636

INDEX.

nature, 255; annular form established byHuyghens , ib.; its position determined,258; discovered to be double, 259; sus-picion of many divisions on the, 260;its magnitude determined,^.; its thick-ness inconsiderable, 261; discovery ofits rotatory motion, 262; time of rota-tion determined, ib. ; physical observa-tions of the ring, 263; not bounded byparallel planes, 264; encompassed by anatmosphere, ib. ; visibility of the unen-lightened side, 265; hypothesis of thephysical origin of the, 267. ( See Appendix .)

Saturn , Satellites of—Researches of Bessel,142; satellites discovered by Huyghens ,267; discovery of four satellites byCassini, 268, 269; discovery of two newsatellites by Herschel ; an eighth satellitediscovered simultaneously by Lassell andBond, 271; variable brightness of thefifth satellite, ib.; conclusion hence de-duced, 272.

Scheiner—observes the solar spots, 214;controversy with Galileo respecting theirreal nature, 214; first remarked that thenucleus and penumbras are separatedby a well-defined boundary, ib.; deter-mines the time of the sun’s rotation, ib.;employs coloured glass in observations ofthe sun, 228; constructs charts of themoon’s surface, 229; first who executed arefracting telescope, 525.

Schroeter—discovers a twilight in the moon,233; his researches on the physical consti-tution of Mercury, 233; determines thetime of rotation of Venus , 234; maintainsthat high mountains exist on the surfaceof Venus , 235; discovers that Venus issurrounded by an atmosphere, ib. ; deter-mines the magnitude of Jupiter ’s satel-lites, 250; observations of Saturn ’s ring,262.

Simpson—computes the motion of the lunarapogee, 46; researches on the theory ofrefraction, 328.

Solar Spots—observed by several persons,213; their motions on the sun’s disk,215; conclusion hence derived, ib.; de-tailed description of their appearance, 217;relative quantities of light emitted by thedifferent parts of which they are com-posed, ib. ; their mode of formation,^.;some are destitute of penumbrse, ih.; pe-numbrse without a nucleus, ib.; greatmagnitude of the spots, 218; rapid changeswhich they undergo, ib.; constantly ob-served near the solar equator, ib.; solarfaculae, ib.; first seen by Galileo , ib.;their immense extent, 219; they are gene-rally brightest on the sun’s limb, ib.;their invariable appearance m the regionof the spots, ib.; discovery of luculi, ib.;seen over the entire disk of the sun, ib.;various explanations of the real nature ofthe spots, ib. ; Scheiner, ib.; La Hire, ib.;

Derham, 220; theory of Dr. Wilson, ib.;objections urged against it, 221; theoryof Bode, ib.; Sir W. Herschel , 223; Sir J. Herschel , 225; how observed by variousastronomers, 227.

Snell—discovers the law of refraction, 321.

South—Observations of double stars, 560.

Stars —- Immense multitude of the, 538;stars which have disappeared from theheavens, ib.; new stars, 539; variablestars, 540; researches on the relativebrightness of the stars, 542; principlesupon which their visibility depends, 543;various attempts to determine their ap-parent diameters, 544; researches on theirparallax, 546; their proper motions dis-covered, 553.

Stars, Double—early observations of, 558;observations of Sir William Herschel ,559; speculations of Michell on the theoryof, ib.; remark of Dr. Hornsby,' ib.; phy-sical theory of, first established upon ob-servation by Sir William Herschel , 560;recent researches of astronomers on thesubject, 560-563.

Struve, F. W. G.—Determines the magni-tudes of Jupiter ’s satellites, 250; assignsthe dimensions of Saturn ’s ring, 260;discovers the ring to be eccentric, 262;determines the maximum value of aber-ration, 340; appointed director of theObservatory of Pulkowa, 505; researcheson the parallax of the fixed stars, 550;determines the parallax of a Lyrce, 551;observations of double stars, 561; re-searches on the physical constitution ofthe Milky Way , 577; speculations on theextinction of light in its passage throughspace, 578.

Struve, Otto—Researches on the mass ofNeptune , 287; investigates the quantityand laws of precession, 320; researcheson the motion of the solar system in space,556.

Taylor, Brooke—investigates the mathema-tical theory of refraction, 327.

Telescope—early notions of, 515; Bacon ,ib.; Digges, 516; Battista Porta, ib .; DeDominis, ib.; first executed in Holland,517; various accounts of its origin, ib.;researches of Van Swinden on the subject,518; Galileo constructs a telescope, 520;his mode of ascertaining the magnifyingpower, 521; he was not an independentinventor, 522; remarks upon the Dutchtelescopes, 523; telescopes introduced intoEngland, 524; refracting telescope ex-plained by Kepler , 525; first executed byScheiner, ib.; first employed in astro-nomical observations by Gascoigne, ib.;improvements in its construction, ib.;Huyghens , ib.; Campani, 526; Auzout,ib.; reflecting telescope, ib.; first exe-cuted by Newton, 527; improvements in