306 Royal Society. 



the interior of our own eye with facility, so as to recognize in what 

 lenticular structure, and what part of it, the cause of any shadow or 

 " diffractive image " resides. He shows that we may make every 

 measurement of interest, may decide all the points just alluded to, at 

 the instant, as it were, by mere inspection ; and he illustrates his 

 optical principles by appropriate experiments. 



The paper then commences its actual elimination of ocular spectres 

 from one another, starting from the appendages of the eye and going 

 on through the ocular tissues in succession to the retina, under 

 several heads, as — 



Optical Effects of the Eye-lashes, Eye-lids, and Conjunctival Fluids. 



These jjroduce phsenomena of reflexion, refraction, and inflection. 

 They may multiply the images of objects which are without or which 

 are within the eye, and occasion us to see the latter. The conjunc- 

 tival fluids render apt illustrations of "recondite" diffractive sha- 

 dows. 



Optical Structure of the Crystalline Lens. 



It is shown that the stelliform figure of our crystalline lens is 

 distinctly visible in divergent light. The lens contains numerous 

 bodies displaying a series of diffractive fringes. The fringes of the 

 border of the iris are likewise conspicuous. Whenever light radiates 

 into the eye from a near point, all these things happen. Hence when 

 a line of radiants (an edge of any body) is before the eye, a mosaic 

 fringe of these coloured shadows will be formed ; and there is an 

 ocular fringe, as well as the fringe on the edge of a body by light 

 inflected at the body. The ocular colours mentioned seem to have 

 been the cause of the belief that it can be proved experimentally that 

 the eye contains no provision for the correction of chromatic disper- 

 sion ; whereas the colours spoken of should only be compared with 

 those that are produced by faivs in the glasses of optical instru- 

 ments. 



The Structure of the Vitreous Body derived from Optical Phenomena. 



On this head the author arrives at the following conclusions. 



In the vitreous body are innumerable vesicular globules, ranging 

 in size from O0008 to 0"005 of a line, which are arranged in un- 

 broken series, in tubes more or less transparent. These tubes pre- 

 cisely resemble veins and arteries in their mode of ramification ; they 

 frequently anastomose and are united to one another by capillary 

 plexuses, and they are of less specific gravity than the vitreous fluid. 

 The trunks of this peculiar system of vessels probably arise in the 

 region of, or at the base of the optic nerve, and ramify in the vitreous 

 humour ; the larger branches passing circumferentially within a 

 limited distance of the hyaloid membrane, and yielding again many 

 branches, which, after repeated subdivisions, end in a capillary net- 

 work exceedingly subtle and close. Many of the terminal loops of 

 the capillaries are attached to the hyaloid membrane, so as to con- 

 fine the majority of the branches in a lax manner to its vicinity. A true 



