1. L. B. Loeb, in “Handbuch der Physik”, Springer-Verlag, Berlin, 1958.
2. W. R. Harper, “Contact and Frictional Electrification”, Oxford University Press, Oxford, England, 1967.
3. D. J. Montgomery, Solid State Phys., 9, 139 (1959).
4. H. Krupp, in “Static Electrification”, Inst. Phys. Conf. Ser., 11, 1 (1971).
5. J. Fuhrmann, J. Electrostat., 4, 109 (1977).