A large version of the Lane discharging electrometers for use with English-type plate electrical machines. The spark gap between the prime conductor and this electrometer can be accurately measured by a vernier and micrometer screw. The instrument has been restored and the glass support replaced by one of aluminum painted red. Originally, it may have been on a longer support and used with one of the two large Nairne machines (inv. 2736 - inv. 2739).

Timothy Lane described this discharging electrometer in 1766. He used it to determine the charge given to a Leyden jar by counting the number of sparks it received from the electrometer set at a constant gap. The instrument became popular in electrotherapy and was used to limit the power of the electrical discharge. Provenance: Lorraine collections.