SLEPIAN, JOSEPH (1891–1969), U.S. electrical engineer. Slepian was born in Boston, Mass., receiving his B.Sc. degree in 1911, M.Sc. in 1912, and Ph.D. in mathematics in 1913 from Harvard. After postdoctoral work at the University of Gottingen in Germany, the Sorbonne in Paris, and Cornell University, he joined the Westinghouse Company in 1916, where he held research posts of increasing seniority at the company's Forest Hills research facility until he retired in 1956. His mathematical knowledge and engineering skills led to many inventions in the electrical supply industry. His research on lightning arresters disclosed the need for surge protection. His studies of ionized gases led to his invention of the deion circuit breaker and the ignitron for initiating and controlling electrical arcs. Late in his working career and after his retirement he worked on plasma methods for isotope separation. He was associated with the Manhattan Project in World War II. He found the atmosphere of a commercial laboratory highly conducive to his work, where he also organized teaching courses in basic and applied physics. His honors included the prestigious Edison Medal (1947).