1. R. F. C. Vessot, M. W. Levine and E. M. Mattison, in Proc. of the 9th Annual Precise Time and Time Interval Conference, 1978 [NASA Tech. Memoeandum No. 78104, 1978 (unpublished)], p. 549.
2. H. E. Peters, Private Communication, 1988.
3. D. Kleppner, H. M. Goldenberg and N. F. Ramsey, Phys. Rev. 126, 603 (1962).
4. C. Audoin, H. E. Peters, and R. F. C. Vessot, Private Communications, 1988.
5. R. F. C. Vessot, Private Communication, 1988.