Leyden jar, 1746.
© Science Museum / Science & Society Picture Library
The Leyden jar was an early capacitor, or a device for storing an electric charge. It was devised in 1746 by Pieter van Muschenbroek, at Leyden in the Netherlands. It is simply a glas jar with metal foil coatings inside and out. The inner coating can be connected to a source electric charge by a chain or other conductor. When one end of a discharger is placed in contact with the outer foil, and the other end is brought near the ball on top of the charged jar, a spark pases between the ball and the discharger. The Leyden jar is interesting because it produced much more powerful electric shocks, or sparks, than anything before it.