1835.] 



Accidental Colours. 



283 



accidental red produced by the green square ; or, in other 

 words, by the superposition of two accidental colours com- 

 plementary to each other. If, then, the eyes be suddenly 

 and completely covered, by means of a handkerchief, this 

 image will appear perfectly black, having on its right a red 

 image, and on its left, a green image, (supposing that the 

 red and green squares are placed as in the figure) : 



Fig. 1. 



Red. Green. 



[7.] Thus, accidental colours do not result from a simple 

 diminution in the sensibility of the retina, but they are new 

 sensations, of an opposite nature to the direct corresponding 

 sensations. 



In order to designate more clearly the two kinds of oppo- 

 site impressions, I shall generally call accidental colours or 

 impressions, negative impressions, and real colours, or direct 

 impressions, 1 shall call positive impressions, or colours. 

 {To be continued. J 



Article VI. 



On the Theory of Accidental and Complementary Colours, with 

 Additional ^Experiments and Observations, By Charles 

 ToMLiNSON, Esq. 



1. In two papers already published in this Journal, (vol. i. 

 p. 439, and vol. ii. p. 21), on Accidental and Complementary 

 Colours, I stated that my experiments were at variance with 

 the existing theories of this interesting branch of optics ; 

 and that I was aware of the existence of a new theory, by 

 Monsieur Plateau, which I had not seen. Recently, how- 

 ever, through the kindness of the Editor of this Journal, 

 I have perused M.. Plateau's paper, which it is my present 



