§40. PERCEPTION OF COLOUR. 57 



Defects like these cannot be overcome either by study 

 or by rules. But though study and the contemplation of 

 good examples will not remedy such defects, nor give at 

 once a true perception of the harmony of colours even to those 

 whose vision is not defective, still they are very necessary 

 for their instruction, as they might otherwise continue to be 

 unable to distinguish between a concord and a discord, from 

 the want of that natural gift. Again, those who do possess 

 that natural perception may not always be able to combine 

 colours, though they may readily perceive whether colours 

 are or are not harmoniously united in a composition ; as 

 any one with an ear for sound may detect false notes without 

 being able himself to arrange any in an air. But the first 

 and indispensable condition in furnishing examples, or rules, 

 is that the subject should be thoroughly understood; and the 

 required knowledge can only be derived from a natural per- 

 ception of the harmony of colours improved and matured by 

 observation. 



40. In examining into the effect of colours, we have to in- 

 quire what it is when presented to the eye, not what it ought 

 to be according to this or that theory ; and nothing will be 

 understood on the subject unless the eye is first allowed to 

 be the judge. It is the perceptive faculty which is to be 

 appealed to, and we must begin by ascertaining certain facts 



violet ; crimson and pink appear to have no relation to scarlet : 3rd, green is a 

 most perplexing colour, it is not only confounded with red, but with black, 

 white, or grey, orange, yellow, blue, violet, and brown: 4th, violet is con- 

 founded with blue and grey, and orange with yellow : 5th, more difficulty is 

 manifested with light or dark tones of compound colours than with full ones." 

 It is certainly remarkable that while blue and yellow are seen perfectly well, 

 their effect should be so different when combined together as green; and this is 

 explained by the white of the colour-blind person being green, one of the 

 three elements (red) being wanting to him, and he having only blue end 

 yeliow to produce his white. Green is therefore no colour to the colour-blind. 

 He has only two sensations of colour, blue and yellow. Red and green are 

 then, both, shades of yellow. 



