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HUTTONIAN THEORY. 



393 



fiderably, if its centre of gravity has been high 

 above its point of fupport, and if its furface has 

 had much convexity : Thus the horizontal may 

 very far exceed the perpendicular motion ; and, 

 in the courfe of ages, the ftone may travel to a 



great 



diftance. A ftone, however, which tra- 



vels in this manner, mull diminifh as it pro- 

 ceeds, and muft have been much greater in the 

 beginning than it is at prefent;. 



354. This kind of motion may be aided by 

 particular circumftances. When a ftone refts on 

 an inclined plane, fo as to be in a ftate not very 

 remote from equilibrium, if a part be taken 

 away from the upper fide, the equilibrium will 



I 



be loft, and the ftone will thereby be put in mo- 



That ftones which lie on other ftones, 

 may, by wearing, be brought very near an equi- 

 librium, is proved by what are called rockhig- 

 Jlones, or in Cornwall Logan Jlones, v/hich hav 

 fometimes been miftaken for works of art ; but 



that are certainly nothing elfe than ftones, 



tion. 



u 



which have been fubjeded to the univerfal law 

 of wafting and decay, in fuch peculiar circum- 

 ftances, as nearly to bring about an equilibrium 

 of that ftable kind, which, when flightly difturb- 

 ed, re-eftabliflies itfelf*. The logan ftone at 



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the 



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* I do not prefume fo far as to fay, that all rocking- 



ftones are produced hj natural means ; I have not fufli- 



cient 



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