S28 



OF SOUND. 



glass, as may be perceived in drawing a wet finger 

 on the edge of a drinking glass. 



The vibration of sonorous bodies may be easily 

 seen in musical strings. 



If the middle of a string which is fixed at both 

 ends, A B, (Plate 25. fig. 6.) be drawn to one side, 

 as to C, it will, when let loose, vibrate to D, and 

 then will return back only to E, having lost some- 

 thing of the velocity which it had acquired during 

 the first vibration, from the resistance of the air 

 and friction : it will next move back to E, thus 

 making every succeeding vibration less than the 

 former one, till at last it ceases to vibrate. 



The difference of musical tones depends on the 

 different number of vibrations communicated to 

 the air in a given time by the tremors of the 

 sounding body; the quicker the succession of 

 vibrations, the acuter is the tone; and the slower 

 the vibrations, the graver the tone. 



The vibrations of a musical chord grow less and 

 less after it has been struck, and the sound con- 

 sequently gradually diminishes ; but it is a curious 

 property, that notwithstanding this, the vibrations, 

 whether great or small, are all performed in the 

 same time. This is the reason why the same chord 

 always gives the same note. 



The number of the vibrations given in a certain 

 time depends upon the length, size, and tension of 

 the strings. This is very well illustrated in the 

 violin. 



The harmony or concord of two notes is owing 

 to the vibrations of the air occasioned by them 

 arriving at the ear at the same instant; and this 

 may be the case, although their vibrations are 

 different; for one may give two vibrations, while 

 the other performs one only; this is the concord 



