Tempe, 60.
Terminator, observations on, 48, 63, 64; irregularities on, 63; of Moon, 169; of Mars, 170.
Tisserand, on polar flattening of Mars, 28.
Trivium Charontis, 103, 133, 181; shape of, 179.
Twilight, on Mars, measured by Mr. Douglass, 26.
Twilight arc, of Mars, 42.
Typhon, the, double, 195.
Uranus, relative orbit and size of, 5; ellipticity of disk of, 25; evidence of atmosphere of, 57; critical velocity of, Appendix, Note I.
Variations, of surface of Mars. (See Changes.)
Vegetation, on Mars, 122, 164; visibility of, 130, 198.
Velocity, critical, of planets, Appendix, Note I.
Venus, cloud-covered, 2; ellipticity of disk of, 25; evidence of atmosphere of, 57; cusps of, 57; critical velocity of, Appendix, Note I.
Water, 79, 83, 92; necessary to life, 76, 127; theoretic reflection from, 109; amount of, on Mars, 122; direction of, when flowing from pole, 125; as fresh, 175.
Weather, on Mars, 58.
Winter, length of, on Mars, 24.
Worlds, other than our own, 3.
