All astrophysicists are acquainted with the fundamental works ofS. Chandrasekhar [6] and M. Schwarzschild [1] concerning the internal structure of stars. Although both of these works accentuate the principal mathematical devices of the theory (and use, for this reason, notations that are rather perplexing for the non-specialist), the work of Schwarzschild is distinguished by care in demonstrating the physical meaning of the principal equations, while that of Chandrasekhar makes every effort not to skip a single step in the calculations. On the other hand, Schwarz schild , who considers his two introductory chapters as simple reviews of results which are already known, passes a bit rapidly over certain difficult arguments, and Chandrasekhar never goes far enough in the analysis of the physical mechanisms involved. From another point of view, the excellent review articles published in the Ency clopedia of Physics [5] by M. H. Wrubel, P. Ledoux, and others, and those published in Stars and Stellar Systems [4] by H. Reeves, B. Stromgren, R. L. Sears and R. R. Brownlee, and others, are principally intended for research workers who are already initiated into the theory of internal structure. These monographs are on a level that is clearly too high for the general physicist who is approaching these astrophysical questions for the first time, and more particularly for the post-graduate student.