Leyden jar Earliest and simplest device for storing static electricity, developed c.1745 in Leyden, Holland. The original electrical condenser (capacitor), it consists of a foil-lined glass jar partly filled with water and closed with a cork through which protrudes a brass rod wired to the foil. To charge the jar, friction is applied to the tip of the rod.

Ley·den jar • n. an early form of capacitor consisting of a glass jar with layers of metal foil on the outside and inside.