1. P.P. Ewald, Dissertation, Univ. of Munich, 1912;
2. P.P. Ewald, Ann. Phys. 49, 1 (1915).
3. C.W. Oseen, Ann. Phys. 48, 1 (1915).
4. For a detailed account of the theorem see M. Born and E. Wolf, Principles of Optics (Pergamon Press, Oxford and New York, 1970) 4th ed., §2.4,
5. L. Rosenfeld, Theory of Electrons (North-Holland Publishing Co., Amsterdam, 1951) Chapt. VI, §4.