254 
SIR DAVID BREWSTER ON THE CHANGES IN THE STRUCTURE 
Plate XV. fig 1 . 1., in which only two structures, or two series of positive sectors, are 
visible *. The lens was now a day old, and there seemed to be a faint light within 
the two black rings, especially in the outer one, which was either the remains of an 
old, or the germ of a new structure. If this were the case, then the anomalous 
combination of two positive structures would be converted into a combination of 
four structures, in which a negative and a positive one alternated. 
On the following day I prepared the other lens with the same care, and found my 
conjecture completely verified. In the middle black ring, which was distinctly 
brownish in the first lens, the negative structure had evidently commenced at one 
part, and the colour of the whole ring was a brighter brown than in the first lens. 
In the outer black ring another negative structure had also appeared, and had ad- 
vanced considerably upon the positive structure. These phenomena I have repre- 
sented in fig. 2., where the four structures are distinctly seen, the second being a faint 
blue of the first order. On the third day the two new structures had become more 
prominent. The structure No. 2, now a pale white of the first order, was com- 
pletely developed, having encroached upon and almost obliterated the third structure. 
The structure No. 4, which was not in existence on the first day, had now the maxi- 
mum tint, namely a bright white of the first order. On the fourth day the struc- 
tures No. 2 and 4, which at first were not in existence, are now the structures with 
the maximum tints, and No. 3, which had the maximum tint, is now almost oblite- 
rated, a little faint brown light remaining in one of the quadrants. 
On the fifth day the four sectors of the inner structure No. 1, have almost disap 
peared. No. 3 has disappeared entirely, and No. 2, which is almost the only polar- 
izing structure, exhibits a more intense white of the first order than appeared in any 
part of the lens. The ring No. 2 divides the radius of the lens equally. 
On the sixth day the structure No. 2 was still bright and uniform, but the polar- 
ized light had disappeared from every other part of the lens. 
On the seventh day the lens, which was always placed in water, burst its capsule, 
and there was no longer any trace of distinct polarizing structures. 
My next observations were made on the lenses of a cow nearly twenty years old. 
The following were the dimensions of the eye and the lenses. 
Inch. 
Diameter of eyeball .......... L66 
Chord of the cornea (largest) T30 
Chord of the cornea (shortest) ...... 1 -02 
Longest diameter of lens ........ 0"827 
Shortest diameter of lens 0'793 
Thickness of lens . 0‘50 
* Upon referring to my earlier observations, I find that in both the lenses of an ox there was only one struc- 
ture which was a positive one, and which had not yet divided itself into two structures, as in that of the cow 
under consideration. There was the appearance of a black space near the margin of the lens, but the polar- 
ized light both within and without that black ring was positive. 
In the lens of another ox, and of a bull, I found the positive structure separated into two positive structures 
by a distinct black ring, while an external negative structure was clearly developed. 
