Bell's Telephonic Researches 



I have formerly stated that Helmholtz was en- 

 abled to produce vowel sounds artificially by com- 

 bining musical tones of different pitches and in- 

 tensities. His apparatus is shown in Fig. 2. 

 Tuning forks of different pitch are placed be- 

 tween the poles of electro-magnets (ai, 02, &c.), 

 and are kept in continuous vibration by the action 

 of an intermittent current from the fork b. Reso- 

 nators, i, 2, 3, etc., are arranged so as to rein- 

 force the sounds in a greater or less degree, ac- 

 cording as the exterior orifices are enlarged or 

 contracted. 



Thus it will be seen that upon Helmholtz 's plan 

 the tuning forks themselves produce tones of 

 uniform intensity, the loudness being varied 

 by an external reinforcement; but it struck me 

 that the same results would be obtained, and in 

 a much more perfect* manner, by causing the 

 tuning forks themselves to vibrate with different 

 degrees of amplitude. I therefore devised the 

 apparatus shown in Fig. 3, which was my first 

 form of articulating telephone. In this figure a 

 harp of steel rods is employed, attached to the 

 poles of a permanent magnet, N. S. When any 

 one of the rods is thrown into vibration an un- 

 dulatory current is produced in the coils of the 

 electro-magnet E, and the electro-magnet E' at- 

 tracts the rods of the harp H' with a varying 

 force, throwing into vibration that rod which is 

 in unison with that vibrating at the other end 

 of the circuit. Not only so, but the amplitude of 

 vibration in the one will determine the amplitude 

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