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SCIENCE OF HOME AND COMMUNITY 



The piano. The essential sound-producing portion of the 

 piano consists of three parts : the strings, whose vibrations 

 produce the sound, the keys for setting the strings in vi- 

 bration, and the sounding board. (See figure 39.) The pur- 

 pose of the sounding board is to increase the volume of the 

 sound. The volume of sound given out by the wires alone 

 would be too small to make a satisfactory instrument. 



If one looks at the strings on a piano, he will find that they 

 differ in three ways, in length, in size, and in material. 

 There is another difference which one cannot see, namely, 



FIG. 39. Piano. 



in tension. The different tones are produced by various 

 combinations of these differences. Large strings, long 

 strings, strings under small tension, and heavy strings tend 

 to produce notes of low pitch; while small strings, short 

 strings, light strings, and strings under a high tension tend 

 to produce notes of a high pitch. The strings in a piano are 

 attached at one end to screws which may be turned ; thus 

 the strain on the strings may be changed. By this means 

 a piano is tuned, as this difference in tension affects the pitch. 

 The mechanism which sets the strings in vibration is a 

 system of levers so arranged that by pressing down a key 

 a hammer strikes the wire. Usually several wires are struck 



