Rudolf Julius Emanuel Clausius (1822-88), German mathematical physicist, who was one of the founders of the science of thermodynamics. He was born in Köslin (now Koszalin, Poland) and educated at the universities of Berlin and Halle. From 1855 until his death he was successively a professor at the Polytechnic Institute in Zürich and the universities of Würzburg and Bonn. Clausius was the first to enunciate (1850) the so-called second law of thermodynamics: Heat cannot of itself pass from a colder body to a hotter body. He was one of the first to apply the laws of thermodynamics, particularly the concept of entropy, to the theory of the steam engine. He also played an important part in the development of the kinetic theory of gases. His theory of electrolysis anticipated in part the ionic theory of the Swedish chemist Svante Arrhenius.