The battery contains 35 jars (seven rows of five). Of these, 15 jars are original and 20 are reproductions. (Diamond-shaped marks on the sides of the jars indicate the replacements.) Each jar is covered with foil to a height of 9 inches and has a wooden cap from which contact wires project within. The Leyden jar was developed in 1745-47 by scientist Pieter van Musschenbroeck of the University of Leyden (today Leiden) in the Netherlands. A Leyden jar builds and stores electricity. The parts of a Leyden jar are: 1.) a cylinder made of an insulating material like glass or plastic, lined inside and out with metal foil; 2.) water or other conducting material within the jar; and 3.) a metal rod or wire that passes through the cork that seals the bottle. When an electrical charge is given to the jar, the charge passes along the rod and is held within the insulated vessel until the energy is released by the touching of a conducting element to the ends of the rods or wires (closing the circuit). Franklin first used a battery of jars in 1747, and is considered to be the originator of this method of increasing the electrical charge that could be produced by a Leyden jar.
Believed to have been willed by Franklin to Hopkinson