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.
V Velocity, of Mercury in orbit, 63. of satellites about primary, Notes 245. of major planets, in orbit, Notes 245. Venus, 73-90. surface markings, 74, 77, 79, 80, 83, 220, 221. brilliancy due to cloudless atmosphere, 75. importance of rotation period, 75, 76. turns same face to the Sun, 77-80, 134, 220, 221. ice on the night side, causes ashen light, 82. Very, Professor, 16, 191, 192, 194. Vesta, 101. Vogel, 52. Volcanoes, avenues to earlier state, 160. Von Zach, 96.
W Walker, Mr., 123, 124. Water, becoming more scarce, 203, 204, 211. lacking on Moon, 204. Water-vapor, in atmosphere of Jupiter, 53. in atmosphere of Mars, 91, 161. smaller planet has less hold on, 207. Williams, Mr. Stanley, 103. Witt, de, 94. Wolf, Dr., 13. Wolf, Max, 94. Wolf-Rayet stars, 13, 48. Wright, 13, 43.
Y Year, of Uranus, 116. Yerkes Observatory, 232. Young, 46.
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