508 



PHYSICAL SCIENCES. 



ORBITS. 



plane of the ecliptic, 18, 19 ; stable 

 and unstable in form, 21, 22; 

 influence of the ethereal medium 

 on, 22 ; principle facilitating ob- 

 servations on secular inequalities, 

 23, 24 ; revolutions of Saturn 

 compared with Jupiter, 25 ; peri- 

 odic inequality increased by secular 

 variations in their elements, 26 ; 

 comets revolving in, 381, 382 ; 

 cause of diversity in form of, 

 382. 



Orbits of satellites, forms of Jupiter's, 

 27 ; their inclinations, 28 ; in- 

 clinations of Saturn's, 32 ; positions 

 of Uranus's, 33 ; forms of data in 

 computing a planet's place in the 

 heavens, 59. 



Orinoco, the cataracts of the, heard 

 by day and by night, 135 ; area 

 occupied by forests on, 243. 



Orion, the Milky Way between An- 

 tinous and, 385, 386 ; position of, 

 390 ; variable star in, 393, 394 ; 

 multiple system in, 395 ; nebula 

 in, 408. 



Oersted, Professor, discovery of, sug- 

 gesting the theory of electro-mag- 

 netism, 312 ; science founding the 

 reputation of, 316. 



Oscillations, wide-spreading, produced 

 by gravitation, 2 ; mechanical 

 principle affecting small, 11 ; of 

 the sines and cosines of circular 

 arcs, 20 ; invariable plane whence 

 they may be estimated, 24 ; of the 

 pendulum retarded, 32 ; of the 

 pendulum, experiments founded on, 

 -50, 51 ; experiments testing the 

 earth's density, 57 ; a measure of 

 time, 83 ; produced by tides, 95, 

 96 ; instruments measuring atmo- 

 spheric, 113; barometer affected 

 by periodic atmospheric, 120, 122 ; 

 of ears of corn, 129, 130; pro- 

 ducing musical notes, 140-142 ; 

 instances of forced sympathetic, 

 148 ; causing vicissitudes in cli- 

 mates, 247 ; of the pendulum, dis- 

 turbed by effects of temperature, 

 272 ; measuring variation of elec- 

 trical intensity, 287. 



PARAMAGNETISM. 



Otaheite, transit of Venus observed 

 at, 53. 



Otto, M., motions of the heavenly 

 bodies observed by, 405. 



Oxidation of metals, electricity de- 

 veloped by, 298 ; by the Voltaic- 

 discharge on polished silver, 305. 



Oxides decomposed by electricity, 

 307 ; alkalies resolved into metal- 

 lic, 307. 



Oxygen, in crystals, 109 ; proportion 

 of, in water and carbonic oxide, 

 111 ; in the atmosphere, 117 ; 

 chemical combination with, evolving 

 light and heat, 270 ; action of 

 electricity on, 284 ; electricity 

 afforded by combination of metals 

 with, 298 ; spectrum from, 303 ; 

 separated from water by electricity, 

 307 ; paramagnetic, 344. 



Ozone, produced by electricity. 284. 



PACIFIC Ocean, mean depth of, 77 ; 

 course of tidal waves down, 93 ; 

 mean depth of, 96 ; currents, 100. 



PadorbDrn, fulgorites from, 293. 



Pallas, inclination of its orbit to the 

 ecliptic, 10 ; diameter of, 21 ; astro- 

 nomical tables, 63 ; ellipticity of 

 its orbit compared with the terres- 

 trial, 74 ; height of its atmosphere, 

 226 ; comet revolving between the 

 orbits of Mercury and, 367. 



Pan's pipes, vibrations in the air pass- 

 ing over, 142. 



Parabolic motion, ratio of forces pro- 

 curing, 382. 



Parallax of the sun, circumstance 

 favourable to its correction, 21. 



of an object defined, 43. 



, definition, mode of ascertaining, 



52 ; distances computed from, 5'2- 

 54 ; calculation from the moon's 

 horizontal, 55. 



of fixed stars, 387-390. 



of meteors, 421, 422. 



Paramagnetic substances, 335, 336. 



Paranragnetism defined, 335 ; sub- 

 stances it is resident in, 336 ; modes 

 of imparting, ib. ; a dual power, ib. ; 

 imparted by induction, 337 ; law 

 of its intensity, 338 ; a property of 



