Dr Brewster and Dr Gordon on the Human Eye. 
phers, has made the refractive power of the vitreous humoui* 
1.336, the very same number which he obtained for water. 
This similarity in the refractive powers of these two fluids, 
appeared to us in some measure improbable, as the albumen, which 
enters in a slight degree into the composition of the aqueous and 
vitreous humours, is known to have a much higher refractive 
power than water, and as there is no example of any fluid or 
solid body being inferior to water, or even so low, in its action^ 
upon light. 
In order to determine this point, we formed a hollow prism 
•with two plates of parallel glass, fixed at an invariable angle, 
and, that there might be the least possible chance of error, we 
compared the refractions occasioned by the two humours, di- 
rectly with that produced by water. The difference of the de- 
viations arising from refraction, afforded an accurate measure of 
the refractive powers, by comparing them with that of water, 
which is fixed at 1.3358. A portion detached from the outer 
coat of the crystalline lens, and a portion detached from a coat 
nearer the centre, were compared in a similar manner with wa- 
ter ; and in order to obtain an average result for the whole of 
the crystalline lens, we placed it in its entire state in the hol- 
low prism, and measured the refractive deviation which it occa- 
sioned. From these and other measurements we obtained the 
following results : 
Refractive power of water, 1 .3358 
Ditto, of the aqueous humour, 1.3366 
— ■' ■ — vitreous humour, l.SSd^f 
— outer coat of crystalline,.. 1.3767 
middle coat of ditto, 1.3786 
— central part of ditto, 1.3990 
■ of the whole crystalline, 1.3839 
‘ Inch. Thous, 
Diameter of the crystalline, 0.378 
cornea, 0.400 
Thickness of the crystalline, 0.172 
cornea, 0.042 
When the human crystalline was exposed to polarised light, it 
exhibited the phenomena of double refraction, and produced 
