1. R. V. Pound and G. A. Rebka, Jr.,Phys. Rev. Lett. 4, 337 (1960).
2. A. F. Boyle and H. E. Hall,Rep. Prog. Phys. 25, §2.2.1 (1962).
3. S. G. De Benedetti,Sci. Am. 1960 (April), 73.
4. C. Kittel, W. Knight, and M. A. Ruderman,Mechanics (McGraw-Hill, 1962), p. 431.
5. E. P. Ney,Electromagnetism and Relativity (Harper Reprint, 1965), p. 106.