CH. LVIL] 



THE VOICE AND SPEECH 



807 



ments do not loud themselves to this form of graphic record, but their 

 vibrations can be rendered visible by allowing them to act on a small 

 sensitive gas-flame ; this bobs up and down, and if the reflection of 

 this flame is allowed to fall on a series of mirrors, the top of the con- 

 tinuous image formed is seen to present waves. The mirrors are 

 usually arranged on the four lateral sides of a cube which is rapidly 

 rotated (fig. 506). If one sings a note on to the membrane in the 

 side of the gas-chamber with which the flame is in connection, the 

 waves seen are not simple up and down ones, but the primary large 

 waves are complicated by smaller ones on their surface, at twice, 



FIG. 506. Kouig's apparatus for ob.ainmg flame pictures of musical notes. 



thrice, etc., the rate of the primary vibration. The richer a voice, 

 the richer the sound of a musical instrument, the more numerous 

 are these overtones or harmonics. The range of the voice is 

 seldom, except in celebrated singers, more than two-and-a-half 

 octaves, and for different voices this is in different parts of the 

 musical scale. 



Speech. 



Speech is due to the modification produced in the fundamental 

 laryngeal notes, by the resonating cavities above the vocal cords. 

 By modifying the size and shape of the pharynx, mouth, and nose, 

 certain overtones or harmonics are picked out and exaggerated : this 

 gives us the vowel sounds ; the consonants are produced by inter- 

 ruptions, more or less complete, of the outflowing air in different 

 situations. When the larynx is passive, and the resonating cavities 

 alone come into play, then we get whispering. 



