Index. 313 



of, which have been adopted ; the day, 4 to 14 the 

 month and the year, 14, 15 cause of the difference be- 

 tween mean and solar, 5. 



Tin, when oxidized, ii. 228 chemical properties of, 252. 



Tornadoes, what, i. gl. 



Torpedo, nature of the shock communicated by the, i. 



127- 



Torricellian experiment, i. 67. 



Tourmalin, electrical phenomena exhibited by the stone 



called, i. 12?. 



Trade winds explained, i. 85. 353. 

 Transits of Venus in the years 176! and l/(j() : important 



points ascertained by means of them, i. 301 to 303. 

 Transparency and opakeness, the principles of, i. 142. 



143. 



Transparent, reason why objects appear, i. 137- 142. 

 Trine, meaning of the term, i. 269. 

 Twilight explained, ii.- 12 to 14. 

 Tychonic system of the universe, i. 255. 



Unformed stars, i. 26l. 



Universe, lecture on the system of, i. 250. See System. 



Uranus. See Georgium Sidus. 



t rea, nature of, ii. 288. 



V. 



Valencia, principle of this instrument, i. 4g. 



Vapour, nature of, i. 93 its formation is one of the general 

 effects of heat, ii. 74 how to compare the weight of 

 steam or vapour with that of water, 75 the vaporific or 

 boiling point differs widely in different bodies, and is re- 

 markably influenced by mechanical pressure, 76 the 

 sensible heat is not the immediate cause of the conver- 

 sion of a fluid into vapour, 78 explanation of the pro- 

 cesses of evaporation, distillation, and sublimation, 81 

 operation of heat on animal and vegetable substance?, 

 82. 



Vegetable acids considered, ii. 163 to 168. 



Vegetable substances, chemical lecture on them, ii, 2/4 to 

 290. 

 VOL. ii. p 



