1. D. H. Eckhardt, Proc. Soc. Photo-Opt. Instrum. Eng. 157, 172 (1978).
2. M.O. Scully, in Proceedings of the Fifth International Conference on Laser Spectroscopy, H. Walther and K. Rothe, eds. (Springer-Verlag, Berlin, 1979);
3. M.P. Haugan, M.O. Scully, and K. Just, Phys. Lett. 77A, 88 (1980).
4. J.H. Simpson, Astron. & Aeron. 2, #10, p. 42 (1964).
5. G. Sagnac, Compt. Rend. 157, 708 (1913).