§ 47—49. ACCIDENTAL COLOURS. 73 



to the white paper, we shall see on it an image of that spot 

 of a blueish green colour. And the images of other coloured 

 wafers will he changed according to the accidental colour of 

 each, red becoming a blueish green, orange a blue, yellow an 

 indigo, green a reddish violet, blue an orange-red, indigo an 

 orange-yellow, violet a yellow-green, black a white, and white 

 a black. The accidental colour is what the other wants to 

 make white light, and some style it the " complementary," 

 others the " opposite." The reason of the green image of the 

 red being seen Brewster shows to be, that " the part of the 

 retina occupied by the red image is strongly excited," or 

 " deadened by its continual action." The sensibility to red 

 light will therefore be diminished ; " the deadened part of the 

 retina will be insensible to the red rays which form part of 

 the white light from the paper, and will see the paper of that 

 colour which arises from all the rays in the white light of the 

 paper but red," i. e. blueish green. Again, " when a black 

 wafer is on a white ground, the portion of the retina on which 

 the black image falls, in place of being deadened, is protected, 

 as it were, by the absence of light, while all the surrounding 

 parts of the retina, being excited by the white light of the 

 paper, will be deadened by its continued action." Hence, the 

 eye " will see a white circle corresponding to the black image 

 on the retina." But it does not therefore follow that any two 

 colours which are accidental to each other should harmonise 

 — they may, or they may not ; nor is there any necessity that 

 the colours which are intended to convey to the eye the 

 actual impression of several distinct ones harmoniously com- 

 bined should be of the same quantity as when they are 

 required to make white light. 



49. If any effect is to be produced by a polychrome ornament, 

 it must be totally distinct from that of white light, as I have 

 already shown (p. 60). Again, two of the three primaries 

 accord with each other in very different ways. Eed and blue, 



