The duration of the life of the worlds appears to have been in proportion with their masses. The Moon cooled and mineralized more quickly than the Earth. Jupiter is still fluid.

The progress of optics brings us already very close to this neighboring province. 'Tis a pity we can not get a little nearer!

A telescopic magnification of 2,000 puts the Moon at 384,000/2000 or 192 kilometers (some 120 miles) from our eye. Practically we can obtain no more, either from the most powerful instruments, or from photographic enlargements. Sometimes, exceptionally, enlargements of 3,000 can be used. This = 384000/3000 or 128 kilometers (some 80 miles). Undoubtedly, this is an admirable result, which does the greatest honor to human intelligence. But it is still too far to enable us to determine anything in regard to lunar life.

Any one who likes to be impressed by grand and magnificent sights may turn even a modest field-glass upon our luminous satellite, at about first quarter, when the relief of its surface, illuminated obliquely by the Sun, is at its greatest value. If you examine our neighbor world at this period, for choice at the hour of sunset, you will be astonished at its 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, nothing purer, and more celestial, than this lunar globe floating in the silence of space, and sending back to us as in some fairy dream the solar illumination that floods it. But yesterday I received the same impression, watching a great ring half standing out, and following the progress of the Sun as it mounted the lunar horizon to touch these silvered peaks. And I reflected that it is indeed inconceivable that 999,999/1,000,000 of the inhabitants of our planet should pass their lives without ever having attended to this pageant, nor to any of those others which the divine Urania scatters so profusely beneath the wondering gaze of the observers of the Heavens.



CHAPTER X

THE ECLIPSES

Among all the celestial phenomena at which it may be our lot to assist during our contemplation of the universe, one of the most magnificent and 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. We gladly allow our thoughts, mute questioners of the mysteries of the firmament, to rest upon the brilliant, golden trail they leave behind them. These unknown travelers bring a message from eternity; they tell us the tale of their distant journeys. Children of space, their ethereal beauty speaks of the immensity of the universe.

The eclipses, on the other hand, are phenomena that touch us more nearly, and take place in our vicinity.

In treating of them, we remain between the Earth and the Moon, in our little province, and witness the picturesque effects of the combined movements 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 solar rays. The azure vault of the firmament crowns the Earth with a dome of dazzling light. The fires of the orb of day shed their beneficent influence generally upon the world.

Yet, see! The radiance diminishes. The luminous disk of the Sun is gradually corroded. Another disk, as black as ink, creeps in front of it, and little by little invades it entirely. The atmosphere takes on a wan, sepulchral hue; astonished nature is hushed in profound silence; an immense veil of sadness spreads over the world. Night comes on suddenly, and the stars shine out in the Heavens. It seems as though by some mysterious cataclysm the Sun had disappeared forever. But this tribulation is soon over. The divine orb is not extinct. A flaming jet emerges from the shadow, announcing his return, and when he reappears we see that he has lost nothing in splendor or beauty. He is still the radiant Apollo, King of Day, watching over the life of the planetary worlds.

This sudden night, darkening the Heavens in the midst of a fine day, can not fail to produce a vivid impression upon the spectators of the superb phenomenon.

The eclipse lasts only for a few moments, but long enough to make a deep impression upon our minds, and indeed to inspire anxious spirits with terror and agitation—even at this epoch, when we know that there is nothing 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 invisible hand throwing the somber veil of night over the celestial torch?

Had not the Earth strayed off her appointed path, and were we not all to be deprived eternally of the light of our good Sun? Was some monstrous dragon perhaps preparing to devour the orb of day?

The fable of the dragon devouring the Sun or Moon during the eclipses is universal in Asia as in Africa, and still finds acceptance under more than one latitude. But our readers already know that we may identify the terrible celestial dragon with our gentle friend the Moon, who would not be 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 a month. In consequence of this motion, the nocturnal orb is sometimes between the Sun and the Earth, sometimes behind us, sometimes at a right angle in relation to the Sun and the Earth. Now, the eclipses of the Sun occur invariably at the time of New Moon, when our satellite passes between the Sun and ourselves, and the eclipses of the Moon, at the moment of Full Moon, when the latter is opposite to the Sun, and behind us.

This fact soon enabled the astronomers of antiquity to discover the causes to which eclipses are due.

The Moon, passing at the beginning of its revolution between the Sun and the Earth, may conceal a greater or lesser portion of the orb of day. In this case there is an eclipse of the Sun. On the other hand, when it is on the other side of the Earth in relation to the Sun, at the moment of Full Moon, our planet may intercept the solar rays, and prevent them from reaching our satellite. The Moon is plunged into the shadow of the Earth, and is then eclipsed. Such is the very simple explanation of the phenomenon. 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 the Sun, it would eclipse the Sun at each New Moon, and would be itself eclipsed in our shadow at each Full Moon. But the plane of the lunar orbit dips a little upon the plane of the terrestrial orbit, and the eclipses can only be produced when the New Moon or the Full Moon occur at 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 majority of cases, instead of interposing itself directly in front of the sovereign of our system, our satellite passes a little above or a little below him, just as its passage behind us is nearly always effected a little 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 the light of the radiant orb, and conceals a greater or less portion of the solar disk. The eclipse is partial if the Moon covers only a portion of the Sun; total if she covers it entirely; annular, if the solar disk is visible all round the lunar disk, as appears when the Moon, in her elliptical orbit, is beyond medium distance, toward the apogee.

On the other hand, when the Moon arrives immediately within the cone of shadow 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 the more marked in that she owes all her brilliancy to the light of the orb of day. The Moon's obscurity is complete if she is entirely plunged into the cone of shadow. In this case, the eclipse is total. But if a portion of her disk emerges from the cone, that part remains illuminated while the light of the other dies out. In that case there is a partial eclipse, and the rounded form of the Earth's shadow can be seen projected upon our satellite, a celestial witness to the spherical nature of our globe.

Under certain conditions, then, the Moon can deprive us of the luminous rays of the Sun, by concealing the orb of day, and in other cases is herself effaced in crossing our shadow. Despite the fables, fears, and anxieties it has engendered, this phenomenon is perfectly natural: the Moon 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 of terrifying ignorant mortals, either when the orb of light and life seemed on the verge of extinction, or when the beautiful Phoebus was covered 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 have been influenced by eclipses, sometimes for good, more often with disastrous consequences. The recital of these tragic stories would not be devoid of interest; it would illustrate the possibilities of ignorance and superstition, and the power man gains from intellectual culture and scientific study.

Herodotus records that the Scythians, having some grievance against Cyaxarus, King of the Medes, revenged themselves by serving up the limbs of one of his children, whom they had murdered, at a banquet as rare game. The scoundrels who committed this atrocious crime took refuge at the Court of the King of Lydia, who was ill judged enough to protect them. War was accordingly declared between the Medes and Lydians, but a total eclipse of the Sun occurring just when the battle was imminent, had the happy effect of disarming the combatants, who prudently retired each to their own country. This eclipse, which seems to have occurred on May 28, 584 B.C., had been predicted by Thales. The French painter Rochegrosse has painted a striking picture of the scene (Fig. 75).

In the year 413 B.C. the Athenian General Nicias prepared to return to Greece after an expedition to Sicily. But, terrified by an eclipse of the Moon, and fearing the malign influence of the phenomenon, he put off his departure, and lost the chance of retreat. This superstition cost him his life. The Greek army was destroyed, and this event marks the commencement 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 his address to reassure his panic-stricken soldiers.

Agathocles, King of Syracuse, blocked by the Carthaginians in the port of this city, had the good fortune to escape, but was disturbed on the second day of his flight by the arrival of a total eclipse of the Sun which 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 of March 2, 310.)



On June 29, 1033, an epoch at which the approaching end of the world struck terror into all hearts, an annular eclipse of the Sun occurring about midday frustrated the designs of a band of conspirators who intended to strangle the Pope at the altar. This Pope was Benedict IX, a youth of less than twenty, whose conduct is said to have been anything but 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 Christopher Columbus. He was threatened with death by starvation in Jamaica, where the contumacious savages refused to give him provisions. Forewarned of the arrival of this eclipse by the astronomical almanacs, he threatened to deprive the Caribs of the light of the Moon—and kept his word. The eclipse had hardly begun when the terrified Indians flung themselves at his feet, and brought him all that he required.

In all times and among all people we find traces of popular superstitions connected with eclipses. Here, the abnormal absence of the Moon's light is regarded as a sign of divine anger: the humble penitents betake themselves to prayer to ward off the divine anger. There, the cruelty of the dread dragon is to be averted: he must be chased away by cries and threats, and the sky is bombarded with shots to deliver the victim from his monstrous oppressor.

In France the announcement of a solar eclipse for August 21, 1560, so greatly disturbed our ancestors' peace of mind as to make them idiotic. Preparations were made for assisting at an alarming phenomenon that threatened Humanity with deadly consequences! The unhappy eclipse had been preceded by a multitude of ill omens! Some expected a great revolution in the provinces and in Rome, others predicted a new universal deluge, or, on the other hand, the conflagration of the world; the most optimistic thought the air would be contaminated. To preserve themselves from so many dangers, and in accordance with the physicians' orders, numbers of frightened people shut themselves up in tightly closed and perfumed cellars, where they awaited the decrees of Fate. The approach of the phenomenon increased the panic, and it is said that one village cure, being unable to hear the confessions of all his flock, who wanted to discharge their souls of sin before taking flight for a better world, was fain to tell them "there was no hurry, because the eclipse had been put off a fortnight on account of the number of penitents"!



These fears and terrors are still extant among ignorant peoples. In the night of February 27, 1877, an eclipse of the Moon produced an indescribable panic among the inhabitants of Laos (Indo-China). In order to frighten off the Black Dragon, the natives fired shots at the half-devoured orb, accompanying their volley with the most appalling yells. Dr. Harmand has memorialized the scene in the lively sketch given on p. 269.

During the solar eclipse of March 15, 1877, an analogous scene occurred among the Turks, who for the moment forgot their preparations for war with Russia, in order to shoot at the Sun, and deliver him from the toils 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 of saucepans, samovars and various implements struck together again and again by willing hands that sought to deliver the Moon from the demon Tchaitan who was devouring her.

In China, eclipses are the object of imposing ceremonies, whose object is to reestablish the regularity of the celestial motions. Since the Emperor is regarded as the Son of Heaven, his government must in some sort be a reflection of the immutable order of the sidereal harmonies. As eclipses were regarded by astrologers as disturbances of the divine order, their appearance indicates some irregularity in the government of the Celestial Empire. Accordingly, they are received with all kinds of expiatory ceremonies prescribed thousands of years ago, and still in force to-day.

In the twentieth century, as in the nineteenth, the eighteenth, or in ancient epochs, the same awe and terror operates upon the ignorant populations 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 and the New Moon reached the line of intersection, known as the line of nodes, 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 to the Sun at the end of eighteen years, eleven days, we have only to register the eclipses observed during this period in order to know all that 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 of Saros.

On examining this cycle, composed of 223 lunations, we see that there can not be more than seven eclipses in one year, nor less than two. When there 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 the latitude of Paris. The Moon, on the contrary, may be entirely eclipsed for nearly two hours.

Eclipses of the Sun are very rare for a definite spot. Thus not one occurred for Paris during the whole of the nineteenth century, the last which happened exactly above the capital of France having been on May 22, 1724. I have calculated all those for the twentieth century, and find that two will take place close to Paris, on April 17, 1912, at eighteen minutes past noon (total for Choisy-le-Roi, Longjumeau, and Dourdan, but very brief: seven seconds), and August 11, 1999, at 10.28 A.M. (total for Beauvais, Compiegne, Amiens, St. Quentin, fairly long: two minutes, seventeen seconds). Paris itself will not be favored before August 12, 2026. In order to witness the phenomenon, one must go and look 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 traced beforehand on maps that serve to show the favored countries for which our satellite will dispense her ephemeral night. The above figure shows the trajectory of the total phase of the 1900 eclipse in Portugal, Spain, Algeria, and Tunis.



The immutable splendor of the celestial motions had never struck the author so impressively as during the observation of this grandiose phenomenon. With the absolute precision of astronomical calculations, our satellite, gravitating round the Earth, arrived upon the theoretical line drawn from the orb of day to our planet, and interposed itself gradually, slowly, and exactly, in front of it. The eclipse was total, and occurred at the moment predicted by calculation. Then the obscure globe of the Moon pursued its regular course, discovered the radiant orb behind, and gradually and slowly completed its transit in front of him. Here, to all observers, was a double philosophical lesson, a twofold impression: that of the greatness, the omnipotence of the inexorable forces that govern the universe, and that of the inexorable valor of man, of this thinking atom straying upon another atom, who by the travail of his feeble intelligence has arrived at the knowledge of the laws by which he, like the rest of the world, is borne away through space, through time, and through eternity.

The line of centrality passed through Elche, a picturesque city of 30,000 inhabitants, not far from Alicante, and we had chosen this for our station on account of the probability of fine weather.

From the terrace of the country house of the hospitable Mayor, a farm transformed into an observatory by our learned friend, Count de la Baume Pluvinel, there were no obstacles between ourselves and any part of the sky or landscape. The whole horizon lay before us. In front was a town of Arab aspect framed in a lovely oasis of palm-trees; a little farther off, the blue sea beyond the shores of Alicante and Murcia: on the other side a belt of low mountains, and near us fields and gardens. A Company of the Civic Guard kept order, and prevented the entrance of too many curious visitors, of whom over ten thousand had arrived.

At the moment when the first contact of the lunar disk with the solar disk was observed in the telescope, we fired a gun, in order to announce the precise commencement of the occultation to the 40,000 persons who were awaiting the phenomenon, and to discover what difference would exist between this telescopic observation and those made with the unaided eyes (protected simply by a bit of smoked glass) of so many improvised spectators. This had already been done by Arago at Perpignan in 1842. The verification was almost immediate for the majority of eyes, and may be estimated at eight or ten seconds. So that the commencement of the eclipse was confirmed almost as promptly for the eye as with the astronomical 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 only from the moment when more than half the solar disk is covered by the lunar disk that the phenomenon is imposing in its grandeur. At this phase, I called the attention of the people standing in the court to the visibility of the stars, and indicating the place of Venus in the sky asked if any with long sight could perceive her. Eight at once responded in the affirmative. It should be said that the planet was at that time at its period of maximum brilliancy, when for observers blessed with good sight, it is always visible to the unaided eye.

When some three-quarters of the Sun were eclipsed, the pigeons which had flown back to the farm huddled into a corner, and made no further movement. They told me that evening that the fowls had done the same a little later, returning to the hen-house as though it had been night, and that the small children (who were very numerous at Elche, where the population is certainly not diminishing) left off their games, and came back to their mothers' skirts. The birds flew anxiously to their nests. The ants in one garden were excessively agitated, no doubt disconcerted in their strategics. The bats came out.

A few days before the eclipse I had prepared the inhabitants of this part of Spain for the observation of the phenomenon by the following description, which sums up the previous accounts of the astronomers:

"The spectacle of a total eclipse of the Sun is one of the most magnificent and imposing that it is possible to see in nature. At the exact moment indicated by calculation, the Moon arrives in front of the Sun, eats into it gradually, and at last entirely covers it. The light of the day lessens and is transformed. A sense of oppression is felt by all nature, the birds are hushed, the dog takes refuge with his master, the chickens hide beneath their mother's wing, the wind drops, the temperature falls, an appalling stillness is everywhere perceptible, as though the universe were on the verge of some imminent catastrophe. Men's faces assume a cadaverous hue similar to that given at night by the flame of spirits of wine and salt, a livid funereal light, the sinister illumination of the world's last hour.

"At the moment when the last line of the solar crescent disappears, we see, instead of the Sun, a black disk surrounded with a splendid luminous aureole shooting immense jets into space, with roseate flames burning at the base.

"A sudden night has fallen on us, a weird, wan night in which the brightest of the stars are visible in the Heavens. The spectacle is splendid, grandiose, solemn, and sublime."

This impression was actually felt by us all, as may be seen from the following 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 with remarkable clearness from the horizon, and seeming to approach us.

"3.55 P.M. Fall of temperature very apparent. Cold wind blowing through the atmosphere.

"3.56 P.M. Profound silence through nature, which seems to participate in the celestial phenomenon. Silence in all the groups.

"3.57 P.M. Light considerably diminished, becoming wan, strange, and sinister. Landscape leaden gray, sea looks black. This diminution of light is not that of every day after the sunset. There is, as it were, a tint of sadness spread over the whole of nature. One becomes accustomed to it, and yet while we know that the occultation of the Sun by the Moon is a natural phenomenon, we can not escape a certain sense of uneasiness. The approach of some extraordinary spectacle is imminent."

At this point we examined the effects of the solar light upon the seven colors of the spectrum. In order to determine as accurately as possible the tonality of the light of the eclipse, I had prepared seven great sheets, each painted boldly in the colors of the spectrum, violet, indigo, blue, green, yellow, orange, red; and a similar series in pieces of silk. These colors were laid at our feet upon the terrace where my wife, as well as Countess de la Baume, were watching with me. We then saw the first four disappear successively and entirely and turn black in a few seconds, in the following order: violet, indigo, blue, green. The three other colors were considerably attenuated by the darkness, but remained visible.

It should be noted that in the normal order of things—that is, every evening—the contrary appears; violet remains visible after the red.

This experiment shows that the last light emitted by the eclipsed Sun belongs to the least refrangible rays, to the greatest wave-lengths, to the slowest vibrations, to the yellow and red rays. Such therefore is the predominating color of the solar atmosphere.

This experiment completed, we turn back to the Sun. Magical and splendid spectacle! Totality has commenced, the Sun has disappeared, the black disk of the Moon covers it entirely, leaving all round it a magnificent corona 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 a pretty equal depth, equivalent to about the third of half the solar diameter. 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 the equatorial zone of the Sun, and of the belt of activity of the spots and prominences.

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, which shines like a dazzling star of first magnitude, and seems placed there expressly to give us the extent and direction of the solar aureole.

I draw these various aspects (which, moreover, change with the movement of the Moon), and what strikes me most is the distinction in light between this aureole and the coronal atmosphere; the latter appears to be a brilliant silvery white, the former is grayer and certainly less dense.

My impression is that there are two solar envelopes of entirely different nature, the corona belonging to the globe of the Sun, and forming its atmosphere properly so-called, very luminous; the aureole formed of particles that circulate independently round it, probably arising from eruptions, their form as a whole being possibly due to electric or magnetic forces, counterbalanced by resistances of various natures. In our own atmosphere the volcanic eruptions are distinct from the aerial envelope.

The general configuration of this external halo, spreading more particularly in the equatorial zone, is sufficiently like that of the eclipse of 1889, published in my Popular Astronomy, which also corresponded with a minimum of solar energy. The year 1900 is in fact close upon the minimum of the eleven-year period. This equatorial form is, moreover, what all the astronomers were expecting.



There can no longer be the slightest doubt that the solar envelope varies with the activity of the Sun....

"But the total eclipse lasted a much shorter time than I have taken to write these lines. The seventy-nine seconds of totality are over. A dazzling light bursts from the Sun, and tells that the Moon pursuing its orbit has left it. The splendid sight is over. It has gone like a shadow.

"Already over! It is almost a disillusion. Nothing beautiful lasts in this world. Too sad! If only the celestial spectacle could have lasted two, 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 silence are over. The Sun reappears in his splendor, and the life of nature resumes its momentarily suspended course.

"While I was making my drawing, M. l'Abbe Moreux, my colleague from the Astronomical Society of France, who accompanied me to Spain for this observation, was taking one of his own, without any reciprocal communication. These two sketches are alike, and confirmatory.

"The differential thermometers that I exposed to the Sun, hanging freely, and protected from reflection from the ground, were read every five minutes. The black thermometer went down from 33.1 deg. to 20.7 deg., that is 12.4 deg.; the white from 29 deg. to 20.2 deg.—that is, 8.8 deg. The temperature in the shade only varied three degrees.

"The light received during totality was due: first, to the luminous envelope of the Sun; second, to that of the terrestrial atmosphere, illuminated at forty kilometers (twenty-five miles) on the one side and the other of the line of centrality. It appeared to be inferior to that of the Full Moon, on account of the almost sudden transition. But, in reality, it was more intense, for only first-magnitude stars were visible 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 the contemplation of a total eclipse of the Sun is one of the most marvelous spectacles that can be admired upon our planet.

Some persons assured me that they saw the shadow of the Moon flying rapidly over the landscape. My attention was otherwise occupied, and I was unable to verify this interesting observation. The shadow of the Moon in effect took only eleven minutes (3.47 P.M. to 3.58 P.M.) to traverse the Iberian Peninsula from Porto to Alicante, i.e., a distance of 766 kilometers (475 miles). It must therefore have passed over the ground at a velocity of sixty-nine kilometers per minute, or 1,150 meters per second, a speed higher than that of a bullet. It can easily be watched from afar, on the mountains.

Some weeks previous to this fine eclipse, when I informed the Spaniards of the belt along which it could be observed, I had invited them to note all the interesting phenomena they might witness, including the effects produced by the eclipse upon animals. Birds returned hurriedly to their nests, swallows lost themselves, sheep huddled into compact packs, partridges were hypnotized, frogs croaked as if it were night, fowls took refuge in the hen-house, and cocks crowed, bats came out, and were surprised by the sun, chicks gathered under their mothers' wing, cage-birds ceased their songs, some dogs howled, others crept shivering to their masters' feet, ants returned to the antheap, grasshoppers chirped as at sunset, pigeons sank to the ground, a swarm of bees went silently back to their hive, and so on.

These creatures behaved as though the night had come, but there were also signs of fear, surprise, even of terror, differing only "in degree" from those manifested during the grandiose phenomenon of a total eclipse by human beings unenlightened by a scientific education.

At Madrid the eclipse was only partial. The young King of Spain, Alfonso XIII, took care to photograph it, and I offer the photograph to my readers (Fig. 79), as this amiable sovereign did me the honor to give it me a few days after the eclipse.



The technical results of these observations of solar eclipses relate more especially to the elucidation of the grand problem of the physical constitution of the Sun. We alluded to them in the chapter devoted to this orb. The last great total eclipses have been of immense value to science.

The eclipses of the Moon are less important, less interesting, than the eclipses of the Sun. Yet their aspect must not be neglected on this account, and it may be said to vary for each eclipse.

Generally speaking, our satellite does not disappear entirely in the Earth's cone of shadow; the solar rays are refracted round our globe by our atmosphere, and curving inward, illumine the lunar globe with a rosy tint that reminds one of the sunset. Sometimes, indeed, this refraction does not occur, owing doubtless to lack of transparency in the atmosphere, and the Moon becomes invisible. This happened recently, on April 11, 1903.

For any spot, eclipses of the Moon are incomparably more frequent than eclipses of the Sun, because the cone of lunar shadow that produces the solar eclipses is not very broad at its contact with the surface of the globe (10, 20, 30, 50, 100 kilometers, according to the distance of the Moon), whereas all the countries of the Earth for which the Moon is above 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 to the Heavens, and I strongly advise my readers on no account to forego it.



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 be alarmed 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 good enough to take me on faith when I have spoken of the distances of the Sun and Moon, and Stars, or of the weight of bodies at the surface of Mars, they retain some curiosity as to how the astronomers solve these problems. Hence it will be as interesting as it is useful to complete the preceding statements by a brief summary of the methods employed for acquiring these bold conclusions.

The Sun seems to touch the Earth when it disappears in the purple mists of twilight: an immense abyss separates us from it. The stars go hand in hand down the constellated sky; and yet one can not think of their inconceivable distance without a shiver.

Our neighbor, Moon, floats in space, a stone's throw from us: but without calculation we should never know the distance, which remains an impassable desert to us.

The best educated persons sometimes find it difficult to admit that these distances of Sun and Moon are better determined and more precise than those of certain points on our minute planet. Hence, it is of particular moment for us to give an exact account of the means employed in determining them.

The calculation of these distances is made by "triangulation." This process is the same that surveyors use in the measurement of terrestrial distances. There is nothing very alarming about it. If the word repels us a little at first, it is from its appearance only.

When the distance of an object is unknown, the only means of expressing its apparent size is by measurement of the angle which it subtends before our eyes.

We all know that an object appears smaller, in proposition with its distance from us. This diminution is not a matter of chance. It is geometric, and proportional to the distance. Every object removed to a distance of 57 times its diameter measures an angle of 1 degree, whatever its real dimensions. Thus a sphere 1 meter in diameter measures exactly 1 degree, if we see it at a distance of 57 meters. A statue measuring 1.80 meters (about 5 ft. 8 in.) will be equal to an angle of 1 degree, if distant 57 times its height, that is to say, at 102.60 meters. 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 any circumference. On a table 3.60 meters round, an angle of one degree is a centimeter, seen from the center of the table. Trace on a sheet of paper a circle 0.360 meters round—an angle of 1 degree is a millimeter.



If the circumference of a circus measuring 180 meters be divided into 360 places, each measuring 0.50 meters in width, then when the circus is full a person placed at the center will see each spectator occupying an angle of 1 degree. The angle does not alter with the distance, and whether it be measured at 1 meter, 10 meters, 100 kilometers, or in the infinite spaces of Heaven, it is always the same angle. Whether a degree be represented by a meter or a kilometer, it always remains a degree. As angles measuring less than a degree often have to be calculated, this angle has been subdivided into 60 parts, to which the name of minutes has been given, and each minute into 60 parts or seconds. Written short, the degree is indicated by a little zero (deg.) placed above the figure; the minute by an apostrophe ('), and the second by two ("). These minutes and seconds of arc have no relation with the same terms as employed for the division of the duration of time. These latter ought never 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 an angle 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 part of a degree) measured in the sky may correspond to millions of kilometers.

Now the measure of the Moon's diameter gives us an angle of a little more than half a degree. If it were exactly half a degree, we should know 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 is 110 times its diameter.

Hence we have very simply obtained a first idea of the distance of the Moon by the measure of its diameter. Nothing could be simpler than this method. The first step is made. Let us continue.

This approximation tells us nothing as yet of the real distance of the orb of night. In order to know this distance in miles, we need to know the width in miles of the lunar disk.



This problem has been solved, as follows:

Two observers go as far as possible from each other, and observe the Moon simultaneously, from two stations situated on the same meridian, but having a wide difference of latitude. The distance that separates the two points of observation forms the base of a triangle, of which the two long sides come together on the Moon.



It is by this proceeding that the distance of our satellite was finally established, in 1751 and 1752, by two French astronomers, Lalande and Lacaille; the former observing at Berlin, the latter at the Cape of Good Hope. The result of their combined observations showed that the angle formed at the center of the lunar disk by the half-diameter of the Earth is 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 not dispense with in discussing the distance of the stars. This astronomical term will soon become familiar in the course of the present lesson, where it will frequently recur, and always in connection with the measurement of celestial distances. "Do not let us fear," wrote Lalande in his Astronomie des Dames, "do not let us fear to use the term parallax, despite its scientific aspect; it is convenient, and this term explains a very simple and very familiar effect."

"If one is at the play," he continues, "behind a woman whose hat is too large, and prevents one from seeing the stage [written a hundred years ago!], one leans to the left or right, one rises or stoops: all this is a parallax, a diversity of aspect, in virtue of which the hat appears to correspond with another part of the theater from that in which are the actors." "It is thus," he adds, "that there may be an eclipse of the Sun in Africa and none for us, and that we see the Sun perfectly, because we are high enough to prevent the Moon's hiding it from us."

See how simple it is. This parallax of 57 minutes proves that the Earth is removed from the Moon at a distance of about 60 times its half-diameter (precisely, 60.27). From this to the distance of the Moon in kilometers is only a step, because it suffices to multiply the half-diameter of the Earth, which is 6,371 kilometers (3,950 miles) by this number. The distance of our satellite, accordingly, is 6,371 kilometers, multiplied by 60.27—that is, 384,000 kilometers (238,000 miles). The parallax of the Moon not only tells us definitely the distance of our planet, but also permits us to calculate its real volume by the measure of its apparent volume. As the diameter of the Moon seen from the Earth subtends an angle of 31', while that of the Earth seen from the Moon is 114', the real diameter of the orb of night must be to that of the terrestrial globe in the relation of 273 to 1,000. That is a little more than a quarter, or 3,480 kilometers (2,157 miles), the diameter of our planet being 12,742 kilometers (7,900 miles).

This distance, calculated thus by geometry, is positively determined with greater precision than that employed in the ordinary measurements of 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 undeniable that the distance separating the Earth from the Moon is measured with greater care than, for instance, the length of the road from Paris to Marseilles, or the weight of a pound of sugar at the grocer's. (And we may add without comment, that the astronomers are incomparably more conscientious in their measurements than the most scrupulous shop-keepers.)

Had we conveyed ourselves to the Moon in order to determine its distance and its diameter directly, we should have arrived at no greater precision, and we should, moreover, have had to plan out a journey which in itself is the most insurmountable of all the problems.

The Moon is at the frontier of our little terrestrial province: one might say that it traces the limits of our domain in space. And yet, a distance of 384,000 kilometers (238,000 miles) separates the planet from the satellite. This space is insignificant in the immeasurable distances of Heaven: for the Saturnians (if such exist!) the Earth and the Moon are 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 second would travel 8 days, 5 hours to reach the Moon. A train started at a speed of one kilometer per minute, would arrive at the end of an uninterrupted 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 the Queen of Night, a telegraphic message would convey our news to the Moon in one and a quarter seconds.

Long-distance travelers who have been round the world some dozen times have journeyed a greater distance.

The other stars (beginning with the Sun) are incomparably farther from us. Yet it has been found possible to determine their distances, and the same method has been employed.

But it will at once be seen that different measures are required in calculating the distance of the Sun, 388 times farther from us than the Moon, for from here to the orb of day is 12,000 times the breadth of our planet. Here we must not think of erecting a triangle with the diameter of the Earth for its base: the two ideal lines drawn from the extremities of this diameter would come together between the Earth and the Sun; there would be no triangle, and the measurement would be absurd.

In order to measure the distance which separates the Earth from the Sun, we have recourse to the fine planet Venus, whose orbit is situated inside the terrestrial orbit. Owing to the combination of the Earth's motion with that of the Star of the Morning and Evening, the capricious Venus 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, in June, 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 in December, 1882. The next will be in June, 2004, and June, 2012. At these eagerly anticipated epochs, astronomers watch the transit of Venus across the Sun at two terrestrial stations as far as possible removed from each other, marking the two points at which the planet, seen from their respective stations, appears to be projected at the same moment on the solar disk. This measure gives the width of an angle formed by two lines, which starting from two diametrically opposite points of the Earth, cross upon Venus, and form an identical angle upon the Sun. Venus is thus at the apex of two equal triangles, the bases of which rest, respectively, upon the Earth and on the Sun. The measurement of this angle gives what is called the parallax of the Sun—that is, the angular dimension at which the Earth would be seen at the distance of the Sun.



Thus, it has been found that the half-diameter of the Earth viewed from the Sun measures 8.82". Now, we know that an object presenting an angle of one degree is at a distance of 57 times its length.

The same object, if it subtends an angle of a minute, or the sixtieth part of a degree, indicates by the measurement of its angle that it is 60 times more distant, i.e., 3,438 times.

Finally, an object that measures one second, or the sixtieth part of a minute, is at a distance of 206,265 times its length.

Hence we find that the Earth is at a distance from the Sun of 206,265/8.82—that is, 23,386 times its half-diameter, that is, 149,000,000 kilometers (93,000,000 miles). This measurement again is as precise 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 distance of the two great celestial torches to which we owe the radiant light of day 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 are based on the velocity of light. The propagation of light is not instantaneous, and notwithstanding the extreme rapidity of its movements, a certain time is required for its transmission from one point to another. On the Earth, this velocity has been measured as 300,000 kilometers (186,000 miles) per second. To come from Jupiter to the Earth, it requires thirty to forty minutes, according to the distance of the planet. Now, in examining the eclipses of Jupiter's satellites, it has been discovered that there is a difference of 16 minutes, 34 seconds in the moment of their occurrence, according as Jupiter is on one side or on the other of the Sun, relatively to the Earth, at the minimum and maximum distance. If the light takes 16 minutes, 34 seconds to traverse the terrestrial orbit, it must take less than 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, the distance 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 a confirmatory result. A familiar example will explain it: Let us imagine ourselves exposed to a vertical rain; the degree of inclination of our umbrella will depend on the relation between our speed and that of the drops of rain. The more quickly we run, the more we need to dip our umbrella in order not to meet the drops of water. Now the same thing occurs for light. The stars, disseminated in space, shed floods of light upon the Heavens. If the Earth were motionless, the luminous rays would reach us directly. But our planet is spinning, racing, with the utmost speed, and in our astronomical observations we are forced to follow its movements, and to incline our telescopes in the direction of its advance. This phenomenon, known under the name of aberration of light, is the result of the combined effects of the velocity of light and of the Earth's motion. It shows that the speed of our globe is equivalent to 1/10000 that of light, i.e., = about 30 kilometers (19 miles) per second. Our planet accordingly accomplishes her revolution round the Sun along an orbit which she traverses at a speed of 30 kilometers (better 29-1/2) per second, or 1,770 kilometers per minute, or 106,000 kilometers per hour, or 2,592,000 kilometers per day, or 946,080,000 kilometers (586,569,600 miles) in the year. This is the length of the elliptical path described by the Earth in her annual translation.

The length of orbit being thus discovered, one can calculate its diameter, the half of which is exactly the distance of the Sun.

We may cite one last method, whose data, based upon attraction, are provided by the motions of our satellite. The Moon is a little disturbed in the regularity of her course round the Earth by the influence of the powerful Sun. As the attraction varies inversely with the square of the distance, the distance may be determined by analyzing the effect it has upon the Moon.

Other means, on which we will not enlarge in this summary of the methods employed for determinations, confirm the precisions of these measurements with certainty. Our readers must forgive us for dwelling at some length upon the distance of the orb of day, since this measurement is of the highest importance; it serves as the base for the valuation of all stellar distances, and may be considered as the meter of the universe.

This radiant Sun to which we owe so much is therefore enthroned in space at 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 exerted upon us to such a manifest extent, it being the very condition of our existence, and reaching out as far as Neptune, thirty times more remote than ourselves from the solar focus.

It is on account of its great distance that the Sun appears to us no larger than the Moon, which is only 384,000 kilometers (238,000 miles) from here, and is itself illuminated by the brilliancy of this splendid orb.

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 have already done for the Moon, we may attempt to picture this abyss. The train cited just now would, if started at a speed of a kilometer a minute, 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 celestial excursion before the bold travelers could bring back news of the expedition to us.

Sound is transmitted through the air at a velocity of 340 meters (1,115 feet) per second. If our atmosphere reached to the Sun, the noise of an explosion sufficiently formidable to be heard here would only reach us at the end of 13 years, 9 months. But the more rapid carriers, such as the telegraph, would leap across to the orb of day in 8 minutes, 17 seconds.

Our imagination is confounded before this gulf of 93,000,000 miles, across which we see our dazzling Sun, whose burning rays fly rapidly through 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 now to be employed is quite different, but equally precise in its results.

It is obvious that the revolution of a planet round the Sun will be longer in proportion as the distance is greater, and the orbit that has to be traveled vaster. This is simple. But the most curious thing is that there is a geometric proportion in the relations between the duration of the revolutions of the planets and their distances. This proportion 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 mean distances from the Sun."

This is enough to alarm the boldest reader. And yet, if we unravel this somewhat incomprehensible phrase, we are struck with its simplicity.

What is a square? We all know this much; it is taught to children of ten years old. But lest it has slipped your memory: a square is simply a number multiplied by itself.

Thus: 2 x 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 multiplied twice by itself.

For instance: 2 multiplied by 2 and again by 2 equals 8. So 8 is the cube of 2. 3 x 3 x 3 = 27; 27 is the cube of 3, and so on.

Now let us take an example that will show the simplicity and precision of the formula enunciated above. Let us choose a planet, no matter which. Say, Jupiter, the giant of the worlds. He is the Lord of our planetary group. This colossal star is five times (precisely, 5.2) as far from us as the Sun.

Multiply this number twice by itself 5.2 x 5.2 x 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 of the number 11.85 is equal to the cube of the number 5.2. This very simple law regulates all the heavenly bodies.

Thus, to find the distance of a planet, it is sufficient to observe the time of its revolution, then to discover the square of the given number by multiplying it into itself. The result of the operation gives simultaneously the cube of the number that represents the distance.

To express this distance in kilometers (or miles), it is sufficient to multiply it by 149,000,000 (in miles 93,000,000), the key to the system of the world.

Nothing, then, could be less complicated than the definition of these methods. A few moments of attention reveal to us in their majestic simplicity the immutable laws that preside over the immense harmony of the Heavens.

* * * * *

But we must not confine ourselves to our own solar province. We have yet to speak of the stars that reign in infinite space far beyond our radiant Sun.

Strange and audacious as it may appear, the human mind is able to cross these heights, to rise on the wings of genius to these distant suns, and to plumb the depths of the abyss that separates us from these celestial kingdoms.

Here, we return to our first method, that of triangulation. And the distance that separates us from the Sun must serve in calculating the distances of the stars.

The Earth, spinning round the Sun at a distance of 149,000,000 kilometers (93,000,000 miles), describes a circumference, or rather an ellipse, of 936,000,000 kilometers (580,320,000 miles), which it travels over in a year. The distance of any point of the terrestrial orbit from the diametrically opposite point which it passes six months later is 298,000,000 kilometers (184,760,000 miles), i.e., the diameter of this orbit. This immense distance (in comparison with those with which we are familiar) 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 consists in observing the little luminous point persistently for a whole year, to see if this star is stationary, or if it describes a minute ellipse reproducing in perspective the annual revolution of the Earth.

If it remains fixed, it is lost in such depths of space that it is impossible to gage the distance, and our 298,000,000 kilometers have no meaning 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 the reflection, the perspective in miniature, of the revolution of our planet round the Sun.

The annual parallax of a star is the angle under which one would see the radius, or half-diameter, of the terrestrial orbit from it. This radius of 149,000,000 kilometers (93,000,000 miles) is indeed, as previously observed, the unit, the meter of celestial measures. The angle is of course smaller in proportion as the star is more distant, and the apparent motion of the star diminishes in the same proportion. But the stars are all so distant that their annual displacement of perspective is almost imperceptible, and very exact instruments are required for its detection.



The researches of the astronomers have proved that there is not one star for which the parallax is equal to that of another. The minuteness of this angle, and the extraordinary difficulties experienced in measuring the distance of the stars, will be appreciated from the fact that the value of a second is so small that the displacement of any star corresponding with it could be covered by a spider's thread.

A second of arc corresponds to the size of an object at a distance of 206,265 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 in excess of those actually obtained. In fact:—the apparent displacement of 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 terrestrial orbit is reduced to this infinitesimal dimension. Now in order that the length of any straight line seen from the front be reduced until it appear to subtend no more than an angle of 0.75", it must be removed to a distance 275,000 times its length. As the radius of the terrestrial orbit is 149,000,000 kilometers (93,000,000 miles), the distance which separates [alpha] of Centaur from our world must therefore = 41,000,000,000,000 kilometers (25,000,000,000,000 miles). And that is the nearest star. We saw in Chapter II that it shines in the southern hemisphere. The next, and one that can be seen in our latitudes, is 61 of Cygnus, which floats in the Heavens 68,000,000,000,000 kilometers (42,000,000,000,000 miles) from here. This little star, of fifth magnitude, was the first of which the distance was determined (by Bessel, 1837-1840).

All the rest are much more remote, and the procession is extended to infinity.

We can not conceive directly of such distances, and in order to imagine them 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 4 years, 128 days. If we would follow it, we must not jump from start to finish, for that would not give us the faintest idea of the distance: we must take the trouble to think out the direct advance of the ray of light, and associate ourselves with its progress. We must see it traverse 300,000 kilometers (186,000 miles) during the first second of the journey; then 300,000 more in the second, which makes 600,000 kilometers; then once more 300,000 kilometers during the third, and so on without stopping for four years and four months. If we take this trouble we may realize the value of the figure; otherwise, as this number surpasses all that we are in the habit of realizing, it will have no significance for us, and will be a dead letter.

If some appalling explosion occurred in this star, and the sound in its flight of 340 meters (1,115 feet) per second were able to cross the void that separates us from it, the noise of this explosion would only reach us in 3,000,000 years.

A train started at a speed of 106 kilometers (65 miles) per hour would have to run for 46,000,000 years, in order to reach this star, our neighbor in the celestial kingdom.

The distance of some thirty of the stars has been determined, but the results 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. Each of these magnificent stars must be a huge sun to burn at such a distance with such luminosity. Some are millions of times larger than the Earth. Most of them are more voluminous than our Sun. On all sides they scintillate at inaccessible distances, and their light strays a long while in space before it encounters the Earth. The luminous ray that we receive to-day from some pale star hardly perceptible to our eyes—so enormous is its distance—may perhaps bring us the last emanation of a sun that expired thousands of years ago.

* * * * *

If these methods have been clear to my readers, they may also be interested perhaps in knowing the means employed in weighing the worlds. The process is as simple and as clear as those of which we have been speaking.

Weighing the stars! Such a pretension seems Utopian, and one asks oneself curiously what sort of balance the astronomers must have adopted in order to calculate the weight of Sun, Moon, planets or stars.

Here, figures replace weights. Ladies proverbially dislike figures: yet it would be easier for some society dame to weigh the Sun at the point of 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 35 kilos, by direct methods.

Weighing the Sun is an amusement like any other, and a change of occupation.

If the Moon were not attracted by the Earth, she would glide through the Heavens along an indefinite straight line, escaping at the tangent. But in virtue of the attraction that governs the movements of all the Heavenly bodies, our satellite at a distance of 60 times the terrestrial half-diameter revolves round us in 27 days, 7 hours, 43 minutes, 11-1/2 seconds, continually leaving the straight line to approach the Earth, and describing an almost circular orbit in space. If at any moment we trace 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 our planet 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 by another 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 to itself upon the surface of the Earth, it drops 4.90 meters during the first 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 then abandon it to the attraction of our planet, it would in the first second fall 4.90 meters divided by the square of 60, or 3,600—that is, of 1-1/3 millimeters, exactly the quantity by which the Moon deviates from the straight line she would pursue if the Earth were not influencing her.

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. In order to know how much the intensity of terrestrial weight would be diminished at such a distance, we should look, in the first place, for the square of the number representing the distance—that is, 23,386 multiplied by itself, = 546,905,000. If we divide 4.90 meters, which represents the attractive force of our planet, by this number, we get 9/1000000 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 trace the annual orbit of the terrestrial globe round the central orb, and we shall find that the Earth falls in each second 2.9 millimeters toward the Sun.

This proportion gives the attractive force of the Sun in relation to that of the Earth, and proves that the Sun is 324,000 times more powerful than our world, for 2.9 millimeters divided by 0.000,009 equals 324,000, if worked out into the ultimate fractions neglected here for the 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, and it is by this method that we are able to affirm that Jupiter is 310 times heavier than the Earth, Saturn 92 times, Neptune 16 times, Uranus 14 times, while Mars is much less heavy, its weight being only two-thirds that of our own.

The planets which have no satellites have been weighed by the perturbations which they cause in other stars, or in the imprudent comets that sometimes tarry in their vicinity. Mercury weighs very much less than the Earth (only 6/100) and Venus about 8/10. So the beautiful star 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 weight has been calculated by reckoning the amount of water she attracts at each tide in the ocean, or by observing the effects of her attraction on the terrestrial globe. When the Moon is before us, in the last quarter, she makes us travel faster, whereas in the first quarter, when she is behind, she delays us.

All the calculations agree in showing us that the orb of night is 81 times less heavy than our planet. There is nearly as much difference in weight between the Earth and the Moon as between an orange and a grape.

* * * * *

Not content with weighing the planets of our system, astronomers have investigated the weight of the stars. How have they been enabled to ascertain the quantity of matter which constitutes these distant Suns—incandescent globes of fire scattered in the depths of space?

They have resorted to the same method, and it is by the study of the attractive influence of a sun upon some other contiguous neighboring star, that the weight of a few of these has been calculated.

Of course this method can only be applied to those double stars of which the distance is known.

It has been discovered that some of the tiny stars that we can hardly see twinkling in the depths of the azure sky are enormous suns, larger and heavier than our own, and millions of times more voluminous than the Earth.

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 creation incessantly renewed, and perpetually transformed by the accumulated centuries.

And what diversity exists in this army of worlds and suns, whose regular harmonious march obeys a mute order....

But we have as yet said nothing about weight on the surface of the worlds, and I see signs of impatience in my readers, for after so much simple if unpoetical demonstration, they will certainly ask me for the explanation that will prove to them that a kilogram transported to Jupiter or Mars would weigh more or less than here.

Give me your attention five minutes longer, and I will restore your faith in the astronomers.

It must not be supposed that objects at the surface of a world like Jupiter, 310 times heavier than our own, weigh 310 times more. That would be a serious error. In that case we should have to assume that a kilogram transported to the surface of the Sun would there weigh 324,000 times more, or 324,000 kilograms. That would be correct if these orbs were 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 our little planet.

Now, weight at the surface of a celestial body depends not only on its mass, but also on its diameter.

In order to know the weight of any body upon the surface of the Sun, we must argue as follows:

Since a body placed upon the surface of the Sun is 108 times farther from 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 of the distance, the intensity of the weight would there be 108 multiplied by 108, or 11,700 times weaker. Now divide the number representing the mass, i.e., 324,000, by this number 11,700, and it results that bodies at the surface of the Sun are 28 times heavier than here. A woman whose weight was 60 kilos would weigh 1,680 kilograms there if organized in the same way as on the Earth, and would find walking very difficult, for at each step she would lift up a shoe that weighed at least ten kilograms.

This reasoning as just stated for the Sun may be applied to the other stars. We know that on the surface of Jupiter the intensity of weight is twice and a third times as great as here, while on Mars it only equals 37/100.

On the surface of Mercury, weight is nearly twice as small again as here. On Neptune it is approximately equal to our own.

With deference to the Selenites, everything is at its lightest on the Moon: a man weighing 70 kilograms on the Earth would not weigh more than 12 kilos there.

So all tastes can be provided for: the only thing to be regretted is that one can not choose one's planet with the same facility as one's residence upon the Earth.



CHAPTER XII

LIFE, UNIVERSAL AND ETERNAL

And now, while thanking my readers for having followed me so far in this descriptive account of the marvels of the Cosmos, I must inquire what philosophical impression has been produced on their minds by these celestial excursions to the other worlds? Are you left indifferent to the pageant of the Heavens? When your imagination was borne away to these distant stars, suns of the infinite, these innumerable stellar systems disseminated through a boundless eternity, did you ask what existed there, what purpose was served by those dazzling spheres, what effects resulted from these forces, radiations, energies? Did you reflect that the elements which upon our little Earth determined a vital activity so prodigious and so varied must needs have spread the waves of an incomparably vaster and more diversified existence throughout the immensities of the Universe? Have you felt that all can not be dead and deserted, as we are tempted by the illusions of our terrestrial senses and of our isolation to believe in the silence of the night: that on the contrary, the real aim of Astronomy, instead of ending with statements of the positions and movements of the stars, is to enable us to penetrate to them, to make us divine, and know, and appreciate their physical constitution, their degree of life and intellectuality in the universal order?

On the Earth, it is Life and Thought that flourish; and it is Life and Thought that we seek again in these starry constellations strewn to Infinitude amid the immeasurable fields of Heaven.

The humble little planet that we inhabit presents itself to us as a brimming cup, overflowing at every outlet. Life is everywhere. From the bottom of the seas, from the valleys to the mountains, from the vegetation that carpets the soil, from the mold in the fields and woods, from the air we breathe, arises an immense, prodigious, and perpetual murmur. Listen! it is the great voice of Nature, the sum of all the unknown and mysterious voices that are forever calling to us, from the ocean waves, from the forest winds, from the 300,000 kinds of insects that are redundant everywhere, and make a lively community on the surface of our globe. A drop of water contains thousands of curious and agile creatures. A grain of dust from the streets of Paris is the home of 130,000 bacteria. If we turn over the soil of a garden, field, or meadow, we find the earthworms working to produce assimilable slime. If we lift a stone in the path, we discover a crawling population. If we gather a flower, detach a leaf, we everywhere find little insects living a parasitic existence. Swarms of midges fly in the sun, the trees of the wood are peopled with nests, the birds sing, and chase each other at play, the lizards dart away at our approach, we trample down the antheaps and the molehills. Life enwraps us in an inexorable encroachment of which we are at once the heroes and the victims, perpetuating itself to its own detriment, as imposed upon it by an eternal reproduction. And this from all time, for the very stones of which we build our houses are full of fossils so prodigiously multiplied that one gram of such stone will often contain millions of shells, marvels of geometrical perfection. The infinitely little is equal to the infinitely great.

Life appears to us as a fatal law, an imperious force which all obey, as the result and the aim of the association of atoms. This is illustrated for us upon the Earth, our only field of direct observation. We must be blind not to see this spectacle, deaf not to hear its reaching. On what pretext could one suppose that our little globe which, as we have seen, has received no privileges from Nature, is the exception; and that the entire 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 conditions other than terrestrial, and that the other worlds can only be inhabited on the condition of being similar to our own. But terrestrial nature itself demonstrates to us the error of this way of thinking. We die in the water: fishes die out of the water. Again, short-sighted naturalists affirm categorically that Life is impossible at the bottom of the sea: 1, because it is in complete darkness; 2, because the terrible pressure would burst any organism; 3, because all motion would be impossible there, and so on. Some inquisitive person sends down a dredge, and brings up lovely creatures, so delicate in structure that the daintiest touch must proceed with circumspection. There is no light in these depths: they make it with their own phosphorescence. Other inquirers visit subterranean caverns, and discover animals and plants whose organs have been transformed by adaptation to their gloomy environment.

What right have we to say to the vital energy that radiates round every Sun of the Universe: "Thus far shalt thou come, and no further"? In the name of Science? An absolute mistake. The Known is an infinitesimal island in the midst of the vast ocean of the Unknown. The deep seas which seemed to be a barrier are, as we have seen, peopled with special life. Some one objects: But after all, there is air there, there is oxygen: oxygen is indispensable: a world without oxygen would be a world of death, an eternally sterile desert. Why? Because we have not yet come across beings that can breathe without air, and live without oxygen? Another mistake. Even if we did not know of any, it would not prove that they do not exist. But as it happens, we do know of such: the anaerobia. These beings live without air, without oxygen. Better still: oxygen kills them!

All the evidence goes to show that in interpreting as we ought the spectacle of terrestrial life, and the positive facts acquired by Science, we should enlarge the circle of our conceptions and our judgments, and not limit extra-terrestrial existence to the servile image of what is in existence here below. Terrestrial organic forms are due to local causes upon our planet. The chemical constitution of water and of the atmosphere, temperature, light, density, weight, are so many elements that have gone to form our bodies. Our flesh is composed of carbon, 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 man who eats the beef. All organized terrestrial matter is only carbon combined in variable proportions with hydrogen, nitrogen, oxygen, etc.

But we have no right to forbid Nature to act differently in worlds from which carbon is absent. A world, for example, in which silica replaces carbon, silicic acid carbonic acid, might be inhabited by organisms absolutely different from those which exist on the Earth, different not only in form, but also in substance. We already know stars and suns for which spectral analysis reveals a predominance of silica, e.g., Rigel and Deneb. In a world where chlorine predominated, we might expect to find hydrochloric acid, and all the fecund family of chlorides, playing an important part in the phenomena of life. Might not bromine be associated in other formations? Why, indeed, should we draw the line at terrestrial chemistry? What is to prove that these elements are really simple? May not hydrogen, carbon, oxygen, nitrogen, and sulphur all be compounds? Their equivalents are multiples of the first: 1, 6, 8, 14, 16. And is even hydrogen the most simple of the elements? Is not its molecule composed of atoms, and may there not exist a single species of primitive atom, whose geometric arrangement and various associations might constitute the molecules of the so-called simple elements?

In our own solar system we discover the essential differences between certain planets. In the spectrum of Jupiter, for instance, we are aware of the action of an unknown substance that manifests itself by a marked absorption of certain red rays. This gas, which does not exist upon the Earth, is seen still more obviously in the atmospheres of Saturn and Uranus. Indeed, upon this last planet the atmosphere appears, apart from its water vapor, to have no sort of analogy with our own. And in the solar spectrum itself, many of the lines have not yet been identified with terrestrial substances.

The interrelation of the planets is of course incontrovertible, since they are all children of the same parent. But they differ among themselves, not merely in respect of situation, position, volume, mass, density, temperature, atmosphere, but again in physical and chemical constitution. And the point we would now accent is that this diversity should not be regarded as an obstacle to the manifestations of life, but, on the contrary, as a new field open to the infinite fecundity of the 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 unknown worlds that gravitate round the suns disseminated in space, we have no plausible reason for imagining that the inhabitants of these other worlds of Heaven resemble us in any way, whether in form, or even in organic substance.

The substance of the terrestrial human body is due to the elements of our planet, and notably to carbon. The terrestrial human form derives from the ancestral animal forms to which it has gradually raised itself by the continuous progress of the transformation of species. To us it seems 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 of course. That we are constituted as we are, is simply the result of our pro-simian ancestors having also had a head, a heart, lungs, legs, and arms—less elegant than your own, it is true, Madam, but still of the same anatomy. And more and more, by the progress of paleontology, we are delving down to the origin of beings. As certain as it is that the bird derives from the reptile by a process of organic evolution, so certain is it that terrestrial Humanity represents the topmost branches of the huge genealogical tree, whereof all the limbs are brothers, and the roots of which are plunged into the very rudiments of the most elementary and primitive organisms.

The multitude of worlds is surely peopled by every imaginable and unimaginable form. Terrestrial man is endowed with five senses, or perhaps it is better to say six. Why should Nature stop at this point? Why, for instance, may she not have given to certain beings an electrical sense, a magnetic sense, a sense of orientation, an organ able to perceive the ethereal vibrations of the infra-red or ultra-violet, or permitted them to hear at a distance, or to see through walls? We eat and digest like coarse animals, we are slaves to our digestive tube: may there not be worlds in which a nutritive atmosphere enables its fortunate inhabitants to dispense with this absurd process? The least sparrow, even the dusky bat, has an advantage over us in that it can fly through the air. Think how inferior are our conditions, since the man of greatest genius, the most exquisite woman, are nailed to the soil like any vulgar caterpillar before its metamorphosis! Would it be a disadvantage to inhabit a world in which we might fly whither we would; a world of scented luxury, full of animated flowers; a world where the winds would be incapable of exciting a tempest, where several suns of different colors—the diamond glowing with the ruby, or the emerald with the sapphire—would burn night and day (azure nights and scarlet days) in the glory of an eternal spring; with multi-colored moons sleeping in the mirror of the waters, phosphorescent mountains, aerial inhabitants,—men, women, or perhaps of other sexes,—perfect in their forms, gifted with multiple sensibilities, luminous at will, incombustible as asbestos, perhaps immortal, unless they commit suicide out of curiosity? Lilliputian atoms as we are, let us once for all be convinced that our imagination is but sterility, in the midst of an infinitude hardly glimpsed by the telescope.

One important point seems always to be ignored expressly by those who blindly deny the doctrine of the plurality of worlds. It is that this doctrine does not apply more particularly to the present epoch than to any other. Our time is of no importance, no absolute value. Eternity is the field of the Eternal Sower. There is no reason why the other worlds should be inhabited now more than at any other epoch.

What, indeed, is the Present Moment? It is an open trap through which the 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, and cemeteries. In all probability Jupiter is not yet inhabited. What does this prove? The Earth was not inhabited during its primordial period: what did that prove to the inhabitants of Mars or of the Moon, who were perhaps observing it at that epoch, a few million years ago?

To pretend that our globe must be the only inhabited world because the others do not resemble it, is to reason, not like a philosopher, but, as we remarked before, like a fish. Every rational fish ought to assume that it is impossible to live out of water, since its outlook and its philosophy do not extend beyond its daily life. There is no answer to this order of reasoning, except to advise a little wider perception, and extension 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 altogether inadequate, although it is the only possible basis of our reasoning. We must learn to see with the eyes of our spirit.

As to the planetary systems other than our own, we are no longer reduced to hypotheses. We already know with certainty that our Sun is no exception, 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 system composed of a central sun, and of one or more stars gravitating round him, the plane of such a system should fall just within our line of vision, and that it should revolve in such a way that the globes of which it is composed pass exactly between this sun and ourselves in turning round him, eclipsing him more or less during this transit. As, on the other hand, the eclipses would be our only means of determining the existence of these unknown planets (save indeed from perturbation, as in the case of Sirius and Procyon), it might have seemed quixotic to hope for like conditions in order to discover solar systems other than our own. But these exceptional circumstances have reproduced themselves at different parts of the Heavens.

Thus, for instance, we have seen that the variable star Algol owes its variations in brilliancy, which reduce it from second to fourth magnitude every sixty-nine hours, to the interposition of a body between itself and the Earth, and celestial mechanics has already been able to determine accurately the orbit of this body, its dimensions and its mass, and even the flattening of the sun Algol. Here, then, is a system in which we know the sun and an enormous planet, whose revolution is effected in sixty-nine hours with extreme rapidity, as measured by the spectroscope.

The star [delta] of Cepheus is in the same case: it is an orb eclipsed in a period of 129 hours, and its eclipsing planet also revolves in the plane of our vision. The variable star in Ophiuchus has an analogous system, and observation has already revealed a great number of others.

Since, then, a certain number of solar systems differing from our own have been revealed, as it were in section, to terrestrial observation, this affords us sufficient evidence of the existence of an innumerable quantity 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 as Sirius, Procyon, Altair, proves that these distant orbs have companions,—planets not yet discovered by the telescope, and that perhaps never will be discovered, because they are obscure, and lost in the radiation of the star.

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Some savants have asserted that Life can not germinate if the conditions of the environment differ too much from terrestrial conditions.

This hypothesis is purely gratuitous, and we will now discuss it.

In order to examine what is happening on the Earth, let us mount the ladder of time for a moment, to follow the evolutions of Nature.

There was an epoch when the Earth did not exist. Our planet, the future world of our habitation, slept in the bosom of the solar nebula.

At last it came to birth, this cherished Earth, a gaseous, luminous ball, poor reflection of the King of Orbs, its parent. Millions of years rolled by before the condensation and cooling of this new globe were sufficiently transformed to permit life to manifest itself in its most rudimentary aspects.