1. Bateman, H. (1915).The Mathematical Analysis of Electrical and Optical Wave-Motion, Chap. VIII. Cambridge. Cambridge University Press.
2. Bonnor, W. B. (1969).Communications in Mathematical Physics 13, 163.
3. Ferraro, V. C. A. (1962).Electromagnetic Theory, p. 527, Athlone Press, London.
4. Kundt, W. (1961).Zeitschrift für Physik,163, 77.
5. Sommerfeld, A. (1905).Gesell Wiss. Göttingen Nachr. Math. Phys. Klasse, 229.