252 BELL SYSTEM TECHNICAL JOURNAL 



very extensive use of fine-gauge cables in the plant of the Bell System 

 was, to a large extent, made possible by the development of more 

 efficient transmitters and receivers. Further perfecting of these 

 instruments promises additional improvements in service and some 

 further economies. 



Telephony, restricting the term to ordinary two-way talking 

 between individuals, involves an element not present in any other 

 service. It does not greatly concern one customer of an electric light 

 or power company whether another customer chooses to use inadequate 

 or inefficient or poorly located lamps or other equipment. That is, 

 each user of the service is, under any ordinary conditions, independent 

 of all other users. In the case of telephony, however, the problem is 

 entirely different; for one user of the telephone is greatly concerned 

 with not only the apparatus furnished to any one with whom he has 

 occasion to talk but also with other factors afifecting the use of this 

 apparatus, such as the amount of noise in the room where the apparatus 

 is located, the user's habits of speech, and whether his ability to hear 

 is normal. Telephone instrumentalities must therefore be so designed 

 and the plant so engineered as to meet reasonably wide variations 

 from what may be termed normal conditions, and ratings of per- 

 formance should be similarly established. 



I believe telephony in your country as in ours will find an increasingly 

 wide field of service, and there is no single factor more important to 

 a sound development of this art than the subscriber apparatus. With 

 your permission, therefore, I will broadly outline certain work of the 

 Bell Telephone Laboratories which has had a very direct bearing on 

 these telephone instrumentalities and the form they are likely to 

 assume. I will first discuss the research program which has been 

 carried on in these laboratories, and then indicate to you the general 

 trend which development and design have taken. 



The research program basic to the development and design of 

 transmission instruments has itself been a matter of development as a 

 better understanding of the problems unfolded and as the need for 

 research in this or that direction became apparent. The research 

 problem basic to the development and design of transmission instru- 

 ments may be described as having the following very broad scope: 

 an understanding of their physical operation viewed as electro- 

 mechanical structures; an understanding of speech mechanism and an 

 accurate physical definition of speech air waves; an understanding of 

 the hearing processes and a determination of how hearing is affected 

 by factors present in telephony. Also, our research program may be 

 said to have included research upon certain materials, the results of 



