A German physicist and physiologist, Hermann von Helmholtz made the first precise formulation of the principle of conservation of energy. During physiological studies of muscle action and animal heat, Helmholtz developed this idea as a result of studying the oxidation of food by animals. His formulation led to the first law of thermodynamics, which states that the total energy of a system and its surrounding remains constant even during a phase change. Helmholtz also contributed to the fields of hydrodynamics and electrodynamics, attempting to formulate a general unified theory. In addition, Helmholtz made significant discoveries in the physiology of vision and hearing. He invented the ophthalmoscope and promoted the three-color theory of vision to investigate color vision and color blindness. By the enormous breadth of his scientific contributions and the exactness of his work, Helmholtz dominated German science during the middle of the nineteenth century. He helped make Germany the focus of attention for the world's scientific community. Helmholtz and his students took classical mechanics to its limits, helping to set the stage for the revolution in physics at the beginning of the twentieth century, represented by quantum theory and the theory of relativity. This revolution was mainly carried out by German scientists, applying the rigorous mathematical and experimental standards set by Helmholtz.
