Willem Einthoven (1860-1927) was a professor physiology at the University of Leiden. In 1924 he won the Nobel Prize in Medicine for his work on the electrocardiogram.
At the heart of this instrument was the extraordinarily sensitive instrument known as the string electrometer. This was a long, taut conducting filament of negligible mass that passed through a magnetic field. The slightest current would cause a deflection of the filament, and the motion could be recorded photographically. Because of the small mass of the filament it could respond to rapidly-occuring transient effects.
This demonstration of the galvanometer is in the apparatus collection of Case Western Reserve University in Cleveland, Ohio. It was locally made, and the magnet is missing.