1. A. Eichenwald, Ann. d. Phys.11, 1, 1903.
2. E. Bergstrand, Arkiv Fysik2, 119, 1950;3, 479, 1951.
3. R. W. Cohen, K. M. Crowe andS. W. M. Dumond, Fundamental Constants of Physics, Interscience Publ., N. Y., 1957, p. 111.
4. E. B. Rosa andN. E. Dorsay, Bull. Bureau Stand.,3, 605, 1907.
5. G. Sagnac, Comptes Rendus,15, 708 and 1410, 1913.