______CHELSEA SCIENTIFIC BOOKS______ "The exposition proceeds by easy stages with examples and illustrations at every turn." —Bulletin of the A. M. S. VARIATIONSRECHNUNG IM GROS-SEN, (Theorie von Marston Morse), By H. Seifert and W. Threlfall. 1938. 120 pages. 6x9. $2.75 The brilliant expository talents of Professors Seifert and Threlfall—familiar to the many readers of their Lehrbuch der Topologie—are here devoted to an eminently readable account of the calculus of variations in the large. Topologically the book is self-contained. DIOPHANTISCHE GLEICHUNGEN, By T. Skolem. 1938. ix+130 pages. 5^x8>4. Cloth. Originally published at $6.50. $3.50 From the famous series Ergebnisse der Mathe-matik. "This comprehensive presentation . . . should be warmly welcomed. We recommend the book most heartily."—Ada Szeged. ALGEBRAISCHE THEORIE DER KOERPER, By E. Steinitz. 177 pages, including two appendices. 5%x8j4. $3.25 "epoch-making."—A. Hoar, Ada Szeged. "will always be considered as one of the classics... "I should like to recommend the book to students of algebra; for teachers of advanced algebra it would make a very suitable nucleus for a short seminar on abstract fields."—Bulletin of the A.MS. INTERPOLATION, By ]. F. Steffensen. 1950. Second edition, 256 pages. 5%x8>4. Originally published at $8.00. $3.50 "Prof. Steffensen's book is intended as a text for students in American colleges and requires as mathematical equipment only an elementary knowledge of the differential and integral calculus. . . . The topics covered are (1) the general theory of interpolation and extrapolation including the standard formulas . . . of Newton, Gauss, Bessel and others; (2) numerical differentiation; (3) numerical integration; (4) numerical solution of differential equations. "more rigorous than is usual in books on interpolation, ... It should not be supposed, however, that this adds to the difficulty of reading the text. The style is clear and ... the book should prove very valuable. The formulas and methods are illustrated by simple numerical examples." —Bulletin of the A.MS.