TELESCOPE:—VARIOUS METHODS OF MOUNTING LARGE TELESCOPES (Chap. XX.), 293-327; refracting, 73-89; Galilean, 73; magnifying power of the telescope, 76, 79; Scheiner’s telescope, 78; focal length of early telescopes, 79; achromatic, 86; reflecting, 100-108; Gregory’s telescope, 101; Newton’s, 102; Cassegrain’s, 103; Sir W. Herschel’s 103, 108; Lord Rosse’s, De La Rue’s, Lassell’s, Foucault’s, Grubb’s, 108; eyepieces, 109-116; Huyghen’s eyepiece, 110; Ramsden’s eyepiece, 112; magnifying power of eyepieces, 116; lenses and specula, 117-138; flint glass for lenses, 119; the “optick tube,” 139-151; the modern telescope, 152-172; magnifying and space penetrating power, 154, 155; illuminating power, 158; defining power, 160; reflecting and refracting compared, 170; permanence of optical qualities, 170; “telescopic sight,” 219; Sir Wm. Herschel’s at Slough, 294; Lord Rosse’s reflector, 294, 311, 312; refractor on alt-azimuth tripod, 296; simple equatorial mounting, 298; the German mounting, 299; Washington great equatorial, 309; English mounting, 310; forked mounting, 310; Greenwich equatorial, 310; Melbourne reflector, 312, 313; Paris reflector, 314; driving clock, 318; Newall’s refractor with spectroscope, 427; De La Rue’s, 459; Rutherfurd’s, 466; Newall’s, 459; Melbourne, 459 Telescope, zenith (_see_ Zenith Telescope) Temperature, its effect on the pendulum, 187, 193 Terrestrial globe, 23 Thales, his employment of the gnomon, 17 Theodolite, 288 Theodolite, astronomical, 287 Thermometry, 374, 384 Thermopile, 374 Time; first reckoning of, 19; early measurements, 36, 44, 175; modern measurement of, 253; sidereal, solar, and mean, 254, 256 TIME AND SPACE MEASURERS (Book III.), 175-232 Time, Greenwich (_see_ Greenwich Time) Time, local, 281 Time balls for distributing Greenwich time, 275 Time signals, 278, 281, 283 Timocharis, his observations in the Alexandrian museum, 19 Tourmaline, in polarization of light, 443 TRANSIT CIRCLE, THE (Chap. XVI.), 233-252; system of wires in eyepiece, 220; at Greenwich and Cambridge (U.S.), 247, 248, 251; mode of using, 253, 284 TRANSIT CLOCK, THE (Chap. XVII.), 253-270 Transit instrument, 171, 234, 236, 237; mode of using, 253; Römer’s, 284; Struve’s, 285 Transit of Venus, photographic observations, 475 Trigonometrical tables, first construction of, 17 Tropics, defined by Euclid, 12 Trouvelot, ring of Saturn observed with the Washington refractor, 161 Tube of the telescope, 139-151