Arnold Sommerfeld (1868-1951), German physicist. Sommerfeld was a brilliant theoretician who worked on many mathematical and physical problems. He developed Neils Bohr's atomic theory to include elliptical electron orbits. His work on Einstein's special relativity aided the acceptance of the then radical theory by its skeptics. He became one of the founders of quantum mechanics, and also worked on the theory of electromagnetism. He was awarded the Lorentz Medal for contributions to theoretical physics in 1939. This portrait is from the Bain News Service, one of America's oldest news picture agencies, which holds images dating from the 1890s to the 1930s.