Dr Stark 07i (he Injfuence of Colour on Heat 81 



and assume the appearance of zig-zag lines and specks. These, 

 again, as the season advances, give place to the pure immaculate 

 plumage which distinguishes both sexes in winter.*" * 



The display of colours in the plumage of the birds of tropi- 

 cal climates is also in strict accordance with the observed facts 

 of the influence of colour over the absorption and radiation of 

 heat. The metallic reflexions and polished surface of the whole 

 family of humming-birds is admirably suited to their habits; 

 and the colours of the wings of the Lepidoptera in the class of 

 Insects, there is little doubt, serves some similar purpose, in 

 maintaining the temperature of the animals at a proper mean. 

 In proportion to the diminution of temperature, and the dis- 

 tance from the equator, a corresponding dilution of colour in 

 animals takes place, till, in temperate countries, it is almost uni- 

 formly of a sober grey. In the arctic regions, all colour ex- 

 cept white and black disappears, — modifications of which, with 

 very little variety of other colours, form the summer and winter 

 clothing of most of the northern tribes of birds. 



In the vegetable kingdom, I am disposed to believe that the 

 colours of the petals of flowers serve some useful purpose, in re- 

 gard to preserving the temperature of the parts necessary for 

 reproduction at the proper mean, and that the varied pencilling 

 of Nature has thus an object beyond merely pleasing the eye. 

 In this view, the quality of colour, so widely extended, and so 

 varied and blended in every class of natural bodies, acquires a 

 further interest, in addition to its ministering to the pleasures of 

 sight, and affbrds a new instance of that benevolence and wisdom 

 by which all the arrangements of matter are calculated to excite 

 and gratify the mind directed to their investigation. 



Even in the inorganic portion of Nature, and in northern cli- 

 mates, the portion of heat imbibed by the soil during a short 

 summer, is prevented from escaping by the covering of snow 

 which falls in the beginning of winter, and thus the temperature 

 necessary for the scanty vegetation is kept up. By this white 

 covering, vegetables are enabled to sustain a lengthened torpidity 

 without suffering from the injurious effects of frost, and the 

 ground is preserved from partial alternations of temperature, 



• Selby's Illustrations of British Ornithology, part i. p. 312. 

 VOL. XVII. NO. XXXII. JULY 1834. F 



