Page:In the high heavens.djvu/383

Rh Gravitation, comets and the law, 199 the law outside our system, 200-204 gravitation and the binary stars, 203 what is known about gravitation, 204-206 gravitation on the moon, 47 ""Jupiter, 50 ""the sun, 371 Helmholtz's solar theory, 371-372 Great Bear, the, in remote antiquity, 20 now and 36,000 years hence, 173, 175 100,000 years hence, 177 the system of Mizar, 192 detection of Mizar's spectroscopic double, 193 distance and mass of its components, 194-195 period of Xi Ursæ Majoris, 202 Groombridge No. 1830, velocity of, 12, 209 its distance and proper motion, 208 its relation to our sidereal system, 211

, Prof., and the study of the solar prominences, 86-87 and sun-spot photographs, 292 Hall, Prof. Asaph, and the satellites of Mars, S9 Heavens, the aspect of the, a million years ago, 12, 15-18, 20 changes in the, due to the "fixed" stars, 21 Heat, the "heat-wave" of 1892, 276 complexity of the causes. 280 illustration from the tides, 281 elements of the tide problem, 282 tide prediction, 285 Lord Kelvin's predicting machine, 285, 286 Heat, illustration from star showers, 283 a temperature-predicting machine, 286-290 the true thermal measure of the "heat-wave," 291 climate and sun-spots, 292 (See also Sun) Helmholtz and the problem of solar heat, 269-270, 369 Herschel, Sir W., and the voyage of the solar system, 24 and the Great Nebula in Andromeda, 158 and the movements of binary stars, 202 his Nebular Hypothesis examined, 212-217 Hipparchus and the movements of the pole, 57 Huggins, Sir William, and the spectroscope, 148, 151 the colour problem of double stars, 153 spectrum of a nebula, 155 movement in the line of sight, 159 the spectrum of the sun compared with that of the earth at sun-heat, 169 the elements of the universe. 206

or "dark" stars, 211-212, 240 more numerous than the bright, 241, 245

in the carboniferous epoch, 19 his clouds, 41 the "great red spot," 42 conditions of life on, 49-50 orbit of, 106 period of revolution, 108 rotation of, 111 physical character of, 113 collision with Loxell's comet, 306