VOLUME XVm JANUARY, 1939 number 1 



THE BELL SYSTEM 



TECHNICAL JOURNAL 



DEVOTED TO THE SCIENTinC AND ENGINEERING ASPECTS 

 OF ELECTRICAL COMMUNICATION 



Electrostatic Electron-Optics — Frank Gray 1 



Equivalent Modulator Circuits — E. Peterson and L, W, Hussey 32 



An Improved Three-Channel Carrier Telephone System 



—7. T. O'Leary, E, C. Blessing and J, W, Beyer 49 



Crossbar Dial Telephone Switching System 



— F. J. Scudder and J. N, Reynolds 76 



A Twelve-Channel Carrier Telephone System for Open- Wire 

 Liaes—B,W, Kendall and H. A. Aff el 119 



Recent Developments in the Meastirement of Telegraph 

 Transmission — R, B, Shanck, F, A, Cowan and S, L Cory 143 



Contemporary Advances in Physics, XXXII. Particles of the 

 Cosmic Rays — Karl K, Darrow 190 



Hurricane and Flood — September 1938 — W, H, Harrison . . 218 



A Terrain Clearance Indicator 



— Lloyd Espenschied and R. C. Newhouse 222 



Transcontinental Telephone Lines — 7. J. Pilliod 235 



Abstracts of Technical Papers 246 



Contributors to this Issue 251 



AMERICAN TELEPHONE AND, TELEGRAPH COMPANY 



NEW YORK 



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