Leyden jar

Leyden jar, simplest and earliest form of capacitor, a device for storing electric charge, developed at the University of Leiden, Holland, in the 18th century. It consists of a glass jar coated inside and out with metal foil, and a conducting rod that passes through the jar's insulated stopper to connect with the inner foil. The jar is usually charged from an electrostatic generator. The device is now little used outside the classroom.