473 



A paper was read, entitled, On the development and extinction 

 of regular doubly refracting structures in the crystalline lenses of 

 animals after death." By Sir David Brewster, K.H., L.L.D., F.R.S. 



Since the year 1816, when the author communicated to the Royal 

 Society an account of the doubly refracting structures which exist in 

 the crystalline lenses of fishes and other animals, he has examined a 

 great variety of recent lenses with the view of ascertaining the origin 

 of these structures, the order of their succession in different lenses, 

 and the purpose which they answer in the animal economy. He had 

 discovered in the lenses of many fishes the alternation of portions, 

 exerting, the one a positive, and the other a negative refractive 

 action ; but in his subsequent investigations he met with the greatest 

 discrepancy as to the regularity of their arrangement. He found 

 that in quadrupeds the central structure is positive ; while in fishes, 

 where there are three structures, it is always negative ; but their po- 

 sitive structure in the former case sometimes exists alone, with faint 

 traces of a negative structure, and sometimes it is followed by 

 another positive structure separated from the first by a black neutral 

 circle, in which the double refraction disappears j at other times va- 

 rious other combinations of these structures are presented. Occa- 

 sionally, in the dark neutral line which separated two positive struc- 

 tures, he perceived a trace of an intervening structure, which seemed 

 to be either about to disappear or about to be developed. This con- 

 jecture was satisfactorily verified by a series of observations which he 

 made on the lenses of the sheep, the ox, and the horse, at different 

 ages, and also on the same lens, during the spontaneous changes 

 it undergoes when kept in distilled water. The negative structure 

 was in these experiments gradually developed at the space inter- 

 vening between the portions of the lens which had possessed the 

 positive structure ; and thus the same parts assumed in succession 

 doubly refractive actions of opposite kinds. The author intimates 

 his intention of pointing out, in a separate paper, the conclusions 

 deducible from these facts respecting the cause and cure of cataract. 



June 8, 1837. 



WILLIAM LAWRENCE, Esq., V.P., in the Chair. 



Robert Bigsby, Esq., George Edward Frere, Esq., and Captain 

 Joseph Ellison Portlock, R.E., were elected Fellows of the Society. 



A paper was in part read, entitled " Observations on the minute 

 structure of the higher forms of Polypi, with observations on their 

 classification." By Arthur Farre, M.B. Communicated by Richard 

 Owen, Esq., F.R.S. 



June 15, 1837. 



FRANCIS BAILY, Esq., V.P. and Treasurer, in the Chair. 

 James F. W. Johnston, Esq., A.M., was elected a Fellow of the 

 Society. 



The following papers were then read, viz. : 



