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.
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.
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.