614 ELECTRICAL CONDENSERS. 



Third, the apparatus is again arranged as at C 

 in fig. 322, without discharging the lower disc, and 

 positive electricity is communicated to the upper disc 

 while a proof-plane is kept in contact with the lower 

 disc. When the electricity of the proof- plane is tested 

 it is found to be positive. 



The electricity communicated to the upper disc 

 effects a separation of the two electricities of the lower 

 disc. The electricity of the same kind in our experi- 

 ments positive is repelled, and passes in the first ex- 

 periment into the ground, in the last experiment into 

 the proof-plane. The electricity of the opposite kind 

 in our case negative is bound by the electricity of the 

 upper disc, but when first the conducting wire and 

 then the upper disc and the insulating plate are re- 

 moved, this electricity becomes free and may be tested 

 by the electroscope. The two electricities, viz., that 

 communicated to the upper disc and that of opposite 

 kind induced by it in the lower disc, exert mutual at- 

 traction, but are prevented from uniting by the inter- 

 vening insulating layer. Their mutual attraction over- 

 comes the tendency which they have to escape, that is, 

 their tension, and under the circumstances of these ex- 

 periments it becomes thus possible to accumulate much 

 more electricity within a given small space than could 

 be done without taking advantage of the attraction 

 which one kind of electricity exerts upon the opposite 

 kind. 



That each of the two electricities is really bound 

 may be proved by charging the upper disc as in the 

 first experiment and afterwards removing the conduct- 

 ing wire. If now first the upper and then the lower 



