CLAUSIUS, RUDOLF JULIUS EMMANUEL (1822— 1888), German physicist, was born at Koslin, in Pomerania. After attending the Gymnasium at Stettin, he studied at Ber lin university from 1840 to 1844. In 1848 he took his degree at Halle, and in 1850 was appointed professor of physics in the royal artillery and engineering school at Berlin and privatdocent in the university. In 1855 he became an ordinary professor at Zurich Polytechnic, and professor in the University of Zürich. In 1867 he moved to Wiirzburg as professor of physics, and two years later was appointed to the same chair at Bonn, where he died. The work of Clausius, who was a mathematical rather than an experimental physicist, was concerned with many of the most abstruse problems of molecular physics. By his restatement of Carnot's principle he put the theory of heat on a truer and sounder basis, and he deserves the credit of having made thermo dynamics a science; he enunciated the second law, in a paper con tributed to the Berlin Academy in 185o, in the well-known form, "Heat cannot of itself pass from a colder to a hotter body." His results he applied to an exhaustive development of the theory of the steam-engine, laying stress in particular on the conception of entropy. The kinetic theory of gases owes much to his researches. He raised it, on the basis of the dynamical theory of heat, to the level of a theory, and he carried out many numerical determina tions in connection with it, e.g., of the mean free path of a mole cule. Clausius also made an important advance in the theory of electrolysis, suggesting that molecules in electrolytes are continu ally interchanging atoms, the electric force not causing, but merely directing the interchange. This view found little favour until 1887, when it was taken up by S. A. Arrhenius, who made it the basis of the theory of electrolytic dissociation. In addition to many scientific papers he wrote Die Potentialfunktion and das Potential (1864) and Abhandlungen fiber die mechanisclie IVarme tlieorie