He found, in fact, that when gold-leaf which had been electrified by contact with excited glass was brought near to an excited piece of copal,[1] an attraction was manifested between them. "I had expected," he writes, "quite the opposite effect, since, according to my reasoning, the copal and gold-leaf, which both electrified, should have repelled each other." Proceeding with his experiments he found that the gold-leaf, when electrified and repelled by glass, was attracted by all electrified resinous substances, and that when repelled by the latter it was attracted by the glass. “We see, then," he continues, "that there are two electricities of a totally different nature — namely, that of transparent solids, such as glass, crystal, &e., and that of bituminous or resinous bodies, such as amber, copal, sealing-wax, &e. Each of them repels bodies which have contracted an electricity of the same nature as its own, and attracts those whose electricity is of the contrary nature. We see even that bodies which are not themselves electrics can acquire either of these electricities, and that then their effects are similar to those of the bodies which have communicated it to them."
To the two kinds of electricity whose existence was thus demonstrated, du Fay gave the names vitreous and resinous, by which they have ever since been known.
An interest in electrical experiments seems to have spread from du Fay to other members of the Court circle of Louis XV; and from 1745 onwards the Memoirs of the Academy contain a series of papers on the subject by the Abbé Jean-Antoine Nollet (b. 1700, d. 1770), afterwards preceptor in natural philosophy to the Royal Family. Nollet attributed electric phenomena to the movement in opposite directions of two currents of a fluid, "very subtle and inflammable," which he supposed to be present in all bodies under all circumstances.[2] When all electric is excited by friction, part of this fluid escapes from its pores, forming an effluent stream; and this loss is repaired by an
