to loosen it if necessary. The tuning of the piano is the adjustment
of the strings so that each shall produce a tone of the right pitch.
When the strings are tightened, the pitch rises; when the strings are
loosened, the pitch falls.

What has been said of the piano applies as well to the violin, guitar,
and mandolin. In the latter instruments the strings are few in number,
generally four, as against eighty-eight in the piano; the hammer of
the piano is replaced in the violin by the bow, and in the guitar by
the fingers; varying pitches on any one string are obtained by sliding
a finger of the left hand along the wire, and thus altering its
length.

Frequent tuning is necessary, because the fine adjustments are easily
disturbed. The piano is the best protected of all the stringed
instruments, being inclosed by a heavy framework, even when in use.

[Illustration: FIG. 180.--Front view of an open piano.]

267. Strings and their Tones. Fasten a violin string to a wooden
frame or box, as shown in Figure 181, stretching it by means of some
convenient weight; then lay a yardstick along the box in order that
the lengths may be determined accurately. If the stretched string is
plucked with the fingers or bowed with the violin bow, a clear musical
sound of definite pitch will be produced. Now divide the string into
two equal parts by inserting the bridge midway between the two ends;
and pluck either half as before. The note given forth is of a
decidedly higher pitch, and if by means of the siren we compare the
pitches in the two cases, we find that the note sounded by the half
wire is the octave of the note sounded by the entire wire; the
frequency has been doubled by halving the length. If now the bridge is
placed so that the string is divided into two unequal portions such as
1:3 and 2:3, and the shorter portion is plucked, the pitch will be
still higher; the shorter the length plucked, the higher the pitch
produced. This movable bridge corresponds to the finger of the
violinist; the finger slides back and forth along the string, thus
changing the length of the bowed portion and producing variations in
pitch.

[Illustration: FIG. 181.--The length of a string influences the
pitch.]

[Illustration: FIG. 182.--Only one half of the string is bowed, but
both halves vibrate.]

If there were but one string, only one pitch could be sounded at any
one time; the additional strings of the violin allow of the
simultaneous pro