26 NATURAL THEOLOGY. 



only try to execute the same; he will find that his 

 threads and strings must be disposed with great 

 consideration and contrivance, to make a circle 

 which shall continually change its diameter yet 

 preserve its form. This is done in the eye by 

 an apphcation of fibres, i. e. of strings similar, in 

 their position and action, to what an artist would 

 and must employ, if he had the same piece of 

 workmanship to perform. 



[This figure represents the iris separated from the eye and laid 

 out flat. We perceive the straight fibres passing towards the 

 inner margin, and the circular fibres running round the margin.] 



II. The second difficulty which has been stated 

 was the suiting of the same organ to the percep- 

 tion of objects that lie near at hand, w^ithin a few 

 inches, we will suppose, of the eye, and of objects 

 which are placed at a considerable distance from 

 it, that, for example, of as many furlongs, (I speak 

 in both cases of the distance at which distinct 

 vision can be exercised.) Now this, according to 

 the principles of optics, that is, according to the 

 laws by which the transmission of light is regula- 



