t>LACE OF A SOUNl) FROM A MUSICAL STRING* 323 



guage it is the only one of the number, which the observer 

 hears. 



Now three sets of vibrations are evidently going on at the A vibiating 

 Same time, in the first experiment; these are the primary set the"Jrtof^r"^ 

 of the wire, and the two derivative sets existing in the table drumstick 

 at one end of it, and in the wooden pin at the other. But°hQj.J^^^QJ' 

 the length of the string enables the ear to ascertain which >5kc. 

 one of the three sets gives the seat of the sound ; and this 

 is the vibratory motion of the table ; consequently the table 

 is the sounding body, and the wire does nothing more than 

 perform the part of a drumstick in causing the surface of it 

 lo vibrate with great celerity. This discovery points out a 

 distant analogy connecting the thundering noise of a drum 

 and the smooth sounds of a harp or lute. They are, how- 

 ever, very distinct to sense for obvious reasons : the cover of 

 the former instrument is highly elastic, and the sound of it 

 continues to die away for some seconds after it has been 

 struck; each stroke of the drumstick renews this sound, 

 and the interval between two succeeding strokes is sufficient- 

 ly large to be observed by the ear ; and hence proceeds the 

 thundering noise of a drum. On the contrary, the sound 

 derived from the wooden frame of a stringed instrument by 

 U single stroke is very transient ; but the impulses of the 

 strings beat upon it with a celerity, which docs not permit 

 the sound to suffer a sensible diminution of force in the 

 interval of two successive strokes ; which is the cause of 

 smoothness in tones of this sort. 



In the second experiment, the vibrations, communicated The necessity 

 from the wire to the cylinder of yew, are imparted bv con- "^ ^^^^^n^ive 



. ^ surfaces in the 



tact to the other table, which thereby becomes the seat of production af 

 sound; because, being nearer the peison of the experimenter, ^""'^'^" 

 it makes a more powerful impression on his ear, than the 

 first table; which stands at a greater distance from him. 

 But so soon as the cylinder ceases io touch the board, 

 that supports it, the experimenter hears the sound from the 

 opposite table; notwithstanding it is farther from his ear 

 than the wooden pin in his hand. Hence we discover the uti- 

 lity, and even the necessity of extensive surfaces in the pro- 

 duction of sounds; for the impulses received from the Tri- 

 turating wire, by the table and cylinder, are equal in num* 

 Iber and magnitude ; but of the three sets of contemporary 

 Vibrations, that existing in the table is alone heard. 



