Richardson, a graduate (1900) of Trinity College, Cambridge, and a student of J.J. Thomson (Thomson, Sir J.J.) at the Cavendish Laboratory, was appointed professor of physics at Princeton University (1906–13). In 1911 he proved that electrons are emitted from hot metal and not from the surrounding air, as some had thought. That same year he proposed a mathematical equation that relates the rate of electron emission to the absolute temperature of the metal. This equation, called Richardson's law or the Richardson-Dushman equation, became an important aid in electron-tube research and technology. (See also thermionic emission.) In 1914 Richardson became professor of physics and, 10 years later, director of research at King's College of the University of London, retiring in 1944. He was knighted in 1939.