520 



PHYSICAL SCIENCES. 



TRADE. 



186, 187 ; changed by compression, 

 3 89 ; heat polarized by, 265 ; elec- 

 tricity communicated to, 284. 

 Trade winds, friction of, not affecting 

 the earth's velocity, 72 ; action on 

 the general motion of the sea, 100 ; 

 system of, accounting for atmo- 

 spheric anomalies, 120 ; theory 

 of their origin, phenomena con- 

 nected with, 122, 123; becoming 

 monsoons, 124. 



Transits of Venus, 52, 53. 



, two consecutive, of any star, a 



measure of time, 83. 



Transmission of radiant heat, 258, 

 262 ; of electricity, 284, 285 ; of 

 voltaic electricity, 298 ; molecular 

 structure affecting, 303 ; method 

 of, determining the influence of 

 electric currents, 317 ; of gravity, 

 an unsolved question, 355 ; pro- 

 bable agent, 356 ; medium of, in 

 space, 424. 



Transparent bodies, temperature of, 

 unaffected by the sun's rays, 227. 



Trees, number of species of forest, 

 found in America and Europe, 252. 



Tribes, apparently distinct, of the 

 human race, 255. 



Triple stars, 395 ; periods of revolu- 

 tion in, 400. 



Tropical year, change in its length, 

 80 ; period of, 83 ; difficulty of 

 adjusting its estimation, 85. 



revolution of the major axis of 



the solar ellipse, its period, 86. 



vegetation, the luxuriance of, 



248. 



Tuileries, clock in the, showing deci- 

 mal time, 84. 



Twilight, caused by refraction, 154; 

 effect of reflection, 158. 



Tyndall, Professor, his experiments 

 proving diamagnetic polarity, 348 ; 

 on magnetic action in crystals, 349. 



UNDULATIONS, theory of, 99 ; of the 

 atmosphere, 121, 122 ; of the 

 waves of sound, 129, 130; inter- 

 vals produced by interference, 139 ; 

 giving musical notes, 142, 143 ; 

 sympathetic, 147, 149 ; of the 



VALZ. 



luminous ether, 169, 170; in re- 

 fraction and reflection, 177 ; pro- 

 ducing fluorescence, 197 ; different, 

 in light and sound, 199, 200 ; con- 

 stituting a sunbeam, 223 ; heat 

 propagated by, 267 ; of light, evolu- 

 tion of latent force in extinguished, 

 279, 280 ; of natural forces identi- 

 cal, 281. 



Undulatory theory of light, 168-170 ; 

 law of motion affecting, 176, 177 ; 

 phenomena proving, 198 ; objection, 

 from the different action of light 

 and sound, refuted, 199 ; proving 

 the existence of the ethereal medium, 

 358 ; acceleration in comet's mo- 

 tion proving, 367. 



theory, experiments determin- 

 ing in favour of, 200, 201 ; final 

 and decisive experiment, 202 ; of 

 heat, 267. 



Unison, note in, 142. 



United States, astronomical observa- 

 tions made in, 371, 373. 



Uranium, phosphorescent property of, 

 296 ; peculiar luminous properties 

 of, 296. 



Uranus, effect of reciprocal attraction 

 between Neptune and, 22 ; periods 

 of the revolutions of his satellites, 

 33 ; distance from the sun, 54 ; 

 astronomical tables of, 60 ; disco- 

 very suggested by his perturbations, 

 61 ; observations on, leading to 

 Neptune's discovery, 62 ; sun's in- 

 fluence in, 225 ; action of, on Hal- 

 ley's comet, 363 ; appearance of the 

 sun to, 380, 381 ; comets in his 

 orbit, 381, 382. 



Ursa Major, periodic time of a double 

 star in, 398; nebulous region of, 417. 



Utah, deserts of, causing monsoons, 

 124. 



VACUUM produced by shell-fish, 117 ; 

 existing in the air, 118. 



Valz, M., telescopic planet discovered 

 by, 21; comet observed by, 358; 

 observations on a comet's approach 

 to the sun, 364; cause assigned 

 by, for contraction in diameter of 

 comets, 377, 378. 



