134 Scientific Proceedings, Royal Dublin Society. 
Notre spy J. Lepwines, a.R.c.sc. 
As suggested by Professor Barrett, I add a brief statement of 
the appearances presented to me by the phenomena which the 
Professor has described. 
1. Haidinger’s tufts——The yellow sectors appear to me also 
very like an hour-glass in shape ; the blue or violet areas at right 
angles to the yellow I see clearly ; they much resemble the shape 
of the moon in her third quarter (see fig. 1, Plate VI.), and some- 
times seem to unite across the narrow part of the hour-glass-shaped 
area. In general the tufts vanish with me in rather less than 
three seconds, so that the Nicol must be kept moving to see them 
continuously. When a blue glass or a blue solution of the oxalate 
of chromium and potassium is held before the Nicol, the tufts 
occupy a slightly smaller area than the claret-coloured area due to 
the macula lutea or yellow spot, as I have noticed a fringe of the 
claret colour on the outside of the three-quarter-moon-shaped area 
of the tufts. This agrees with my measurement of the macuda and 
the tufts; the former appears to be approximately 1 mm. and the 
latter 0°8 mm. in their longest diameter. In repeating the double 
pinhole experiment described by Prof. Barrett, I could only see a 
single image of the tufts, no matter what part of the duplicated 
image of the pupil the gaze was directed to, thus verifying the 
Professor's observation. I tried whether the tufts could be seen 
by focusing a polarized pencil of rays from the electric arc on 
the sclerotic, but could not see them; the non-appearance of the 
tufts may, of course, be due to their extreme faintness under these 
conditions, or to the fact that the rays did not fall on the yellow 
spot. The existence of Haidinger’s tufts show that the light of 
direct vision is always polarized. This fact seems to me one of 
considerable interest in the theory of vision. 
2. Purkinje’s figures.—Plate VIIL., fig. 1, is a careful drawing 
of Purkinje’s figures as I see them when a brilliant point of light 
falls on the sclerotic. In the central part there appears to be 
