More sensitive instrument as leaf deï¬ection 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.