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.] INDEX _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. Air-waves, 250, 251, 273. Albedo, low, 162, 167. Algæ, 349. _Amenthes_, hibernation of, 317-324. Animalcula, in almost boiling geysers, 349. _Aonium Sinus_, two doubles suspected in, 242. _Aquae Calidae_, 208, 253, 315. Archæan age of the earth, 132, 133, 138. Areography, 20-31; beginning and progress of, 109; three periods in, 24. Arizona, 16; in desert belt, 13; plateau of, 18. _Arnon_, convergent double, 240. 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. Autumn, length of Martian, in northern hemisphere, 35, 48; in southern, 35, 48. Axial tilt, 34, 36, 55, 155, 161; determinations of, 34, 36, 155; determines character of seasons, 34, 36; effect of, on presentation of arctic and antarctic regions, 70; effect of, on temperature of arctic and temperate regions, 88. Bacteria, plasm-eating beings, 353. Barometric pressure, 63, 85. Beer, 23, 26, 109. Bilateralism, 208; inherent attribute of canals, 209. Blue band, surrounding polar caps, 39, 40, 42, 43, 56, 61, 63, 71, 161, 162, 168, 338, 339. Blue-green areas (see Dark Regions), 32, 67, 163; taken for seas, 110. British Nautical Almanac, 35. _Brontes_, development of, 304-312. Cambrian era of Earth, 139.