asmodic actions._

1. On looking at the meridian sun as long as the eyes can well bear its
brightness, the disk first becomes pale, with a luminous crescent, which
seems to librate from one edge of it to the other, owing to the
unsteadiness of the eye; then the whole phasis of the sun becomes blue,
surrounded with a white halo; and on closing the eyes, and covering them
with the hands, a yellow spectrum is seen, which in a little time changes
into a blue one.

M. de la Hire observed, after looking at the bright sun, that the
impression in his eye first assumed a yellow appearance, and then green,
and then blue; and wishes to ascribe these appearances to some affection of
the nerves. (Porterfield on the Eye, Vol. I. p. 313.)

2. After looking steadily on about an inch square of pink silk, placed on
white paper, in a bright sunshine, at the distance of a foot from my eyes,
and closing and covering my eyelids, the spectrum of the silk was at first
a dark green, and the spectrum of the white paper became of a pink. The
spectra then both disappeared; and then the internal spectrum was blue; and
then, after a second disappearance, became yellow, and lastly pink, whilst
the spectrum of the field varied into red and green.

These successions of different coloured spectra were not exactly the same
in the different experiments, though observed, as near as could be, with
the same quantity of light, and other similar circumstances; owing, I
suppose, to trying too many experiments at a time; so that the eye was not
quite free from the spectra of the colours which were previously attended
to.

The alternate exertions of the retina in the preceding section resembled
the oscitation or pandiculation of the muscles, as they were performed in
directions contrary to each other, and were the consequence of fatigue
rather than of pain. And in this they differ from the successive dissimilar
exertions of the retina, mentioned in this section, which resemble in
miniature the more violent agitations of the limbs in convulsive diseases,
as epilepsy, chorea S. Viti, and opisthotonos; all which diseases are
perhaps, at first, the consequence of pain, and have their periods
afterwards established by habit.

VIII. _The retina, after having been excited into action by a stimulus
somewhat greater than the last mentioned, falls into a fixed spasmodic
action, which continues for some days._

1. After having looked long at the meridian