410 TROPICAL NATURE 



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 considera- 

 tion 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 dis- 

 tinct sensations differ only in wave-length and rate of vibra- 

 tion, 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 perceptions 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 delicate gradations of light and 

 shade would be perceived, and there seems no reason why a 

 visual capacity might not have been developed as perfect as 

 our own, or even more so in respect of light and shade, but 

 entirely insensible to differences of colour, except in so far 

 as these implied a difference in the quantity of light. The 

 world would in that case appear somewhat as we see it in 

 good stereoscopic photographs ; and we all know how ex- 

 quisitely beautiful such pictures are, and how completely 

 they give us all requisite information as to form, surface- 

 texture., solidity, and distance, and even to some extent as to 

 colour, for almost all colours are distinguishable in a photo- 

 graph by some differences of tint, and it is quite conceivable 



