Slater leaves Harvard University for Massachusetts Institute of Technology in 1930 (Karl Compton) to build up Physics Department there; work on quantum electrodynamics. Growth of MIT Physics Department in the 1930s and 1940s, relations between experimentalists and theorists; discussion of works and publications during the 1930s. Changes in U.S. physics; overview of post-World War II physics to 1951, and reasons for establishing own research group; establishment of the Radiation Lab, 1940; magnetron work; Bell Labs visits, 1941-1942 and 1943-1945.