312 
c 1 
Dr. Brewster on the structure of the 
Having found that the doubly refracting structure could be 
communicated to glass and other bodies, by giving them a 
variable density either through the agency of heat or mecha- 
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nfcal pressure, I was led to conclude, that the same structure 
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would be foimd in the crystalline lens of fishes and other 
animals, which was known, by direct experiment, to increase 
in density towards the centre. I had formerly examined 
the action of the crystalline upon polarised light, without ob- 
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taming any new result; but I now placed such reliance on 
11 
the truth of the general principle, that I resumed the subject 
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With the utmost confidence of success. 
: :: . 
Upon exposing to a polarised ray the crystalline lens of a 
lar^b cod, inclufiedf in its capsuTe 1 , 1 ! 9 could tioc percei ve, as hap- 
pened'' in'^my" early experiments, any very distinct indications 
of a peculiar action. I plunged it, however, in Canada balsam 
contained in a hollow parallelepiped of gl ass, and was sur- 
prised to observe a regular optical figure varying its shape 
p . • 
during the revolution of the crystalline. 
I now turned the spherical crystalline, till the diameter 
which corresponded to the axis of the eye, or the line joining 
'.if ^noliufovd'r e.lo- sg’nioft bm rti p.srnii 'tudf hr .. . . ° 
the poles to which the fibres converge, was parallel to the 
polarised ray, and I observed the appearance shown in Fig. i. 
(PI. XII.) consisting of twelve luminous sectors, i, 2, 3, 4, 5, 
6 3 7, separated from^ eacH other by a black 
cross, and by two dark concentric circles. The interior sec- 
tors, i, 2, 7, 8, were small and exhibited a White tint of the 
first order, increasing in brilliancy towards the centre. The 
middle sectors 3, 4, 9, 10, which are very large, are sepa- 
rated from the interior ones, by a broad dark circle, and dis- 
in'Vj 
play a white tint of the same intensity. The outer sectors 
