NATURAL THKOLOGT. 43 



eye. It is the little ball we take out of a fish's eye. 

 Immediately behind the chrystaline, is situated the 

 last glass of the eye, something in the shape of the 

 water glass in front, and is called the vitreous humor, 

 , from its resemblance to melted glass. The light, by 

 passing through all these glasses, so to term them, is 

 drawn to a little round spot, such as is made by a 

 burning-glass ; and this spot contains an image of the 

 object at which we look. Thus, if we hold up a 

 a spectacle or telescope glass between the window 

 and a sheet of paper, there will be a small bright spot 

 on the paper, and in that spot we shall see the image 

 of the window and the objects on the outside. The 

 glasses in the eye do the same ; and it is so contrived, 

 that the image falls exactly upon the delicate sub- 

 stance of the nerve which is spread out on the back 

 part of the eye, like a sheet of paper, and is called 

 the retina. If the skin on the hinder part of an ox's 

 eye be carefully removed, and the eye be held up to 

 the window, the images of objects in the street will 

 be seen distinctly painted on the back, where the re- 

 tina is situated. If any injury happen to the eye to 

 prevent the image from being formed, we are unable 

 to see. This, therefore, is the demonstration of de- 

 sign, nature requiring an image for the purposes of 

 vision, has furnished an instrument perfectly adapted 

 to produce it ; a mechanical and complicated instru- 

 ment ; in sho"rt, a literal telescope. 



T. You spoke of the roundness of the eyebalL 

 Is it a perfect sphere ? 



