the cylinder form of
record, the groove varies in depth with the vibrations of the
diaphragm. In the disk type of phonograph, the groove varies sidewise
from its normal true spiral.

If the disk record be dusted with talcum powder, wiped, and examined
with a magnifying glass, the waving spiral line may be seen. Its
variations are the result of the blows struck upon the diaphragm by a
train of sound waves.

In reproducing a phonograph record, increasing the speed of the record
rotation causes the pitch to rise, because the blows upon the air are
increased in frequency and the wave-lengths shortened. A transitory
decrease in speed in recording will cause a transitory rise in pitch
when that record is reproduced at uniform speed.

_Timbre._ Character of sound denotes that difference of effect
produced upon the ear by sounds otherwise alike in pitch and loudness.
This characteristic is called timbre. It is extraordinarily useful in
human affairs, human voices being distinguished from each other by it,
and a great part of the joy of music lying in it.

A bell, a stretched string, a reed, or other sound-producing body,
emits a certain lowest possible tone when vibrated. This is called its
_fundamental tone_. The pitch, loudness, and timbre of this tone
depend upon various controlling causes. Usually this fundamental tone
is accompanied by a number of others of higher pitch, blending with it
to form the general tone of that object. These higher tones are called
_harmonics_. The Germans call them _overtones_. They are always of a
frequency which is some multiple of the fundamental frequency. That
is, the rate of vibration of a harmonic is 2, 3, 4, 5, or some other
integral number, times as great as the fundamental itself. A tone
having no harmonics is rare in nature and is not an attractive one.
The tones of the human voice are rich in harmonics.

In any tone having a fundamental and harmonics (multiples), the
wave-train consists of a complex series of condensations and
rarefactions of the air or other transmitting medium. In the case of
mere noises the train of vibrations is irregular and follows no
definite order. This is the difference between vowel sounds and other
musical tones on the one hand and all unmusical sounds (or noises) on
the other.

Human Voice. Human beings communicate with each other in various
ways. The chief method is by speech. Voice is sound vibration produced
by the vocal cords, these being two