Contact Theory of Galvanism.. 211 



electrometrical apparatus constructed on different principles, 

 namely, that the intensity of the electricity of two heterogeneous 

 plates in contact is in the inverse ratio of the magnitude of their 

 surfaces or magnitude of conduction; consequently, if the super- 

 ficies of the electrometer be considerably larger than that of the 

 potassium, and moreover the former be not well insulated, 

 no result can be expected. In effect I could no longer ob- 

 tain those signs of electricity which I had previously recog- 

 nised with such complete certainty, if 1 held the potassium 

 in a dry insulating forceps and touched my electrometer with 

 the platinum wire of the potassium. I completely succeeded, 

 however, even with this fine experiment in the following 

 manner. I had an electrometer purposely made with the 

 smallest surface possible, consisting solely of a very thin and 

 short brass wire, which, as the axis of a surrounding gum 

 lac cylinder, traversed the perforated bottom of an inverted 

 drinking-glass, and from which within the glass was suspended 

 between the pole plates of the pile of the electrometer a very 

 small gold-leaf, 24 inches long, while the electricity could be 

 transferred to the prominent end of the brass without the 

 glass. Into the potassium ball was inserted a thin platinum 

 wire, as short as the convenience of transfer of the electricity 

 allowed, and the ball itself, for the purpose of increasing 

 its surface, was pressed between two copper plates which 

 had been soaked in petroleum, as smooth as was possible 

 without cutting the potassium ball with the platinum wire. 

 Thus the entire electrometer might have been somewhat about 

 double the size of the surfaces of the potassium*. 



With this arrangement I now repeated the former experi- 

 ments in the air, holding at times the potassium with the in- 

 sulating forceps, at times the platinum, while the other metal 

 was each time brought into connexion with the electroscope. 

 If clear, opposite divergence of the gold-leaf could in this 

 case be observed with the most complete certainty ; for this 

 arrangement, if the combination of potassium and platinum 

 was not insulated, proved to be much more sensitive than the 

 one previously employed, and gave without the condenser the 

 most evident divergences, (opposite by the opposite arrange- 

 ment,) which might easily be increased up to the striking of 

 the gold-leaf against the pole plates, if these were merely se- 

 parated so far from one another (7^ lin.) as was necessary for 

 the stability of the gold-leaf. 1 now placed the potassium 



* I endeavoured to unite several balls of potassium by pressure, but did 

 not succeed, either from the petroleum which remained attached to them, 

 or from the oxide which immediately formed at the surfaces of the fresh 

 sections. 



P2 



