Leyden, << LY duhn, >> jar was one of the first devices used to store an electric charge. It was invented in Leiden (sometimes spelled Leyden), the Netherlands, in 1746. A Leyden jar is a glass jar that is sealed with a cork. Sheets of metal foil cover about half of the inside and outside of the Leyden jar. The metal foil conducts electricity, but the glass does not. A brass rod is inserted through the cork and brought in contact with the foil in the jar.
When the brass rod is connected to a source of electricity, current travels through the rod and charges the inner foil. Current cannot pass through the glass, but the foil on the outside becomes charged by induction if it is properly grounded (see Induction, Electric ). The outer foil has a charge opposite to the charge inside the jar. When the flow of current into the jar stops, a charge remains stored in the jar. If the inner layers of foil and outer layers of foil are then connected by a conductor, their opposite charges will cause a spark that discharges the jar.
