A galvanometer measures an electrical current by means of the electromagnetical properties of an induction coil and the Lorentz force. The instrument contains various coils with different numbers of windings (2, 50, 500) which can be enabled as required. The current can then be read from the scale centered in the main body of the instrument.
The instrument has levelling screws so that it can be adjusted in the horizontal plane. The precursor to the tangent galvanometer is the tangent bussole, which used a ring of plain copper instead of the induction coils.
The tangent galvanometer in our HistoLab is labelled "Philip Harris Ltd. Birmingham, England, No. 17890". This company provided measurement devices in the chemical and physical sciences for the british market throughout the 19th century.