54 Experiments on a new Theory of Vision. 



and form an oblong image of the wafer, as thus represented: 



f'\/ '\ . From these experiments, and many others hereafter to 



be related in the 2d volume of the Experimental Outlines, not a 

 doubt remained on my mind, that reflected erect and not inverted 

 images gave mental impressions of a visible world. Surely, if any 

 thing can increase our admiration of the power and wisdom of a 

 supreme Being, it is the conviction that a beautiful and ever- 

 varving landscape is painted in miniature on the transparent cor- 

 nea. When we consider that the black choroid shines through 

 the retina, we must adn)it that it is very unfit to be the reflecting 

 mirror of the mind. To bring this to the test of experiment, I 

 turned out the aqueous, vitreous and crystalline humours of an 

 ox's eve. On bringing the inverted image of the black letter T, 

 pasted on the window, by means of a convex lens, to float on the 

 retina, I found that in some places it was perfectly invisible, in 

 other places confused, indistinct in all. Indeed the retina, were 

 it free from this and many other objections, and also free from 

 the large blood-vessels and nerves running over its surface, being 

 of a gray colour, like pounded glass or animal jelly, would be very 

 unfit, and could never form an image of a gray object perfectly 

 similar to itself: neither could objects the colour of the choroid 

 coat ever be seen. We might as well think of writing with black 

 hik on a sheet of black paper, as attempt the formation of dark 

 images on a dark grovmd. On the other hand, how admirably 

 fitted both for reflexion and transmission is the cornea ! both suf- 

 ficiently transparent and sufficiently opaque: no coloured sub- 

 stance could ansu'cr the purpose. It has hitherto been the re- 

 ceived opinion, that the two optic axes, concurring at the object, 

 make an angle according to the size of which the object appears 

 large or small ; — but this ojnnion, whose inconsistency has already 

 been pointed out by Bishop Berkeley, must yield to the more ra- 

 tional theory that the mind takes the apparent magnitude and 

 distance from the size of the corneal image, and not from lines 

 and angles beyond the nervous influence, or from invisible rays ; 

 all rays being iuvisible which are transparent until intercepted 

 and reflected. " In vain (savs Berkeley) shall all the mathema- 

 ticians in the world tell me that I perceive certain lines and an- 

 gles wnich introduce into my mind the various ideas of distance, 

 SQ long as I myself am conscious of no such thing." Indeed we 

 might as vvcU believe in ghosts and hobgoblins, as to believe that 

 we would see an object, or the image of an object, beyond the 

 nerves, that is, beyond the transparent cornea. Here lies the 

 Rubicon, the utmost limit, beyond which the mind can never tra- 

 vel. Surrounding objects are brought to the eye, bv means of the 

 solar rays of light ; hence the nerves convey them to the senso- 



rium. 



