English: A drawing of a Leyden jar a piece of antique physics apparatus used to store electric charge, from an antique physics book. Invented in 1745 by Pieter von Musschenbroek of Leiden, it was the first form of capacitor. It is sectioned through the center, to show construction. It consists of a glass jar with a layer of metal foil (B) cemented to the outside, and loose metal foil pieces (A) filling the inside. The stopper is pierced by a brass electrode (A'), which made contact with the inside foil, so the jar could be charged. In use, the outside of the jar was connected to ground, and the central electrode was attached to the terminal of an electrostatic machine. The machine charged the inside foil of the jar with a high voltage charge of static electricity, and the outside foil with an equal charge of the opposite polarity. if the outside foil and inner electrode were bridged with a metal wire, a large spark would jump, discharging the jar.