Appell, P. and Thiry, R.: 1955,Traité de mécanique rationelle (2nd edn), tome V, Gauthier-Villars, Paris.
Canuto, V., Adams, P. J., Hsieh, S. H. and Tsiang, E.: 1977,Phys. Rev. 16, 1643.
Dirac, P.: 1973,Proc. Roy. Soc., London A333, 403.
Eddington, A. S.: 1923,The Mathematical Theory of Relativity, Cambridge University Press (see also Chelsea Publ. Co., New York, 1975).
Hoyle, F. and Narlikar, J. V.: 1964,Proc. Roy. Soc. A282, 191.
Hoyle, F. and Narlikar, J. V.: 1974,Action at a Distance in Physics and Cosmology, W. H. Freeman and Co., San Francisco.
Maeder, A.: 1977,Astron. Astrophys. (in press).
Trautmann, A.: 1964,Lectures on General Relativity, Brandeis Institute.
Weinberg, S.: 1972,Gravitation and Cosmology, J. Wiley, New York.
Weyl, H.: 1921,Raum-Zeit-Materie, Springer Co. (see also Dover Edition, 1955).