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Every simple body is moved with one motion 

 according to nature. 



DEFINITIONS. 



That is heavy which is moved towards the 

 middle. 



That is light which is moved from the middle. 



That is said to be moved in a circle which is 

 continually borne from the same to the same. 



Contrary motions are from contraries to con- 

 traries. 



One motion is contrary to one. 



Time is the number of the motion of the celes- 

 tial bodies. 



The motion is one which is without difference 

 according to species, and belongs to one subject, 

 and is produced in a continued time. 



THEOREM 1. 



Things which are naturally moved in a circle 

 are simple. 



Demonstration. Let AB be that which is natu- 

 rally moved in a circle. I say that AB is simple : 

 for, since the motion in a circle is a simple motion ; 

 but every simple motion is the motion of a simple 

 body; hence AB is a simple body. Things, there- 

 fore, which are naturally moved in a circle are 

 simple. 



