604 PHILOSOPHICAL TRANSACTIONS. [aNNO l76g. 



kept a part of the same quantity exposed in a similar manner : but he could per- 

 ceive no difference between them after several days. 



fa The track, of an electrical explosion on the surface of the cabbage-leaf, being 

 so well defined, suggested an experiment to ascertain whether there was any sen- 

 sible momentum in the electric fluid, when it is rushing with violence from one 

 side of a battery to the other. For this purpose he made the explosion pass over 

 the leaves when they were cut in right and acute angles ; so that the shortest 

 path, from the inside to the outside of the battery, was to turn close at the 

 angle ; and observed that it was not diverted from its course, in the least degree, 

 by the rapidity of its own motion^ but that it had turned exactly at the angle, 

 and kept as close to the opposite side, as if the motion had begun at the angle. 

 The electric matter had however been evidently attracted by the veins of the 

 cabbage-leaf, having pursued them a little way, at least having sensibly affected 

 them, wherever it met with them in its passage. 



This experiment suggested another, intended to determine whether the force of 

 an explosion was at all diminished by being diverted from a right-lined course, 

 and made to turn in a great number of angles. To do this, he first found, by a 

 great number of trials, what length of a small iron wire he was able to melt 

 with a battery of about 20 square feet, in the middle of a circuit of about 3 

 yards of brass wire, considerably thicker than the iron, and stretched in two 

 right lines, suspended on silken strings. The length of the iron wire, melted in 

 these circumstances, was about 3 inches. He then took the same brass wire, 

 and fixing pins into a board of baked wood, twisted it about them, making it 

 turn in a very great number of acute angles ; and he put 3 inches of the same 

 iron wire in the middle of this crooked circuit, that he had done in the straight 

 one ; so that the electric matter in the explosion was obliged to make a great 

 number of turns at acute angles, before it could come to the iron wire ; but he 

 always found that the same length of iron wire was melted in these circum- 

 stances as in the other, and not the least difference was perceived in the force. 

 But though the form of the wire through which an explosion passed, made no 

 difference in its force, he found a very remarkable difference occasioned by the 

 length of the circuit in wires of the same thickness ; and which surprised him 

 very much. 



To ascertain the practicability of firing mines by electrical explosions. Dr. P. 

 took Qi'l yards of small brass wire (but so thick, however, that he could not have 

 melted the least part of it by the force of any battery he had ever constructed), 

 and extending it along a dry boarded floor, with a small piece of iron wire, and a 

 cartridge of gunpowder about it, in the place that was most remote from the 

 battery ; he found that, on the discharge, the wire was not melted, nor the gun- 

 powder exploded ; also the report was very faint. In other circumstances, a 



