Hermann Helmholtz (1821 - 1894) Germany
He extended Joule's results to include light, electricity and magnetism. Needed state aid in order to attend college. He had to study medicine because of the aid he received and also serve in the military. Received Ph.D. in 1843 and was a Professor of Physics and also Professor of Physiology during his career. (His students complained when he mixed physics in with his physiology classes.) In 1847 published a paper "On the Conservation of Force" which clearly stated the principle of conservation of energy.