U.S. physical chemist and physicist who demonstrated the electron to be the charge-carrying particle in the flow of electricity in metals and determined its mass.

Tolman became professor and dean of graduate studies at the California Institute of Technology (1922–48), Pasadena. He published treatises on statistical mechanics (1927, 1938) and relativity theory (1927, 1934). During World War II he was vice chairman of the National Defense Research Committee and chief science adviser to Brig. Gen. Leslie R. Groves, head of military affairs concerning the development of the atomic bomb. After the war he was adviser to Bernard M. Baruch, then U.S. representative to the United Nations Atomic Energy Commission.