308 



VOICE AND SPEECH 



which of them sets up sympathetic resonance in the air of the mouth, 

 and so causes its sound to be intensified. The fundamental tone is 

 lowest for u (as in lute). Next comes o ; then a (as in path) ; then a (as 

 in fane) ; then i ; while e is highest of all. A simple illustration of 

 this may be found in the fact that when the vowels are whispered in 

 the order given, the pitch rises. When u or o is sounded, the buccal 

 cavity has the form of a wide-bellied flask, with a short and narrow neck 

 for u, a still shorter but wider neck for o. For e the tongue is raised 

 and almost in contact with the palate, and the cavity of the mouth 

 is shaped like a flask with a long narrow neck and a very short belly. 

 For i the shape is similar, but the neck is not so narrow. For a (as in 

 path) the vowel-cavity is intermediate in form between that of u and e, 

 being roughly funnel-shaped, and the mouth is rather widely opened. 

 For u (oo) the resonating cavity is made as long as possible, the larynx 

 being depressed and the lips protruded ; for e the resonating cavity is 

 at its shortest, the larynx being raised as much as possible and the lips 

 retracted (Figs. 146 to 148). 



According to Helmholtz, all that the resonating cavity does is to 

 strengthen certain of the partials or overtones of the laryngeal note. 



ou 



Fig. 146. 



Fig. 147. 



Fig. 148. 



If this is true, the partials which give a vowel-sound the timbre by 

 which we recognize it as different from other vowel-sounds cannot 

 preserve the same numerical relation to the fundamental tone when 

 the pitch of the latter is altered. Suppose, for example, that a given 

 vowel is sounded with a pitch corresponding to 100 vibrations a second, 

 and that the partial which is particularly strengthened by the resonance 

 of the mouth cavity is the fifth overtone, corresponding to 600 vibra- 

 tions. Then when the same vowel is sounded with a pitch of 200 vibra- 

 tions, the reinforced partial which will now give the quality to the sound 

 will still correspond to 600 vibrations a second, since this is the rate 

 which most easily elicits the resonance, but it will not now be the fifth 

 but the second overtone. 



Universally accepted for a time, the Helmholtz theory has been in 

 recent years assailed, especially by Hermann, who bases his criticism 

 on microscopic examination of curves obtained by the Edison phono- 

 graph, and on reproductions of such records obtained by photographing 

 on a moving drum covered with sensitive paper a beam of light re- 

 flected from a small mirror attached to a system of levers whose move- 

 ments follow the curves faithfully and greatly magnify them. Hermann 



