Life upon the planets, 157. Light curves, 205. Light, nature of, 75. Light year, 190. Limits of eclipses, 68. Longitude, 56. determination of, 58. Lunation, 60. Magnifying power of telescope, 79. Magnitude, stellar, 9, 186. Mars, atmosphere, temperature, 150. canals, 154. orbit, 30. polar caps, 152. rotation, 151. satellites, 155. surface markings, 150. Mass, determination of, 37. of comets, 164. of double stars, 200. of moon, 94. of planets, 40, 133. Measurements, accurate, 1. Mercury, 149. motion of its perihelion, 43. orbit of, 30. Meridian, 19, 21. Meteors, nature of, 165, 169. number of, 167. velocity, 170. Meteors and comets, relation of, 175. Meteor showers, radiant, 171. Leonids, capture of, 172, 173. perturbations, 174. Milky Way, 219. Mira, ο Ceti, 204. Mirrors, 77. Month, 60. Moon, 91. albedo, 97. atmosphere, 103. changes in, 108. density, surface gravity, 95. development of, 241. harvest moon, 93. influence upon the earth, 109, 233. librations, 98. map of, 101. mass and size, 94. motion, 24, 92. mountains and craters, 104. phases, 91, 92. physical condition, 100, 107. Month, 60. Morning star, 31. Motion in line of sight, 89, 193. Multiple stars, 202. Names of stars, 8. Nebulæ, 214. density, 217. development of, 245. motion, 218. spectra, 216. types and classes of, 215. Nebular hypothesis, 230. objections to, 231. Neptune, 146. discovery of, 41. Newton's laws of motion, 34. law of gravitation, 37, 43. Nodes, 39. relation to eclipses, 67, 71. Nucleus, of comet, 160. Objective, of telescope, 78. Obliquity of ecliptic, 25. Observations, of stars, 10. Occultation of stars, 103. Orbits, of comets, 161. of double stars, 199. of moon, 92. of planets, 28. Orion nebula, 215. Parabola, 35, 38, 161. Parabolic velocity, 38. Parallax, 114, 188. Penumbra, 64, 121. Perihelion, 38. Periodic comets, 176. Personal equation, 82. Perturbations, 39. of meteors, 174. Phases, of the moon, 91, 92. Photography, 81. of stars, 13. Photosphere, of sun, 121. Planets, 26, 133. distances from the sun, 134. how to find, 29. mass, density, size, 133. motion of, 27, 38. periodic times of, 30. Planetary nebulæ, 215. Pleiades, 16, 215. Plumb-line apparatus, 11, 18. Poles, 21. Precession, 46. Prisms, 84. Problem of three bodies, 39. Prominences, solar, 125. Proper motions, 191. Protractor, 2. Ptolemaic system, 32. Radiant energy, 75. Radiant, of meteor shower, 171. Radius victor, 33. Reference lines and circles, 17. Refraction, 50. Right ascension, 16, 20, 21. Roche's limit, 239.