1. Lense, J. (1981). Private communication.
2. Brans, C. H. (1977).Phys. Rev. Lett.,39, 856.
3. Shapiro, I. I. (1980). InGeneral Relativity and Gravitation: One Hundred Years After the Birth of Albert Einstein, Vol. 2, Held, A., ed. (Plenum Press, New York), p. 469.
4. Hughes, V. W., Robinson, H. G., and Beltran-Lopez, V. (1960).Phys. Rev. Lett.,4, 342.
5. Drever, R. W. P. (1961).Philos. Mag.,6, 683.