Sommerfeld, Arnold Johannes Wilhelm (ärˈnōlt yōhänˈəs vĭlˈhĕlm zômˈərfĕlt) [key], 1868–1951, German physicist and teacher. He received a Ph.D. at Königsburg Univ. in 1891 and was a professor of physics at the Univ. of Munich from 1906 to 1940. During his early years at Munich his research was devoted principally to a study of the wave character of X rays. In 1915, Sommerfeld made a major contribution to Niels Bohr's atomic theory by extending the theory to include elliptical paths for electrons. In 1916 he devised a formula for the structure of spectral lines and a general quantum theory of spectral lines. Applying quantum theory to the structure of metals, in 1927 he developed a theory of electrons in metals. His book Atombau und Spektrallinien, published in 1919, became a standard in the field of theoretical spectroscopy. Sommerfeld was awarded the 1948 Oersted Medal in recognition of his service as an outstanding teacher.