80 Dr Stark on the Influence of Colour on Heat, 



is reason to believe the quality of modifying the individual tem- 

 perature, and keeping it at the proper mean. This adaptation 

 of colour may perhaps be traced in the inhabitants of every de- 

 gree of latitude, and may be found to correspond with the causes 

 which limit the range of plants and animals. The effect of the 

 exposure to the sun in our own country in warm seasons is tem- 

 porarily to change the colour of the parts submitted to its in- 

 fluence, and to render them less susceptible of injury from the 

 heating rays. 



The influence of colour, as modifying the effects of heat, is 

 also strikingly illustrated in other classes of the animal kingdom. 

 The quadrupeds, for instance, which pass the winter in northern 

 latitudes, besides the additional protection from cold they re- 

 ceive in the growth of downy fur, change their colour on the 

 approach of the cold season. The furs of various hues which 

 form their summer dress are thrown off", and a white covering 

 takes its place. Hence the white foxes, the white hares, and 

 the ermine of the arctic regions. Even in more temperate cli- 

 mates, and in our own country, the hare, in severe winters, of- 

 ten acquires a white fur ; and the stoat or ermine is found with 

 its summer dress more or less exchanged for a winter clothing 

 of pure white. Some writers on natural history state these 

 changes as means of protection to the animals from their ene- 

 mies, by assimilating their colour to the winter snow. Without 

 denying that this may be one final cause for the periodical 

 change of colour, I am rather disposed to consider it as accom- 

 modating the animal to the changes of season it undergoes. 

 The white winter coating, as is evident from my experiments, 

 does not throw off" heat so rapidly as any of the other colours; 

 and hence its use in preserving the animal temperature. 



The feathered tribes which inhabit northern latitudes, afford 

 still more remarkable instances of the adaptation of colour to the 

 changes of temperature. The summer dress of many families 

 is so different from their winter plumage, as to have led man}'^ 

 ornithologists to multiply species as the animal was described in 

 its winter or summer plumage. The ptarmigan is a familiar ex- 

 ample. Mr Selby remarks, that " the black deep ochreous yel- 

 low plumage of the ptarmigan in spring and summer gradually 

 gives place to a greyish-white ; the black spots become broken, 



