244 PHILOSOPHICAL TRANSACTIONS. [aNNO l668, 



eye, i. e. to the place where is made the picture of the objects we directly 

 look on ; and that in man it is somewhat higher, and on the side towards the 

 nose ; to make therefore the rays of an object fall upon the optic nerve of my 

 eye, and to find the consequence thereof, I made this experiment : 



I fastened on an obscure wall, about the height of my eye, a small round 

 paper to serve me for a fixed point of vision ; and such another on the side 

 towards my right hand, at the distance of about two feet ; but somewhat 

 lower than the first, that it might strike the optic nerve of my right eye, while 

 I kept my left shut. Then I placed myself over against the first paper, and 

 drew back by little and little, keeping my right eye fixed and very steady upon 

 the same ; and being about ten feet distant, the second paper totally dis- 

 appeared. 



That this cannot be imputed to the oblique position of the second paper, is 

 evident, as I can see other objects further to the side of it ; so that one would 

 believe that the second paper was taken away, if one did not find it again by 

 the least stirring of the eye. 



This experiment I made often, varying it by different distances, and remov- 

 ing or approaching the papers to one another proportionally. I made it also 

 with my left eye, by keeping my right shut, after I had fastened the second 

 paper on the left side of my point of vision, so that from the situation of the 

 parts of the eye it cannot be doubted but that this deficiency of vision is upon 

 the optic nerve. 



This discovery I communicated to many of my friends, who found the same 

 thing, though not always at the same distances ; which difference I ascribed to 

 the different situation of the optic nerve. Some at the distances mentioned 

 have lost sight of a paper eight inches large, but others not so soon, which 

 must be caused by the different magnitudes of the optic nerve in different eyes. 

 This experiment has given me cause to doubt, whether vision was indeed 

 performed in the retina (as is the common opinion) or rather in that other 

 membrane which at the bottom of the eye is seen through the retina, and is 

 called the choroides. For if vision were made in the retina, it seems that then it 

 should be made wherever the retina is ; and since the same covers the whole 

 nerve, as well as the rest of the bottom of the eye, there appears no reason to 

 me why there should be no vision in the place of the optic nerve where it is : 



good mathematician for the age he lived in, and was the first French philosopher who applied much to 

 experimental physics. The law of the shock or collision of bodies, the theoiy of the pressure and 

 motion of fluids, the nature of vision, and of the air, more particularly engaged his attention. And 

 he was remarkable for carrying into his philosophical researches that spirit of scrutiny and investiga- 

 tion, so necessary to those who would make any considerable progress in discovery or improvement. 



