Rosse, Earl of, 6-foot reflector, 12; colouring of Jupiter, 158, 159; telescope, resolution of Orion nebula, 260; drawing of Orion nebula with, 262; spiral character of M. 51, 265 Rotation period of Mercury, 85; of Venus, 95, 96 S Satellite of Venus, question of, 97, 98; of Mars, 142-144; of Jupiter, 166-169 Saturn, orbit of, sun-heat received by, period of, diameter of, compression and density of, 172; features of globe, rotation period, 173; varying aspects of rings, 178; measures of rings, 178; constitution of rings, 179; satellites of, 186-189; satellites, transits of, 189 Scheiner, construction of refractors, 2 Scheiner, Julius, spectrum of Andromeda nebula, 264 Schiaparelli, rotation of Mercury, 85; surface of Mercury, 86; rotation of Venus, 96; discovery of Martian canals, 135-137; connection of comets and meteors, 214, 224 Schmidt, lunar map, 114; observation of comet 1882 (iii.), 217, 218; observes Nova Cygni, 253 Schröter, observations of Venus, 94; lunar mountains, 118; rills, 118; lunar atmosphere, 126 Schwabe, discovery of sun-spot period, 61, 62 See, Dr., duration of sun's light and heat, 80 Serenitatis, Mare, serpentine ridge on, 110, 111; crossed by ray from Tycho, 120 Shackleton photographs spectrum of reversing layer, 75 Sidereal month, 103 Siderites and siderolites, 227 Sinus Iridum, 117 Sirius, companion of, discovered, 8; brightness, 234; colour, 235; brilliancy compared with Venus, 90; with Jupiter, 156 Sirsalis cleft, 119 Smyth, Admiral, on amateur observers, 18, 19, 45 Sodium in chromosphere, 73 Solar system, translation of, 269-272 South, Sir James, 12-inch telescope, 6 Spectroscope, 73, 76 Spectroscopic observations of rotation of Venus, 96; of Martian atmosphere, 140; investigations of Saturn's rings, 180; of Uranus, 195 Spectrum of reversing layer, 75; of chromosphere, 73 Spencer, Herbert, relation of stars and nebulæ, 267 Spica Virginis, 234 Stars, distance of, 231; number of, 232, 233; magnitudes, 234; numbers in different magnitudes, 235; colours, 235-237; change of colour in, 236, 237; constellations, 237, 238; double, 240; multiple, 243; binary, 244; spectroscopic binaries, 245-248; variable, 248-251; new or temporary, 251-255; constitution of, 268 Struve, F. G. W., 'Mensuræ Micrometricæ,' 278 Struve (Otto) discovers satellite of Uranus, 196; verifies discovery of Neptune's satellite, 201 Sun, size, distance, 47, 48; rotation period of, 57-59; methods of observing, 65-67; atmosphere of, 75; light and heat of, 78 Sun-spots, 49, 50; rapid changes in, 54, 55; period of, 62; zones and variation of latitude of, 62 Synodic period, 103 Syrtis Major, 145 Swift, Dean, satellites of Mars, 142