PAGEAiry, Astronomer Royal,1Allis, photographs comet,101Andromeda nebula,28temporary star,28,29,45Apex, of solar motion, explained,221Aquila, constellation, temporary star in,40Arctic regions, position of pole in,194Argo, constellation, variable star in,205Association, international geodetic,139Asteroids, first discovery by Piazzi,59,106discovery by photography,64group of,63photography of, invented by Wolf,104Astronomer, royal,1working, description of,152Astronomer's Pole, the,184Astronomy, journalistic,176practical uses of,112Atmospheric refraction, explained,193Axis, of figure of the earth,136of rotation of the earth,136polar, of telescope,173Barnard, discovers satellite of Jupiter,51Bessel, measures Pleiades,15Bond, discovers crape ring of Saturn,144Bradley, observes at Greenwich,219Brahe, Tycho, his temporary star,40Bruce, endows polar photography,197Campbell, observes Pole-star,18Cape of Good Hope, observatory, photography at,101telescope,170,174Capriccio, Galileo's,55Cassini, shows Saturn's rings to be double,144Cassiopeia, temporary star in,40Celestial pole,184Central sun theory,223Centre of gravity,217Chart-room, on ship-board,5Chronometer, invention of,8Circle, meridian, explained,189Clerk Maxwell, discusses Saturn's rings,146Clock, affected by temperature,117affected by barometric pressure,117astronomical,115astronomical, how mounted,116astronomical, its dial,116error of, determined with transit,118jeweller's regulator,114of telescope,175Clusters of stars, photography of,98Columbia University Observatory, latitude observations,139polar photography,196Common, his reflecting telescope,32Confusion of dates, in Pacific Ocean,125Congress of Astronomers, Paris, 1887,102Constellations,162Control, "mouse," for photography,88Copernican theory of universe,53,56demonstration,94Corkscrew tunnels,220Crape ring of Saturn,144Cumulative effect, in photography,84Date, confusion of, in Pacific Ocean,125Date-line, international, explained,126Development of photograph,81Dial, of astronomical clock,116"Dialogue" of Galileo,53Differences of time, explained,121Directions, telescopic measurement of,21Directory of the heavens,103Distance, of light-source in photography,83of stars,94,106,158of Sun,67,97,106Donner, polar photography,195Double telescopes, for photography,86Earth, motions of its pole,131rotation of,136,162,171,184shape of,135Eclipses, photography of,109Elkin, measures Pleiades,15Equatorial telescope, explained,170Eros, discovered by Witt,66,105its importance,67Error of clock, determined by transit,118Exposure, length of, in photography,84Feldhausen, Herschel's observatory near Capetown,204Fiji Islands, their date,126Fixed polar telescope,197"Following" the stars,88,173Four-day cycle of pole-star,24France, outside time-zone system,129Fundamental longitude meridian,124Galileo,47and the Church,48discoveries of,49observes Saturn,141Galle, discovers Neptune,61Gauss, computes first asteroid orbit,60Gautier, Paris, constructs big telescope,179Geodetic Association, international,139Geography, maps, astronomical side of,112Geology, polar motion in,131Gill, photographs comet,100Gilliss, at Naval Observatory, Washington,169Goldsborough, at Naval Observatory, Washington,169Grande Lunette, Paris, 1900,176,180Gravitation,13in Pleiades,14,212law of, Newton's,212Gravity, centre of,217Greenwich, origin of longitudes,7,124time,7Groombridge, English astronomer,1Harrison, inventor of chronometer,8Head, of heliometer,156Heidelberg, photography at,104Heliometer,152head of,156how used,157principle of,154scales of,158semi-lenses of,155Helsingfors observatory, polar photography at,195Henry, measures Pleiades,11,17Hercules, constellation, solar motion toward,222Herschel, discovers apex of solar motion,221discovers Uranus,59,141John, the moon hoax,200Hipparchus, discovers precession,186early star-catalogue,21,39invents star magnitudes,91Huygens, announces rings of Saturn,142his logogriph,143Ice-cap, of Earth,131Index Librorum Prohibitorum,53International, date-line, explained,126geodetic association,139Inter-stellar motion, in clusters,98in Pleiades,14Islands of Pacific, their longitude and time,125Japan, latitude station in,139Jewellers' correct time,121Journalistic astronomy,176Jupiter's satellites, discovered by Galileo,50discovered by Barnard,51Keeler, observes Saturn's rings,140,147,150photographs nebulæ,32"Keyhole" nebula,205Lambert, determines longitude of Washington,168Laplace, discusses Saturn's rings,146nebular hypothesis,33stability of solar system,210Latitude, changes of,133,138definition of,134determining the,6Leverrier, predicts discovery of Neptune,61,142Lick Observatory, Keeler's observations,140Light, undulatory theory of,19,148Light-waves, measuring length of,20,149Logogriph, by Huygens,143Long-exposure photography,85Longitude, counted East and West,125determining,6determining by occultations,167effect on time differences,123explained,123of Washington, first determined,168Maclear, observes Eta Argus,205Magnitudes, stellar,91Manila, its time,127Maps, astronomical side of,112Meridian circle, explained,189Milky-way, poor in nebulæ,33Minor Planets, seeAsteroids.Moon, Hoax,199motion among stars,163mountains discovered by Galileo,49size of, measured,166Motion of moon,163Motionsof theEarth'sPole,131Mounting Great Telescopes,170Naked-eye nebulæ,28Naples, Royal Observatory, latitude observations,139Naval Observatory, Washington, noon signal,120Navigation,1before chronometers,3use of astronomy in,113Nebulæ,27Nebula, in Andromeda,28in Orion,30"keyhole",205Nebular, hypothesis,33structure in Pleiades,17Nebulous stars,31Negative, and positive, in photography,82Neptune, discovery predicted by Leverrier,61,142discovery by Galle,61Newcomb, fixes apex of solar motion,222Newton, law of gravitation,212longitude commission,8New York, its telegraphic time system,120Noon Signal, Washington,120Number, of nebulæ,31,33of temporary stars,38Nutation, explained,188Occultations,161explained,165Occultations, use of,166,167Orion nebula,30Pacific islands, their longitude and time,125Parallax, solar,67,106stellar,94,106measured with heliometer,158Paris, congress of astronomers, 1887,102exposition of 1900,176Periodic motion of earth's pole,133Perseus, constellation, temporary star in,46Philippine Islands, their time,127Photography, asteroid, invented by Wolf,104congress of astronomical,102cumulative effect of light,84distance of light-source,83double telescopes for,86general star-catalogue,102In Astronomy,81in discovery of asteroids,64,104in solar physics,109in spectroscopy,108length of exposure,84measuring-machine, Rutherfurd,93motion of telescope for,87"mouse" control of telescope,88of eclipses,109of inter-stellar motion,99Paris congress, 1877,102polar,191Rutherfurd pioneer in,90star-clusters,98star-distances measured by,94summarized,110wholesale methods in,103Piazzi, discovers first asteroid,59,106Pitkin, report to House of Representatives,168Planetary nebulæ,31Planet of 1898,58Planetoids, seeAsteroids.Planets known to ancients,58Pleiades,10gravitation among,212motion among,14,16,98nebular structure,17number visible,11Polar axis, of telescope,173Polar photography,191at Helsingfors,195Pole, celestial,184of the earth, motions of,131the Astronomer's,184Pole-Star,18as a binary,25as a triple,18,26change of,187its four-day cycle,24motion toward us,24Positive, and negative, in photography,82Potsdam, observatory, photographic star-catalogue,103Practical uses of astronomy,112Precession, explained,186Prize, for invention of chronometer,8Ptolemaic theory of universe,56Ptolemy, writes concerning Hipparchus,39Railroad time, explained,127Refraction, atmospheric, explained,193"Regulator," the jeweller's clock,114Ring-nebulæ,31Rings, of Saturn, seeSaturn's rings.Roberts, Andromeda nebula,28Rotation, of Earth,136,162,171,184of Saturn,150Royal Astronomer, his duties,2Royal Observatory, Greenwich,124Greenwich, Bradley's observations,219Naples, latitude observations,139Rutherfurd, cluster photography,99invents photographic apparatus,93pioneer in photography,90stellar parallax,94Sagredus, character in Galileo's Dialogue,55Salusbury, Galileo's translator,50,54Salviati, character in Galileo's Dialogue,55Samoa, its date,126Saturn's Rings,140analogy to planetoids,147announced by Huygens,142observed with spectroscope,147shown to be double by Cassini,144structure and stability,145Scales, of heliometer,158Scorpio, constellation, temporary star in,39Semi-lenses of heliometer,155Sextant, how used,4Sicily, latitude station in,139Sidereus Nuncius, published by Galileo,52Simplicio, character in Galileo's Dialogue,55Sirius, brightest star,205Size of Moon, measured,166Société de l'Optique,177Solar parallax, seeSun's distance.physics, by photography,109system, stability of,210Spectroscope, its use explained,147used on pole-star,19to observe Saturn's rings,147Spiral nebulæ,31Stability, of Saturn's rings,145of Solar System,210Standards, time, of the world,111table of,130"Standard" time, explained,127Star-catalogue, general photographic,102Star-clusters, photography of,98Star-distances94,106measured with heliometer,158Rutherfurd,94Star magnitudes,91Star-motion, toward us,21Star-tables, astronomical,118Stars, variable,42St Gothard railway, tunnels,220Sun, newspaper, the moon hoax,201Sun-Dial, How to Make a,69Sun's, Destination,210distance, compared with star distance,97measured with Eros,67,106motion, apex of,221Sun-spots, discovered by Galileo,49Systema Saturnium, Huygens,143Telescope, clock,175at Paris Exposition,176,180double, for photography,86equatorial, explained,170first used by Galileo,49motion of,87mounting great,170unmoving, for polar photography,197Temporary Stars,37in Andromeda nebula,28,29,45in Aquila,40in Cassiopeia,40in Perseus,46in Scorpio,39their number,38theory of,42Time, correct, determined astronomically,113differences between different places,121Time Standards of the World,111standards of the World, table of,130system, in New York,120zones, explained,128Trails, photographic,191Transit, for determining clock error,118Tycho Brahe, his temporary star,40Ulugh Beg, early star-catalogue,21Undulatory theory, of light,19,148Universe, theories of,34,53,56Uranus, discovered by Herschel,59,142Use of occultations,166,167Uses of astronomy, practical,112Variable stars,42in Argo,205Vega, future pole-star,187Visibility of stars, in day-time,191Vision, phenomenon of,20,149Washington, its longitude first determined,168Waves, explained,148of light,20,148Wilkes, at Naval Observatory, Washington,169Wilkins, imaginary voyage of,208Witt, discovers Eros,66,105Wolf, M, invents asteroid photography,104measures Pleiades,11World's time standards, table of,130Yale College, Pleiades measured at,15Zones, time, explained,128