respects the two are similar. The violoncello, because of
the length and thickness of its strings, is pitched a whole
octave lower than the violin; otherwise it is similar. The
unusual length and thickness of the strings of the double
bass make it produce very low notes, so that it is
ordinarily looked upon as the "bass voice" of the orchestra.

_c_. The harp has always been considered one of the most
pleasing and perfect of musical instruments. Here the
skilled performer has absolutely free scope for his genius,
because his fingers can pluck the strings at will and hence
regulate the overtones, and his feet can regulate at will
the tension, and hence the pitch of the strings.

Guitar and mandolin are agreeable instruments for amateurs,
but are never used in orchestral music.

[Illustration: FIG. 187.--A harp.]

272. Wind Instruments. In the so-called wind instruments, sound is
produced by vibrating columns of air inclosed in tubes or pipes of
different lengths. The air column is thrown into vibration either
directly, by blowing across a narrow opening at one end of a pipe as
in the case of the whistle, or indirectly, by exciting vibrations in a
thin strip of wood or metal, called a reed, which in turn communicates
its vibrations to the air column within.

The shorter the air column, the higher the pitch. This agrees with the
law of vibrating strings which gives high pitches for short lengths.

[Illustration: FIG. 188.--Open organ pipes of different pitch.]

The pitch of the sound emitted by a column of air vibrating within a
pipe varies according to the following laws:

1. The shorter the pipe, the higher the pitch.

2. The pitch of a note emitted by an open pipe is one octave higher
than that of a closed pipe of equal length.

3. Air columns vibrate in segments just as do strings, and the tone
emitted by a pipe of given length is complex, consisting of the
fundamental and one or more overtones. The greater the number of
overtones present, the richer the tone produced.

273. How the Various Pitches are Produced. With a pipe of fixed
length, for example, the clarinet (Fig. 189, 1), different pitches are
obtained by pressing keys which open holes in the tube and thus
shorten or lengthen the vibrating air column and produce a rise or
fall in pitch. Changes in pitch are also produced by variation in the
player's breathing. By blowing hard or