DEVELOPMENT OF TELEPHONE SERVICE 



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equipment, the rapid displacement of open wires with cable, etc. Then, 

 in August, 1877, Graham Bell showed the advantage of twisting 'the 

 direct and return wires around one another, so they should be abso- 

 lutely equidistant from the disturbing wires ' in order to neutralize 

 the effect of the inductive current and eliminate the noise. 



Many experiments were made to invent an improved transmitter 

 that would overcome the inductive effect and yet retain the marvelous 

 simplicity of the hand telephone, with its entailed low cost of main- 

 tenance. But eventually it was perceived that the displacement of the 

 magnets in the simple self-contained telephone was possible only 



Fig. 31. 



through the introduction of a battery current and the employment of 

 much mechanism that has always carried relatively heavy maintenance 

 charges. 



In the winter of 1878-9, the more progressive companies began 

 to install the Blake transmitter in combination with the rubber-encased 

 Bell receiver and the magneto bell. At the close of 1878, 246 Blake 

 transmitters were in service, and by July 1, 1879, the number had in- 

 creased to 7,000. On noisy circuits this change afforded a marked 

 improvement in service that was highly appreciated by local sub- 

 scribers. Several modifications in the form of these telephone sets 

 (Fig. 30) were sent out before a standard type was selected. Even 

 then, as there were several factories licensed to manufacture under 

 Bell patents, the output of each, while not essentially different, bope" 

 distinctive trade-marks. In each the battery wires were led into ,the 





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