of square cm., distant cm., the expression
which is again a length.
Bodies constructed for holding an electric charge, that is, intended to condense electricity on their surfaces, are technically termed condensers. The first condenser used by physicists was the so-called "Leyden Jar" accidentally discovered by Musschenbroek (1692-1761), Professor of Physics in Leyden, Holland. In the eighteenth century electricity was considered a "fluid," and Musschenbroek attempted to collect some of this fluid in a glass filled with water. He held the glass in the hand, and electrified the water by a wire placed in the glass and projecting sufficiently far out so that he could touch the conductor of his frictional machine with the wire. When removing the glass and taking out the wire, he received an electric shock much more violent than he could obtain from his machine directly. In this case the water formed the inner conductor and the hand the outer shell, whilst the space between the two was filled by glass.
This form of condenser has become known under the name of Leyden Jar, and is used to this day by physicists. It consists
