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A Confusion-Test for Colour-Blindness. 

 By George J. Buech, M.A, D.Sc. Oxon, F.R.S. 

 (Received December 22, 1911 —Read March 28, 1912.) 



The work described in this paper was done in conjunction with 

 Lieut.-Col. W. R. L. Scott, late of the 62nd Foot, who was very nearly, but 

 not quite, red-blind. He could not under ordinary circumstances distinguish 

 the red coat of a soldier from the black coat of the civilian, though on closer 

 inspection it seemed " not so good a black." His colour-sensations are given 

 in my paper on "Artificial Temporary Colour-Blindness."* 



He continued to take an active interest in the subject, and gave me a 

 good deal of help from time to time in testing the colour-seusations of other 

 people, in which he was very successful, his own colour-blindness enabling 

 him to win their confidence. It had been intended that his name should 

 appear as joint-author of this paper, but he died on April 9, 1911, aged 78. 



In the summer of 1903 we arranged to collaborate in painting a series of 

 test-cards, accurately adjusted to his colour-sensations, oil-colours being 

 selected, as easier of manipulation than water-colours, and less likely to fade. 



I. For the first, I painted the half of an Academy board, 9 inches by 7, 

 with two coats of vermilion, using very little medium and painting as solidly 

 as possible. When this was dry, several different kinds of green were mixed, 

 spread on strips of wood, and held near the red background, the most 

 satisfactory being selected by Lieut.-Col. Scott, who indicated which of the 

 colours on the palette might improve it. This I tried until he expressed 

 himself completely satisfied with the match. My function was to make the 

 colours as unlike as possible to normal eyes, and his to make them match 

 perfectly to the red-blind. The other half of the board was then painted 

 with the mixture, which was about the colour of a year-old ivy leaf, and it 

 was allowed a fortnight in which to dry and also to see if any change of 

 colour occurred on drying. 



I then painted, in his absence, on the green part of the card the words 

 DON'T GO, the letters N'T being in vermilion and the rest in blue. The 

 blue he could see immediately — in fact there seems to have been to him as 

 much difference between green and blue as there is to us between red and 

 green. But he read the inscription as DO GO, being absolutely unable to 

 distinguish the letters in vermilion. After a while, by holding the panel 

 sideways, so as to get the light on the brush- marks, he managed to decipher 

 them, but he could see no difference in colour. In order to prevent the 

 * ' Phil. Trans.,' B, vol. 191, p. 29. 

 VOL. LXXXV. — B. G 



