- noun a historical form of electrostatic capacitor comprising a glass jar coated inside and outside with metal foil with a conducting rod passing through an insulated stopper
- An early type of capacitor usually utilized for demonstrations. It may consist, for instance, of a cylindrical glass jar which is covered on the inside and outside with aluminum foil. A brass rod extends through the jar's insulating lid, with a knob on the outer end of said rod, and a chain which makes contact with the inner foil surface affixed to the other end. A voltage is then applied to the knob, making the jar a capacitor in which the glass is the dielectric, and the foil conductors are the plates.