Leyden jar

A Leyden jar, or Leiden jar, is a device that "stores" static electricity between two electrodes on the inside and outside of a glass jar. A Leyden jar typically consists of a glass jar with metal foil cemented to the inside and the outside surfaces, and a metal terminal projecting vertically through the jar lid to make contact with the inner foil. It was the original form of a capacitor (originally known as a "condenser").

It was invented independently by German cleric Ewald Georg von Kleist on 11 October 1745 and by Dutch scientist Pieter van Musschenbroek of Leiden (Leyden) in 1745–1746. The invention was named after the city.

The Leyden jar was used to conduct many early experiments in electricity, and its discovery was of fundamental importance in the study of electrostatics. The Leyden jar was the first means of storing an electric charge which then could be discharged at the experimenter's will. Leyden jars are still used in education to demonstrate the principles of electrostatics.

The Ancient Greeks already knew that pieces of amber could attract lightweight particles after being rubbed. The amber becomes electrified by triboelectric effect, mechanical separation of charge in a dielectric. The Greek word for amber is ηλεκτρον ("elektron") and is the origin of the word "electricity".

Around 1650, Otto von Guericke built a crude electrostatic generator: a sulphur ball that rotated on a shaft. When Guericke held his hand against the ball and turned the shaft quickly, a static electric charge built up. This experiment inspired the development of several forms of "friction machines", that greatly helped in the study of electricity.

The Leyden jar was effectively discovered independently by two parties: German deacon Ewald Georg von Kleist, who made the first discovery and Dutch scientists Pieter van Musschenbroek and Andreas Cunaeus who figured out how it worked only when held in the hand.

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