New slide-wire potentiometer
14 October 1932
The potentiometer is of a type commonly employed in telephony, in which a constant impedance is maintained, and the contacter is required to bridge between two resistances. The novel feature of the instrument lies in the contact, which consists of a phosphor-bronze ball, running in a rather coarse spiral groove cut in a cylinder which is rotated by the control knob. The ball makes contact with the two resistances, which are wound on cylindrical formers, and it is claimed that the combination of rolling and sliding motions provides for adequate cleaning of contacts, while giving little wear on the wire.