.

Before discussing our subject further it is desirable that some
attention be given to a few of the fundamental principles of that
department of physics termed _acoustics_, and which deals with the
subject of sound. If the student has the opportunity to study this
subject theoretically and practically, as it is set forth in some good
work on physics, he will have no reason to regret the time spent. A
deep knowledge of the laws of sound is not absolutely essential, or
even highly necessary, for a sufficient understanding of the
principles involved in voice-production. It is, however, all-important
that a few facts and principles be thoroughly grasped.

For those who feel that they have the time for a study of acoustics,
the author would especially recommend Tyndall's work on sound, in
which the subject is treated with wonderful clearness and charm. What
we endeavor now to bring before the reader we have found sufficient
for nearly all the purposes of the voice-user.

An observer on the street, looking at a military band, notices certain
movements of one member of the organization which result in what he
termed the sound of the drum; but a deaf man by his side, though he
sees the movements, hears nothing. This, being analyzed, means that
the movements of the drummer's arm, conveyed through the drumstick to
the membrane of the drum, give rise to movements in it which set up
corresponding movements of the air within the drum, which again cause
movements of the body of the instrument, the whole causing movements
of the external air; and here the purely physical process ends. The
movements other than muscular ones are not readily observed, but
experiments not only prove that they exist, but demonstrate their
nature, even to their exact rate of occurrence, their size, etc. These
movements are termed _vibrations_, and, as has been indicated
previously, they are the sole physical cause of sound. But that the
latter is not due wholly to a physical origin is evident from the fact
that sound for the deaf does not exist. It must, therefore, be a
personal, a subjective experience, and as the sleeping, unconscious
person does not necessarily hear a sound, the process is not wholly a
corporeal or physiological process; it is finally an experience of the
mind, the consciousness, and so is psychological as well as
physiological.

The fact that sound has a physical basis in the vibrations of bodies,
either solid, liquid, or gaseo