606 Proceedings of the Poyal Society 
ances similar to those from which I was suffering, I determined to 
watch it, transitory as it was, feeling assured that I should have 
many opportunities of observing it. After two nights’ practice, I 
found myself getting dangerously skilful in reproducing it, and 
decided, somewhat reluctantly, that I must give it up. What I 
observed, however, has already been almost completely described 
as having been seen on the very first occasion. I endeavoured to 
prepare myself to note any possible difference of colour in the crim- 
son field, as distinguished from mere difference of intensity of illu- 
mination, and I could perceive none. I also endeavoured to 
ascertain the nature of the transition from this state to the normal 
one, but this was so exceedingly rapid that I could form no conclu- 
sion, and I found that under the necessary circumstances of the 
observation, viz., as it could be made only at the instant of awaken- 
ing, it was impossible for me to estimate, even approximately, the 
duration of the crimson appearance. 
Several possible modes of explaining the phenomenon at once 
occurred to me. Of these, however, I shall mention but three, 
and give reasons for rejecting two of them, while not pretending 
to specify them in the order in which they occurred to me. 
It cannot be ascribed to any visual defects in my eyes, which 
are normal as to colour sensations, and very perfect optically. 
ls£, I imagined it might be due to light passing through the almost 
closed eyelid, or through a portion of the eyeball temporarily filled 
with blood. Besides feeling certain that my eyes were fully 
open, I had the additional argument against this explanation, that 
I could not reproduce the phenomenon by carefully and gradually 
closing them, and that I am not aware that an effusion of blood 
in any part of the eye could possibly disappear so rapidly. 2c?, 
It might be due to diffraction either by my eyelashes or by small 
particles, whether on the cornea or in the transparent substances of 
the eye, coarse enough to produce nearly the same tint for some 
distance round the flame. This is negatived by several considera- 
tions, among which (in addition to those urged against the preced- 
ing explanation) it is only necessary to mention again the facts, 
that the colour is not one which can be produced by diffraction 
under such circumstances, and that it appeared to be the same on 
the more illuminated, as well as on the darker part of the field. 
