"The process called condensation of electricity consists in increasing the capacity of a conductor by bringing near it another conductor connected with earth. The two conductors are usually thin plates or sheets of metal, placed parallel to one another, with a larger plate of non-conducting material between them" (Deschanel 1891,606). "A condenser is an apparatus for condensing a large quantity of electricity on a comparatively small surface. The form may vary considerably, but in all cases consists essentially of two insulated conductors, separated by a non-conductor, and the working depends on the action of induction" (Ganot 1890,737). Condensers are now called capacitors, and the insulating materials are called dielectrics.
The original condenser was the Leyden Jar (108-111). It consists of a glass bottle with metal foil inside and out, the foil layers being the conductors, and the glass the insulating material. The jar is charged by connecting one of the coatings (as the foil layers are called) with the ground, and the other with the source of electricity. Turner (1983,189) records that the true inventor of the jar was probably the German experimenter, Ewald Georg von Kleist (c1700-1748) in 1745. But the jar is called after the Dutch town where Pieter van Musschenbroek (1692-1761) found, in early 1746, that an enormous shock was received when a glass jar containing water was electrified. Gillispie (1981,VII,403) records that von Kleist was interested in the ignition of spirits by sparks. He placed a nail in a "narrow-necked medicine glass" containing alcohol. He was quite unprepared for the shock he received when he grasped the nail after touching it to his electrical machine. This only happened when he held the bottle in his hand. By holding the jar, he grounded it, transforming the nail into the positive coating of a condenser. McLaughlin (1955,614-8) describes von Kleist as "Bishop of Pomerania".

105 Callan Condensers
106 Aepinus Variable Condenser
110 Leyden Jar

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Dip Needles / Balances