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 Ursæ 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), 121-122, 124 Yerkes Telescope Great, 117, 303 Young, 94, 137, 166 Zenith, 174 Zinc, 145 Zodiacal light, 181 Zone of asteroids, 30-31, 227 THE END Printed by BALLANTYNE, HANSON & CO. Edinburgh & London THE SCIENCE OF TO-DAY SERIES _With many illustrations. Extra Crown 8vo. 5s. net._ BOTANY OF TO-DAY. A Popular Account of the Evolution of Modern Botany. By Prof. G.F. SCOTT ELLIOT, M.A., B.Sc., Author of "The Romance of Plant Life," _&c. &c._ "One of the books that turn botany from a dryasdust into a fascinating study."--_Evening Standard._ AERIAL NAVIGATION OF TO-DAY. A Popular Account of the Evolution of Aeronautics. By CHARLES C. TURNER. "Mr. Turner is well qualified to write with authority on the subject. The book sets forth the principles of flight in plain non-technical language. One is impressed by the complete thoroughness with which the subject is treated."--_Daily Graphic._