1911.] Simultaneous Colour Contrast. 



553 



spectrum to \ 646. There is considerable absorption from X 646 to \ 588. 

 The yellow rays are partially obstructed, whilst the glass is practically 

 transparent to the green, blue, and violet rays. When objects are viewed 

 through these spectacles not a trace of red is to be seen either directly 

 or by contrast. An ordinary coal fire appears to consist of only yellow 

 or yellow-green flames, no orange or red being visible. The yellow light of 

 the spectrum or a yellow object adjacent to a green one still appears yellow, 

 and the colour appears if anything to incline towards green rather than red. 

 Eeds appear black, or in a very bright light, and when they reflect orange 

 rays, a dull brown. Yellow, green, blue, and violet can be seen through the 

 blue-green glasses. White objects at first appear blue-green, but after 

 a short time again appear white. Objects corresponding to the dominant 

 wave-length of the blue-green glass appear white or pale blue or pale green 

 according to the composition of the colour. All contrasts are modified in 

 a similar manner. For instance a grey square on a green ground, in circum- 

 stances which give a bright rose contrast colour, appears pale blue through 

 the blue-green glasses, and a grey on a blue ground yellow-green. No colour 

 is seen the light of which cannot pass through the blue-green glass. 

 Sir W. Kamsay, whose vision on my classification* is trichromic (that is he 

 describes the bright spectrum as consisting of red, red-green, green, green- 

 violet, and violet), examined my series of contrasts through the blue-green 

 glasses and in no instance called yellow red. He rather tended to call 

 yellow yellow-green, or, to use the term which he prefers, green with a very 

 small amount of red in it. It would appear, therefore, that the exaggerated 

 simultaneous contrast which I have found to be characteristic of these cases 

 is not found in the absence of the objective exciting light. 



These facts point to the conclusion that the sensation of red is not 

 produced by simultaneous contrast in the absence of objective red light. 

 They also support the conclusion at which I had previously arrived from the 

 study of colour fatiguef that yellow is a simple sensation and not compounded 

 of a red and a green sensation. I can also find no evidence of the induction 

 of colour by simultaneous contrast in the absence of objective light of that 

 colour. 



Summary. 



1. The colours seen by simultaneous contrast are due to the exaggerated 

 perception of a real, objective, relative difference which exists in the light- 

 reflected from the two adjacent surfaces. 



* ' Hunterian Lectures on Colour Vision and Colour Blindness,' Kegan Paul and Co. 

 1911, p. 24. 



t ' Trans. Ophth. Soc.,' 1909, p. 211. 



