Masterpieces of Science 



entirely due to the imperfection of the instru- 

 ment. I will not trouble you by detailing the 

 various stages through which the apparatus 

 passed, but shall merely say that after a time I 

 produced the form of instrument shown inFig.g, 

 which served very well as a receiving telephone. 

 In this condition my invention was, in 1876, 

 exhibited at the Centennial Exhibition in Phila- 

 delphia. The telephone shown in Fig. 8 was 



Fig. 9 



used as a transmitting instrument, and that in 

 Fig. 9 as a receiver, so that vocal communication 

 was only established in one direction. 



The articulation produced from the instru- 

 ment shown in Fig. 9 was remarkably distinct, 

 but its great defect consisted in the fact that it 

 could not be used as a transmitting instrument, 

 and thus two telephones were required at each 

 station, one for transmitting and one .for receiv- 

 ing spoken messages. 



It was determined to vary the construction of 

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