1. C. Brans andR. H. Dicke:Phys. Rev.,124, 925 (1961);R. H. Dicke andH. M. Goldenberg:Phys. Rev. Lett.,18, 313 (1967).
2. M. Sachs:Nuovo Cimento,55 B, 199 (1968).
3. M. Sachs:Nuovo Cimento,47 B, 759 (1967).
4. See, for example,R. Adler, M. Bazin andM. Schiffer:Introduction to General Relativity (New York, 1965).
5. See, for example, the proposal byJ. G. Laframboise andM. Sachs:A general relativity test using two or more satellites, inAstronautica Acta, in press.