272 New Outlines bf Chemical Philosophy. 



Indeed, the Professor himself seems to have had some doubt* 

 respecting the results of his experiments ; for he observes, that 

 *' the reader avIio is at all conversant with electrical experi- 

 ments, will be sensible that these experiments are delicate, re- 

 quiring the greatest dryness of air, and every attention to pre- 

 vent the dissipation of electricity during the performance. This, 

 by changing the state of the conductors and electrometers, will 

 frecjuently occasion irregularities. The electrometers are most 

 apt to change in this respect, it being scarcely possible to make 

 them perfectly smooth, and free from sharp angles. It may 

 therefore hajipen, tiiat when the conductors have affected them 

 for some time, by the action of the disturbing electric, the re- 

 moval of this electric will not cause the electrometers to hang 

 perpendicular ; they will often be attracted by the conductors, and 

 often repelled"'"." Now it is evident, from these irregularities, 

 that the Professor's experinrents are very far from being con- 

 clusive. 



Mr. Bonnet's electrometer has also been used to prove that 

 electricity by induction is not permanent, but vanishes as soon 

 as the exciting cause is removed. But this is still a more im- 

 perfect instmment for this purpose than the Professor's short 

 conductors. For when an excited surface is brought near the 

 cap of this instrument, without producing a spark, the element 

 contained in it, of the same kind as that possessed by the ex- 

 cited surface, is repelled from it, through the gold-leaves and 

 tinfoil, into the earth. And as soon as the exciting surface i.« 

 removed, an equal portion of the same element, as that which 

 was repelled from the cap, returns into it again from the earth, 

 restores the equilibrium, and all electrical signs vanish, there 

 being a free communication between the cap and the earth. 



The conductor I use in making ex])eriments on inducted elec- 

 'tricity consists of a brass rod 12 inches in length, a quarter of an 

 inch thick, with a brass ball one inch in diameter screwed upon 

 each end. This is mounted upon a glass rod 14 inches in 

 length and two-tenths of an inch in diameter. Now, as elec- 

 tricity is carrieil off from the surfaces of bodies by the air, or 

 the conducting particles that float in that fluid, the less surface 

 any body has, the more perfectly it will insulate : consequently 

 a glass rod of two-tenths of an inch in diameter is 25 timet 

 more perfect than another rod of the same leiigth of one inch 

 in diameter ; for as 4 is to lOl), so is 1 to 25 ; the surfaces of 

 cylinders of the same length being to one another, as the squares 

 tif their diameters. 



In a former paper I gave an account of some experiments 

 * Ency. Crit. Sup. vol. ii. p. 5T3. 



made 



