One of the most versatile scientists who ever lived, Hermann von Helmholtz was born in Potsdam, Germany, in 1821, the son of a "Gymnasium" (high school) teacher. From an early age he wanted to be a physicist, but his family could not afford the money required for his education. Instead, his father persuaded him to take up medicine, since his son's education as a physician would be subsidized by the state on the condition that he serve as a doctor in the Prussian army after he received his degree. Helmholtz attended the Institute for Medicine and Surgery in Berlin from 1838 to 1842 and fulfilled his obligation as an army surgeon from 1843 to 1848. His real interest, however, was always research; even in the army barracks he set up a small laboratory for research in physiology and physics.

On July 23, 1847, Helmholtz presented a paper on the...