OVERTONES HARMONICS 363 



touched. Close to the string these vibrations are 



easily observed ; at a distance they may be rendered 



visible by riders placed on the second string, which 



ire thrown off as soon as the first string is set in vibra- 



ion ; or immediately after the first string is sounded 



t may be touched in several places by the fingers : its 



/ibrations will thus be stopped, so that it can no longer 



>roduce sound, but as the note is still heard, it is clear 



hat the second string is sounding. Vibrations com- 



;nunicated in this manner by one body to another are 



sometimes called sympathetic vibrations, and when the 



Communicated vibrations produce sound, the whole 



phenomenon is called resonance. Whenever it happens 



hat a body capable of performing independent sonorous 



ibrations is reached by the sound-waves of a tone of 



he same pitch as that which it would itself emit, reson- 



nce is produced. In our last experiment the motion 



f one string is transferred to the other by the inter- 



ening solid particles of wood ; but transference of 



onorous vibrations may also be effected and resonance 



reduced by the mere undulations of the air itself. Let 



piano be opened and the monochord be held by two 



ersons a little above the strings ; as soon as the funda- 



jiental note of the strings is struck on the piano, they 



ill commence to vibrate, as may be seen by the motion 



jf riders. When a piece of music is played on the 



too, some particular note is often unpleasantly ac- 



;>mpanied by the jingling of some object of glass or 



^tal which is in the room. If we find out what body 



is that jingles and strike it so as to make it sound, 



will be found to give out the same note as that 



'hich, when played on the piano, causes it to chime in. 



