1. Erdelyi, Magnus, Oberhettinger, and Tricomi,Higher Transcendental Functions(McGraw-Hill Book Company, Inc., New York, 1953), Vol. 1, Eq. (1) p. 108, and Eq. (12) p. 110.
2. W. R. Smythe,Static and Dynamic Electricity(McGraw-Hill Book Company, Inc., New York, 1950), Eq. (5), p. 268.
3. H. Geiger and Karl Scheel,Handbuch der Physik(Verlag Julius Springer, Berlin, 1927), Vol. XII, p. 485.