1. H. Bondi, “Les proprietes physiques des ondes gravitationelles,” Colloque International Sur Les Theories Relativistes de la Gravitation, Royaumont, 21–27 June 1959 (to be published).
2. G. C. McVittie,General Relativity and Cosmology(Chapman and Hall, Ltd., London, England, 1956), Secs. 6.1 and 6.2.