INDEX. 



507 



NON-CONDUCTORS. 



volution, 37 ; secular inequality 

 affecting, 38 ; influence of, on 

 eclipses, 39 ; cause of their rapid 

 motion, 55 ; points of rest on a 

 vibrating string, 141 ; in the vi- 

 brations of an undulating column 

 of air, 142 ; in vibrations of solids, 

 147. 



Non-conductors of electricity, 284, 

 285. 



Non-electrics, 285. 



North Atlantic, the, winds in, 124. 



Polar Ocean, tide in the, 94. 



Norway, course of the tidal wave to, 

 94. 



Notes in music, 142, 143. 



Nubecula, Major and Minor, 417, 

 418. 



Nucleus, of Halley's comet, changes in 

 its aspect, 364 ; disappearance of, 

 in Encke's, 369 ; division, in Biela's, 

 369, 370 ; diaphanous, 373 ; so- 

 lidity of, tested, 374; of a spiral 

 nebula, 409. 



Nuremburp;, observations on a comet 

 from, 370. 



Nutations produced by the moon's 

 nearness to the earth, 7 ; in Ju- 

 piter's equator, 29 ; in the planet- 

 ary axes, 66 ; effect of, on the pole 

 of the equator, longitudes and lati- 

 tudes altered by, 81. 



Nysa, nearness of its orbit to the 

 earth, 21. 



OAKS, range of, near the equator, 

 250. 



Occultation, central, by Halley's 

 comet, 364 ; geographical position 

 ascertained by, 384 ; prospective, 

 by a sun of a Centauri, 400. 



Occultations of stars, 42, 43. 



Ocean, the, density and mean depth 

 of, 51 ; mean density, compared 

 with the earth's, 77 ; its form in 

 equilibrio, when revolving round 

 an axis, 92 ; solar and lunar attrac- 

 tion disturbing its equilibrium, ib. ; 

 inequalities in periodic motions, 

 93 ; motions of the tidal wave in, 

 95 ; stability of its equilibrium, 

 100 ; circulation of currents in, 



ORBITS. 



ib. ; stratum of constant tempera- 

 ture in, 101 ; zones of, ib. ; de- 

 crease and increase of temperature 

 with depth, 231^ absorption and 

 radiation of heat by, 242 ; electri- 

 city evolved from, 291. 



Oceans of light and heat, processes 

 producing, 225. 



Ochotzk, the sea of, depression of the 

 barometer observed in, 120. 



October, 1832, position of Saturn's 

 rings in, 67. 



Olbers, M., computations for a comet 

 by, 367 ; period of his comet, 

 370 ; comet of 1811 observed by, 

 374. 



Opaque bodies, mode in which heat is 

 developed in, 227. 



Ophiuchi 70, anomalies in the mo- 

 tions of, 400. 



Ophiuchus, clusters of the Milky Way 

 between the Shield and, 387 ; new 

 star disappearing from, 393. 



Optic axis, the, of crystals, 183 ; 

 phenomena exhibited by transmis- 

 sion of a polarized ray along, 187, 

 188 ; affected by compression, 189. 



Orbit, the, of the earth, attraction 

 intensified by its diminished ex- 

 centricity, 37 ; excentricity of, 

 affecting temperature, 74, 75 ; 

 crossed by comets, 368. 



of the moon, force ruling, 4 ; 



its excentricity, 34; changes in, 

 35 ; its inclination to the plane of 

 the ecliptic, 79. 



of a nebula, 415. 



of the solar system,. 405, 406. 



Orbits of comets, subject to variation, 

 361; examples, 361-363; pros- 

 pective changes in, 369, 370 ; of 

 Donati's, 379 ; forces determining 

 their forms, 382, 383. 



of double stars, 396-400. 



of planets, force regulating a 



planet's velocity in, 8 ; measure- 

 ment of their excentricity, 9 ; seven 

 elements of, determining their po- 

 sition in space, 10 ; unequal move- 

 ments in, 15 ; variation from 

 elliptical to circular, 17 ; secular 

 variations of, in inclination to the 

 Z 2 



