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XL — On a Case of Colour Blindness. By Wm. Peddie, D.Sc. (With a Plate.) 



Part I.* 



(Read 7th January, 18th February, and 3rd June 1895.) 



Introduction. 



The case under consideration was brought to my notice while I was attempting to 

 arrange a colour match by the well-known disc method. The colour was somewhat like 

 lilac, though rather more red. A number of onlookers — including the gentleman whom I 

 afterwards found to be colour-blind, and whom I shall in this paper denote as Mr A. — 

 pronounced the match fairly satisfactory. Mr A. subsequently remarked to me that he 

 sometimes had a difficulty in distinguishing greens and blues. He said, also, that he had, 

 though much less frequently, a difficulty with reds. This condition is so abnormal that 

 I at once handed him a direct vision spectroscope and asked him to name the colours 

 which he saw in succession from one end of the spectrum to the other. He said that 

 red was the first. "And after the red?" I asked; "green," he said: "and after the 

 green V ; " blue." And when asked what followed the blue, he said that the rest of the 

 spectrum was blue throughout the whole extent. When asked if he saw white light 

 between the red and green colours, he was very undecided, but said that he did not think 

 he would call it white — it might be yellow. 



Except for the fact that green and blue were distinguished in the spectrum, the case 

 seemed most like one of blindness to yellow and blue, or " violet-blindness " as it was 

 termed on the original Young-Helmholtz theory. 



Next day I showed Mr A. the spectrum formed by a more powerful instrument which 

 gave such dispersion that only about one- quarter of the length of the spectrum could 

 be seen at one time. I asked him to adjust, if he could, tbe wires to a part which 

 seemed colourless to him. The part which he marked was near the line D on the 

 more refrangible side. I asked him to move the spectrum across the field of vision 

 towards the more refrangible end and name the colours as they passed the centre of the 

 field. He said that there was only one colour, which he called red. The point of 

 strongest red colour he placed near the line C on the less refrangible side, and the 

 spectrum was visible throughout the full normal range towards the red end. In 

 the same way, all the range of the spectrum on the more refrangible side of the' 

 neutral point was said to be of one colour, which was called blue. The point of 

 maximum colour was placed between the lines b and F — rather nearer the latter 

 than midway between them — and the spectrum was visible to the full normal range 



* This part contains results communicated to the Society as follows : — Introduction, 7th January 1895 ; com- 

 parison with the case described by v. Vintschgau and Heeing, 18th February 1895 ; and the rest, 3rd June 1895. 



VOL. XXXVIII. PART II. (NO. ll). 3 X 



