Page:The evolution of worlds - Lowell.djvu/303

Rh 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, 95100. 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.

T Temperature, of Moon, 191, 192. of Mars, 192, 194, 196. defined, 230. no such thing as, in space, 230. Tercidina, periodic variability of, 102. Tertiary times, entrance of color with, 189, 190. Tidal action, 143-147, 216-218. causes loss of energy, 144. inoperative, 144, 145, 147. changes retrograde rotation of planet to direct, 145-147, 217. on satellites, 147. slows down spin, 148, 217. brings plane of rotation down to orbital plane, 217. lengthens day to infinity, 219. analytically expressed, 224. greatest on planets near Sun, 135, 224. Tidal action, disruptive, 130. exemplified by spiral nebulæ, 24, 25. hinted at, by meteorites, 55. theory corroborated by densities of planets, 51. theory corroborated by atmospheres of planets, 52-55. on comets, 139. cause of Saturn's rings, 139. Tisserand, 68. Titius, 95. Todd, 68. Trees, deciduous, first appearance of, 189. Trilobites, blindness of, 178, 179. Twining, 33. Tycho Brahe, 5.

U Uranus, 114-118. history of discovery, 114, 115, 119. a ball of vapor, 115, 117. belts of, 115, 116, 168. tilt of axis to ecliptic, great, 115. spectroscopic revelations of, 117, 118. in an early amorphous state, 118. further advanced than the giant planets, 168.