82 THE GREEK SCHOOL PHILOSOPHY. 



of them as distinct and appropriate to the facts, must 

 be more fully and formally set forth, when we come 

 to the philosophy of the subject. In the mean 

 time, the reader will probably have no difficulty in 

 conceiving that, for each class of Facts, there is some 

 special set of Ideas, by means of which the facts 

 can be included in general scientific truths; and that 

 these Ideas, which may thus be termed appropriate, 

 must be possessed with entire distinctness and clear- 

 ness, in order that they may be successfully applied. 

 It was the want of Ideas having this reference to 

 material phenomena, which rendered the ancient 

 philosophers, with very few exceptions, helpless and 

 unsuccessful speculators on physical subjects. 



This must be illustrated by one or two examples. 

 One of the facts which Aristotle endeavours to 

 explain is this ; that when the sun's light passes 

 through a hole, whatever be the form of the hole, 

 the bright image, if formed at any considerable dis- 

 tance from the hole, is round, instead of imitating 

 the figure of the hole, as shadows resemble their 

 objects in form. We shall easily perceive this 

 appearance to be a necessary consequence of the 

 circular figure of the sun, if we conceive light to be 

 diffused from the luminary by means of straight rays 

 proceeding from every point of the sun's disk and 

 passing through every point within the boundary of 

 the hole. By attending to the consequences of this 

 mode of conception, it will be seen that each point 

 of the hole will be the vertex of a double cone of 



