CAUSE OF ITS FAILURE. 87 



history of the ancient Greek mind, can question, that in acuteness, in 

 ingenuity, in the power of close and distinct reasoning, they have never 

 been surpassed. The common opinion, which considers the defect of 

 their philosophical character to reside rather in the exclusive activity 

 of such qualities, than in the absence of them, is at least so far just. 



5. We come back again, therefore, to the question, What was the 

 radical and fatal defect in the physical speculations of the Greek phi- 

 losophical schools ? 



To this I answer : The defect was, that though they had in their 

 possession Facts and Ideas, the Ideas were not distinct and appropriati 

 to the Facts. 



The peculiar characteristics of scientific ideas, which I have endear - 

 ored to express by speaking 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 

 clearness, 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 endeavors 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 distance 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 pro- 

 ceeding from every point of the sun's disk and passing through every 

 point within the boundary of the hole. By attending to the conse- 

 quences of this mode of conception, it w : ill be seen that each point of 

 the hole will be the vertex of a double cone of rays which has the suns 

 disk for its base on one side and an image of the sun on the other ; 

 and the figure of the image of the hole will be determined by suppos- 

 ing a series of equal bright circles, images of the sun, to be placed 

 along the boundary of an image equal to the hole itself. The figure 

 of the image thus determined will partake of the form of the hole, and 



