88 THE GKEEK SCHOOL PHILOSOPHY. 



of the circular form of the sun's image : but these circular images be- 

 come larger and larger as they are farther from the hole, while the 

 central image of the hole remains always of the original size ; and 

 thus at a considerable distance from the hole, the trace of the hole's 

 form is nearly obliterated, and the image is nearly a perfect circle. 

 Instead of this distinct conception of a cone of rays which has the sun's 

 disk for its basis, Aristotle has the following loose conjecture. 15 " Is 

 ii because light is emitted in a conical form ; and of a cone, the base 

 is a circle ; so that on whatever the rays of the sun fall, they appear 

 more circular ?" And thus though he applies the notion of rays to 

 this problem, he possesses this notion so indistinctly that his explana- 

 tion is of no value. He does not introduce into his explanation the 

 consideration of the sun's circular figure, and is thus prevented from 

 giving a true account of this very simple optical phenomenon. 



6. Again, to pass to a more extensive failure : why was it that Aris- 

 totle, knowing the property of the 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 connection 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 diffi- 

 culties 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 

 something more wonderful still. Now the most wonderful 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 qualities ; for it is both convex and con- 

 cave. In the next place, it has, at the same time, opposite motions, 

 for it moves forward and backward at the same time. For the circum- 

 ference, setting out from any point, comes to the same point again, so 



15 Problem. 15, baa fiaOtijiar'tKiii, &C. 



