1. M. Born, Zeit. Physik, 1, 45 (1920).
2. O. Stern, Zeit, für Elektrochem., 20, 508 (1924).
3. Y. Esin and B. Markov, Acta Physicochim. U.S.S.R., 10, 353 (1939); see also Zhur. Fiz. Khim., 17, 236 (1943).
4. R. G. Sachs and D. C. Dexter, J. Appl. Phys., 21, 1304 (1950).
5. J. Bardeen, Phys. Rev., 58, 727 (1940).