1. The reader interested in further reading should be warned against the use of most relativistic models contained in books published before 1972. A few excellent books fill this lacuna: (i) Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity, by Steven Weinberg (Wiley, N. Y., 1972); and (ii) Gravitation, by C.W. Misner, K.S. Thorne, and J. A. Wheeler (W.H. Freemen and Company, San Francisco, 1973).
2. Other books, especially designed for the general educated reader are, (iii) Modern Cosmology, by D.W. Sciama (Cambridge University Press, reprinted with corrections, 1972); (iv) Space, Time, and Gravity, by R.M. Wald, University of Chicago Press, Chicago, 1977; (v) Cosmology and Geophysics, by P. S. Wesson, Adam Hilger, Bristol, 1978; and (vi) General Relativity and Cosmology, by J. V. Narlikar, MacMillan Press, London, 1979. A classic book on this subject was written in 1933 by R.C. Tolman. It is entitled Relativity, Thermodynamics and Cosmology (Oxford Press, 1933), and is perhaps one of the best books ever written on relativity. However, its thermodynamical and cosmological portions could not stand the test of time. Updated surveys on relativistic thermodynamics and kinetic theories are available in two volumes edited by this author: Critical Review (of Classical and Relativistic) Thermodynamics, Mono, Baltimore, 1970, [CRT], and Modern Developments in Thermodynamics, Wiley, N. Y. 1974 [MDT].
3. Some familiarity with vector and tensor algebra is assumed for Section III.2. The concepts of stress tensor, conservation equations, conservative fields, momentum, mass density and energy fields were discussed in Lecture II.
4. Phys. Rev. Lett. 2 6, 27-30 (1971)
5. Proceedings of the Conference on Experimental Tests of Gravitational Theories, Davies, R. W. ed. Calif. Inst. Tech., J. P. L., T. M. 33-499, Nov. 11-13 (1971), pp. 111-135 (Anderson, J. D. et. al and Shapiro et. al).