William Thomson Kelvin, 1st Baron 1824-1907, British mathematician and physicist, b. Belfast. He was professor of natural philosophy at the Univ. of Glasgow (1846-99). He is known especially for his work on heat and electricity. In thermodynamics his work of coordinating the theories of heat held by various leading scientists of his time established firmly the law of the conservation of energy as proposed by Joule. He introduced the Kelvin temperature scale , or absolute scale, of temperature . He also discovered the Thomson effect in thermoelectricity . The importance of the discoveries and improvements that he made in connection with the transmission of messages by submarine cables led to his establishment as a leading authority in this field. He invented the reflecting galvanometer and the siphon recorder, an instrument by which telegraphic messages are recorded in ink fed from a siphon. His brother, James Thomson, 1822-92, an engineer, was professor at Queen's College, Belfast, from 1857 to 1873. He is known for his studies of the variation in melting point with pressure as well as for his research in hydraulics. Bibliography: See biographies of Baron Kelvin by S. P. Thompson (1910) and A. G. King (1925).