Figure 53. — One of the Baudot multiplex receivers, showing 

 the distributor commutator on top of the case. From La 

 Lumiere electrique, 1882, vol. 6, p. 128. 



Figure 54. — The Reis telephone transmitter {left) and receiver that Joseph 

 Henry showed Alexander Graham Bell in 1875. {USNM idoiyg; Smithsonian 

 bhotos 3053-/, 47876-E.) 



was energized by a current, a sound could be heard 

 in the electromagnet.''- Helmholtz's classic Die Lehre 

 der Tonempfindungen, the first edition of which appeared 

 in 1862, showed how electromagnets could be used 

 to drive tuning forks, how a tuning fork could be used 

 to produce an alternating current of a given fre- 

 quency, and how only a tuning fork of the right 

 frequency would respond to a given alternating 

 current. But this was not a new discovery, for Abbe 



*- Charles Page, "The Production of Galvanic Music," 

 American Journal of Science, 1837, vol. 32, pp. 396—397; "Experi- 

 ments in Electro-Magnetism," American Journal of Science, 1838, 

 vol. 33, pp. 118-120. 



Laborde*^ had already suggested in 1860 that a 

 multiple telegraph system might be based upon the 

 proper combination of electrically driven tuning 

 forks. 



One of the first inventors of a practical communica- 

 tions system using alternating currents of different 

 frequencies was Elisha Gray,''* superintendent of the 



^3 Abbe Laborde, "'Vibrations transmises et reproduces a 

 distance par I'electricite," Comptes rendus, 1860, vol. 50, pp. 

 692-694. 



" Lloyd W. Taylor, "The Untold Story of the Telephone," 

 American Physics Teacher, 1937, vol. 5, pp. 243-251. Many of 

 the instruments that Gray invented for his harmonic multiple 

 telegraph may still be seen in the Museum of History and 

 Technology of the Smithsonian Institution. 



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