William Altar, 95, theoretical physicist whose work led to development of the magneto-ionic theory that explains the propagation of radio waves in the earth's atmosphere. Further development of the research led to the Nobel Prize in physics for Edward Appleton in 1947. A 1982 assessment of the history of radio transmission research by C. Stewart Gillmor of Wesleyan University in the Proceedings of the American Philosophical Society made the argument that Altar should have shared Appleton's prize because of their early collaborative work. A native of Vienna, Altar earned his doctorate at the University of Vienna, worked with Appleton at King's College in London and was later a research fellow at Princeton. He taught physics and electrical engineering at several universities, did important work with radar during World War II, and later undertook research for Westinghouse, TRW, the Aerospace Corp. and Douglas Aircraft. He was a lieutenant colonel with the Naval Research Laboratory when he retired in 1972. On Sunday in Brentwood of complications from a stroke.