Helmholtz, Hermann Ludwig Ferdinand von (1821–1894),
German physicist and physiologist. Helmholtz made fundamental contributions to physiology, optics, electrodynamics, and meteorology. He is best known for his statement of the conservation of energy, which he presented in 1847. He invented the ophthalmoscope in 1851, and he determined the mechanisms of focusing in the eye and of the motion of the eyeballs to give single vision. In 1852 he revived the theory of color vision that Young had first postulated in 1801—only to refute it. In 1858 he reversed his position, amending Young's original theory and becoming its foremost advocate. He also examined the structure and function of the organs and bones of the ear and developed the theory that harmonics are determinants of musical tone.