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 retina 

 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 colour destitute of red. 



The folio wing Table exhibits the Natural Colours, with 

 their corresponding Accidental ones. 



Natural Colours. Acci ;al 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 

 in 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. 



