1. Hull, Elec. Eng., 53, 1435 (1934).
2. Loeb, "Fundamental Processes of Electrical Discharge in Gases", 629 (John Wiley, 1939).
3. Smith, Phys. Rev., 62, 48 (1942).
4. Teago and Gill, "Mercury Arcs", 12 (Methuen, 1936).
5. Lord, Electronics, 11 (May 1936).