THE TIDES. (APP. A.} 195 



moon were stuck on the two ends of a strong 

 bar, and put at rest in space, then the attrac- 

 tion of the moon would draw the waters of the 

 earth to the side of the earth next to the moon. 

 But in reality things are very different from that 

 supposition. There is no rigid bar connecting the 

 moon and the earth. Why then does not the moon 

 fall towards the earth ? According to Newton's 

 theory, the moon is always falling towards the earth. 

 Newton compared the fall of the moon, in his 

 celebrated statement, with the fall of a stone at the 

 earth's surface, as he recounted, after the fall of an 

 apple from the tree, which he perceived when sit- 

 ting in his garden musing on his great theory. 

 The moon is falling towards the earth, and falls in 

 an hour as far as a stone falls in a second. It 

 chances that the number 60 is nearly enough, as I 

 have said before, a numerical expression for the dis- 

 tance of the moon from the earth in terms of the 

 earth's radius. It is only by that chance that the 

 comparison between the second and hour can be here 

 introduced. Since there are 60 times 60 seconds 

 in an hour, and about 60 radii of the earth in 

 the distance from the moon, we are led to the 

 comparison now indicated, but I am inverting the 

 direction of Newton's comparison. He found by 

 observation that the moon falls as far in an hour as 

 a stone falls in a second, and hence inferred that 

 the force on the moon is a 6oth of the 6oth of the 

 force per equal mass on the earth's surface. Then 



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