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 Polar sea, 79 et seq., 92, 114, 119.

Polar snows, relation of, to surface activity, 113.

Pole, south, of cold not coincident with pole of rotation, 85.

Poles, of Mars, tilt of, 22.

Presentation, meaning of, note, 156.

Proctor, map of Mars, 141.

Projections, on terminator of Mars, 63, 64.

Protei Regio, 72.

Psychic effect, on seeing, 158-160.

Pyriphlegethon, the, oases detected on, 182.

Rifts, in south polar cap, 85, 87.

Rotation, of Mars, time of, 21, 22, 95, 107.

Satellites, of Mars, Appendix, Note IV.

Saturn, relative orbit and size of, 5; critical velocity of, Appendix, Note I.

Schiaparelli, on tilt of Martian poles, 77; map of Mars, 94; first detection of canals, 136 et seq.

Sea of the Sirens, the, 120.

Seas, of Mars, so called, 96, 107 et seq., 123, 126, 127; variation in tint of, 110, 118, 120; of the Moon, 123.

Seasons, of Mars, 23; length of, 24; phenomenally hot season in southern hemisphere of Mars, 91.

Seeing, conditions conducive to, 138, 139.

Shape, of Mars, 14; of oases, 179.

Sinus Titanum, 101, 134; canals near, 156, 182.

Size, of Mars, 14; of oases, 179.

Snow, on Mars, 33.

Snow-caps. (See South polar cap.)

Solar system, size of the, 4, 14, 15.

Solis Lacus, 99 ; canals near, 155; size of, 180; polariscope observations on, 185; bright causeways in, 194.

Solstices, of Mars, 77; summer solstice of southern hemisphere, 114.

Southern hemisphere, of Mars, seasons in, 24; terminator of, 64.

South polar cap, irradiation from, 27; dwindling of, 33; size of, in June, 76; disappearance of, 79, 90; constitution of, 80, 83, 94; history of, 84 et seq.; eccentricity of, 85; rift in, 85, 87; starlike points in, 86, 87; detached portions of, 89; different levels of, 89; disappearance of, 90.

South polar sea, 94.

South pole, of cold on Mars not coincident with geographical pole, 85.

Spectroscope, observations on stars, 4; observations of atmosphere of Mars by, Appendix III.

Spots, in bright areas (see Oases); on border of dark areas, 197; as terminals to canals, 197; in dark areas, 198; list of, 199.

Spring, length of, on Mars, 24.

Stars, Mars as one, 1; relative distance of, 5.

Stoney, G. Johnstone, 53.

Storms, on Mars, 59.

Straits, in dark areas, 114, 115, 117, 163, 173.

Struve, Hermann, 29.

Summer, length of. on Mars, 24.

Sun, relative size of, 4; effect on planet's age, 206.

Surface, of Mars, features of, 93.

Syrtis Major, 20, 105, 119, 141.