The physician Hermann von Helmholtz, born in Potsdam, was, on his mother’s side, a descendent of William Penn, founder of Pennsylvania. His contributions to science—which included physiology, optics, electrodynamics, and meteorology— were numerous.

His doctoral thesis, begun in 1842, was on the connection between nerve fibres and nerve cells and he graduated from the Medical School in 1843. His demonstration in isolated preparations that muscles are the main source of animal heat, led him to his best known discovery, the law of conservation of energy and his paper in 1847 Über die Erhaltung der Kraft (on the Conservation of Force). In 1850 he became the first to measure the velocity of nerve impulses in the …