Vision of the Retina. 45 



sometimes dilating, but always contrary to the contraction and 

 dilation of the retina itself. 



Does not this fact prove that the meshes of the retina must 

 be of an elastic nature ? Perhaps its use in some way is to 

 keep the pupil, or the opening of the pupil, of a certain dimen- 

 sion. Nothing can be more beautiful than the appearance of 

 the spectrum thus seen when the eyes are closed ; the diamond 

 beetle is not more brilliant : but I have observed that two 

 things are requisite to our seeing this phenomenon in per- 

 fection; — one is a sudden and broad glare of light, and the other 

 is the rest which all eyes have by sleep and closed lids. Even 

 after a doze in the afternoon, and with the precaution of keep- 

 in" the eyes shut before the light is thrown on the closed lids, 

 the appearance is not so brilliant if the eyes have been rubbed 

 or the lids opened : practice, however, will soon enable others 

 to see all the variations which take place. 



The wavy lines of which I speak are only seen under parti- 

 cular circumstances, — when the eyes are a little depressed by 

 the hands in the afternoon, when the light is first thrown on 

 them. The peculiar wavy appearance certainly arises from 

 the irregular compression of the meshes or intersections of the 

 retina. When these meshes are first seen, they are composed 

 of straight lines forming squares, and these squares are nar- 

 rowed off, as anything of a reticular or net-work-like form 

 would be, or would have the appearance of being, to the eye, 

 if seen painted on a vaulted or concave surface. The unnatural 

 pressure of the eyeballs by the fingers forces the net-work out 

 of its regularity, and two sides of the square bulge out and form 

 a curve, the convexity being outward: the other two sides are 

 wavy, being bent in two regular curves, thus elongating the 

 squares. 



This must now confirm the opinion that the seat of vision 

 does not exist in the eye at all ; that the eye does no more 

 than modify and transmit to the sensory the light which ema- 

 nates from the surface of all bodies ; and that no image, while 

 the eye is living, can be found on the hinder part of the eye. 

 The retina, too, from its peculiar shape, being square, would 

 not seem to be suited to the purpose of conveying rays of light 

 of different density even if it was not now certain that we can 

 see it; and as to the appearance of an inverted image on the 

 hinder part of the eye when dead, that of itself would be con- 

 clusive against the supposition that the retina is the seat of 

 vision, for the camera obscura, and several other optical in- 

 struments, show the image inverted likewise, and there is 

 nothing in these glasses of the nature or character of the re- 



