454 VOICE AND SPEECH 



of the vocal chords. In aphonia from paralysis of the vocal muscles of 

 the larynx, patients can articulate distinctly in whispering ; but in cases 

 of chronic bulbar paralysis (glosso-labio-laryngeal paralysis) speech is 

 entirely lost. 



The Phonograph and Telephone. In 1877 a remarkable invention 

 was made in this country, by Mr. Thomas A. Edison, which possesses 

 considerable physiological importance. Mr. Edison constructed a simple 

 instrument, called the phonograph, which will repeat, with a certain 

 degree of accuracy, the peculiar characters of the human voice both in 

 speaking and singing as well as the pitch and quality of musical instru- 

 ments. This demonstrates conclusively the fact that the qualities of 

 vocal sounds depend upon the form of the sonorous vibrations. The 

 following are the main features in the construction of this instrument : 

 It consists of a cylinder of iron provided with very fine shallow grooves 

 in the form of a close spiral. Upon the cylinder a sheet of tin-foil 

 is accurately fitted. Bearing on the tin-foil is a steel-point connected 

 with a vibrating plate of mica or of thin iron. The vibrating plate is 

 connected with a mouth-piece which receives the vibrations of the voice 

 or of a musical instrument. The cylinder is turned with a crank, and 

 at the same time the plate is thrown into vibration by speaking into 

 the mouth-piece. As the disk vibrates in consonance with the voice, 

 the vibrations are marked by little indentations upon the tin-foil. 

 When this has been done, the cylinder is moved back to the starting 

 point and is turned again at the same rate as before. As the steel-point 

 passes over the indentations in the tin-foil, the plate is thrown into 

 vibration, and the sound of the voice is actually repeated, although 

 diminished in intensity. Many improvements have lately been made in 

 the phonograph, which have added much to its character illustrating the 

 various qualities of the human voice. The telephone illustrates conduc- 

 tion of the form of sound-waves. As is well known, it is easy to recog- 

 nize peculiarities of voice in using this instrument. 



