NATURAL HISTORY. 101 



from some other sense, we can never tell accurately 

 whether the sound be great or small. It is not till 

 we have by experience become acquainted with any 

 particular sound, that we can judge of the distance 

 whence we hear it. When, for example, Ave know the 

 tone of a bell, we are then at no great loss to determine 

 how far it is from us. 



Every body that strikes against another produces a 

 sound, which is simple in such bodies as are not elastic, 

 but which is often repeated in such as are. If we strike 

 a bell, for instance, a single blow produces a sound, 

 which is repeated by the undulations of the sonorous 

 body, and which is multiplied as often as it happens to 

 undulate or vibrate. These undulations succeed each 

 other so fast, that the ear supposes them one continued 

 sound ; whereas they form many sounds. Sounding 

 bodies are therefore of two kinds, to wit, non-elastic 

 and elastic. The former when struck return but a 

 single sound, and the latter return a succession of 

 sounds, which form a tone. This tone may be con- 

 sidered as a great number of sounds, all produced one 

 after the other, by the same body, as we find in a bell 

 which continues to sound for some time after it is struck. 

 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. 



To know the manner in which musical sounds be- 

 come pleasing, it must be observed, no one continu- 

 ing tone 3 how loud or swelling soever, can afford us 

 delight. We must have a succession of them, and 

 those in the most pleasing proportion. The nature 

 of this proportion may be thus conceived. If we 

 strike a body incapable of vibration with a double 



