1. Summary early studies and history see J. J. and G. P. Thomson: Conduction of Electricity Through Gases, Third Edit., vol. 1, p. 19ff. Cambridge: University Press 1928.
2. Loeb, L. B.: Fundamental Processes of Electrical Discharge in Gases, chap. II. New York: John Wiley & Sons 1939.
3. Loeb, L. B.: Fundamental Processes, loc. cit. chap. II, and especially
4. L. B. Loeb: Basic Processes of Gaseous Electronics, chap. VI. Berkeley: University of California Press 1955.
5. Bragg, W. H., and R. D. Kleeman: Phil. Mag. 11, 466 (1906).