TELEPHONE SYSTEM OF THE UNITED STATES 79 



Moving picture houses in the important cities and towns are already 

 equipped to show pictures of this type and it appears destined to 

 revolutionize the motion picture art. 



A study of speech and hearing in connection with telephone service 

 has led to the development of various devices of value to those having 

 abnormal hearing or speech. This work has been carried out in close 

 cooperation with interested members of the medical profession. One 

 of these devices, the "audiometer," is useful in determining the con- 

 dition of hearing of individuals by determining the smallest volume 

 of sound at a considerable number of different frequencies which 

 the individual can hear. This device, in rapidly testing large groups 

 of people such as in the public schools, is believed to be of consider- 

 able importance. Sound amplifying devices are provided for those 

 hard of hearing. 



Another interesting by-product is an artificial larynx for those who 

 have lost their natural larynx as a result of pathological conditions. 

 Apparatus has also been constructed to permit the totally deaf to 

 understand speech sounds by holding their fingers against a moving 

 diaphragm. In one form the individual fingers and thumb are held 

 against separate vibrating bodies and the important range of speech 

 sounds is divided by electrical filters and one part of it applied to 

 each of these five vibrating bodies. This partial electrical analysis 

 of sound appears to be of considerable help in this tactual apprecia- 

 tion of sound. 



Other tools of interest to the medical profession include electrical 

 stethescopes and electro-cardiographs. The first of these permits 

 any desired number to listen to chest or other sounds in medical 

 patients. Electrical filters may be interposed in such arrangements 

 to exaggerate or subordinate certain part of the sound. The electro- 

 cardiograph, by permitting the amplification and recording of slight 

 differences of electrical potential between selected points of the skin 

 of a patient give an indication of the condition of his heart beat. 



Conclusion 



In the above discussion, while emphasis has been placed upon engi- 

 neering matters, it has naturally been impossible in the discussion 

 of results to separate engineering considerations from many other 

 important phases of the telephone communication problem. While 

 engineering is essential to the results that have been obtained, they 

 are due also to these other factors, commercial and general in their 

 character, and to the policies as regards service and operations which 

 guide the Bell Telephone System. Furthermore, the solution worked 



