1. A. A. Michelson and E. W. Morley, Am. J. Sci. 34, 333 (1887).
2. A. Brillet and J. L. Hall, Phys. Rev. Lett. 42 549 (1979).
3. H. P. Robertson, Rev. Mod. Phys. 21, 378 (1949); H. P. Robertson and T. W. Noonan, Relativity and Cosmology ( Saunders, Philadelphia, 1968 ).
4. R. Mansouri and R. U. Sexl, General Relativity and Gravitation Vol. 8, 1977, pp. 497–513; 515–524; 809–814.
5. This kind of idea was already discussed in Ref. 3 from a somewhat different aspect, but was only recently crystallized by the work of Ref. 4.