EQUATORIAL OBSERVATORY, THE (Chap. XXII.), 337-342 (_see_ Observatories) EQUATORIAL, THE; its ordinary work, (Chap. XXIV.), 349-368 Equinoctial circle, observations of, by Euclid, 11 Equinoxes, first observations of, 15, 16, 17, 22; precession of the, 33 Eratosthenes, observations of, 17; his measurement of the earth, and inclination of the ecliptic, 19; meridian circle invented by, 20 Erecting eyepiece, 113 Errors, collimation and deviation, in the transit instrument, 238, 240, 247, 328 Errors; personal equation, 259; adjustments of the equatorial, 329 Ertel, vertical circle designed by, 290 Escapements of clocks, 196-205; ancient, 177; anchor, 197; Graham’s, 199; Mudge’s, 200; Greenwich clock, 203; detached lever, 208; chronometer escapement, 209 Ethereal vibrations, 373, 401, 410, 420, 449, 450 Euclid, his observations of the stars, 8, 9, 10; of great circles, horizon, meridian and tropics, 11, 12; theory of the earth’s position, 12; pole star, 14 Extra-meridional observations, first employment of, 23, 25 “Eye and ear” method in transit observations, 259 Eyeball, section of the, 66 Eyepieces, Huyghen’s, 110; Ramsden’s, Dollond’s, 112; erecting or “day eyepiece,” 112; Dawes’s solar eyepiece, 114; magnifying power of, 116 Eyepiece of Greenwich transit circle, 246; of transit instrument, 257 F. Faye, M., celestial photography, 456 Feil and Chance, manufacture of flint glass discs, 119, 305 Fixed stars (_see_ Stars) Flame of salts in a Bunsen’s burner, 407 Flint-glass prisms, 83, 84; lenses, 86, 170 Flint-glass, improvements in the manufacture of discs of, 118, 119, 305 Focal length of telescopes, 82, 458; of lenses, 62, 63; of convex mirrors, 94 Foucault; his reflecting telescope, 108; improvement of specula, 117; mode of polishing specula, 134, 136; mounting of his telescope, 311; governor of driving clock for large telescopes, 323; siderostat, 343; spectrum analysis, 410; heliostat, 424 Fraunhofer; manufacture of flint-glass discs, 118; large telescopes, 303; lines in the solar spectrum, 392; spectrum analysis, 402, 410, 422, 425, 432, 438 Frederick II. of Denmark, his patronage of Tycho Brahe, 38 Fusee for chronometers, 209 G. Galileo; his telescopes, 73, 78; their magnifying power, 77; the pendulum, 183, 184 Gascoigne, eyepieces and circle reading, 212; cross wires for “telescopic sight,” 219 Gateshead, Mr. Newall’s refractor, 302 Geissler’s tubes, 413 German mounting of large telescopes, 299 Gizeh, great pyramid of, an astronomical instrument, 6 Glasgow, electric time-gun, 278 Glass, injurious effects of the duty on, 305 Glass specula, methods of silvering, 137 Globe, celestial, 23; terrestrial, 23 Gnomon; its invention and early use, 16; improvements in, 18, 175 Graham; dead-beat escapement, 192, 199; mercurial pendulum, 188