Part 18

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

International, date-line, explained, 126 geodetic association, 139

Inter-stellar motion, in clusters, 98 in Pleiades, 14

Islands of Pacific, their longitude and time, 125

Japan, latitude station in, 139

Jewellers' correct time, 121

Journalistic astronomy, 176

Jupiter's satellites, discovered by Galileo, 50 discovered by Barnard, 51

Keeler, observes Saturn's rings, 140, 147, 150 photographs nebulæ, 32

"Keyhole" nebula, 205

Lambert, determines longitude of Washington, 168

Laplace, discusses Saturn's rings, 146 nebular hypothesis, 33 stability of solar system, 210

Latitude, changes of, 133, 138 definition of, 134 determining the, 6

Leverrier, predicts discovery of Neptune, 61, 142

Lick Observatory, Keeler's observations, 140

Light, undulatory theory of, 19, 148

Light-waves, measuring length of, 20, 149

Logogriph, by Huygens, 143

Long-exposure photography, 85