Hermann Ludwig Ferdinand von Helmholtz, German physicist and physiologist. Helmholtz studied medicine and graduated in 1842 at the Royal Medicochirurgical Institute of Berlin. He made careful studies of the ear and the eye. In 1851 Helmholtz invented the ophthalmoscope and the ophthalmometer: the former is used to study the eye's interior and the latter to measure the eye's curvature. His main achievement as a physicist was the formulation of the Law of the Conservation of Energy which he developed at the same time as, but independently from, the German physicist Mayer and the French physicist Joule.