Leyden jar

The Leyden jar, or Leiden jar, is a device that "stores" static electricity between two electrodes on the inside and outside of a jar. It was invented independently by German cleric Ewald Georg vonKleist on 11th October 1744 and by Dutch scientist Pieter van Musschenbroek of Leiden (Leyden) in 1745—1746[1]. The invention was named for this city. It was the original form of the capacitor. TheLeyden jar was used to conduct many early experiments in electricity, and its discovery was of fundamental importance in the study of electricity. Previously, researchers had to resort to insulatedconductors of large dimensions to store charge. The Leyden jar provided a much more compact alternative.
A typical design consists of a glass jar with conducting metal foil coating the inner and outersurfaces. The foil coatings stop short of the mouth of the jar, to prevent the charge from arcing between the foils. A rod electrode projects through the mouth of the jar, electrically connected by somemeans (usually a chain) to the inner foil, to allow it to be charged. The jar is charged by an electrostatic generator, or other source of electric charge, connected to the inner electrode while theouter foil is grounded. The inner and outer surfaces of the jar store equal but opposite charges.
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Cross-section diagram from about 1900 showing construction.
The original form of thedevice was just a glass bottle partially filled with water, with a metal wire passing through a cork closing it. The role of the outer plate was provided by the hand of the experimenter. Soon it wasfound that it was better to coat the exterior of the jar with metal foil (Watson, 1746), leaving the (accidentally) impure water inside acting as a conductor, connected by a chain or wire to an externalterminal, a sphere to avoid losses by corona discharge. It was initially believed that the charge was stored in the water. Benjamin Franklin investigated the Leyden jar, and concluded that the...