a.  The piano is too well known to need comment.  In passing, it may be mentioned that in the construction of the modern concert piano approximately 40,000 separate pieces of material are used.  The large number of pieces is due, partly, to the fact that the single string corresponding to any one key is usually replaced by no less than three or four similar strings in order that greater volume of sound may be obtained.  The hammer connected to a key strikes four or more strings instead of one, and hence produces a greater volume of tone.

b.  The viola is larger than the violin, has heavier and thicker strings, and is pitched to a lower key; in all other 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 gently, the number of vibrations of the reed is increased or decreased and hence the pitch is altered.