INTRODUCTION: COLOUR NAMES 161 



A fortiori such deductions are most untrustworthy amongst those 

 whose colour vision is defective. Just as a person whose stereoscopic 

 vision is defective may learn to estimate distances and judge solid shapes 

 by accessory aids, such as apparent size, distinctness, shadows, the 

 correlation of tactile sensations, and so on, and may even be wholly 

 unconscious of his defect and of the greater endowment of the majority 

 of his fellow-creatures, so too the colour-blind. His vocabulary of 

 colour terms is often as full and comprehensive as that of his fellows in 

 a similar walk of life. Experience teaches him that these terms are 

 applied with a general consistency to the various objects of every-day 

 life. These objects are generally well-defined to his senses by other 

 criteria than colour, such as shape, size, and general relationship to other 

 objects. He may therefore pass through life without being conscious 

 of any inferiority of perception as compared with his fellows, and he 

 may also fail to make any glaring mistakes, such as would convey to 

 others a suggestion of his deficiency. Hence if we wish to analyse his 

 sensations and to arrive at some idea of their divergence from ours we 

 must take care to remove those accessory aids upon which he uncon- 

 sciously or consciously relies. Because he calls a cherry red it does not 

 follow that his sensation of red agrees with ours. We know indeed that 

 in many cases the hue of the cherry is very little different to him from 

 that of the cherry leaves ; yet he never calls a cherry green. If we show 

 him small spots of coloured light he may or may not give them the names 

 which we regard as correct. The fact that he is often right proves that 

 his accessory aids are more complex than those already mentioned. 

 It is our main object to study these accessory aids so that we may 

 eliminate them and place him hors de combat. 



It will suffice for our present purpose if it is clearly understood that 

 the names which the colour-blind use for various colour sensations must 

 not be relied upon as accurate criteria of their sensations as compared 

 with the normal. On the other hand, to the practised examiner these 

 names are full of suggestion and will often indicate the lines which the 

 examination should pursue. When we deal with practical tests for 

 colour blindness, the main object of which is to determine whether the 

 colour-defective are dangerous for certain occupations, the problem is 

 quite different and the colour names used by the examinee are them- 

 selves indications of his fitness or unfitness. 



With regard to what is commonly known as " colour ignorance ' 

 it is found that there are very few civilised people who do not know 

 the fundamental terms for colours, whereas many people are ignorant 



p. c. v. 11 



