376 Report of the Committee on Colour- Vision. 



blues, violets, purples, pinks, browns, and greys. Several 

 shades of each colour, with at least five gradations of each tint, 

 should be procured, from the deepest to the lightest greens and 

 greys. Varieties of pinks, blues, and violets, and of light grey, 

 together with shades of brown, yellow, red, and pink, must be 

 especially well represented. The test skeins with which the 

 examinees are to compare the colours should be three in number : a 

 light green, a pale purple or pink, and a bright red. These three 

 colours will suffice to indicate approximately the amount and 

 kind of colour-blindness which may exist. The light green skein, 

 which is a tolerably pure green mixed with a large proportion 

 of white, is chosen as the colour which closely matches the 

 spectrum colour which the red- and green-blind distinguish as 

 white or grey. It is chosen of a pale tint, as it then becomes 

 puzzling to the colour-blind to distinguish its colour by its 

 luminosity. A light grey or drab skein will present the same 

 brightness to him that this pale colour does, and although he 

 may be trained to distinguish bright colours by their relative 

 luminosities, in the case of these pale varieties he will be unable 

 to do so. The light purple or pink is chosen for similar reasons, 

 and in fact it is nearly a complementary colour to the green. 

 The purple is, according to the Young-Helmholtz theory, a mixture 

 of two fundamental colours, the blue and the red, and as in 

 the green-blind it excites both the blue and red sensations it 

 may be confused with grey, or with a green. In the red colour- 

 blind it excites in excess the blue sensation mixed with what they 

 call white. A blue or violet may therefore be matched with it. 

 The method of examination is as follows: — 



" Method of Examination and Diagnosis. 



"The Berlin wools are placed in a heap on a large table, 

 covered by a white cloth, and in broad daylight. A skein of the 

 test-colour is taken from the pile, and laid far enough away 

 from the others not to be confounded with them during the 

 examination. The person examined is requested to select other 

 skeins from the pile most nearly resembling it in colour, and to 

 place them by the side of the sample. At the outset, it is 

 necessary that he should thoroughly understand that he is required 

 to search the heap for the skeins which make an impression on 

 his chromatic sense, and quite independently of any name he 

 may give the colour, similar to that made by the test-skein. 

 The examiner should explain that resemblance in every respect 

 is not necessary; that there are no two specimens exactly 

 alike ; that the only question is the resemblance of the colour ; 

 and that, consequently, he must endeavour to find something 

 similar in shade, something lighter and darker of the same 

 colour, &c. If the person examined cannot succeed in under- 

 standing this by a verbal explanation, resort must be had to 

 action. " The examiner should himself pick out the skeins, 

 thereby showing in a practical manner what is meant by a shade, 



