f, 84

Themis, 240

"Tidal drag," 180, 188, 208, 344

Tide areas, 179-180

Tides, 178-180, 338-339

_Time Machine_, 344

Tin, 145

Titan, 240

Titius, 245

Total phase, 71-72

Totality, 72;
track of, 66

Trail of a minor planet, 226-227

Transit, 62, 150-154;
of Mercury, 62, 151, 154;
of Venus, 62, 151-152, 154, 211

Trifid Nebula, 316

Triple stars, 300

Tubeless telescopes, 110-111, 243

Tubes used by ancients, 110

Tuttle's Comet, 274

Twilight, 167, 202

Twinkling of stars, 168

Twins (constellation). _See_ Gemini

Tycho Brahe, 290, 311

Tycho (lunar crater), 204

Ulugh Beigh, 107

Umbra of sunspot, 134-135

Universe, early ideas concerning, 17-18, 158, 177, 342

Universes, possibility of other, 330-331

Uranus, 22-24, 31, 210, 243, 245, 275;
comet family of, 252;
discovery of, 22, 210, 243;
rotation period of 34, 245;
satellites of, 26, 245;
"year" in, 35-36

Ursa Major (constellation), 279, 281, 291, 295, 314;
minor, 177, 279, 293-294

Ursae Majoris, ([z]) Zeta. _See_ Mizar

Variable stars, 307-310

Variations in apparent sizes of sun and moon, 67, 80, 178

Vault, shape of the celestial, 194-196

Vega, 177, 278, 280, 282-283, 285, 290, 294, 302, 307, 323

Vegetation on Mars, 221, 217-218;
on moon, 205

Venus, 20, 22, 31, 71, 90, 108-109, 111, Chap. XIV., 246, 311;
rotation period of, 34, 155

Very, F.W., 314

Vesta, 225, 227

Violet (rays of light), 121-122, 125

Virgil, 19

Volcanic theory of lunar craters, 203-204, 214

Volume, 38

Volumes of sun and planets compared, 38-39

"Vulcan," 25

Wallace, A.R., on Mars, 220-223

Water, lack of, on moon, 201-202

Water vapour, 202, 213, 222

Wargentin, 103

Warner and Swasey Co., 117

Weather, moon and, 206-207

Weathering, 202

Webb, Rev. T.W., 204

Weight, 43, 165-166

Wells, H.G., 344

Whale (constellation). _See_ Cetus

Whewell, 190

Willamette meteorite, 277

Wilson, Mount, 118

Wilson, W.E., 313

"Winged circle" (or "disc"), 87

Winter, 175, 178

Witt, 227

Wolf, Max, 226-227, 232

Wright, Thomas, 319, 334

Wybord, 89

Xenophon, 101

Year, 35

"Year" in Uranus and Neptune, 35-36

Year, number of eclipses in a, 68

"Year of the Stars," 270

Yellow (rays of light),