How does theLeyden jar work?

A Leyden jar is a device used to store static electricity. It consists of a glass jar coated inside and out with metal foil with a metal rod or wire passing through the lid to make contact with the inner foil. When a high voltage charge is applied to the inner foil via the rod, the charge is stored in the glass insulator until it is discharged through the outer foil, creating a spark.