ANIMALS. 339 



ttieir own peculiar blow : hut they succeed so fast, one behind 

 the other, that the ear supposes them one continued, sound • 

 whereas, in reality, they make many. A person who should, foi 

 the first time, hear the toll of the bell, would, very probably, be 

 able to distinguish these breaks of sound ; and, in fact, we can readi. 

 ly ourselves perceive an intention and premission in the sound. 



In this manner, sounding bodies are of two kinds ; those un- 

 elastic ones, which, being struck, return but a single sound ; and 

 those more elastic, returning a succession of sounds ; which 

 uniting together, form a tone. This tone may be considered as 

 a great number of sounds, all produced one after the other, by 

 the same body, as we find in a bell, or the string of a harpsichord, 

 which continues to sound for some time after it is sti'uck. A 

 continuing tone may also be produced from a non-elastic body, 

 by repeating the blow quick and often, as when we beat a drum, 

 or when we draw a bow along the string of a fiddle. 



Considering the subject in this light, if we should multiply 

 the number of blows, or repeat them at quicker intervals upon 

 the sounding body, as upon the drum, for instance, it is evident 

 that this will have no effect in altering the tone ; it will only 

 make it either more even, or more distinct. But it is other- 

 wise, if we increase the force of the blow : if we strike the body 

 with double weight, this will produce a tone twice as loud as the 

 former. If, for instance, I strike a table with a switch, this will 

 be very different from the sound produced by striking it with a 

 cudgel. Hence, therefore, we may infer, that ;ill bodies give a 

 louder and graver tone, not in proportion to the number of 

 times they are struck, but in proportion to the force that strikes 

 them. And, if this be so, those philosophers who make the 

 tone of a sonorous body, of a bell, or the string of a harpsichord, 

 for instance, to depend upon the innnber only of its \ibrations, 

 and not the force, have mistaken what is only an effect for a cause. 

 A bell, or an elastic string, can only be considered as a drum beat- 

 en ; and the frequency of the blows can make no alteration what- 

 ever in the tone. The largest bells, and the longest and thickest 

 strings, have the most forceful vibrations ; and, therefore, their 

 tones are the most loud and the most grave. 



To know the manner in which sounds thus produced become 

 pleasing, it must be observed, no one continuing tone, how loud 

 and swelling soever, can give ns satisfaction; we must have a 



