on lunar craters, 224.

Neptune, description of, 208-210.

Newcomb, Simon, on Olbers's theory, 141.

Newton, lunar crater, 222.

Olbers's theory of planetary explosion, 138.
on Vesta's light, 138.

Pallas, an asteroid, 129.

Perrotin sees canals on Mars, 92.

Phobos, satellite of Mars, 125.

Pickering, E.C., discovers ninth moon of Saturn, 195.
finds Eros on Harvard plates, 133.
on shape of Eros, 136.
on light of Eros, 137.

Pickering, W.H., on lunar atmosphere, 247.
observes changes in moon, 244.
sees Mars's canals, 92.
theory of Tycho's rays, 246.
on Venus's atmosphere, 54.

Planets, classification of, 15.
how to find, 256, 273.
resemblances among, 12.

Plato, lunar ring plain, 225.

Plurality of worlds in literature, 2.
subject ignored, 8.

Proctor, R.A., on Jupiter's moons, 180.
on other worlds, 8.

Roche's limit, 201.

Rosse, Lord, on temperature of moon, 255.

Saturn, age of, 189.
composition of, 190.
density of, 188.
distance of, 186.
the gauze ring, 199-202.
gravity on, 188.
inclination of axis, 187.
interior of, 206.
length of year, 186.
popular telescopic object, 185.
rings of, 185, 196.
gaps in, 197.
origin of, 200.
periodic disappearance of, 198.
seen from planet, 207.
shadow of, 198.
rotation of, 187.
satellites of, 195.
size of, 187.

Schiaparelli discovers canals on Mars, 90.
describes Martian canals, 93.
discovers Mercury's rotation, 30, 32.
on rotation of Venus, 76.

Solar system, shape and size of, 14.
unity of, 9.
viewed from space, 11.

Stoney, Johnstone, on atmospheres of planets, 116.
on escape of gases from moon, 231.

Sun, the, isolation in space, 13.
no life on, 10.
resemblances with Jupiter, 174.

Swedenborg, on Saturn's rings, 204.

Tidal friction, 80, 81, 236, 253.

Tycho, lunar crater, 222.

Ultra-Neptunian planet, 210.

Uranus, description of, 208-210.

Venus, age of, 58.
atmosphere of, 53, 55, 59, 61, 68.
absence of seasons on, 51.
density of, 47.
distance of, 47, 50.
gravity on, 46, 47.
inclination of axis, 50.
life on, 57, 58, 61, 65, 67, 68, 82, 117.
light and heat on, 50-57.
orbit of, 50.
phases of, 49.
resemblances of, to earth, 46.
rotation of, 76, 79, 80.
size of, 46.
twilight on, 83.
visibility of, 47.

Vesta, an asteroid, 129, 130, 138.

Vogel on Mercury's atmosphere, 21.

Wirele