Galvanometer string, brass, in wooden case, made by Cambridge Instrument Co., English, 1921
A galvanometer measures small electric currents. It is sometimes used during physiological experiments studying muscle contractions. Electrodes placed upon the body pick up minute electrical impulses. These cause a string within the galvanometer to move. Movement is recorded photographically to make a tracing. The galvanometer is one of the earliest instruments used to detect and record electrical activity in the heart. It forms the basis of electrocardiograph machines.