English: A Leyden jar being discharged, from an 1878 science text. Discharger appliances with insulated handles like the one shown were used to discharge Leyden jars safely, because they could give nasty shocks. A Leyden jar consists of a glass jar with metal foil cemented to the inner and outer surfaces. The hooked electrode projecting from the mouth of the jar at top is in contact with the inner foil. The jar can be charged with electricity by grounding the outside foil and touching the terminal of an electrostatic machine to the electrode. To discharge it, the metal discharger is touched to the outer foil and the other end brought near the center electrode. A spark will jump between the two electrodes, and charge will flow from one foil to the other, neutralizing the charge on the foils