A commutator is used for delivering or interrupting electricity in a circuit and for making it flow in one direction or the other.
Different kinds of commutators have been invented. The one on display here is a simplified version of the Ruhmkorff commutator which was one of the most common in the 19th and beginning of the 20th centuries.
It consists of a rectangular support of polished wood (18 cm x 11.5 cm) on which are fixed the rotating inverting device worked by means of a knob and four brass wire clamps, two for connection to the pile and two for connection of the device to be powered.