stringgalvanometer

The string galvanometer, often associated with Willem Einthoven, is an early instrument used to measure very small electrical currents, notably for recording the electrocardiogram (ECG). Developed in the early 20th century, it was the standard device for cardiac electrical activity before the advent of modern electronic recorders.

Principle and design: A thin, taut filament or string is suspended within a strong magnetic field. When an electric current passes through the filament, the Lorentz force causes the string to deflect laterally. The amount of deflection is proportional to the current, and an optical system translates this movement into a graphical trace on a recording surface, such as smoked paper or a photographic plate. The apparatus amplifies minute bioelectric signals so they can be observed and analyzed.

Construction and operation: The device comprises a very fine conductive string under high tension, a magnet assembly to provide the magnetic field, and an illumination/recording setup to visualize the string’s movement. Leads from the patient carry the heart’s electrical signals to the string, producing a deflection that is captured as a continuous waveform over time, yielding the characteristic ECG trace.

Impact and legacy: The string galvanometer was instrumental in the early clinical development of electrocardiography and helped establish standard ECG lead concepts and waveform interpretation. Although highly sensitive, it required careful maintenance and was eventually supplanted by more compact and robust electronic recording methods and, later, digital ECG systems.