286 



COMPOSITION OF SOUND WAVES. 



FIG. 224. 



magnet, around one end of which is wound a coil, B, of 

 fine copper wire carefully insulated. The ends of this 



coiled wire are 

 attached to the 

 larger wires CC, 

 which communi- 

 cate with the 

 binding posts 

 DD. In front of 

 the magnet and 

 coil is the soft iron diaphragm E, which corresponds to 

 the disc #, of Fig. 203. The distance between E and the 

 end of A is delicately adjusted by the screw S. In front 

 of the diaphragm is a wooden mouth-piece with a hole 

 about the size of a dime, at the middle of the diaphragm 

 and opposite the end of the magnet. The outer case is made 

 of wood or hard rubber. The external 

 appearance of the complete instrument 

 is represented by Fig. 225. The bind- 

 ing posts of one instrument being con- 

 nected by wires with the binding posts 

 of another at a distance, conversation 

 may be carried on between them. 



446. Action of the Tele- 

 phone. When the mouth-piece is 

 brought before the lips of a person who I 

 is talking, air waves beat upon the dia- 1 

 phragm and cause it to vibrate. The 

 nature of these vibrations depends upon 

 the loudness, pitch, and timbre of the 

 sounds uttered. Each vibration of the diaphragm induces 



FIG. 225. 



