INDEX.

635

tions, 55; Poisson ’s researches on thevariation of the mean distance, 109;theory of the variation of elements, 110;researches on the secular variations of theinclinations, 116.

Planets, (Jltra-zodiacal—researches on theirperturbations, 132; circumstances con-nected with their discovery, 238; dis-covery of Geres, 239; Pallas, ib.; Juno,240 ; Yesta, 241; speculations of Olbers on their origin, 240; researches of La-grange on the subject, 241; discovery ofAstrea, 242; Hebe, ib.; Iris, 243 ; Flora,ib.; Metis , ib.; Hygeia ,ib. (SeeAppendix.)

Plantamour—Researches on Biela’s comet,136.

Plateau—Researches on the irradiation oflight, 355.

Plutarch—Statement respecting the luminousring seen during total eclipses of the sun,

377.

pond—succeeds Maskelyne at the Obser-vatory of Greenwich, 491; introduces thepractice of observing with two muralcircles, 493; controversy with Brinkleyon the parallax of the fixed stars, 550.

Pontecoulant—calculates the perturbations |of Halley’s comet, 137.

Poisson —his researches on the variations ofthe mean distances of the planets, 109;developes the method of the variation ofarbitrary constants, 112; researches on thelunar theory, 120; investigates the phy-sical libration of the moon, 142; researcheson the motion of the earth’s axis, 160.

Pound—calculates ecliptic tables in time ofthe first satellite of Jupiter, 81; measuresthe dimensions of Saturn ’s ring, 260.

Powell—Researches on the irradiation oflight, 356; explanation of the luminousring seen during total eclipses of thesun, 387; theory of the beads andthreads observed during annular eclipses,411; explanation of a phenomenon seenduring the transit of Mercury, 418.

Precession of the Equinoxes—Researches onits quantitative value, 318; erroneous de-termination of the annual value by Pto­ lemy , ib. ; conclusion hence deduced, ib .;its quantity determined by the Arabianastronomers, 319; modern evaluations,ib.; researches of Bessel, 320; OttoStruve, ib.

Prime Vertical Telescope—first employedby Roemer, 464.

Principia—Publication of the, 28; synopsisof its contents, 32.

Problem of Three Bodies—Solutions of the,obtained by various geometers, 44, 47.

Ptolemy —estimates the value of the solarparallax, 211; his erroneous evaluationof the quantity of precession, 318; firstpoints out the effects of atmospheric re-fraction, 321; describes the instrumentsused by the Greek astronomers, 436.

Reflecting Octant—first invented by Ne wton,482; reinvented by Hadley and Godfrey,ib.

Refraction, atmospheric—its influence onthe apparent position of a celestial bodyfirst recognised by Ptolemy , 321; firstapplied as a uranographical correction byTycho Brahe , ib.; table calculated byKepler , ib. ; law of refraction discoveredby Snell, ib. ; researches of Cassini, ib .;influence of temperature remarked byPicard, 323 ; researches of Newton, ib .;mathematical theory of, investigated byTaylor, 327; researches of Bouguer, 328;Simpson, ib.; influence of the pressure ofthe atmosphere pointed out by Halley,329; researches of Bradley, ib. ; Mayer,330 ; Lacaille, ib.; improvements in thetheory of, effected by Kramp, ib. ; re-searches of Laplace, 331; Brinkley, 332;Ivory, 333; researches of modern astro-nomers on the subject, 335; Bessel, ib.Repeating Circle—principle of the, sug-gested by Mayer, 488.

Right Ascension of a Star—how deter-mined by Tyclio Brahe, 443; method ofFlamsteed for effecting the 6ame object,472.

Robinson—Researches on the Irradiation ofLight, 353.

Roemer—invents the transit instrument,461; perceives the superior advantages ofinstruments composed of complete circles,463; invents the meridian circle, ib. ;prime vertical telescope, 464; methods ofadjustment practised by him, 464; con-structs an altitude and azimuth circle,465; equatorial instrument, 466; at-tempts to determine the parallax of thefixed stars, 548.

Rosse, Earl of—attains unrivalled excellencein the construction of reflecting telescopes,536 -; observations of nebulae, 569.Rumker—observes the comet of Encke atParamatta, 134; catalogue of stars, 512.

Saturn—long inequality of, 47; accountedfor by Laplace upon the principles of thetheory of gravitation, 59; determinationof its mass by Newton, 131; modernevaluations of the same element, ib.;bands on his disk discovered, 251; theyindicate a rotatory motion, ib.; time ofrotation determined, ib. ; discovered to bespheroidal, 252; value of the ellipticity* determined, ib. ; irregularity in the figureof, suspected by Herschel, ib.; figure de-monstrated by Bessel to be truly elliptical,253; surrounded by an atmosphere, ib.;appearances observed about the polar re-gions of, 254.

Saturn , Rings of—their condition of equi-librium investigated by Laplace, 76;early observations of Galileo , 254; im-perfect attempts to ascertain its real