Willem Einthoven was a Dutch physiologist awarded the 1924 Nobel Prize for Physiology or Medicine for his invention of, and investigation of heart action with, the electrocardiograph (see electrocardiogram). He became professor at Leiden University in 1886. In 1903 he devised the string galvanometer, a single fine wire placed under tension in a magnetic field. Current passed through the wire causes a deflection which can be measured, for greater accuracy, by microscope. This galvanometer was sensitive enough for him to use it to record the electrical activity of the heart.