84 THE GREEK SCHOOL PHILOSOPHY. 



lever, and many other mechanical truths, was unable 

 to form them into a science of mechanics, as Archi- 

 medes afterwards did ? 



The reason was, that, instead of considering rest 

 and motion directly, and distinctly, with reference 

 to the Idea of Cause, that is Force, he wandered in 

 search of reasons among other ideas and notions, 

 which could not be brought into steady connexion 

 with the facts; the ideas of properties of circles, 

 of proportions of velocities, -the notions of "strange" 

 and "common," of "natural" and "unnatural." 

 Thus, in the Proem to his Mechanical Problems, 

 after stating some of the difficulties which he has 

 to attack, he says, " Of all such cases, the circle 

 contains the principle of the cause. And this is 

 what might be looked for ; for it is nothing absurd, 

 if something wonderful is derived from some- 

 thing more wonderful still. Now the most won- 

 derful thing is, that opposites should be combined; 

 and the circle is constituted of such combinations 

 of opposites. For it is constructed by a stationary 

 point and a moving line, which are contrary to 

 each other in nature; and hence we may the less 

 be surprised at the resulting contrarieties. And 

 in the first place, the circumference of the circle, 

 though a line without breadth, has opposite qua- 

 lities; for it is both convex and concave. In the 

 next place, it has, at the same time, opposite mo- 

 tions, for it moves forward and backward at the 

 same time. For the circumference, setting out from 



