at aterrific speed to prodigious heights. For years astronomers were greatly perplexed as to the nature of theseincandescent masses, known as prominences, which shot out likefireworks, and were only visible during the total eclipses of the Sun. But now, thanks to an ingenious invention of Janssen and Lockyer, theseeruptions can be observed every day in the spectroscope, and have beenregistered since 1868, more particularly in Rome and in Catania, wherethe Society of Spectroscopists was founded with this especial object, and publishes monthly bulletins in statistics of the health of the Sun. These prominences assume all imaginable forms, and often resemble ourown storm-clouds; they rise above the chromosphere with incrediblevelocity, often exceeding 200 kilometers (124 miles) per second, andare carried up to the amazing height of 300, 000 kilometers (186, 000miles). [Illustration: FIG. 31. --Rose-colored solar flames 228, 000 kilometers(141, 500 miles) in height, _i. E. _, 18 times the diameter of the Earth. ] The Sun is surrounded with these enormous flames on every side;sometimes they shoot out into space like splendid curving roseateplumes; at others they rear their luminous heads in the Heavens, likethe cleft and waving leaves of giant palm-trees. Having illustrated aremarkable type of solar spot, it is interesting to submit to the readera precise observation of these curious solar flames. That reproducedhere was observed in Rome, January 30, 1885. It measured 228, 000kilometers (141, 500 miles) in height, eighteen times the diameter of theearth (represented alongside in its relative magnitude). (Fig. 31. ) Solar eruptions have been seen to reach, in a few minutes, a height ofmore than 100, 000 kilometers (62, 000 miles), and then to fall back in aflaming torrent into that burning and inextinguishable ocean. Observation, in conjunction with spectral analysis, shows theseprominences to be due to formidable explosions produced within theactual substance of the Sun, and projecting masses of incandescenthydrogen into space with considerable force. Nor is this all. During an eclipse one sees around the black disk of theMoon as it passes in front of the Sun and intercepts its light, abrilliant and rosy aureole with long, luminous, branching feathersstreaming out, like aigrettes, which extend a very considerable distancefrom the solar surface. This aureole, the nature of which is stillunknown to us, has received the name of _corona_. It is a sort ofimmense atmosphere, extremely rarefied. Our superb torch, accordingly, is a brazier of unparalleled activity--a globe of gas, agitated byphenomenal tempests whose flaming streamers extend afar. The smallest ofthese flames is so potent that it would swallow up our world at a singlebreath, like the bombs shot out by Vesuvius, that fall back within thecrater. What now is the real heat of this incandescent focus? The most accurateresearches estimate the temperature of the surface of the Sun at7, 000°C. The internal temperature must be considerably higher. Acrucible of molten iron poured out upon the Sun would be as a stream ofice and snow. We can form some idea of this calorific force by making certaincomparisons. Thus, the heat given out appears to be equal to that whichwould be emitted by a colossal globe of the same dimensions (that is, asvoluminous as twelve hundred and eighty thousand terrestrial globes), entirely covered with a layer of incandescent coal 28 kilometers (18miles) in depth, all burning at equal combustion. The heat emitted bythe Sun, at each second, is equal to that which would result from thecombustion of eleven quadrillions six hundred thousand milliards of tonsof coal, all burning together. This same heat would bring to the boil inan hour, two trillions nine hundred milliards of cubic kilometers ofwater at freezing-point. Our little planet, gravitating at 149, 000, 000 kilometers (93, 000, 000miles) from the Sun, arrests on the way, and utilizes, only the half ofa milliard part of this total radiation. How is this heat maintained? One of the principal causes of the heat ofthe Sun is its condensation. According to all probabilities, the solarglobe represents for us the nucleus of a vast nebula, that extended inprimitive times beyond the orbit of Neptune, and which in itscontraction has finally produced this central focus. In virtue of thelaw of transformation of motion into heat, this condensation, which hasnot yet reached its limit, suffices to raise this colossal globe to itslevel of temperature, and to maintain it there for millions of years. Inaddition, a substantial number of meteors is forever falling into it. This furnace is a true pandemonium. The Sun weighs three hundred and twenty-four thousand times more thanthe Earth--that is to say, eighteen hundred and seventy octillions ofkilograms: 1, 870, 000, 000, 000, 000, 000, 000, 000, 000, 000 (1, 842, 364, 532, 019, 704, 433, 497, 536, 945 tons). In Chapter XI we shall explain the methods by which it has been foundpossible to weigh the Sun and determine its exact distance. * * * * * I trust these figures will convey some notion of the importance andnature of the Sun, the stupendous orb on whose rays our very existencedepends. Its apparent dimension (which is only half a degree, 32', andwould be hidden from sight, like that of the full moon, which is aboutthe same, by the tip of the little finger held out at arm's length), represents, as we have seen, a real dimension that is colossal, _i. E. _, 1, 383, 000 kilometers (more than 857, 000 miles), and this is owing to theenormous distance that separates us from it. This distance of149, 000, 000 kilometers (93, 000, 000 miles) is sufficiently hard toappreciate. Let us say that 11, 640 terrestrial globes would be requiredto throw a bridge from here to the Sun, while 30 would suffice from theEarth to the Moon. The Moon is 388 times nearer to us than the Sun. Wemay perhaps conceive of this distance by calculating that a train, moving at constant speed of 1 kilometer (0. 6214 mile) a minute, wouldtake 149, 000, 000 minutes, that is to say 103, 472 days, or 283 years, tocross the distance that separates us from this orb. Given the normalduration of life, neither the travelers who set out for the Sun, northeir children, nor their grandchildren, would arrive there: only theseventh generation would reach the goal, and only the fourteenth couldbring us back news of it. Children often cry for the Moon. If one of these inquisitive littlebeings could stretch out its arms to touch the Sun, and burn its fingersthere, it would not feel the burn for one hundred and sixty-seven years(when it would no longer be an infant), for the nervous impulse ofsensation can only be transmitted from the ends of the fingers to thebrain at a velocity of 28 meters per second. 'Tis long. A cannon-ball would reach the Sun in ten years. Light, thatrapid arrow that flies through space at a velocity of 300, 000 kilometers(186, 000 miles per second), takes only eight minutes seventeen secondsto traverse this distance. * * * * * This brilliant Sun is not only sovereign of the Earth; he is also thehead of a vast planetary system. The orbs that circle round the Sun are opaque bodies, spherical inshape, receiving their light and heat from the central star, on whichthey absolutely depend. The name of planets given to them signifies"wandering" stars. If you observe the Heavens on a fine starry night, and are sufficiently acquainted with the principal stars of the Zodiacas described in a preceding chapter, you may be surprised on certainevenings to see the figure of some zodiacal constellation slightlymodified by the temporary presence of a brilliant orb perhaps surpassingin its luminosity the finest stars of the first magnitude. If you watch this apparition for some weeks, and examine its positioncarefully in regard to the adjacent stars, you will observe that itchanges its position more or less slowly in the Heavens. These wanderingorbs, or _planets_, do not shine with intrinsic light; they areilluminated by the Sun. The planets, in effect, are bodies as opaque as the Earth, travelinground the God of Day at a speed proportional to their distance. Theynumber eight principal orbs, and may be divided into two quite distinctgroups by which we may recognize them: the first comprises four planets, of relatively small dimensions in comparison with those of the secondgroup, which are so voluminous that the least important of them islarger than the other four put together. In order of distance from the Sun, we first encounter: MERCURY, VENUS, THE EARTH, AND MARS These are the worlds that are nearest to the orb of day. The four following, and much more remote, are, still in order ofdistance: JUPITER, SATURN, URANUS, AND NEPTUNE This second group is separated from the first by a vast space occupiedby quite a little army of minute planets, tiny cosmic bodies, thelargest of which measures little more than 100 kilometers (62 miles) indiameter, and the smallest some few miles only. The planets which form these three groups represent the principalmembers of the solar family. But the Sun is a patriarch, and each of hisdaughters has her own children who, while obeying the paternal influenceof the fiery orb, are also obedient to the world that governs them. These secondary asters, or _satellites_, follow the planets in theircourse, and revolve round them in an ellipse, just as the others rotateround the Sun. Every one knows the satellite of the Earth, the Moon. Allthe other planets of our system have their own moons, some being evenmore favored than ourselves in this respect, and having several. Marshas two; Jupiter, five; Saturn, eight; Uranus, four; and Neptune, one(at least as yet discovered). In order to realize the relations between these worlds, we mustappreciate their distances by arranging them in a little table: Distance in Distance in Millions of Millions of Kilometers. Miles. Mercury 57 35 Venus 108 67 The Earth 149 93 Mars 226 140 Jupiter 775 481 Saturn 1, 421 882 Uranus 2, 831 1, 755 Neptune 4, 470 2, 771 The Sun is at the center (or, more properly speaking, at the focus, forthe planets describe an ellipse) of this system, and controls them. Neptune is thirty times farther from the Sun than the Earth. Thesedisparities of distance produce a vast difference in the periods of theplanetary revolutions; for while the Earth revolves round the Sun in ayear, Venus in 224 days, and Mercury in 88, Mars takes nearly 2 years toaccomplish his journey, Jupiter 12 years, Saturn 29, Uranus 84, andNeptune 165. Even the planets and their moons do not represent the Sun's completepaternity. There are further, in the solar republic, certain vagabondand irregular orbs that travel at a speed that is often most immoderate, occasionally approaching the Sun, not to be consumed therein, but, as itappears, to draw from its radiant source the provision of forcesnecessary for their perigrinations through space. These are the_Comets_, which pursue an extremely elongated orbit round the Sun, towhich at times they approximate very closely, at other times beingexcessively distant. And now to recapitulate our knowledge of the Solar Empire. In the firstplace, we see a colossal globe of fire dominating and governing theworlds that belong to him. Around him are grouped planets, in numbereight principal, formed of solid and obscure matter, gravitating roundthe central orb. Other secondary orbs, the satellites, revolve round theplanets, which keep them within the sphere of their attraction. Andlastly, the comets, irregular celestial bodies, track the whole extentof the great solar province. To these might be added the whirlwinds ofmeteors, as it were disaggregated comets, which also circle round theSun, and give origin to shooting stars, when they come into collisionwith the Earth. Having now a general idea of our celestial family, and an appreciationof the potent focus that controls it, let us make direct acquaintancewith the several members of which it is composed. CHAPTER V THE PLANETS _A. _--MERCURY, VENUS, THE EARTH, MARS And now we are in the Solar System, at the center, or, better, at thefocus of which burns the immense and dazzling orb. We have appreciatedthe grandeur and potency of the solar globe, whose rays spread out inactive waves that bear a fecundating illumination to the worlds thatgravitate round him; we have appreciated the distance that separates theSun from the Earth, the third of the planets retained within his domain, or at least I trust that the comparisons of the times required bycertain moving objects to traverse this distance have enabled us toconceive it. We said that the four planets nearest to the Sun are Mercury, at adistance of 57 million kilometers (35, 000, 000 miles); Venus, at 108million (67, 000, 000 miles); the Earth, at 149 million (93, 000, 000miles); and Mars at 226 million (140, 000, 000 miles). Let us begin ourplanetary journey with these four stations. MERCURY A little above the Sun one sometimes sees, now in the West, in thelingering shimmer of the twilight, now in the East, when the tenderroseate dawn announces the advent of a clear day, a small star of thefirst magnitude which remains but a very short time above the horizon, and then plunges back into the flaming sun. This is Mercury, the agileand active messenger of Olympus, the god of eloquence, of medicine, ofcommerce, and of thieves. One only sees him furtively, from time totime, at the periods of his greatest elongations, either after thesetting or before the rising of the radiant orb, when he presents theaspect of a somewhat reddish star. This planet, like the others, shines only by the reflection of the Sunwhose illumination he receives, and as he is in close juxtaposition withit, his light is bright enough, though his volume is inconsiderable. Heis smaller than the Earth. His revolution round the Sun beingaccomplished in about three months, he passes rapidly, in a month and ahalf, from one side to the other of the orb of day, and is alternately amorning and an evening star. The ancients originally regarded it as twoseparate planets; but with attentive observation, they soon perceivedits identity. In our somewhat foggy climates, it can only be discoveredonce or twice a year, and then only by looking for it according to theindications given in the astronomic almanacs. [Illustration: FIG. 32. --Orbits of the four Planets nearest to the Sun. ] Mercury courses round the Sun at a distance of 57, 000, 000 kilometers(35, 000, 000 miles), and accomplishes his revolution in 87 days, 23hours, 15 minutes; _i. E. _, 2 months, 27 days, 23 hours, or a little lessthan three of our months. If the conditions of life are the same thereas here, the existence of the Mercurians must be four times as short asour own. A youth of twenty, awaking to the promise of the life he isjust beginning in this world, is an octogenarian in Mercury. There thefair sex would indeed be justified in bewailing the transitory nature oflife, and might regret the years that pass too quickly away. Perhaps, however, they are more philosophic than with us. [Illustration: FIG. 33. --Orbits of the four Planets farthest from theSun. ] The orbit of Mercury, which of course is within that of the Earth, isnot circular, but elliptical, and very eccentric, so elongated that atcertain times of the year this planet is extremely remote from the solarfocus, and receives only half as much heat and light as at the oppositeperiod; and, in consequence, his distance from the Earth variesconsiderably. [Illustration: FIG. 34. --Mercury near quadrature. ] This globe exhibits _phases_, discovered in the seventeenth century byGalileo, which recall those of the Moon. They are due to the motions ofthe planet round the Sun, and are invisible to the unaided eye, but witheven a small instrument, one can follow the gradations and study Mercuryunder every aspect. Sometimes, again, he passes exactly in front of theSun, and his disk is projected like a black point upon the luminoussurface of the flaming orb. This occurred, notably, on May 10, 1891, andNovember 10, 1894; and the phenomenon will recur on November 12, 1907, and November 6, 1914. Mercury is the least of all the worlds in our system (with the exceptionof the cosmic fragments that circulate between the orbit of Mars andthat of Jupiter). His volume equals only 5/100 that of the Earth. Hisdiameter, in comparison with that of our planet, is in the ratio of 373to 1, 000 (a little more than 1/3) and measures 4, 750 kilometers (2, 946miles). His density is the highest of all the worlds in the great solarfamily, and exceeds that of our Earth by about 1/3; but weight there isless by almost 1/2. Mercury is enveloped in a very dense, thick atmosphere, which doubtlesssensibly tempers the solar heat, for the Sun exhibits to the Mercuriansa luminous disk about seven times more extensive than that with which weare familiar on the Earth, and when Mercury is at perihelion (that is, nearest to the Sun), his inhabitants receive ten times more light andheat than we obtain at midsummer. In all probability, it would beimpossible for us to set foot on this planet without being shattered bya sunstroke. Yet we may well imagine that Nature's fecundity can have engenderedbeings there of an organization different from our own, adapted to anexistence in the proximity of fire. What magnificent landscapes maythere be adorned with the luxuriant vegetation that develops rapidlyunder an ardent and generous sun? [Illustration: FIG. 35. --The Earth viewed from Mercury. ] Observations of Mercury are taken under great difficulties, just becauseof the immediate proximity of the solar furnace; yet some have detectedpatches that might be seas. In any case, these observations arecontradictory and uncertain. Up to the present it has been impossible to determine the duration ofthe rotation. Some astronomers even think that the Sun's close proximitymust have produced strong tides, that would, as it were, haveimmobilized the globe of Mercury, just as the Earth has immobilized theMoon, forcing it perpetually to present the same side to the Sun. Fromthe point of view of habitation, this situation would be somewhatpeculiar; perpetual day upon the illumined half, perpetual night uponthe other hemisphere, and a fairly large zone of twilight between thetwo. Such a condition would indeed be different from the succession ofterrestrial days and nights. As seen from Mercury, the Earth we inhabit would shine out in the starrysky[9] as a magnificent orb of first magnitude, with the Moonalongside, a faithful little companion. They should form a fine doublestar, the Earth being a brilliant orb of first magnitude, and the Moonof third, a charming couple, and admired doubtless as an enchanted andprivileged abode. It is at midnight during the oppositions of the Earth with the Sun thatour planet is the most beautiful and brilliant, as is Jupiter forourselves. The constellations are the same, viewed from Mercury or fromthe Earth. But is this little solar planet inhabited? We do not yet know. We canonly reply: why not? VENUS When the sunset atmosphere is crimson with the glorious rays of the Kingof Orbs, and all Nature assumes the brooding veil of twilight, the mostindifferent eyes are often attracted and captivated by the presence of astar that is almost dazzling, and illuminates with its white and limpidlight the heavens darkened by the disappearance of the God of Day. Hail, Venus, Queen of the Heavens! the "Shepherd's Star, " gentle motherof the loves, goddess of beauty, eternally adored and cherished, sungand immortalized upon Earth, by poets and artists. Her splendidbrilliancy attracted notice from earliest antiquity, and we find her, radiant and charming, in the works of the ancients, who erected altarsto her and adorned their poetry with her grace and beauty. Homer callsher Callisto the Beautiful; Cicero names her Vesper, the evening star, and Lucifer, the star of the morning--for it was with this divinity aswith Mercury. For a long while she was regarded as two separate planets, and it was only when it came to be observed that the evening and themorning star were always in periodic succession, that the identity ofthe orb was recognized. Her radiant splendor created her mythological personality, just as theagility of Mercury created that of the messenger of the gods. We do not see her aerial chariot in the Heavens drawn by a flight ofdoves with white and fluttering wings, but we follow the lustrous orbled on through space by solar attraction. And in the beautiful eveningswhen she is at her greatest distance from our Sun, the whole worldadmires this white and dazzling Venus reigning as sovereign over ourtwilight[10] for hours after sunset, and in addition to the _savants_who are practically occupied with astronomy, millions of eyes are raisedto this celestial splendor, and for a moment millions of human beingsfeel some curiosity about the mysteries of the Infinite. The brutalitiesof daily life would fain petrify our dreams, but thought is not yetstifled to the point of checking all aspirations after eternal truth, and when we gaze at the starry sky it is hard not to ask ourselves thenature of those other worlds, and the place occupied by our own planetin the vast concert of sidereal harmony. [Illustration: FIG. 36. --The Evening Star. ] Even through a small telescope, Venus offers remarkable phases. [Illustration: FIG. 37. --Successive phases of Venus. ] Fig. 37 gives some notion of the succession of these, and of theplanet's variations in magnitude during its journey round the Sun. Imagine it to be rotating in a year of 224 days, 16 hours, 49 minutes, 8seconds at a distance of 108 million kilometers (67, 000, 000 miles), theEarth being at 149 million kilometers (93, 000, 000 miles). Like Mercury, at certain periods it passes between the Sun and ourselves, and as itsilluminated hemisphere is of course turned toward the orb of day, we atthose times perceive only a sharp and very luminous crescent. At suchperiods Venus is entirely, so to say, against the Sun, and presents tous her greatest apparent dimension (Fig. 38). Sometimes, again, likeMercury, she passes immediately in front of the Sun, forming a perfectlyround black spot; this happened on December 8, 1874, and December 6, 1882; and will recur on June 7, 2004, and June 5, 2012. These transitshave been utilized in celestial geometry in measuring the distance ofthe Sun. You will readily divine that the distance of Venus varies considerablyaccording to her position in relation to the Earth: when she is betweenthe Sun and ourselves she is nearest to our world; but it is just atthose times that we see least of her surface, because she exhibits to usonly a slender crescent. Terrestrial astronomers are accordingly verybadly placed for the study of her physical constitution. The bestobservations can be made when she is situated to right or left of theSun, and shows us about half her illuminated disk--during the day forchoice, because at night there is too much irradiation from her dazzlinglight. These phases were discovered by Galileo, in 1610. His observations wereamong the first that confirmed the veracity of the system of Copernicus, affording an evident example of the movement of the planets round thesun. They are often visible to the unaided eye with good sight, eitherat dusk, or through light clouds. [Illustration: FIG. 38. --Venus at greatest brilliancy. ] Venus, surrounded by a highly dense and rarefied atmosphere, whichincreases the difficulties of observing her surface, might be called thetwin sister of the Earth, so similar are the dimensions of the twoworlds. But, strange as it may seem to the many admirers, who are readyto hail in her an abode of joy and happiness, it is most probable thatthis planet, attractive as she is at a distance, would be a lessdesirable habitation than our floating island. In fact, the atmosphereof Venus is perpetually covered with cloud, so that the weather theremust be always foggy. No definite geographical configuration can bediscovered on her, despite the hopes of the eighteenth-centuryastronomers. We are not even sure that she rotates upon herself, socontradictory are the observations, and so hard is it to distinguishanything clearly upon her surface. A single night of observationsuffices to show the rotation of Mars or of Jupiter; but the beautifulEvening Star remains obstinately veiled from our curiosity. Several astronomers, and not the least considerable, think that thetides produced by the Sun upon her seas, or globe in its state ofpristine fluidity, must have been strong enough to seize and fix her, asthe Earth did for the Moon, thus obliging her to present always the sameface to the Sun. Certain telescopic observations would even seem toconfirm this theoretical deduction from the calculations of celestialmechanics. The author ventures to disagree with this opinion, its apparentprobability notwithstanding, because he has invariably received acontrary impression from all his telescopic observations. He has quiterecently (spring of 1903) repeated these observations. Choosing aremarkably clear and perfectly calm atmosphere, he examined the splendidplanet several times with great attention in the field of the telescope. The right or eastern border (reversed image) was dulled by theatmosphere of Venus; this is the line of separation between day andnight. Beneath, at the extreme northern edge, he was attracted on eachoccasion by a small white patch, a little whiter than the rest of thesurface of the planet, surrounded by a light-gray penumbra, giving theexact effect of a polar snow, very analogous to that observed at thepoles of Mars. To the author this white spot on the boreal horn ofVenus does not appear to be due to an effect of contrast, as hassometimes been supposed. Now, if the globe of Venus has poles, it must turn upon itself. Unfortunately it has proved impossible to distinguish any sign upon thedisk, indicative of the direction and speed of its rotary movement, although these observations were made, with others, under excellentconditions. --Three o'clock in the afternoon, brilliant sun, sky clearblue, the planet but little removed from the meridian--at which time itis less dazzling than in the evening. There is merely the impression; but it is so definite as to prevent theauthor from adopting the new hypothesis, in virtue of which the planet, as it gravitates round the Sun, presents always the same hemisphere. If this hypothesis were a reality, Venus would certainly be a verypeculiar world. Eternal day on the one side; eternal night on the other. Maximum light and heat at the center of the hemisphere perpetuallyturned to the Sun; maximum cold and center of night at the antipodes. This icy hemisphere would possibly be uninhabitable, but the resourcesof Nature are so prodigious, and the law of Life is so imperious, sopersistent, under the most disadvantageous and deplorable terrestrialconditions, that it would be transcending our rights to declare animpossibility of existence, even in this eternal night. The currents ofthe atmosphere would no doubt suffice to set up perpetual changes oftemperature between the two hemispheres, in comparison with which ourtrade-winds would be the lightest of breezes. Yes, mystery still reigns upon this adjacent earth, and the mostpowerful instruments of the observatories of the whole world have beenunable to solve it. All we know is that the diameter, surface, volumeand mass of this planet, and its weight at the surface, do not differsensibly from those that characterize our own globe: that this planet issister to our own, and of the same order, hence probably formed of thesame elements. We further know that, as seen from Venus (Fig. 39), theEarth on which we live is a magnificent star, a double orb morebrilliant even than when viewed from Mercury. It is a dazzling orb offirst magnitude, accompanied by its moon, a star of the second and ahalf magnitude. And thus the worlds float on in space, distant symbols of hopes notrealized on any one of them, all at different stages of their degree ofevolution, representing an ever-growing progress in the sequence of theages. [Illustration: FIG. 39. --The Earth viewed from Venus. ] When we contemplate this radiant Venus, it is difficult, even if we cannot form any definite idea as to her actual state as regards habitation, to assume that she must be a dreary desert, and not, on the contrary, to hail in her a celestial land, differing more or less from our owndwelling-place, travailing with her sisters in the accomplishment of thegeneral plan of Nature. Such are the characteristic features of our celestial neighbor. Inquitting her, we reach the Earth, which comes immediately next her inorder of distance, 149 million kilometers (93, 000, 000 miles) from theSun, but as we shall devote an entire chapter to our own planet, we willnot halt at this point, but cross in one step the distance thatseparates Mars from Venus. Let us only remark in passing, that our planet is the largest of thefour spheres adjacent to the Sun. Here are their comparative diameters: The Earth = 1. In Kilometers. In Miles. Mercury 0. 373 4, 750 2, 946 Venus 0. 999 12, 730 7, 894 Earth 1. 000 12, 742 7, 926 Mars 0. 528 6, 728 4, 172 It will be seen that Venus is almost identical with the Earth. MARS Two hundred and twenty-six millions of kilometers (140, 000, 000 miles)from the Sun is the planet Mars, gravitating in an orbit exterior tothat which the Earth takes annually round the same center. Unfortunate Mars! What evil fairy presided at his birth? Fromantiquity, all curses seem to have fallen upon him. He is the god of warand of carnage, the protector of armies, the inspirer of hatred amongthe peoples, it is he who pours out the blood of Humanity ininternational hecatombs. Here, again, as in the case of Mercury andVenus, the appearance has originated the idea. Mars, in fact, burns likea drop of blood in the depths of the firmament, and it is this ruddycolor that inspired its name and attributes, just as the dazzlingwhiteness of Venus made her the goddess of love and beauty. Why, indeed, should the origins of mythology be sought elsewhere than in astronomy? While Humanity was attributing to the presumptive influence of Mars thedefects inherent in its own terrestrial nature, this world, unwitting ofour sorrows, pursued the celestial path marked out for it in space bydestiny. This planet is, as we have said, the first encountered after the Earth. Its orbit is very elongated, very eccentric. Mars accomplishes it in aperiod of 1 year, 321 days, 22 hours, _i. E. _, 1 year, 10 months, 21days, or 687 days. The velocity of its transit is 23 kilometers (14. 5miles) per second; that of the Earth is 30 (19 miles). Our planet, traveling through space at an average distance of 149 million kilometers(93, 000, 000 miles) from the central focus, is separated from Mars by anaverage distance of 76 million kilometers (47, 000, 000 miles); but as itsorbit is equally elliptic and elongated it follows that at certainepochs the two planets approach one another by something less than 60million kilometers (37, 000, 000 miles). These are the periods selectedfor making the best observations upon our neighbor of the ruddy rays. The oppositions of Mars arrive about every twenty-six months, but theperiods of its greatest proximity, when this planet approaches to within56 million kilometers (34, 700, 000 miles) of the Earth, occur only everyfifteen years. Mars is then passing perihelion, while our world is at aphelion (orgreatest distance from the Sun). At such epochs this globe presents tous an apparent diameter 63 times smaller than that of the Moon, _i. E. _, a telescope that magnifies 63 times would show him to us of the samemagnitude as our satellite viewed with the unaided eye, and aninstrument that magnified 630 times would show him ten times larger indiameter. In dimensions he differs considerably from our world, being almost halfthe size of the Earth. In diameter he measures only 6, 728 kilometers(4, 172 miles), and his circumference is 21, 125 kilometers (13, 000miles). His surface is only 29/100 of the terrestrial surface, and hisvolume only 15/100 of our own. This difference in volume causes Mars to be an earth in miniature. Whenwe study his aspects, his geography, his meteorology, we seem to see inspace a reduction of our own abode, with certain dissimilarities thatexcite our curiosity, and make him even more interesting to us. The Martian world weighs nine times and a half less than our own. If werepresent the weight of the Earth by 1, 000, that of Mars would berepresented by 105. His density is much less than our own; it is only7/10 that of the Earth. A man weighing 70 kilograms, transported to theadjacent globe, would weigh only 26 kilograms. The earliest telescopic observations revealed the existence of more orless accentuated markings upon the surface of Mars. The progress ofoptics, admitting of greater magnifications, exhibited the form of thesepatches more clearly, while the study of their motions enabled theastronomers to determine with remarkable precision the diurnal rotationof this planet. It occurs in 24 hours, 37 minutes, 23. 65 seconds. Dayand night are accordingly a little longer on Mars than on the Earth, butthe difference is obviously inconsiderable. The year of Mars consists of668 Martian days. The inclination of the axis of rotation of this globeupon the plane of its orbit is much the same as our own. Inconsequence, its seasons are analogous to ours in intensity, while twicethe length, the Martian year being almost equal to two of our years. Theintensity of the seasons is indeed more accentuated than upon the Earth, since the orbit of Mars is very elongated. But there, as here, are threequite distinct zones: the torrid, the temperate, and the glacial. By means of the telescope we can follow the variations of the Martianseasons, especially in what concerns the polar snows, which regularlyaggregate during the winter, and melt no less regularly during the heatof the summer. These snows are very easily observed, and stand outclearly with dazzling whiteness. The reader can judge of them by theaccompanying figure, which sums up the author's observations during oneof the recent oppositions of Mars (1900-1901). The size of the polar capdiminished from 4, 680 kilometers to 840. The solstice of the Martiansummer was on April 11th. The snows were still melting on July 6th. Sometimes they disappear almost entirely during the Martian month thatcorresponds to our month of August, as never happens with our polar ice. Hence, though this planet is farther away from the Sun than ourselves, it does not appear to be colder, or, at any rate, it is certain that thepolar snows are much less thick. On the other hand, there are hardly ever clouds on Mars; the Martianatmosphere is almost always limpid, and one can say that fine weather isthe chronic state of the planet. At times, light fogs or a little vaporwill appear in certain regions, but they are soon dissipated, and thesky clears up again. [Illustration: FIG. 40. --Diminution of the polar snows of Mars duringthe summer. ] Since the invention of the telescope, a considerable number of drawingshave been made, depicting Mars under every aspect, and the agreementbetween these numerous observations gives us a sufficient acquaintancewith the planet to admit of our indicating the characteristic featuresof its geography, and of drawing out _areographic_ maps (_Ares_, Mars). Its appearance can be judged of from the two drawings here reproduced, as made (February, 1901) at the Observatory of Juvisy, and from thegeneral chart drawn from the total sum of observations (Figs. 41, 42 and43). It will be seen at the first glance that the geography of Mars is verydifferent from that of our own globe: while three-quarters of the Earthare covered with the liquid element, Mars seems to be more evenlydivided, and must indeed have rather more land than water. We find noimmense oceans surrounding the continents, and separating them likeislands; on the contrary, the seas are reduced to long gulfs compressedbetween the shores, like the Mediterranean for example, nor is it evencertain that these gray spots do all represent true seas. It has beenagreed to term _sea_ the parts that are lightly tinged with green, andto give the name of _continent_ to the spots colored yellow. That is thehue of the Martian soil, due either to the soil itself, which wouldresemble that of the Sahara, or, to take a less arid region, that seenon the line between Marseilles and Nice, in the vicinity of theEsterels; or perhaps to some peculiar vegetation. During ascents in aballoon, the author has often remarked that the hue of the ripe corn, with the Sun shining on it, is precisely that presented to us by thecontinents of Mars in the best hours for observation. [Illustration: FIG. 41. --Telescopic aspect of the planet Mars (Feb. , 1901). ] As to the "seas, " it is pretty certain that there must be water, orsome kind of liquid, deriving above all from the melting of the polarsnows in spring and summer; but it may possibly be in conjunction withsome vegetation, aquatic plants, or perhaps vast meadows, which appearto us from here to be the more considerable in proportion as the waterthat nourishes them has been more abundant. [Illustration: FIG. 42. --Telescopic aspect of the planet Mars (Feb. , 1901). ] Mars, like our globe, is surrounded with a protective atmosphere, whichretains the rays of the Sun, and must preserve a medium temperaturefavorable to the conservation of life upon the surface of the planet. But the circulation of the water, so important to terrestrial life, whether animal or vegetable, which is effected upon our planet by theevaporation of the seas, clouds, winds, rains, wells, rivers andstreams, comes about quite differently on Mars; for, as was remarkedabove, it is rarely that any clouds are observed there. Instead of beingvertical, as here, this circulation is horizontal: the water coming fromthe source of the polar snows finds its way into the canals and seas, and returns to be condensed at the poles by a light drift of invisiblevapors directed from the equator to the poles. There is never any rain. We have spoken of _canals_. One of the great puzzles of the Martianworld is incontestably the appearance of straight lines that furrow itssurface in all directions, and seem to connect the seas. M. Schiaparelli, the distinguished Director of the Observatory of Milan, who discovered them in 1877, called them canals, without, however, postulating anything as to their real nature. Are they indeed canals?These straight lines, measuring sometimes 600 kilometers (372 miles) inlength, and more than 100 kilometers (62 miles) in breadth, have muchthe same hue as the seas on which they open. For a quarter of a centurythey have been surveyed by the greater number of our observers. But itmust be confessed that, even with the best instruments, we only approachMars at a distance of 60, 000 kilometers (37, 200 miles), which is still alittle far off, and we may be sure that we do not distinguish the truedetails of the surface. [11] These details at the limits of visibilityproduce the appearance of canals to our eyes. They may possibly be linesof lakes, or oases. The future will no doubt clear up this mystery forus. [Illustration: FIG. 43. --Chart of Mars. ] As to the inhabitants of Mars, this world is in a situation asfavorable as our Earth for habitation, and it would be difficult todiscover any reason for perpetual sterility there. It appears to us, onthe contrary, by its rapid and frequent variations of aspect, to be avery living world. Its atmosphere, which is always clear, has not thedensity of our own, and resembles that of the highest mountains. Theconditions of existence there vary from ours, and appear to be moredelicate, more ethereal. There as here, day succeeds to night, spring softens the rigors ofwinter; the seasons unfold, less disparate than our own, of which wehave such frequent reason to complain. The sky is perpetually clear. There are never tempests, hurricanes, nor cyclones, the wind never getsup any force there, on account of the rarity of the atmosphere, and thelow intensity of weight. Differing from ours, this world may well be a more congenialhabitation. It is more ancient than the Earth, smaller, less massive. Ithas run more quickly through the phases of its evolution. Its astrallife is more advanced, and its Humanity should be superior to our own, just as our successors a million years hence, for example, will be lesscoarse and barbarous than we are at present: the law of progress governsall the worlds, and, moreover, the physical constitution of the planetMars is less dense than our own. There is no need to despair of entering some day into communication withthese unknown beings. The luminous points that have been observed are nosignals, but high summits or light clouds illuminated by the rising orsetting sun. But the idea of communication with them in the future is nomore audacious and no less scientific than the invention of spectralanalysis, X-rays, or wireless telegraphy. We may suppose that the study of astronomy is further advanced in Marsthan on the Earth, because humanity itself has advanced further, andbecause the starry sky is far finer there, far easier to study, owing tothe limpidity of its pure, clear atmosphere. Two small moons (hardly larger than the city of Paris) revolve rapidlyround Mars; they are called Phobos and Deimos. The former, at a distanceof 6, 000 kilometers (3, 730 miles) from the surface, accomplishes itsrevolution rapidly, in seven hours, thirty-nine minutes, and thus makesthe entire circle of the Heavens three times a day. The secondgravitates at 20, 000 kilometers (12, 400 miles), and turns round itscenter of attraction in thirty hours and eighteen minutes. These twosatellites were discovered by Mr. Hall, at the University of Washington, in the month of August, 1877. * * * * * Among the finest and most interesting of the celestial phenomena admiredby the Martians, at certain epochs of the year, --now at night when theSun has plunged into his fiery bed, now in the morning, a little beforethe aurora, --is a magnificent star of first magnitude, never far removedfrom the orb of day, which presents to them the same aspects as doesVenus to ourselves. This splendid orb, which has doubtless received themost flattering names from those who contemplate it, this radiant starof a beautiful greenish blue, courses in space accompanied by a littlesatellite, sparkling like some splendid diamond, after sunset, in theclear sky of Mars. This superb orb is the Earth, and the little staraccompanying it is the Moon. [Illustration: FIG. 44. --The Earth viewed from Mars. ] Yes, to the Martians our Earth is a star of the morning and evening;doubtless they have determined her phases. Many a vow, and many a hopemust have been wafted toward her, more than one broken heart must havepermitted its unrealized dreams to wander forth to our planet as to anabode of happiness where all who have suffered in their native worldmight find a haven. But our planet, alas! is not as perfect as theyimagine. We must not dally upon Mars, but hasten our celestial excursion towardJupiter. CHAPTER VI THE PLANETS _B. _--JUPITER, SATURN, URANUS, NEPTUNE. Before we attack the giant world of our system, we must halt for a fewmoments upon the minor planets which circulate between the orbit of Marsand that of Jupiter. These minute asters, little worlds, the largest ofwhich measures scarcely more than 100 kilometers (62 miles) in diameter, are fragments of cosmic matter that once belonged to a vast ring, formedat the time when the solar system was only an immense nebula; and which, instead of condensing into a single globe coursing between Mars andJupiter, split up into a considerable quantity of particles constitutingat the present time the curious and highly interesting Republic of theAsteroids. These lilliputian worlds at first received the names of the morecelebrated of the minor mythological divinities--Ceres, Pallas, Juno, Vesta, etc. , but as they rapidly increased in number, it was foundnecessary to call them by modern, terrestrial names, and more than onedaughter of Eve, the Egeria of some astronomer, now has her nameinscribed in the Heavens. The first minor planet was discovered on thefirst day of the nineteenth century, January 1, 1801, by Piazzi, astronomer at Palermo. While he was observing the small stars in theconstellation of the Bull beneath the clear Sicilian skies, this famousastronomer noticed one that he had never seen before. The next night, directing his telescope to the same part of the Heavens, he perceived that the fair unknown had moved her station, and theobservations of the following days left him no doubt as to the nature ofthe visitor: she was a planet, a wandering star among theconstellations, revolving round the Sun. This newcomer was registeredunder the name of Ceres. Since that epoch several hundreds of them have been discovered, occupying a zone that extends over a space of more than 400 millionkilometers (249, 000, 000 miles). These celestial globules are invisibleto the naked eye, but no year passes without new and numerous recruitsbeing added to the already important catalogue of these minute asters bythe patient observers of the Heavens. To-day, they are most frequentlydiscovered by the photographic method of following the displacement ofthe tiny moving points upon an exposed sensitive plate. JUPITER And now let us bow respectfully before Jupiter, the giant of the worlds. This glorious planet is indeed King of the Solar System. While Mercury measures only 4, 750 kilometers (2, 946 miles) in diameter, and Mars 6, 728 kilometers (4, 172), Jupiter is no less than 140, 920kilometers (87, 400 miles) in breadth; that is to say, eleven timeslarger than the Earth. He is 442, 500 kilometers (274, 357 miles) incircumference. In volume he is equivalent to 1, 279 terrestrial globes; hence he is onlya million times smaller than the Sun. The previously described planetsof our system, Mercury, Venus, the Earth, and Mars combined, would formonly an insignificant mass in comparison with this colossus. A hundredand twenty-six Earths joined into one group would present a surfacewhose extent would still not be quite as vast as the superficies of thistitanic world. This immense globe weighs 310 times more than that whichwe inhabit. Its density is only the quarter of our own; but weight istwice and a half times as great there as here. The constituents ofthings and beings are thus composed of materials lighter than those uponthe Earth; but, as the planet exerts a force of attraction twice and ahalf times as powerful, they are in reality heavier and weigh more. Agraceful maiden weighing fifty kilograms would if transported to Jupiterimmediately be included in the imposing society of the "Hundred Kilos. " Jupiter rotates upon himself with prodigious rapidity. He accomplisheshis diurnal revolution in less than ten hours! There the day lasts halfas long as here, and while we reckoned fifteen days upon our calendar, the Jovian would count thirty-six. As Jupiter's year equals nearlytwelve of ours, the almanac of that planet would contain 10, 455 days!Obviously, our pretty little pocket calendars would never serve toenumerate all the dates in this vast world. This splendid globe courses in space at a distance of 775, 000, 000kilometers (480, 500, 000 miles) from the Sun. Hence it is five times(5. 2) as remote from the orb of day as our Earth, and its orbit is fivetimes vaster than our own. At that distance the Sun subtends a diameterfive times smaller than that which we see, and its surface istwenty-seven times less extensive; accordingly this planetary abodereceives on an average twenty-seven times less light and heat than weobtain. In the telescope Jupiter presents an aspect analogous to that likely tobe exhibited by a world covered with clouds, and enveloped in densevapors (Fig. 45). It is, in fact, the seat of formidable perturbations, of strangerevolutions by which it is perpetually convulsed, for although of moreancient formation than the Earth, this celestial giant has not yetarrived at the stable condition of our dwelling-place. Owing to itsconsiderable volume, this globe has probably preserved its originalheat, revolving in space as an obscure Sun, but perhaps still burning. In it we see what our own planet must have been in its primordial epoch, in the pristine times of terrestrial genesis. [Illustration: FIG. 45. --Telescopic aspect of Jupiter. ] Since its orbital revolution occupies nearly twelve years, Jupitercomes back into opposition with the Sun every 399 days, _i. E. _, 1 year, 34 days, that is with one month and four days' delay each year. At theseperiods it is located at the extremity of a straight line which, passingby the Earth, is prolonged to the Sun. These are the epochs to beselected for observation. It shines then, all night, like some dazzlingstar of the first magnitude, of excessive whiteness: nor can it beconfounded either with Venus, more luminous still (for she is nevervisible at midnight, in the full South, but is South-west in theevening, or South-east in the morning), nor with Mars, whose fires areruddy. In the telescope, the immense planet presents a superb disk that anenlargement of forty times shows us to be the same size to allappearance as that of the Moon seen with the unaided eye. Its shape isnot absolutely spherical, but spheroid--that is, flattened at the poles. The flattening is 1/17. We know that the Earth's axis dips a certain quantity on the plane ofher orbit, and that it is this inclination that produces the seasons. Now it is not the same for Jupiter. His axis of rotation remains almostvertical throughout the course of his year, and results in the completeabsence of climates and seasons. There is neither glacial zone, nortropic zone; the position of Jupiter is eternally that of the Earth atthe season of the equinox, and the vast world enjoys, as it were, perpetual spring. It knows neither the hoar-frost nor the snows ofwinter. The heat received from the Sun diminishes gradually from theequator to the poles without abrupt transitions, and the duration of dayand night is equal there throughout the entire year, under everylatitude. A privileged world, indeed! It is surrounded by a very dense, thick atmosphere, which undergoes moreextensive variations than could be produced by the Sun at such adistance. Spectral analysis detects a large amount of water-vapor, showing that this planet still possesses a very considerable quantity ofintrinsic heat. Most conspicuous upon this globe are the larger or smaller bands ormarkings (gray and white, sometimes tinted yellow, or of a maroon orchocolate hue) by which its surface is streaked, particularly in thevicinity of the equator. These different belts vary, and are constantlymodified, either in form or color. Sometimes, they are irregular, andcut up; at others they are interspersed with more or less brilliantpatches. These patches are not affixed to the surface of the globe, likethe seas and continents of the Earth; nor do they circulate round theplanet like the satellites, in more or less elongated and regularrevolutions, but are relatively mobile, like our clouds in theatmosphere, while observation of their motion does not give the exactperiod of the rotation of Jupiter. Some only appear upon the agitateddisk to vanish very quickly; others subsist for a considerable period. One has been observed for over a quarter of a century, and appears to bealmost immobile upon this colossal globe. This spot, which was red atits first appearance, is now pale and ghostly. It is oval (_vide_ Fig. 45) and measures 42, 000 kilometers (26, 040 miles) in length by 15, 000kilometers (9, 300 miles) in width. Hence it is about four times as longas the diameter of our Earth; that is, relatively to the size ofJupiter, as are the dimensions of Australia in proportion to our globe. The discussion of a larger number of observations leads us to see in ita sort of continent in the making, a scoria recently ejected from themobile and still liquid and heated surface of the giant Jupiter. Thepatch, however, oscillates perceptibly, and appears to be a floatingisland. We must add that this vast world, like the Sun, _does not rotate all inone period_. Eight different currents can be perceived upon its surface. The most rapid is that of the equatorial zone, which accomplishes itsrevolution in 9 hours, 50 minutes, 29 seconds. A point situated on theequator is therefore carried forward at a speed of 12, 500 meters (7miles) per second, and it is this giddy velocity of Jupiter that hasproduced the flattening of the poles. From the equator to the poles, theswiftness of the currents diminishes irregularly, and the differenceamounts to about five minutes between the movement of the equatorialstream, and that of the northern and southern currents. But what is morecurious still is that the velocity of one and the same stream is subjectto certain fluctuations; thus, in the last quarter of a century, thespeed of the equatorial current has progressively diminished. In 1879, the velocity was 9 hours, 49 minutes, 59 seconds, and now it is, as wehave already seen, 9 hours, 50 minutes, 29 seconds, which represents asubstantial reduction. The rotation of the red patch, at 25 degrees ofthe southern latitude, is effected in 9 hours, 55 minutes, 40 seconds. We are confronted with a strange and mysterious world. It is the worldof the future. This giant gravitates in space accompanied by a suite of fivesatellites. These are: Names. Distance from surface of Jupiter. Time of revolution. Kilometers. Miles. Days. Hours. 5. 200, 000 124, 000 11 1. Io 430, 000 266, 000 1 18 2. Europa 682, 000 422, 840 3 13 3. Ganymede 1, 088, 000 674, 560 7 4 4. Callisto 1, 914, 000 1, 186, 680 16 16 The four principal satellites of Jupiter were discovered at the sametime, on the same evenings (January 7 and 8, 1610), by the twoastronomers who were pointing their telescopes at Jupiter: Galileo inItaly, and Simon Marius in Germany. On September 9, 1892, Mr. Barnard, astronomer of the Lick Observatory, California, discovered a new satellite, extremely minute, and very nearthe enormous planet. It has so far received no name, and is known as thefifth, although the four principal are numbered in the order of theirdistances. [Illustration: FIG. 46. --Jupiter and his four principal satellites. ] The four classical satellites are visible in the smallest instruments(Fig. 46): the third is the most voluminous. Such is the splendid system of the mighty Jupiter. Once, doubtless, thisfine planet illuminated the troop of worlds that derived their treasureof vitality from him with his intrinsic light: to-day, however, thesemoons in their turn shed upon the extinct central globe the pale softlight which they receive from our solar focus, illuminating the briefJovian nights (which last less than five hours, on account of thetwilight) with their variable brilliancy. At the distance of the first satellite, Jupiter exhibits a disk_fourteen hundred times_ vaster than that of the Full Moon! What adazzling spectacle, what a fairy scene must the enormous star afford tothe inhabitants of that tiny world! And what a shabby figure must ourEarth and Moon present in the face of such a body, a real miniature ofthe great solar system! Our ancestors were well inspired when they attributed the sovereignty ofOlympus to this majestic planet. His brilliancy corresponds with hisreal grandeur. His dominion in the midnight Heavens is unique. Hereagain, as for Venus, Mars, and Mercury, astronomy has created the legendof the fables of mythology. Let us repeat in conclusion that our Earth becomes practically invisiblefor the inhabitants of the other worlds beyond the distance of Jupiter. SATURN Turn back now for a moment to the plan of the Solar System. We had to cross 775 million kilometers (480, 000, 000 miles) when we leftthe Sun, in order to reach the immense orb of Jupiter, which courses inspace at 626 million kilometers (388, 000, 000 miles) from the terrestrialorbit. From Jupiter we had to traverse a distance of 646 millionkilometers (400, 000, 000 miles) in order to reach the marvelous system ofSaturn, where our eyes and thoughts must next alight. Son of Uranus and Vesta, Saturn was the God of Time and Fate. He isgenerally represented as an aged man bearing a scythe. His mythologicalcharacter is only the expression of his celestial aspect, as we haveseen for the brilliant Jupiter, for the pale Venus, the ruddy Mars, andthe agile Mercury. The revolution of Saturn is the slowest of any amongthe planets known to the ancients. It takes almost thirty years for itsaccomplishment, and at that distance the Saturnian world, though itstill shines with the brilliancy of a star of the first magnitude, exhibits to our eyes a pale and leaden hue. Here is, indeed, the god ofTime, with slow and almost funereal gait. Poor Saturn won no favor with the poets and astrologers. He bore thehorrid reputation of being the inexhaustible source of misfortune andevil fates, --whereof he is wholly innocent, troubling himself not at allwith our world nor its inhabitants. This world travels in the vastness of the Heavens at a distance of 1, 421million kilometers (881, 000, 000 miles) from the Sun. Hence it is tentimes farther from the orb of day than the Earth, though stillilluminated and governed by the Sun-God. Its gigantic orbit is ten timeslarger than our own. Its revolution round the Sun is accomplished in 10, 759 days, _i. E. _, 29years, 167 days, and as this strange planet rotates upon itself withgreat rapidity in 10 hours, 15 minutes, its year comprises no less than25, 217 days. What a calendar! The Saturnians must needs have aprodigious memory not to get hopelessly involved in this interminablenumber of days. A curious world, where each year stands for almostthirty of our own, and where the day is more than half as short again asours. But we shall presently find other and more extraordinarydifferences on this planet. In the first place it is nearly nine and a half times larger than ourworld. It is a globe, not spherical, but spheroidal, and the flatteningof its poles, which is one-tenth, exceeds that of all the other planets, even Jupiter. It follows that its equatorial diameter is 112, 500kilometers (69, 750 miles), while its polar diameter measures only110, 000 kilometers (68, 200). In volume, Saturn is 719 times larger than the Earth, but its density isonly 128/1000 of our own; _i. E. _, the materials of which it is composedare much less heavy, so that it weighs only 92 times more than ourEarth. Its surface is 85 times vaster than that of the Earth, noinsignificant proportion. [Illustration: FIG. 47. --Saturn. ] The dipping of Saturn's axis of rotation is much the same as our own. Hence we conclude that the seasons of this planet are analogous to oursin relative intensity. Only upon this far-off world each season lastsfor seven years. At the distance at which it gravitates in space, theheat and light which it receives from the Sun are 90 times less activethan such as reach our selves; but it apparently possesses an atmosphereof great density, which may be constituted so that the heat ispreserved, and the planet maintained in a calorific condition but littleinferior to our own. In the telescope, the disk of Saturn exhibits large belts that recallthose of Jupiter, though they are broader and less accentuated (Fig. 47). There are doubtless zones of clouds or rapid currents circulatingin the atmosphere. Spots are also visible whose displacement assists incalculating the diurnal motions of this globe. The most extraordinary characteristic of this strange world is, however, the existence of a vast _ring_, which is almost flat and very large, andentirely envelops the body of the planet. It is suspended in theSaturnian sky, like a gigantic triumphal arch, at a height of some20, 000 kilometers (12, 400 miles) above the equator. This splendid archis circular, like an immense crown illuminated by the Sun. From here weonly see it obliquely, and it appears to us elliptical; a part of thering seems to pass in front of Saturn, and its shadow is visible on theplanet, while the opposite part passes behind. This ring, which measures 284, 000 kilometers (176, 080 miles) indiameter, and less than 100 kilometers (62 miles) in breadth, is dividedinto three distinct zones: the exterior is less luminous than thecenter, which is always brighter than the planet itself; the interior isvery dark, and spreads out like a dusky and faintly transparent veil, through which Saturn can be distinguished. What is the nature of these vast concentric circles that surround theplanet with a luminous halo? They are composed of an innumerable numberof particles, of a quantity of cosmic fragments, which are swept off ina rapid revolution, and gravitate round the planet at variable speed anddistance. The nearer particles must accomplish their revolution in 5hours, 50 minutes, and the most distant in about 12 hours, 5 minutes, toprevent them from being merged in the surface of Saturn: their owncentrifugal force sustains them in space. [Illustration: FIG. 48. Varying perspective of Saturn's Rings, as seenfrom the Earth. ] With a good glass the effect of these rings is most striking, and onecan not refrain from emotion on contemplating this marvel, whereby oneof the brothers of our terrestrial country is crowned with a goldendiadem. Its aspects vary with its perspective relative to the Earth, asmay be seen from the subjoined figure (Fig. 48). We must not quit the Saturnian province without mentioning the eightsatellites that form his splendid suite: Names. Distance from the planet. Time of revolution. Kilometers. Miles. Days. Hours. Minutes. 1. Mimas 207, 000 128, 340 22 37 2. Enceladus 257, 600 159, 712 1 8 53 3. Tethys 328, 800 203, 856 1 21 18 4. Dione 421, 200 261, 144 2 17 41 5. Rhea 588, 400 364, 808 4 12 25 6. Titan 1, 364, 000 845, 680 15 22 41 7. Hyperion 1, 650, 000 1, 023, 000 21 6 39 8. Japhet 3, 964, 000 2, 457, 680 79 7 54 Here is a marvelous system, with, what is more, eight different kinds ofmonths for the inhabitants of Saturn; eight moons with constantlyvarying phases juggling above the rings! Now we shall cross at a bound the 1, 400 million kilometers (868, 000, 000miles) that separate us from the last station but one of the immensesolar system. URANUS On March 13, 1781, William Herschel, a Hanoverian astronomer who hademigrated to England, having abandoned the study of music to devotehimself to the sublime science of the Heavens, was observing the vastfields with their constellations of golden stars, when he perceived aluminous point that appeared to him to exceed that of the othercelestial luminaries in diameter. He replaced the magnification of histelescope by more powerful eye-pieces, and found that the apparentdiameter of the orb increased proportionately with the amplification ofthe power, which does not happen in the case of stars at infinitedistance. His observations on the following evenings enabled him to notethe slow and imperceptible movement of this star upon the celestialsphere, and left him in no further doubt: there was no star, but somemuch nearer orb, in all probability a comet, for the great astronomerdared not predict the discovery of a new planet. And it was thus, underthe name of cometary orb, that the seventh child of the Sun wasannounced. The astronomers sought to determine the motions of the newarrival, to discover for it an elliptical orbit such as most cometshave. But their efforts were vain, and after several months' study theconclusion was reached that here was a new planet, throwing back thelimits of the solar system to a point far beyond that of the Saturnianfrontier, as admitted from antiquity. This new world received the name of Uranus, father of Saturn, hisnearest neighbor in the solar empire. Uranus shines in the firmament asa small star of sixth magnitude, invisible to the unaided eye fornormal sight, at a distance of 2, 831, 000, 000 kilometers (1, 755, 000, 000miles) from the Sun. Smaller than Jupiter and Saturn, this planet is yetlarger than Mercury, Venus, Mars, and the Earth together, thuspresenting proportions that claim our respect and admiration. His diameter may be taken at about 55, 000 kilometers (34, 200 miles), that is, rather more than four times the breadth of the terrestrialdiameter. Sixty-nine times more voluminous than the Earth, and seventeentimes more extensive in surface, this new world is much less than ourown in density. The matter of which it is composed is nearly five timeslighter than that of our globe. Spectral analysis shows that this distant planet is surrounded with anatmosphere very different from that which we breathe, enclosing gasesthat do not exist in ours. The Uranian globe courses over the fields of infinity in a vast orbitseventeen times larger than our own, and its revolution lasts 36, 688days, _i. E. _, 84 years, 8 days. It travels slowly and sadly under thepale and languishing rays of the Sun, which sends it nearly threehundred times less of light and heat than we receive. At this distancethe solar disk would present a diameter seventeen times smaller thanthat which we admire, and a surface three hundred times less vast. Adull world indeed! And what an interminable year! The idle people whoare in the habit of being bored must find time even longer upon Uranusthan upon our little Earth, where the days pass so rapidly. And ifmatters are arranged there as here, a babe of a year old, beginning tobabble in its nurse's arms, would already have lived as long as an oldman of eighty-four in this world. But what most seriously complicates the Calendar of the Uranians is thefact that the four moons which accompany the planet accomplish theirrevolution in four different kinds of months, in two, four, eight, andthirteen days, as is shown in the following table: Distance from the planet. Time of revolution. Kilometers. Miles. Days. Hours. Minutes. 1. Ariel 196, 000 121, 520 2 12 29 2. Umbriel 276, 000 171, 120 4 3 27 3. Titania 450, 000 279, 000 8 16 56 4. Oberon 600, 000 372, 000 13 11 7 The most curious fact is that these satellites do not rotate like thoseof the other planets. While the moons of the Earth, Mars, Jupiter, andSaturn accomplish their revolution from east to west, the satellites ofUranus rotate in a plane almost perpendicular to the ecliptic, and it isdoubtless the same for the rotation of the planet. If we had to quit the Earth, and fixate ourselves upon another world, we should prefer Mars to Uranus, where everything must be so differentfrom terrestrial arrangements? But who knows? Perhaps, after all, thisplanet might afford us some agreeable surprises. _Il ne faut jurer derien. _ NEPTUNE And here we reach the frontier of the Solar System, as actually known tous. In landing on the world of Neptune, which circles through theHeavens in eternal twilight at a distance of more than four milliardkilometers (2, 480, 000, 000 miles) from the common center of attraction ofthe planetary orbs, we once again admire the prodigies of science. Uranus was discovered with the telescope, Neptune by calculation. Inaddition to the solar influence, the worlds exert a mutual attractionupon each other that slightly deranges the harmony ordered by the Sun. The stronger act upon the weaker, and the colossal Jupiter alone causesmany of the perturbations in our great solar family. Now during regularobservations of the position of Uranus in space, some inexplicableirregularities were soon perceived. The astronomers having full faith inthe universality of the law of attraction, could not do otherwise thanattribute these irregularities to the influence of some unknown planetsituated even farther off. But at what distance? A very simple proportion, known as Bode's law, has been observed, whichindicates approximately the relative distances of the planets from theSun. It is as follows: Starting from 0, write the number 3, and doublesuccessively, 0 3 6 12 24 48 96 192 384. Then, add the number 4 to each of the preceding figures, which gives thefollowing series: 4 7 10 16 28 52 100 196 388. Now it is a very curious fact that if the distance between the Earth andthe Sun be represented by 10, the figure 4 represents the orbit ofMercury, 7 that of Venus, 16 of Mars; the figure 28 stands for themedium distance of the minor planets; the distances of Jupiter, Saturn, and Uranus agree with 52, 100, and 196. The immortal French mathematician Le Verrier, who pursued the solutionof the Uranian problem, supposed naturally that the disturbing planetmust be at the distance of 388, and made his calculations accordingly. Its direction in the Heavens was indicated by the form of thedisturbances; the orbit of Uranus bulging, as it were, on the side ofthe disturbing factor. On August 31, 1846, Le Verrier announced the position of theultra-Uranian planet, and on September 23d following, a Germanastronomer, Galle, at the Observatory of Berlin, who had just receivedthis intelligence, pointed his telescope toward the quarter of theHeavens designated, and, in fact, attested the presence of the new orb. Without quitting his study table, Le Verrier, by the sole use ofmathematics, had detected, and, as it were, touched at pen's point themysterious stranger. Only, it is proved by observation and calculation that it is less remotethan was expected from the preceding law, for it gravitates at adistance of 300, given that from the Earth to the Sun as 10. This planet was called Neptune, god of the seas, son of Saturn, brotherof Jupiter. The name is well chosen, since the King of the Ocean livesin darkness in the depths of the sea, and Le Verrier's orb is alsoplunged in the semi-obscurity of the depths of the celestial element. But it was primarily selected to do justice to an English astronomer, Adams, who had simultaneously made the same calculations as Le Verrier, and obtained the same results--without publishing them. His workremained in the records of the Greenwich Observatory. The English command the seas, and wherever they dip their finger intothe water and find it salt, they feel themselves "at home, " and knowthat "Neptune's trident is the scepter of the world, " hence thiscomplimentary nomenclature. Neptune is separated by a distance of four milliards, four hundredmillion kilometers from the solar center. At such a distance, thirty times greater than that which exists betweenthe Sun and our world, Neptune receives nine hundred times less lightand heat than ourselves; _i. E. _, Spitzbergen and the polar regions ofour globe are furnaces compared with what must be the Neptuniantemperature. Absolutely invisible to the unaided eye, this worldpresents in the telescope the aspect of a star of the eighth magnitude. With powerful magnifications it is possible to measure its disk, whichappears to be slightly tinged with blue. Its diameter is four timeslarger than our own, and measures about 48, 000 kilometers (29, 900miles), its surface is sixteen times vaster than that of the Earth, andto attain its volume we should have to put together fifty-five globessimilar to our own. Weight at its surface must be about the same ashere, but its medium density is only 1/3 that of the Earth. It gravitates slowly, dragging itself along an orbit thirty times vasterthan that of our globe, and its revolution takes 164 years, 281 days, _i. E. _, 164 years, 9 months. A single year of Neptune thus coversseveral generations of terrestrial life. Existence must, indeed, bestrange in that tortoise-footed world! While in their rotation period, Mercury accomplishes 47 kilometers(29-3/8 miles) per second, and the Earth 29-1/2 (18-1/8 miles), Neptunerolls along his immense orbit at a rate of only 5-1/2 kilometers (about3-1/4 miles) per second. The vast distance that separates us prevents our distinguishing anydetails of his surface, but spectral analysis reveals the presence of anabsorbent atmosphere in which are gases unknown to the air of ourplanet, and of which the chemical composition resembles that of theatmosphere of Uranus. One satellite has been discovered for Neptune. It has a considerableinclination, and rotates from east to west. * * * * * And here we have reached the goal of our interplanetary journey. Aftervisiting the vast provinces of the solar republic, we feel yet greateradmiration and gratitude toward the luminary that governs, warms, andilluminates the worlds of his system. In conclusion, let us again insist that the Earth, --a splendid orb asviewed from Mercury, Venus, and Mars, --begins to disappear from Jupiter, where she becomes no more than a tiny spark oscillating from side toside of the Sun, and occasionally passing in front of him as a smallblack dot. From Saturn the visibility of our planet is even morereduced. As to Uranus and Neptune, we are invisible there, at least toeyes constructed like our own. We do not possess in the Universe theimportance with which we would endow ourselves. Neptune up to the present guards the portals of our celestial system; wewill leave him to watch over the distant frontier; but before returningto the Earth, we must glance at certain eccentric orbs, at the mad, capricious comets, which imprint their airy flight upon the realms ofspace. CHAPTER VII THE COMETS SHOOTING STARS, BOLIDES, URANOLITHS OR METEORIC STONES What marvels have been reviewed by our dazzled eyes since the outset ofthese discussions! We first surveyed the magnificent host of stars thatpeople the vast firmament of Heaven; next we admired and wondered atsuns very differently constituted from our own; then returning from thedepths of space, crossing at a bound the abyss that separates us fromthese mysterious luminaries, the distant torches of our somber night, terrible suns of infinity, we landed on our own beloved orb, the superband brilliant day-star. Thence we visited his celestial family, hissystem, in which our Earth is a floating island. But the journey wouldbe incomplete if we omitted certain more or less vagabond orbs, thatoccasionally approach the Sun and Earth, some of which may even collidewith us upon their celestial path. These are in the first place thecomets, then the shooting stars, the fire-balls, and meteorites. Glittering, swift-footed heralds of Immensity, these comets with goldenwings glide lightly through Space, shedding a momentary illumination bytheir presence. Whence come they? Whither are they bound? What problems they propound to us, when, as in some beautiful display ofpyrotechnics, the arch of Heaven is illuminated with their fantasticlight! But first of all--what is a Comet? If instead of living in these days of the telescope, of spectrumanalysis, and of astral photography, we were anterior to Galileo, and tothe liberation of the human spirit by Astronomy, we should reply thatthe comet is an object of terror, a dangerous menace that appears tomortals in the purity of the immaculate Heavens, to announce the mostfatal misfortunes to the inhabitants of our planet. Is a comet visiblein the Heavens? The reigning prince may make his testament and prepareto die. Another apparition in the firmament bodes war, famine, theadvent of grievous pestilence. The astrologers had an open field, andtheir fertile imagination might hazard every possible conjecture, seeingthat misfortunes, great or small, are not altogether rare in thissublunar world. How many intellects, and those not the most vulgar, from antiquity tothe middle of the last century cursed the apparition of these hirsutestars, which brought desolation to the heart of man, and poured theirfatal effluvia upon the head of poor Humanity. The history of thesuperstitions and fears that they inspired of old would furnish matterfor the most thrilling of romances. But, on the other hand, the volumewould be little flattering to the common-sense of our ancestors. Despitethe respect we owe our forefathers, let us recall for a moment theprejudices attaching to the most famous comets whose passage, asobserved from the Earth, has been preserved to us in history. [Illustration: FIG. 49. --Great Comet of 1858. ] * * * * * Without going back to the Deluge, we note that the Romans established arelation between the Great Comet of 43 B. C. And the death of Cæsar, whohad been assassinated a few months previously. It was, they asserted, the soul of their great Captain, transported to Heaven to reign in theempyrean after ruling here below. Were not the Emperors Lords of bothEarth and Heaven? We must in justice recognize that certain more independent spiritsemancipated themselves from these superstitions, and we may cite thereply of Vespasian to his friends, who were alarmed at the evil presageof a flaming comet: "Fear nothing, " he said, "this bearded star concernsme not; rather should it threaten my neighbor the King of the Parthians, since he is hairy and I am bald. " In the year 837 one of these mysterious visitants appeared in theHeavens. It was in the reign of Lewis the Debonair. Directly the Kingperceived the comet, he sent for an astrologer, and asked what he was toconclude from the apparition. As the answers were unsatisfactory hetried to avert the augury by prayers to Heaven, by ordaining a generalfast to all his Court, and by building churches. Notwithstanding, hedied three years later, and the historians profited by this slendercoincidence to set up a correlation between the fatal star and the deathof the Sovereign. This comet, famous in history, is no other than thatof Halley, in one of its appearances. This comet returned to explore the realms near the Sun in 1066, at themoment when William of Normandy was undertaking the Conquest of England, and was misguided enough to go across and reign in London, instead ofstaying at home and annexing England, thus by his action founding theeverlasting rivalry between France and this island. A beneficialinfluence was attributed to the comet in the Battle of Hastings. A few centuries later it again came into sight from the Earth, in 1456, three years after the capture of Constantinople by the Turks. Feelingran high in Europe, and this celestial omen was taken for a proof of theanger of the Almighty. The moment was decisive; the Christians had to berescued from a struggle in which they were being worsted. At thisconjuncture, Pope Calixtus resuscitated a prayer that had fallen intodisuse, the _Angelus_; and ordered that the bells of the churches shouldbe rung each day at noon, that the Faithful might join at the same hourin prayer against the Turks and the Comet. This custom has lasted downto our own day. Again, to the comet of 1500 was attributed the tempest that caused thedeath of Bartholomew Diaz, a celebrated Portuguese navigator, whodiscovered the Cape of Good Hope. In 1528 a bearded star of terrific aspect alarmed the world, and themore serious spirits were influenced by this menacing comet, whichburned in the Heavens like "a great and gory sword. " In a chapter onCelestial Monsters the celebrated surgeon Ambroise Paré describes thisawful phenomenon in terms anything but seductive, or reassuring, showingus the menacing sword surrounded by the heads it had cut off (Fig. 50). [Illustration: FIG. 50. --What our Ancestors saw in a Comet. _After Ambroise Paré (1528). _] [Illustration: FIG. 51. --Prodigies seen in the Heavens by ourForefathers. ] Omens of battle, 1547. Deer and warriors, July 19, 1550. Cavalry, and a bloody branch crossing the sun, June 11, 1554. ] Our fathers saw many other prodigies in the skies; their descendants, less credulous, can study the facsimile reproduced in Fig. 51, of thedrawings published in the year 1557 by Conrad Lycosthenes in his curiousBook of Prodigies. So, too, it is asserted that Charles V renounced the jurisdiction of hisEstates, which were so vast that "the Sun never slept upon them, "because he was terrified by the comet of 1556 which burned in the skieswith an alarming brilliancy, into passing the rest of his days in prayerand devotion. It is certain that comets often exhibit very strange characteristics, but the imagination that sees in them such dramatic figures must indeedbe lively. In the Middle Ages and the Renaissance these were swords offire, bloody crosses, flaming daggers, etc. , all horrible objects readyto destroy our poor human race! At the time of the Romans, Pliny made some curious distinctions betweenthem: "The Bearded Ones let loose their hair like a majestic beard; theJavelin darts forth like an arrow; if the tail is shorter and ends in apoint, it is called the Sword; this is the palest of all the Comets; itshines like a sword, without rays; the Plate or Disk is named inconformity with its figure; its color is amber, the Barrel is actuallyshaped like a barrel, as it might be in smoke, with light streamingthrough it; the Horn imitates the figure of a horn erected in the sky, and the Lamp that of a burning flame; the Equine represents a horse'smane, shaken violently with a circular motion. There are bristledcomets; these resemble the skins of beasts with the fur on them, and aresurrounded by a nebulosity. Lastly, the tails of certain comets havebeen seen to menace the sky in the form of a lance. " These hairy orbs that appear in all directions, and whose trajectoriesare sometimes actually perpendicular to the plane of the ecliptic, appear to obey no regular law. Even in the seventeenth century theperspicacious Kepler had not divined their true character, seeing inthem, like most of his contemporaries, emanations from the earth, a sortof vapor, losing itself in space. These erratic orbs could not beassimilated with the other members of our grand solar family where, generally speaking, everything goes on in regular order. And even in our own times, have we not seen the people terrified at thesight of a flaming comet? Has not the end of the world by the agency ofcomets been often enough predicted? These predictions are so to speakperiodic; they crop up each time that the return of these cosmicalformations is announced by the astronomers, and always meet with acertain number of timid souls who are troubled as to our destinies. * * * * * To-day we know that these wanderers are subject to the general lawsthat govern the universe. The great Newton announced that, like theplanets, they were obedient to universal attraction; that they mustfollow an extremely elongated curve, and return periodically to thefocus of the ellipse. From the basis of these data Halley calculated theprogress of the comet of 1682, and ascertained that its motionspresented such similarity with the apparitions of 1531 and 1607, that hebelieved himself justified in identifying them and in announcing itsreturn about the year 1759. Faithful to the call made upon it, irresistibly attracted by the Orb of Day, the comet, at first pale, thenardent and incandescent, returned at the date assigned to it bycalculation, three years after the death of the illustrious astronomer. Shining upon his grave it bore witness to the might of human thought, able to snatch the profoundest secrets from the Heavens! This fine comet returns every seventy-six years, to be visible from theEarth, and has already been seen twenty-four times by the astonishedeyes of man. It appears, however, to be diminishing in magnitude. Itslast appearance was in 1835, and we shall see it again in 1910, a littlesooner than its average period, the attraction of Jupiter having thistime slightly accelerated its course, while in 1759 it retarded it. The comets thus follow a very elongated orbit, either elliptic, turninground the Sun, or parabolic, dashing out into space. In the first case, they are periodic (Fig. 52), and their return can be calculated. In thesecond they surprise us unannounced, and return to the abysses ofeternity to reappear no more. [Illustration: FIG. 52. --The orbit of a Periodic Comet. ] Their speed is even greater than that of the planets, it is equivalentto this, multiplied by the square root of 2, that is to say by 1. 414. Thus at the distance of the Earth from the Sun this velocity = 29, 500meters (18 miles) per second, multiplied by the above number, that is, 41, 700 meters (over 25 miles). At the distance of Mercury it = 47 ×1. 414 or 66, 400 meters (over 40 miles) per second. Among the numerous comets observed, we do not as yet know more than sometwenty of which the orbit has been determined. Periodicity in thesebearded orbs is thus exceptional, if we think of the innumerablemultitude of comets that circle through the Heavens. Kepler did notexaggerate when he said "there are as many comets in the skies as thereare fishes in the sea. " These scouts of the sidereal world constitute aregular army, and if we are only acquainted with the dazzling generalsclad in gold, it is because the more modest privates can only bedetected in the telescope. Long before the invention of the latter, these wanderers in the firmament roamed through space as in our own day, but they defied the human eye, too weak to detect them. Then they wereregarded as rare and terrible objects that no one dared to contemplate. To-day they may be counted by hundreds. They have lost in prestige andin originality; but science is the gainer, since she has thus endowedthe solar system with new members. No year passes without theannouncement of three or four new arrivals. But the fine apparitionsthat attract general attention by their splendor are rare enough. These eccentric visitors do not resemble the planets, for they have noopaque body like the Earth, Venus, Mars, or any of the rest. They aretransparent nebulosities, of extreme lightness, without mass nordensity. We have just photographed the comet of the moment, July, 1903:the smallest stars are visible through its tail, and even through thenucleus. They arrive in every direction from the depths of space, as though toreanimate themselves in the burning, luminous, electric solar center. Attracted by some potent charm toward this dazzling focus, they comeinquisitive and ardent, to warm themselves at its furnace. At first paleand feeble, they are born again when the Sun caresses them with hisfervid heat. Their motions accelerate, they haste to plunge wholly intothe radiant light. At length they burst out luminous and superb, whenthe day-star penetrates them with his burning splendor, illuminates themwith a marvelous radiance, and crowns them with glory. But the Sun isgenerous. Having showered benefits upon these gorgeous celestialbutterflies that flutter round him as round some altar of the gods, hegrants them liberty to visit other heavens, to seek fresh universes. . . . The original parabola is converted into an ellipse, if the imprudentadventurer in returning to the Sun passes near some great planet, suchas Jupiter, Saturn, Uranus, or Neptune, and suffers its attraction. Itis then imprisoned by our system, and can no longer escape from it. After reenforcement at the solar focus, it must return to the identicalpoint at which it felt the first pangs of a new destiny. Henceforward, it belongs to our celestial family, and circles in a closed curve. Otherwise, it is free to continue its rapid course toward other suns andother systems. * * * * * As a rule, the telescope shows three distinct parts in a comet. There isfirst the more brilliant central point, or _nucleus_, surrounded by anebulosity called the _hair_, or _brush_, and prolonged in a luminousappendix stretching out into the _tail_. The _head_ of the comet is thebrush and the nucleus combined. [Illustration: FIG. 53. --The tails of Comets are opposed to the Sun. ] It is usually supposed that the tail of a comet follows it throughoutthe course of its peregrinations. Nothing of the kind. The appendix mayeven precede the nucleus; it is always opposite the Sun, --that is tosay, it is situated on the prolongation of a straight line, startingfrom the Sun, and passing through the nucleus (Fig. 53). The tail doesnot exist, so long as the comet is at a distance from the orb of day;but in approaching the Sun, the nebulosity is heated and dilates, givingbirth to those mysterious tails and fantastic streamers whosedimensions vary considerably for each comet. The dilations andtransformations undergone by the tail suggest that they may be due to arepulsive force emanating from the Sun, an electric charge transmitteddoubtless through the ether. It is as though Phoebus blew upon themwith unprecedented force. Telescopic comets are usually devoid of tail, even when they reach thevicinity of the Sun. They appear as pale nebulosities, rounded or oval, more condensed toward the center, without, however, showing any distinctnucleus. These stars are only visible for a minute fraction of theircourse, when they reach a point not far from the Sun and the terrestrialorbit. The finest comets of the last century were those of 1811, 1843, 1858, 1861, 1874, 1880, 1881, and 1882. The Great Comet of 1811, afterspreading terror over certain peoples, notably in Russia, became theprovidence of the vine-growers. As the wine was particularly good andabundant that year, the peasants attributed this happy result to theinfluence of the celestial visitant. In 1843 one of these strange messengers from the Infinite appeared inour Heavens. It was so brilliant that it was visible in full daylight onFebruary 28th, alongside of the Sun. This splendid comet wasaccompanied by a marvelous rectilinear tail measuring 300, 000, 000kilometers (186, 000, 000 miles) in length, and its flight was so rapidthat it turned the solar hemisphere at perihelion in two hours, representing a speed of 550 kilometers (342 miles) a second. But the most curious fact is that this radiant apparition passed so nearthe Sun that it must have traversed its flames, and yet emerged fromthem safe and sound. Noteworthy also was the comet of 1858 (Fig. 49), discovered at Florenceby Donati. Its tail extended to a length of 90, 000, 000 kilometers(55, 900, 000 miles), and its nucleus had a diameter of at least 900kilometers (559 miles). It is a curious coincidence that the wine wasremarkably excellent and abundant in that year also. The comet of 1861 almost rivaled the preceding. Coggia's Comet, in 1874, was also remarkable for its brilliancy, but wasvery inferior to the last two. Finally, the latest worthy of mentionappeared in 1882. This magnificent comet also touched the Sun, travelingat a speed of 480 kilometers (299 miles) per second. It crossed thegaseous atmosphere of the orb of day, and then continued its coursethrough infinity. On the day of, and that following, its perihelion, itcould be detected with the unaided eye in full daylight, enthroned inthe Heavens beside the dazzling solar luminary. For the rest, it wasneither that of 1858 nor of 1861. Since 1882 we have not been favored with a visit from any fine comet;but we are prepared to give any such a reception worthy of theirmagnificence: first, because now that we have fathomed them we are nolonger awestruck; second, because we would gladly study them moreclosely. * * * * * In short, these hirsute stars, whose fantastic appearance impressed theimagination of our ancestors so vividly, are no longer formidable. Theirmass is inconsiderable; they seem to consist mainly of the lightest ofgases. Analysis of their incandescence reveals a spectrum closelyresembling that of many nebulæ; the presence of carbon is moreparticularly obvious. Even the nucleus is not solid, and is oftentransparent. It is fair to say that the action of a comet might be deleterious if oneof these orbs were to arrive directly upon us. The transformation ofmotion into heat, and the combination of the cometary gases with theoxygen of our atmosphere might produce a conflagration, or a generalpoisoning of the atmosphere. But the collision of a comet with a planet is almost an impossibility. This phenomenon could only occur if the comet crossed the planetaryorbit at the exact moment at which the planet was passing. When wethink of the immensity of space, of the extraordinary length of waytraversed by a world in its annual journey round the Sun, and the speedof its rotation, we see why this coincidence is hardly likely to occur. Thus, among the hundreds of comets catalogued, a few only cut theterrestrial orbit. One of them, that of 1832, traversed the path of ourglobe in the nights of October 29 and 30 in that year; but the Earthonly passed the same point thirty days later, and at the critical periodwas more than 80, 000, 000 kilometers (50, 000, 000 miles) away from thecomet. On June 30, 1861, however, the Earth passed through the extremity of thetail of the Great Comet of that year. No one even noticed it. Theeffects were doubtless quite immaterial. In 1872 we were to collide with Biela's Comet, lost since 1852; now, aswe shall presently see, we came with flying colors out of thatdisagreeable situation, because the comet had disintegrated, and wasreduced to powder. So we may sleep in peace as regards future dangerlikely to come to us from comets. There is little fear of thedestruction of humanity by these windy bags. These ethereal beauties whose blond locks float carelessly upon theazure night are not concerned with us; they seem to have no otherpreoccupation than to race from sun to sun, visiting new Heavens, indifferent to the astonishment they produce in us. They speedrestlessly and tirelessly through infinity; they are the Amazons ofspace. What suns, what worlds must they have visited since the moment of theirbirth! If these splendid fugitives could relate the story of theirwanderings, how gladly should we listen to the enchanting descriptionsof the various abodes they have journeyed to! But alas! these mysteriousexplorers are dumb; they tell none of their secrets, and we must needsrespect their enigmatic silence. Yet, some of them have left us a modest token of remembrance, an almostimpalpable nothing, sufficient, however, to enable us to address ourthanks to the considerate messenger. * * * * * Can there be any one upon the Earth who has not been struck by thephosphorescent lights that glide through the somber night, leaving abrilliant silver or golden track--the luminous, ephemeral trail of ameteor? Sometimes, when Night has silently spread the immensity of her wingsabove the weary Earth, a shining speck is seen to detach itself in theshades of evening from the starry vault, shooting lightly through theconstellations to lose itself in the infinitude of space. [Illustration: FIG. 54. --A Meteor. ] These bewitching sparks attract our eyes and chain our senses. Fascinating celestial fireflies, their dainty flames dart in everydirection through space, sowing the fine dust of their gilded wings uponthe fields of Heaven. They are born to die; their life is only a breath;yet the impression which they make upon the imagination of mortals is ofthe profoundest. The young girl dreaming in the delicious tranquillity of the transparentnight smiles at this charming sister in the Heavens (Fig. 54). What cannot this adorable star announce to the tender and loving heart? Is itthe shy messenger of the happiness so long desired? Its unpremeditatedappearance fills the soul with a ray of hope and makes it tremble. It isa golden beam that glides into the heart, expanding it in the thrills ofa sudden and ephemeral pleasure. . . . The radiant meteor seems to quit thevelvet of the deep blue sky to respond to the appeal of the imploringvoice that seeks its succor. What secrets has it not surprised! And who bears malice against it? Itis the friend of the betrothed who invoke its passage to confide theirwishes, and associate it with their dreams. Tradition holds that if awish be formulated during the visible passage of a meteor it willcertainly be fulfilled before the year is out. Between ourselves, however, this is but a surviving figment of the ancestral imagination, for this celestial jewel takes no such active part in the doings ofHumanity. . . . Besides, try to express a wish distinctly in a second! It is a curious fact that while comets have so often spread terror onthe Earth, shooting stars should on the contrary have been regarded withbenevolent feelings at all times. And what is a shooting star? Thesedainty excursionists from the celestial shores are not, as is supposed, true stars. They are atoms, nothings, minute fragments deriving ingeneral from the disintegration of comets. They come to us from a vastdistance, from millions on millions of miles, and circle in swarmsaround the Sun, following a very elongated ellipse which closelyresembles that of the cometary orbit. Their flight is extremely rapid, reaching sometimes more than 40 kilometers (25 miles) per second, acometary speed that is, as we have seen, greatly above that of ourterrestrial vehicle, which amounts to 29 to 30 kilometers (about 19miles). These little corpuscles are not intrinsically luminous; but when theorbit of a swarm of meteors crosses our planet, a violent shock arises, the speed of which may be as great as 72 kilometers (45 miles) in thefirst second if we meet the star shower directly; the average rate, however, does not exceed 30 to 40 kilometers (19 to 25 miles), for thesemeteors nearly always cross our path obliquely. The height at which theyarrive is usually 110 kilometers (68 miles), and 80 kilometers (50miles) at the moment of disappearance of the meteor; but shooting starshave been observed at 300 kilometers (186 miles). The friction caused by this collision high up in the atmospheretransforms the motion into heat. The molecules incandesce, and burn liketrue stars with a brilliancy that is often magnificent. But their glory is of short duration. The excessive heat resulting fromthe shock consumes the poor firefly; its remains evaporate, and dropslowly to the Earth, where they are deposited on the surface of the soilin a sort of ferruginous dust mixed with carbon and nickel. Some onehundred and forty-six milliards of them reach us annually, as seen bythe unaided eye, and many more in the telescope; the effect of theseshowers of meteoric matter is an insensible increase in the mass of ourglobe, a slight lessening of its rotary motion, and the acceleration ofthe lunar movements of revolution. Although the appearance of shooting stars is a common enough phenomenon, visible every night of the year, there are certain times when theyarrive in swarms, from different quarters of the sky. The mostremarkable dates in this connection are the night of August 10th and themorning of November 14th. Every one knows the shooting stars of August10th, because they arrive in the fine warm summer evenings so favorableto general contemplation of the Heavens. The phenomenon lasts till the12th, and even beyond, but the maximum is on the 10th. When the sky isvery clear, and there is no moon, hundreds of shooting stars can becounted on those three nights, sometimes thousands. They all seem tocome from the same quarter of the Heavens, which is called the_radiant_, and is situated for the August swarm in the constellation ofPerseus, whence they have received the name of _Perseids_. Ourforefathers also called them the tears of St. Lawrence, because thefeast of that saint is on the same date. These shooting stars describe avery elongated ellipse, and their orbit has been identified with that ofthe Great Comet of 1862. The shower of incandescent asteroids on November 14th is often much moreabundant than the preceding. In 1799, 1833, and 1866, the meteors wereso numerous that they were described as showers of rain, especially onthe first two dates. For several hours the sky was furrowed with fallingstars. An English mariner, Andrew Ellicot, who made the drawing wereproduce (Fig. 55), described the phenomenon as stupendous and alarming(November 12, 1799, 3 A. M. ). The same occurred on November 13, 1833. Themeteors that scarred the Heavens on that night were reckoned at 240, 000. These shooting stars received the name of _Leonids_, because theirradiant is situated in the constellation of the Lion. [Illustration: FIG. 55. --Shooting Stars of November 12, 1799. _From a contemporary drawing. _] This swarm follows the same orbit as the comet of 1866, which travels asfar as Uranus, and comes back to the vicinity of the Sun everythirty-three years. Hence we were entitled to expect another splendidapparition in 1899, but the expectations of the astronomers weredisappointed. All the preparations for the appropriate reception ofthese celestial visitors failed to bring about the desired result. Thenotes made in observatories, or in balloons, admitted of theregistration of only a very small number of meteors. The maximum wasthirteen. During that night, some 200 shooting stars were counted. Therewere more in 1900, 1901, and, above all, in 1902. This swarm has becomedisplaced. The night of November 27th again is visited by a number of shootingstars that are the disaggregated remains of the Comet of Biela. Thiscomet, discovered by Biela in 1827, accomplished its revolution in sixand a half years, and down to 1846 it responded punctually to theastronomers who expected its return as fixed by calculation. But onJanuary 13, 1846, the celestial wanderer broke in half: each fragmentwent its own way, side by side, to return within sight from the Earth in1852. It was their last appearance. That year the twin comets couldstill be seen, though pale and insignificant. Soon they vanished intothe depths of night, and never appeared again. They were looked for invain, and were despaired of, when on November 27, 1872, instead of theshattered comet, came a magnificent rain of shooting stars. They fellthrough the Heavens, numerous as the flakes of a shower of snow. The same phenomenon recurred on November 27, 1885, and confirmed thehypothesis of the demolition and disaggregation of Biela's Comet intoshooting stars. * * * * * There is an immense variety in the brilliancy of the shooting stars, from the weak telescopic sparks that vanish like a flash of lightning, to the incandescent _bolides_ or _fire-balls_ that explode in theatmosphere. Fig. 56 shows an example of these, and it represents a fire-ballobserved at the Observatory of Juvisy on the night of August 10, 1899. It arrived from Cassiopeia, and burst in Cepheus. This phenomenon may occur by day as well as by night. It is oftenaccompanied by one or several explosions, the report of which issometimes perceptible to a considerable distance, and by a shower ofmeteorites. The globe of fire bursts, and splits up into luminousfragments, scattered in all directions. The different parts of thefire-ball fall to the surface of the Earth, under the name of aerolites, or rather of uranoliths, since they arrive from the depths of space, andnot from our atmosphere. From the most ancient times we hear of showers of uranoliths to whichpopular superstitions were attached; and the Greeks even gave the nameof _Sideros_ to iron, the first iron used having been sidereal. [Illustration: FIG. 56. --Fire-Ball seen from the Observatory at Juvisy, August 10, 1899. ] [Illustration: FIG. 57. --Explosion of a Fire-Ball above Madrid, February 10, 1896. ] No year passes without the announcement of several showers ofuranoliths, and the phenomenon sometimes causes great alarm to those whowitness it. One of the most remarkable explosions is that which occurredabove Madrid, February 10, 1896, a fragment from which, sent me by M. Arcimis, Director of the Meteorological Institute, fell immediately infront of the National Museum (Fig. 57). The phenomenon occurred at 9. 30A. M. , in brilliant sunshine. The flash of the explosion was so dazzlingthat it even illuminated the interior of the houses; an alarming clap ofthunder was heard seventy seconds after, and it was believed that anexplosion of dynamite had occurred. The fire-ball burst at a height offourteen miles, and was seen as far as 435 miles from Madrid! In one of Raphael's finest pictures (_The Madonna of Foligno_) afire-ball may be seen beneath a rainbow (Fig. 58), the painter wishingto preserve the remembrance of it, as it fell near Milan, on September4, 1511. This picture dates from 1512. The dimensions of these meteorites vary considerably; they are of allsizes, from the impalpable dust that floats in the air, to the enormousblocks exposed in the Museum of Natural History in Paris. Many of themweigh several million pounds. That represented below fell in Mexicoduring the shower of meteors of November 27, 1885. It weighed about fourpounds. [Illustration: FIG. 58. --Raphael's Fire-Ball (_The Madonna ofFoligno_). ] These bolides and uranoliths come to us from the depths of space; butthey do not appear to have the same origin as the shooting stars. Theymay arise from worlds destroyed by explosion or shock, or even fromplanetary volcanoes. The lightest of them may have been expelled fromthe volcanoes of the Moon. Some of the most massive, in which ironpredominates, may even have issued from the bowels of the Earth, projected into space by some volcanic explosion, at an epoch when ourglobe was perpetually convulsed by cataclysms of extraordinary violence. They return to us to-day after being removed from the Earth to distancesproportional to the initial speed imparted to them. This origin seemsthe more admissible as the stones that fall from the skies exhibit amineral composition identical with that of the terrestrial materials. [Illustration: FIG. 59. --A Uranolith. ] In any case, these uranoliths bring us back at least by their fall toour Earth, and from henceforward we will remain upon it, to study itsposition in space, and to take account of the place it fills in theUniverse, and of the astronomical laws that govern our destiny. CHAPTER VIII THE EARTH Our grand celestial journey lands us upon our own little planet, on thisglobe that gravitates between Mars and Venus (between War and Love), circulating like her brothers of the solar system, around the colossalSun. The Earth! The name evokes in us the image of Life, and calls up thetheater of our activities, our ambitions, our joys and sorrows. Does itnot, in fact, to ignorant eyes, represent the whole of the universe? And yet, what is the Earth? The Earth is a star in the Heavens. We learned this much in our firstlesson. It is a globe of opaque material, similar to the planetsMercury, Venus, Mars, Jupiter, etc. , as previously described. Isolatedon all sides in space, it revolves round the Sun, along a vast orbitthat it accomplishes in a year. And while it thus glides along the linesof solar attraction, the terrestrial ball rotates rapidly upon itself intwenty-four hours. These statements may appear dubious at first sight, and contradictory tothe evidence of our senses. Now that the surface of the Earth has been explored in all directions, there is no longer room to doubt that it is a globe, a sort of ball thatwe adhere to. A journey round the world is common enough to-day, andalways yields the most complete evidence of the spherical nature of theEarth. On the other hand, the curvature of the seas is a no less certainproof. When a ship reaches the dark-blue line that appears to separatethe sky from the ocean, it seems to be hanging on the horizon. Little bylittle, however, as it recedes, it drops below the horizon line; thetops of the masts being the last to disappear. The observer on boardship witnesses the same phenomenon. The low shores are first todisappear, while the high coasts and mountains are much longer visible. The aspect of the Heavens gives another proof of the Earth's rotundity. As one travels North or South, new stars rise higher and higher abovethe horizon in the one direction or the other, and those which shine inthe latitude one is leaving, gradually disappear. If the surface of theEarth were flat, the ships on the sea would be visible as long as oursight could pierce the distance, and all the stars of the Heavens wouldbe equally visible from the different quarters of the world. Lastly, during the eclipses of the Moon, the shadow projected by theEarth upon our satellite is always round. This is another proof of thespherical nature of the terrestrial globe. We described the Earth as an orb in the Heavens, similar to all theother planets of the great solar family. We see these sister planets ofour world circulating under the starry vault, like luminous points whosebrilliancy is sometimes dazzling. For us they are marvelous celestialbirds hovering in the ether, upheld by invisible wings. The Earth isjust the same. It is supported by nothing. Like the soap-bubble thatassumes a lovely iridescence in the rays of the Sun, or, better, likethe balloon rapidly cleaving the air, it is isolated from every kind ofsupport. Some minds have difficulty in conceiving this isolation, because theyform a false notion of weight. The astronomers of antiquity, who divined it, knew not how to preventthe Earth from falling. They asked anxiously what the strong bandscapable of holding up this block of no inconsiderable weight could be. At first they thought it floated on the waters like an island. Then theypostulated solid pillars, or even supposed it might turn on pivotsplaced at the poles. But on what would all these imaginary supports haverested? All these fanciful foundations of the Earth had to be given up, and it was recognized as a globe, isolated in every part. This illusionof the ancients, which still obtains for a great many citizens of ourglobule, arises, as we said, from a false conception of weight. Weight and attraction are one and the same force. A body can only fall when it is attracted, drawn by a more importantbody. Now, in whatever direction we may wander upon the globe, our feetare always downward. _Down_ is therefore the _center_ of the Earth. The terrestrial globe may be regarded as an immense ball of magnet, andits attraction holds us at its surface. We weigh toward the center. Wemay travel over this surface in all directions; our feet will always bebelow, whatever the direction of our steps. For us, "below" is theinside of our planet, and "above" is the immensity of the Heavens thatextend above our heads, right round the globe. This once understood, where could the Earth fall to? The question is anabsurdity. "Below" being toward the center, it would have to fall out ofitself. Let us then picture the Earth as a vast sphere, detached from all thatexists around it, in the infinity of the Heavens. A point diametricallyopposed to another is called its _antipodes_. New Zealand isapproximately the antipodes to France. Well, for the inhabitants of NewZealand and of France the top is reciprocally opposed, and the bottom, or the feet, are diametrically in opposition. And yet, for one as forthe other, the bottom is the soil they are held to, and the top isspace above their heads. The Earth turns on itself in twenty-four hours. Whatever is above us, _e. G. _, at midday, we call high; twelve hours later, at midnight, wegive the same qualification to the part of space that was under our feetat noon. What is in the sky, and over our heads, at a given hour, isunder our feet, and yet always in the sky, twelve hours later. Ourposition, in relation to the space that surrounds us, changes from hourto hour, and "top" and "bottom" vary also, relatively to our position. Our planet is thus a ball, slightly flattened at the poles (by about1/292). Its diameter, at the equator, is 12, 742 kilometers (7, 926miles); from one pole to the other is a little less, owing to theflattening of the polar caps. The difference is some 43 kilometers(about 27 miles). Its circumference is 40, 000 kilometers (24, 900 miles). This ball issurrounded by an aerial envelope, the atmosphere, the height of whichcan not be less than 300 kilometers (186 miles), according to theobservations made on certain shooting stars. We all know that this layer of air, at the bottom of which we live, is abeautiful azure blue that seems to separate us from the sidereal abyss, spreading over our heads in a kind of vault that is often filled withclouds, and giving the illusion of resting far off on the circle of thehorizon. But this is only an illusion. In reality, there is neithervault nor horizon; space is open in all directions. If the atmospheredid not exist, or if it were completely transparent, we should see thestars by day as by night, for they are continually round us, at noon asat midnight, and we can see them in the full daylight, with the help ofastronomical instruments. In fact, certain stars (the radiant Venus andthe dazzling Jupiter) pierce the veil of the atmosphere, and are visiblewith the unaided eye in full daylight. The terrestrial surface is 510, 000, 000 square kilometers (200, 000, 000square miles). The waters of the ocean cover three-quarters of thissurface, _i. E. _, 383, 200, 000 square kilometers (150, 000, 000 squaremiles), and the continents only occupy 136, 600, 000 square kilometers(55, 000 square miles). France represents about the thousandth part ofthe total superficies of the globe. Despite the asperities of mountain ranges, and the abysses hollowed outby the waters, the terrestrial globe is fairly regular, and in relationto its volume its surface is smoother than that of an orange. Thehighest summits of the Himalaya, the profoundest depths of the somberocean, do not attain to the millionth part of its diameter. In weight, the Earth is five and a half times heavier than would be aglobe of water of the same dimensions. That is to say: 6, 957, 930, 000, 000, 000, 000, 000, 000 kilograms (6, 833, 000, 000, 000, 000, 000, 000 tons). The atmospheric atmosphere with which it is surrounded represents. 6, 263, 000, 000, 000, 000, 000 kilograms (6, 151, 000, 000, 000, 000 tons). Each of us carries an average weight of some 17, 000 kilograms (16 tons)upon his shoulders. Perhaps some one will ask how it is that we are notcrushed by this weight, which is out of all proportion with ourstrength, but to which, nevertheless, we appear insensible. It isbecause the aerial fluid enclosed within our bodies exerts a pressureequal and opposite to the external atmospheric pressure, and thesepressures are at equilibrium. The Earth is characterized by no essential or particular differencesrelatively to the other worlds of our system. Like Venus of the limpidrays, like the dazzling Jupiter, like all the planets, she coursesthrough space, carrying into Infinitude our hopes and destinies. Biggerthan Mercury, Venus, and Mars, she presents a very modest figure incomparison with the enormous Jupiter, the strange system of Saturn, ofUranus, and even of Neptune. For us her greatest interest is that sheserves as our residence, and if she were not our habitation we shouldscarcely notice her. Dark in herself, she burns at a distance like astar, returning to space the light she receives from the Sun. At thedistance of our satellite, she shines like an enormous moon, fourteentimes larger and more luminous than our gentle Phoebe. Observed fromMercury or Venus, she embellishes the midnight sky with her sparklingpurity as Jupiter does for us. Seen from Mars, she is a brilliantmorning and evening star, presenting phases similar to those which Marsand Venus show from here. From Jupiter, the terrestrial globe is littlemore than an insignificant point, nearly always swallowed up in thesolar rays. As to the Saturnians, Uranians, and Neptunians, if suchpeople exist, they probably ignore our existence altogether. And in alllikelihood it is the same for the rest of the universe. We must cherish no illusions as to the importance of our natal world. Itis true that the Earth is not wanting in charm, with its verdant plainsenameled in the delicious tones of a robust and varied vegetation, itsplants and flowers, its spring-time and its birds, its limpid riverswinding through the meadows, its mountains covered with forests, itsvast and profound seas animated with an infinite variety of livingcreatures. The spectacle of Nature is magnificent, superb, admirableand marvelous, and we imagine that this Earth fills the universe, andsuffices for it. The Sun, the Moon, the stars, the boundless Heavens, seem to have been created for us, to charm our eyes and thoughts, toillumine our days, and shed a gentle radiance upon our nights. This isan agreeable illusion of our senses. If our Humanity were extinguished, the other worlds of the Heavens, Venus, Mars, etc. , would none the lesscontinue to gravitate in the Heavens along with our defunct planet, andthe close of human life (for which everything seems to us to have beencreated) would not even be perceived by those other worlds, thatnevertheless are our neighbors. There would be no revolution, nocataclysm. The stars would go on shining in the firmament, just as theydo to-day, shedding their divine light over the immensity of theHeavens. Nothing would be changed in the general aspect of the Universe. The Earth is only a modest atom, lost in the innumerable army of theworlds and suns that people the universe. * * * * * Every morning the Sun rises in the East, setting fire with his ardentrays to the sky, which is dazzling with his splendor. He ascends throughspace, reaches a culminating point at noon, and then descends toward theWest, to sink at night into the purple of the sunset. And then the stars, grand lighthouses of the Heavens, in their turnincandesce. They too rise in the East, ascend the vault of Heaven, andthen descend to the West, and vanish. All the orbs, Sun, Moon, planets, stars, appear to revolve round us in twenty-four hours. This journey of the orbs around us is only an illusion of the senses. Whether the Earth be at rest, and the sky animated with a rotarymovement round her, or whether, on the contrary, the stars are fixed, and the Earth in motion, in either case, for us appearances are thesame. If the Earth turns, carrying all that pertains to it in itsmotion--the seas, the atmosphere, the clouds, and ourselves, --we areunable to perceive it, because all the objects that surround us keeptheir respective positions among themselves. Hence we must resort tologic, and reason out the two hypotheses. For the accomplishment of this rapid journey of the Sun and stars aroundthe Earth, it would be necessary that all the orbs of the sky should bein some way attached to a vault, or to circles, as was formerlysupposed. This conception is childish. The peoples of antiquity had nonotion of the size of the universe, and their error is almost excusable. The distance separating Heaven from the Infernal Regions has beenmeasured, according to Hesiod, by Vulcan's anvil, which fell from theskies to the Earth in nine days and nine nights, and it would havetaken as long again to continue its journey from the surface of theEarth to the bowels of Hades. To-day we have a more exact notion of the grandeur of the Universe. Weknow that millions and trillions of miles separate the stars from oneanother. And by representing these distances, we can form some idea ofthe difficulty there would be in admitting the rotation of the universeround the Earth. The distance from here to the Sun is 149, 000, 000 kilometers (93, 000, 000miles). In order to turn in twenty-four hours round the Earth, that orbwould have to fly through Space at a velocity of more than 10, 000kilometers (6, 200 miles) a second. Yes! the Sun, splendid orb, source of our existence and of that of allthe planets, a colossal globe, over a million times more voluminous thanthe Earth, and 324 thousand times heavier, would have to accomplish thisimmense revolution in order to turn round the minute point that is ourlilliputian world! This in itself would suffice to convince us of the want of logic in suchan argument. But the Sun is not alone in the Heavens. We should have tosuppose that all the planets and all the stars were engaged in the samefantastic motions. Jupiter is about five times as far off as the Sun; his velocity wouldhave to be 53, 000 kilometers (32, 860 miles) per second. Neptune, thirty times farther off, would have to execute 320, 000kilometers (198, 000 miles) per second. The nearest star, [alpha] of the Centaur, situated at a distance 275, 000times that of the Sun, would have to run, to fly through space, at arate of 2, 941, 000, 000 kilometers (1, 823, 420, 000 miles) per second. All the other stars are incomparably farther off, at infinity. And this fantastic rotation would all be accomplished round a minutepoint! To put the problem in this way is to solve it. Unless we deny theastronomic measures, and the most convincing geometric operations, theEarth's diurnal motion of rotation is a certainty. To suppose that the stars revolve round the Earth is to suppose, as oneauthor humorously suggests, that in order to roast a pheasant thechimney, the kitchen, the house, and all the countryside must needs turnround it. If the Earth turns in twenty-four hours upon itself, a point upon theequator would simply travel at a rate of 465 meters (1, 525 feet) persecond. This speed, while considerable in comparison with the movementsobserved upon the surface of our planet, is as nothing compared withthe fantastic rapidity at which the Sun and stars would have to move, inorder to rotate round our globe. Thus we have to choose between these two hypotheses: either to make theentire Heavens turn round us in twenty-four hours, or to suppose ourglobe to be animated by a motion of rotation upon itself. For us, theimpression is the same, and as we are insensible to the motion of theEarth, its immobility would seem almost natural to us. So that, in lastresort, here as in many other instances, the decision must be made bysimple common sense. Science long ago made its choice. Moreover, all theprogress of Astronomy has confirmed the rotary movement of the Earth intwenty-four hours, and its movement of revolution round the Sun in ayear; while at the same time a great number of other motions have beendiscovered for our wandering planet. The learned philosophers of antiquity divined the double movement of ourplanet. The disciples of Pythagoras taught it more than two thousandyears ago, and the ancient authors quote among others Nicetas ofSyracuse, and Aristarchus of Samos, as being among the first to promotethe doctrine of the Earth's movement. But at that remote period no onehad any idea of the real distances of the stars, and the argument didnot seem to be based on any adequate evidence. Ptolemy, after a longdiscussion of the diurnal motion of our planet, refutes it, giving ashis principal reason that if the Earth turned, the objects that were notfixed to its surface would appear to move in a contrary direction, andthat a body shot into the air would fall back to the West of itsstarting-point, the Earth having turned meantime from West to East. Thisobjection has no weight, because the Earth controls not only all theobjects fixed to the soil, but also the atmosphere, and the clouds thatsurround it like a light veil, and all that exists upon its surface. Theatmosphere, the clouds, the waters of the ocean, things and beings, allare adherent to it and make one body with it, participating in itsmovement, as sometimes happens to ourselves in the compartment of atrain, or the car of an aerostat. When, for instance, we drop an objectout of such a car, this object, animated with the acquired velocity, does not fall to a point below the aerostat, but follows the balloon, asthough it were gliding along a thread. The author has made thisexperiment more than once in aerial journeys. Thus, the hypothesis of the Earth's motion has become a certainty. Butin addition to reasoning, direct proof is not wanting. 1. The spheroidal shape of the Earth, slightly flattened at the polesand swollen at the equator, has been produced by the rotary motion, bythe centrifugal force that it engenders. 2. In virtue of this centrifugal force, which is at its maximum at theequator, objects lose a little of their weight in proportion as they arefarther removed from the polar regions where centrifugal force is almost_nil_. 3. In virtue of this same centrifugal force, the length of the pendulumin seconds is shorter at the equator than in Paris, and the differenceis one of 3 millimeters. 4. A weight abandoned to itself and falling from a certain height, should follow the vertical if the Earth were motionless. Experiment, frequently repeated, shows a slight deviation to the East, of theplumb-line that marks the vertical. We more especially observed this atthe Pantheon during the recent experiments. 5. The magnificent experiment of Foucault at the Pantheon, just renewedunder the auspices of the Astronomical Society of France, demonstratesthe rotary motion of the Earth to all beholders. A sufficiently heavyball (28 kilograms, about 60 pounds) is suspended from the dome of theedifice by an excessively fine steel thread. When the pendulum is inmotion, a point attached to the bottom of the ball marks its passageupon two little heaps of sand arranged some yards away from the center. At each oscillation this point cuts the sand, and the furrow getsgradually longer to the right hand of an observer placed at the centerof the pendulum. The plane of the oscillations remains fixed, but theEarth revolves beneath, from West to East. The fundamental principle ofthis experiment is that the plane in which any pendulum is made tooscillate remains invariable even when the point of suspension isturned. This demonstration enables us in some measure to see the Earthturning under our feet. The annual displacements of the stars are again confirmatory of theEarth's motion round the Sun. During the course of the year, the starsthat are least remote from our solar province appear to describe minuteellipses, in perspective, in the Heavens. These small apparentvariations in the position of the nearest stars reproduce the annualrotation of the Earth round the Sun, in perspective. We could adduce further observations in favor of this double movement, but the proofs just given are sufficiently convincing to leave no doubtin the mind of the reader. Nor are these two the only motions by which our globe is rocked inspace. To its diurnal rotation and its annual rotation we may addanother series of _ten more motions_: some very slow, fulfillingthemselves in thousands of years, others, more rapid, being constantlyrenewed. It is, however, impossible in these restricted pages to enterinto the detail reserved for more complete works. We must not forgetthat our present aim is to sum up the essentials of astronomicalknowledge as simply as possible, and to offer our readers only the "bestof the picking. " * * * * * The two principal motions of which we have just spoken give us themeasure of time, the day of twenty-four hours, and the year of 365-1/4days. The Earth turning upon itself in twenty-four hours from West to East, presents all its parts in succession to the Sun fixed in space. Illuminated countries have the day, those opposite, in the shadow of theEarth, are plunged into night. The countries carried by the Earth towardthe Sun have morning, those borne toward his shadow, evening. Thosewhich receive the rays of the day-star directly have noon; those whichare just opposite have midnight. The rotation of our planet in this way gives us the measure of time; ithas been divided arbitrarily into twenty-four periods called hours; eachhour into sixty minutes; each minute into sixty seconds. In consequence, each country turns in twenty-four hours round the axisof the Earth. The difference in hours between the different regions ofthe globe is therefore regulated by the difference of geographicalposition. The countries situated to the West are behind us; the Sun onlygets there after it has shone upon our meridian. When it is midday inParis, it is only 11. 51 A. M. In London; 11. 36 A. M. In Madrid; 11. 14 A. M. At Lisbon; 11. 12 A. M. At Mogador; 7. 06 A. M. At Quebec; 6. 55 A. M. At NewYork; 5. 14 A. M. In Mexico; and so on. The countries situated to the Eastare, on the contrary, ahead of us. When it is noon in Paris, it isalready 56 minutes after midday at Vienna; 1. 25 P. M. At Athens; 2. 21P. M. At Moscow; 3. 16 P. M. At Teheran; 4. 42 P. M. At Bombay; and so on. Weare here speaking of real times, and not of the conventional times. [Illustration: FIG. 60. --Motion of the Earth round the Sun. ] If we could make the tour of the world in twenty-four hours, startingat midday from some place to go round the globe, and traveling westwardwith the Sun, we should have him always over our heads. In travelinground the world from West to East, one goes in front of the Sun, andgains by one day; in taking the opposite direction, from East to West, one loses a day. In reality, the exact duration of the Earth's diurnal rotation istwenty-three hours, fifty-six minutes, four seconds. That is thesidereal day. But, while turning upon itself, the Earth circulates uponits orbit, and at the end of a diurnal rotation it is still obliged toturn during three minutes, fifty-six seconds in order to present exactlythe same meridian to the fixed Sun which, in consequence of the rotaryperiod of our planet, is a little behind. The solar day is thus one oftwenty-four hours. There are 366 rotations in the year. And now let us come back to the consequences of the Earth's motion. Inthe first place our planet does not turn vertically nor on its side, butis tipped or inclined a certain quantity: 23° 27'. Now, throughout its annual journey round the Sun, the inclinationremains the same. That is what produces the seasons and climates. Thecountries which have a larger circle to travel over in the hemisphere ofthe solar illumination have the longer days, those which have a smallercircle, shorter days. At the equator there is constantly, and allthrough the year, a twelve-hour day, and a night of twelve hours. [Illustration: FIG. 61. --Inclination of the Earth. ] In summer, the pole dips toward the Sun, and the rays of the orb of daycover the corresponding hemisphere with their light. Six months laterthis same hemisphere is in winter, and the opposite hemisphere is in itsturn presented to the Sun. June 21 is the summer solstice for thenorthern hemisphere, and is at the same time winter for the southernpole. Six months later, on December 21, we have winter, while thesouthern hemisphere is completely exposed to the Sun. Between these twoepochs, when the radiant orb shines exactly upon the equator, that is onMarch 21, we have the spring equinox, that delicious flowering seasonwhen all nature is enchanting and enchanted; on September 21 we have theautumn equinox, melancholy, but not devoid of charm. The terrestrial sphere has been divided into different zones, with whichthe different climates are in relation: 1. The tropical zone, which extends 23° 27' from one part to the otherof the equator. This is the hottest region. It is limited by the circleof the tropics. 2. The temperate zones, which extend from 23° 27' to 66° 23' oflatitude, and where the Sun sets every day. 3. The glacial zones, drawn round the poles, at 66° 33' latitude, wherethe Sun remains constantly above or below the horizon for several days, or even several months. These glacial zones are limited by the polarcircles. We must add that the _axis_ of the Earth is a straight line that issupposed to pass through the center of the globe and come out at twodiametrically opposite points called the _poles_. The diurnal rotationof the Earth is effected round this axis. The name _equator_ is given to a great circle situated between the twopoles, at equal distance, which divides the globe into two hemispheres. The equator is divided into 360 parts or degrees, by other circles thatgo from one pole to the other. These are the _longitudes_ or meridians(see Fig. 62). The distance between the equator and the pole is dividedinto larger or smaller circles, which have received the name of_latitudes_, 90 degrees are reckoned on the one side and the other ofthe equator, in the direction of the North and South poles, respectively. The longitudes are reckoned from some point either to Eastor West: the latitudes are reckoned North and South, from the equator. In going from East to West, or inversely, the longitude changes, but inpassing from North to South of any spot, it is the latitude that alters. [Illustration: FIG. 62. --The divisions of the globe. Longitudes andlatitudes. ] The circles of latitude are smaller in proportion as one approaches thepoles. The circumference of the world is 40, 076, 600 meters at theequator. At the latitude of Paris (48° 50') it is only 26, 431, 900meters. A point situated at the equator has more ground to travel overin order to accomplish its rotation in twenty-four hours than a pointnearer the pole. We have already stated that this velocity of rotation is 465 meters persecond at the equator. At the latitude of Paris it is not more than 305meters. At the poles it is _nil_. The longitudes, or meridians, are great circles of equal length, dividing the Earth into quarters, like the parts of an orange or amelon. These circumvent the globe, and measure some 40, 000, 000(40, 008, 032) meters. We may remember in passing that the length of themeter has been determined as, by definition, the ten-millionth part ofthe quarter of a celestial meridian. Thus, while rotating upon itself, the Earth spins round the Sun, along avast orbit traced at 149, 000, 000 kilometers (93, 000, 000 miles) from thecentral focus, a sensibly elliptical orbit, as we have already pointedout. It is a little nearer the Sun on January 1st than on July 1st, atits perihelion (_peri_, near, _helios_, Sun), than at its aphelion(_apo_, far, _helios_, Sun). The difference = 6, 000, 000 kilometers(3, 720, 000 miles), and its velocity is a little greater at perihelionthan at aphelion. This second motion produces the _year_. It is accomplished in threehundred and sixty-five days, six hours, nine minutes, nine seconds. Such is the complete revolution of our planet round the orb of day. Ithas received the name of sidereal year. But this is not how we calculatethe year in practical life. The civil year, known also as the tropicalyear, is not equivalent to the Earth's revolution, because a very slowgyratory motion, called "the precession of the equinoxes, " the cycle ofwhich occupies 25, 765 years, drags the spring equinox back some twentyminutes in each year. The civil year is, accordingly, three hundred and sixty-five days, fivehours, forty-eight minutes, forty-six seconds. In order to simplify the calendar, this accumulating fraction of fivehours, forty-eight minutes, forty-six seconds (about a quarter day) isadded every four years to a bissextile year (leap-year), and thus wehave uneven years of three hundred and sixty-five, and three hundred andsixty-six days. Every year of which the figure is divisible by four is aleap-year. By adding a quarter day to each year, there is a surplus ofeleven minutes, fourteen seconds. These are subtracted every hundredyears by not taking as bissextile those secular years of which theradical is not divisible by four. The year 1600 was leap-year: 1700, 1800, and 1900 were not; 2000 will be. The agreement between thecalendar and nature has thus been fairly perfect, since theestablishment of the Gregorian Calendar in 1582. Since the terrestrial orbit measures not less than 930, 000, 000kilometers (576, 600, 000 miles), which must be traversed in a year, theEarth flies through Space at 2, 544, 000 kilometers (1, 577, 280 miles) aday, or 106, 000 kilometers (65, 720 miles) an hour, or 29, 500 meters (18miles) per second on an average, a little faster at perihelion, a littleslower at aphelion. This giddy course, a thousand times more rapid thanthe speed of an express-train, is effected without commotion, shock, ornoise. Reasoning alone enables us to divine the prodigious movement thatcarries us along in the vast fields of the Infinite, in mid-heaven. Returning to the calendar, it must be remarked in conclusion, that thehuman race has not exhibited great sense in fixing the New Year onJanuary 1. No more disagreeable season could have been selected. Andfurther, as the ancient Roman names of the months have been preserved, which in the time of Romulus began with March, the "seventh" month, "September, " is our ninth month; October (the eighth) is the tenth;November (the ninth) has become the eleventh; and December (the tenth)has taken the place of the twelfth. Verily, we are not hard to please! These months, again, are unequal, as every one knows. Witness thesimple expedient of remembering the long and short months, by closingthe left hand and counting the knobs and hollows of the fist, the formercorresponding to the long months, the latter to the short: first knob =January; first hollow, February; second knob, March; and so on. [12] [Illustration: FIG. 63. --To find the long and short months. ] Should not the real renewal of the year coincide with the awakening ofNature, with the spring on the terrestrial hemisphere occupied by thegreater portion of Humanity, with the date of March 21st? Should not themonths be equalized, and their names modified? Why should we not followthe beautiful evolution dictated by the Sun and by the movement of ourplanet? But our poor Earth may roll on a long time yet before itsinhabitants will become reasonable. CHAPTER IX THE MOON It is the delightful hour when all Nature pauses in the tranquil calm ofthe silent night. The Sun has cast his farewell gleams upon the weary Earth. All sound ishushed. And soon the stars will shine out one by one in the bosom of thesomber firmament. Opposite to the sunset, in the east, the Full Moonrises slowly, as it were calling our thoughts toward the mysteries ofeternity, while her limpid night spreads over space like a dew fromHeaven. In the odorous woods, the trees are silhouetted strangely upon the sky, seeming to stretch their knotted arms toward this celestial beauty. Onthe river, smooth as a mirror, wherein the pale Phoebe reflects hersplendor, the maidens go to seek the floating image of their futurespouse. And in response to their prayers, she rends the veil of cloudthat hides her from their eyes, and pours the reflection of her gentlebeams upon the sleeping waters. From all time the Moon has had the privilege of charming the gaze, andattracting the particular attention of mortals. What thoughts have notbeen wafted to her pale, yet luminous disk? Orb of mystery and ofsolitude, brooding over our silent nights, this celestial luminary is atonce sad and splendid in her glacial purity, and her limpid rays provokea reverie full of charm and melancholy. Mute witness of terrestrialdestinies, her nocturnal flame watches over our planet, following it inits course as a faithful satellite. The human eye first uplifted to the Heavens was struck, above all, withthe brilliancy of this solitary globe, straying among the stars. TheMoon first suggested an easy division of time into months and weeks, andthe first astronomical observations were limited to the study of herphases. Daughter of the Earth, the Moon was born at the limits of theterrestrial nebula, when our world was still no more than a vast gaseoussphere, and was detached from her at some critical period of colossalsolar tide. Separating with regret from her cradle, but attached to theEarth by indissoluble ties of attraction, she rotates round us in amonth, from west to east, and this movement keeps her back a little eachday in relation to the stars. If we watch, evening by evening, beginningfrom the new moon, we shall observe that she is each night a littlefarther to the left, or east, than on the preceding evening. Thisrevolution of the Moon around our planet produces the phases, and givesthe measure of our months. [Illustration: FIG. 64. --The Full Moon slowly rises. ] During her monthly journey she always presents the same face to us. Onemight think that the fear of losing us had immobilized her globe, andprevented her from turning. And so we only know of her the vague sketchof a human face that has been observed through all the ages. It seems, in fact, as though she were looking down upon us from theHeavens, the more so as the principal spots of her disk vaguely recallthe aspect of a face. If we try to draw it without the aid ofinstruments we observe dark regions and clear regions that eachinterprets in his own fashion. To the author, for instance, the fullMoon has the appearance represented in the following figure. The spotsresemble two eyes and the sketch of a nose; resulting in a vague humanfigure, as indicated on the lower disk. Others see a man carrying abundle of wood, a hare, a lion, a dog, a kangaroo, a sickle, two headsembracing, etc. [13] But generally speaking, there is a tendency to see ahuman figure in it. If this appearance is helped a little by drawing, it gives the profileof a man's head fairly well sketched, and furnished with an abundantcrop of hair (Fig. 66). Others go much more into detail, and draw awoman's head that is certainly too definite, like this of M. Jean Sardou(Fig. 67). Others, again, like M. Zamboni, see behind the man's profilethe likeness of a young girl being embraced by him (Fig. 68). There iscertainly some imagination about these. And yet, on the first suitableoccasion, look at the Moon through an opera-glass, a few days after thefirst quarter, and you will not fail to see the masculine profile justdescribed, and even to imagine the "kiss in the Moon. " [Illustration: FIG. 65. --The Moon viewed with the unaided eye. ] [Illustration: FIG. 66. --The Man's head in the Moon. ] These vague aspects disappear as soon as the Moon is examined with eventhe least powerful instruments: the spots are better defined, and theillusions of indistinct vision vanish. Compare this direct photograph ofthe Moon, taken by the author some years ago (Fig. 69): here is neithera human figure, man, dog, hare, nor faggot; simply deep geographicalconfigurations, and in the lower region, a luminous point whence certainlight bands spread out, some being prolonged to a considerable distance. And yet, from a little way off, does it not form the man's face aboveindicated? [Illustration: FIG. 67. --Woman's head in the Moon. ] From the earliest astronomical observations made with the aid ofinstruments by Galileo, in 1609, people tried to find out what the darkspots could represent, and they were called seas, because water absorbslight, and reflects it less than _terra firma_. The Moon of itselfpossesses no intrinsic light, any more than our planet, and only shinesby the light of the Sun that illuminates it. As it rotates round theEarth, and constantly changes its position with respect to the Sun, wesee more or less of its illuminated hemisphere, and the result is thephases that every one knows so well. [Illustration: FIG. 68. --The kiss in the Moon. ] [Illustration: FIG. 69. --Photograph of the Moon. ] At the commencement of each lunation, the Moon is between the Sun andthe Earth, and its non-illuminated hemisphere is turned toward us. Thisis the New Moon, invisible to us; but two days later, the slim crescentof Diana sheds a gentle radiance upon the Earth. Gradually the crescentenlarges. When the Moon arrives at right angles with ourselves and withthe Sun, half the illuminated hemisphere is presented to us. This is thefirst quarter. At the time of Full Moon, it is opposite the Sun, and wesee the whole of the hemisphere illuminated. Then comes the decline: thebrilliant disk is slightly corroded at first; it diminishes from day today, and about a week before the New Moon our fair friend only shows herprofile before she once more passes in front of the Sun: this is thelast quarter. [Illustration: FIG. 70. --The Moon's Phases. ] When the Moon is crescent, in the first evenings of the lunation, andafter the last quarter, the rest of the disk is visible, illuminatedfeebly by a pale luminosity. This is known as the ashy light. It is dueto the shine of the Earth, reflecting the light received from the Suninto space. Accordingly the ashy light is the reflection of our own sentback to us by the Moon. It is the reflection of a reflection. This rotation of the Moon round the Earth is accomplished intwenty-seven days, seven hours, forty-three minutes, eleven seconds; butas the Earth is simultaneously revolving round the Sun, when the Moonreturns to the same point (the Earth having become displaced relativelyto the Sun), the Moon has to travel two days longer to recover itsposition between the Sun and the Earth, so that the lunar month islonger than the sidereal revolution of the Moon, and takes twenty-ninedays, twelve hours, forty-four minutes, three seconds. This is theduration of the sequence of phases. This revolution is accomplished at a distance of 384, 000 kilometers(238, 000 miles). The velocity of the Moon in its orbit is more than 1kilometer (0. 6214 mile) per second. But our planet sweeps it throughspace at a velocity almost thirty times greater. The diameter of the Moon represents 273/1000 that of the Earth, _i. E. _, 3, 480 kilometers (2, 157 miles). Its surface = 38, 000, 000 square kilometers (15, 000, 000 square miles), alittle more than the thirteenth part of the terrestrial surface, which= 510, 000, 000 (200, 000, 000 square miles). In volume, the Moon is fifty times less than the Earth. Its mass orweight is only 1/81 that of the terrestrial globe. Its density = 0. 615, relatively to that of the Earth, _i. E. _, a little more than three timesthat of water. Weight at its surface is very little: 0. 174. A kilogramtransported thither would only weigh 174 grams. * * * * * At the meager distance of 384, 000 kilometers (238, 000 miles) thatseparates us from it (about thirty times the diameter of the Earth), theMoon is a suburb of our terrestrial habitation. What does this smalldistance amount to? It is a mere step in the universe. A telegraphic message would get there in one and a half second; aprojectile fired from a gun would arrive in eight days, five hours; anexpress-train would be due in eight months, twenty-two days. It is onlythe 1/388 part of the distance that separates us from the Sun, and onlythe 100/1, 000, 000 part of the distance of the stars nearest to us. Manymen have tramped the distance that separates us from the Moon. A bridgeof thirty terrestrial globes would suffice to unite the two worlds. Owing to this great proximity, the Moon is the best known of all thecelestial spheres. Its geographical (or more correctly, selenographical, _Selene_, moon) map was drawn out more than twocenturies ago, at first in a vague sketch, and afterward with moredetails, until to-day it is as precise and accurate as any of ourterrestrial maps of geography. Before the invention of the telescope, from antiquity to the seventeenthcentury, people lost themselves in conjectures as to the nature of thisstrange lunar figure. It was held to be a mysterious world, the moreextraordinary in that it always presented the same face to us. Somecompared it to an immense mirror reflecting the image of the Earth. Others pictured it as a silver star, an enchanted abode where all waswealth and happiness. For many a long day it was the fashion to think, quite irrationally, that the inhabitants of the Moon were fifteen timesbigger than ourselves. The invention of telescopes, however, brought a little order and a grainof truth into these fantastic assumptions. The first observations ofGalileo revolutionized science, and his discoveries filled thebest-ordered minds with enthusiasm. Thenceforward, the Moon became ourproperty, a terrestrial suburb, where the whole world would gladly haveinstalled itself, had the means of getting there been as swift as thewings of the imagination. It became easy enough to invent a thousandenchanting descriptions of the charms of our fair sister, and no onescrupled to do so. Soon, it was observed that the Moon closely resembledthe Earth in its geological features; its surface bristles with sharpmountain peaks that light up in so many luminous points beneath the raysof the Sun. Alongside, dark and shaded parts indicate the plains;moreover, there are large gray patches that were supposed to be seasbecause they reflect the solar light less perfectly than the adjacentcountries. At that epoch hardly anything was known of the physicalconstitution of the Moon, and it was figured as enveloped with anatmospheric layer, analogous to that at the bottom of which we carry onour respiration. To-day we know that these "seas" are destitute of water, and that if thelunar globe possesses an atmosphere, it must be excessively light. The Moon became the favorite object of astronomers, and the numerousobservations made of it authorized the delineation of very interestingselenographic charts. In order to find one's way among the seas, plains, and mountains that make up the lunar territory, it was necessary to namethem. The seas were the first to be baptized, in accordance with theirreputed astrological influences. Accordingly, we find on the Moon, theSea of Fecundity, the Lake of Death, the Sea of Humors, the Ocean ofTempests, the Sea of Tranquillity, the Marsh of Mists, the Lake ofDreams, the Sea of Putrefaction, the Peninsula of Reverie, the Sea ofRains, etc. With regard to the luminous parts and the mountains, it was at firstproposed to call them after the most illustrious astronomers, but thefear of giving offense acted as a check on Hevelius and Riccioli, authors of the first lunar maps (1647, 1651), and they judged it moreprudent to transfer the names of the terrestrial mountains to the Moon. The Alps, the Apennines, the Pyrenees, the Carpathians, are all to befound up there; then, as the vocabulary of the mountains was notadequate, the scientists reasserted their rights, and we meet in theMoon, Aristotle, Plato, Hipparchus, Ptolemy, Copernicus, Kepler, Newton, as well as other more modern and even contemporaneous celebrities. We have not space to reproduce the general chart of the Moon (thatpublished by the author measures not less than a meter, with thenomenclature); but the figure subjoined gives a summary sufficient forthe limits of this little book. Here are the names of the principallunar mountains, with the numbers corresponding to them upon the map. [Illustration: FIG. 71. --Map of the Moon. (From Fowler's "Telescopic Astronomy. ") 1 Furnerius 2 Petavius 3 Langrenus 4 Macrobius 5 Cleomedes 6 Endymion 7 Altas 8 Hercules 9 Romer 10 Posidonius 11 Fracastorius 12 Theophilus 13 Piccolomini 14 Albategnius 15 Hipparchus 16 Manilius 17 Eudoxus 18 Aristotle 19 Cassini 20 Aristillus 21 Plato 22 Archimedes 23 Eratosthenes 24 Copernicus 25 Ptolemy 26 Alphonsus 27 Arzachel 28 Walter 29 Clavius 30 Tycho 31 Bullialdus 32 Schiller 33 Schickard 34 Gassendi 35 Kepler 36 Grimaldi 37 Aristarchus A Mare Crisum B Mare Fercunditatis C Mare Nectaris D Mare Tranquilitatis E Mare Serenitatis F Mare Imbrium G Sinus Iridum H Oceanus Procellarum I Mare Humorum K Mare Nubium V Altai Mountains W Mare Vaporum X Apennine Mountains Y Caucasus Mountains Z Alps] The constantly growing progress of optics leads to perpetual newdiscoveries in science, and at the present time we can say that we knowthe geography of the Moon as well as, and even better than, that of ourown planet. The heights of all the mountains of the Moon are measured towithin a few feet. (One cannot say as much for the mountains of theEarth. ) The highest are over 7, 000 meters (nearly 25, 000 feet). Relatively to its proportions, the satellite is much more mountainousthan the planet, and the plutonian giants are much more numerous therethan here. If we have peaks, like the Gaorisankar, the highest of theHimalayas and of the whole Earth, whose elevation of 8, 840 meters(29, 000 feet) is equivalent to 1/1140 the diameter of our globe, thereare peaks on the Moon of 7, 700 meters (25, 264 feet), _e. G. _, those ofDoerfel and Leibniz, the height of which is equivalent to 1/470 thelunar diameter. Tycho's Mountain is one of the finest upon our satellite. It is visiblewith the naked eye (and perfectly with opera-glasses) as a white pointshining like a kind of star upon the lower portion of the disk. At thetime of full moon it is dazzling, and projects long rays from afar uponthe lunar globe. So, too, Mount Copernicus, whose brilliant whitenesssparkles in space. But the strangest thing about these lunar mountainsis that they are all hollow, and can be measured as well in depth as inheight. A type of mountain as strange to us as are the seas withoutwater! In effect, these mountains of the moon are ancient volcaniccraters, with no summits, nor covers. At the top of the highest peaks, there is a large circular depression, prolonged into the heart of the mountain, sometimes far below the levelof the surrounding plains, and as these craters often measure severalhundred kilometers, one is obliged, if one does not want to go all roundthem in crossing the mountain, to descend almost perpendicularly intothe depths and cross there, to reascend the opposite side, and return tothe plain. These alpine excursions incontestably deserve the name ofperilous ascents! No country on the Earth can give us any notion of the state of the lunarsoil: never was ground so tormented; never globe so profoundly shatteredto its very bowels. The mountains are accumulations of enormous rockstumbled one upon the other, and round the awful labyrinth of craters onesees nothing but dismantled ramparts, or columns of pointed rocks likecathedral spires issuing from the chaos. As we said, there is no atmosphere, or at least so little at the bottomof the valleys that it is imperceptible. No clouds, no fog, no rain norsnow. The sky is an eternally black space, vaultless, jeweled with starsby day as by night. Let us suppose that we arrive among these savage steppes at daybreak:the lunar day is fifteen times longer than our own, because the Suntakes a month to illuminate the entire circuit of the Moon; there are noless than 354 hours from the rising to the setting of the Sun. If wearrive before the sunrise, there is no aurora to herald it, for in theabsence of atmosphere there can be no sort of twilight. Of a sudden onthe dark horizon come flashes of the solar light, striking the summitsof the mountains, while the plains and valleys are still in darkness. The light spreads slowly, for while on the Earth in central latitudesthe Sun takes only two minutes and a quarter to rise, on the Moon ittakes nearly an hour, and in consequence the light it sends out is veryweak for some minutes, and increases excessively slowly. It is a kind ofaurora, but lasts a very short time, for when at the end of half anhour, the solar disk has half risen, the light appears as intense to theeye as when it is entirely above the horizon; the radiant orb is seenwith its protuberances and its burning atmosphere. It rises slowly, likea luminous god, in the depths of the black sky, a profound and formlesssky in which the stars shine all day, since they are not hidden by anyatmospheric veil such as conceals them from us during the daylight. [Illustration: FIG. 72. --The Lunar Apennines. ] The absence of sensible atmosphere must produce an effect on thetemperature of the Moon analogous to that perceived on the highmountains of our globe, where the rarefaction of the air does not permitthe solar heat to concentrate itself upon the surface of the soil, as itdoes below the atmosphere, which acts as a forcing-house: the Sun's heatis not kept in by anything, and incessantly radiates out toward space. In all probability the cold is extremely and constantly rigorous, notonly during the nights, which are fifteen times longer than our own, buteven during the long days of sunshine. We give two different drawings to represent these curious aspects oflunar topography. The first (Fig. 72) is taken in the neighborhood ofthe Apennines, and shows a long chain of mountains beneath which arethree deep rings, Archimedes, Aristillus, and Autolycus: the second(Fig. 73) depicts the lunar ring of Flammarion, [14] whose outline isconstructed of dismantled ramparts, and whose depths are sprinkled withlittle craters. The first of these two drawings was made in England byNasmyth, the second in Germany by Krieger: they both give an exact ideaof what one sees in the telescope with different modes of solarillumination. In the Moon's always black and starry sky a majestic star that is notvisible from the Earth, and exhibits this peculiarity that it isstationary in the Heavens, while all the others pass behind it, mayconstantly be admired, by day as well as by night; and it is also ofconsiderable apparent magnitude. This orb, some four times as large asthe Moon in diameter, and thirteen to fourteen times more extensive insurface, is our Earth, which presents to the Moon a sequence of phasessimilar to those which our satellite presents to us, but in the inversedirection. At the moment of New Moon, the Sun fully illuminates theterrestrial hemisphere turned toward our satellite, and we get "FullEarth"; at the time of Full Moon, on the contrary, the non-illuminatedhemisphere of the Earth is turned toward the satellite, and we get "NewEarth": when the Moon shows us first quarter, the Earth is in lastquarter, and so on. The drawing subjoined gives an idea of theseaspects. [Illustration: FIG. 73. --Flammarion's Lunar Ring. ] What a curious sight our globe must be during this long night offourteen times twenty-four hours! Independent of its phases, which bringit from first quarter to full earth for the middle of the night, andfrom full earth to last quarter for sunrise, how interested we should beto see it thus stationary in the sky, and turning on itself intwenty-four hours. [Illustration: FIG. 74. --Lunar landscape with the Earth in the sky. ] Yes, thanks to us, the inhabitants of the lunar hemisphere turned towardus are gratified by the sight of a splendid nocturnal torch, doubtlessless white than our own despite the clouds with which the terrestrialglobe is studded, and shaded in a tender tone of bluish emerald-green. The royal orb of their long nights, the Earth, gives them moonlight ofunparalleled beauty, and we may say without false modesty that ourpresence in the lunar sky must produce marvelous and absolutelyfairy-like effects. Maybe, they envy us our globe, a dazzling dwelling-place whose splendorradiates through space; they see its greenish clarity varying with theextent of cloud that veils its seas and continents, and they observe itsmotion of rotation, by which all the countries of our planet arerevealed in succession to its admirers. We are talking of these pageants seen from the Moon, and of theinhabitants of our satellite as if they really existed. The sterile anddesolate aspect of the lunar world, however, rather brings us to theconclusion that such inhabitants are non-existent, although we have noauthorization for affirming this. That they have existed seems to mebeyond doubt. The lunar volcanoes had a considerable activity, in anatmosphere that allowed the white volcanic ashes to be carried a longway by the winds, figuring round the craters the stellar rays that arestill so striking. These cinders were spread over the soil, preservingall its asperities of outline, a little heaped up on the side to whichthey were impelled. The magnificent photographs recently made at theParis Observatory by MM. Loewy and Puiseux are splendid evidence ofthese projections. In this era of planetary activity there were liquidsand gases on the surface of the lunar globe, which appear subsequentlyto have been entirely absorbed. Now the teaching of our own planet isthat Nature nowhere remains infertile, and that the production of Lifeis a law so general and so imperious that life develops at its ownexpense, sooner than abstain from developing. Accordingly, it isdifficult to suppose that the lunar elements can have remained inactive, when only next door they exhibited such fecundity upon our globe. Yes, the Moon has been inhabited by beings doubtless very different fromourselves, and perhaps may still be, although this globe has run throughthe phases of its astral life more rapidly than our own, and thedaughter is relatively older than the mother. The duration of the life of the worlds appears to have been inproportion with their masses. The Moon cooled and mineralized morequickly than the Earth. Jupiter is still fluid. The progress of optics brings us already very close to this neighboringprovince. 'Tis a pity we can not get a little nearer! A telescopic magnification of 2, 000 puts the Moon at 384, 000/2000 or 192kilometers (some 120 miles) from our eye. Practically we can obtain nomore, either from the most powerful instruments, or from photographicenlargements. Sometimes, exceptionally, enlargements of 3, 000 can beused. This = 384000/3000 or 128 kilometers (some 80 miles). Undoubtedly, this is an admirable result, which does the greatest honor to humanintelligence. But it is still too far to enable us to determine anythingin regard to lunar life. Any one who likes to be impressed by grand and magnificent sights mayturn even a modest field-glass upon our luminous satellite, at aboutfirst quarter, when the relief of its surface, illuminated obliquely bythe Sun, is at its greatest value. If you examine our neighbor world atthis period, for choice at the hour of sunset, you will be astonished atits brilliancy and beauty. Its outlines, its laces, and embroideries, give the image of a jewel of shining silver, translucent, fluid, palpitating in the ether. Nothing could be more beautiful, nothingpurer, and more celestial, than this lunar globe floating in the silenceof space, and sending back to us as in some fairy dream the solarillumination that floods it. But yesterday I received the sameimpression, watching a great ring half standing out, and following theprogress of the Sun as it mounted the lunar horizon to touch thesesilvered peaks. And I reflected that it is indeed inconceivable that999, 999/1, 000, 000 of the inhabitants of our planet should pass theirlives without ever having attended to this pageant, nor to any of thoseothers which the divine Urania scatters so profusely beneath thewondering gaze of the observers of the Heavens. CHAPTER X THE ECLIPSES Among all the celestial phenomena at which it may be our lot to assistduring our contemplation of the universe, one of the most magnificentand imposing is undoubtedly that which we are now going to consider. The hirsute comets, and shooting stars with their graceful flight, captivate us with a mysterious and sometimes fantastic attraction. Wegladly allow our thoughts, mute questioners of the mysteries of thefirmament, to rest upon the brilliant, golden trail they leave behindthem. These unknown travelers bring a message from eternity; they tellus the tale of their distant journeys. Children of space, their etherealbeauty speaks of the immensity of the universe. The eclipses, on the other hand, are phenomena that touch us morenearly, and take place in our vicinity. In treating of them, we remain between the Earth and the Moon, in ourlittle province, and witness the picturesque effects of the combinedmovements of our satellite around us. Have you ever seen a total eclipse of the Sun? The sky is absolutely clear: no fraction of cloud shadows the solarrays. The azure vault of the firmament crowns the Earth with a dome ofdazzling light. The fires of the orb of day shed their beneficentinfluence generally upon the world. Yet, see! The radiance diminishes. The luminous disk of the Sun isgradually corroded. Another disk, as black as ink, creeps in front ofit, and little by little invades it entirely. The atmosphere takes on awan, sepulchral hue; astonished nature is hushed in profound silence; animmense veil of sadness spreads over the world. Night comes on suddenly, and the stars shine out in the Heavens. It seems as though by somemysterious cataclysm the Sun had disappeared forever. But thistribulation is soon over. The divine orb is not extinct. A flaming jetemerges from the shadow, announcing his return, and when he reappears wesee that he has lost nothing in splendor or beauty. He is still theradiant Apollo, King of Day, watching over the life of the planetaryworlds. This sudden night, darkening the Heavens in the midst of a fine day, cannot fail to produce a vivid impression upon the spectators of the superbphenomenon. The eclipse lasts only for a few moments, but long enough to make a deepimpression upon our minds, and indeed to inspire anxious spirits withterror and agitation--even at this epoch, when we know that there isnothing supernatural or formidable about it. In former days, Humanity would have trembled, in uneasy consternation. Was it a judgment from Heaven? Must it not be the work of some invisiblehand throwing the somber veil of night over the celestial torch? Had not the Earth strayed off her appointed path, and were we not all tobe deprived eternally of the light of our good Sun? Was some monstrousdragon perhaps preparing to devour the orb of day? The fable of the dragon devouring the Sun or Moon during the eclipses isuniversal in Asia as in Africa, and still finds acceptance under morethan one latitude. But our readers already know that we may identify theterrible celestial dragon with our gentle friend the Moon, who would notbe greatly flattered by the comparison. We saw in the preceding lesson that the Moon revolves round us, describing an almost circular orbit that she travels over in about amonth. In consequence of this motion, the nocturnal orb is sometimesbetween the Sun and the Earth, sometimes behind us, sometimes at a rightangle in relation to the Sun and the Earth. Now, the eclipses of the Sunoccur invariably at the time of New Moon, when our satellite passesbetween the Sun and ourselves, and the eclipses of the Moon, at themoment of Full Moon, when the latter is opposite to the Sun, and behindus. This fact soon enabled the astronomers of antiquity to discover thecauses to which eclipses are due. The Moon, passing at the beginning of its revolution between the Sun andthe Earth, may conceal a greater or lesser portion of the orb of day. Inthis case there is an eclipse of the Sun. On the other hand, when it ison the other side of the Earth in relation to the Sun, at the moment ofFull Moon, our planet may intercept the solar rays, and prevent themfrom reaching our satellite. The Moon is plunged into _the shadow of theEarth_, and is then eclipsed. Such is the very simple explanation of thephenomenon. But why is there not an eclipse of the Sun at each New Moon, and an eclipse of the Moon at each Full Moon? If the Moon revolved round us in the same plane as the Earth round theSun, it would eclipse the Sun at each New Moon, and would be itselfeclipsed in our shadow at each Full Moon. But the plane of the lunarorbit dips a little upon the plane of the terrestrial orbit, and theeclipses can only be produced when the New Moon or the Full Moon occurat the line of intersection of these two planes, _i. E. _, when the Sun, the Moon, and the Earth are upon the same straight line. In the majorityof cases, instead of interposing itself directly in front of thesovereign of our system, our satellite passes a little above or a littlebelow him, just as its passage behind us is nearly always effected alittle above or below the cone of shadow that accompanies our planet, opposite the Sun. When the Moon intervenes directly in front of the Sun, she arrests thelight of the radiant orb, and conceals a greater or less portion of thesolar disk. The eclipse is partial if the Moon covers only a portion ofthe Sun; total if she covers it entirely; annular, if the solar disk isvisible all round the lunar disk, as appears when the Moon, in herelliptical orbit, is beyond medium distance, toward the apogee. On the other hand, when the Moon arrives immediately within the cone ofshadow that the Earth projects behind it, it is her turn to be eclipsed. She no longer receives the rays of the Sun, and this deprivation is themore marked in that she owes all her brilliancy to the light of the orbof day. The Moon's obscurity is complete if she is entirely plunged intothe cone of shadow. In this case, the eclipse is total. But if a portionof her disk emerges from the cone, that part remains illuminated whilethe light of the other dies out. In that case there is a partialeclipse, and the rounded form of the Earth's shadow can be seenprojected upon our satellite, a celestial witness to the sphericalnature of our globe. Under certain conditions, then, the Moon can deprive us of the luminousrays of the Sun, by concealing the orb of day, and in other cases isherself effaced in crossing our shadow. Despite the fables, fears, andanxieties it has engendered, this phenomenon is perfectly natural: theMoon is only playing hide-and-seek with us--a very harmless amusement, as regards the safety of our planet. But as we said just now, these phenomena formerly had the power ofterrifying ignorant mortals, either when the orb of light and lifeseemed on the verge of extinction, or when the beautiful Phoebus wascovered with a veil of crape and woe, or took on a deep coppery hue. It would take a volume to describe all the notable events which havebeen influenced by eclipses, sometimes for good, more often withdisastrous consequences. The recital of these tragic stories would notbe devoid of interest; it would illustrate the possibilities ofignorance and superstition, and the power man gains from intellectualculture and scientific study. Herodotus records that the Scythians, having some grievance againstCyaxarus, King of the Medes, revenged themselves by serving up the limbsof one of his children, whom they had murdered, at a banquet as raregame. The scoundrels who committed this atrocious crime took refuge atthe Court of the King of Lydia, who was ill judged enough to protectthem. War was accordingly declared between the Medes and Lydians, but atotal eclipse of the Sun occurring just when the battle was imminent, had the happy effect of disarming the combatants, who prudently retiredeach to their own country. This eclipse, which seems to have occurred onMay 28, 584 B. C. , had been predicted by Thales. The French painterRochegrosse has painted a striking picture of the scene (Fig. 75). In the year 413 B. C. The Athenian General Nicias prepared to return toGreece after an expedition to Sicily. But, terrified by an eclipse ofthe Moon, and fearing the malign influence of the phenomenon, he put offhis departure, and lost the chance of retreat. This superstition costhim his life. The Greek army was destroyed, and this event marks thecommencement of the decadence of Athens. In 331 B. C. An eclipse of the Moon disorganized the troops of Alexander, near Arbela, and the great Macedonian Captain had need of all hisaddress to reassure his panic-stricken soldiers. Agathocles, King of Syracuse, blocked by the Carthaginians in the portof this city, had the good fortune to escape, but was disturbed on thesecond day of his flight by the arrival of a total eclipse of the Sunwhich alarmed his companions. "What are you afraid of?" said he, spreading his cloak in front of the Sun. "Are you alarmed at a shadow?"(This eclipse seems to be that of August 15, 309, rather than that ofMarch 2, 310. ) [Illustration: FIG. 75. --Battle between the Medes and Lydians arrestedby an Eclipse of the Sun. ] On June 29, 1033, an epoch at which the approaching end of the worldstruck terror into all hearts, an annular eclipse of the Sun occurringabout midday frustrated the designs of a band of conspirators whointended to strangle the Pope at the altar. This Pope was Benedict IX, ayouth of less than twenty, whose conduct is said to have been anythingbut exemplary. The assassins, terrified at the darkening of the Sun, dared not touch the Pontiff, and he reigned till 1044. [15] On March 1, 1504, a lunar eclipse saved the life of ChristopherColumbus. He was threatened with death by starvation in Jamaica, wherethe contumacious savages refused to give him provisions. Forewarned ofthe arrival of this eclipse by the astronomical almanacs, he threatenedto deprive the Caribs of the light of the Moon--and kept his word. Theeclipse had hardly begun when the terrified Indians flung themselves athis feet, and brought him all that he required. In all times and among all people we find traces of popularsuperstitions connected with eclipses. Here, the abnormal absence of theMoon's light is regarded as a sign of divine anger: the humble penitentsbetake themselves to prayer to ward off the divine anger. There, thecruelty of the dread dragon is to be averted: he must be chased away bycries and threats, and the sky is bombarded with shots to deliver thevictim from his monstrous oppressor. In France the announcement of a solar eclipse for August 21, 1560, sogreatly disturbed our ancestors' peace of mind as to make them idiotic. Preparations were made for assisting at an alarming phenomenon thatthreatened Humanity with deadly consequences! The unhappy eclipse hadbeen preceded by a multitude of ill omens! Some expected a greatrevolution in the provinces and in Rome, others predicted a newuniversal deluge, or, on the other hand, the conflagration of the world;the most optimistic thought the air would be contaminated. To preservethemselves from so many dangers, and in accordance with the physicians'orders, numbers of frightened people shut themselves up in tightlyclosed and perfumed cellars, where they awaited the decrees of Fate. Theapproach of the phenomenon increased the panic, and it is said that onevillage _curé_, being unable to hear the confessions of all his flock, who wanted to discharge their souls of sin before taking flight for abetter world, was fain to tell them "there was no hurry, because theeclipse had been put off a fortnight on account of the number ofpenitents"! [Illustration: FIG. 76. --Eclipse of the Moon at Laos (February 27, 1877). ] These fears and terrors are still extant among ignorant peoples. In thenight of February 27, 1877, an eclipse of the Moon produced anindescribable panic among the inhabitants of Laos (Indo-China). In orderto frighten off the Black Dragon, the natives fired shots at thehalf-devoured orb, accompanying their volley with the most appallingyells. Dr. Harmand has memorialized the scene in the lively sketch givenon p. 269. During the solar eclipse of March 15, 1877, an analogous scene occurredamong the Turks, who for the moment forgot their preparations for warwith Russia, in order to shoot at the Sun, and deliver him from thetoils of the Dragon. The lunar eclipse of December 16, 1880, was not unnoticed at Tackhent(Russian Turkestan), where it was received with a terrific din ofsaucepans, samovars and various implements struck together again andagain by willing hands that sought to deliver the Moon from the demonTchaitan who was devouring her. In China, eclipses are the object of imposing ceremonies, whose objectis to reestablish the regularity of the celestial motions. Since theEmperor is regarded as the Son of Heaven, his government must in somesort be a reflection of the immutable order of the sidereal harmonies. As eclipses were regarded by astrologers as disturbances of the divineorder, their appearance indicates some irregularity in the government ofthe Celestial Empire. Accordingly, they are received with all kinds ofexpiatory ceremonies prescribed thousands of years ago, and still inforce to-day. In the twentieth century, as in the nineteenth, the eighteenth, or inancient epochs, the same awe and terror operates upon the ignorantpopulations who abound upon the surface of our planet. To return to astronomical realities. We said above that these phenomena were produced when the Full Moon andthe New Moon reached the line of intersection, known as the line ofnodes, when the plane of the lunar orbit cuts the plane of the ecliptic. As this line turns and comes back in the same direction relatively tothe Sun at the end of eighteen years, eleven days, we have only toregister the eclipses observed during this period in order to know allthat will occur in the future, and to find such as happened in the past. This period was known to the Greeks under the name of the Metonic Cycle, and the Chaldeans employed it three thousand years ago under the name ofSaros. On examining this cycle, composed of 223 lunations, we see that therecan not be more than seven eclipses in one year, nor less than two. Whenthere are only two, they are eclipses of the Sun. The totality of a solar eclipse can not last more than seven minutes, fifty-eight seconds at the equator, and six minutes, ten seconds in thelatitude of Paris. The Moon, on the contrary, may be entirely eclipsedfor nearly two hours. Eclipses of the Sun are very rare for a definite spot. Thus not oneoccurred for Paris during the whole of the nineteenth century, the lastwhich happened exactly above the capital of France having been on May22, 1724. I have calculated all those for the twentieth century, andfind that two will take place close to Paris, on April 17, 1912, ateighteen minutes past noon (total for Choisy-le-Roi, Longjumeau, andDourdan, but very brief: seven seconds), and August 11, 1999, at 10. 28A. M. (total for Beauvais, Compiègne, Amiens, St. Quentin, fairly long:two minutes, seventeen seconds). Paris itself will not be favored beforeAugust 12, 2026. In order to witness the phenomenon, one must go andlook for it. This the author did on May 28, 1900, in Spain. The progress of the lunar shadow upon the surface of the Earth is tracedbeforehand on maps that serve to show the favored countries for whichour satellite will dispense her ephemeral night. The above figure showsthe trajectory of the total phase of the 1900 eclipse in Portugal, Spain, Algeria, and Tunis. [Illustration: FIG. 77. --The path of the Eclipse of May 28, 1900. ] The immutable splendor of the celestial motions had never struck theauthor so impressively as during the observation of this grandiosephenomenon. With the absolute precision of astronomical calculations, our satellite, gravitating round the Earth, arrived upon the theoreticalline drawn from the orb of day to our planet, and interposed itselfgradually, slowly, and exactly, in front of it. The eclipse was total, and occurred at the moment predicted by calculation. Then the obscureglobe of the Moon pursued its regular course, discovered the radiant orbbehind, and gradually and slowly completed its transit in front of him. Here, to all observers, was a double philosophical lesson, a twofoldimpression: that of the greatness, the omnipotence of the inexorableforces that govern the universe, and that of the inexorable valor ofman, of this thinking atom straying upon another atom, who by thetravail of his feeble intelligence has arrived at the knowledge of thelaws by which he, like the rest of the world, is borne away throughspace, through time, and through eternity. The line of centrality passed through Elche, a picturesque city of30, 000 inhabitants, not far from Alicante, and we had chosen this forour station on account of the probability of fine weather. From the terrace of the country house of the hospitable Mayor, a farmtransformed into an observatory by our learned friend, Count de la BaumePluvinel, there were no obstacles between ourselves and any part of thesky or landscape. The whole horizon lay before us. In front was a townof Arab aspect framed in a lovely oasis of palm-trees; a little fartheroff, the blue sea beyond the shores of Alicante and Murcia: on theother side a belt of low mountains, and near us fields and gardens. ACompany of the Civic Guard kept order, and prevented the entrance of toomany curious visitors, of whom over ten thousand had arrived. At the moment when the first contact of the lunar disk with the solardisk was observed in the telescope, we fired a gun, in order to announcethe precise commencement of the occultation to the 40, 000 persons whowere awaiting the phenomenon, and to discover what difference wouldexist between this telescopic observation and those made with theunaided eyes (protected simply by a bit of smoked glass) of so manyimprovised spectators. This had already been done by Arago at Perpignanin 1842. The verification was almost immediate for the majority of eyes, and may be estimated at eight or ten seconds. So that the commencementof the eclipse was confirmed almost as promptly for the eye as with theastronomical instruments. The sky was splendidly clear; no cloud, no mist, deep blue; blazing Sun. The first period of the eclipse showed nothing particular. It is onlyfrom the moment when more than half the solar disk is covered by thelunar disk that the phenomenon is imposing in its grandeur. At thisphase, I called the attention of the people standing in the court to thevisibility of the stars, and indicating the place of Venus in the skyasked if any with long sight could perceive her. Eight at onceresponded in the affirmative. It should be said that the planet was atthat time at its period of maximum brilliancy, when for observersblessed with good sight, it is always visible to the unaided eye. When some three-quarters of the Sun were eclipsed, the pigeons which hadflown back to the farm huddled into a corner, and made no furthermovement. They told me that evening that the fowls had done the same alittle later, returning to the hen-house as though it had been night, and that the small children (who were very numerous at Elche, where thepopulation is certainly not diminishing) left off their games, and cameback to their mothers' skirts. The birds flew anxiously to their nests. The ants in one garden were excessively agitated, no doubt disconcertedin their strategics. The bats came out. A few days before the eclipse I had prepared the inhabitants of thispart of Spain for the observation of the phenomenon by the followingdescription, which sums up the previous accounts of the astronomers: "The spectacle of a total eclipse of the Sun is one of the mostmagnificent and imposing that it is possible to see in nature. At theexact moment indicated by calculation, the Moon arrives in front of theSun, eats into it gradually, and at last entirely covers it. The lightof the day lessens and is transformed. A sense of oppression is felt byall nature, the birds are hushed, the dog takes refuge with his master, the chickens hide beneath their mother's wing, the wind drops, thetemperature falls, an appalling stillness is everywhere perceptible, asthough the universe were on the verge of some imminent catastrophe. Men's faces assume a cadaverous hue similar to that given at night bythe flame of spirits of wine and salt, a livid funereal light, thesinister illumination of the world's last hour. "At the moment when the last line of the solar crescent disappears, wesee, instead of the Sun, a black disk surrounded with a splendidluminous aureole shooting immense jets into space, with roseate flamesburning at the base. "A sudden night has fallen on us, a weird, wan night in which thebrightest of the stars are visible in the Heavens. The spectacle issplendid, grandiose, solemn, and sublime. " This impression was actually felt by us all, as may be seen from thefollowing notes, written in my schedule of observation during the event, or immediately after: "3. 50 P. M. Light very weak, sky leaden gray, mountains standing out withremarkable clearness from the horizon, and seeming to approach us. "3. 55 P. M. Fall of temperature very apparent. Cold wind blowing throughthe atmosphere. "3. 56 P. M. Profound silence through nature, which seems to participatein the celestial phenomenon. Silence in all the groups. "3. 57 P. M. Light considerably diminished, becoming wan, strange, andsinister. Landscape leaden gray, sea looks black. This diminution oflight is not that of every day after the sunset. There is, as it were, atint of sadness spread over the whole of nature. One becomes accustomedto it, and yet while we know that the occultation of the Sun by the Moonis a natural phenomenon, we can not escape a certain sense ofuneasiness. The approach of some extraordinary spectacle is imminent. " At this point we examined the effects of the solar light upon the sevencolors of the spectrum. In order to determine as accurately as possiblethe tonality of the light of the eclipse, I had prepared seven greatsheets, each painted boldly in the colors of the spectrum, violet, indigo, blue, green, yellow, orange, red; and a similar series in piecesof silk. These colors were laid at our feet upon the terrace where mywife, as well as Countess de la Baume, were watching with me. We thensaw the first four disappear successively and entirely and turn black ina few seconds, in the following order: violet, indigo, blue, green. Thethree other colors were considerably attenuated by the darkness, butremained visible. It should be noted that in the normal order of things--that is, everyevening--the contrary appears; violet remains visible after the red. This experiment shows that the last light emitted by the eclipsed Sunbelongs to the least refrangible rays, to the greatest wave-lengths, tothe slowest vibrations, to the yellow and red rays. Such therefore isthe predominating color of the solar atmosphere. This experiment completed, we turn back to the Sun. Magical and splendidspectacle! Totality has commenced, the Sun has disappeared, the blackdisk of the Moon covers it entirely, leaving all round it a magnificentcorona of dazzling light. One would suppose it to be an annular eclipse, with the difference that this can be observed with the naked eye, without fatigue to the retina, and drawn quietly. This luminous coronal atmosphere entirely surrounds the solar disk, at apretty equal depth, equivalent to about the third of half the solardiameter. It may be regarded as the Sun's atmosphere. Beyond this corona is an aureole, of vaster glory but less luminous, which sends out long plumes, principally in the direction of theequatorial zone of the Sun, and of the belt of activity of the spots andprominences. At the summit of the disk it is conical in shape. Below it is double, and its right-hand portion ends in a point, not far from Mercury, whichshines like a dazzling star of first magnitude, and seems placed thereexpressly to give us the extent and direction of the solar aureole. I draw these various aspects (which, moreover, change with the movementof the Moon), and what strikes me most is the distinction in lightbetween this aureole and the coronal atmosphere; the latter appears tobe a brilliant silvery white, the former is grayer and certainly lessdense. My impression is that there are _two solar envelopes of entirelydifferent nature_, the corona belonging to the globe of the Sun, andforming its atmosphere properly so-called, very luminous; the aureoleformed of particles that circulate independently round it, probablyarising from eruptions, their form as a whole being possibly due toelectric or magnetic forces, counterbalanced by resistances of variousnatures. In our own atmosphere the volcanic eruptions are distinct fromthe aerial envelope. The general configuration of this external halo, spreading moreparticularly in the equatorial zone, is sufficiently like that of theeclipse of 1889, published in my _Popular Astronomy_, which alsocorresponded with a minimum of solar energy. The year 1900 is in factclose upon the minimum of the eleven-year period. This equatorial formis, moreover, what all the astronomers were expecting. [Illustration: FIG. 78. --Total eclipse of the Sun, May 28, 1900, asobserved from Elche (Spain). ] There can no longer be the slightest doubt that the solar envelopevaries with the activity of the Sun. . . . "But the total eclipse lasted a much shorter time than I have taken towrite these lines. The seventy-nine seconds of totality are over. Adazzling light bursts from the Sun, and tells that the Moon pursuing itsorbit has left it. The splendid sight is over. It has gone like ashadow. "Already over! It is almost a disillusion. Nothing beautiful lasts inthis world. Too sad! If only the celestial spectacle could have lastedtwo, three, or four minutes! It was too short. . . . "Alas! we are forced to take things as they are. "The surprise, the oppression, the terror of some, the universal silenceare over. The Sun reappears in his splendor, and the life of natureresumes its momentarily suspended course. "While I was making my drawing, M. L'Abbé Moreux, my colleague from theAstronomical Society of France, who accompanied me to Spain for thisobservation, was taking one of his own, without any reciprocalcommunication. These two sketches are alike, and confirmatory. "The differential thermometers that I exposed to the Sun, hangingfreely, and protected from reflection from the ground, were read everyfive minutes. The black thermometer went down from 33. 1° to 20. 7°, thatis 12. 4°; the white from 29° to 20. 2°--that is, 8. 8°. The temperature inthe shade only varied three degrees. "The light received during totality was due: first, to the luminousenvelope of the Sun; second, to that of the terrestrial atmosphere, illuminated at forty kilometers (twenty-five miles) on the one side andthe other of the line of centrality. It appeared to be inferior to thatof the Full Moon, on account of the almost sudden transition. But, inreality, it was more intense, for only first-magnitude stars werevisible in the sky, whereas on a night of full moon, stars of second, and even of third magnitude are visible. We recognized, among others, Venus, Mercury, Sirius, Procyon, Capella, Rigel, Betelgeuse. " * * * * * From these notes, taken on the spot, it is evident that thecontemplation of a total eclipse of the Sun is one of the most marvelousspectacles that can be admired upon our planet. Some persons assured me that they saw the shadow of the Moon flyingrapidly over the landscape. My attention was otherwise occupied, and Iwas unable to verify this interesting observation. The shadow of theMoon in effect took only eleven minutes (3. 47 P. M. To 3. 58 P. M. ) totraverse the Iberian Peninsula from Porto to Alicante, _i. E. _, adistance of 766 kilometers (475 miles). It must therefore have passedover the ground at a velocity of sixty-nine kilometers per minute, or1, 150 meters per second, a speed higher than that of a bullet. It caneasily be watched from afar, on the mountains. Some weeks previous to this fine eclipse, when I informed the Spaniardsof the belt along which it could be observed, I had invited them to noteall the interesting phenomena they might witness, including the effectsproduced by the eclipse upon animals. Birds returned hurriedly to theirnests, swallows lost themselves, sheep huddled into compact packs, partridges were hypnotized, frogs croaked as if it were night, fowlstook refuge in the hen-house, and cocks crowed, bats came out, and weresurprised by the sun, chicks gathered under their mothers' wing, cage-birds ceased their songs, some dogs howled, others crept shiveringto their masters' feet, ants returned to the antheap, grasshopperschirped as at sunset, pigeons sank to the ground, a swarm of bees wentsilently back to their hive, and so on. These creatures behaved as though the night had come, but there werealso signs of fear, surprise, even of terror, differing only "in degree"from those manifested during the grandiose phenomenon of a totaleclipse by human beings unenlightened by a scientific education. At Madrid the eclipse was only partial. The young King of Spain, AlfonsoXIII, took care to photograph it, and I offer the photograph to myreaders (Fig. 79), as this amiable sovereign did me the honor to give itme a few days after the eclipse. [Illustration: FIG. 79. --The Eclipse of May 28, 1900, as photographed byKing Alfonso XIII, at Madrid. ] The technical results of these observations of solar eclipses relatemore especially to the elucidation of the grand problem of the physicalconstitution of the Sun. We alluded to them in the chapter devoted tothis orb. The last great total eclipses have been of immense value toscience. The eclipses of the Moon are less important, less interesting, than theeclipses of the Sun. Yet their aspect must not be neglected on thisaccount, and it may be said to vary for each eclipse. Generally speaking, our satellite does not disappear entirely in theEarth's cone of shadow; the solar rays are refracted round our globe byour atmosphere, and curving inward, illumine the lunar globe with a rosytint that reminds one of the sunset. Sometimes, indeed, this refractiondoes not occur, owing doubtless to lack of transparency in theatmosphere, and the Moon becomes invisible. This happened recently, onApril 11, 1903. For any spot, eclipses of the Moon are incomparably more frequent thaneclipses of the Sun, because the cone of lunar shadow that produces thesolar eclipses is not very broad at its contact with the surface of theglobe (10, 20, 30, 50, 100 kilometers, according to the distance of theMoon), whereas all the countries of the Earth for which the Moon isabove the horizon at the hour of the lunar eclipse are able to see it. It is at all times a remarkable spectacle that uplifts our thoughts tothe Heavens, and I strongly advise my readers on no account to foregoit. CHAPTER XI ON METHODS HOW CELESTIAL DISTANCES ARE DETERMINED, AND HOW THE SUN IS WEIGHED I will not do my readers the injustice to suppose that they will bealarmed at the title of this Lesson, and that they do not employ some"method" in their own lives. I even assume that if they have been goodenough to take me on faith when I have spoken of the distances of theSun and Moon, and Stars, or of the weight of bodies at the surface ofMars, they retain some curiosity as to how the astronomers solve theseproblems. Hence it will be as interesting as it is useful to completethe preceding statements by a brief summary of the methods employed foracquiring these bold conclusions. The Sun seems to touch the Earth when it disappears in the purple mistsof twilight: an immense abyss separates us from it. The stars go hand inhand down the constellated sky; and yet one can not think of theirinconceivable distance without a shiver. Our neighbor, Moon, floats in space, a stone's throw from us: butwithout calculation we should never know the distance, which remains animpassable desert to us. The best educated persons sometimes find it difficult to admit thatthese distances of Sun and Moon are better determined and more precisethan those of certain points on our minute planet. Hence, it is ofparticular moment for us to give an exact account of the means employedin determining them. The calculation of these distances is made by "_triangulation_. " Thisprocess is the same that surveyors use in the measurement of terrestrialdistances. There is nothing very alarming about it. If the word repelsus a little at first, it is from its appearance only. When the distance of an object is unknown, the only means of expressingits apparent size is by measurement of the angle which it subtendsbefore our eyes. We all know that an object appears smaller, in proposition with itsdistance from us. This diminution is not a matter of chance. It isgeometric, and proportional to the distance. Every object removed to adistance of 57 times its diameter measures an angle of 1 degree, whatever its real dimensions. Thus a sphere 1 meter in diameter measuresexactly 1 degree, if we see it at a distance of 57 meters. A statuemeasuring 1. 80 meters (about 5 ft. 8 in. ) will be equal to an angle of 1degree, if distant 57 times its height, that is to say, at 102. 60meters. A sheet of paper, size 1 decimeter, seen at 5. 70 meters, represents the same magnitude. In length, a degree is the 57th part of the radius of a circle, _i. E. _, from the circumference to the center. The measurement of an angle is expressed in parts of the circumference. Now, what is an angle of a degree? It is the 360th part of anycircumference. On a table 3. 60 meters round, an angle of one degree is acentimeter, seen from the center of the table. Trace on a sheet of papera circle 0. 360 meters round--an angle of 1 degree is a millimeter. [Illustration: FIG. 80. --Measurement of Angles. ] If the circumference of a circus measuring 180 meters be divided into360 places, each measuring 0. 50 meters in width, then when the circus isfull a person placed at the center will see each spectator occupying anangle of 1 degree. The angle does not alter with the distance, andwhether it be measured at 1 meter, 10 meters, 100 kilometers, or in theinfinite spaces of Heaven, it is always the same angle. Whether a degreebe represented by a meter or a kilometer, it always remains a degree. Asangles measuring less than a degree often have to be calculated, thisangle has been subdivided into 60 parts, to which the name of _minutes_has been given, and each minute into 60 parts or _seconds_. Writtenshort, the degree is indicated by a little zero (°) placed above thefigure; the minute by an apostrophe ('), and the second by two ("). These minutes and seconds of _arc_ have no relation with the same termsas employed for the division of the duration of time. These latter oughtnever to be written with the signs of abbreviation just indicated, though journalists nowadays set a somewhat pedantic example, by writing, _e. G. _, for an automobile race, 4h. 18' 30", instead of 4h. 18m. 30s. This makes clear the distinction between the relative measure of anangle and the absolute measures, such, for instance, as the meter. Thus, a degree may be measured on this page, while a second (the 3, 600th partof a degree) measured in the sky may correspond to millions ofkilometers. Now the measure of the Moon's diameter gives us an angle of a littlemore than half a degree. If it were exactly half a degree, we shouldknow by that that it was 114 times the breadth of its disk away from us. But it is a little less, since we have more than half a degree (31'), and the geometric ratio tells us that the distance of our satellite is110 times its diameter. Hence we have very simply obtained a first idea of the distance of theMoon by the measure of its diameter. Nothing could be simpler than thismethod. The first step is made. Let us continue. This approximation tells us nothing as yet of the real distance of theorb of night. In order to know this distance in miles, we need to knowthe width in miles of the lunar disk. [Illustration: FIG. 81. --Division of the Circumference into 360degrees. ] This problem has been solved, as follows: Two observers go as far as possible from each other, and observe theMoon simultaneously, from two stations situated on the same meridian, but having a wide difference of latitude. The distance that separatesthe two points of observation forms the base of a triangle, of which thetwo long sides come together on the Moon. [Illustration: FIG. 82. --Measurement of the distance of the Moon. ] It is by this proceeding that the distance of our satellite was finallyestablished, in 1751 and 1752, by two French astronomers, Lalande andLacaille; the former observing at Berlin, the latter at the Cape of GoodHope. The result of their combined observations showed that the angleformed at the center of the lunar disk by the half-diameter of the Earthis 57 minutes of arc (a little less than a degree). This is known as the_parallax_ of the Moon. Here is a more or less alarming word; yet it is one that we can notdispense with in discussing the distance of the stars. This astronomicalterm will soon become familiar in the course of the present lesson, where it will frequently recur, and always in connection with themeasurement of celestial distances. "Do not let us fear, " wrote Lalandein his _Astronomie des Dames_, "do not let us fear to use the termparallax, despite its scientific aspect; it is convenient, and this termexplains a very simple and very familiar effect. " "If one is at the play, " he continues, "behind a woman whose hat is toolarge, and prevents one from seeing the stage [written a hundred yearsago!], one leans to the left or right, one rises or stoops: all this isa parallax, a diversity of aspect, in virtue of which the hat appears tocorrespond with another part of the theater from that in which are theactors. " "It is thus, " he adds, "that there may be an eclipse of the Sunin Africa and none for us, and that we see the Sun perfectly, because weare high enough to prevent the Moon's hiding it from us. " See how simple it is. This parallax of 57 minutes proves that the Earthis removed from the Moon at a distance of about 60 times itshalf-diameter (precisely, 60. 27). From this to the distance of the Moonin kilometers is only a step, because it suffices to multiply thehalf-diameter of the Earth, which is 6, 371 kilometers (3, 950 miles) bythis number. The distance of our satellite, accordingly, is 6, 371kilometers, multiplied by 60. 27--that is, 384, 000 kilometers (238, 000miles). The parallax of the Moon not only tells us definitely thedistance of our planet, but also permits us to calculate its real volumeby the measure of its apparent volume. As the diameter of the Moon seenfrom the Earth subtends an angle of 31', while that of the Earth seenfrom the Moon is 114', the real diameter of the orb of night must be tothat of the terrestrial globe in the relation of 273 to 1, 000. That is alittle more than a quarter, or 3, 480 kilometers (2, 157 miles), thediameter of our planet being 12, 742 kilometers (7, 900 miles). This distance, calculated thus by geometry, is positively determinedwith greater precision than that employed in the ordinary measurementsof terrestrial distances, such as the length of a road, or of a railway. This statement may seem to be a romance to many, but it is undeniablethat the distance separating the Earth from the Moon is measured withgreater care than, for instance, the length of the road from Paris toMarseilles, or the weight of a pound of sugar at the grocer's. (And wemay add without comment, that the astronomers are incomparably moreconscientious in their measurements than the most scrupulousshop-keepers. ) Had we conveyed ourselves to the Moon in order to determine its distanceand its diameter directly, we should have arrived at no greaterprecision, and we should, moreover, have had to plan out a journeywhich in itself is the most insurmountable of all the problems. The Moon is at the frontier of our little terrestrial province: onemight say that it traces the limits of our domain in space. And yet, adistance of 384, 000 kilometers (238, 000 miles) separates the planet fromthe satellite. This space is insignificant in the immeasurable distancesof Heaven: for the Saturnians (if such exist!) the Earth and the Moonare confounded in one tiny star; but for the inhabitants of our globe, the distance is beyond all to which we are accustomed. Let us try, however, to span it in thought. A cannon-ball at constant speed of 500 meters (547 yards) per secondwould travel 8 days, 5 hours to reach the Moon. A train started at aspeed of one kilometer per minute, would arrive at the end of anuninterrupted journey in 384, 000 minutes, or 6, 400 hours, or 266 days, 16 hours. And in less than the time it takes to write the name of theQueen of Night, a telegraphic message would convey our news to the Moonin one and a quarter seconds. Long-distance travelers who have been round the world some dozen timeshave journeyed a greater distance. The other stars (beginning with the Sun) are incomparably farther fromus. Yet it has been found possible to determine their distances, andthe same method has been employed. But it will at once be seen that different measures are required incalculating the distance of the Sun, 388 times farther from us than theMoon, for from here to the orb of day is 12, 000 times the breadth of ourplanet. Here we must not think of erecting a triangle with the diameterof the Earth for its base: the two ideal lines drawn from theextremities of this diameter would come together between the Earth andthe Sun; there would be no triangle, and the measurement would beabsurd. In order to measure the distance which separates the Earth from the Sun, we have recourse to the fine planet Venus, whose orbit is situatedinside the terrestrial orbit. Owing to the combination of the Earth'smotion with that of the Star of the Morning and Evening, the capriciousVenus passes in front of the Sun at the curious intervals of 8 years, 113-1/2 years less 8 years, 8 years, 113-1/2 years plus 8 years. Thus there was a transit in June, 1761, then another 8 years after, inJune, 1769. The next occurred 113-1/2 years less 8 years, _i. E. _, 105-1/2 years after the preceding, in December, 1874; the next inDecember, 1882. The next will be in June, 2004, and June, 2012. At theseeagerly anticipated epochs, astronomers watch the transit of Venusacross the Sun at two terrestrial stations as far as possible removedfrom each other, marking the two points at which the planet, seen fromtheir respective stations, appears to be projected at the same moment onthe solar disk. This measure gives the width of an angle formed by twolines, which starting from two diametrically opposite points of theEarth, cross upon Venus, and form an identical angle upon the Sun. Venusis thus at the apex of two equal triangles, the bases of which rest, respectively, upon the Earth and on the Sun. The measurement of thisangle gives what is called the parallax of the Sun--that is, the angulardimension at which the Earth would be seen at the distance of the Sun. [Illustration: FIG. 83. --Measurement of the distance of the Sun. ] Thus, it has been found that the half-diameter of the Earth viewed fromthe Sun measures 8. 82". Now, we know that an object presenting an angleof one degree is at a distance of 57 times its length. The same object, if it subtends an angle of a minute, or the sixtiethpart of a degree, indicates by the measurement of its angle that it is60 times more distant, _i. E. _, 3, 438 times. Finally, an object that measures one second, or the sixtieth part of aminute, is at a distance of 206, 265 times its length. Hence we find that the Earth is at a distance from the Sun of206, 265/8. 82--that is, 23, 386 times its half-diameter, that is, 149, 000, 000 kilometers (93, 000, 000 miles). This measurement again is asprecise and certain as that of the Moon. I hope my readers will easily grasp this simple method of triangulation, the result of which indicates to us with absolute certainty the distanceof the two great celestial torches to which we owe the radiant light ofday and the gentle illumination of our nights. The distance of the Sun has, moreover, been confirmed by other means, whose results agree perfectly with the preceding. The two principal arebased on the velocity of light. The propagation of light is notinstantaneous, and notwithstanding the extreme rapidity of itsmovements, a certain time is required for its transmission from onepoint to another. On the Earth, this velocity has been measured as300, 000 kilometers (186, 000 miles) per second. To come from Jupiter tothe Earth, it requires thirty to forty minutes, according to thedistance of the planet. Now, in examining the eclipses of Jupiter'ssatellites, it has been discovered that there is a difference of 16minutes, 34 seconds in the moment of their occurrence, according asJupiter is on one side or on the other of the Sun, relatively to theEarth, at the minimum and maximum distance. If the light takes 16minutes, 34 seconds to traverse the terrestrial orbit, it must take lessthan that time, or 8 minutes, 17 seconds, to come to us from the Sun, which is situated at the center. Knowing the velocity of light, thedistance of the Sun is easily found by multiplying 300, 000 by 8 minutes, 17 seconds, or 497 seconds, which gives about 149, 000, 000 kilometers(93, 000, 000 miles). Another method founded upon the velocity of light again gives aconfirmatory result. A familiar example will explain it: Let us imagineourselves exposed to a vertical rain; the degree of inclination of ourumbrella will depend on the relation between our speed and that of thedrops of rain. The more quickly we run, the more we need to dip ourumbrella in order not to meet the drops of water. Now the same thingoccurs for light. The stars, disseminated in space, shed floods of lightupon the Heavens. If the Earth were motionless, the luminous rays wouldreach us directly. But our planet is spinning, racing, with the utmostspeed, and in our astronomical observations we are forced to follow itsmovements, and to incline our telescopes in the direction of itsadvance. This phenomenon, known under the name of _aberration_ of light, is the result of the combined effects of the velocity of light and ofthe Earth's motion. It shows that the speed of our globe is equivalentto 1/10000 that of light, _i. E. _, = about 30 kilometers (19 miles) persecond. Our planet accordingly accomplishes her revolution round the Sunalong an orbit which she traverses at a speed of 30 kilometers (better29-1/2) per second, or 1, 770 kilometers per minute, or 106, 000kilometers per hour, or 2, 592, 000 kilometers per day, or 946, 080, 000kilometers (586, 569, 600 miles) in the year. This is the length of theelliptical path described by the Earth in her annual translation. The length of orbit being thus discovered, one can calculate itsdiameter, the half of which is exactly the distance of the Sun. We may cite one last method, whose data, based upon attraction, areprovided by the motions of our satellite. The Moon is a little disturbedin the regularity of her course round the Earth by the influence of thepowerful Sun. As the attraction varies inversely with the square of thedistance, the distance may be determined by analyzing the effect it hasupon the Moon. Other means, on which we will not enlarge in this summary of the methodsemployed for determinations, confirm the precisions of thesemeasurements with certainty. Our readers must forgive us for dwellingat some length upon the distance of the orb of day, since thismeasurement is of the highest importance; it serves as the base for thevaluation of all stellar distances, and may be considered as the meterof the universe. This radiant Sun to which we owe so much is therefore enthroned in spaceat a distance of 149, 000, 000 kilometers (93, 000, 000 miles) from here. Its vast brazier must indeed be powerful for its influence to be exertedupon us to such a manifest extent, it being the very condition of ourexistence, and reaching out as far as Neptune, thirty times more remotethan ourselves from the solar focus. It is on account of its great distance that the Sun appears to us nolarger than the Moon, which is only 384, 000 kilometers (238, 000 miles)from here, and is itself illuminated by the brilliancy of this splendidorb. No terrestrial distance admits of our conceiving of this distance. Yet, if we associate the idea of space with the idea of time, as we havealready done for the Moon, we may attempt to picture this abyss. Thetrain cited just now would, if started at a speed of a kilometer aminute, arrive at the Sun after an uninterrupted course of 283 years, and taking as long to return to the Earth the total would be 566 years. Fourteen generations of stokers would be employed on this celestialexcursion before the bold travelers could bring back news of theexpedition to us. Sound is transmitted through the air at a velocity of 340 meters (1, 115feet) per second. If our atmosphere reached to the Sun, the noise of anexplosion sufficiently formidable to be heard here would only reach usat the end of 13 years, 9 months. But the more rapid carriers, such asthe telegraph, would leap across to the orb of day in 8 minutes, 17seconds. Our imagination is confounded before this gulf of 93, 000, 000 miles, across which we see our dazzling Sun, whose burning rays fly rapidlythrough space in order to reach us. * * * * * And now let us see how the distances of the planets were determined. We will leave aside the method of which we have been speaking; that nowto be employed is quite different, but equally precise in its results. It is obvious that the revolution of a planet round the Sun will belonger in proportion as the distance is greater, and the orbit that hasto be traveled vaster. This is simple. But the most curious thing isthat there is a geometric proportion in the relations between theduration of the revolutions of the planets and their distances. Thisproportion was discovered by Kepler, after thirty years of research, and embodied in the following formula: "The squares of the times of revolution of the planets round the Sun(the periodic times) are proportional to the cubes of their meandistances from the Sun. " This is enough to alarm the boldest reader. And yet, if we unravel thissomewhat incomprehensible phrase, we are struck with its simplicity. What is a square? We all know this much; it is taught to children of tenyears old. But lest it has slipped your memory: a square is simply anumber multiplied by itself. Thus: 2 × 2 = 4; 4 is the square of 2. Four times 4 is 16; 16 is the square of 4. And so on, indefinitely. Now, what is a cube? It is no more difficult. It is a number multipliedtwice by itself. For instance: 2 multiplied by 2 and again by 2 equals 8. So 8 is thecube of 2. 3 × 3 × 3 = 27; 27 is the cube of 3, and so on. Now let us take an example that will show the simplicity and precisionof the formula enunciated above. Let us choose a planet, no matterwhich. Say, Jupiter, the giant of the worlds. He is the Lord of ourplanetary group. This colossal star is five times (precisely, 5. 2) asfar from us as the Sun. Multiply this number twice by itself 5. 2 × 5. 2 × 5. 2 = 140. On the other hand, the revolution of Jupiter takes almost twelve years(11. 85). This number multiplied by itself also equals 140. The square ofthe number 11. 85 is equal to the cube of the number 5. 2. This verysimple law regulates all the heavenly bodies. Thus, to find the distance of a planet, it is sufficient to observe thetime of its revolution, then to discover the square of the given numberby multiplying it into itself. The result of the operation givessimultaneously the cube of the number that represents the distance. To express this distance in kilometers (or miles), it is sufficient tomultiply it by 149, 000, 000 (in miles 93, 000, 000), the key to the systemof the world. Nothing, then, could be less complicated than the definition of thesemethods. A few moments of attention reveal to us in their majesticsimplicity the immutable laws that preside over the immense harmony ofthe Heavens. * * * * * But we must not confine ourselves to our own solar province. We have yetto speak of the stars that reign in infinite space far beyond ourradiant Sun. Strange and audacious as it may appear, the human mind is able to crossthese heights, to rise on the wings of genius to these distant suns, and to plumb the depths of the abyss that separates us from thesecelestial kingdoms. Here, we return to our first method, that of triangulation. And thedistance that separates us from the Sun must serve in calculating thedistances of the stars. The Earth, spinning round the Sun at a distance of 149, 000, 000kilometers (93, 000, 000 miles), describes a circumference, or rather anellipse, of 936, 000, 000 kilometers (580, 320, 000 miles), which it travelsover in a year. The distance of any point of the terrestrial orbit fromthe diametrically opposite point which it passes six months later is298, 000, 000 kilometers (184, 760, 000 miles), _i. E. _, the diameter of thisorbit. This immense distance (in comparison with those with which we arefamiliar) serves as the base of a triangle of which the apex is a star. The difficulty in exact measurements of the distance of a star consistsin observing the little luminous point persistently for a whole year, tosee if this star is stationary, or if it describes a minute ellipsereproducing in perspective the annual revolution of the Earth. If it remains fixed, it is lost in such depths of space that it isimpossible to gage the distance, and our 298, 000, 000 kilometers have nomeaning in view of such an abyss. If, on the contrary, it is displaced, it will in the year describe a minute ellipse, which is only thereflection, the perspective in miniature, of the revolution of ourplanet round the Sun. The annual parallax of a star is the angle under which one would see theradius, or half-diameter, of the terrestrial orbit from it. This radiusof 149, 000, 000 kilometers (93, 000, 000 miles) is indeed, as previouslyobserved, the unit, the meter of celestial measures. The angle is ofcourse smaller in proportion as the star is more distant, and theapparent motion of the star diminishes in the same proportion. But thestars are all so distant that their annual displacement of perspectiveis almost imperceptible, and very exact instruments are required for itsdetection. [Illustration: FIG. 84. --Small apparent ellipses described by the starsas a result of the annual displacement of the Earth. ] The researches of the astronomers have proved that there is not one starfor which the parallax is equal to that of another. The minuteness ofthis angle, and the extraordinary difficulties experienced in measuringthe distance of the stars, will be appreciated from the fact that thevalue of a second is so small that the displacement of any starcorresponding with it could be covered by a spider's thread. A second of arc corresponds to the size of an object at a distance of206, 265 times its diameter; to a millimeter seen at 206 meters'distance; to a hair, 1/10 of a millimeter in thickness, at 20 meters'distance (more invisible to the naked eye). And yet this value is inexcess of those actually obtained. In fact:--the apparent displacementof the nearest star is calculated at 75/100 of a second (0. 75"), _i. E. _, from this star, [alpha] of Centaur, the half-diameter of the terrestrialorbit is reduced to this infinitesimal dimension. Now in order that thelength of any straight line seen from the front be reduced until itappear to subtend no more than an angle of 0. 75", it must be removed toa distance 275, 000 times its length. As the radius of the terrestrialorbit is 149, 000, 000 kilometers (93, 000, 000 miles), the distance whichseparates [alpha] of Centaur from our world must therefore =41, 000, 000, 000, 000 kilometers (25, 000, 000, 000, 000 miles). And that isthe nearest star. We saw in Chapter II that it shines in the southernhemisphere. The next, and one that can be seen in our latitudes, is 61of Cygnus, which floats in the Heavens 68, 000, 000, 000, 000 kilometers(42, 000, 000, 000, 000 miles) from here. This little star, of fifthmagnitude, was the first of which the distance was determined (byBessel, 1837-1840). All the rest are much more remote, and the procession is extended toinfinity. We can not conceive directly of such distances, and in order to imaginethem we must again measure space by time. In order to cover the distance that separates us from our neighbor, [alpha] of Centaur, _light_, the most rapid of all couriers, takes 4years, 128 days. If we would follow it, we must not jump from start tofinish, for that would not give us the faintest idea of the distance: wemust take the trouble to think out the direct advance of the ray oflight, and associate ourselves with its progress. We must see ittraverse 300, 000 kilometers (186, 000 miles) during the first second ofthe journey; then 300, 000 more in the second, which makes 600, 000kilometers; then once more 300, 000 kilometers during the third, and soon without stopping for four years and four months. If we take thistrouble we may realize the value of the figure; otherwise, as thisnumber surpasses all that we are in the habit of realizing, it will haveno significance for us, and will be a dead letter. If some appalling explosion occurred in this star, and the sound in itsflight of 340 meters (1, 115 feet) per second were able to cross thevoid that separates us from it, the noise of this explosion would onlyreach us in 3, 000, 000 years. A train started at a speed of 106 kilometers (65 miles) per hour wouldhave to run for 46, 000, 000 years, in order to reach this star, ourneighbor in the celestial kingdom. The distance of some thirty of the stars has been determined, but theresults are dubious. The dazzling Sirius reigns 92, 000, 000, 000, 000 kilometers(57, 000, 000, 000, 000 miles), the pale Vega at 204, 000, 000, 000, 000. Eachof these magnificent stars must be a huge sun to burn at such a distancewith such luminosity. Some are millions of times larger than the Earth. Most of them are more voluminous than our Sun. On all sides theyscintillate at inaccessible distances, and their light strays a longwhile in space before it encounters the Earth. The luminous ray that wereceive to-day from some pale star hardly perceptible to our eyes--soenormous is its distance--may perhaps bring us the last emanation of asun that expired thousands of years ago. * * * * * If these methods have been clear to my readers, they may also beinterested perhaps in knowing the means employed in weighing the worlds. The process is as simple and as clear as those of which we have beenspeaking. _Weighing the stars!_ Such a pretension seems Utopian, and one asksoneself curiously what sort of balance the astronomers must have adoptedin order to calculate the weight of Sun, Moon, planets or stars. Here, figures replace weights. Ladies proverbially dislike figures: yetit would be easier for some society dame to weigh the Sun at the pointof her pen, by writing down a few columns of figures with a little care, than to weigh a 12 kilogram case of fruit, or a dress-basket of 35kilos, by direct methods. Weighing the Sun is an amusement like any other, and a change ofoccupation. If the Moon were not attracted by the Earth, she would glide through theHeavens along an indefinite straight line, escaping at the tangent. Butin virtue of the attraction that governs the movements of all theHeavenly bodies, our satellite at a distance of 60 times the terrestrialhalf-diameter revolves round us in 27 days, 7 hours, 43 minutes, 11-1/2seconds, continually leaving the straight line to approach the Earth, and describing an almost circular orbit in space. If at any moment wetrace an arc of the lunar orbit, and if a tangent is taken to this arc, the deviation from the straight line caused by the attraction of ourplanet is found to be 1-1/3 millimeter per second. This is the quantity by which the Moon drops toward us in each second, during which she accomplishes 1, 017 meters of her orbit. On the other hand, no body can fall unless it be attracted, drawn byanother body of a more powerful mass. Beings, animals, objects, adhere to the soil, and weigh upon the Earth, because they are constantly attracted to it by an irresistible force. Weight and universal attraction are one and the same force. On the other hand, it can be determined that if an object is left toitself upon the surface of the Earth, it drops 4. 90 meters during thefirst second of its fall. We also know that attraction diminishes with the square of the distance, and that if we could raise a stone to the height of the Moon, and thenabandon it to the attraction of our planet, it would in the first secondfall 4. 90 meters divided by the square of 60, or 3, 600--that is, of1-1/3 millimeters, exactly the quantity by which the Moon deviates fromthe straight line she would pursue if the Earth were not influencingher. The reasoning just stated for the Moon is equally applicable to the Sun. The distance of the Sun is 23, 386 times the radius of the Earth. Inorder to know how much the intensity of terrestrial weight would bediminished at such a distance, we should look, in the first place, forthe square of the number representing the distance--that is, 23, 386multiplied by itself, = 546, 905, 000. If we divide 4. 90 meters, whichrepresents the attractive force of our planet, by this number, we get9/1000000 of a millimeter, and we see that at the distance of the Sun, the Earth's attraction would really be almost _nil_. Now let us do for our planet what we did for its satellite. Let us tracethe annual orbit of the terrestrial globe round the central orb, and weshall find that the Earth falls in each second 2. 9 millimeters towardthe Sun. This proportion gives the attractive force of the Sun in relation tothat of the Earth, and proves that the Sun is 324, 000 times morepowerful than our world, for 2. 9 millimeters divided by 0. 000, 009 equals324, 000, if worked out into the ultimate fractions neglected here forthe sake of simplicity. A great number of stars have been weighed by the same method. Their mass is estimated by the movement of a satellite round them, andit is by this method that we are able to affirm that Jupiter is 310times heavier than the Earth, Saturn 92 times, Neptune 16 times, Uranus14 times, while Mars is much less heavy, its weight being onlytwo-thirds that of our own. The planets which have no satellites have been weighed by theperturbations which they cause in other stars, or in the imprudentcomets that sometimes tarry in their vicinity. Mercury weighs very muchless than the Earth (only 6/100) and Venus about 8/10. So the beautifulstar of the evening and morning is not so light as her name might imply, and there is no great difference between her weight and our own. As the Moon has no secondary body submitted to her influence, her weighthas been calculated by reckoning the amount of water she attracts ateach tide in the ocean, or by observing the effects of her attraction onthe terrestrial globe. When the Moon is before us, in the last quarter, she makes us travel faster, whereas in the first quarter, when she isbehind, she delays us. All the calculations agree in showing us that the orb of night is 81times less heavy than our planet. There is nearly as much difference inweight between the Earth and the Moon as between an orange and a grape. * * * * * Not content with weighing the planets of our system, astronomers haveinvestigated the weight of the stars. How have they been enabled toascertain the quantity of matter which constitutes these distantSuns--incandescent globes of fire scattered in the depths of space? They have resorted to the same method, and it is by the study of theattractive influence of a sun upon some other contiguous neighboringstar, that the weight of a few of these has been calculated. Of course this method can only be applied to those double stars of whichthe distance is known. It has been discovered that some of the tiny stars that we can hardlysee twinkling in the depths of the azure sky are enormous suns, largerand heavier than our own, and millions of times more voluminous than theEarth. Our planet is only a grain of dust floating in the immensity of Heaven. Yet this atom of infinity is the cradle of an immense creationincessantly renewed, and perpetually transformed by the accumulatedcenturies. And what diversity exists in this army of worlds and suns, whose regularharmonious march obeys a mute order. . . . But we have as yet said nothing about weight on the surface of theworlds, and I see signs of impatience in my readers, for after so muchsimple if unpoetical demonstration, they will certainly ask me for theexplanation that will prove to them that a kilogram transported toJupiter or Mars would weigh more or less than here. Give me your attention five minutes longer, and I will restore yourfaith in the astronomers. It must not be supposed that objects at the surface of a world likeJupiter, 310 times heavier than our own, weigh 310 times more. Thatwould be a serious error. In that case we should have to assume that akilogram transported to the surface of the Sun would there weigh 324, 000times more, or 324, 000 kilograms. That would be correct if these orbswere of the same dimensions as the Earth. But to speak, for instance, only of the divine Sun, we know that he is 108 times larger than ourlittle planet. Now, weight at the surface of a celestial body depends not only on itsmass, but also on its diameter. In order to know the weight of any body upon the surface of the Sun, wemust argue as follows: Since a body placed upon the surface of the Sun is 108 times fartherfrom its center than it is upon a globe of the dimensions of the Earth, and since, on the other hand, attraction diminishes with the square ofthe distance, the intensity of the weight would there be 108 multipliedby 108, or 11, 700 times weaker. Now divide the number representing themass, _i. E. _, 324, 000, by this number 11, 700, and it results that bodiesat the surface of the Sun are 28 times heavier than here. A woman whoseweight was 60 kilos would weigh 1, 680 kilograms there if organized inthe same way as on the Earth, and would find walking very difficult, forat each step she would lift up a shoe that weighed at least tenkilograms. This reasoning as just stated for the Sun may be applied to the otherstars. We know that on the surface of Jupiter the intensity of weight istwice and a third times as great as here, while on Mars it only equals37/100. On the surface of Mercury, weight is nearly twice as small again ashere. On Neptune it is approximately equal to our own. With deference to the Selenites, everything is at its lightest on theMoon: a man weighing 70 kilograms on the Earth would not weigh more than12 kilos there. So all tastes can be provided for: the only thing to be regretted isthat one can not choose one's planet with the same facility as one'sresidence upon the Earth. CHAPTER XII LIFE, UNIVERSAL AND ETERNAL And now, while thanking my readers for having followed me so far in thisdescriptive account of the marvels of the Cosmos, I must inquire whatphilosophical impression has been produced on their minds by thesecelestial excursions to the other worlds? Are you left indifferent tothe pageant of the Heavens? When your imagination was borne away tothese distant stars, suns of the infinite, these innumerable stellarsystems disseminated through a boundless eternity, did you ask whatexisted there, what purpose was served by those dazzling spheres, whateffects resulted from these forces, radiations, energies? Did youreflect that the elements which upon our little Earth determined a vitalactivity so prodigious and so varied must needs have spread the waves ofan incomparably vaster and more diversified existence throughout theimmensities of the Universe? Have you felt that all can not be dead anddeserted, as we are tempted by the illusions of our terrestrial sensesand of our isolation to believe in the silence of the night: that on thecontrary, the real aim of Astronomy, instead of ending with statementsof the positions and movements of the stars, is to enable us topenetrate to them, to make us divine, and know, and appreciate theirphysical constitution, their degree of life and intellectuality in theuniversal order? On the Earth, it is Life and Thought that flourish; and it is Life andThought that we seek again in these starry constellations strewn toInfinitude amid the immeasurable fields of Heaven. The humble little planet that we inhabit presents itself to us as abrimming cup, overflowing at every outlet. Life is everywhere. From thebottom of the seas, from the valleys to the mountains, from thevegetation that carpets the soil, from the mold in the fields and woods, from the air we breathe, arises an immense, prodigious, and perpetualmurmur. Listen! it is the great voice of Nature, the sum of all theunknown and mysterious voices that are forever calling to us, from theocean waves, from the forest winds, from the 300, 000 kinds of insectsthat are redundant everywhere, and make a lively community on thesurface of our globe. A drop of water contains thousands of curious andagile creatures. A grain of dust from the streets of Paris is the homeof 130, 000 bacteria. If we turn over the soil of a garden, field, ormeadow, we find the earthworms working to produce assimilable slime. Ifwe lift a stone in the path, we discover a crawling population. If wegather a flower, detach a leaf, we everywhere find little insects livinga parasitic existence. Swarms of midges fly in the sun, the trees of thewood are peopled with nests, the birds sing, and chase each other atplay, the lizards dart away at our approach, we trample down theantheaps and the molehills. Life enwraps us in an inexorableencroachment of which we are at once the heroes and the victims, perpetuating itself to its own detriment, as imposed upon it by aneternal reproduction. And this from all time, for the very stones ofwhich we build our houses are full of fossils so prodigiously multipliedthat one gram of such stone will often contain millions of shells, marvels of geometrical perfection. The infinitely little is equal to theinfinitely great. Life appears to us as a fatal law, an imperious force which all obey, asthe result and the aim of the association of atoms. This is illustratedfor us upon the Earth, our only field of direct observation. We must beblind not to see this spectacle, deaf not to hear its reaching. On whatpretext could one suppose that our little globe which, as we have seen, has received no privileges from Nature, is the exception; and that theentire Universe, save for one insignificant isle, is devoted to vacancy, solitude, and death? We have a tendency to imagine that Life can not exist under conditionsother than terrestrial, and that the other worlds can only be inhabitedon the condition of being similar to our own. But terrestrial natureitself demonstrates to us the error of this way of thinking. We die inthe water: fishes die out of the water. Again, short-sighted naturalistsaffirm categorically that Life is impossible at the bottom of the sea:1, because it is in complete darkness; 2, because the terrible pressurewould burst any organism; 3, because all motion would be impossiblethere, and so on. Some inquisitive person sends down a dredge, andbrings up lovely creatures, so delicate in structure that the daintiesttouch must proceed with circumspection. There is no light in thesedepths: they make it with their own phosphorescence. Other inquirersvisit subterranean caverns, and discover animals and plants whose organshave been transformed by adaptation to their gloomy environment. What right have we to say to the vital energy that radiates round everySun of the Universe: "Thus far shalt thou come, and no further"? In thename of Science? An absolute mistake. The Known is an infinitesimalisland in the midst of the vast ocean of the Unknown. The deep seaswhich seemed to be a barrier are, as we have seen, peopled with speciallife. Some one objects: But after all, there is air there, there isoxygen: oxygen is indispensable: a world without oxygen would be aworld of death, an eternally sterile desert. Why? Because we have notyet come across beings that can breathe without air, and live withoutoxygen? Another mistake. Even if we did not know of any, it would notprove that they do not exist. But as it happens, we do know of such: the_anærobia_. These beings live without air, without oxygen. Better still:oxygen kills them! All the evidence goes to show that in interpreting as we ought thespectacle of terrestrial life, and the positive facts acquired byScience, we should enlarge the circle of our conceptions and ourjudgments, and not limit extra-terrestrial existence to the servileimage of what is in existence here below. Terrestrial organic forms aredue to local causes upon our planet. The chemical constitution of waterand of the atmosphere, temperature, light, density, weight, are so manyelements that have gone to form our bodies. Our flesh is composed ofcarbon, nitrogen, hydrogen, and oxygen combined in the state of water, and of some other elements, among which we may instance sodium chloride(salt). The flesh of animals is not chemically different from our own. All this comes from the water and the air, and returns to them again. The same elements, in very minute quantities, make up all living bodies. The ox that browses on the grass is formed of the same flesh as the manwho eats the beef. All organized terrestrial matter is only carboncombined in variable proportions with hydrogen, nitrogen, oxygen, etc. But we have no right to forbid Nature to act differently in worlds fromwhich carbon is absent. A world, for example, in which silica replacescarbon, silicic acid carbonic acid, might be inhabited by organismsabsolutely different from those which exist on the Earth, different notonly in form, but also in substance. We already know stars and suns forwhich spectral analysis reveals a predominance of silica, _e. G. _, Rigeland Deneb. In a world where chlorine predominated, we might expect tofind hydrochloric acid, and all the fecund family of chlorides, playingan important part in the phenomena of life. Might not bromine beassociated in other formations? Why, indeed, should we draw the line atterrestrial chemistry? What is to prove that these elements are reallysimple? May not hydrogen, carbon, oxygen, nitrogen, and sulphur all becompounds? Their equivalents are multiples of the first: 1, 6, 8, 14, 16. And is even hydrogen the most simple of the elements? Is not itsmolecule composed of atoms, and may there not exist a single species ofprimitive atom, whose geometric arrangement and various associationsmight constitute the molecules of the so-called simple elements? In our own solar system we discover the essential differences betweencertain planets. In the spectrum of Jupiter, for instance, we are awareof the action of an unknown substance that manifests itself by a markedabsorption of certain red rays. This gas, which does not exist upon theEarth, is seen still more obviously in the atmospheres of Saturn andUranus. Indeed, upon this last planet the atmosphere appears, apart fromits water vapor, to have no sort of analogy with our own. And in thesolar spectrum itself, many of the lines have not yet been identifiedwith terrestrial substances. The interrelation of the planets is of course incontrovertible, sincethey are all children of the same parent. But they differ amongthemselves, not merely in respect of situation, position, volume, mass, density, temperature, atmosphere, but again in physical and chemicalconstitution. And the point we would now accent is that this diversityshould not be regarded as an obstacle to the manifestations of life, but, on the contrary, as a new field open to the infinite fecundity ofthe universal mother. When our thoughts take wing, not only to our neighbors, Moon, Venus, Mars, Jupiter, or Saturn, but still more toward the myriads of unknownworlds that gravitate round the suns disseminated in space, we have noplausible reason for imagining that the inhabitants of these otherworlds of Heaven resemble us in any way, whether in form, or even inorganic substance. The substance of the terrestrial human body is due to the elements ofour planet, and notably to carbon. The terrestrial human form derivesfrom the ancestral animal forms to which it has gradually raised itselfby the continuous progress of the transformation of species. To us itseems obvious that we are man or woman, because we have a head, a heart, lungs, two legs, two arms, and so on. Nothing is less a matter ofcourse. That we are constituted as we are, is simply the result of ourpro-simian ancestors having also had a head, a heart, lungs, legs, andarms--less elegant than your own, it is true, Madam, but still of thesame anatomy. And more and more, by the progress of paleontology, we aredelving down to the origin of beings. As certain as it is that the birdderives from the reptile by a process of organic evolution, so certainis it that terrestrial Humanity represents the topmost branches of thehuge genealogical tree, whereof all the limbs are brothers, and theroots of which are plunged into the very rudiments of the mostelementary and primitive organisms. The multitude of worlds is surely peopled by every imaginable andunimaginable form. Terrestrial man is endowed with five senses, orperhaps it is better to say six. Why should Nature stop at this point?Why, for instance, may she not have given to certain beings anelectrical sense, a magnetic sense, a sense of orientation, an organable to perceive the ethereal vibrations of the infra-red orultra-violet, or permitted them to hear at a distance, or to see throughwalls? We eat and digest like coarse animals, we are slaves to ourdigestive tube: may there not be worlds in which a nutritive atmosphereenables its fortunate inhabitants to dispense with this absurd process?The least sparrow, even the dusky bat, has an advantage over us in thatit can fly through the air. Think how inferior are our conditions, sincethe man of greatest genius, the most exquisite woman, are nailed to thesoil like any vulgar caterpillar before its metamorphosis! Would it be adisadvantage to inhabit a world in which we might fly whither we would;a world of scented luxury, full of animated flowers; a world where thewinds would be incapable of exciting a tempest, where several suns ofdifferent colors--the diamond glowing with the ruby, or the emerald withthe sapphire--would burn night and day (azure nights and scarlet days)in the glory of an eternal spring; with multi-colored moons sleeping inthe mirror of the waters, phosphorescent mountains, aerialinhabitants, --men, women, or perhaps of other sexes, --perfect in theirforms, gifted with multiple sensibilities, luminous at will, incombustible as asbestos, perhaps immortal, unless they commit suicideout of curiosity? Lilliputian atoms as we are, let us once for all beconvinced that our imagination is but sterility, in the midst of aninfinitude hardly glimpsed by the telescope. One important point seems always to be ignored expressly by those whoblindly deny the doctrine of the plurality of worlds. It is that thisdoctrine does not apply more particularly to the present epoch than toany other. _Our_ time is of no importance, no absolute value. Eternityis the field of the Eternal Sower. There is no reason why the otherworlds should be inhabited _now_ more than at any other epoch. What, indeed, is the Present Moment? It is an open trap through whichthe Future falls incessantly into the gulf of the Past. The immensity of Heaven bears in its bosom cradles as well as tombs, worlds to come and perished worlds. It abounds in extinct suns, andcemeteries. In all probability Jupiter is not yet inhabited. What doesthis prove? The Earth was not inhabited during its primordial period:what did that prove to the inhabitants of Mars or of the Moon, who wereperhaps observing it at that epoch, a few million years ago? To pretend that our globe must be the only inhabited world because theothers do not resemble it, is to reason, not like a philosopher, but, aswe remarked before, like a fish. Every rational fish ought to assumethat it is impossible to live out of water, since its outlook and itsphilosophy do not extend beyond its daily life. There is no answer tothis order of reasoning, except to advise a little wider perception, andextension of the too narrow horizon of habitual ideas. For us the resources of Nature may be considered infinite, and"positive" science, founded upon our senses only, is altogetherinadequate, although it is the only possible basis of our reasoning. Wemust learn to see with the eyes of our spirit. As to the planetary systems other than our own, we are no longer reducedto hypotheses. We already know with certainty that our Sun is noexception, as was suggested, and is still maintained, by some theorists. The discovery in itself is curious enough. It is surely an exceptional situation that, given a sidereal systemcomposed of a central sun, and of one or more stars gravitating roundhim, the plane of such a system should fall just within our line ofvision, and that it should revolve in such a way that the globes ofwhich it is composed pass exactly between this sun and ourselves inturning round him, eclipsing him more or less during this transit. As, on the other hand, the eclipses would be our only means of determiningthe existence of these unknown planets (save indeed from perturbation, as in the case of Sirius and Procyon), it might have seemed quixotic tohope for like conditions in order to discover solar systems other thanour own. But these exceptional circumstances have reproduced themselvesat different parts of the Heavens. Thus, for instance, we have seen that the variable star Algol owes itsvariations in brilliancy, which reduce it from second to fourthmagnitude every sixty-nine hours, to the interposition of a body betweenitself and the Earth, and celestial mechanics has already been able todetermine accurately the orbit of this body, its dimensions and itsmass, and even the flattening of the sun Algol. Here, then, is a systemin which we know the sun and an enormous planet, whose revolution iseffected in sixty-nine hours with extreme rapidity, as measured by thespectroscope. The star [delta] of Cepheus is in the same case: it is an orb eclipsedin a period of 129 hours, and its eclipsing planet also revolves in theplane of our vision. The variable star in Ophiuchus has an analogoussystem, and observation has already revealed a great number of others. Since, then, a certain number of solar systems differing from our ownhave been revealed, as it were in section, to terrestrial observation, this affords us sufficient evidence of the existence of an innumerablequantity of solar systems scattered through the immensities of space, and we are no longer reduced to conjecture. On the other hand, analysis of the motions of several stars, such asSirius, Procyon, Altaïr, proves that these distant orbs havecompanions, --planets not yet discovered by the telescope, and thatperhaps never will be discovered, because they are obscure, and lost inthe radiation of the star. * * * * * Some _savants_ have asserted that Life can not germinate if theconditions of the environment differ too much from terrestrialconditions. This hypothesis is purely gratuitous, and we will now discuss it. In order to examine what is happening on the Earth, let us mount theladder of time for a moment, to follow the evolutions of Nature. There was an epoch when the Earth did not exist. Our planet, the futureworld of our habitation, slept in the bosom of the solar nebula. At last it came to birth, this cherished Earth, a gaseous, luminousball, poor reflection of the King of Orbs, its parent. Millions of yearsrolled by before the condensation and cooling of this new globe weresufficiently transformed to permit life to manifest itself in its mostrudimentary aspects. The first organic forms of the protoplasm, the first aggregations ofcells, the protozoons, the zoophytes or plant-animals, the gelatinousmussels of the still warm seas, were succeeded by the fishes, then bythe reptiles, the birds, the mammals, and lastly man, who at presentoccupies the top of the genealogical tree, and crowns the animalkingdom. Humanity is comparatively young upon the Earth. We may attribute somethousands of centuries of existence to it . . . And some five years ofreason! The terrestrial organisms, from the lowest up to man, are the resultantof the forces in action at the surface of our planet. The earliest seemto have been produced by the combinations of carbon with hydrogen andnitrogen; they were, so to speak, without animation, save for some veryrudimentary sensibility; the sponges, corals, polyps, and medusæ, giveus a notion of these primitive beings. They were formed in the tepidwaters of the primary epoch. As long as there were no continents, noislands emerging from the level of the universal ocean, there were nobeings breathing in the air. The first aquatic creatures were succeededby the amphibia, the reptiles. Later on were developed the mammals andthe birds. What, again, do we not owe to the plant-world of the primary epoch, ofthe secondary epoch, of the tertiary epoch, which slowly prepared thegood nutritious soil of to-day, in which the roses flourish, and thepeach and strawberry ripen? Before it gave birth to a Helen or a Cleopatra, life manifested itselfunder the roughest forms, and in the most varied conditions. Along-period comet passing in sight of the Earth from time to time wouldhave seen modifications of existence in each of its transits, inaccordance with a slow evolution, corresponding to the variation of theconditions of existence, and progressing incessantly, for if Life is thegoal of nature, Progress is the supreme law. The history of our planet is the history of life, with all itsmetamorphoses. It is the same for all the worlds, with some exceptionsof orbs arrested in their development. The constitution of living beings is in absolute relation with thesubstances of which they are composed, the environment in which theymove, temperature, light, weight, density, the length of day and night, the seasons, etc. --in a word, with all the cosmographic elements of aworld. If, for example, we compare between themselves two worlds such as theEarth and Neptune, utterly different from the point of view of distancefrom the Sun, we could not for an instant suppose that organicstructures could have followed a parallel development on these planets. The average temperature must be much lower on Neptune than on the Earth, and the same holds for intensity of light. The years and seasons thereare 165 times longer than with us, the density of matter is three timesas weak, and weight is, on the contrary, a little greater. Underconditions so different from our own, the activities of Nature wouldhave to translate themselves under other forms. And doubtless theelementary bodies would not be found there in the same proportions. Consequently we have to conclude that organs and senses would not be thesame there as here. The optic nerve, for instance, which has formed anddeveloped here from the rudimentary organ of the trilobite to themarvels of the human eye, must be incomparably more sensitive uponNeptune than in our dazzling solar luminosity, in order to perceiveradiations that we do not perceive here. In all probability, it isreplaced there by some other organ. The lungs, functioning there inanother atmosphere, are different from our own. So, too, for the stomachand digestive organs. Corporeal forms, animal and human, can notresemble those which exist upon the Earth. Certain _savants_ contend that if the conditions differed too much fromterrestrial conditions, life could not be produced there at all. Yet wehave no right to limit the powers of Nature to the narrow bounds of oursphere of observation, and to pretend that our planet and our Humanityare the type of all the worlds. That is a hypothesis as ridiculous as itis childish. Do not let us be "personal, " like children, and old people who never seebeyond their room. Let us learn to live in the Infinite and the Eternal. From this larger point of view, the doctrine of the plurality of worldsis the complement and the natural crown of Astronomy. What interests usmost in the study of the Universe is surely to know what goes on there. * * * * * These considerations show that, in all the ages, what really constitutesa planet is not its skeleton but the life that vibrates upon itssurface. And again, if we analyze things, we see that for the Procession ofNature, life is all, and matter nothing. What has become of our ancestors, the millions of human beings whopreceded us upon this globe? Where are their bodies? What is left ofthem? Search everywhere. Nothing is left but the molecules of air, water, dust, atoms of hydrogen, nitrogen, oxygen, carbon, etc. , whichare incorporated in turn in the organism of every living being. The whole Earth is a vast cemetery, and its finest cities are rooted inthe catacombs. But now, in crossing Paris, I passed for at least thethousandth time near the Church of St. Germain-l'Auxerrois, and wasobliged to turn out of the direct way, on account of excavations. Ilooked down, and saw that immediately below the pavement, they had justuncovered some stone coffins still containing the skeletons that hadreposed there for ten centuries. From time immemorial the passers-by hadtrampled them unwittingly under foot. And I reflected that it is muchthe same in every quarter of Paris. Only yesterday, some Roman tombs anda coin with the effigy of Nero were found in a garden near theObservatory. And from the most general standpoint of Life, the whole world is in thesame case, and even more so, seeing that all that exists, all thatlives, is formed of elements that have already been incorporated inother beings, no longer living. The roses that adorn the bosom of thefair . . . But I will not enlarge upon this topic. And you, so strong and virile, of what elements is your splendid bodyformed? Where have the elements you absorb to-day in respiration andassimilation been drawn from, what lugubrious adventures have they beensubject to? Think away from it: do not insist on this point: on noaccount consider it. . . . And yet, let us dwell on it, since this reality is the most evidentdemonstration of the ideal; since what exists is you, is all of us, is_Life_; and matter is only its substance, like the materials of a house, and even less so, since its particles only pass rapidly through theframework of our bodies. A heap of stones does not make a house. Quintillions of tons of materials would not represent the Earth or anyother world. Yes, what really exists, what constitutes a complete orb, is the city ofLife. Let us recognize that the flower of life flourishes on the surfaceof our planet, embellishing it with its perfume; that it is just thislife that we see and admire, --of which we form part, --and which is the_raison d'être_ of things; that matter floats, and crosses, and crossesback again, in the web of living beings, --and the reality, the goal, isnot matter--it is the life matter is employed upon. Yes, matter passes, and being also, after sharing in the concertedsymphony of life. And indeed everything passes rapidly! What irrepressible grief, what deep melancholy, what ineffaceableregrets we feel, when as age comes on we look back, when we see ourfriends fallen upon the road one after the other, above all when wevisit the beloved scenes of our childhood, those homes of other years, that witnessed our first start in terrestrial existence, our firstgames, our first affections--those affections of childhood that seemedeternal--when we wander over those fields and valleys and hills, whenwe see again the landscape whose aspect has hardly changed, and whoseimage is so intimately linked with our first impressions. There nearthis fireside the grandfather danced us on his knee, and told usblood-curdling stories; here the kind grandmother came to see if we werecomfortably tucked in, and not likely to fall out of the big bed; inthis little wood, along these alleys that seemed endless, we spread ournets for birds; in this stream we fished for crayfish; there on the pathwe played at soldiers with our elders, who were always captains; onthese slopes we found rare stones and fossils, and mysteriouspetrifactions; on this hill we admired the fine sunsets, the appearanceof the stars, the form of the constellations. There we began to live, tothink, to love, to form attachments, to dream, to question everyproblem, to breathe intellectually and physically. And now, where isthis beloved grandfather? the good grandmother? where are all whom weknew in infancy? where are our dreams of childhood? Winged thoughtsstill seem to flutter in the air, and that is all. People, caresses, voices, all have gone and vanished. The cemetery has closed over themall. There is a silent void. Were all those fine and sunny hours anillusion? Was it only to weep one day over this negation that ourchildish hearts were so tenderly attached to these fleeting shadows? Isthere nothing, down the long length of human history, but eternaldelusion? It is here, above all, that we find ourselves in presence of thegreatest problems. Life is the goal, it is Life that produces theconditions of Thought. Without Thought, where would be the Universe? We feel that without life and thought, the Universe would be an emptytheater, and Astronomy itself, sublime science, a vain research. We feelthat this is the truth, veiled as yet to actual science, and that humanraces kindred with our own exist there in the immensities of space. Yes, we _feel_ that this is truth. But we would fain go a little further in our knowledge of the universe, and penetrate in some measure the secret of our destinies. We would knowif these distant and unknown Humanities are not attached to us bymysterious cords, if our life, which will assuredly be extinguished atsome definite moment here below, will not be prolonged into the regionsof Eternity. A moment ago we said that nothing is left of the body. Millions oforganisms have lived, there are no remains of them. Air, water, smoke, dust. _Memento, homo, quia pulvis es et in pulverem revertebis. _Remember oh man! that dust thou art, and unto dust thou shalt return, says the priest to the faithful, when he scatters the ashes on the dayafter the carnival. The body disappears entirely. It goes where the corpse of Cæsar went anhour after the extinction of his pyre. Nor will there be more remains ofany of us. And the whole of Humanity, and the Earth itself, will alsodisappear one day. Let no one talk of the Progress of Humanity as anend! That would be too gross a decoy. If the soul were also to disappear in smoke, what would be left of thevital and intellectual organization of the world? Nothing. On this hypothesis, _all_ would be reduced to _nothing_. Our reason is not immense, our terrestrial faculties are sufficientlylimited, but this reason and these faculties suffice none the less tomake us feel the improbability, the absurdity, of this hypothesis, andwe reject it as incompatible with the sublime grandeur of the spectacleof the universe. Undoubtedly, Creation does not seem to concern itself with us. Itproceeds on its inexorable course without consulting our sensations. With the poet we regret the implacable serenity of Nature, opposing theirony of its smiling splendor to our mourning, our revolts, and ourdespair. Que peu de temps suffit pour changer toutes choses! Nature au front serein, comme vous oubliez! Et comme vous brisez dans vos métamorphoses Les fils mystérieux où nos coeurs sont liés. D'autres vont maintenant passer où nous passâmes; Nous y sommes venus, d'autres vont y venir, Et le songe qu'avaient ébauché nos deux âmes, Ils le continueront sans pouvoir le finir. Car personne ici-bas ne termine et n'acheve; Les pires des humains sont comme les meilleurs; Nous nous éveillons tous au même endroit du rêve: Tout commence en ce monde et tout finit ailleurs. Répondez, vallon pur, répondez, solitude! O Nature, abritée en ce désert si beau, Quand nous serons couchés tous deux, dans l'attitude Que donne aux morts pensifs la forme du tombeau, Est-ce que vous serez à ce point insensible, De nous savoir perdus, morts avec nos amours, Et de continuer votre fête paisible Et de toujours sourire et de chanter toujours?[16] _Note. --Free Translation. _ How brief a time suffices for all things to change! Serene-fronted Nature, too soon you will forget!. . . In your metamorphoses ruthlessly snapping the cords that bind our hearts together! Others will pass where we pass; we have arrived, and others will arrive after us: the thought sketched out by our souls will be pursued by theirs . . . And they will not find the solution of it. For no one here begins or finishes: the worst are as the best of humans; we all awake at the same moment of the dream: we all begin in this world, and end otherwhere. Reply, sweet valley, reply, solitude; O Nature, sheltering in this splendid desert, when we are both asleep, and cast by the tomb into the attitude of pensive death. Will you to the last verge be so insensible, that, knowing us lost, and dead with our loves, you will pursue your cheerful feast, and smile, and sing always? Yes, mortals may say that when they are sleeping in the grave, springand summer will still smile and sing; husband and wife may askthemselves if they will meet again some day, in another sphere; but dowe not _feel_ that our destinies can not be terminated here, and thatshort of absolute and final nonentity for everything, they must berenewed beyond, in that starry Heaven to which every dream has flowninstinctively since the first origins of Humanity? As our planet is only a province of the Infinite Heavens, so our actualexistence is only a stage in Eternal Life. Astronomy, by giving uswings, conducts us to the sanctuary of truth. The specter of death hasdeparted from our Heaven. The beams of every star shed a ray of hopeinto our hearts. On each sphere Nature chants the pæan of Life Eternal. THE END INDEX A Aberration, 300 Adams, 168 Agnesi, Marie, 5 Alcar, 34 Aldebaran, 44, 66 Alexandria, 3 Algol, 39 Ancients, views of, 30 Andrew Ellicot, 195 Andromeda, 37, 38 Angles, 289 Antares, 45, 66, 70 Antipodes, 208 Arago, 275 Arcturus, 39, 66 Asteroids, 146, 195 Astronomie des Dames, 9 Attraction, 208 Aureole, 279 Autumn Constellations, 54 Axis, 225 B Babylonian Tables, 30 Bartholomew Diaz, 176 Bear, Little, 35 Great, 32, 34, 35 Betelgeuse, 49, 66 Biela's Comet, 189, 198 Bode's law, 167 Bolides, 201 C Cancer, 72 Capella, 38, 66 Cassiopeia, 36 Castor, 44, 68 Catalogue of Lalande, 65 Catharine of Alexandria, 3 Centaur, 52, 64, 65, 80 Ceres, 147 Chaldean pastors, 30 Chaldeans, 271 Chariot of David, 32 Charioteer, 38 Chart of Mars, 140 Châtelet, Marquise du, 4 Chiron, The Centaur, 30, 51 Chromosphere, 102 Clairaut, 3 Clerke, Agnes, 7 Cnidus, 31 Coggia's Comet, 187 Comet of Biela, 197 of 1811, 186 of 1858, 174 Comets, 111, 185 Constellations, 28 figures of, 31 Autumn, 54 Constellations, Spring, 52 Summer, 53 Winter, 51 Copernicus, 125 Corona Borealis, 40 Corona of the Sun, 104 Cygnus, 40 D de Blocqueville, Madame, 5 de Breteuil, Gabrielle-Émilie, 4 de Charrière, Madame, 5 Deneb, 41 des Brosses, 5 Diaz, Bartholomew, 176 Dipper, 32, 34 Donati, 187 Double star, stellar dial of, 86 Double stars, 68, 70 Dragon, 36 du Châtelet, Marquise, 4 E Eagle, 41 Earth, 205 ancient notions of, 19 distance from the sun, 215 how sustained, 21 inclination, 224 in space, 20 motion of, round the Sun, 222 movement of, 217 rotundity of, 206 viewed from Mars, 144 viewed from Mercury, 119 viewed from Venus, 130 weight, 210 Eclipse of Sun, May, 1900, 273 Eclipses, 259 Ellicot, Andrew, 195 Entretiens sur la Pluralité des mondes, 9 Equator, 225 Eudoxus, 31 Evening Star, 123 F Faculæ, 98, 100 Fire-balls, 198 Flammarion's Lunar Ring, 253 Fleming, Mrs. , 7 Fontenelle, 9 Foucault, 219 G Galileo, 95, 98, 125, 244 Galle, 168 Globe, divisions of, 226 Great Bear, 32, 34, 35 Great Dog, 50 Grecian Calendar, 229 Greek alphabet, 33 H Hall, Mr. , 143 Halley, 181 Halley's Comet, 3, 175 Heavens, map of, 61 Hercules, 41, 66, 79 Herdsman, 39 Herschel, Caroline, 6 Hevelius, 246 Hipparchus, 31 Houses of the Sun, 43 Huggins, Lady, 8 Huyghens, 49 Hyades, 44 Hypatia, 3 J Janssen, 102 Jupiter, 148 satellites, 155 telescopic aspect of, 150 K Klumpke, Miss, 7 Kovalevsky, Sophie, 6 L Lacaille, 292 Lalande, 3, 9, 65, 292 Latitudes, 226 Leonids, 195 Lepaute, Madame Hortense, 3, 4 Le Verrier, 167 Little Bear, 35 Little Dog, 50 Lockyer, 102 Longitudes, 226 Lucifer, 122 Lunar Apennines, 251 landscape, 254 topography, 252 Lyre, 40 M Mars, 131 chart of, 140 Measurement, 289 Medes and Lydians, 266 Mercury, 114 Meteorites, 201 Meteors, 190, 191 Metonic Cycle, 271 Milky Way, 78, 87 Mira Ceti, 77 Mitchell, Maria, 7 Mizar, 34, 69 Moon, 232 diameter of, 242 distance of, 292 geological features of, 245 map of, 247 mountains of, 246 phases of, 241 photograph of, 240 revolution of, 234 rotation of, 242 size of, 242 temperature of, 250 total eclipse of, 263 N Nebula, in Andromeda, 81 in Orion, 81 in the Greyhounds, 82 Neptune, 65, 166 revolution of, 169 Newton, 181 Nucleus, 95, 185 O Orion, 48, 49, 81 P Parallax, 292, 293 annual, 306 Pearl, 40 Pegasus, 38 Penumbra, 96 Periodic Comet, orbit of, 182 Perseids, 195 Perseus, 38, 70, 78 Phenician navigators, 30 Phoebus, 67 Photosphere, 101 Piazzi, 147 Planets, 109, 113, 146 distances, 110, 302 orbits of, 115 orbits of, 116 Pleiades, 38, 39, 44, 83 occultation of, 85 Pleione, 84 Polaris, 63 Pole-star, 34, 63 Poles, 225 Pollux, 44 Pope Calixtus, 176 Prodigies in the heavens, 178 Ptolemy, 31, 217 R Radiant, 195 Riccioli, 246 Rigel, 49, 70 Roberts, Mrs. Isaac, 7 S Saidak, 34 Saros, 271 Satellites, 110 Saturn, 156 revolution of, 157 satellites, 162, 165 volume, 158 Saturn's rings, 161 Scarpellini, Madame, 7 Scheiner, 95 Schiaparelli, 139 Secchi, Father, 7 Seven Oxen, 32 Sextuple star, 74 Shepherd's Star, 11 Shooting stars, 193, 194, 196 Sirius, 66, 309 _Solar storms_, 100 flames, 105 system, 65 Somerville, Mrs. , 6 Spring constellations, 52 Stars, distances, 62 double, 68, 70 first magnitude, 57 number of, 60 quadruple, 73 second magnitude, 58 shooting, 193, 194 temporary, 77 Stars, triple, 72 variable, 75 weight of, 313 Star cluster in Hercules, 79 in the Centaur, 80 St. Catherine, 3 Summer constellations, 53 Sun, 88 houses of the, 43 measurement of distance, 297 photograph of, 96 rotation, 99 temperature of, 105 total eclipse of, 276 weight, 106 Sun and Earth, comparative sizes of, 93 Sun-spots, 95, 101 telescopic aspect of, 97 T Temporary stars, 77, 78 Three Kings, 49 Total eclipse of the moon, 263 of sun, 276 Triangulation, 288 Triple Star, 72 U Umbra, 95 Universe, 22, 23, 90 Urania, 8, 9 Uranoliths, 201, 204 Uranus, 162 V Variable stars, 75 Vega, 40 Venus, 121, 296 phases of, 124 Vesper, 122 Victor Hugo, 24 W Weighing worlds, 309 Winter constellations, 51 Z Zodiac, constellations of, 46, 47 Zones, 225 FOOTNOTES: [1] The French edition of this book is entitled Astronomy forWomen. --TRANSLATOR. [2] 1 kilometer = 0. 6214 mile; 100 kilometers may be taken as 62 miles. 1 kilogram is about 2. 2 lb. ; 5 kilograms = 11 lb. --TRANSLATOR. [3] It is useful to know the letters of the Greek Alphabet. They areeasily learned, as follows: [alpha] Alpha [beta] Beta [gamma] Gamma [delta] Delta [epsilon] Epsilon [zeta] Zeta [eta] Eta [theta] Theta [iota] Iota [kappa] Kappa [lambda] Lambda [mu] Mu [nu] Nu [xi] Xi [omicron] Omicron [pi] Pi [rho] Rho [sigma] or [sigma] Sigma [tau] Tau [upsilon] Upsilon [phi] Phi [chi] Chi [psi] Psi [omega] Omega [4] All the stars visible at any hour during the year can easily befound with the help of the author's Planisphere mobile. [5] Let it be remarked in passing that the stars might be much fartheroff than they are, and invisible to our eyes; the Heavens would thenassume the aspect of an absolutely empty space, the moon and planetsalone remaining. [6] 14" = 14 seconds of arc. One second of the circle is an exceedinglyminute quantity. It is 1 millimeter seen at a distance of 206 meters. One millimeter seen at a distance of 20 m. 62 = 10 secs. These valuesare invisible to the unaided eye. [7] These fine double stars can be observed with the help of thesmallest telescope. [8] For the explanation of the angular distances of degrees, minutes, and seconds, see Chapter XI, on Methods of Measurement. [9] The author has endeavored on the plates to represent the aspect ofthe Earth in the starry sky of Mercury, Venus, and Mars; but in allrepresentations of this kind the stars are necessarily made too large. By calculation the diameters of the Earth and Moon as seen from theplanets, and their distances, are as follows: Diameter of Diameter of Distance the Earth. The Moon. Earth-Moon. Of Mercury (opposition) 20" 8" 871" Of Venus (opposition) 64" 17" 1, 928" Of Mars (quadrature) 15" 4" 464" Of Jupiter (quadrature) 3. 5" 0. 1" 105" These aspects will be appreciated if we remember that the distance ofthe components of [epsilon] Lyre = 207", that of Atlas in Pleione =301", and that of the stars Mizar and Alcor = 708". [10] A few evenings ago, after observing Venus in the calm and silentHeavens at the close of day, my eyes fell upon a drawing sent me by myfriend Gustave Dore, which is included in the illustrations of hiswonderful edition of Dante's Divina Commedia. This drawing seems to bein place here, and I offer my readers a poor reproduction of it, takenfrom the fine engraving in the book. Dante and Virgil, in the peacefulevening, are contemplating _lo bel pianeta ch'ad amar conforta_ (thebeautiful planet that incites to love). [11] Strictly speaking, 1 kilometer = 0. 6214 mile. Here, as throughout, the equivalents are only given in round numbers. --TRANSLATOR. [12] Translator: Compare the well-known English rhyme: Thirty days hath September, April, June, and November. While all the rest have thirty-one, Excepting February alone, In which but twenty-eight appear And twenty-nine when comes Leap Year. [13] Fifty-eight different pictures of the aspect of the Moon to theunaided eye will be found in the Monthly Bulletins of the AstronomicalSociety of France, for the year 1900, in pursuance of an investigationmade by the author among the different members of the Society. [14] My readers are charged not to speak of this property (which isfairly extensive), lest the Budget Commission, at the end of itsresources, should be tempted to put on an unexpected tax. This ring, which the astronomers presented to me in the year 1887, is almost in thecenter of the lunar disk, to the north of Ptolemy and Herschel. [15] "La fin du Monde. " Flammarion, p. 186. [16] Victor Hugo. _Tristesse d'Olympia. _