Accidental and Complementary Colours. 213 



9. When I place a red wafer upon white ground, and fix 

 my eye upon it for a second or two, a green ring or segment 

 of a ring begins to play around the wafer, and on directing 

 my eye to another part of the white paper, I see a green 

 circular spot. Now, by the principle of homo-chromatic 

 attraction, the red colour of the wafer exerts an attractive 

 influence upon the red rays of the white paper. I believe, 

 that under such circumstances, there is an affinity of red 

 for red, and that this affinity extends to a considerable dis- 

 tance. If such be the case, the explanation is easy. The 

 red rays immediately around the wafer are attracted to 

 itself and leave the contiguous white paper deprived of 

 red — hence, the green ring appears — the red colour of the 

 wafer gradually becomes more sombre, because we see the 

 red wafer through a faint accidental green, and green and 

 red by super-position appear black : but there is only suffi- 

 cient of the green to give a sombre appearance to the red, 

 and not enough to make it black. The eye is removed to 

 another part of the paper, and for a few seconds perceives 

 a green spot ; the red wafer has exerted its influence upon 

 the white ground, decomposed it, in fact ; retained a large 

 portion of the red rays, and left the paper in a condition to 

 send green to the eye. Thus, the red wafer exerts a col- 

 lective influence over the red rays of the white paper, 

 collects a number of them, and becomes more red itself,* 

 by depriving the white ground of a portion of its red rays,t 

 the retina by persistance of impression retains the form, 

 and the decomposed ground gives it a new colour ; or, 

 rather the eye had received the accidental impression from 

 the ground immediately contiguous to the wafer, and bears 

 the impression to any other part of the same ground. This 

 impression lasts only for a short time, and in order to pro- 

 duce a new effect, the same process must be repeated. 



• While the eye is gazing steadily at a red wafer upon white ground, without 

 shifting tlie eye, place another red wafer hy the side of it, the second wafer will 

 appear of a very light red, compared with the first, although the two tints are 

 precisely the same. 



t If we observe a green ground covered with white spots, (such as a lady's 

 gown, &c.) the spots appear red ; if the ground be blue and the spots white, the 

 latter appear yellow, and so on. White stripes upon coloured grounds present 

 similar appearances, and these effects strike the eye the moment tlie observationa 

 are made. 



