Clausius, Rudolf Julius Emanuel (ro͞o`dôlf yo͞o`lyo͝os āmä`no͞oĕl klou`zēo͝os), 1822–88, German mathematical physicist. A pioneer in the science of thermodynamics, he introduced the concept of entropy and restated the second law of thermodynamics: heat cannot of itself pass from a colder to a hotter body. He applied his researches on heat, electricity, and molecular physics to the development of the kinetic theory of gases and in formulating a theory of electrolysis wherein he states that electric forces are merely directing agents in the interchange of ions. A professor at the Polytechnic Institute, Zürich (1855–67), and at the universities of Würzburg (1867–69) and Bonn (from 1869), he wrote Die Potentialfunktion und das Potential (1859) and Die mechanische Wärmetheorie (1865–67; tr. The Mechanical Theory of Heat, 1879).