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THEOREM 2. 



Things naturally moved in a circle, are neither 

 the same with those moved in a right line, nor 

 with those which are composed from things moved 

 in a right line. 



Demonstration. Let AB be that which is natu- 

 rally moved in a circle. I say that it is not the 

 same with those things which are moved in a right 

 line. For, if it is the same with any one of these, 

 it must either be naturally moved upwards or 

 downwards. But every simple body is moved with 

 one simple motion according to nature. Hence, 

 that which is naturally moved in a circle, is not the 

 same with anything moved in a right line. But 

 neither is it the same with anything compounded. 

 For it has been shown that everything which na- 

 turally moves in a circle is simple ; but that which 

 consists from things moved in a right line is a com- 

 posite. AB therefore, which is naturally moved 

 in a circle, is neither the same with things moved 

 in a right line, nor with those composed from 

 these. 



THEOREM 3. 



Things which are naturally moved in a circle, 

 neither participate of gravity nor levity. 



Demonstration. For if AB is either heavy or 

 light, it is either naturally moved to the middle, or 



