CAUSE OF ITS FAILURE. 83 



rays which has the sun's 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 supposing 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 of the circular form of the sun's image: 

 let these circular images become 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 obli- 

 terated, 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 it 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 explanation 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. 



Again, to pass to a more extensive failure : why 

 was it that Aristotle, knowing the property of the 



" Problem. 15. ora /Kd0i//aaTiKfj?, &0. 



G2 



