194 PHILOSOPHY OF ZOOLOGY. 
= ’ 
Thus, as has been already stated, if we look’ steadily at a 
white spot, and afterwards turn the eye towards white bo- 
dies, a dark spot will be perceived by the eye. If we look 
at a red spot on a white ground, and then direct the eye to 
another part of the white ground, a green spot approaching 
to blue will be perceived. In the first case, the retina was 
fatigued by the white colour, and could not be excited by 
any other colour, having the rays which constituted it in its 
composition. 'The accidental colour was, therefore, black. 
In like manner, after looking at the red spot, the retima 
was insensible to the impression of a compound colour, ha- 
ving red rays in its composition; hence, the accidental. co- 
lour consisted of the other rays of the prismatic spectrum, 
forming a coleur destitute, of red. 
The following Table exhibits the Natural Colours, with 
their corresponding Accidental ones. 
Natural Colours. Accidental Colours. 
Red, Blue, with a small mixture of green. 
Orange, Blue, with nearly an equal mixture of indigo. 
Yellow, Indigo, with a considerable mixture of violet. 
Green, Violet with a mixture of red. 
Blue, Red, with a mixture of orange. 
Indigo, Yellow, with a considerable mixture of orange. 
Violet, Green, with a considerable mixture of blue*. 
The eye, in general, communicates accurate information 
with regard to the direction of objects. The sources of error 
im this case.are few ; and seldom interfere with the wants or 
the enjoyments of the species. They arise either from the 
reflection or refraction of the rays which proceed from the 

* Accidental Colours, Edin. Encyclop. vol. i, p. 90. 
