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
H
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
I
more numerous than the bright, 241, 245
J
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
