Inclination of the ecliptic, 17; measured by Eratosthenes, 19 Index error, adjustments of the equatorial, 330 Iron, line spectrum of, 406, 418 Irrationality of the spectrum, 87 J. Janssen (Dr.), solar photography, 471; discoveries in solar physics, 472 Jupiter, in Ptolemy’s system, 3; in Tycho Brahe’s, 46; as a telescopic object, 351; photographs of, 465, 466 Jupiter’s moons, observation of their eclipses to determine “local time,” 282 K. Kepler’s treatise on dioptrics, 386 Kew Observatory, photographs of the sun and sun-spots, 460, 465, 470, 475 Kirchhoff; spectroscope, 396; spectrum analysis, 402, 403, 412, 422, 428 Kitchener (Dr.), improved eyepiece, 113; stars in Orion, 164 Knobel’s photometer, 378 Knott, star magnitudes, 381 L. Lamp for equatorial telescope, 325 Lamp, electric (_see_ Electric Lamp) Lassell; his Newtonian telescope, 108, 311; production, polishing, and mounting metallic specula, 121, 132, 144 Latitude; observations of Posidonius, 8; parallels of, 23 Lattice-work for tubes of telescopes, 172 Lenses; action of, 55, 58, 85; concave and convex, 61, 71, 75; amount of colour produced by, 81; achromatic, 84; Hall and Dollond’s experiments, 85; correction for colour, 87; correction for aberration in eyepieces, 109, 116; production of, 117 Lens, crystalline, of the eye, 67 Lewis (Sir G. C.), his “Astronomy of the Ancients,” 9 Liebig, improvement in specula, 117 Light; refraction, 55-72; deviation and dispersion, 79, 80, 82, 83; decomposition and recomposition, 83; reflection, 90-99; action of a reflecting surface, 91; angles of incidence and reflection, 92; concave and convex mirrors, 94-98; velocity of, 159; loss due to reflection, 168; effective, in reflectors, 169; vibration of particles, 373, 401; polarization, 441-453 LIGHT OF STARS, DETERMINATION OF (Chap. XXVI.), 377-385 Lindsay (Lord), siderostat at his observatory, 347 Local time, 281 Longitude, meridians of, 23; as determined by Hipparchus and Tycho Brahe, 44; determined by clock and transit instrument, 280; expressed in degrees and time, 280 M. Magnesium vapour; colour of, 416; in the sun, 435 Magnifying power of large telescopes, 154, 155; stars in Orion, a test of, 163 Magnitude of stars, 377 Malus, discovery of polarization by reflection, 442, 448 Malvasia (Marquis), his micrometer, 219, 221 Manlius, gnomon erected by him at Rome, 18 Maps of the stars (_see_ Stars) Mars, in Ptolemy’s system, 3; in Tycho Brahe’s, 46; as a telescopic object, 350 Martin’s method of silvering glass specula, 138 Mauritius, photoheliograph at, 469 Mean time, 254 Mean solar time clock at Greenwich, 268