818 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1952 



tion of passive terminating impedances. It is concluded that the loss maj' ap- 

 proach zero db only m those cases where the image impedances seen at the ends 

 of the system are purely resistive. Moreover, in such cases, the method of over- 

 coming the transmission loss, whether by conventional repeaters or by series and 

 shunt negative impedance loading, or otherwise, is quite immaterial to the ex- 

 ternal behavior of the system as long as the image impedances are not changed. 

 The use of impedance-correcting networks provides one means of insuring that 

 the phase of the image impedance of the over-all s^'stem approaches zero. Gen- 

 eral relations are derived which connect the image impedance and the image 

 gain of an active system with its over-all performance properties. 



The Arithmetic of Menage Numbers. J. Riordan\ Duke Math. JL, 

 19, pp. 27-30, March, 1952. 



^4 Recurrence Relation for Three-Line Latin Rectangles. J. Riordan\ 

 Am. Math. Monthly, 59, pp. 159-162, March, 1952. 



Capacitors arid Comynunications. Inductive Coordination of Lines. A. 

 R. Waehner^ and W. E. BloeckerI Elec. Light and Power, 30, pp. 105- 

 108, 114, March, 1952. 



Although the use of capacitors on power lines has been expanding, their use 

 has caused relatively few cases of noise on communication lines and these have 

 been satisfactorilj' corrected. The causes of trouble and remedial measures were 

 the subject of a recent, joint E.E.I.-Bell System study described here. 



Book Reviews 



Antennas: Theory and Practice. By Sergei A. Schelkunoff and 

 Harald T, Friis, 639 + xxii pages, John Wiley and Sons, Inc., New York 

 (1952). Price: $10.00. 



This is a recent addition to Wiley's Applied Mathematics Series edited by 

 I. S. Sokolnikoff. It contains a thorough and balanced treatment of electro- 

 magnetic radiation and electrical properties of various tj^^es of antennas. In 

 these days of rapid expansion of microwave engineering it would have been easy 

 to neglect the older and less glamorous long-wave and short-wave antennas. 

 The authors are to be congratulated on their impartiality. The exposition is 

 lucid. While the entire quantitative theory of antennas is based on Maxwell's 

 equations, unnecessary mathematics is conspicuous b}' its absence, and physical 

 explanations are abundant. 



The book begins with a long chapter on Physical Principles of Radiation. 

 This chapter is almost a book within the book. It touches upon the most impor- 

 tant ideas and problems of antenna analysis and contains a number of simple 

 but useful formulas. Circuit and field concepts are compared, and the similari- 

 ties as well as the differences between them are exliibited. Maxwell's equations 

 are stated in a form which is particularly easy to understand. In this form, one 



^ Bell Telephone Laboratories. 



2 American Telephone and Telegraph Company. 



^ Line Material Company. 



