MUSIC AND SOUND INSTRUMENTS 



437 



in front of an electric magnet, of which we have learned in the last 

 chapter. 



FIG. 331. X-ray tele- 

 phone receiver. 



FIG. 332. Telephone transmitter. 



These currents cause the disc on the other end to vibrate, be- 

 cause of the attraction of the disc to the magnet, according to the 



FIG. 333. Some of the changes in the electrical current which take place on 

 the telephone circuit when the word "San Francisco" is spoken into the 

 telephone. 



FIG. 334. Some of the changes in the electrical current which take place in 

 the telephone circuit when the word "New York" is spoken into the 

 telephone. 



increase and decrease in the strength of the current passing over 

 the wire. If the sound waves could travel from New York to San 



