CIRCUIT

, Electrical, denotes the course of the electric fluid from the charged surface of an electric body, to the opposite surface, into which the discharge is made. Some electricians at first apprehended, that the same particles of the electric fluid that were thrown on one side of the charged glass, actually made the whole circuit of the intervening conductors, and arrived at the opposite side: whereas Dr. Franklin's theory only requires, that the redundancy of electric matter on the charged surface should pass into those bodies which form that part of the circuit which is contiguous to it, driving forward that part of the fluid which they naturally possess; and that the desiciency of the exhausted surface should be supplied by the neighbouring conductors, which form the last part of the circuit. On this supposition, a vibrating motion is successively communicated through the whole length of the circuit.

Many attempts were made, both in France and England, at an early period in the practice of electricity, to ascertain the distance to which the electric shock might be carried, and the velocity of its motion. The French philosophers, at different times, caused it to pals through circuits of 900 and even 2000 toises, or about 2 English miles and a half; and they discharged the Leyden phial through a bason of water, whose surface | was equal to about one acre. M. Monier found that, in passing through an iron wire of 950 toises in length, it did not spend a quarter of a second; and that its motion was instantaneous through a wire of 1319 feet. In 1747, Dr. Watson, and other English philosophers, after many experiments of a similar kind, conveyed the electric matter through a circuit of 4 miles; and, from two several trials, they concluded that its passage is instantaneous. By all which doubtless is meant, that its motion is too rapid to be measured. Priestley's Hist. of Elect. vol. 1, pa. 128, 8vo edit.