40 PHILOSOPHICAL TRANSACTIONS. [aNNO 1770. 



several bodies, and the jar too, charged positively, they all equally contracted 

 positive electricity by the discharge. 



In this state of the experiments, he had no idea of the possibility of the lateral 

 spark, not communicating electricity to the insulated body ; but he imagined that 

 the kind of electricity communicated depended on some circumstance in the dis- 

 position of the apparatus, that he was not sufficiently aware of. At length 

 recollecting, that this last experiment resembled, in some respects, that curious 

 one of Professor Richman, mentioned in the History of Electricity, p. 272, in 

 which it appeared, that when the coating of either side of a plate of glass com- 

 municated with the ground, the opposite electricity of the other side was more 

 vigorous ; he was satisfied that the negative electricity of the bodies that formed 

 the circuit in the imperfect discharge, was produced by the greater difficulty with 

 which the outside of the jar was supplied, than the inside was discharged ; so 

 that the outside was comparatively in a state of insulation, and therefore would 

 communicate negative electricity to all bodies within its reach. And from this he 

 was led to conclude, that, provided the jar was insulated, and the inside was 

 made to part with its electricity with more difficulty than the outside received it, 

 the bodies that formed the circuit would contract positive electricity ; and the 

 result answered exactly his expectations. He also concluded, that, making the 

 interruption in the middle of the circuit, since, in this case, the inside would 

 give, and the outside receive, with equal difficulty, the bodies in the circuit, 

 placed between the place of interruption and the inside of the jar, would be 

 charged positively ; and those placed between the place of interruption and the 

 outside, would be charged negatively ; and this also was verified by experiment. 

 In this state of things. Dr. P. found that he could give the insulated circuit 

 what kind of electricity he pleased, provided there was any kind of interruption 

 in some part of the circuit ; and conjecturing that the electricity of bodies 

 placed near the circuit would be the same with that of the bodies that com- 

 posed it, he sometimes placed the rod that supported the pith balls near the cir- 

 cuit, and sometimes introduced it into the circuit ; and found, that, in both 

 cases, it contracted the same electricity. This tended to confirm him in the 

 supposition, that the lateral explosion was always attended with a giving or re- 

 ceiving of electricity, according to the nature of the circuit, and the place 

 where it was situated ; and he again overlooked the disproportion between the 

 cause and the effect. 



Presently after this, it occurred to him, that what may be called the redun- 

 dant electricity of the outside or inside of the jar, separates from that which is 

 in the glass, and constitutes the charge, must have some concern in this event ; 

 and the supposition was verified by fact. For insulating a jar, charged posi- 

 tively, he observed, that when he touched the outside coating last (as is com- 



