TRANSACTIONS OF THE SECTIONS. 5 
After lying for a considerable time in distilled water, the capsule of the lens had 
separated from the lens itself, the space between them being filled with albuminous 
water of a greater refractive power than the distilled water. The capsule at last 
burst near the vertex of the lens; but a short time before this took place, another 
capsule or bag was raised up by the expansion of the lens, and the space between it 
and the lens filled with albuminous water of a still greater refractive power. This 
water was contained in a membrane never before described, and investing the whole 
of the lens within the capsule. This membrane, during the swelling of the lens, rose 
to different heights in different places, giving the surface of the lens an irregular 
appearance. This membrane was striated, but the striz gave no colours, while the 
fibres of the lens immediately below this membrane exhibited beautiful colours. 
The lens itself had two concentric polarizing structures, the central ones being 
positive and the external ones negative. 
On the Optical Properties of the Cyanurets of Platinum and Magnesia, and 
of Barytes and Platinum. By Sir Davip Brewster, K.H,, D.C.L., 
F.R.S. Lond. ὃ V.P.RS. Edin. 
The author gave a very general notice of the optical properties of these interesting 
salts, which he had received from his friend M. Haidinger of Vienna. Although 
these crystals gave different colours by reflected and transmitted light, they were not 
in the proper sense of the word dichroitic. In the general and remarkable property 
of giving coloured pencils differently polarized by reflected light, they resembled 
murexide and the chrysammate of potash, the optical properties of which were several 
years ago described to the Association*. In these new salts the coloured reflected 
tint is polarized in a plane perpendicular to the plane of reflexion, when the plane of 
reflexion coincides with. the direction of the principal axis, and in that plane when 
the plane of reflexion is at right angles to the direction of the principal axis. At in- 
termediate directions the plane of polarization continues in the plane of reflexion, but 
in passing from 0° to 90° of azimuth, the light of the principal coloured pencil passes 
gradually into the other pencil which is polarized in the plane of reflexion, a small por- 
tion of the former being still left at an azimuth of 90° polarized perpendicular to the 
plane of reflexion. The cyanuret of barytes and platinum has a powerful double refrac- 
tion and a high dispersing power. It has two axes, the principal one of which is 
positive, like the axis οὗ quartz ; and it possesses the property of internal dispersion, 
the dispersed light being a brilliant green, while the transmitted light is yellow. The 
colour of the pencil reflected from its surfaces in all azimuths is blue, but the strongest 
of the reflected pencils, viz. that which is polarized perpendicular to the plane of reflex- 
ion, is a brilliant blue near the maximum polarizing angle, becoming purple at greater, 
and less blue at smaller angles of incidence. We have here then the remarkable phe- 
nomenon of double reflexion, in which the principal coloured pencil is not only pola- 
rized in a plane perpendicular to the plane of reflexion, but varies in intensity, at the 
same angle of incidence, with the angle of azimuth which the plane of reflexion forms 
with the principal axis of double refraction. 
On the Polarizing Structure of the Eye. 
By Sir Davip Brewster, K.H., D.C.L., F.RS. Lond. § V.P.R.S. Edin. 
M. Haidinger of Vienna discovered the beautiful property of the eye, in virtue of 
which it is able, without any assistance, to determine the plane in which light is 
polarized, by means of two yellow brushes or pencils, as they have been called, or 
sectors, as Sir David Brewster calls them, from their resemblance to the sectors of 
circular crystals, as discovered and described by Mr. Fox Talbot. Viewing the 
phenomenon as one of circular crystallization, the author endeavoured to point out 
the particular structures and membranes of the eye by which the phenomenon of cir- 
cular crystallization was produced in the polarized light, and the analysis effected. 
* See Report for 1846, p. 7. 
