Index. 307 



Pendulum, principle of its construction, i. 219 experi- 

 ments with the, at different places, 238. 



Pendulums, why made of two kinds of metals, ii. 60. 



Percussion, a method of producing heat, ii. 112. 



Periaecii, the, i. 266. 



Phases of the moon explained, i. 313, 314. 



Philosophical fire works, how to make, ii. 201. 



Phenomenon, meaning of the word, i. 78. 



Phosphori, solar, account of, i. 137- 



Phosphoric acid, nature and properties of, ii. 107. 



Phosphorus, a simple combustible substance, ii. 36 che- 

 mical account of it, 50. 201 to 208. 28g Dr. Thomp- 

 son's process of preparing, 202. 



Pisa, safety of the leaning, tower of, i. 230. 



Plane mirrors, or speculums, what, i. 144 manner in 

 which they reflect, 165 to 168. 



Planets, forms of the-orbjts of, and respective speed of 

 the, i. 270 lecture on the primary ones, 286 nature 

 of these bodies, arid laws of their motion, 225. 286 

 the superior and inferior planets, 288 tables of the 

 diameters, magnitude, density, and solidity of the sun 

 and the primary planets, 2yO to 2Q4 table of the in- 

 clination of the orbits of the primary planets from the 

 plane of the ecliptic, 295 method of measuring the 

 distance of the heavenly bodies from the earth ; the 

 horizontal parallax of the moon and of the sun ascer- 

 tained, 290. 300 tables of the mean distance of the 

 primary planets from the sun, and of their revolutions, 

 304, 305 planets which have been lately discovered, 

 305 particulars concerning the different primary pla- 

 nets ; Mercury, ib. Venus, Mars, Ceres, Pallas, Juno, 

 Vesta, and Jupiter, 306 ; Saturn, and the Georgium 

 Sidus, 307 lecture on the secondary planets, 312 of 

 the moon, ib. the satellites of Jupiter, Saturn, and 

 the Georgium Sidus, 325. 



Planetary motions, foundation of the system of, i. 225. 



Plants, bitter, and other principles of, ii. 279, 280, 281 

 alkalies, earths, and metals, found in, 284. 



Platinum, chemical properties of this metal, ii. 246. 



Pneumatics, lecture on, i.6l composition of atmospheric 

 air, ib. different classes of elastic fluids, 58 weight of 

 air, proved by experiment, 62 its gravity varies at dif- 

 ferent altitudes, 63 experiments to prove the pressure 

 of the atmosphere, 65, 66 principle of the baiomeier a 



