244 TROPICAL NATURE, AND OTHER ESSAYS. 



while at its two extremities we find yellow, red, and 

 violet — colours which we best appreciate in smaller 

 masses, and when contrasted with the other two, or with 

 light neutral tints. We have here probably the founda- 

 tions of a natural theory of harmonious colouring, derived 

 from the order in which our colour-sensations have arisen 

 and the nature of the emotions with which the several 

 tints have been always associated. The agreeable and 

 soothing influence of green light may be in part due to 

 the green rays having little heating power ; but this can 

 hardly be the chief cause, for the blue and violet, 

 though they contain less heat, are not generally felt 

 to be so cool and sedative. But when we consider how 

 dependent are all the higher animals on vegetation, and 

 that man himself has been developed in the closest 

 relation to it, we shall find, probably, a sufiicient ex- 

 planation. The green mantle with which the earth is 

 overspread caused this one colour to predominate over 

 all others that meet our sight, and to be almost always 

 associated with the satisfaction of human wants. Where 

 the grass is greenest, and vegetation most abundant and 

 varied, there has man always found his most suitable 

 dwelling-place. In such spots hunger and thirst are 

 unknown, and the choicest productions of nature gratify 

 the appetite and please the eye. In the greatest heats 

 of summer, coolness, shade, and moisture are found in 

 the green forest glades ; and we can thus understand how 

 our visual apparatus has become especially adapted to 

 receive pleasurable and soothing sensations from this 

 class of rays. 



Supposed increase of Colour-perception within the 

 Historical Period. — Some writers believe that our 



