284 



COMPOSITION OF SOUND WAVES. 



vibrate at the same rate as do the sonorous waves that set 

 it in motion. Thus the vibrations of the strings may pro- 

 duce sonorous waves, and the waves in turn may produce 

 vibrations in another string. The most important feature 

 of the phenomenon is that the string absorbs only the 

 particular kind of vibration that it is capable of 

 producing. (Read Tyndall " On Sound," Chap. IX, 4.) 



FIG. 222. 



(.) Tune to unison two strings upon the same sonometer (Fig. 

 222). Upon one string place two or three paper riders. With a 

 violin bow, set the other string in vibration. The sympathetic 

 vibrations thus produced will be shown by the dismounting of the 

 riders, whether the vibrations be audible or not. Change the tension 

 of one of the strings, thus destroying tlie unison. Repeat the experi- 

 ment and notice that the sympathetic vibrations are not produced. 



(6.) Place several feet apart two tuning-forks mounted upon reso- 

 nant cases. The forks should have the same tone, and the cases 

 should rest upon pieces of rubber tubing to 

 prevent the transf errence of vibratory motion to 

 and through the table. Sound the first fork by 

 rapidly separating the two prongs with a rod. 

 Notice the pitch. At the end of a second or 

 two touch the prongs to stop their motion and 

 sound. It will be found that the second fork 

 has been set in motion by the repeated blows 

 of the air, and is giving forth a sound of the 

 same pitch as that originally produced by the 

 first fork. Fasten, by means of wax, a 3-cent silver piece or other 

 small weight to one of the prongs of the second fork. An attempt 

 to repeat the experiment will fail. 



FIG. 223. 



