NATURAL THEOLOGY. 



19 



I know no better method of introducing so large 

 a subject, than that of comparing a single thing 

 with a single thing: an eye, for example, with a 

 telescope. As far as the examination of the instru- 

 ment goes, there is precisely the same proof that 

 the eye was made for vision, as there is that the 

 telescope was made for assisting it. They are 

 made upon the same principles ; both being ad- 

 justed to the laws by which the transmission and 

 refraction of rays of light are regulated. I speak 

 not of the origin of the laws themselves ; but such 

 laws being fixed, the construction in both cases is 

 adapted to them. For instance ; these laws re- 

 quire, in order to produce the same effect, that the 

 rays of light, in passing from water into the eye, 

 should be refracted by a more convex surface 

 than when it passes out of air into the eye. Ac- 

 cordingly we find that the eye of a fish, in that 

 part of it called the crystalline lens, is much rounder 

 than the eye of terrestrial animals. What plainer 

 manifestation of design can there be in this differ- 

 ence? What could a mathematical instrument 

 maker have done more to show his knowledge of 

 his principle, his application of that knowledge, 



