IMPROVED. Jii 



properly and wonderfully difpofed, with Con'vex and 

 Diaphanous Mediums the better to receive fuch Rays, 

 cannot but ftrike very fenfibly upon the fine Medul- 

 lary Fibres of the Retina ; but whether it be com- 

 municp.ted to the Soul by Undulation or Vibration, 

 is what I ihall not pretend to determine. 



The Eye may be confidered as a Camera Ohfcura Camera 

 or dark Chamber, to make which, fhut the Doors 0^^<^\'^^ 

 and Window-fhutters of a Room very tight and ^^^^*^^^*^^'^* 

 clofe, fo as no Light be admitted to come in but by 

 a fmall Hole in one of the Shutters : Then place a 

 Sheet of white Paper, which may be fuppofed to 

 reprefent the Retina in the Eye : I fay, place this 

 at a convenient Dillance from the Hole, and the 

 Rays refle£led from Objeds without, or in the 

 Street, will crofs one another in the Hole, and 

 paint the Image inverted or topfyturvy on the Pa- 

 per, though but faintly. 



Thus it would do upon the Retina, although Vifion par- 

 there were no Humours in the Eye, neither Cryftal-'^^l^'^ 

 line. Vitreous, nor Aqueous, no nor even the Cornea ^-^'^ Crvt- 

 ©r homy Coat, provided there was only a fmall talline or 

 Hole,, fuch as the Pupil, for the Rays to pafs other Hu- 

 through, as in the Camera Ohfcura ; fo that it is ii^<M,ifS» 

 poffible for a Creature to fee without the help of the 

 Cryftalline Humour j and perhaps this may have 



made Dr. 7" r imagine, that he turns the whole 



Body of the Cryftalline Humour out of its Place, 

 when he couches a Catara6l. But he muft be only 

 a Smatterer in Opticks that knov/s not thus far, to 

 wit, that if the Cryftalline Humour were totally 

 removed out of its Place, the Images of Objefts 

 would be fo faintly painted upon the Retina, that a 

 Perfon might be near as v/ell blind. So that all the 

 Parts of the Eye ( as I fhall ftiew hereafter,) contri- 

 bute to the greater Perfetlion of Sight. 



For Example, a hens or Speflacle-Glafs, we may The Rays 

 fuppofe to be the Cryftalline Humour behind the ^'^ L^ght 

 Pupil or Sight of the Eye; I fay fuch Glafs, being ^^^"^^^S^^ 

 placed betwixt the Hole and the Paper, will make cryilallinc 



theHumour, 



