These temporary stars, which appear spontaneously to the observers on the Earth, and quickly vanish again, are doubtless due to collisions, conflagrations, or celestial cataclysms. But we only see them long after the epoch at which the phenomena occurred, years upon years, and centuries ago. For instance, the conflagration photographed by the author in 1901, in Perseus, must have occurred in the time of Queen Elizabeth. 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 fleeting glance within these limits. They present a field of infinite variety.

Who has not noticed the Milky Way, the pale belt that traverses the entire firmament and is so luminous on clear evenings in the Constellations 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 we divine the starry constitution: a small telescope shows us marvels. Eighteen millions of stars were counted there with the gauges of William Herschel.

Now this Milky Way is a symbol, not of the Universe, but of the Universes 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 our feet as well as over our heads. It consists of a very considerable mass of star-clusters, varying greatly in extent and number, some projected in front of others, while the whole forms an agglomeration.



Among this mass of star-groups, several thousands of which are already known to us, we will select one of the most curious, the Cluster in Hercules, which can be distinguished with the unaided eye, between the stars [eta] and [zeta] of that constellation. Many photographs of it have been taken in the author's observatory at Juvisy, showing some thousands of stars; and one of these is reproduced in the accompanying figure (Fig. 21). Is it not a veritable universe?



Another of the most beautiful, on account of its regularity, is that of the Centaur (Fig. 22).

These groups often assume the most extraordinary shapes in the telescope, such as crowns, fishes, crabs, open mouths, birds with outspread wings, etc.

We must also note the gaseous nebulae, universes in the making, e.g., the famous Nebula in Orion, of which we obtained some notion a while ago in connection with its sextuple star: and also that in Andromeda (Fig. 23).



Perhaps the most marvelous of all is that of the Greyhounds, which evolves in gigantic spirals round a dazzling focus, and then loses itself far off in the recesses of space. Fig. 24 gives a picture of it.



Without going thus far, and penetrating into telescopic depths, my readers can get some notion of these star-clusters with the help of a small telescope or opera-glasses, or even with the unaided eye, by looking at the beautiful group of the Pleiades, already familiar to us on another page, and using it as a test of vision. The little map subjoined (Fig. 25) will be an assistance in recognizing them, and in estimating 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. Celaeno 6.5. Asterope 6.8.

Good eyes distinguish the first six, sharp sight detects the three others.

In the times of the ancient Greeks, seven were accounted of equal brilliancy, and the poets related that the seventh star had fled at the time of the Trojan War. Ovid adds that she was mortified at not being embraced by a god, as were her six sisters. It is probable that only the best sight could then distinguish Pleione, as in our own day. The angular distance from Atlas to Pleione is 5'.

The length of this republic, from Atlas and Pleione to Celaeno, is 4'/23" of time, or 1 deg. 6' of arc; the breadth, from Merope to Asterope, is 36'.[8]

In the quadrilateral, the length from Alcyone to Electra is 36', and the breadth from Merope to Maia 25'. To us it appears as though, if the Full Moon were placed in front of this group of nine stars, she would cover it entirely, for to the naked eye she appears much larger than all the Pleiades together. But this is not so. She only measures 31', less than half the distance from Atlas to Celaeno; she is hardly broader than the distance from Alcyone to Atlas, and could pass between Merope and Taygeta without touching either of these stars. This is a perennial and very curious optical illusion. When the Moon passes in front of the Pleiades, and occults them successively, it is hard to believe one's eyes. The fact occurred, e.g., on July 23, 1897, during a fine occultation observed at the author's laboratory of Juvisy (Fig. 26).



Photography here discovers to us, not 6, 9, 12, 15, or 20 stars, but hundreds and millions.

These are the most brilliant flowers of the celestial garden.

of the Virgin.]

We, alas, can but glance at them rapidly. In contemplating them we are transported into immensities both of space and time, for the stellar periods measured by these distant universes often overpower in their magnitude the rapid years in which our terrestrial days are estimated. For instance, one of the double stars we spoke of above, [gamma] of the Virgin, sees its two components, translucent diamonds, revolve around their common center of gravity, in one hundred and eighty years. How many events took place in France, let us say, in a single year of this star!—The Regency, Louis XV, Louis XVI, the Revolution, Napoleon, Louis XVIII, Louis Philippe, the Second Republic, Napoleon III, the Franco-German War, the Third Republic.... What revolutions here, during a single year of this radiant pair! (Fig. 27.)

But the pageant of the Heavens is too vast, too overwhelming. We must end our survey.

Our Milky Way, with its millions of stars, represents for us only a portion of the Creation. The illimitable abysses of Infinitude are peopled by other universes as vast, as imposing, as our own, which are renewed in all directions through the depths of Space to endless distance. Where is our little Earth? Where our Solar System? We are fain to fold our wings, and return from the Immense and Infinite to our floating island.



CHAPTER IV

OUR STAR THE SUN

In the incessant agitation of daily life in which we are involved by the thousand superfluous wants of modern "civilization," one is prone to assume that existence is complete only when it reckons to the good an incalculable number of petty incidents, each more insignificant than the last. Why lose time in thinking or dreaming? We must live at fever heat, must agitate, and be infatuated for inanities, must create imaginary desires and torments.

The thoughtful mind, prone to contemplation and admiration of the beauties of Nature, is ill at ease in this perpetual vortex that swallows everything—satisfaction, in a life that one has not time to relish; love of the beautiful, that one views with indifference; it is a whirlpool that perpetually hides Truth from us, forgotten forever at the bottom of her well.

And why are our lives thus absorbed in merely material interests? To satisfy our pride and vanity! To make ourselves slaves to chimeras! If the Moon were inhabited, and if her denizens could see us plainly enough to note and analyze the details of human existence on the surface of our planet, it would be curious and perhaps a little humiliating for us, to see their statistics. What! we should say, is this the sum of our lives? Is it for this that we struggle, and suffer, and die? Truly it is futile to give ourselves such trouble.

And yet the remedy is simple, within the power of every one; but one does not think of it just because it is too easy, although it has the immense advantage of lifting us out of the miseries of this weary world toward the inexpressible happiness that must always awaken in us with the knowledge of the Truth: we need only open our eyes to see, and to look out. Only—one hardly ever thinks of it, and it is easier to let one's self be blinded by the illusion and false glamor of appearances.

Think what it would be to consecrate an hour each day to voluntary participation in the harmonious Choir of Nature, to raise one's eyes toward the Heavens, to share the lessons taught by the Pageant of the Universe! 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 of man as much as the Sun, the God of Light, the fecundating orb, without which our planet and its life would never have issued from nonentity, the visible image of the invisible god, as said Cicero, and the poets of antiquity. And yet how many beyond the circle of those likely to read these pages know that this Sun is a star in the Milky Way, and that every star is a sun? How many take any account of the reality and grandeur of the Universe? Inquire, and you will find that the number of people who have any notion, however rudimentary, of its construction, is singularly restricted. Humanity is content to vegetate, much after the fashion 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 other systems of worlds, our splendid Sun is only a more or less brilliant, luminous point, according as the spot from which it is observed is nearer or farther off. But to us its "terrestrial" importance renders it particularly precious; we forget all the sister stars on its account, and even the most ignorant hail it with enthusiasm without exactly knowing what its role in the universe may be, simply because they feel that they depend on it, and that without it life would become extinct on this globe. Yes, it is the beneficent rays of the Sun that shed upon our Earth the floods of light and heat to which Life owes its existence and its perpetual propagation.

Hail, vast Sun! a little star in Infinitude, but for us a colossal and portentous luminary. Hail, divine Benefactor! How should we not adore, when we owe him the glow of the warm and cheery days of summer, the gentle caresses by which his rays touch the undulating ears, and gild them with the touch? The Sun sustains our globe in Space, and keeps it within his rays by the mysteriously powerful and delicate cords of attraction. It is the Sun that we inhale from the embalmed corollas of the flowers that uplift their gracious heads toward his light, and reflect his splendors back to us. It is the Sun that sparkles in the foam of the merry wine; that charms our gaze in those first days of spring, when the home of the human race is adorned with all the charms of verdant and flowering youth. Everywhere we find the Sun; everywhere we recognize his work, extending from the infinitely great to the infinitely little. We bow to his might, and admire his power. When in the sad winter day he disappears behind the snowy eaves, we think his fiery globe will never rise to mitigate the short December days which are alleviated with his languid beams.

April restores him to superb majesty, and our hearts are filled with hope 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 distant creations that we lost sight of our cherished luminary.

But we remember that he burns yonder, in the midst of the pale cosmic cloud we term the Milky Way. Let us approach him, now that we have visited the Isles of Light in the Celestial Ocean; let us traverse the vast 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 our Universe. Soon we perceive a tiny speck, scintillating feebly in the depths of Space, and recognize it as our own celestial quarters. This little star shines like the head of a gold pin, and increases in size as we advance toward it. We traverse a few more trillion miles in our rapid course, and it shines out like a fine star of the first magnitude. It grows larger and larger. Soon we divine that it is our humble Earth that is shining before us, and gladly alight upon her. In future we shall not quit our own province of the Celestial Kingdom, but will enter into relations with this solar family, which interests us the more in that it affects us so closely.



The Sun, which is manifested to us as a fine white disk at noon, while it is fiery red in the evening, at its setting, is an immense globe, whose colossal dimensions surpass those of our terrestrial atom beyond all conceivable proportion.

In diameter, it is, in effect, 108-1/2 times as large as the Earth; that is 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 on the accompanying figure (Fig. 28), which is in exact proportion.

If our world were set down upon the Sun, with all its magnificence, all its wealth, its mountains, its seas, its monuments, and its inhabitants, it would only be an imperceptible speck. It would occupy less space in the central orb than one grain in a grenade. If the Earth were placed in the center of the Sun, with the Moon still revolving round it at her proper distance of 384,000 kilometers (238,500 miles), only half the solar surface would be covered.

In volume the Sun is 1,280,000 times vaster than our abode, and 324,000 times heavier in mass. That the giant only appears to us as a small though very brilliant disk, is solely on account of its distance. Its apparent dimensions by no means reveal its majestic proportions to us.

When observed with astronomical instruments, or photographed, we discover that its surface is not smooth, as might be supposed, but granulated, presenting a number of luminous points dispersed over a more somber background. These granulations are somewhat like the pores of a fruit, e.g., a fine orange, the color of which recalls the hue of the Sun when it sinks in the evening, and prepares to plunge us into darkness. At times these pores open under the influence of disturbances that arise upon the solar surface, and give birth to a Sun-Spot. For centuries scientists and lay people alike refused to admit the existence of these spots, regarding them as so many blemishes upon the King of the Heavens. Was not the Sun the emblem of inviolable purity? To find any defect in him were to do him grievous injury. Since the orb of day was incorruptible, those who threw doubt on his immaculate splendor were fools and idiots. And so when Scheiner, one of the first who studied the solar spots with the telescope, published the result of his experiments in 1610, no one would believe his statements.

Yet, from the observations of Galileo and other astronomers, it became necessary to accept the evidence, and stranger still to recognize that it is by these very spots that we are enabled to study the physical constitution of the Sun.

They are generally rounded or oval in shape, and exhibit two distinct parts; first, the central portion, which is black, and is called the nucleus, or umbra; second, a clearer region, half shaded, which has received the name of penumbra. These parts are sharply defined in outline; the penumbra is gray, the nucleus looks black in relation to the dazzling brilliancy of the solar surface; but as a matter of fact it radiates a light 2,000 times superior in intensity to that of the full moon.



Some idea of the aspect of these spots may be obtained from the accompanying reproduction of a photograph of the Sun (taken September 8, 1898, at the author's observatory at Juvisy), and from the detailed drawing of the large spot that broke out some days later (September 13), crossed by a bridge, and furrowed with flames. As a rule, the spots undergo rapid transformations.



These spots, which appear of insignificant dimensions to the observers on the Earth, are in reality absolutely gigantic. Some that have been measured are ten times as large as the Earth's diameter, i.e., 120,000 kilometers (74,500 miles).

Sometimes the spots are so large that they can be seen with the unaided eye (protected with black or dark-blue glasses). They are not formed instantaneously, but are heralded by a vast commotion on the solar surface, exhibiting, as it were, luminous waves or faculae. Out of this agitation arises a little spot, that is usually round, and enlarges progressively to reach a maximum, after which it diminishes, with frequent segmentation and shrinkage. Some are visible only for a few days; others last for months. Some appear, only to be instantly swallowed in the boiling turmoil of the flaming orb. Sometimes, again, white incandescent waves emerge, and seem to throw luminous bridges across the central umbra. As a rule the spots are not very profound. They are funnel-shaped depressions, inferior in depth to the diameter of the Earth, which, as we have seen, is 108 times smaller than that of the Sun.

* * * * *

The Sun-Spots are not devoid of motion, and from their movements we learn that the radiant orb revolves upon itself in about twenty-five days. This rotation was determined in 1611, by Galileo, who, while observing the spots, saw that they traversed the solar disk from east to west, following lines that are oblique to the plane of the ecliptic, and that they disappear at the western border fourteen days after their arrival at the eastern edge. Sometimes the same spot, after being invisible for fourteen days, reappears upon the eastern edge, where it was observed twenty-eight days previously. It progresses toward the center of the Sun, which is reached in seven days, disappears anew in the west, and continues its journey on the hemisphere opposed to us, to reappear under observation two weeks later, if it has not meantime been extinguished. This observation proves that the Sun revolves upon itself. The reappearance of the spots occurs in about twenty-seven days, because the Earth is not stationary, and in its movement round the burning focus, a motion effected in the same direction as the solar rotation, the spots are still visible two and a half days after they disappeared from the point at which they had been twenty-five days previously. In reality, 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 different parts of the solar surface, diminish from the Sun's equator toward its poles. The period is twenty-five days at the equator, twenty-six at the twenty-fourth degree of latitude, north or south, twenty-seven at the thirty-seventh degree, twenty-eight at the forty-eighth. The spots are usually formed between the equator and this latitude, more especially between the tenth and thirtieth degrees. They have never been seen round the poles.

Toward the edges of the Sun, again, are very brilliant and highly luminous regions, which generally surround the spots, and have been termed faculae (facula, a little torch). These faculae, which frequently occupy a very extensive surface, seem to be the seat of formidable commotions that incessantly revolutionize the face of our monarch, often, as we said, preceding the spots. They can be detected right up to the poles.

Our Sun, that appears so calm and majestic, is in reality the seat of fierce conflagrations. Volcanic eruptions, the most appalling storms, the worst cataclysms that sometimes disturb our little world, are gentle zephyrs compared with the solar tempests that engender clouds of fire capable at one burst of engulfing globes of the dimensions of our planet.

To compare terrestrial volcanoes with solar eruptions is like comparing the modest night-light that consumes a midge with the flames of the fire that destroys a town.

The solar spots vary in a fairly regular period of eleven to twelve years. In certain years, e.g., 1893, they are vast, numerous and frequent; in other years, e.g., 1901, they are few and insignificant. The statistics are very carefully preserved. Here, for instance, is the surface showing sun-spots expressed in millionths of the extent of the visible 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 auroras exhibit an oscillation parallel to that of the solar spots, and apparently 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 heat and light. The dazzling surface of this globe is called a photosphere (light sphere). It is in perpetual motion, like the waves of an ocean of fire, whose roseate and transparent flames measure some 15,000 kilometers (9,300 miles) in height. This stratum of rose-colored flames has received the name of chromosphere (color sphere). It is transparent; it is not directly visible, but is seen only during the total eclipses of the Sun, when the dazzling disk of that luminary is entirely concealed by the Moon; or with the aid of the spectroscope. The part of the Sun that we see is its luminous surface, or photosphere.

From this agitated surface there is a constant ejection of gigantic eruptions, immense jets of flame, geysers of fire, projected at a terrific speed to prodigious heights.

For years astronomers were greatly perplexed as to the nature of these incandescent masses, known as prominences, which shot out like fireworks, and were only visible during the total eclipses of the Sun. But now, thanks to an ingenious invention of Janssen and Lockyer, these eruptions can be observed every day in the spectroscope, and have been registered since 1868, more particularly in Rome and in Catania, where the 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 our own storm-clouds; they rise above the chromosphere with incredible velocity, often exceeding 200 kilometers (124 miles) per second, and are carried up to the amazing height of 300,000 kilometers (186,000 miles).



The Sun is surrounded with these enormous flames on every side; sometimes they shoot out into space like splendid curving roseate plumes; at others they rear their luminous heads in the Heavens, like the cleft and waving leaves of giant palm-trees. Having illustrated a remarkable type of solar spot, it is interesting to submit to the reader a precise observation of these curious solar flames. That reproduced here was observed in Rome, January 30, 1885. It measured 228,000 kilometers (141,500 miles) in height, eighteen times the diameter of the earth (represented alongside in its relative magnitude). (Fig. 31.)

Solar eruptions have been seen to reach, in a few minutes, a height of more than 100,000 kilometers (62,000 miles), and then to fall back in a flaming torrent into that burning and inextinguishable ocean.

Observation, in conjunction with spectral analysis, shows these prominences to be due to formidable explosions produced within the actual substance of the Sun, and projecting masses of incandescent hydrogen into space with considerable force.

Nor is this all. During an eclipse one sees around the black disk of the Moon as it passes in front of the Sun and intercepts its light, a brilliant and rosy aureole with long, luminous, branching feathers streaming out, like aigrettes, which extend a very considerable distance from the solar surface. This aureole, the nature of which is still unknown to us, has received the name of corona. It is a sort of immense atmosphere, extremely rarefied. Our superb torch, accordingly, is a brazier of unparalleled activity—a globe of gas, agitated by phenomenal tempests whose flaming streamers extend afar. The smallest of these flames is so potent that it would swallow up our world at a single breath, like the bombs shot out by Vesuvius, that fall back within the crater.

What now is the real heat of this incandescent focus? The most accurate researches estimate the temperature of the surface of the Sun at 7,000 deg.C. The internal temperature must be considerably higher. A crucible of molten iron poured out upon the Sun would be as a stream of ice and snow.

We can form some idea of this calorific force by making certain comparisons. Thus, the heat given out appears to be equal to that which would be emitted by a colossal globe of the same dimensions (that is, as voluminous as twelve hundred and eighty thousand terrestrial globes), entirely covered with a layer of incandescent coal 28 kilometers (18 miles) in depth, all burning at equal combustion. The heat emitted by the Sun, at each second, is equal to that which would result from the combustion of eleven quadrillions six hundred thousand milliards of tons of coal, all burning together. This same heat would bring to the boil in an hour, two trillions nine hundred milliards of cubic kilometers of water at freezing-point.

Our little planet, gravitating at 149,000,000 kilometers (93,000,000 miles) from the Sun, arrests on the way, and utilizes, only the half of a milliard part of this total radiation.

How is this heat maintained? One of the principal causes of the heat of the Sun is its condensation. According to all probabilities, the solar globe represents for us the nucleus of a vast nebula, that extended in primitive times beyond the orbit of Neptune, and which in its contraction has finally produced this central focus. In virtue of the law of transformation of motion into heat, this condensation, which has not yet reached its limit, suffices to raise this colossal globe to its level of temperature, and to maintain it there for millions of years. In addition, 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 than the Earth—that is to say, eighteen hundred and seventy octillions of kilograms:

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 found possible to weigh the Sun and determine its exact distance.

* * * * *

I trust these figures will convey some notion of the importance and nature of the Sun, the stupendous orb on whose rays our very existence depends. Its apparent dimension (which is only half a degree, 32', and would be hidden from sight, like that of the full moon, which is about the 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 the enormous distance that separates us from it. This distance of 149,000,000 kilometers (93,000,000 miles) is sufficiently hard to appreciate. Let us say that 11,640 terrestrial globes would be required to throw a bridge from here to the Sun, while 30 would suffice from the Earth to the Moon. The Moon is 388 times nearer to us than the Sun. We may perhaps conceive of this distance by calculating that a train, moving at constant speed of 1 kilometer (0.6214 mile) a minute, would take 149,000,000 minutes, that is to say 103,472 days, or 283 years, to cross the distance that separates us from this orb. Given the normal duration of life, neither the travelers who set out for the Sun, nor their children, nor their grandchildren, would arrive there: only the seventh generation would reach the goal, and only the fourteenth could bring us back news of it.

Children often cry for the Moon. If one of these inquisitive little beings could stretch out its arms to touch the Sun, and burn its fingers there, 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 of sensation can only be transmitted from the ends of the fingers to the brain at a velocity of 28 meters per second.

'Tis long. A cannon-ball would reach the Sun in ten years. Light, that rapid arrow that flies through space at a velocity of 300,000 kilometers (186,000 miles per second), takes only eight minutes seventeen seconds to traverse this distance.

* * * * *

This brilliant Sun is not only sovereign of the Earth; he is also the head of a vast planetary system.

The orbs that circle round the Sun are opaque bodies, spherical in shape, receiving their light and heat from the central star, on which they 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 Zodiac as described in a preceding chapter, you may be surprised on certain evenings to see the figure of some zodiacal constellation slightly modified by the temporary presence of a brilliant orb perhaps surpassing in its luminosity the finest stars of the first magnitude.

If you watch this apparition for some weeks, and examine its position carefully in regard to the adjacent stars, you will observe that it changes its position more or less slowly in the Heavens. These wandering orbs, or planets, do not shine with intrinsic light; they are illuminated by the Sun.

The planets, in effect, are bodies as opaque as the Earth, traveling round the God of Day at a speed proportional to their distance. They number eight principal orbs, and may be divided into two quite distinct groups by which we may recognize them: the first comprises four planets, of relatively small dimensions in comparison with those of the second group, which are so voluminous that the least important of them is larger 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 of distance:

JUPITER, SATURN, URANUS, AND NEPTUNE

This second group is separated from the first by a vast space occupied by quite a little army of minute planets, tiny cosmic bodies, the largest of which measures little more than 100 kilometers (62 miles) in diameter, and the smallest some few miles only.

The planets which form these three groups represent the principal members of the solar family. But the Sun is a patriarch, and each of his daughters has her own children who, while obeying the paternal influence of the fiery orb, are also obedient to the world that governs them. These secondary asters, or satellites, follow the planets in their course, and revolve round them in an ellipse, just as the others rotate round the Sun. Every one knows the satellite of the Earth, the Moon. All the other planets of our system have their own moons, some being even more favored than ourselves in this respect, and having several. Mars has 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 must appreciate 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, for the planets describe an ellipse) of this system, and controls them. Neptune is thirty times farther from the Sun than the Earth. These disparities of distance produce a vast difference in the periods of the planetary revolutions; for while the Earth revolves round the Sun in a year, Venus in 224 days, and Mercury in 88, Mars takes nearly 2 years to accomplish his journey, Jupiter 12 years, Saturn 29, Uranus 84, and Neptune 165.

Even the planets and their moons do not represent the Sun's complete paternity. There are further, in the solar republic, certain vagabond and irregular orbs that travel at a speed that is often most immoderate, occasionally approaching the Sun, not to be consumed therein, but, as it appears, to draw from its radiant source the provision of forces necessary for their perigrinations through space. These are the Comets, which pursue an extremely elongated orbit round the Sun, to which at times they approximate very closely, at other times being excessively distant.

And now to recapitulate our knowledge of the Solar Empire. In the first place, we see a colossal globe of fire dominating and governing the worlds that belong to him. Around him are grouped planets, in number eight principal, formed of solid and obscure matter, gravitating round the central orb. Other secondary orbs, the satellites, revolve round the planets, which keep them within the sphere of their attraction. And lastly, the comets, irregular celestial bodies, track the whole extent of the great solar province. To these might be added the whirlwinds of meteors, as it were disaggregated comets, which also circle round the Sun, and give origin to shooting stars, when they come into collision with the Earth.

Having now a general idea of our celestial family, and an appreciation of the potent focus that controls it, let us make direct acquaintance with 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 the focus of which burns the immense and dazzling orb. We have appreciated the grandeur and potency of the solar globe, whose rays spread out in active waves that bear a fecundating illumination to the worlds that gravitate round him; we have appreciated the distance that separates the Sun from the Earth, the third of the planets retained within his domain, or at least I trust that the comparisons of the times required by certain moving objects to traverse this distance have enabled us to conceive it.

We said that the four planets nearest to the Sun are Mercury, at a distance of 57 million kilometers (35,000,000 miles); Venus, at 108 million (67,000,000 miles); the Earth, at 149 million (93,000,000 miles); and Mars at 226 million (140,000,000 miles). Let us begin our planetary journey with these four stations.

MERCURY

A little above the Sun one sometimes sees, now in the West, in the lingering shimmer of the twilight, now in the East, when the tender roseate dawn announces the advent of a clear day, a small star of the first magnitude which remains but a very short time above the horizon, and then plunges back into the flaming sun. This is Mercury, the agile and active messenger of Olympus, the god of eloquence, of medicine, of commerce, and of thieves. One only sees him furtively, from time to time, at the periods of his greatest elongations, either after the setting or before the rising of the radiant orb, when he presents the aspect of a somewhat reddish star.

This planet, like the others, shines only by the reflection of the Sun whose illumination he receives, and as he is in close juxtaposition with it, his light is bright enough, though his volume is inconsiderable. He is smaller than the Earth. His revolution round the Sun being accomplished in about three months, he passes rapidly, in a month and a half, from one side to the other of the orb of day, and is alternately a morning and an evening star. The ancients originally regarded it as two separate planets; but with attentive observation, they soon perceived its identity. In our somewhat foggy climates, it can only be discovered once or twice a year, and then only by looking for it according to the indications given in the astronomic almanacs.



Mercury courses round the Sun at a distance of 57,000,000 kilometers (35,000,000 miles), and accomplishes his revolution in 87 days, 23 hours, 15 minutes; i.e., 2 months, 27 days, 23 hours, or a little less than three of our months. If the conditions of life are the same there as here, the existence of the Mercurians must be four times as short as our own. A youth of twenty, awaking to the promise of the life he is just beginning in this world, is an octogenarian in Mercury. There the fair sex would indeed be justified in bewailing the transitory nature of life, and might regret the years that pass too quickly away. Perhaps, however, they are more philosophic than with us.



The orbit of Mercury, which of course is within that of the Earth, is not circular, but elliptical, and very eccentric, so elongated that at certain times of the year this planet is extremely remote from the solar focus, and receives only half as much heat and light as at the opposite period; and, in consequence, his distance from the Earth varies considerably.



This globe exhibits phases, discovered in the seventeenth century by Galileo, which recall those of the Moon. They are due to the motions of the planet round the Sun, and are invisible to the unaided eye, but with even a small instrument, one can follow the gradations and study Mercury under every aspect. Sometimes, again, he passes exactly in front of the Sun, and his disk is projected like a black point upon the luminous surface of the flaming orb. This occurred, notably, on May 10, 1891, and November 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 exception of the cosmic fragments that circulate between the orbit of Mars and that of Jupiter). His volume equals only 5/100 that of the Earth. His diameter, in comparison with that of our planet, is in the ratio of 373 to 1,000 (a little more than 1/3) and measures 4,750 kilometers (2,946 miles). His density is the highest of all the worlds in the great solar family, and exceeds that of our Earth by about 1/3; but weight there is less by almost 1/2.

Mercury is enveloped in a very dense, thick atmosphere, which doubtless sensibly tempers the solar heat, for the Sun exhibits to the Mercurians a luminous disk about seven times more extensive than that with which we are familiar on the Earth, and when Mercury is at perihelion (that is, nearest to the Sun), his inhabitants receive ten times more light and heat than we obtain at midsummer. In all probability, it would be impossible for us to set foot on this planet without being shattered by a sunstroke.

Yet we may well imagine that Nature's fecundity can have engendered beings there of an organization different from our own, adapted to an existence in the proximity of fire. What magnificent landscapes may there be adorned with the luxuriant vegetation that develops rapidly under an ardent and generous sun?



Observations of Mercury are taken under great difficulties, just because of the immediate proximity of the solar furnace; yet some have detected patches that might be seas. In any case, these observations are contradictory and uncertain.

Up to the present it has been impossible to determine the duration of the rotation. Some astronomers even think that the Sun's close proximity must have produced strong tides, that would, as it were, have immobilized the globe of Mercury, just as the Earth has immobilized the Moon, forcing it perpetually to present the same side to the Sun. From the point of view of habitation, this situation would be somewhat peculiar; perpetual day upon the illumined half, perpetual night upon the other hemisphere, and a fairly large zone of twilight between the two. Such a condition would indeed be different from the succession of terrestrial days and nights.

As seen from Mercury, the Earth we inhabit would shine out in the starry sky[9] as a magnificent orb of first magnitude, with the Moon alongside, a faithful little companion. They should form a fine double star, the Earth being a brilliant orb of first magnitude, and the Moon of third, a charming couple, and admired doubtless as an enchanted and privileged abode.

It is at midnight during the oppositions of the Earth with the Sun that our planet is the most beautiful and brilliant, as is Jupiter for ourselves. The constellations are the same, viewed from Mercury or from the Earth.

But is this little solar planet inhabited? We do not yet know. We can only reply: why not?

VENUS

When the sunset atmosphere is crimson with the glorious rays of the King of Orbs, and all Nature assumes the brooding veil of twilight, the most indifferent eyes are often attracted and captivated by the presence of a star that is almost dazzling, and illuminates with its white and limpid light the heavens darkened by the disappearance of the God of Day.

Hail, Venus, Queen of the Heavens! the "Shepherd's Star," gentle mother of the loves, goddess of beauty, eternally adored and cherished, sung and immortalized upon Earth, by poets and artists. Her splendid brilliancy attracted notice from earliest antiquity, and we find her, radiant and charming, in the works of the ancients, who erected altars to her and adorned their poetry with her grace and beauty. Homer calls her Callisto the Beautiful; Cicero names her Vesper, the evening star, and Lucifer, the star of the morning—for it was with this divinity as with 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 the morning star were always in periodic succession, that the identity of the orb was recognized.

Her radiant splendor created her mythological personality, just as the agility of Mercury created that of the messenger of the gods.

We do not see her aerial chariot in the Heavens drawn by a flight of doves with white and fluttering wings, but we follow the lustrous orb led on through space by solar attraction. And in the beautiful evenings when she is at her greatest distance from our Sun, the whole world admires this white and dazzling Venus reigning as sovereign over our twilight[10] for hours after sunset, and in addition to the savants who are practically occupied with astronomy, millions of eyes are raised to this celestial splendor, and for a moment millions of human beings feel some curiosity about the mysteries of the Infinite. The brutalities of daily life would fain petrify our dreams, but thought is not yet stifled 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 the nature of those other worlds, and the place occupied by our own planet in the vast concert of sidereal harmony.



Even through a small telescope, Venus offers remarkable phases.



Fig. 37 gives some notion of the succession of these, and of the planet'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, 8 seconds at a distance of 108 million kilometers (67,000,000 miles), the Earth being at 149 million kilometers (93,000,000 miles). Like Mercury, at certain periods it passes between the Sun and ourselves, and as its illuminated hemisphere is of course turned toward the orb of day, we at those times perceive only a sharp and very luminous crescent. At such periods Venus is entirely, so to say, against the Sun, and presents to us her greatest apparent dimension (Fig. 38). Sometimes, again, like Mercury, she passes immediately in front of the Sun, forming a perfectly round black spot; this happened on December 8, 1874, and December 6, 1882; and will recur on June 7, 2004, and June 5, 2012. These transits have been utilized in celestial geometry in measuring the distance of the Sun.

You will readily divine that the distance of Venus varies considerably according to her position in relation to the Earth: when she is between the Sun and ourselves she is nearest to our world; but it is just at those times that we see least of her surface, because she exhibits to us only a slender crescent. Terrestrial astronomers are accordingly very badly placed for the study of her physical constitution. The best observations can be made when she is situated to right or left of the Sun, and shows us about half her illuminated disk—during the day for choice, because at night there is too much irradiation from her dazzling light.

These phases were discovered by Galileo, in 1610. His observations were among the first that confirmed the veracity of the system of Copernicus, affording an evident example of the movement of the planets round the sun. They are often visible to the unaided eye with good sight, either at dusk, or through light clouds.



Venus, surrounded by a highly dense and rarefied atmosphere, which increases the difficulties of observing her surface, might be called the twin sister of the Earth, so similar are the dimensions of the two worlds. But, strange as it may seem to the many admirers, who are ready to hail in her an abode of joy and happiness, it is most probable that this planet, attractive as she is at a distance, would be a less desirable habitation than our floating island. In fact, the atmosphere of Venus is perpetually covered with cloud, so that the weather there must be always foggy. No definite geographical configuration can be discovered on her, despite the hopes of the eighteenth-century astronomers. We are not even sure that she rotates upon herself, so contradictory are the observations, and so hard is it to distinguish anything clearly upon her surface. A single night of observation suffices to show the rotation of Mars or of Jupiter; but the beautiful Evening Star remains obstinately veiled from our curiosity.

Several astronomers, and not the least considerable, think that the tides produced by the Sun upon her seas, or globe in its state of pristine fluidity, must have been strong enough to seize and fix her, as the Earth did for the Moon, thus obliging her to present always the same face to the Sun. Certain telescopic observations would even seem to confirm this theoretical deduction from the calculations of celestial mechanics.

The author ventures to disagree with this opinion, its apparent probability notwithstanding, because he has invariably received a contrary impression from all his telescopic observations. He has quite recently (spring of 1903) repeated these observations. Choosing a remarkably clear and perfectly calm atmosphere, he examined the splendid planet several times with great attention in the field of the telescope. The right or eastern border (reversed image) was dulled by the atmosphere of Venus; this is the line of separation between day and night. Beneath, at the extreme northern edge, he was attracted on each occasion by a small white patch, a little whiter than the rest of the surface of the planet, surrounded by a light-gray penumbra, giving the exact effect of a polar snow, very analogous to that observed at the poles of Mars. To the author this white spot on the boreal horn of Venus does not appear to be due to an effect of contrast, as has sometimes 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 the disk, indicative of the direction and speed of its rotary movement, although these observations were made, with others, under excellent conditions.—Three o'clock in the afternoon, brilliant sun, sky clear blue, the planet but little removed from the meridian—at which time it is less dazzling than in the evening.

There is merely the impression; but it is so definite as to prevent the author 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 very peculiar world. Eternal day on the one side; eternal night on the other. Maximum light and heat at the center of the hemisphere perpetually turned to the Sun; maximum cold and center of night at the antipodes. This icy hemisphere would possibly be uninhabitable, but the resources of Nature are so prodigious, and the law of Life is so imperious, so persistent, under the most disadvantageous and deplorable terrestrial conditions, that it would be transcending our rights to declare an impossibility of existence, even in this eternal night. The currents of the atmosphere would no doubt suffice to set up perpetual changes of temperature between the two hemispheres, in comparison with which our trade-winds would be the lightest of breezes.

Yes, mystery still reigns upon this adjacent earth, and the most powerful instruments of the observatories of the whole world have been unable to solve it. All we know is that the diameter, surface, volume and mass of this planet, and its weight at the surface, do not differ sensibly from those that characterize our own globe: that this planet is sister to our own, and of the same order, hence probably formed of the same elements. We further know that, as seen from Venus (Fig. 39), the Earth on which we live is a magnificent star, a double orb more brilliant even than when viewed from Mercury. It is a dazzling orb of first magnitude, accompanied by its moon, a star of the second and a half magnitude.

And thus the worlds float on in space, distant symbols of hopes not realized on any one of them, all at different stages of their degree of evolution, representing an ever-growing progress in the sequence of the ages.



When we contemplate this radiant Venus, it is difficult, even if we can not 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 own dwelling-place, travailing with her sisters in the accomplishment of the general plan of Nature.

Such are the characteristic features of our celestial neighbor. In quitting her, we reach the Earth, which comes immediately next her in order of distance, 149 million kilometers (93,000,000 miles) from the Sun, but as we shall devote an entire chapter to our own planet, we will not halt at this point, but cross in one step the distance that separates Mars from Venus.

Let us only remark in passing, that our planet is the largest of the four 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 to that which the Earth takes annually round the same center.

Unfortunate Mars! What evil fairy presided at his birth? From antiquity, all curses seem to have fallen upon him. He is the god of war and of carnage, the protector of armies, the inspirer of hatred among the peoples, it is he who pours out the blood of Humanity in international hecatombs. Here, again, as in the case of Mercury and Venus, the appearance has originated the idea. Mars, in fact, burns like a drop of blood in the depths of the firmament, and it is this ruddy color that inspired its name and attributes, just as the dazzling whiteness 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 the defects inherent in its own terrestrial nature, this world, unwitting of our sorrows, pursued the celestial path marked out for it in space by destiny.

This planet is, as we have said, the first encountered after the Earth. Its orbit is very elongated, very eccentric. Mars accomplishes it in a period of 1 year, 321 days, 22 hours, i.e., 1 year, 10 months, 21 days, or 687 days. The velocity of its transit is 23 kilometers (14.5 miles) 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 an average distance of 76 million kilometers (47,000,000 miles); but as its orbit is equally elliptic and elongated it follows that at certain epochs the two planets approach one another by something less than 60 million kilometers (37,000,000 miles). These are the periods selected for making the best observations upon our neighbor of the ruddy rays. The oppositions of Mars arrive about every twenty-six months, but the periods of its greatest proximity, when this planet approaches to within 56 million kilometers (34,700,000 miles) of the Earth, occur only every fifteen years.

Mars is then passing perihelion, while our world is at aphelion (or greatest distance from the Sun). At such epochs this globe presents to us 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 same magnitude as our satellite viewed with the unaided eye, and an instrument that magnified 630 times would show him ten times larger in diameter.

In dimensions he differs considerably from our world, being almost half the size of the Earth. In diameter he measures only 6,728 kilometers (4,172 miles), and his circumference is 21,125 kilometers (13,000 miles). His surface is only 29/100 of the terrestrial surface, and his volume only 15/100 of our own.

This difference in volume causes Mars to be an earth in miniature. When we study his aspects, his geography, his meteorology, we seem to see in space a reduction of our own abode, with certain dissimilarities that excite our curiosity, and make him even more interesting to us.

The Martian world weighs nine times and a half less than our own. If we represent the weight of the Earth by 1,000, that of Mars would be represented by 105. His density is much less than our own; it is only 7/10 that of the Earth. A man weighing 70 kilograms, transported to the adjacent globe, would weigh only 26 kilograms.

The earliest telescopic observations revealed the existence of more or less accentuated markings upon the surface of Mars. The progress of optics, admitting of greater magnifications, exhibited the form of these patches more clearly, while the study of their motions enabled the astronomers to determine with remarkable precision the diurnal rotation of this planet. It occurs in 24 hours, 37 minutes, 23.65 seconds. Day and night are accordingly a little longer on Mars than on the Earth, but the difference is obviously inconsiderable. The year of Mars consists of 668 Martian days. The inclination of the axis of rotation of this globe upon the plane of its orbit is much the same as our own. In consequence, its seasons are analogous to ours in intensity, while twice the length, the Martian year being almost equal to two of our years. The intensity of the seasons is indeed more accentuated than upon the Earth, since the orbit of Mars is very elongated. But there, as here, are three quite distinct zones: the torrid, the temperate, and the glacial.

By means of the telescope we can follow the variations of the Martian seasons, especially in what concerns the polar snows, which regularly aggregate during the winter, and melt no less regularly during the heat of the summer. These snows are very easily observed, and stand out clearly with dazzling whiteness. The reader can judge of them by the accompanying figure, which sums up the author's observations during one of the recent oppositions of Mars (1900-1901). The size of the polar cap diminished from 4,680 kilometers to 840. The solstice of the Martian summer was on April 11th. The snows were still melting on July 6th. Sometimes they disappear almost entirely during the Martian month that corresponds 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 the polar snows are much less thick.

On the other hand, there are hardly ever clouds on Mars; the Martian atmosphere is almost always limpid, and one can say that fine weather is the chronic state of the planet. At times, light fogs or a little vapor will appear in certain regions, but they are soon dissipated, and the sky clears up again.



Since the invention of the telescope, a considerable number of drawings have been made, depicting Mars under every aspect, and the agreement between these numerous observations gives us a sufficient acquaintance with the planet to admit of our indicating the characteristic features of 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 the general chart drawn from the total sum of observations (Figs. 41, 42 and 43).

It will be seen at the first glance that the geography of Mars is very different from that of our own globe: while three-quarters of the Earth are covered with the liquid element, Mars seems to be more evenly divided, and must indeed have rather more land than water. We find no immense oceans surrounding the continents, and separating them like islands; on the contrary, the seas are reduced to long gulfs compressed between the shores, like the Mediterranean for example, nor is it even certain that these gray spots do all represent true seas. It has been agreed to term sea the parts that are lightly tinged with green, and to give the name of continent to the spots colored yellow. That is the hue of the Martian soil, due either to the soil itself, which would resemble that of the Sahara, or, to take a less arid region, that seen on the line between Marseilles and Nice, in the vicinity of the Esterels; or perhaps to some peculiar vegetation. During ascents in a balloon, 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 the continents of Mars in the best hours for observation.



As to the "seas," it is pretty certain that there must be water, or some kind of liquid, deriving above all from the melting of the polar snows in spring and summer; but it may possibly be in conjunction with some vegetation, aquatic plants, or perhaps vast meadows, which appear to us from here to be the more considerable in proportion as the water that nourishes them has been more abundant.



Mars, like our globe, is surrounded with a protective atmosphere, which retains the rays of the Sun, and must preserve a medium temperature favorable 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 the evaporation of the seas, clouds, winds, rains, wells, rivers and streams, comes about quite differently on Mars; for, as was remarked above, it is rarely that any clouds are observed there. Instead of being vertical, as here, this circulation is horizontal: the water coming from the 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 invisible vapors directed from the equator to the poles. There is never any rain.

We have spoken of canals. One of the great puzzles of the Martian world is incontestably the appearance of straight lines that furrow its surface 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) in length, and more than 100 kilometers (62 miles) in breadth, have much the same hue as the seas on which they open. For a quarter of a century they have been surveyed by the greater number of our observers. But it must be confessed that, even with the best instruments, we only approach Mars at a distance of 60,000 kilometers (37,200 miles), which is still a little far off, and we may be sure that we do not distinguish the true details of the surface.[11] These details at the limits of visibility produce the appearance of canals to our eyes. They may possibly be lines of lakes, or oases. The future will no doubt clear up this mystery for us.



As to the inhabitants of Mars, this world is in a situation as favorable as our Earth for habitation, and it would be difficult to discover any reason for perpetual sterility there. It appears to us, on the contrary, by its rapid and frequent variations of aspect, to be a very living world. Its atmosphere, which is always clear, has not the density of our own, and resembles that of the highest mountains. The conditions of existence there vary from ours, and appear to be more delicate, more ethereal.

There as here, day succeeds to night, spring softens the rigors of winter; the seasons unfold, less disparate than our own, of which we have such frequent reason to complain. The sky is perpetually clear. There are never tempests, hurricanes, nor cyclones, the wind never gets up any force there, on account of the rarity of the atmosphere, and the low intensity of weight.

Differing from ours, this world may well be a more congenial habitation. It is more ancient than the Earth, smaller, less massive. It has run more quickly through the phases of its evolution. Its astral life is more advanced, and its Humanity should be superior to our own, just as our successors a million years hence, for example, will be less coarse and barbarous than we are at present: the law of progress governs all the worlds, and, moreover, the physical constitution of the planet Mars is less dense than our own.

There is no need to despair of entering some day into communication with these unknown beings. The luminous points that have been observed are no signals, but high summits or light clouds illuminated by the rising or setting sun. But the idea of communication with them in the future is no more audacious and no less scientific than the invention of spectral analysis, X-rays, or wireless telegraphy.

We may suppose that the study of astronomy is further advanced in Mars than on the Earth, because humanity itself has advanced further, and because the starry sky is far finer there, far easier to study, owing to the limpidity of its pure, clear atmosphere.

Two small moons (hardly larger than the city of Paris) revolve rapidly round Mars; they are called Phobos and Deimos. The former, at a distance of 6,000 kilometers (3,730 miles) from the surface, accomplishes its revolution rapidly, in seven hours, thirty-nine minutes, and thus makes the entire circle of the Heavens three times a day. The second gravitates at 20,000 kilometers (12,400 miles), and turns round its center of attraction in thirty hours and eighteen minutes. These two satellites 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 admired by the Martians, at certain epochs of the year,—now at night when the Sun has plunged into his fiery bed, now in the morning, a little before the aurora,—is a magnificent star of first magnitude, never far removed from the orb of day, which presents to them the same aspects as does Venus to ourselves. This splendid orb, which has doubtless received the most flattering names from those who contemplate it, this radiant star of a beautiful greenish blue, courses in space accompanied by a little satellite, sparkling like some splendid diamond, after sunset, in the clear sky of Mars. This superb orb is the Earth, and the little star accompanying it is the Moon.



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 hope must have been wafted toward her, more than one broken heart must have permitted its unrealized dreams to wander forth to our planet as to an abode of happiness where all who have suffered in their native world might find a haven. But our planet, alas! is not as perfect as they imagine.

We must not dally upon Mars, but hasten our celestial excursion toward Jupiter.



CHAPTER VI

THE PLANETS

B.—JUPITER, SATURN, URANUS, NEPTUNE.

Before we attack the giant world of our system, we must halt for a few moments upon the minor planets which circulate between the orbit of Mars and that of Jupiter. These minute asters, little worlds, the largest of which measures scarcely more than 100 kilometers (62 miles) in diameter, are fragments of cosmic matter that once belonged to a vast ring, formed at the time when the solar system was only an immense nebula; and which, instead of condensing into a single globe coursing between Mars and Jupiter, split up into a considerable quantity of particles constituting at the present time the curious and highly interesting Republic of the Asteroids.

These lilliputian worlds at first received the names of the more celebrated of the minor mythological divinities—Ceres, Pallas, Juno, Vesta, etc., but as they rapidly increased in number, it was found necessary to call them by modern, terrestrial names, and more than one daughter of Eve, the Egeria of some astronomer, now has her name inscribed in the Heavens. The first minor planet was discovered on the first day of the nineteenth century, January 1, 1801, by Piazzi, astronomer at Palermo. While he was observing the small stars in the constellation of the Bull beneath the clear Sicilian skies, this famous astronomer 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 the observations of the following days left him no doubt as to the nature of the visitor: she was a planet, a wandering star among the constellations, revolving round the Sun. This newcomer was registered under 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 million kilometers (249,000,000 miles). These celestial globules are invisible to the naked eye, but no year passes without new and numerous recruits being added to the already important catalogue of these minute asters by the patient observers of the Heavens. To-day, they are most frequently discovered by the photographic method of following the displacement of the 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 140,920 kilometers (87,400 miles) in breadth; that is to say, eleven times larger than the Earth. He is 442,500 kilometers (274,357 miles) in circumference.

In volume he is equivalent to 1,279 terrestrial globes; hence he is only a million times smaller than the Sun. The previously described planets of our system, Mercury, Venus, the Earth, and Mars combined, would form only an insignificant mass in comparison with this colossus. A hundred and twenty-six Earths joined into one group would present a surface whose extent would still not be quite as vast as the superficies of this titanic world. This immense globe weighs 310 times more than that which we inhabit. Its density is only the quarter of our own; but weight is twice and a half times as great there as here. The constituents of things and beings are thus composed of materials lighter than those upon the Earth; but, as the planet exerts a force of attraction twice and a half times as powerful, they are in reality heavier and weigh more. A graceful maiden weighing fifty kilograms would if transported to Jupiter immediately be included in the imposing society of the "Hundred Kilos."

Jupiter rotates upon himself with prodigious rapidity. He accomplishes his diurnal revolution in less than ten hours! There the day lasts half as long as here, and while we reckoned fifteen days upon our calendar, the Jovian would count thirty-six. As Jupiter's year equals nearly twelve of ours, the almanac of that planet would contain 10,455 days! Obviously, our pretty little pocket calendars would never serve to enumerate all the dates in this vast world.

This splendid globe courses in space at a distance of 775,000,000 kilometers (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 five times vaster than our own. At that distance the Sun subtends a diameter five times smaller than that which we see, and its surface is twenty-seven times less extensive; accordingly this planetary abode receives on an average twenty-seven times less light and heat than we obtain.

In the telescope Jupiter presents an aspect analogous to that likely to be exhibited by a world covered with clouds, and enveloped in dense vapors (Fig. 45).

It is, in fact, the seat of formidable perturbations, of strange revolutions by which it is perpetually convulsed, for although of more ancient formation than the Earth, this celestial giant has not yet arrived at the stable condition of our dwelling-place. Owing to its considerable volume, this globe has probably preserved its original heat, 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.



Since its orbital revolution occupies nearly twelve years, Jupiter comes 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 these periods it is located at the extremity of a straight line which, passing by the Earth, is prolonged to the Sun. These are the epochs to be selected for observation. It shines then, all night, like some dazzling star of the first magnitude, of excessive whiteness: nor can it be confounded either with Venus, more luminous still (for she is never visible at midnight, in the full South, but is South-west in the evening, or South-east in the morning), nor with Mars, whose fires are ruddy.

In the telescope, the immense planet presents a superb disk that an enlargement of forty times shows us to be the same size to all appearance as that of the Moon seen with the unaided eye. Its shape is not 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 of her orbit, and that it is this inclination that produces the seasons. Now it is not the same for Jupiter. His axis of rotation remains almost vertical throughout the course of his year, and results in the complete absence of climates and seasons. There is neither glacial zone, nor tropic zone; the position of Jupiter is eternally that of the Earth at the season of the equinox, and the vast world enjoys, as it were, perpetual spring. It knows neither the hoar-frost nor the snows of winter. The heat received from the Sun diminishes gradually from the equator to the poles without abrupt transitions, and the duration of day and night is equal there throughout the entire year, under every latitude. A privileged world, indeed!

It is surrounded by a very dense, thick atmosphere, which undergoes more extensive variations than could be produced by the Sun at such a distance. Spectral analysis detects a large amount of water-vapor, showing that this planet still possesses a very considerable quantity of intrinsic heat.

Most conspicuous upon this globe are the larger or smaller bands or markings (gray and white, sometimes tinted yellow, or of a maroon or chocolate hue) by which its surface is streaked, particularly in the vicinity of the equator. These different belts vary, and are constantly modified, either in form or color. Sometimes, they are irregular, and cut up; at others they are interspersed with more or less brilliant patches. These patches are not affixed to the surface of the globe, like the seas and continents of the Earth; nor do they circulate round the planet like the satellites, in more or less elongated and regular revolutions, but are relatively mobile, like our clouds in the atmosphere, while observation of their motion does not give the exact period of the rotation of Jupiter. Some only appear upon the agitated disk to vanish very quickly; others subsist for a considerable period.

One has been observed for over a quarter of a century, and appears to be almost immobile upon this colossal globe. This spot, which was red at its first appearance, is now pale and ghostly. It is oval (vide Fig. 45) and measures 42,000 kilometers (26,040 miles) in length by 15,000 kilometers (9,300 miles) in width. Hence it is about four times as long as the diameter of our Earth; that is, relatively to the size of Jupiter, as are the dimensions of Australia in proportion to our globe. The discussion of a larger number of observations leads us to see in it a sort of continent in the making, a scoria recently ejected from the mobile and still liquid and heated surface of the giant Jupiter. The patch, however, oscillates perceptibly, and appears to be a floating island.

We must add that this vast world, like the Sun, does not rotate all in one period. Eight different currents can be perceived upon its surface. The most rapid is that of the equatorial zone, which accomplishes its revolution in 9 hours, 50 minutes, 29 seconds. A point situated on the equator is therefore carried forward at a speed of 12,500 meters (7 miles) per second, and it is this giddy velocity of Jupiter that has produced the flattening of the poles. From the equator to the poles, the swiftness of the currents diminishes irregularly, and the difference amounts to about five minutes between the movement of the equatorial stream, and that of the northern and southern currents. But what is more curious still is that the velocity of one and the same stream is subject to certain fluctuations; thus, in the last quarter of a century, the speed of the equatorial current has progressively diminished. In 1879, the velocity was 9 hours, 49 minutes, 59 seconds, and now it is, as we have already seen, 9 hours, 50 minutes, 29 seconds, which represents a substantial reduction. The rotation of the red patch, at 25 degrees of the southern latitude, is effected in 9 hours, 55 minutes, 40 seconds.

We are confronted with a strange and mysterious world. It is the world of the future.

This giant gravitates in space accompanied by a suite of five satellites. 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 same time, on the same evenings (January 7 and 8, 1610), by the two astronomers who were pointing their telescopes at Jupiter: Galileo in Italy, 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 near the enormous planet. It has so far received no name, and is known as the fifth, although the four principal are numbered in the order of their distances.



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, this fine planet illuminated the troop of worlds that derived their treasure of vitality from him with his intrinsic light: to-day, however, these moons in their turn shed upon the extinct central globe the pale soft light which they receive from our solar focus, illuminating the brief Jovian nights (which last less than five hours, on account of the twilight) 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 a dazzling spectacle, what a fairy scene must the enormous star afford to the inhabitants of that tiny world! And what a shabby figure must our Earth and Moon present in the face of such a body, a real miniature of the great solar system!

Our ancestors were well inspired when they attributed the sovereignty of Olympus to this majestic planet. His brilliancy corresponds with his real grandeur. His dominion in the midnight Heavens is unique. Here again, as for Venus, Mars, and Mercury, astronomy has created the legend of the fables of mythology.

Let us repeat in conclusion that our Earth becomes practically invisible for 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 left the Sun, in order to reach the immense orb of Jupiter, which courses in space at 626 million kilometers (388,000,000 miles) from the terrestrial orbit. From Jupiter we had to traverse a distance of 646 million kilometers (400,000,000 miles) in order to reach the marvelous system of Saturn, where our eyes and thoughts must next alight.

Son of Uranus and Vesta, Saturn was the God of Time and Fate. He is generally represented as an aged man bearing a scythe. His mythological character is only the expression of his celestial aspect, as we have seen for the brilliant Jupiter, for the pale Venus, the ruddy Mars, and the agile Mercury. The revolution of Saturn is the slowest of any among the planets known to the ancients. It takes almost thirty years for its accomplishment, and at that distance the Saturnian world, though it still 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 of Time, with slow and almost funereal gait.

Poor Saturn won no favor with the poets and astrologers. He bore the horrid reputation of being the inexhaustible source of misfortune and evil fates,—whereof he is wholly innocent, troubling himself not at all with our world nor its inhabitants.

This world travels in the vastness of the Heavens at a distance of 1,421 million kilometers (881,000,000 miles) from the Sun. Hence it is ten times farther from the orb of day than the Earth, though still illuminated and governed by the Sun-God. Its gigantic orbit is ten times larger than our own.

Its revolution round the Sun is accomplished in 10,759 days, i.e., 29 years, 167 days, and as this strange planet rotates upon itself with great rapidity in 10 hours, 15 minutes, its year comprises no less than 25,217 days. What a calendar! The Saturnians must needs have a prodigious memory not to get hopelessly involved in this interminable number of days. A curious world, where each year stands for almost thirty of our own, and where the day is more than half as short again as ours. But we shall presently find other and more extraordinary differences on this planet.

In the first place it is nearly nine and a half times larger than our world. It is a globe, not spherical, but spheroidal, and the flattening of its poles, which is one-tenth, exceeds that of all the other planets, even Jupiter. It follows that its equatorial diameter is 112,500 kilometers (69,750 miles), while its polar diameter measures only 110,000 kilometers (68,200).

In volume, Saturn is 719 times larger than the Earth, but its density is only 128/1000 of our own; i.e., the materials of which it is composed are much less heavy, so that it weighs only 92 times more than our Earth. Its surface is 85 times vaster than that of the Earth, no insignificant proportion.



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 ours in relative intensity. Only upon this far-off world each season lasts for seven years. At the distance at which it gravitates in space, the heat and light which it receives from the Sun are 90 times less active than such as reach our selves; but it apparently possesses an atmosphere of great density, which may be constituted so that the heat is preserved, and the planet maintained in a calorific condition but little inferior to our own.

In the telescope, the disk of Saturn exhibits large belts that recall those of Jupiter, though they are broader and less accentuated (Fig. 47). There are doubtless zones of clouds or rapid currents circulating in the atmosphere. Spots are also visible whose displacement assists in calculating 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, and entirely envelops the body of the planet. It is suspended in the Saturnian sky, like a gigantic triumphal arch, at a height of some 20,000 kilometers (12,400 miles) above the equator. This splendid arch is circular, like an immense crown illuminated by the Sun. From here we only see it obliquely, and it appears to us elliptical; a part of the ring seems to pass in front of Saturn, and its shadow is visible on the planet, while the opposite part passes behind.

This ring, which measures 284,000 kilometers (176,080 miles) in diameter, and less than 100 kilometers (62 miles) in breadth, is divided into three distinct zones: the exterior is less luminous than the center, which is always brighter than the planet itself; the interior is very 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 the planet with a luminous halo? They are composed of an innumerable number of particles, of a quantity of cosmic fragments, which are swept off in a rapid revolution, and gravitate round the planet at variable speed and distance. The nearer particles must accomplish their revolution in 5 hours, 50 minutes, and the most distant in about 12 hours, 5 minutes, to prevent them from being merged in the surface of Saturn: their own centrifugal force sustains them in space.



With a good glass the effect of these rings is most striking, and one can not refrain from emotion on contemplating this marvel, whereby one of the brothers of our terrestrial country is crowned with a golden diadem. Its aspects vary with its perspective relative to the Earth, as may be seen from the subjoined figure (Fig. 48).

We must not quit the Saturnian province without mentioning the eight satellites 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 of months for the inhabitants of Saturn; eight moons with constantly varying phases juggling above the rings!

Now we shall cross at a bound the 1,400 million kilometers (868,000,000 miles) that separate us from the last station but one of the immense solar system.

URANUS

On March 13, 1781, William Herschel, a Hanoverian astronomer who had emigrated to England, having abandoned the study of music to devote himself to the sublime science of the Heavens, was observing the vast fields with their constellations of golden stars, when he perceived a luminous point that appeared to him to exceed that of the other celestial luminaries in diameter. He replaced the magnification of his telescope by more powerful eye-pieces, and found that the apparent diameter of the orb increased proportionately with the amplification of the power, which does not happen in the case of stars at infinite distance. His observations on the following evenings enabled him to note the slow and imperceptible movement of this star upon the celestial sphere, and left him in no further doubt: there was no star, but some much nearer orb, in all probability a comet, for the great astronomer dared not predict the discovery of a new planet. And it was thus, under the name of cometary orb, that the seventh child of the Sun was announced. The astronomers sought to determine the motions of the new arrival, to discover for it an elliptical orbit such as most comets have. But their efforts were vain, and after several months' study the conclusion was reached that here was a new planet, throwing back the limits of the solar system to a point far beyond that of the Saturnian frontier, as admitted from antiquity.

This new world received the name of Uranus, father of Saturn, his nearest neighbor in the solar empire. Uranus shines in the firmament as a small star of sixth magnitude, invisible to the unaided eye for normal sight, at a distance of 2,831,000,000 kilometers (1,755,000,000 miles) from the Sun. Smaller than Jupiter and Saturn, this planet is yet larger than Mercury, Venus, Mars, and the Earth together, thus presenting 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 terrestrial diameter. Sixty-nine times more voluminous than the Earth, and seventeen times more extensive in surface, this new world is much less than our own in density. The matter of which it is composed is nearly five times lighter than that of our globe.

Spectral analysis shows that this distant planet is surrounded with an atmosphere very different from that which we breathe, enclosing gases that do not exist in ours.

The Uranian globe courses over the fields of infinity in a vast orbit seventeen times larger than our own, and its revolution lasts 36,688 days, i.e., 84 years, 8 days. It travels slowly and sadly under the pale and languishing rays of the Sun, which sends it nearly three hundred times less of light and heat than we receive. At this distance the solar disk would present a diameter seventeen times smaller than that which we admire, and a surface three hundred times less vast. A dull world indeed! And what an interminable year! The idle people who are in the habit of being bored must find time even longer upon Uranus than upon our little Earth, where the days pass so rapidly. And if matters are arranged there as here, a babe of a year old, beginning to babble in its nurse's arms, would already have lived as long as an old man of eighty-four in this world.