116 Scientific Proceedings, Royal Dublin Society. 
caused the phenomenon.t He compared the cornea to a pile of 
watch-glasses, or layers of lenses centred on a common axis. 
Jamin states that when such a system is held before the eye and 
examined with polarized light, an appearance is seen in shape 
somewhat like Haidinger’s tufts. If now a thin bi-refracting 
erystalline plate, with its axis inclined to the plane of polarization, 
be placed before this system, when polarized light is transmitted, 
the appearance of the tufts is fairly well reproduced, as they are 
now seen coloured with the complementary tints due to the 
erystal. 
Examining the cornea of a pig’s eye, which much resembles 
the human eye, I found it to be strongly bi-refracting ; but no 
appearance resembling Haidinger’s tufts was seen when it was 
placed on the stage of a polariscope.* Moreover, there are many 
objections to Jamin’s theory that the tufts are due to the cornea. 
The small angular magnitude of the tufts is against this theory ; 
if produced by the whole pencil of rays passing through the cornea 
and pupil, they should occupy practically the entire field of view 
instead of the small area actually observed. The Rev. J. Power, 
of Cambridge, on the other hand, maintains that only a small 
portion of the cornea is concerned in their production; and he 
shows by mathematical investigation that under such conditions the 
eurves of equal intensity of light will be equilateral hyperbolas, 
which, in fact, appear to correspond with the shape of the tufts.° 
Sir David Brewster,‘ however, in an important paper, published 
in the Comptes Rendus, which appears little known in England, 
pointed out a number of valid objections tc the corneal origin of 
the tufts. It is needless to summarize these. Brewster shows 
that even when an opaque screen, with a very minute aperture, 
=& of an inch (half a millimetre) in diameter, was held before 
the eye, the tufts were still seen of the same size and shape, 
though much enfeebled in light; nor was any change in their 
appearance produced when a very narrow slit replaced the minute 
aperture, and the slit slowly rotated in front of the cornea. 
1 Comptes Rendus, 1848, vol. xxvi., p. 197, 
? Hither with or without the analyser. 
3 Phil. Mag., 1858, vol. xvi., p. 69. 
* Comptes Rendus, 1859, vol. xlviii., p. 614. 
