68 AN ESSAY ON SINGLE VISION. 



and if two such points of the retina were deter- 

 mined, I think the chief difficulty in this matter 

 would then be overcome. But as it appears to 

 me, that the structure of the eye has not yet 

 been sufficiently explained, to enable any person 

 to take this first step, I forbear saying any thing 

 more upon the subject* 



