Davy, Sir Humphry, on Saturn, 190.

Dawes sees canals on Mars, 93.

Deimos, satellite of Mars, 125.

Denning, W.F., description of Jupiter, 175.

De Vico on rotation of Venus, 76.

Dewar, James, discovers free hydrogen in air, 232.

De Witt discovers Eros, 133.

Dick, Thomas, on Saturn, 201.

Douglass, A.E., sees Mars's canals, 92.
sees clouds in Mars, 119.

Doppler's principle, 79, 200.

Earth and moon's orbit, 217.
birth of moon from, 236.
change of distance from sun, 27.
less advanced than Mars, 89.
older than Venus, 58.
seen from Mercury, 41.
seen from Venus, 69-71, 75.
seen from moon, 214.

Earth, similarity to Venus, 46.
supposed signals to and from Mars, 110.

Elger, T.G., on cracks in moon, 227.
on Tycho's rays, 246.

Ephemeris, how to use, 260, 264.

Eros, an asteroid, 131-134, 136, 137.

Flammarion, C., observes Venus's atmosphere, 56.
on plurality of worlds, 8.

Forbes, Prof. George, on ultra-Neptunian planet, 210.

Galileo on lunar world, 215.

Gravity, as affecting life on planets, 20, 46.

Hall, Asaph, discovers Mars's moons, 90.

Herodotus, lunar crater, 227.

Herschel, Sir John, on Saturn, 185.

Holden, E.S., on photograph of lunar crater, 242.

Huggins on Mercury's atmosphere, 21.

Inhabitants of foreign planets, 1, 4, 5.

Interplanetary communication, 1, 3, 72, 110, 112.

Juno, an asteroid, 129.

Jupiter, cloudy aspect of, 165.
density of, 162.
distance of, 161.
equatorial belts on, 165.
future of, 180.
gravity on, 162.
great red spot on, 169.
markings outside the belts, 168.
and the nebular theory, 178.
once a companion star, 179.
polar compression of, 161.
possibly yet incandescent, 177.
question of a denser core, 176.
resemblance of, to sun, 174.
rotation of, 161, 173.
satellites of, 166, 181.
seen from satellites, 182.
size of, 160.
solar light and heat on, 182.
south belt of, 172.
surface conditions of, 163.
theories about the red spot, 170.
trade-winds and the belts of, 167.
various rates of rotation of, 173.
visibility of rotation of, 166.

Keeler, J.E., on Saturn's rings, 200.

Kepler, lunar crater, 223.

Kinetic theory of gases, 116.

Kirkwood, Daniel, on asteroids, 131.

Lagrange on Olbers's theory, 139.

Lick Observatory and Mars's canals, 92.

Life, a planetary phenomenon, 10.
in sea depths, 62.
on planets, 62, 63.
prime requisites