310 Index. 



Semipellucid bodies, principle of, i. 211. 



Sensible horizon, the, 263. 



Shafts in mines, cause of the opposite currents of air down 

 in summer and winter, ii. ll/. 



Shock, electric, explained, i. 102. 10?. 



Sideral time, difference between and solar, i. 279. 



Signs of the zodiac, i. 25Q present difference between 

 their nominal and real places, 274. 



Silica, or flint, chemical account of, considered as one of 

 the kinds of earths, ii. 186 to 1QI. 



Silver proved not to be a fixed metal, ii. 82, 83 chemical 

 properties of, 246. 



Simple substances in chemistry, list of the, ii. 246. 



Sirocco, wind so called, i. <jO. 



Sky, blue colour of the, accounted for, i. 212. 



Snow, phenomenon of, i. 4 its formation explained, 

 g5 (] O es not contain a salt, ii. 5Q mannerand degree 

 in which it keeps the ground warm, 03. 



Soap, its nature and composition, ii. 146. 222. 



Soda, its nature and properties, ii. 140 to 142. 



Solar phosphori, nature of the, i. 138. 



Solar system, lectures on. See Sun, Planets, Comets, and 

 Earth. 



Solders, how formed, ii. 237- 



Solution, some of its principal laws, ii. 98 description of 

 vessels used in this chemical process, 111. 



Sound, rate at which it travels, i. 13/3. 



Specific gravity, explanation of this phrase, i. 16 prin- 

 ciple of the tables of specific gravities how com- 

 puted, 43, 44 the specific gravity of bodies differs with 

 the degree of heat, ii. 6l variation of, on the mixture 

 of metals, 237,238. 



Spectacles, invention of, i. 18Q principle of those proper 

 for short-sighted persons,l6l. 187 for the weak-sighted, 



187. 



Spirit of wine (highly rectified) affords more than its own 

 weight of water by combustion, ii. 85. 



Spirits, best mode of ascertaining the strength of, ii. 213. 



Spots on the sun's disc, their number and magnitude, i. 

 280 conjecture concerning them, 281 discovery pro- 

 duced by means of them, ib. 



Springs on the tops of mountains accounted for, i. 3Q 

 principle of intermittent springs, 52. 



Steatites, nature and use of, ii. 1Q4. 



Stalactites, how formed, ii. 162. 



