o« Animal JLJeBncity. 309 



fome time in its place, and not to remove it till the moment 

 when the metals in contaft are removed and the machine 

 put in motion. To render the infulation complete, and 

 make the contaft of the metals immediate, without the leaft 

 moifture, which would be highly prejudicial, it will be pro- 

 per to place the apparatus in the fun. Half an hour, and 

 often lefs, will then be fufficient to obtain the required 

 eleftricity, &c. ; whereas, in other cafes, feveral hours are 

 neceflary before the defired refult can be obtained. A re- 

 prefentation of this experiment is exhibited by fig. %i, 32, 

 23 and 24, (Plate I.) LLL (fig. 21 and aa) are the three 

 brafs plates of the doubler; A the piece of filver which is 

 in contaA with one of thefe plates ; E the piece of tin 

 applied to the other plate, which is oppofite to the former j 

 *a the moift conductor, or chain of moift conductors 

 which form a communication with the pieces of metal. 

 When the filver, as in fig. 31, is in contaft with the ante- 

 rior moveable plate, it gives up to it a little of the eledlric 

 fluid, and the latter accumulates as much of it as poflible ; 

 confcqucntly the elcAricity of the plate becomes pofiiive, as 

 the fign + of the plate (hews : whereas the tin attrafts the 

 eleftric fluid from the correfponding fixed plate, which by 

 thefe means has negative eleftricity, as the fign ( — ) of the 

 plate indicates ; and it even communicates this eleftricity to 

 the other fixed plate, which therefore has the fign ( — ) alfo. 



In fig. 32, every thing is revcrfed : the moveable plate is 

 negatively eleftrified (— E), while the two fixed plates be- 

 come pofitive (-HE). 



Laftly, in the 23d and 24th figure, it is feen, that the tin 

 abftra6ts the eleftric fluid from the brafs plate with which 

 it is in contaft. This plate is therefore negatively elcftri- 

 ficd, or has — E ; and by the aftion of its atmofphere occa- 

 fions pofitive eleftriclty ( + E) in the other plate (landing 

 oi)pofite, which is in communication, either with the third 

 plate, as fig. 23, or, what is (lill better, with other con- 

 tluitors, a» fig. 24. Thefe oppofite elc6lricitics increafc af.. 

 X 3 tcrwards 



