DESIGN VERSUS NECESSITY. 79 



design of a watchmaker. He thinks this very reason- 

 able, and, although he sees a difference between the 

 works of Nature and those of mere human art, yet if he 

 can find in any organic body, or part of a body, the 

 same adaptation to its use that he finds in a watch, this 

 truth will go very far toward proving, if it is not en- 

 tirely conclusive, that, in making it, the powers of life by 

 which it grew were directed by an intelligent, reason- 

 ing master. Under the guidance of Paley he takes an 

 eye, which, although an optical, and not a mechanical 

 instrument like the watch, is as well adapted to testify 

 to design. He sees, first, that the eye is transparent 

 when every other part of the body is opaque. Was 

 this the result of a mere Epicurean or Lucretian " for- 

 tuitous concourse " of living " atoms % " He is not yet 

 certain it mi^ht not be so. Next he sees that it is 

 spherical, and that this convex form alone is capable 

 of changing the direction of the light which proceeds 

 from a distant body, and of collecting it so as to form 

 a distinct image within its globe. Next he sees at the 

 exact place where this image must be formed a curtain 

 of nerve-work, ready to receive and convey it, or excite 

 from it, in its own mysterious way, an idea of it in the 

 mind. Last of all, he comes to the crystalline lens. 

 Now, he has before learned that without this lens an 

 eye would by the aqueous and vitreous humors alone 

 form an image upon the retina, but this image would 

 be indistinct from the light not being sufficiently 

 refracted, and likewise from having a colored fringe 

 round its edges. This last effect is attributable to the 

 refrangibility of light, that is, to some of the colors 

 being more refracted than others. He likewise knows 



