One of the things that makes Mars of such transcendent interest to man is the foresight it affords of the course earthly evolution is to pursue. On our own world we are able only to study our present and our past; in Mars we are able to glimpse, in some sort, our future. Different as the course of life on the two planets undoubtedly has been, the one helps, however imperfectly, to better understanding of the other.
Another, more abstract but no less alluring, appeals to that desire innate in man to know about the cosmos of which he forms a part and which we call by the name of science. Study of Mars responds to this craving both directly by revelation of the secrets of another world and indirectly by the bearing of what we thus learn upon our understanding of the laws of the universe. For the facts thus acquired broaden our conceptions in every branch of science. Some day our own geology, meteorology, and the rest will stand indebted to study of the planet Mars for advance along their respective lines. Already the most alert of those professing them are lending ear to information from this source, and such cosmopolitanism can but increase as the years roll on. Today what we already know is helping to comprehension of another world; in a not distant future we shall be repaid with interest, and what that other world shall have taught us will redound to a better knowledge of our own, and of that cosmos of which the two form part.
[Illustration: _Lowell Observatory._ MARS 1905.]
_Adamas_, unmistakable double in 1903, 214.
_Aeria_, white in, 76; ruddy color of, 148.
Air (see Atmosphere), 86; necessity of, to life, 166, 167; as important to astronomical calculations, 7.
Animalcula, in almost boiling geysers, 349.
_Aonium Sinus_, two doubles suspected in, 242.
Areography, 20-31; beginning and progress of, 109; three periods in, 24.
Arizona, 16; in desert belt, 13; plateau of, 18.
Artificiality, of canal system, 366, 368, 369, 370, 374; of oases, 366, 371.
_Ascraeus Lucus_, 331; embraced by the double Gigas, 257.
_Astaboras_, connection with Lucus Ismenius, 260-263.
Atmosphere, of Mars, 62, 63, 71, 78, 79, 87; shown to exist, 80, 82, 83, 84, 163, 167; rare, 85, 86, 162, 167; effect on temperature, 80; constituents of, 162, 164, 166, 168.