1.03 !N. (O.D.) 

 0.06 LB 



Headpiece. — A panorama of loading coils 1904-1948. 



The Evolution of Inductive Loading for Bell System 

 Telephone Facilities 



By THOMAS SHAW 

 Introduction 



THIS is the story of the contributions of inductive loading in the growth 

 of the Bell Telephone System to its present great stature. In particu- 

 lar, it tells how these contributions have been made. We see in it the great 

 economic value of organized research, of research scientists and design and 

 development engineers, of manufacturing skill and care, and of the applica- 

 tion of sound engineering principles to the design of the telephone plant. 



The story told here is almost entirely concerned with series inductance 

 coil loading, since other types of loading have had very little use in the Bell 

 System. To make the story more complete, however, a brief account is 

 included of Bell System developments and applications of continuous load- 

 ing. 



The main story starts soon after the turn of the century, following the 

 development of the first standard loading coils and loading systems, and 

 carries through to the end of 1949. In the beginning of this period emphasis 

 was placed on urgently needed increases in the range of telephone trans- 

 mission over open-wire lines and cables, and in the use of cheaper cables. 

 In this connection it should be remembered that a really satisfactory type 



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