forced upwards through the windpipe. The lungs are able to expel air
regularly and gently, with no more expense of energy than ordinary
breathing requires. But the lungs can also force air out with
tremendous power--power enough to carry sound over hundreds of yards.
In ordinary repose the outward moving breath produces no sound
whatever, for it meets in its passage no obstruction.

Producing Tone. At the upper end of the windpipe is a triangular
chamber, the front angle of which forms the Adam's apple. In this are
the vocal cords. These cords are two tapes of membrane which can be
brought closely together, and by muscular tension stretched until
passing air causes them to vibrate. They in turn cause the air above
them to vibrate, much as the air in an organ pipe vibrates. Thus tone
is produced.

The air above the vocal cords may fill all the open spaces above the
larynx--the throat, the mouth, the nasal cavity in the head, the
nostrils. This rather large amount of air, vibrating freely, produces
a sound low in pitch. The larger the cavities are made the lower the
pitch. You can verify this by producing a note. Then place your finger
upon your Adam's apple. Produce a sound lower in pitch. Notice what
your larynx does. Sing a few notes down the scale or up to observe the
same principle of the change of pitch in the human voice.

Producing Vowels. If the mouth be kept wide open and no other organ be
allowed to modify or interrupt the sound a vowel is produced. In
speech every part of the head that can be used is brought into action
to modify these uninterrupted vibrations of vocal cords and air. The
lips, the cheeks, the teeth, the tongue, the hard palate, the soft
palate, the nasal cavity, all coöperate to make articulate speech.