50 Experiments on a new Theory of Vision. 



I placed ;i liglited candle in front. An inverted image was seen 

 as if floating on t!ie retina. I now placed a plano-convex lens 

 between the candle and the cornea, at such a distance as to form 

 an inverted image on the ])npil. The retinal image remained 

 inverted. On now placing a concavo-concave lens at a little di- 

 stance before the convex one, the corneal and inverted image 

 became erect, while the retinal inverted image was not in the 

 least changed as to position. Here is a direct experimental proof, 

 that even if an inverted image were painted on the retina, that 

 inverted image, not undergoing any change opposition by the in- 

 tervention of the glasses, could not be theimacre conveved to the 

 mind. To suppose for one moment, that an inverted image on 

 the retina could produce both the idea of inversion and erection, 

 would I)e adding another inconsistency to Kepler's catalogue. 

 In this experiment the changes of the corneal image were ac- 

 companied by simultaneous changes in the mind ; therefore that, 

 and that alone, must have produced the sensation. On placing 

 a glass globe about two inches diameter filled with water oppo- 

 site the letter T on the window, and then interposing a convex 

 lens, the posterior inverted image was obliterated,the rays of black 

 light not being sufficiently strong. The same thing took place 

 with a concave lens. Dr. Priestley, who wrote a number of me- 

 taphysical works, gravely informs his readers, " that the want of 

 an inverted image might produce the sensation of an erect one." 

 With great respect for the Doctor's opinions, we might just as 

 readily believe that the want of a man's dinner would get him a 

 supper ! 



There is no inverted image ever painted on the retina. 



Having removed the tat and coats from the back part of an 

 ox's eye, and thus bared the retina, in imitation of Kepler's and 

 Scheiner's experiments, I placed a lighted candle on a table in 

 front; and on looking througii the retina, my eye being placed 

 beyond the principal focus of the sphere (or rather two segments 

 of one), I certainly did perceive a beautiful and inverted image of 

 the candle as if floating on the retina. So far the experiment 

 seemed to accord with the retinal theory of vision ; for, if the rays 

 were refracted and converged, as represented by optical writers, 

 by means of the cornea, aqueous humour, crystalline lens, and vi- 

 treous humour, they should cross nearly in the centre of the eye, 

 and finally paint an inverted image on the retina. However, on 

 approaching my eye nearer to the retina, I perceived the inverted 

 image to become large, confused; and when my eye was very close, 

 it opened into two curved and inverted images, which receded 

 laterally, and at a yet nearer approach formed into a circle, 

 through the centre of which I perceived a very distinct and erect 

 image of the candle, evidently coming from the anterior surface of 



the 



