1. O. W. Richardson, Emission of Electricity by Hot Bodies (Longmans, Green, 1921).
2. T. J. Jones, Thermionic Emission (Methuen and Company, London, 1936).
3. Wahlin, Phys. Rev. 34, 164 (1929); PHRVAO0031-899X
4. Wahlin, 35, 653 (1930); PHRVAO0031-899X, Phys. Rev.
5. Wahlin, 45, 886 (1934).PHRVAO0031-899X, Phys. Rev.