1. O. Heaviside:Electromagnetic Theory (London, 1893), appendix 1.
2. O. Heaviside:Electromagnetic Theory (London, 1893), appendix 2
3. A. Einstein:Ann. Phys. (Leipzig.),49, 769 (1916).
4. L. D. Landau andE. M. Lifshitz:Course of Theoretical Physics, Vol.2 (London, 1975).
5. P. A. M. Dirac:Proc. R. Soc. London Ser. A,167, 148 (1938).