CHAPTER XVI. 



THE SENSE OF SIGHT. 



1. THIS is the most refined and admirable of all our senses. 

 By it especially we hold converse with the external world ; 

 and without it, we should not only be deprived of a large 

 portion of the pleasures we now enjoy, but we should be un- 

 able to maintain our existence for any length of time. The 

 wisdom, power, and benevolence of God are chiefly mani- 

 fested to us through the sense of vision/ 5 



2. The eye is the organ of sight, and the most beautiful 

 of all the organs of the senses. So admirable is its struc- 

 ture, so wonderful the provisions which adapt it to the pur 

 poses for which it was designed by our Creator, that I shall 

 give as full a description of it as my limits will allow ; and 

 in order to an easy and clear comprehension of its structure 

 and function, I shall first describe the coats of the eye, in- 

 cluding the retina, or the expansion of the nerve of vision ; 

 then the humours of the eye, by the agency of which, the_ 

 rays of light are concentrated so as to form an image upon 

 the retina ; and lastly, explain the laws of vision, the motions 

 of the eye, and the means of protection against injury. 



3. The Coats of the Eye. The coats of the eye are 

 generally reckoned as three in number, viz. the sclerotic, the 

 choroid, and the retina ) besides these, there are the cornea, 

 the iris, and the ciliary processes, /which are viewed and des- 

 cribed as appendages to these coats. 



4.1 The sclerotic,* or outer coat, is the firm, opaque, fibrous 

 substance which preserves the globular figure of the eye ; and 

 besides defending its internal delicate structure, serves for the 

 attachment of those muscles which move the eye. It invests 



* From a Greek word, signifying hard. 



