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 König (_vide_ fig. 14)