Report of the Committee on Colour-Vision. 



295 



the selection of signal colours, these facts have to be taken into 



account. The choice of a red light as a signal light is one in 



which theory and practice really agree, and it is in the selection of 



a colour for a second signal that the difficulty arises. The 



only colour for the latter, which the red-green blind would be 



able with certainty to distinguish from the red, is the pure 



blue, and this has been shown to be an impracticable choice. 



This being the case, the second signal should be of the kind 



most suitable for normal colour-vision without regard to the 



requirements of those who are colour-defective. Evidently 



for carrying power it should be as near the brightest part of the 



spectrum as possible, but far enough away from the red to render 



the signals easily distinguishable. A yellow or greenish-yellow 



is inadmissible, as it might be mistaken for a white light under 



some circumstances, as is also the case with those greens which, 



when sufficiently light to be effective, allow some red rays to pass. 



It is for reasons such as these that most railway companies have Colours for 



adopted as a danger signal a rich ruby-red, and for a safety signals 



signal (where a white light is not used) a blue-green, which adopted by 



varies slightly in hue on different lines, as was shown in the raiiw<:| y s - 



table given at page 292. 



The sealed pattern standards of red and green glasses used in Standard 

 the Royal Navy are the best that have come before the Com- signal glasses 

 inittee, and they suggest their adoption both for railways and ^L sed in E °y al 

 the mercantile marine. The sealed pattern green inclines to blue av ^' 

 and cuts off all red light. The blue-green of the spectrum, when 

 mixed with about 25 per cent, of white light, matches the hue of 

 this glass, and owing to this comparatively small dilution it will 

 aiso appear as a fairly saturated colour. Its luminosity also 

 approaches that of the standard red light, which is very desir- 

 able. 



The direct evidence before the Committee is not sufficient to Accidents 

 enable them to say that accidents, either by laud or by water, tn ^ rou g u 

 have conclusively been traced to defective colour- vision, yet this blindness 

 by no means disproves the high probability that accidents have 

 really occurred from such defects.* There can be no doubt that 

 every colour-blind person employed afloat, or upon railways, in 

 certain capacities, must of necessity be a source of danger to 

 the public. As is known, colour-blindness is hereditary to a 

 large extent, and we have it in evidence before us that in the 

 training vessels in which the orphan children of sailors are 

 educated there are about 4 per cent, of colour-blind boys. We 

 may therefore take it, apart from all other evidence, that a 

 considerable number of the fathers of these orphans who were 

 employed as sailors must have suffered from the same defect ; 

 and we have it in direct evidence that a considerable number of 

 colour-blind people, officers and seamen, are actually at sea at 



* In Dr. Joy Jeffries' book on " Colour-blindness ; its Dangers and its 

 Detection," the case of the loss of the " Isaac Bell " is fairly conclusively 

 traced to colour-blindness. Other cases are mentioned in Mr. Bickerton's 

 evidence. 



VOL. LI. v 



