102 NATURAL HISTORY. 



force, or, what amounts to the same thing, with a double 

 mass of matter, it will produce a sound that will be 

 double grave. Music has been said, by the ancients, 

 to have been first invented from the blows of different 

 hammers on an anvil. Suppose then we strike an 

 anvil with a hammer of one pound weight, and again 

 with a hammer of two pounds, it is plain that the two 

 pound hammer will produce a sound twice as grave 

 as the former. But if we strike with a two pound 

 hammer, and then with a three pound, it is evident 

 that the latter will produce a sound one third more 

 grave than the former. If we strike the anvil with 

 a three pound hammer, and then with a four pound, 

 it will likewise follow that the latter will be a quar- 

 ter part more grave than the former. Now, in com- 

 paring between all those sounds, it is obvious that 

 the difference between one and two is more easily 

 perceived than that between two and three, three and 

 four, or any number succeeding in the same propor- 

 tion. The succession of sounds will therefore please 

 in proportion to the ease with which they may be 

 distinguished. That sound which is double the for- 

 mer, or, the octave to the preceding tone, will be the 

 most pleasing. The next to that, which is as two or 

 three, or, the third, will be most agreeable. And 

 thus universally, those sounds whose differences may 

 be most easily compared are the most agreeable. 



Sound has in common with light, the property of 

 being extensively diffused. Like light, it also admits 

 reflection. The laws of this reflection, it is true, are 

 less distinctly understood than those of light. All 

 we know is, that sound is principally reflected by 

 hard bodies, and that their being hollow also some- 

 times increases the reverberation, The internal cavity 



