'Experiments on a neiv Theory of Visio7i. 51 



the eye, and perfectly distinct from the inverted one, considerably 

 magnified in passing through the humour, Kepler, in placing 

 his eye beyond the focus of the ox's eye, which is nothing more 

 than a simple sphere, saw an inverted image formed by the junc- 

 tion of the two images painted on his own cornea, which he mis- 

 took for one on the retina, as a person looking into a concave 

 mirror thinks he sees an inverted image in the glass. Here I think 

 it necessary to give a rough sketch of the passage of the rays 

 through the eye, particularly as my opinions are diametrically 

 opposite to those of all optical writers. 



A glass globe filled with water, and about two inches diameter, 

 may serve those unacquainted with morbid dissections : ab are two 



rays of h'ght coming from the upper and lower parts of the can- 

 dle, mipinge on the transparent cornea at c, and paint an erect 

 image. This image again transmits rays, diverging as they pass 

 through the sphere to g, where the spectator sees a magnified 

 and erect image. The image at the cornea c also sends rays, 

 forming inverted images in consequence of the rays crossing; — 

 these images take the curvature of the glass globe, and, uniting into 

 one inverted image, form what has been denominated the princi- 

 pal refracted focus at /. Now it is evident that Kepler, to have 

 made his experiments correctly, should have placed his eye at g, 

 and not at/; indeed, his eye should almost touch the 'retina; 

 and then, as I have already said, he would have seen an erect 

 magnified iniage of the cand'le, and not an inverted one surrounded 

 by what optical writers denominate a circle of aberration. It is 

 really surprising how any person could for a moment believe that 

 this circle of aberration could produce vision, according to the 

 present theory of vision. Long-sightedness they say is produced 

 by the image being formed beyond the retina. Short-sightedness, 

 by an image formed before the retina in the vitreous humour, — 

 both physical impossibilities ! The rays of light are supposed to 

 be converged in the body of the eye. I would beg leave to put 

 the following question : Would tlie crystalline lens, when em- 

 bedded in the vitreous hiHnour,act in the same manner as it would 

 in air ? Certainly not, as the foilowing easy experiment may 

 show. Take a large basin of water, holding a powerful glass lens 

 m such a position over the water as to form an inverted image 



D 2 or 



