Experiments on a new Theory of Vision. 49 



the changes of this corneal image. I next removed the lens 

 somewhat further from the eye, and on looking into it perceived 

 the letter T to be inverted, and the spectator hkewiie saw it in- 

 verted. He now took the lens in his ov,'n hand, and placing it 

 at different distances before his eye, I was enabled by means of 

 the corneal image to tell him v/hat he saw. Having again re- 

 quested the spectator to fix his eyes on the letter, 1 placed a con- 

 cavo-concave lens before the pupil, and the letter was immedi- 

 atelydiminished; he said he now saw it very small. Here I shall 

 beg leave to remark that these experiments strike at the very first 

 principles as laid down for optical instruments. For we find by 

 these two simple and conclusive experiments, that a convex lens, 

 instead of converging the ravs as first maintained by Maurolycus 

 in his treatise De Lumine el Umbra, actually and londjide di- 

 verges and magnifies the images in all its dimensions ; and on the 

 other hand, that a concave glass converges or diminishes the 

 image. The object of this paper being merely to draw fhe at- 

 tention of the scientific to mv opinions on optics, and particularly 

 on vision, I shall not at present enter more fully into the theory 

 of spectacles, object-glasses, ccc. 



Exp. 2d. — Having placed a plano-convex lens at such a di- 

 stance before the spectator's eye, as to form an inverted image 

 of the letter T on his pupil, I placed a concavo-concave lens be- 

 hind, so as to represent an opeva-glass or Galilean telescope. The 

 inverted corneal image immediately became erect, and the spec- 

 tator said he also saw it erect. 



Exp. 3d. — The above experiments were ma-ie at about four 

 feet from the window. I now requested the si)ectator to remove 

 his chair to within a foot of the object ; and on placing a convex 

 lens immediatelv before the eye, the corneal image was conside- 

 rably magnified : on slowly removing the lens more to the letter, 

 and further from the eye, the black corneal image began to be 

 surrounded with colours; hut did not become inverted, nor did the 

 spectator perceive any change of position ; when close to the ob- 

 ject the corneal image appeared better defined and more distinct. 

 1 next placed a prism before his eye, and desired him to look 

 through the lower refracting angle. As he was unaccustomed to 

 the application of this instrument, he could not regulate it so as to 

 perceive the coloured image of the letter T. I therefore turned 

 the prism until I perceived it on the pupil, and then told him ex- 

 actly what he saw, making a mirror of his eye. Let us now in- 

 quire what changes the intervention of a plano-convex or a con- 

 cave glass would make on the letter T brought to a focus on the 

 retina i)y means of the crystalline and other humours. Having 

 removed the fat and ci>ats from the back part of an ox's eye, as 

 performed bv Kepler and Schcincr, and thus laid bare the retina. 



Vol. 5 4 . No. 2.').') . July 1 S If). D I placed 



