Part II. 7;^/^^ Great I ON. 251 



thro' a coloured Glafs things appear as well more 

 dim and obfcure as tindtur'd with the Colour 

 thereof. 



Secondly, The Parts of the Eye are made con- 

 vex, and efpecially the cryftalline Humour, which 

 is of a lenticular Figure, convex on both fides, 

 that by the Refractions there made, there might 

 be % Direction of many Rays coming from one 

 Point in the Objeft, viz, as many as the Pupil can 

 receive, to one Point anfwerable in the bottom of 

 the Eye, without which the Senfe would be very 

 obfcure, and alfo confused. There would be as 

 much difference in the Clearnefs and Diftindtion 

 of Vifion, were the outward Surface of the Tu^ 

 7iica Cornea plain, and the cryftalline Humour 

 remov'd, as between the Pidture received on white 

 Paper in a dark Room thro' an open or empty 

 Hole, and the fame received through a Hole fur- 

 nifh'd with an exaftly polifli'd lenticular Cryftal ; 

 which, how great it is, any one that hath but 

 feen this Experiment made, knows wxll enough ; 

 indeed, this Experiment doth very much explain 

 the manner of Vifion, the Hole anfwering to the 

 Pupil of the Eye, the cryftalline Humour to the 

 lenticular Glafs, the dark Room to the Cavity 

 containing the vitreous Humour, and the white 

 Paper to the T'unica Retina. 



Thirdly y The uveous Coat^ or Iris of the Eye, 

 hath a mufculous Power, and can dilate and con- 

 trail that round Hole ^ia it call'd the Pupil, or 



Sight 



