VOL. LIX.] PHILOSOPHICAL TRANSACTIONS. 605 



charge of the same battery was able to melt more than Q inches of this iron 

 wire ; and this same cartridge was easily fired near the battery, connected with 

 shorter pieces of the same brass wire ; so that the diminution of force must have 

 been owing to the length of the circuit. 



In the place of this small brass wire. Dr. P. substituted an iron wire 4-th of 

 an inch thick, when about half an inch of the small iron wire was exploded ; so 

 that the force was not lessened so much in a circuit of the thick iron wire, as it 

 had been in one of the small brass wires. To judge how much of the force 

 might be lost by nearer circuits, consisting of less perfect conductors, he joined 

 the middle of the circuit made by the iron wire with water, in which both the 

 wires were immersed. The effect was, that the small iron wire was only made 

 red-hot, but not exploded as before. Being sensible how much depended on 

 avoiding lesser circuits, by which part of the fire of an explosion might return 

 to the battery, without reaching the extremity of the circuit, where he intended 

 the whole of its force to be exerted, in the remaining experiments, he insulated 

 half the circuit of iron wire. There was no occasion for insulating the whole 

 circuit; for if there was but one passage to, or from the middle of it, there 

 could be but one from, or to it. In this method it was easy to ascertain what 

 loss of force was occasioned by the length of the circuit, as every other circum- 

 stance was carefully excluded ; and it presently appeared to be very considerable ; 

 for though he could melt Q inches of the small iron wire at the distance of 15 

 yards from the battery ; when he tried 20 yards, he found that he was just able 

 to make 6 inches of it red-hot. The battery in these experiments was in the 

 house, and the wires of which the circuit consisted were conveyed by silken 

 strings into a garden adjoining to the house. 



Mentioning this loss of force occasioned by the length of the circuit in elec- 

 trical explosions to Dr. Franklin, he said that the same observations had occurred 

 to him, and that he had also been disappointed in an attempt to fire gunpowder 

 at a distance from his battery. Struck with this appearance. Dr. P. endeavoured 

 to ascertain the quantity of this obstruction, by trying what other courses the 

 electric fire would chuse preferably to a long metallic circuit. In the first place, 

 taking about a yard of the small brass wire, mentioned above, he disposed it in 

 the manner described below, connecting one of the ends with the outside of the 

 battery, and the other with the inside. In the first place, he brought the parts 

 near the two extremities into contact, and, on the discharge, found there had 

 been a fusion in that place, and that a great part of the fire had taken the 

 shorter circuit, though it had been obliged to quit the wire in one place, and 

 enter it again in another. Afterwards he removed these parts to a small distance 

 from one another, and, on the explosion, observed a strong spark pass between 

 them. Removing tliem to greater and greater distances, he found the explosion 



