VOLUME XXX APRIL 1951 no. 2 



THE BELL SYSTEM 



TECHNICAL JOURNAL 



DEVOTED TO THE SCIENTIFIC AND ENGINEERING ASPECTS 

 OF ELECTRICAL COMMUNICATION 



The Seventy-fifth Anniversary of the Telephone 213 



Seventy-five Years of the Telephone: An Evolution in 



Technology W. H, Martin 215 



An Improved Telephone Set 



A. H. Inglis and W. L. Tuffnell 239 



Pyroljrtic Film Resistors : Carbon and Borocarbon 



R. 0. Grisdale, A. C. Pfister, and W. van Roosbroeck 271 



The Potential Analogue Method of Network Synthesis 



Sidney Darlington 315 



Zero Temperature Coefficient Quartz Crystals for Very 

 High Temperatures W. P. Mason 366 



Duality as a Guide in Transistor Circuit Design 



R. L. Wallace, Jr. and G, Raisbeck 381 



Some Design Features of the N-1 Carrier Telephone System 



W. E. Kahl and L. Pedersen 418 



The Evolution of Inductive Loading for Bell System Tele- 

 phone Facilities (Continued) Thomas Shaw 447 



Abstracts of Bell System Technical Papers Not Published 



in this Journal 473 



Contributors to This Issue 488 



50i Copyright, 1951 $1.50 



per copy American Telephone and Telegraph Company per Year 



