We now come to an epoch-making discovery--that of the condenser, or, in its conventional laboratory form, the Leyden jar. Professor Muschenbroeck, of the University of Leyden, was struck with the idea that it would be a good plan to try to prevent the dissipation of the electric charge by inclosing the conductor containing it in an insulating envelope. He therefore took a glass jar, partly filled it with water, and electrified the latter. His assistant, who was holding the bottle, accidentally touched the wire which made connection with the water, and received on the instant a shock much more violent than any that the electrical machine was capable of giving. This led to the discovery that as the charge of vitreous electricity had accumulated in the water, a corresponding charge of the opposite kind had gathered upon the outside of the glass and been "bound" there, as it is called, by the attraction exercised upon it by the charge on the inside. It had been enabled to get upon the glass by the fact of the assistant's hand having covered part of the surface of the latter, and, since he stood upon the ground, the electricity had quietly flowed from the latter up through his body to the outside surface of the glass.
The apparatus was quickly perfected by coating both the inside and outside of a jar with tin foil, applying the charge by means of a wire or chain to the inside coating and allowing the outer one to stand upon the earth or upon a conducting substance in electrical contact with the latter. The exaltation of spirit with which the discovery was hailed by the _savants_ appears to have been extraordinary--one student who took a discharge through his body being reported to state that he would not have missed the experience for a fabulous consideration, and that he would not repeat it if it were to save his life. In reality the advance was enormous; it gave a means for literally bottling up electricity in quantities previously unthought of. The prime conductor of an electrical machine could not retain any considerable quantity of electricity for the reason that, a certain small intensity of electrification having been reached, the addition operated to upset the balance, so to speak, and the electricity escaped by a sudden (disruptive) discharge, or spark, or by the brush discharge already alluded to. With the Leyden jar, however, as fast as electricity was supplied to the inside coating it became "bound" there by the charge of opposite sign accumulating on the outside, and the limit of capacity of the jar was simply one of strength of the glass: if too much electricity was supplied, the stress of mutual attraction between the two charges relieved itself by destroying the jar.