Measuring small electric charges was not possible in the eighteenth century. Therefore, a trick was devised, that is increasing the charge to be measured using an instrument: the collector. First both side plates of this instrument are grounded and folded. At the same time, the central plate (the collector) is for a short time brought into contact with a charged object. Then the side plates are lowered. Thus an increased charge is induced on the central plate. The electrometer is able to measure this increased charge and will therefore show a deflection. This collector was devised by Tiberius Cavallo and was used for measuring atmospheric electricity. The instrument is part of a group of four instruments in this cabinet. They are all devised to increase a given minuscule charge, so that it can be measured [ 480, 481, 1147 and 1157].