music.

APPENDIX C

ACOUSTICS

NOTE:--It is usually taken for granted that the student of
music is familiar with the significance of such terms as
_over-tone_, _equal temperament_, etc., and with principles
such as that relating to the relation between vibration rates
and pitches: the writer has in his own experience found,
however, that most students are not at all familiar with such
data, and this appendix is therefore added in the hope that a
few facts at least regarding the laws of sound may be brought
to the attention of some who would otherwise remain in entire
ignorance of the subject.

1. _Acoustics_ is the science which deals with sound and the laws of its
production and transmission. Since all sound is caused by vibration,
_acoustics_ may be defined as the science which treats of the phenomena
of sound-producing vibration.

2. All sound (as stated above) is produced by vibration of some sort:
strike a tuning-fork against the top of a table and _see_ the vibrations
which cause the tone, or, if the fork is a small one and the vibrations
cannot be seen, hold it against the edge of a sheet of paper and hear
the blows it strikes; or, watch one of the lowest strings of the piano
after striking the key a sharp blow; or, look closely at the heavier
strings of the violin (or better still, the cello) and watch them
oscillate rapidly to and fro as the bow moves across them.

The vibrating body may be a string, a thin piece of wood, a piece of
metal, a membrane (cf. drum), the lips (cf. playing the cornet), the
vocal cords, etc. Often it is a column of air whose vibrations give rise
to the tone, the reed or other medium merely serving to set the air in
vibration.

3. Sound is _transmitted_ through the air in somewhat this fashion: the
vibrating body (a string for example) strikes the air-particles in its
immediate vicinity, and they, being in contact with other such
air-particles, strike these others, the latter in turn striking yet
others, and so on, both a forward and backward movement being set up
(oscillation). These particles lie so close together that no movement at
all can be detected, and it is only when the disturbance finally reaches
the air-particles that are in contact with the ear-drum that any effect
is evident.

This phenomenon of sound-transmission may perhaps be made more clear by
the old illustration of a series of eight billiard balls