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XXL On the structure: oj the crystalline lens injhfies and qua- 
drupeds, as ascertained by its action on polarised light. By 
David Brewster, LL.D. F. R. S. Fond, and Fdin, In a 
Letter addressed to the Right Hon. Sir Joseph Banks , Bart. 
G.C.B.P.R.S. . jy. jiyH , I'-’nd'Y):'; 
Read June 3 o,i 8 i 6 . 
Dear Sir, 
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•alt Ofil 1 :o gsffod tei ■ 
There is, perhaps, no subject in natural history which has 
excited so much attention, as the structure and functions of 
the eyes of animals ; and there is certainly none which has 
so ill repaid the anxiety and labour with which it has been 
investigated. The physiologist was naturally led to study 
the mechanism of an organ through which man receives the 
noblest of all his enjoyments ; and the natural philosopher, 
considering it as the work of infinite intelligence, ardently 
anticipated the improvement of optical instruments from the 
imitation of this perfect model. It is discouraging however, to 
estimate the real amount of the labours of the one, and to per- 
ceive how little advantage has been derived from them by the 
other. The most prominent functions of the eye are still very 
imperfectly understood, and the improvement of the tele- 
scope has been retarded, rather than advanced, by the pursuit 
of a false analogy. I have, therefore, some satisfaction in 
being able to throw additional light upon a subject of such 
difficult investigation, and so generally interesting both from 
its optical and physiological relations. 
