340 J. Trowbridge — A Telephone Relay. 



hoping to repeat the almost infinitesimal vibrations of this 

 diaphragm, and to give them an increase of energy by a local 

 batter} 7 . This attempt is an application pure and simple of 

 the principle of the telegraphic relay and therefore marks no 

 progress in the art ; for it was not new in principle and further- 

 more it did not work. The application of the microphonic 

 contact loaded the diaphragm at its most sensitive point and 

 thus prevented the vibrations which one sought to repeat ; 

 moreover, the vibrations of the diaphragm are too minute to 

 cause a sufficient agitation of the microphonic contact. 



The next step in the mind of the inventor was to endeavor 

 to increase the vibration of the center of the telephonic dia- 

 phragm by a lever. This arrangement was found to be inop- 

 erative, for the short arm of the lever exercised a prejudicial 

 pressure on the vibrating diaphragm ; moreover, the funda- 

 mental vibrations of the lever were superposed on the vibra- 

 tions of the diaphragm, thus completely confusing speech. 



It was perhaps natural to suppose that a number of micro- 

 phonic contacts placed on a number of telephonic diaphragms, 

 the telephones being arranged one after the other in tandem, 

 might gather, so to speak, the slight vibrations of each and 

 throw them in a united volume upon the relay line. This 

 chorus arrangement, however, is also a failure ; for the united 

 speech is confused ; much as if a number of persons singing 

 the same note, some through the nose and others imperfectly, 

 should undertake to transmit the note through a number of 

 telephones. The imperfection of each microphonic contact 

 disturbs the final result. 



It must be remembered that the telephone is after all an 

 imperfect instrument and its wonderful adaptiveness is greatly 

 aided by the human brain, which catches at the connection of 

 thought. This can be seen if individual words are transmitted 

 without context, It will be found that the call girl will ask 

 you to repeat such a collocation as " superstitious zoological 

 veneration." Moreover the amount of energy utilized in the 

 telephone is extremely small ; most of the energy of the cur- 

 rents which actuate it and transmit speech is dissipated in heat. 

 Some observers think that less than one per cent of the energy 

 of such currents is transformed into sound waves. We see, 

 therefore, that the problem of the telephone relay calls for all 

 our electrical and mechanical aids to preserve and to transmit 

 this small percentage. 



Since mechanical enlargement of the vibration of the tele- 

 phonic diaphragm by levers is out of the question, the next 

 more promising step seemed to be the bringing in, so to speak, 

 of electromagnetic energy, and it has been proposed to cause the 

 telephonic currents on the circuit to be relayed, to react by 



