INSTRUMENTS FOR THE NEW TELEPHONE SETS 357 



loudness with which the user speaks, the distance between his Hps and 

 the face of the transmitter, the tightness with which he holds the 

 receiver to his ear, etc. Many of these factors are beyond the control 

 of the engineer responsible for the design of the transmitter and 

 receiver and hence can be evaluated, insofar as their reaction on trans- 

 mission is concerned, only by tests made under the conditions of 

 actual use. 



A method has been devised which makes it possible to rate the over- 

 all effect of these factors on transmission in a way representative of the 

 results obtained by the subscribers in their normal use of the instru- 

 ments.^ Numerous tests employing this method of rating were made 

 during the development of the new transmitter and receiver to make 

 certain that the course followed in their development would insure the 

 best possible performance under service conditions. Similar tests 

 were also made of the designs selected for production. These tests 

 show that in many respects the new instruments represent outstanding 

 advances in transmission instrument design and performance. 



References 



1. "Scientific Research Applied to the Telephone Transmitter and Receiver," E. H. 



Colpitts, Bell System Technical Journal, volume 16, July 1937, pages 251-274. 



2. "Transmission Features of the New Telephone Sets," A. H. Inglis, this issue of 



the Bell System Technical Journal. 



3. "Development of a Handset for Telephone Stations," W. C. Jones and A. H. 



Inglis, Bell System Technical Journal, volume 11, April 1932, pages 245-263. 



4. "An Introduction to the Theory of Statistics," G. U. Yule, J. B. Lippincott 



Company, 1916, page 134. 



5. "A Voice and Ear for Telephone Measurements," A. H. Inglis, C. H. G. Gray and 



R. T. Jenkins, Bell System Technical Journal, volume 11, April 1932, pages 

 293-317. 



6. "Magnetic Alloys of Iron, Nickel and Cobalt in Communication Circuits," G. W. 



Elmen, Electrical Engineering, volume 54, December 1935, pages 1292-1299. 



7. "Electrical Vibration Instruments," A. E. Kennelly, The Macmillan Company, 



1923, page 88. 



8. "Rating the Transmission Performance of Telephone Circuits," W. H. Martin, 



Bell System Technical Journal, volume 10, January 1931, pages 116-131. 



