THE EYE. 301 



the cohesive and repulsive forces as they order 

 the changes in the material of the world, and in 

 that of our own frames. Yet these instruments 

 are not in contrast with the eye : but through the 

 comparison of them we discover the wonderful 

 adaptations of that organ, of which it has long 

 ago been said, that it can at one time extend our 

 contemplations to the heavenly bodies and their 

 revolutions, and at another, limit its exercise to 

 things at hand, to the sympathies and affections of 

 our nature visible in the countenance. 



If we put aside the consideration of the living 

 properties of the organ, as the extraordinary va- 

 riety and degrees of sensibility in the nerve of 

 vision, and confine ourselves to points easily com- 

 prehended, as, for example, the mechanism of the 

 eye, and the laws of optics as applicable to the 

 humours, we shall find enough to admire. 



When we look upon the optician's lens, how- 

 ever perfect its polish may be, we can see its con- 

 vex surface : that is to say, the rays of light which 

 strike upon that surface do not all penetrate it, 

 but are in part reflected to our eye, which is 

 the occasion of our seeing it. We do not see 

 the surface of the cornea of the human eye. 

 Here, then, is an obvious superiority, since it im- 

 plies that all the rays of light which strike the cor- 

 nea enter it and are refracted, and none are re- 

 turned to our eye. If we take the optician's lens 

 between our fingers and hold it under water, we 

 can no lon_;er see it, however transparent the 

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