Tycho Brahe; astrolabe, 26; ecliptic astrolabe, 28; discoveries of, 37-52; biography of, 37; list of his instruments, 38; portrait, 39; catalogue of stars, 42; observatory (engraving), 43, 287; his solar system, 46; discovery of comet of 1677, 47; instruments for measuring distances and altitudes of stars, 51; clocks, 179, 184, 196; diagonal scale for measuring space, 213; mural quadrant, 233; transit circle, 284 U. United States Naval Observatory, 341 Uranus, as a telescopic object, 351 Uraniberg, Tycho Brahe’s Observatory, 38 V. Variable stars, 377 Velocity of gases in sun-storms, 440 Venice, ancient clock dials, 257 Venus, in Ptolemy’s system, 3; in Tycho Brahe’s, 46; employed by Tycho Brahe in determining longitude, 44; as a telescopic object, 350; transit of, instrument used in the expedition of 1874, 236; photographic observations, 475 Vibrations, ethereal, 373, 401, 410, 449, 450 Vienna, refracting telescope, 141 Villarceau, Yvon, driving clocks, 324 Vega, heat of, 385 Vernal equinox, its position in the constellations, 34 Vernier, the, 214 Vertical circle, Ertel’s, 290 W. Walther, altitudes measured by, 36 Washington Observatory; great refracting telescope, 302, 309; flint glass discs, 119; ring of Saturn seen through it, 161 Watches, detached lever escapement for, 207 Water clocks, 176 Wave-lengths of light of solar gases, 440 Westminster clock-tower, 277 Wheatstone (Sir C.); “chronographic method” of transit observation, 259; apparatus for controlling clocks, 271 Winlock (Prof.), photographs of the sun, 461 Wires, cross, for circle reading, 212, 216; system of wires in a transit eyepiece, 220, 234, 257; in eyepiece of Greenwich transit circle, 246; wires of the transit instrument, 234 Wire micrometer, 221, 352 Wolfius, correction of chromatic aberration in lenses, 89 Wollaston (Dr.), lines in the solar spectrum, 391; spectrum analysis, 402, 422 Wyck (Henry de), clock made in 1364 by, 178 Y. Ys of the transit instrument, 238, 284 Years, first observation of, 5; determination of their length, 22 Z. Zenith, zenith sector, zenith telescope, reflex zenith tube, at Greenwich, 285 Zenith distances, measurement of, 51 Zodiac, first defined, 8, 9; observations of Euclid, 11, 12; of Denderah, 7 Zöllner’s astrophotometer, 379 Zero of right ascension, 249 Zinc in the sun, 419 THE END. LONDON: R. CLAY, SONS, AND TAYLOR, BREAD STREET HILL, E.C. TRANSCRIBER'S NOTES