THE SENSE OF COLOUR 25 



to which it was blind. And any shades made up of a com- 

 bination of green and violet, in whatever proportions, 

 without any red, provided the tone were the same, would 

 look much the same to him. 



Let us go a step further and imagine him confronted 

 with a combination of orange and green, making a sort of 

 dirty brown: his eye would pick out the red from the 

 combination, and would reject the violet and green; and, the 

 less red there was, the fainter the object would appear. 

 Again, if he were confronted with a combination of green 

 and pink, making another combination of a sort of brown, 

 his eye would select the red and reject the green and violet. 

 And the two quite different shades of brown would look 

 practically identical to him, provided there were the same 

 intensity of red in each. Again, if the combination were 

 violet and orange with the same amount of red in the 

 orange as in the other two combinations, his eye would 

 again select the red and reject that part in those parts of 

 the combination to which he was blind. So that this com- 

 bination would again look the same to him. In fact, his 

 only test of colour would be the extremely simple test, 

 the degree of red in it. If that were constant all colours 

 would look alike. 



Yet one step further and imagine your trout sensitive 

 to red and green, but entirely blind to violet. Then any 

 combination of red and violet entirely free of green, or of 

 green and violet entirely free of red, would be judged by 

 the amount of red or green in it, as the case might 

 be. But if red and green were together in any combined 

 colour, then the fish would begin to be able to perceive 

 distinctions. 



It is unnecessary to drag the reader through the further 

 combinations to make this point clear. 



Now all this is extremely crude, and it is not put forward 



4 



