the various vowel sounds you will observe a distinct difference in the pitch of the note produced.  I will first produce the vowel sound oo and proceed with the vowel sounds to i; you will observe that the pitch rises an octave; that this is due to the changes in the form of the resonator is shown when I percuss the resonator in the position of the different vowel sounds.  You will observe that I start the scale of C with oo on f and proceed through a series of vowel sounds as in whispering who, owe, or, on, ah.  I rise a fifth from f to c, and the diagram shows the change in the form of the resonator cavity to be mainly due to the position of the dorsum of the tongue.  Proceeding from ah to the middle tone of the speaking register, we ascend the scale to i as in me, and the dorsum of the tongue now reaches the roof of the mouth; but the tongue not only rises, it comes forward, and the front segment of the resonator is made a little smaller at every step of the scale while the back segment becomes a little larger.  I consider this diagram of Aikin to be more representative of the changes in the resonator than the description of Helmholtz, who stated that the form of the resonator during the production of the vowel sound u and o is that of a globular flask with a short neck; during the production of a that of a funnel with the wide extremity directed forward; of e and i that of a globular flask with a long narrow neck.

[Footnote A:  This was done by the lecturer placing his left forefinger on the outside of the right cheek, then striking it with the tip of the middle finger of the right hand, just in the same way as he would percuss the chest.—­F.W.M.]

[Illustration:  FIG. 13 I & II To face page 47]

[Description:  FIG. 13.—­Diagram after Aikin.

1.  To show position of tongue and lips in the production of the vowel sounds a, o, oo.

2.  To show successive positions of the tongue in the production of the vowel sounds a, ei, e, i.]

I have already said that Helmholtz showed that each vowel sound has its particular overtones, and the quality or “timbre” of the voice depends upon the proportional strength of these overtones.  Helmholtz was able by means of resonators to find out what were the overtones for each vowel sound when a particular note was sung.  The flame manometer of Koenig (vide fig. 14) shows that if the same note be sung with different vowels the serrated flame image in the mirror is different for each vowel, and if a more complicated form of this instrument be used (such as I show you in a picture on the screen) the overtones of the vowel sounds can be analysed.  You will observe that this instrument consists of a number of resonators placed in front of a series of membranes which cover capsules, each capsule being connected with a jet of gas.