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tually moved. And if anything else moves when 

 A is no more, the motion is not continual ; which 

 is impossible. Hence, that which moves a perpe- 

 tual motion is itself perpetual. 



THEOREM 11. 



That which is immoveable is the leader of things 

 moving and moved. 



Demonstration. For let A be moved by B, and 

 B by C, I say that this will some time or other 

 stop, and that not everything which moves will be 

 itself moved: for, if possible, let this take place. 

 Motions, therefore, are either in a circle, or ad 

 infinitum. But, if things moving and moved are 

 infinite, there will be infinite multitude and mag- 

 nitude : for everything which is moved is divisible, 

 and moves from contact. Hence, that which con- 

 sists from things moving and moved infinite in 

 multitude, will be infinite in magnitude. But it is 

 impossible that any body, whether composite or 

 simple, can be infinite. But if motions are in a 

 circle, some one of things moved at a certain time, 

 will be the cause of perpetual motion, if all things 

 move and are moved by each other in a circle. 

 This, however, is impossible : for that which moves 

 a perpetual motion is perpetual. Neither, there- 

 fore, is the motion of things moved, in a circle, nor 



