312 Index. 



used for ascertaining the sun's horizontal parallax 2Q8. 

 302 tables of the mean distances of the primary planets 

 from the sun and of their revolutions, 304, '305 the sun's 

 influence on the tides, (lecture xxii.) 342, et seq. 

 his eclipses explained, ii. 22 to 28 his rays used as a 

 method of producing heat for chemical purposes, 113. 



Syphon fountain, the, i. 40 principle of the instrument, 

 i. 50, 51 experiments with it, 51, o2 natural syphons, 

 52. 



Syringe, the condensing, i. 79- 



System of the universe, lecture on, i. 250 opinions of the 

 ancient philosophers on this suhject, 252 the Ptole- 

 mean system, 253 the Copernican, 254 theTyconic, 

 255 the stars, planetary and fixed, 25() constellations^ 

 258 unformed stars, 26 1 the milky-way, 262. 



T. 



Talc, or mica, definition of, ii. 192, 103. 



Tan, chemical remarks on, ii. 223. 278, 279. 



Tantalus's cup, experiment of, i. 51. 



Tartaric acid, nature and properties of, ii. 1(54, 165. 



Telescope, invention of the, i. 189 description of its dif- 

 ferent kinds j the dioptric or refracting telescope, 193 

 the achromatic, 196 the reflecting, ib. the Gregorian, 

 197 the Newtonian, 198 Dr. Herschel's great tele- 

 scope, 198. 



Terminations, chemical, ous, ite, ic, and at, distinctions 

 of, ii. 43. 168 uret, 232. 



Thaw, explanation how it is so slow in its operation, ii. 

 70. 



Thunder and lightning, phaenomenon of, i. 4 explana- 

 tion of the phenomenon of, 114 Dr. Franklin's experi- 

 ment, by which he brought lightning down from the 

 heavens, 115 signs of thunder storms, 117 safest 

 situations during them, and method of calculating the 

 distance of the cloud, 118 description and explanation 

 of the conductors fixed to buildings, 1 19. 



Tides, phaenomena of, i. 5 lecture on, 343 ; their daily, 

 monthly, and annual period, 344, 345 Newton's theory 

 of, 346 explanation of their principal phenomena, 

 349. 



Time, lecture on the divisions of, ii. 1 different measures 



