The Cosmic frontiers of general relativity / William J. Kaufmann. Layman's guide to the new universe Kaufmann, William J. (William John) Astronomy. General relativity (Physics) 521 19 KAC Includes index. Cover subtitle : A layman's guide to the new universe. Harmondsworth, England : Penguin, [197-?] [197-?] 1970 Text x, 305 p. : eng