1. M. Conversi andA. Gozzini:Nuovo Cimento,2, 189 (1955).
2. See, f. i.,J. M. Meek andJ. D. Craggs :Electrical breakdown in gasses, (Oxford, 1953), chapter 6;P. Bella andC. Feanzinetti:Nuovo Cimento,10, 1461 (1953).
3. H. S. W. Masset andE. H. S. Burhop:Electronic and Ionic Impact Phenomena, (Oxford, 1952), chapter 5.
4. B. Rossi andH. H. Staub :Ionization Chambers and Counters, (New York, 1949), chapter1.