The German physicist and physiologist Hermann Ludwig Ferdinand von Helmholtz (1821-1894) made the first mathematical analysis of the principle of the conservation of energy and invented the ophthalmoscope. He also investigated the physics of tone and color perception.

Born on August 31, 1821, in Potsdam, Hermann von Helmholtz was the eldest of six children of August Helmholtz, a teacher of philosophy and classics in the local gymnasium, and Caroline Penne Helmholtz, a descendant of the family which took prominent part in the founding of Pennsylvania. At the age of 17 he entered the Friedrich Wilhelm Institute as a scholarship student of medicine. Happily for science, Helmholtz had the genius to absorb medical and physiological training with the mind of a physicist. A great help in this respect was a teacher of his at the institute, Johannes Müller, the foremost German physiologist at that time, who insisted on carrying as...