Hermann Helmholtz was one of the few scientists to master two disciplines: medicine and physics. He conducted breakthrough research on the nervous system, as well as the functions of the eye and ear. In physics, he is recognized (along with two other scientists) as the author of the concept of conservation of energy.

Helmholtz was born into a poor but scholarly family; his father was an instructor of philosophy and literature at a gymnasium in his hometown of Potsdam, Germany. At home, his father taught him Latin, Greek, French, Italian, Hebrew, and Arabic, as well as the philosophical ideas of Immanuel Kant and J. G. Fichte (who was a friend of the family). With this background, Helmholtz entered school with a wide perspective. Though he expressed an interest in the sciences, his father could not afford to send him to a university; instead, he was persuaded to study...