To one unconvinced of the existence of some signs of intelligent activity in Mars the suggestions that have been made to account for certain appearances in the planet will seem absurd. If, on the other hand, he finds himself in agreement with those who believe the markings are the result of intelligent effort, then he is justified in using the various artificial markings of the surface of the Earth as standards of comparison in explaining the many curious markings of Mars. Indeed, he is compelled to do so, just as would be demanded of him if he should stand on some high mountain peak in some hitherto unexplored region of Africa and should minutely scan the hazy stretch of plains below. Large white spots in equatorial regions which could not possibly be snow-covered hills, might be masses of white flowers or cloth-covered areas for the better cultivation of certain plants. Lines that dimly stretched across the surface might be rivers, cañons, rifts, or bands of irrigation, according to their character. As we compare the circular markings on the Moon with our terrestrial craters and fissures, and cracks on its surface with similar fissures on the Earth, so we are forced to compare the markings on the surface of Mars with what seems analogous to them on the surface of our own Earth. Once proved that the markings of Mars are due to erosion, cracks, encircling meteors big enough to raise ridges by their attractive force, then all that has been written in demonstration of their artificial character goes for naught. The intelligent reader unprejudiced in the matter will, however, judge for himself the merits of our contention and will determine the reasonableness of the comparisons that have been made by Lowell in solving the mystery of Mars. INDEX Algebraic formulæ, 73. American astronomers, Holden, Pickering, Young, Swift, Comstock, Barnard, Wilson, drew the more conspicuous canals, 65. Ancient irrigation, 115. Ants surviving at high altitudes, 157; unique intelligence, 156. Astronomer's chief work, 74; conservatism, 75. Astronomers who have seen the canals, 83. Astronomical subjects remote from Martian studies, 72. Atmosphere and moisture, Barnard and others, 134, 135; Sir Robert Ball, 137. Austria's care of water, 117. Ball, Sir Robert, difficulties of observation, 84; life on Mars quite likely, 68, 69; objection to Mars being inhabited, 121. Barbour, W. D., with a four inch achromatic, 88. Barnard's, Dr., description of dark regions, 43. Bees, wasps, and ants, 156. _Canali_ supposed to mean canals, 39. Canals appear double, 41; artificiality of, 42; as distinct as engraved lines, 59; chain of reasoning in regard to, 47; double, 41; of Mars, 40; unchangeable in position, 42. Cassini, 33. Chandler's oscillation of pole, 126. Checkerboard appearance of West, 48. Clerke's, Agnes M., expressions, 55.