Hermann Ludwig Ferdinand von Helmholtz (1821-1894) was a German physician and polymath. Trained in physiology, Helmholtz wrote on many topics, ranging from theoretical physics, to the age of the Earth, to the origin of the solar system. As a physiologist and psychologist he is remembered for his mathematics of the eye, theories of vision, ideas on the visual perception of space, color vision research, and on the sensation of tone, perception of sound, and empiricism. As a physicist for his theories on the conservation of energy, work in electrodynamics, chemical thermodynamics, and on a mechanical foundation of thermodynamics. As a philosopher for his philosophy of science, ideas on the relation between the laws of perception and the laws of nature, the science of esthetics, and ideas on the civilizing power of science. He died in 1894 at the age of 73.