336 



OUR PHYSICAL WORLD 



FIG. 173. The larynx. At left, outside view; 

 at right, sectional view of inside showing vocal 

 cord at V. 



that their cordlike, nearly parallel edges form a slot through 

 which the air rushes, when expelled from the lungs, and throws 

 them into vibration. The sound thus originated passes out 

 through the open mouth and is modified by the resonance of 



the air masses in mouth, 

 nose, and throat. One 

 can sing a note, and 

 then by changing the 

 tension of the cords 

 sing another higher or 

 lower one. By forcing 

 the air more rapidly 

 past the cords, they are 

 made to vibrate more 

 vigorously, and the note 

 sung is made louder. 

 If, while singing or 

 speaking, the nose is pinched shut by the fingers so as to cut off 

 some of the air masses that are customarily thrown into sympa- 

 thetic vibration, the qual- 

 ity of the tone is altered. 

 Similar changes are pro- 

 duced by varying positions 

 of teeth, lips, and tongue, 

 thus changing the shape 

 of the resonance cavities. 

 One of the marvelous 

 inventions of our own 

 times is the phonograph, 

 which reproduces with 

 such remarkable fidelity FIG. i 74 .-A phonograph 



the human voice, the music of the orchestra, and other sounds. 

 Directions for making the instrument are given in the Field and 

 Laboratory Guide in Physical Nature-Study. A hard-rubber 

 disk rotates horizontally on a turntable (Fig. 174). The point 



