28 NATURAL THEOLOGY. 



the state of the organ there must be,) had long 

 formed a subject of inquiry and conjecture. The 

 change, though sufficient for the purpose, is so 

 minute as to elude ordinary observation. Some 

 very late discoveries, deduced from a laborious 

 and most accurate inspection of the structure and 

 operation of the organ, seem at length to have 

 ascertained the mechanical alteration which the 

 parts of the eye undergo. It is found, that by the 

 action of certain muscles, called the straight mus- 

 cles, and which action is the most advantageous 

 that could be imagined for the purpose, it is found 

 I say, that whenever the eye is directed to a near 

 object, three changes are produced in it at the 

 same time, all severally contributing to the adjust- 

 ment required. The cornea, or outermost coat of 

 the eye, is rendered more round and prominent ; 

 the crystalline lens underneath is pushed forward i 

 and the axis of vision, as the depth of the eye is 

 called, is elongated. These changes in the eye 

 vary its power over the rays of light in such a 

 manner and degree as to produce exactly the ef- 

 fect which is wanted, viz. the formation of an im- 

 age tipoiL the j^etina, whether the rays come to the 

 eye in a state of divergency, which is the case 

 when the object is near to the eye, or come paral- 

 lel to one another, which is the case when the ob- 

 ject is placed at a distance. Can anything be 

 more decisive of contrivance than this is ? The 

 most secret laws of optics must have been known 

 to the author of a structure endowed with such a 



