This electrometer, devised by the Englishman Thomas Lane, is one of the earliest attempts to make frictional electricity measurable. The apparatus consists of a Leyden jar (the oldest type of capacitor) and a discharger with a micrometer. Martinus van Marum, the first director of Teylers Museum, used this instrument to compare the strength of different electrostatic generators. After the Leyden jar was charged by one of the electrostatic generators, he observed how large a distance the electric charge could bridge. The larger the distance between the sphere of the Leyden jar and the sphere of the electrometer, the more powerful the electrostatic generator. See also 553 (Instruments Room, cabinet III).