Lecture at Les Houches ,1966 session of summer school of theoretical physics <br/><br/>
High energy astrophysics  V.2 
ed. by C. DeWitt, [et al] 
 - New york  Gordon and Breach, Science Publishers  1967 
 - xii, 332p. 
<br/><br/><label>Dewey Class. No.: </label>523.01  / N67.2