Lane discharging electrometer with sliding electrode secured to a Leyden jar by means of a brass ring, ensuring electrical contact with the outer tin-foil coating. The jar rests on an insulated support consisting of a small glass pillar with a wooden base. The spark gap between the electrode of the electrometer and that of the Leyden jar gives an indication of the quantity of electricity collected in the jar. The instrument was often used in electrical therapies. In such cases, it was also called "bottiglia medica" (medical bottle). Provenance: Lorraine collections.