WHEN, sixteen years ago, I published the last edition of my work—“The Plurality of Inhabited Worlds”—I did not expect to see the speedy confirmation that the progress of astronomy was to give to my essay, by allowing us, so to speak, to put our finger on the manifestations of planetary life. On one hand, those samples of other worlds—the aerolites—have brought us, in their composition, certain elements which play a very extensive role in life—such as oxygen, hydrogen, chloride of sodium, and carbon. The aero- lite which fell at Orgueil (Tarn-et-Garonne) in 1864, brought | us coaly matter—carburets that are due, like peat, to vegetable remains; the one which fell at Lance (Loir-et-Cher), in 1872, brought us salt. They had already brought us water in the form of hydrated oxide of iron. The worlds whence these fragments come, do not differ, then, essentially from our own. On another hand, by means of spectrum analysis, there lias been discovered in the atmospheres of the planets, watery vapor identical with that which produces our fogs, our clouds, and our rains. But of all the studies made during these later years, the telescopic exami-l nation of the planet Mars offers us the most immediate confirmation of the existence of life beyond our globe. This | neighboring world, indeed, presents analogies of the greatest similarity with our own. By its situation, we are per- j mitted to observe its surface under the best of conditinn* for study, and the telescope detects configurations which denote j the closest relationship of this globe with the one we in- ! habit. It was through the continued and persevering study of ! the movements of Mars that Kepler discovered the laws | which govern the system of the universe. To me, it seems certain that it is through a study of this same planet that the theory will be confirmed which will prove the philosophic crowning of astronomy—that of the plurality of worlds. By this double service Mars will have merited the esteem of thinking humanity, and will, perhaps, be able to have those follies and cruelties pardoned with which the god of war has so long inspired the poor unreasonable genus Jwmo which people our earth. Led by a persistent desire to find in practical astronomy itself a direct demonstration of this great truth of the plurality of worlds, I have specially occupied myself with observations of the planet Mars. I have studied it very particularly at those periods when it passed in close proximity with the e-irtb, in 1800, 1871, 1873, 1875, and 1877. On comparing one with another, of the observations made by different astronomers, I have succeeded in collecting tog-ether, in this respect, numerous and decisive documents. The results of these observations and discussions are satisfactory for the solution of the curious problem as to the state of life on the surface of the planets. I propose to bring them together here in a special study of the world of Mars, and I hope that they will interest all those whose thoughts sometimes love to quit the material interests of earth to soar toward the mysteries of the unknown—toward those silent worlds suspended, like our own, in space, and which seem like so many interrogation points placed in the heavens to excite our curiosity and sympathy. Our readers are aware that the planet Mars comes next after our own in the order of distance from, the sun. Our orbit is traced at 95,000,000 of miles from the sun, and that of Mars at 145,000,000. When the two planets are both on the same side of the sun, the difference that separates them is then only 50,000,000 miles; and this may even decrease to 35,000,000, because neither Mars nor the earth moves in a circular orbit, so that their distances from the sun increase or diminish according to epochs. In order that the observation of Mars may give good results, two conditions are requisite, besides that of its relative proximity at the time of its opposition: the atmosphere of the earth must be pure at the place of observation, and the atmosphere of Mars must not be cloudy. In other words, it must be while the inhabitants of the fatter planet are enjoying fine weather. In fact, Mars is surrounded, like our globe, with an aerial atmosphere which, from time to time, becomes covered with clouds just as our own does. Now, these clouds, in stretching out above the continents and seas, form a white veil which hides them from us totally or partially. The study of the surface of Mars in this case is difficult or even impossible. It would be as useless to attempt to distinguish this surface when it is cloudy weather on Mars, as it would be to try to distinguish the villages, rivers, roads, and railroads of our country from a balloon while sailing above an opaque stratum of clouds. From this it will be seen that the observation of this planet is not so easy as one might at first sight suppose. Moreover, the purest and most transparent terrestrial atmosphere is usually traversed by cold or warm currents of air, flowing in different directions above our heads; so that often, during the calmest night, it is almost impossible to succeed in making a passable di aw- ing of a planet like Mars, the image seen in the reflector being wavy, tremulous, and confused. In spite of these trou- blesome conditions the planet Mars is the best known of all. The moon alone, on account of her proximity, the constant transparency of her rare atmosphere, and the absence of clouds, has been the object of a moie assiduous and more particular study, so that her geogiaphy is to-day completely determined. But after the moon, Mars is the best known of all the stars. No planet can be compared with it in this respect. Jupiter, the largest, and Saturn, the most curious (both more important than Mars and more easy of observation in their entirety, on account of their dimensions), are enveloped in an atmosphere constantly loaded with clouds, so that we never see their surface. Uranus and Neptune are only brilliant points. Mercury is almost always eclipsed, like courtiers, in the radiance of the sun. Venus, Venus alone, might be compared to Mars; she is as large as the earth, and consequently twice the diameter of Mars. She is nearer us, and may even come within 25,000,000 miles of us. But she has one fault—that of gravitating between us and the sun, so that, at her nearest proximity, her lighter hemisphere being naturally always on the side toward the sun, we see only her dark hemisphere bordered with a narrow crescent (or, more correctly speaking, we do not see her). The result is that her surface is more -difficult of observation than that of Mars. So she is in this i cspect excelled by the latter, which, of all the sun's family, is the individual whose acquaintance we shall form most quickly. We have already been able to study and map the geography of Mars. The most striking thing on a first examination of the general appearance of this planet, is that its poles are, like those of the earth, marked by two white zones—two caps of snow. Both the north and south poles are at times so brilliant even that they seem to extend beyond the edge of the planet, in consequence of that well known effect of irradiation which makes a white circle appear larger to us than a black one of the same size. The ice varies in extent; it becomes heaped up and extends around the poles during winter, while it melts and retreats during summer. Its en- tire mass occupies a greater superficial area than our polar ice does, and sometimes extends down as far as 45° of latitude, that is, to regions which would correspond to the situation of France on the earth. This polar snow is seen to form a well marked circle on the figure which accompanies this article, and which is reproduced from one of my telescopic drawings made on the 29th of June, 1873. On this day the planet was exhibiting a beginning of phase. At first sight the planet seems to bear some analogy to our own, as regards the division of its climates into frigid, temperate, and torrid zones. An examination of its topography shows us, on the contrary, quite a characteristic dissimilarity between the configuration of this globe and that of our own. In fact, upon the earth there are more seas than lands; three-fourths of our globe are covered with water. It is not the same with the surface of Mars, notwithstanding that attempts have often been made to apply such comparisons to its continental and oceanic divisions. Water does not cover three-fourths of this planet; for there is almost as much land as sea, and the seas are mediterranean. Moreover, several narrow seas, true channels, afford communication between the different latitudes. The continents of Mars are of a yellowish-red shade of color, and its seas present themselves to our eyes under the appearance of grayish-green blotches, | their color still more heightened by the effect of contrast with the reddish color of the continents. It is this prevailing color of the land which gives the planet that ruddy light by which it is at all times distinguished from the other planets and from the fixed stars. The color of the water on Mars appears, then, to be the same as that of terrestrial water. As for the land, why is it red? It was at first supposed that this tint might possibly be due to the atmosphere of the “ warrior planet.” It in no wise follows that because the air of our own world is blue, that of other planets should be of the same color. It mf ght be possible to suppose, then, that the atmosphere of Mars was red; and the poets of the planet would, therefore, extol this glowing shade. Instead of diamonds sparkling in an azure vault, the stars there would be golden fires blazing in scarlet; the white clouds would be suspended in a red heaven, and the splendors of the setting of centupled suns would produce effects no less remarkable than those that we admire upon our sublunary globe. But there is nothing of this. The color of Mars is not due to its atmosphere; for, although this veil extends over the whole planet, neither its seas nor its polar snows come under the influence of this coloration; and Arago, by proving that the limb of the planet is less colored than the center of the disk, has shown that this coloration is not due to the atmosphere, for if it were, the rays reflected from the edges of the planet in order to reach us, having more air to pass through than those that come to us from the center, would be, on the contrary, more deeply colored than the latter. (Jan it be that this characteristic color of Mars, so visible to the naked eye, and which is undoubtedly the cause of the warlike personification with which the ancients invested the planet, is due to the color of the grass and other vegetation which must cover its plains? Can there be red meadows and red forests up there? Can it be that trees with ruddy foliage offer a substitute there for our quiet and delightfully shaded woods; and are our scarlet poppies typical of the botany of Mars? It may be remarked, in fact, that an observer situated on the moon, or even on Venus, would see our continents strangely tinged with a greenish shade. But in autumn he would see this shade disappear in those latitudes where the trees lose their foliage, and afterward would see snow covering the country for entire months. On Mars, the red color is constant, and we remark it in all latitudes, during their winter as well as their summer. It varies only according to the transparency of its atmosphere and of our own. That is no obstacle, however, to the fact of the vegetation of..Mars being the principal cause of this general tint. The ground cannot be everywhere bare like the sands of Sahara. It is probably covered with vegetation of some kind or other; and, as it is not th«e depths of the soil, but its surface, that we see, it must be that the surface-covering— the vegetation, whatever it is—has red for its predominant color, since all the land of Mars offers this same curious aspect. We speak of the vegetation of Mars, we speak of its polar snows, we speak of its seas, of its atmosphere, and of its clouds, as if we had seen them. Are we authorized to create all these analogies? In reality, we see only red, green, and white blotches on the little disk of this planet. Is the red indeed terra firma, is the green really water, and is the white indeed snow? In a word, is this truly a world like our own? ? Yes! Now we are able to assert it. The appearance of, Mars varies constantly. White spots move about over its disk, too often modifying its apparent configuration. These. spots can be nothing but clouds. The white spots at its poles increase or diminish according to the seasons, exactly like our terrestrial circumpolar ice-fields which would offer precisely the same aspect, the same variations, to an observer placed on Venus. Then these white polar spots of Mars are like our frozen water. Each hemisphere of Mars is more difficult of observation during its winter than during its summer, being often covered with clouds over its greater portion. This is also precisely what would happen to an observer from Venus, with respect to our earth; every one knows that the sky is oftener overcast in winter than in | summer, and there are entire weeks during which fogs or clouds prevent us from seeing the heavens.