VOWEL-SOUNDS. 393 



Whatever the pitch of the note produced by the 

 larynx, and whatever difference may exist among the 

 persons uttering these vowels, the sounds produced by 

 the cavity of the mouth remain the same. In whisper- 

 ing, these sounds are produced alone, accompanied only 

 by the sound made by the air when it leaves the cavity 

 of the mouth; in whispering there is a kind of voice 

 produced by the vibrations of the muscular walls of 

 the lips, which thus replace the vocal chords. If 

 tuning-forks which sound the above notes are succes- 

 sively placed before the mouth, and the particular for- 

 mation is given to it which is required for the produc- 

 tion of the corresponding vowel sound, the sound of 

 the tuning-fork will be very considerably increased by 

 the resonance from the cavity of the mouth. 



The acquisition of a whole series of tuning-forks for these experi- 

 ments is rather expensive. It is, however, easy to prepare a fork 

 which gives out W, the note corresponding to o, by filing away a 

 small piece from the prongs of a common a' tuning-fork, and thus 

 raising its pitch. The fork should be clamped for this purpose in 

 the vice, between lead or copper cheeks, so as to project but very 

 little. After a few rasps with not too coarse a file the fork should 

 be again taken out, and its pitch examined. If the student cannot 

 rely upon his ear, the fork should be compared with the note Vj' of 

 a correctly tuned piano ; this is done by striking the fork, placing 

 the stem upon the sounding-box, and striking the key W moder- 

 ately at the same time and keeping it pressed down : as long as both 

 notes are not in unison beats will be heard. 



In order to be able to hold the fork as closely as possible before 

 the mouth without touching the lips and thus stopping the vibra- 

 tions, it is best to perform the experiment before a looking-glass. 

 The fork is held horizontal, the prongs over one another, the free 

 ends before the mouth. It is somewhat difficult at first to form 

 the mouth into the proper shape for each vowel without really pro- 

 ducing the vowel from the larynx ; it is therefore advisable to 

 whisper the vowels one after the other ; as soon as the vowel o is 

 whispered, the sound of the fork will be considerably strengthened ; 



