Report of the Committee on Colour-Vision. 291 



per cent, of soldiers who were colour-defective, without includ- 

 ing those who are classed as having weak colour-vision. The 

 above statistics all point to the prevalence of colour-blindness 

 amongst the male population, and to the fact that such defects 

 are not confined to one nationality or race. The small per- 

 centage of colour-blindness found amongst women is remark- 

 able, but as it does not enter into the questions on which the 

 Committee have to report, it need not be further dwelt upon. 



The Committee have already briefly alluded to the mistakes Eesults and 

 which congenitally colour-blind people are likely to make ; but in dangers of 

 order to emphasize it, they will enter rather more fully into the £°?°^' egg 

 subject. In the first place, let it be remembered that to the red- n ness ' 

 blind and to the green-blind there is one green in the spectrum 

 which they cannot distinguish from white, and which for con- 

 venience may be designated as their neutral colour. On the one side 

 of this neutral band they see but green or red, more or less diluted 

 with their neutral colour, and on the other side blue, also similarly 

 diluted. The dilution increases as the neutral point is approached, 

 and for some little distance on each side of it (unless a comparison 

 with white be at hand) the dilution is so large that the colour 

 may be mistaken- for the neutral colour. 



As all colours in nature, except purples, can be matched by 

 the normal eye with some one spectrum colour (which we may 

 call the dominant colour) more or less diluted with white light, 

 we can, where the dominant spectrum colour of a signal is 

 known, indicate in the terms used by a person possessing normal 

 vision what each class of colour-blind would see. 



Perhaps this is best shown as a tabulated statement : — 



Colour of Signal. 



To a Eed-Blind 

 Observer. 



To a Green-Blind 

 Observer. 



Eed. 



G-reen. 



Eed. 



Green, the dominant spec- 

 trum green being on the 

 red side of the neutral 

 band. 



Grreen mixed with a 

 large proportion of 

 neutral colour. 



Eed mixed with a 

 large proportion of 

 neutral colour. 



Green, the dominant spec- 

 trum green being at the 

 neutral band of the red- 

 blind. 



Neutral colour. 



Eed mixed with a very 

 large proportion of 

 neutral colour. 



Grreen, the dominant spec- 

 trum green being at the 

 neutral band of the 

 green-blind. 



Blue mixed with a very 

 large proportion of 

 neutral colour. 



Neutral colour. 



Grreen, the dominant spec- 

 trum green beiDg well 

 on the blue side of the 

 neutral band. 



Blue mixed with a 

 large proportion of 

 neutral colour. 



Blue mixed with a 

 large proportion of 

 neutral colour. 



White. 



Neutral colour. 



Neutral colour. 



