44 PHILOSOPHICAL TKANSACTIONS. [anNO 1770. 



imagined, might be owing to the obstruction which the electric fluid meets with 

 in passing even through metals ; which appears, by his former experiments, to 

 be much more considerable than was generally imagined. 



On the whole, this remarkable experiment seems to be made to the most 

 advantage in the following circumstances. Let the jar stand upon the table ; 

 let a thick brass rod, insulated, stand contiguous to the coating ; and, near the 

 extremity of this rod, place the body that is to receive the explosion. This body 

 must be 6 or 7 feet in length, and, perhaps, some inches in thickness, or be 

 connected with a body of those dimensions. Lastly, let the explosion be made 

 with the discharging rod resting on the table, close to a chain, the extremity of 

 which reaches within about an inch and a half of the coating of the jar. In 

 this case, the operator will hardly fail of getting a lateral explosion of an inch in 

 length ; which shall enter and leave the insulated body, without making any 

 sensible alteration in the electricity natural to it. 



With large jars, containing 3 or 4 square feet of coated glass, bearing a very 

 high charge. Dr. P. makes no doubt but that this experiment might be made to 

 much more advantage ; but, at the time that he was engaged in this investigation, 

 he happened not to have any such jar, and therefore only used one that contained 

 half a square foot of coated glass. If the interruption in the circuit, which is 

 almost necessary in these experiments, be made by introducing a length of chain 

 into it, rather than by making part of the explosion pass along the tube, there is 

 a medium in the length of chain, that answers better than either a longer or 

 a shorter circuit. In a long interrupted circuit, the electric matter seems to lose 

 the impetus which it discovers in a short one. In all these cases, the electric 

 charge seems to remain for a moment in the parts of the interrupted circuit ; 

 and therefore instantaneously rushes, in all directions as well towards bodies that 

 are not placed along its passage to the jar, as those that are ; but, when the 

 same charge occupies a larger circuit, it has more room to expand itself, and is 

 not so strongly impelled to desert it. He found, however, by repeated trials, 

 that when he made use of 3 yards of brass chain in the circuit, there was a 

 distance to which the lateral explosion would not reach. The same distance 

 it also would not reach, when the circuit consisted of only one brass rod; but it 

 reached it with great ease, when only half a yard of chain was used, even 

 without any other interruption in the circuit. But it reached to a much greater 

 distance, when the chain was very short, and the interruption was greater in 

 other respects. 



Dr. P. had imagined, that, since the body which had received the lateral 

 explosion, contained, for a moment, more than its natural quantity; that if it 

 were acutely pointed, some would escape, and that, on the return of the 

 explosion, the body would be exhausted; but he found no such effect, though he 



