VOLUME XVm JULY, 1939 haJMBERS 



THE BELL SYSTEM 



TECHNICAL JOURNAL 



DEVOTED TO THE SCIENTinC AND ENGINEERING ASPECTS 

 OF ELECTRICAL COMMUNICATION 



Frequency-Modulation: Theory of the Feedback Receiving 



Circuit — John R. Carson 395 



The Application of Negative Feedback to Frequency-Modula- 

 tion Systems — J. G. Chaffee 404 



Survey of Magnetic Materials and Applications in the Tele- 

 phone System — V. E. Legg 438 



Impedance Properties of Electron Streams — Liss C. Peterson 465 



Plastic Materials in Telephone Use 



— J. R. Townsend and W, J. Clarke 482 



The Dielectric Properties of Insulating Materials 



—E, J. Murphy and S. O. Morgan 502 



Abstracts of Technical Papers 538 



Contributors to this Issue 544 



AMERICAN TELEPHONE AND TELEGRAPH COMPANY 



NEW YORK 



50c per Copy $1.50 per Year 



