Vision and Optical Glasses. 181 



is the largest of all in quantity, filling the whole 

 orb of the eye, and giving it a globular shape. 

 It is much of the same consistence as the white 

 of an egg, and very little exceeds water in its 

 refractive power. 



As every point of an object ABC, sends out 

 pencils of rays in all directions, some rays, from 

 every point on the side next the eye, will fall 

 upon the cornea between' E and F ; and by 

 passing on through the humours and pupil of 

 the eye, they will be converged to as many points 

 on the retina or bottom of the eye, and will there 

 form a distinct inverted picture cba of the object. 

 Thus, the pencil of rays qrs, that flows from the 

 point A of the object, will be converged to the 

 point a on the retina ; those from the point B 

 will be converged to the point b ; those from the 

 point C will be converged to the point c ; and so 

 on of all the intermediate points : by which means 

 the whole image abc is formed, and the object 

 made visible. 



That vision is effected in this manner, may l?e 

 demonstrated experimentally. Take a bullock's 

 eye while it is fresh, and having cut off the coats 

 from the back part, quite to the vitreous humour, 

 put a piece of white paper over that part, and 

 hold the eye towards any bright object, and you 

 will see an inverted picture of the object upon 

 the paper. 



It has been a matter of inquiry among scientific 

 persons, why the object appears in an upright 



