350 



ELEMENTS OF PHYSIOLOGY 



within the angle, or ridge, called the Adam's apple. The 

 rear ends are attached to two little movable cartilages at 

 the back of the chamber. The moving of these little car- 

 tilages by the muscles of the larynx brings the edges 

 together and tightens the cords. 



632. Sound Waves, or sound vibrations, are imparted to 

 the air by the tremulous motion of the cords. The limits 

 of the vibrations which the human voice is capable of mak- 

 ing are from 42 vibrations per second for the lowest tone, 

 to over 2000 vibrations per second for the highest tone. 



FlG. 229. The Shape of the Mouth in sounding the Vowels a, e, oo. 



Lower C of the soprano is produced by 256 vibrations per 

 second. The limits of vibrations which the human ear is 

 capable of hearing are from 16 to 50,000 vibrations per 

 second, but until they reach a rate of about 50, the sound 

 is more like a buzz than a tone. Some people cannot 

 hear the voice of mice, or the squeak of a bat, because of 

 the high pitch being beyond the limit of their hearing. 



633. THOUGHT LESSON. How the Voice may vary. - 

 The rate of vibration of a cord, and hence the pitch of a 

 sound, are influenced in several ways. Is the string of 

 a violin or of a guitar tuned up or down by tightening it ? 

 Which is higher in pitch, a long or a short string of a harp 

 or a piano ? Which makes a higher note, the light or the 

 heavy string of a violin or a guitar? The pitch of the 



