3^0 Dr. Darwin’s Experiments on the 
of action, like ofcitation or pandiculation^ as foon as the ftimu* 
ius which has fatigued it is withdrawn ; and that it {till re* 
mains fenfible, that is, liable to be excited into action by any 
other colours at the fame time, except the colour with which 
it has been fatigued. 
vn. T’he retina after having been excited into action by a fimulus 
fomewhat greater than the loft mentioned falls into various 
fuccefive fpafmodic a fit ions . 
1. On looking at the meridian fun as long as the eyes can 
well bear its brightnefs, the difc firft becomes pale, with a lumi- 
nous crefcent, which feems to librate from one edge of it to 
the other, owing to the unfteadiiiefs of the eye ; then the 
whole phafis of the fun becomes blue, fur rounded with a white 
halo; and on doling the eyes, and covering them with the 
hands, a yellow fpedtrum is feen, which in a little time 
changes into a blue one. 
M. de la Hire obferved, after looking at the bright fun, 
that the impreftion in his eye firft aflumed a yellow appearance, 
and then green, and then blue; and wilhes to afcribe thefe 
appearances to fame affeflion of the nerves. (Porterfield on 
the Eye, Vol.T. p. 343-) 
2. After looking fteadily on about an inch fquare of pink 
filk, placed on white paper, in a bright funftiine, at the dif- 
tance of a foot from my eyes, and clofing and covering my 
eyelids, the fpedtrum of the filk was at firft a dark green, and 
the fpedrum of the white paper became of a pink. The 
fpedlra then both difappeared ; and then the internal fpeftrum 
was blue; and then, after a fecond difappearance, became yellow, 
and 
