300 Report of the Committee on Colour-Vision. 



blindness in individual cases. Those of Dr. Grossmann are a 

 good example of this class of test. An opinion has been 

 expressed, and with some plausibility, that the only fair tests by 

 which to prove that a man's colour-vision renders him unfit to 

 distinguish coloured lights or signals are the coloured lights 

 themselves when seen under the same circumstances as those 

 under which they would have to be observed. It has already 

 been shown that, with practice, it may be possible for a colour- 

 blind person to distinguish between colours by their different 

 luminosities and dilution with white, but it has also been pointed 

 out that such recognition would be rendered uncertain by differing 

 states of the atmosphere and by other conditions. If it were 

 possible to eliminate the chances of correct guessing, which 

 would be very large when using such tests, it would be necessary 

 that the examination should be a prolonged one, being repeated 

 many times with differing conditions of weather. If it were not 

 carried to this extent, it might equally well be conducted in a 

 t sting room, where the apparent size of the signals to the eye 

 could be imitated with great exactness. But the uncertainty of 

 this method, even when the variable factor of weather is absent, 

 is exemplified by the results of the examination of railway 

 employes at Swindon, conducted by the Committee. They found, 

 as already stated (see Appendix VII), that several passed the 

 lamp-test who had failed to pass the wool-test, and that some 

 passed one lamp-test, but failed to pass another similar one on 

 the same occasion. Had the examination of these men been to 

 ascertain their fitness for certain employments requiring normal 

 colour- vision, and been conducted by the lamp-test only, some 

 would have been admitted into the service, and have been a 

 source of danger to the public. 

 Colour-ignor- The Committee have had to consider whether what has been 

 a ace. called colour-ignorance, that is, ignorance as to the names 



of colours, is as objectionable as colour-blindness for certain 

 employments. The possibility of the existence of real colour- 

 ignorance, such as would lead to a non-recognition of the 

 true colour of a signal, appeared to them very doubtful until 

 they had taken the evidence of Staff-Surgeon Preston, R.N. ; for 

 it was hard to conceive of ignorance which would lead to con- 

 fusion in naming a red, a green, and a white signal. His evidence, 

 however, was conclusive of its existence at certain recruiting' 

 centres, and more especially in a certain class of recruit. It 

 may be mentioned that in the actual testing of large bodies of 

 men by the Committee, in no case was there a trace of colour- 

 igTiorance exhibited by those possessing normal vision, unless in 

 regard to nondescript colours. Red, green, blue, and white were 

 always correctly named, except where the person examined was 

 proved to be colour-deficient. 



There is one type of colour-ignorance which of course may 

 often be encountered ; a foreigner on board an English-com- 

 manded vessel, would be, practically speaking, colour-ignorant if 



