Page:Popular Science Monthly Volume 4.djvu/204

 to those of the solar spectrum, and this proves that the atmosphere of Mars is analogous to that of earth. But what is that atmospheric matter which produces these significant lines? From an examination of their positions, we find that they are not owing to the presence of oxygen, nitrogen, or carbonic acid, but to watery vapor. Therefore, there is water-vapor in the atmosphere of Mars, as in that of the earth. The green spots on its globe are seas—expanses of water resembling our seas. The clouds are made up of minute vesicles of water, like our own mists; and the snows consist of water solidified by cold. Furthermore, this water, as revealed by the spectroscope, being of the same chemical composition as terrestrial waters, we know that Mars possesses oxygen and hydrogen.

These important data enable us to form an idea of Martial meteorology, and to recognize therein a reproduction of the meteorological phenomena of our own planet. On Mars, as on earth, the sun is the supreme agent of motion and of life. Heat vaporizes the water of the seas, causing it to ascend into the atmosphere. This vapor assumes visible shape by the same processes which produce clouds here, i.e., by differences of temperature and of saturation. Winds arise in virtue of these same differences of temperature. We can observe the clouds on Mars as they are swept along by air-currents over the seas and continents, and several observers have, so to speak, photographed these meteoric variations.

If we are as yet unable precisely to see the rain falling on the plains of Mars, we can at least tell when it is falling, for we can see the clouds dispersing and gathering again. Thus there is on Mars, just as on earth, an atmospheric circulation, and the drop of water which the sun takes from the sea returns thither after it has fallen from the cloud which concealed it. And, although we must sternly resist any tendency to fashion imaginary worlds after the pattern of our own, still Mars presents to us, as in a mirror, such an organic likeness to earth, that it is hard for us not to carry our description a little further.

Thus, then, we behold, in space, millions of miles away, a planet very much like our own, and where all the elements of life exist, as they do here—water, air, heat, light, winds, clouds, rain, streams, valleys, mountains. To complete the resemblance, the seasons there are very much the same as here, the axis of rotation of Mars having an inclination of 27°, while that of the earth is 23°. The Martial day is forty minutes longer than the terrestrial.

In the face of all these facts, can we be content with the conclusions we have so far reached without going further, and considering ulterior consequences? If the same physico-chemical conditions are present on Mars as on earth, why should they not produce the same effects there as here? On earth the smallest drop of water is peopled with myriads of animalcules, and earth and sea are filled with