218 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



cept of the "grand system" for local and toll service, there has likewise been 

 continuing invention, research and development over the years for their 

 advancement in performance and application. While it would be necessary 

 to include also these portions of the telephone system to show the extent 

 of the influence on technology of Bell's vision, the activities covered here 

 will be those in the "station" portion of the plant, and primarily those on 

 the transmitter and receiver. 



In looking back over the progressive development of the telephone, the 

 four factors — invention, experiment, theory, and measurement — may be 

 noted as tending to be dominant in turn for a period. It is perhaps unneces- 

 sary to state that the claimed dominance of any one of these factors in a 

 period does not imply there were not important contributions from the 

 others. It should be added that this succession of dominant factors is not 

 confined to the development of the telephone but exemplifies the progress 

 in adapting other contemporary devices to man's use. It is thought, how- 

 ever, that the development of the telephone has certain distinctions, pos- 

 sibly in degree of complexity and appUcation, and of the effects of subjective 

 performance. 



After discussing these four factors with respect to the development of 

 the telephone instruments, some brief indications will be given of the great 

 effects of the work on the last two — theory and measurement— on the per- 

 formance and design of these devices in the latter part of this seventy-five 

 year period. 



Invention 



Following the transmission of the first sentence, Bell continued to experi- 

 ment in his Boston laboratory and Watson to make models embodying the 

 ideas coming out of this work. By May of 1876, Bell had devised the "iron 

 box"^''^ receiver with its permanent magnet and peripherally supported 

 diaphragm of iron. In October 1876, these two ideas were incorporated in 

 the first "box" telephone^^^ and in May 1877 in the wood-encased hand 

 telephone. ^'^^ This 'box' telephone was used to introduce commercial teleph- 

 ony but was followed soon by the hand-held type. ^^^ 



Bell's invention stimulated others to work and invent in this field. A 

 series of variable resistance transmitters quickly followed Bell's liquid type. 

 In 1878 Blake invented the platinum-carbon contact transmitter, Edison 

 patented his compressed lamp-black carbon transmitter and Runnings ap- 

 plied for a patent in England on a transmitter containing a pulverized form 

 of carbon to secure a large number of microphonic contact points. Edison's 



^^^ Bibliography item 1, p. 30. 



<«) Ibid., p. 176. 



W) Ibid., p. 43. 



(«> Ibid., pp. 176, 177. 



