Take a violin-string in your hand: touch it, and mark the sound
produced--how weak and thin. Now, attach the string to the
violin: touch it again, and see how the resonating instrument
converts the feeble sound of the detached string into a sonorous
wave of vibrating music. Now, the vocal chords are placed in the
throat midway between two resonators--the chest and the head.
These are to the chords what the body of the violin is to the
string. When the stream of air has passed the chords it is
already accompanied by the vibrations of the chest, but the head
is the main contributor. The residual air in the upper portions
of the throat, mouth and nasal cavities is thrown into vibration.

Here the importance of the subject reveals itself. The art that
can convert a screech into pleasing cadences of soft sound is no
trifle. Nasal resonance must not be confounded with nasal twang.
The one is produced by vibrating the air in the cavities, the
twang by expelling it from them. The part played by each organ in
voice production may be briefly summarised:--The lungs send out a
stream of air; the vocal chords, principally, modulate it; the
head and chest give it resonance.

Now, that it is clearly evident God intended us to speak and sing
to the accompaniment of these aerial orchestras concealed in the
head and chest, the only remaining question is--How we shall use
them?

[Side note: Advice how to avoid screech]

Take care never to exhaust these reservoirs of air; if you do the
result will be screech and shout. No matter what demand is made