12 SEVENTH REPORT—1837. 
neutral black ring. The inner portion of this black ring has been 
made to advance inwards, and diminish the size as well as the in- 
tensity of the inner or central series of sectors, while the outer portion 
of the same black ring has encroached in a similar manner upon the 
outer series of positive sectors, and reduced it both in its size and in 
the intensity of its illumination. If the original optical figure of the 
lens consist of one positive structure, or of three structures, the middle 
one of which is zegative, and the two others positive, the changes which 
they undergo by the absorption of water, and the consequent exten- 
sion of the membranous capsule are explicable in the same manner ; 
and not only the character but the numerical value of all the tints 
which are successively generated can be calculated with the greatest 
accuracy by assuming a value of the tint produced by each surface of 
the capsule. In order to remove all ambiguity on the subject, Sir 
David Brewster extended the capsule of the lens of a sheep over a 
plate of glass, and by a slight force he readily produced a white of the 
first order, and of the same numerical value as that which is necessary 
to produce the phenomena in question. In order to obtain a direct 
experimental confirmation of these views we have only to take a cir- 
cular plate of glass which produces, either by rapid cooling, or by the 
transit of heat, a series of luminous sectors of the same value as that 
which is produced by the capsule; and, by combining it with the 
optical figure of the lens, we shall represent all the pheenomena exhibited 
by the lens, when its capsule is expanded by the absorption of water. 
From the property of the capsule of the lens by which it absorbs 
water, it is obvious that in certain states of eye it may become so dis- 
tended with that fluid that it may at length burst, thus giving rise to 
the disease which has been termed soft cataract; in this case the ob- 
vious remedy is to puncture the outer coating of the eye, and thus 
permit the vicious fluid to escape, and afford a chance to the vessels of 
resuming their healthy functions. On the other hand, when the defect 
of the more watery secretions of the eye cuts off the supply, which it 
would seem that the capsule is intended to furnish to the lens, an op- 
posite course may be requisite, and a supply of water may be injected 
into the eye; this has actually been done, although when Sir David 
mentioned the matter in the Medical Section at the last meeting of the 
Association, Dr. Macartney stated very strongly his doubts of the pos- 
sibility of such an operation. Thus, it is probable that optical science 
may have led to an examination of the nature of the membranes of 
this valuable organ, and most probably that examination will issue in 
the proper treatment of a most distressing disease, in each of the di- 
stinct forms which it is found to assume. 
—_— 
On a new Property of Light. By Six D. Brewster. 
The author observed, that his attention had been lately drawn to a 
very curious, and new property of light. While examining the solar 
