S Satellites, 61. of Mars, 92. of Saturn, 108, 112. of Uranus, 116. solid, 117. of Neptune, 118. turn same face to primaries, 134, 147, 148, 225. latest discoveries in regard to motions of, 146. origin of, 147. death of, before planet, 233. impact of interplanetary particles on, Notes 246-250. capture of, Notes 251, 252. Saturn, 108-114. belts of, 109, 168. inherent light, 109, 152. Saturn’s rings, 109-114. mechanical marvel of, not early appreciated, 110. discrete particles, 110, 135. knots upon, 110-113. not flat, but tores, 111-114. show devolution—not pristine state of solar system, 138, 139. once a congeries, 139. Schaeberle, 9. Schiaparelli, 34, 36, 64-66, 69, 76, 77, 221. Schroeter, 65, 77. Seasons, loss of, 71, 83, 217, 218. begin with clearing of sky, 185. fully developed, 189. See, Notes 251. Seeliger, 10. Shooting-stars, 33, 35. radiant of, 33, 36. members of solar system, 36-40. tiny planets, 39. Siderite, 36. Silurian era, 178. Sirona, periodic variability of, 102. Sky, cause of clearing, 187. Slipher, Dr. V. M., 52, 79, 83, 86, 88, 89, 117, 161, 166. Slipher, Mr. E. C., 79, 233. Solar constant, 191. Solar system, evolved from a dark star, 44. evidence of origin, 51, 130. characteristics of, 60-62. evolutionarily one, 62. gap in progression of orbital distances, 95-100. bodies of, egg-shaped, 217. Specific gravity, of stone and iron, 44. Spectroscope, 7, 84. Spectroscopic shift, 84. determining velocity, 3. in Nova Aurigæ, 9. produced by great pressure, 10, 13. produced by anomalous refraction, 10. produced by change of density, 10, 13. explained, 85. variation in, Notes 243, 244. Spectrum, of Nova Persei, 12, 13. nebular, 13, 16, 45-48. peculiarities of nebular, explained, 50. photographic extension of, 52, 117, 161. of major planets, 52, 53, 161. of belts of Jupiter, 166. Spiral structure, implies rotation combined with motion out or in, 22. Stability of a system, condition for, 140, 141. Stoney, Dr. Johnstone, 231. Struve, 109. Suess, 179. Sun, original slow rotation of the, 130. heat of, 234, 235. reversion to a dark star, 235, 236. Sun spots, 104, 166.