ON THE ORIGIN OF THE COLOUR-SENSE. 



Throughout the preceding discussion we have accepted 

 the subjective phenomena of colour that is, our perception 

 of varied hues and the mental emotions excited by them, 

 as ultimate facts needing no explanation. Yet they 

 present certain features well worthy of attention, a brief 

 consideration of which will form a fitting sequel to the 

 present essay. 



The perception of colour seems, to the present writer, 

 the most wonderful and the most mysterious of our 

 sensations. Its extreme diversities and exquisite beauties 

 seem out of proportion to the causes that are supposed 

 to have produced them, or the physical needs to which 

 they minister. If we look at pure tints of red, green, 

 blue, and yellow, they appear so absolutely contrasted 

 and unlike each other, that it is almost impossible to 

 believe (what we nevertheless know to be the fact) that 

 the rays of light producing these very distinct sensations 

 differ only in wave-length and rate of vibration ; and 

 that there is from one to the other a continuous series 

 and gradation of such vibrating waves. The positive 

 diversity we see in them must then depend upon special 

 adaptations in ourselves ; and the question arises for 

 what purpose have our visual organs and mental per- 

 ceptions become so highly specialised in this respect ? 



When the sense of sight was first developed in the 

 animal kingdom, we can hardly doubt that what was 

 perceived was light only, and its more or less complete 

 withdrawal. As the sense became perfected, more deli- 

 cate gradations of light and shade would be perceived ; 



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