resonance-chambers are the _mouth cavity_, in the widest sense,
and the _nasal chambers_. It is highly probable that the vibrations of
the chest walls and of the bones of the head may to some degree modify
the vibrations of the air within the resonance-chambers, chiefly in
the direction of intensification; but the idea that the hollow spaces
in certain of the bones of the head have any appreciable influence on
the tones of the speaker or singer, can at best not be considered as
demonstrated, and it serves no practical purpose to take into account
this possibility.

The great facts, the facts which are so plain that they may be
demonstrated to a child, are these: that the quality of any
tone--_e.g._, a vowel--is absolutely determined by the shape of these
cavities, the mouth and nasal chambers. This subject will be treated
further when the tones, etc., of speech are considered, but inasmuch
as no one can sing, in the proper sense of the term, without the use
of vowels, at least, and as we produce different vowels with
ease, one may at once demonstrate to himself that this is done by
altering the shape of his mouth cavity, and chiefly by the agency of
the tongue and soft palate.

[Illustration: FIG. 46 (Tyndall). Representing water being poured into
the vessel A B, till the air-space is just sufficient to respond to
the vibrations of the tuning-fork. The air thus becomes a resonator of
the fork.]

[Illustration: FIG. 47 (Spalteholz). The mouth is extremely widely
opened. The soft palate is seen terminating in the uvula, and on each
side, extending from it, are the pillars of the fauces, a pair of
folds between which the tonsil is seen to lie.]

[Illustration: FIG. 48. View of the nose, etc., from behind, showing
the parts enumerated above. It is not hard to understand that any
considerable amount of swelling of the lining mucous membrane might
give rise to difficulty in breathing through the nose, and even compel
mouth-breathing.]

[Illustration: FIG. 49 (Spalteholz). Showing well the scroll
(turbinated) bones of the nose, which break up the space and make it
more cavernous. It can be seen that there is free communication
behind, between the mouth and the nasal cavities, and that if the soft
palate and the tongue approximate, the breath-stream must pass into
and through the nose, giving rise to nasality in utterance.]

A short description of a part to which many voice-users remain
strangers all their lives will n