1. R. Clausius, Die Mechanische W. Armtheorie II, Vol. 62, Braunschweig, 1897.
2. D.J. Griffiths, Introduction to Electrodynamics, Prentice-Hall, New Jersey, 1989, p. 192.
3. R. Becker, Electromagnetic Fields and Interactions, Dover, New York, 1982, p. 95.
4. L. Eyges, The Classical Electromagnetic Field, Dover, New York, 1972, p. 111.