480 



PHYSICAL SCIENCES. 



Andes, the, proportion of, to the , 

 earth's mass, 6 ; increasing rarity 

 of the air experienced in ascending, 

 118. 



Andromeda, nebula in, 413 ; nebulous 

 region of, 417. 



Angstrom, the electric spark defined 

 by, 303. 



Animals, specific diversity of, laws re- 

 gulating their distribution, 254, 255. 



Annual equation, the, of the moon, 

 35,36. 



variations in mean values of the 



magnetic elements, 343. 



Annular nebulae, 409 ; in the northern 

 hemisphere, 410, 411. 



Antarctic Ocean, tidal wave rising in, 

 93 ; period of its passage to the 

 Thames, 94 ; depth of the stratum 

 of constant temperature in, 101 ; 

 depression of the barometer observed 

 in, 120. 



Antilles Islands, hurricanes beginning 

 at, 126. 



Antinori, Cav., experiments of, in elec- 

 tricity, 333. 



Antinous, comet observed in the con- 

 stellation of, 372 ; the Milky Way 

 between Orion and, 386. 



Antithesis, the general character of 

 magnetism, 339. 



Aphelion of a planet's path defined, 16. 



Apogee, solar, its coincidence with the 

 solstices, 86, 87. 



April, 1833, disappearance of Saturn's 

 rings, 67 ; apparent and mean time 

 coinciding in, 84. 



Apsides of an axis defined, 9 ; direct, 

 variable motion of, 14 ; cause of 

 their advance, or recession, 16. 



Apures, the mission of the, Humboldt's 

 observations on sound at, 135. 



Aquaeous vapour, proportion of, in the 

 atmosphere, 117. 



Ara, nebula in, 414. 



Arabian Gulf, the, monsoons blowing 

 over, 124. 



Arabs, the, their observations on 

 planetary irregularities, 26 ; lunar 

 eclipses observed by, 38 ; their di- 

 vision of time, 85 ; the pendulum 

 used as a measure of time by, 90. 



ASSYRIANS. 



Arago, Francois, experiment by, in 

 proof of the undulatory theory of 

 light, 200 ; decisive experiment 

 suggested by, 202 ; observations in 

 photography, 213; observations on 

 the moon's atmosphere, 226 ; in- 

 crease of temperature below the 

 earth's surface calculated by, 230 ; 

 slow communication of temperature 

 from the earth, observed, 244; 

 source of magnetism discovered, 

 330 ; theory of his magnetic ex- 

 periments, 332 ; divergent flames 

 of a comet described by, 364 ; his 

 treatise on comets, 368 ; nature of 

 comet's light determined by, 380, 

 381 ; numbers of comets computed, 

 381, 382 ; remark of, on fixed 

 stars, 405. 



Arc, the Voltaic, 303-305. 



Arcet, M.d', vibration of fibres of the 

 retina according to, 178. 



Archer, Scott, stimulus given to pho- 

 tography by, 207. 



Arcs of the meridian, mode of mea- 

 suring, 47. 



Arcturus, comet bearing comparison 

 with, 379 ; rank of, 384. 



Areas, described by the radii vectores 

 of planets, a test of disturbing forces, 

 10; unequable description of, 15. 



Argelander, M., period of a comet cal- 

 culated by, 370 ; his mode of esti- 

 mating distance of fixed stars, 389 ; 

 periods of fluctuation in stars com- 

 puted by, 390, 391 ; sun's motion 

 proved, 405. 



Argentine preparations in photography, 

 chemical energy varying with, 207, 

 208 ; changes effected by washing 

 with alkalies, 210,211. 



Argo, variable star in, 393. 



Aries, season of the sun's entrance 

 into, in Hipparchus' age, 80. 



Arseniate of soda, its crystals, 109. 



Artesian wells, mode of sinking, origin 

 of the name, 230. 



Artie Sea, depth of the zone of con- 

 stant temperature, 101. 



. regions, vegetation found in, 249. 



Asia, indigenous productions of, 249. 



Assyrians, the, division of time by, 85. 



