Photography, asteroid, invented by Wolf, 104 congress of astronomical, 102 cumulative effect of light, 84 distance of light-source, 83 double telescopes for, 86 general star-catalogue, 102 IN ASTRONOMY, 81 in discovery of asteroids, 64, 104 in solar physics, 109 in spectroscopy, 108 length of exposure, 84 measuring-machine, Rutherfurd, 93 motion of telescope for, 87 "mouse" control of telescope, 88 of eclipses, 109 of inter-stellar motion, 99 Paris congress, 1877, 102 polar, 191 Rutherfurd pioneer in, 90 star-clusters, 98 star-distances measured by, 94 summarized, 110 wholesale methods in, 103 Piazzi, discovers first asteroid, 59, 106 Pitkin, report to House of Representatives, 168 Planetary nebulæ, 31 PLANET OF 1898, 58 Planetoids, see Asteroids. Planets known to ancients, 58 PLEIADES, 10 gravitation among, 212 motion among, 14, 16, 98 nebular structure, 17 number visible, 11 Polar axis, of telescope, 173 Polar photography, 191 at Helsingfors, 195 Pole, celestial, 184 of the earth, motions of, 131 THE ASTRONOMER'S, 184 POLE-STAR, 18 as a binary, 25 as a triple, 18, 26 change of, 187 its four-day cycle, 24 motion toward us, 24 Positive, and negative, in photography, 82 Potsdam, observatory, photographic star-catalogue, 103 Practical uses of astronomy, 112 Precession, explained, 186 Prize, for invention of chronometer, 8 Ptolemaic theory of universe, 56 Ptolemy, writes concerning Hipparchus, 39 Railroad time, explained, 127 Refraction, atmospheric, explained, 193 "Regulator," the jeweller's clock, 114 Ring-nebulæ, 31 Rings, of Saturn, see Saturn's rings. Roberts, Andromeda nebula, 28 Rotation, of Earth, 136, 162, 171, 184 of Saturn, 150 Royal Astronomer, his duties, 2 Royal Observatory, Greenwich, 124 Greenwich, Bradley's observations, 219 Naples, latitude observations, 139 Rutherfurd, cluster photography, 99 invents photographic apparatus, 93 pioneer in photography, 90 stellar parallax, 94 Sagredus, character in Galileo's Dialogue, 55 Salusbury, Galileo's translator, 50, 54 Salviati, character in Galileo's Dialogue, 55 Samoa, its date, 126 SATURN'S RINGS, 140 analogy to planetoids, 147 announced by Huygens, 142 observed with spectroscope, 147 shown to be double by Cassini, 144 structure and stability, 145 Scales, of heliometer, 158 Scorpio, constellation, temporary star in, 39 Semi-lenses of heliometer, 155 Sextant, how used, 4 Sicily, latitude station in, 139 _Sidereus Nuncius_, published by Galileo, 52 Simplicio, character in Galileo's Dialogue, 55 Sirius, brightest star, 205 Size of Moon, measured, 166 _Société de l'Optique_, 177 Solar parallax, see Sun's distance. physics, by photography, 109 system, stability of, 210