Gravitational curvature : an introduction to Einstein's theory / Theodore Frankel. Frankel, Theodore, 1929- Relativity (Physics) Gravitation. QC173.55 .F7 531.5 FRG Includes index. Bibliography: p. [167]-168. San Francisco : W. H. Freeman, c1979. c1979. 1979 Text xviii, 172 p. : eng