Mars, age of, 89. atmosphere of, 86, 115, 117. bands of life on, 104. canals on, 90. described by Schiaparelli, 93. gemination of, 91, 105. have builders of, disappeared? 107. and irrigation, 101. and lines of vegetation, 102. and seasonal changes, 99. and water circulation, 100. carbon dioxide on, 118. circular spots or "oases" on, 103. colors of, 89. dimensions of, 86. distance of, 85, 86. enigmatical lights on, 111. gravity on, 86. inclination of axis, 86. length of year, 86. Lowell's theory of, 101. light and heat on, 85. moonlight on, 128. orbit of, 85. polar caps of, 87, 118. possible size of inhabitants, 106. satellites of, 90, 124, 126. seasons on, 87. supposed signals from, 110, 112. temperature of, 120, 122. water vapor on, 117. Mercury, atmosphere of, 21, 28, 43, 44. day and night on, 34, 38, 40. dimensions, 18. earth seen from, 41. habitability of, 33, 40, 44. heavens seen from, 41, 42. heat and light on, 25, 28. holds place of honor, 19. length of year, 24. mass of, 19. moon visible from, 41. resemblances to moon, 43. rotation of, 30. shape of orbit, 23. sun as seen from, 37. velocity in orbit, 23. Venus seen from, 41. virtual fall toward sun, 24. visibility of, 21. water on, 43. Moon, the area of surface, 219. atmosphere of, 7, 215, 231, 247, 248. clouds on, 6, 245. constitution of, 236. craters, 221. day and night on, 254. distance of, 212, 215. density of, 219. former cataclysm on, 237. former life on, 241, 243. giantism on, 228, 229. gravity on, 219, 228, 229. libration of, 249. meteorites and, 230. mountains on, 220. the older world in, 242. origin of, 235. phases and motions of, 250. rotation of, 249. seas of, 234. size of, 218. snow on, 246. speculation about, 212. temperature of, 255. vegetation on, 6, 244, 247. visibility of features of, 213. Nasmyth and Carpenter on lunar craters, 224. Neptune, description of, 208-210. Newcomb, Simon, on Olbers's theory, 141. Newton, lunar crater, 222. Olbers's theory of planetary explosion, 138. on Vesta's light, 138. Pallas, an asteroid, 129. Perrotin sees canals on Mars, 92. Phobos, satellite of Mars, 125. Pickering, E.C., discovers ninth moon of Saturn, 195. finds Eros on Harvard plates, 133. on shape of Eros, 136. on light of Eros, 137. Pickering, W.H., on lunar atmosphere, 247. observes changes in moon, 244. sees Mars's canals, 92. theory of Tycho's rays, 246. on Venus's atmosphere, 54. Planets, classification of, 15. how to find, 256, 273. resemblances among, 12. Plato, lunar ring plain, 225. Plurality of worlds in literature, 2. subject ignored, 8. Proctor, R.A., on Jupiter's moons, 180. on other worlds, 8. Roche's limit, 201. Rosse, Lord, on temperature of moon, 255.