Hermann von Helmholtz (1821-1894). 19th century engraving of the German physiologist and physicist Hermann Ludwig Ferdinand von Helmholtz. Helmholtz studied medicine and made careful studies of the ear and the eye and worked on acoustic theories. He invented the ophthalmoscope and the ophthalmometer. In thermodynamics, he formulated a form of the law of the conservation of energy. He also produced vortex theorems in fluid dynamics, and the Helmholtz differential equation in mathematical physics is named after him. From Weltall und Menscheit (Universe and Humanity), by Hans Kraemer (ca. 1880).