More sensitive instrument as leaf deﬂection is unaffected by air currents or by charges residing on the case. Reacts only to charges which are intentionally brought near or put on them. Comprised of a box made of aluminium with two transparent glass windows to shut out air currents and a plated metal support rod entering from the top through a polyethylene insulator. Two leaves of thin aluminium foil are suspended from the support rod. Supplied with three pairs of aluminium leaves.