THE BELL SYSTEM 



TECHNICAL JOURNAL 



A JOURNAL DEVOTED TO THE 

 SCIENTIFIC AND ENGINEERING 

 ASPECTS OF ELECTRICAL 



COMMUNICATION 



EDITORIAL BOARD 



J.J. Carty Bancroft Gherardi F. B. Jewett 



E. B. Craft L. F. Morehouse O. B. Blackwell 



H. P. Charlesworth E. H. Colpitts H. D. Arnold 



R. W. King — Editor J. O. Perrine — Asst. Editor 



VOLUME VII 

 1928 



AMERICAN TELEPHONE AND TELEGRAPH COMPANY 



NEW YORK 



