Columbia University Observatory, latitude observations, 139 polar photography, 196 Common, his reflecting telescope, 32 Confusion of dates, in Pacific Ocean, 125 Congress of Astronomers, Paris, 1887, 102 Constellations, 162 Control, "mouse," for photography, 88 Copernican theory of universe, 53, 56 demonstration, 94 Corkscrew tunnels, 220 Crape ring of Saturn, 144 Cumulative effect, in photography, 84 Date, confusion of, in Pacific Ocean, 125 Date-line, international, explained, 126 Development of photograph, 81 Dial, of astronomical clock, 116 "Dialogue" of Galileo, 53 Differences of time, explained, 121 Directions, telescopic measurement of, 21 Directory of the heavens, 103 Distance, of light-source in photography, 83 of stars, 94, 106, 158 of Sun, 67, 97, 106 Donner, polar photography, 195 Double telescopes, for photography, 86 Earth, motions of its pole, 131 rotation of, 136, 162, 171, 184 shape of, 135 Eclipses, photography of, 109 Elkin, measures Pleiades, 15 Equatorial telescope, explained, 170 Eros, discovered by Witt, 66, 105 its importance, 67 Error of clock, determined by transit, 118 Exposure, length of, in photography, 84 Feldhausen, Herschel's observatory near Capetown, 204 Fiji Islands, their date, 126 Fixed polar telescope, 197 "Following" the stars, 88, 173 Four-day cycle of pole-star, 24 France, outside time-zone system, 129 Fundamental longitude meridian, 124 GALILEO, 47 and the Church, 48 discoveries of, 49 observes Saturn, 141 Galle, discovers Neptune, 61 Gauss, computes first asteroid orbit, 60 Gautier, Paris, constructs big telescope, 179 Geodetic Association, international, 139 Geography, maps, astronomical side of, 112 Geology, polar motion in, 131 Gill, photographs comet, 100 Gilliss, at Naval Observatory, Washington, 169 Goldsborough, at Naval Observatory, Washington, 169 _Grande Lunette_, Paris, 1900, 176, 180 Gravitation, 13 in Pleiades, 14, 212 law of, Newton's, 212 Gravity, centre of, 217 Greenwich, origin of longitudes, 7, 124 time, 7 Groombridge, English astronomer, 1 Harrison, inventor of chronometer, 8 Head, of heliometer, 156 Heidelberg, photography at, 104 HELIOMETER, 152 head of, 156 how used, 157 principle of, 154 scales of, 158 semi-lenses of, 155 Helsingfors observatory, polar photography at, 195 Henry, measures Pleiades, 11, 17 Hercules, constellation, solar motion toward, 222 Herschel, discovers apex of solar motion, 221 discovers Uranus, 59, 141 John, the moon hoax, 200 Hipparchus, discovers precession, 186 early star-catalogue, 21, 39 invents star magnitudes, 91 Huygens, announces rings of Saturn, 142 his logogriph, 143 Ice-cap, of Earth, 131 _Index Librorum Prohibitorum_, 53