214 
492. This experiment resembles those made by 
M. Buffon, who found, that, by looking for some 
time on two objects of opposite colours, fixed upon 
one another, the sensation of a third colour, different 
from either of the former, was produced, to which 
he gave the name of accidental colour. The produc- 
tion of this colour has, by some philosophers, been 
attributed to a mixture of the differently coloured 
rays reflected by the two objects, combined with a 
certain disposition in the eye, to be acted on by the 
colour which conveys the stronger impression. But 
the experiments of M. M. JEpinus and De la Hire, 
seem to shew, that sensations of different colours 
may successively arise in the eye, where no mixture 
of colours from the object can be supposed to take 
place : thus, if the eye be directed to the sun, and 
then closed, the image upon the retina will be first 
red, then yellow, then green, and last of all blue * ; 
facts which shew that these accidental colours de- 
pend more on the condition of the organ of vision, 
than on the colours of the rays which the luminous 
body emits. The same explanation may, perhaps, 
be extended to the accidental colours produced by 
reflected light ; for by looking long and steadily at 
two differently coloured objects, kept in perpetual 
motion, the eye becomes dazzled and weakened, and 
is unequal, therefore, to that distinctness of vision, 
which at first represented them in their proper 
colours. According to the natural strength, also, of 
the visual organ, the same objects may, to different 
* Priestley's Hist. Vision, vol. ii. p. 6*31. 
