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2. E. Nasser, Fundamentals of Gaseous Ionization and Plasma Electronics, Wiley Interscience, New York, 1971.
3. J. S. Townsend, Electricity in Gases, Clarendon Press, London, 1915
4. J. J. Thomson and G. P. Thomson, Conduction of Electricity Through Gases, Vol. II, p. 512, Cambridge University Press, Cambridge, UK, 1928.
5. J. Slepian, Conduction of Electricity in Gases, p. 78, Westinghouse Electric and Manufacturing Co., Educational Dept., East Pittsburgh, 1933.