ANIMALS. 35 



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 dis- 

 tinct. But it is otherwise 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 all bodies give a 

 louder and graver tone, not in proportion to the 

 number of times they are struck, but in propor- 

 tion to the force that strikes them. And if this 

 be so, those philosophers who made the tone of a 

 sonorous body, of a bell, or the string of a harpsi- 

 chord, for instance, to depend upon the number 

 only of its vibrations, and not the force, have mis- 

 taken what is only an effect for a cause. A bell, 

 or an elastic string, can only be considered as a 

 drum beaten ; and the frequency of the blows can 

 make no alteration whatever 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 pro- 

 duced become pleasing, it must be observed, no 

 one continuing tone, how loud or swelling soever, 

 can give us satisfaction ; we must have a succes- 

 sion of them, and those in the most pleasing pro- 

 portion. The nature of this proportion may be 

 thus conceived. If we strike a body incapable of 

 vibration with a double force, or, what amounts 

 to the same thing, with a double mass of matter, 



