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Comparison prism of the spectroscope, 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

Gravity escapement, 200, 202

Greeks, their early use of the gnomon, 16

Greenwich, Royal Observatory; perspective view and plan of transit circle, 243, 245, 251;

• transit room, 251, 257;
• meridian of, 252;
• chronograph, 260-264;
• computing room, 267;
• standard sidereal clock, 267;
• mean solar time clock, 268;
• standard clock, 274;
• pendulum, 188;
• reflex zenith tube, 286;
• alt-azimuth, 290;
• equatorial, 310;
• thermopile, 384;
• photoheliograph, 469

“Greenwich Time” and the use made of it (Chap. XVIII.), 271-283

Gregorian telescope, 149

Gridiron pendulum, 188, 189, 192

Grinding of lenses and specula, 127

344;

photoheliograph, 469

Pendulum, 183, 185, 187, 188

Personal equation, 259

Phosphatic glass for lenses, 123

Photography, Celestial (Chap. XXXI., XXXII.), 454-483

Photography, stellar, 172

Photoheliograph, for photographs of the sun, 460, 470;

• for transit of Venus (1874), 461

Photometry, 373, 377

PHYSICS, ASTRONOMICAL (Book VI.), 371

Physical Inquiry, General Field of (Chap. XXV.), 371-376

Picard, transit circle, 284

Pisces, its position in the zodiac, 34

Pitch employed in polishing lenses and specula, 128, 132

Plane of the ecliptic, 13, 14

Planets, in Ptolemy’s system, 3;

• first observations of conjunction, 4, 5;
• motions observed by Autolycus, 9;
• in Tycho Brahe’s system, 46;
• Saturn seen with object-glasses of 3¾ and 26 inches, 160, 161;
• as telescopic objects, 350;
• photographs of, 465

Pleiades, the first observations of, 5

PlÜcker, spectrum analysis, 413

Pogson, star magnitudes, 381, 382

Pointers of pre-telescopic instruments, 35, 49, 214, 216

Polar axis of the equatorial, 299, 302, 308, 311, 312, 324, 328, 329, 346

Polariscope, 441-453

Polarization of light, 441-453

Pole, North, 238;

• diagram illustrating how it is found, 249

Pole star, first observations of, 6;

• observations of Euclid, 10, 14;
• its position, 238

Polishing lenses and specula, Solar time, 253, 255

Solstices, first observations of the, 15, 16, 17, 22

Southing of stars, 234

SPACE MEASURERS (Book III.), 135-232;

• circle reading, 211;
• Digges’ diagonal scale, 213;
• the vernier, 214;
• micrometers, 218

Space-penetrating power of the telescope, 154;

• stars in Orion, a test of, 165

Spectroscope, construction of the, 393-400;

• automatic, 397;
• arranged for showing absorption, 409;
• attached to Newall’s refractor, 427;
• solar, Browning’s and Grubb’s forms, 428

Spectrum produced by prisms, irrationality of the, 86, 87

Spectrum, solar, 390, 391, 392

Spectrum analysis, principles of, 401-421

Specula, production of, 117, 120;

• casting, annealing, 121;
• curvature, 122;
• grinding, 127;
• polishing, 128;
• silvering, 137;
• mounting, 142, 169, 172;
• effective light, 169;
• repolishing, 171;
• cost as compared with object-glasses, 172

Spherical aberration, 87;

• diagram illustrating, 104, 105;
• its correction in eyepieces, 109, 111;
• of specula, 123, 124

Sprengel pump, 413

Spring governor of driving-clock for large telescopes, 319, 320

“Spurious disc” of fixed stars, 163

Standard clock at Edinburgh Observatory, 272

Standard sidereal clock of Greenwich Observatory, 267

Standard solar time clock of Greenwich Observatory, 267

Stars, Chemistry of the (Chap. XXVII.-XXX.), 386-453

Stars, Light and Heat of (Chap. XXVI.), 377;

• variable, 377-385

Stars, first observations of the, 4, 5,

                                                                                                                                                                                                                                                                                                           

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