Helmholtz, Hermann Ludwig Ferdinand. A German scientist. Born in Potsdam, 1821, became professor of physiology at Heidelberg, 1858. Helmholtz ranked among the ablest physicists of his time. Helmholtz wrote many valuable works on physiology and the relations of physical forces. Invented the ophthalmoscope, an instrument for the examination of the inner structures of the eye. Helmholtz died in 1894.