THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXIX. — A Telephone Relay ; by John Trowbridge. 



In histories of the invention of telegraphy much stress is 

 placed upon the invention of the telegraphic relay ; for it 

 seemed doubtless to Joseph Henry and to Morse a complete 

 apparatus for indefinite extension of the telegraph over land. 

 In the progress of the telegraphic art, due to better lines and 

 improved instruments, the telegraphic relay has lost the pre- 

 eminent position it once occupied in men's minds ; and the 

 long discussions in the various treatises on the development of 

 the art of telegraphy, in regard to the priority of the inven- 

 tion of the relay, have ceased to interest practical electricians. 



It is natural, with the introduction of telephony, that atten- 

 tion should be directed to an analogous problem, that of the 

 telephonic relay ; a far more difficult problem than the tele- 

 graphic relay ; and the future historian of the progress of tele- 

 phony will find it difficult to analyze the work of hundreds of 

 inventors who have sought to solve the problem. 



When we consider that the telegraphic relay merely 

 responds to one throb, so to speak, one inarticulate impulse, 

 while a telephonic relay must reproduce the whole range of 

 the human voice, we begin to realize the demand that the 

 invention of such a relay must make upon both scientific 

 knowledge of sound and of electricity and magnetism ; and 

 above all, ujDon mechanical skill. It does not, therefore, seem 

 inappropriate to discuss in this Journal, which contains much 

 of the work of Joseph Henry, some scientific points in connec- 

 tion with a telephonic relay. 



The earlier inventors who attacked the problem naturally 

 thought of the simple device of applying a microphonic con- 

 tact immediately to the vibrating diaphragm of a telephone, 



Am. Jour. Sci.— Fourth Series, Vol. XXI, No. 125.— Mat, 1906. 

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