Signedengraved in lid: Knott Boston
Inscribedon paint on side (paint is chipping off): Carnegie GC E740-A
FunctionLeyden jars were the earliest form of capacitor but were still common until the early twentieth century (such as this example). The jar accumulates electric charge when the metal foil outside is at a voltage different to the one of the brass rod and the foil inside of the jar that is connected to it with the chain.