Frictional electrical machine with ground (roughened) glass disk to generate a negative charge instead of the usual positive charge. One of a set of four machines (inv. 2688 - inv. 2689 - inv. 2686) used to demonstrate the effects of different materials on the polarity of the generated charge, positive or negative. The brass prime conductor, supported by a glass pillar, has two curved arms, each terminating in a concave disk with sharp points (the collectors). These end in close proximity to the surface of the glass disk. The amount of charge is controlled by the Lane discharging electrometer with vernier scale on its wooden support. Nearly all the machines of this type seen in European collections are English-made, usually from London. Provenance: Lorraine collections.