INDEX.

037

its construction, 529; views of Newtonon chromatic aberration, 531; he pro-nounces any further improvement of therefracting telescope to be desperate, ib .;researches of Dollond on the dispersion oflight, ib.; constructs achromatic telescopes,532; instruments of this description pre-viously executed by More, 533; reflectingtelescopes of Herschel , ib. ; improve-ments in the construction of refractingtelescopes, 535; Gfuinand, ib.; Frauen-hofer, ib.; Reflecting telescopes, 536;Lord Rosse , ib.

Telescopic Sights—first employed by Gas-coigne, 454.

Tides—shewn by Newton to be a necessaryconsequence of the principle of gravita-tion, 26; researches of Euler , 71; Mac- laurin , ib.; Bernouilli, ib. ; Laplace, ib.;researches of Whewell, 162.

Transit Instrument—invented by Roemer,461.

Transit Observations—recorded in America by means of electro-magnetism, 506.

Transversals, Method of—invented, 442.

Uranus —early observations of, 164; tablescalculated by Delambre, 165; irregula-rities in the longitude of the planet, ib.;tables of Bouvard, ib.; impossibility ofreconciling the modern with the ancientobservations, ib. ; the existence of anexterior planet suspected, ib. ; radiusvector shewn to be erroneous, 167; theirregularities attract the attention of Bes-sel, ib,; researches of Adams on the samesubject, 168; inverse problem of pertur-bation, 169 ; results obtained by Adams,173; new tables calculated by EugeneBouvard, 174; they fail to account forthe irregularities of the planet, 175;theory of the planet investigated by Le Verrier , 175; the results obtained byhim are found to be incompatible withthe observations of the planet, 177; theresearches of Le Verrier on the hypothesisof a disturbing planet, 178 ; first resultswhich he obtained, 183; search for thenew planet undertaken by Prof. Challis,185; second investigation of Le Verrier ,187; final results obtained by him, 188;they are transmitted to the astronomersof Berlin, 191; discovery of the exteriorplanet by Dr. Galle, 192; account ofProf. Challis’ search for the planet, ib.;his observations had effectually securedit, 193; reflections on the comparativemerits of the two geometers who assignedthe position of the exterior planet, 197;discovered by Herschel , 272; first sup-

posed to be a comet, 273; difficultiesexperienced in determining its orbit, ib.;discovered to be a planet, 274; its appa-rent diameter measured, 275; elementsof its orbit determined, 277; suspectedto be spheroidal, ib.; determination of itsellipticity by Miidler, 278; suspected tobe encompassed by a ring, ib.

Uranus , Satellites of—Discovery of twosatellites by Herschel , 279; the elementsof their orbits determined, 280; orbitsfound to be almost perpendicular to theecliptic, 282; their motion found to beretrograde, ib.; discovery of four ad-ditional satellites, ib. ; physical observa-tions of the, 284; researches of Sir John Herschel , 285; Lamont, ib. ; observationsof Lassell, 286; Otto Struve, ib. (SeeAppendix .)

Valz—Speculations of, on the identity ofthe comets of Lexell and Faye, 139 ;suspects the existence of a planet beyondUranus , 166.

Variation of Elements—Method of the, in-vented by Euler , 49.

Venus—Perturbations of, investigated byLaplace, 126 ; long inequality discoveredby Airy, 127; mass of determined byvarious enquirers, ib. ; her phases dis-covered by Galileo , 233; her rotationround a fixed axis discovered, 234; vari-ous determinations of the time of rota-tion, 234, 235; mountains on her surface,ib.; atmosphere surrounding her, ib.

Venus , Transits of—Transit predicted byKepler, 415; transit of, 1639, observedby Horrocks and Crabtree, 421; physicalappearances noticed during the transits of1761 and 1769, 429.

Vernier—Invention of the, 446.

Wallis—prepares the writings of Horrocksfor publication, 423; suggests a methodfor determining the parallax of the fixedstars, 548.

Wargentin—his researches on the motionsof Jupiter ’s satellites, 83; observes thelunar eclipse of 1761, 413.

Whewell—Researches on the tides, 162.

W ilson, Dr.—his theory of the solar spots,220.

Wollaston—experimental researches on thelight of the stars, 547.

Wright—adopts the hypothesis of a centralsun, 558; theory of the Milky Way , 573.

Wrottesley—executes a catalogue of stars,513.

Zaeh, De—calculates tables of aberration andnutation, 343.