THE PTAIOUGAN. 



•l-i7 



answered. IJut when the mountains arc covered with snow, and all around is attired 

 in a mantle of dazzling white, were the plumage of these birds to continue as it was, 

 they would at once attract the Iceland falcon and the Snowy owl. The white feathers, 

 on the contrary, which clothe them at this season, are sure to defend them from their 

 foes. 



The saying of the poet may often bo rooalled in the study of this as well as of other 

 portions of the Divine operations : — 



" In human works, though laboured on with pain, 

 A thousand movements scarce one piu'pose gain ; 

 In God's, one single can its end produce. 

 Yet serves to second, too, some other use." 



And so it is here. The white plumage is a defence against the cold of winter, as are 

 other proA-isions by which it is accompanied. For then the legs of the ptarmigan, which 

 have been covered with feathers of a hair-like and downj- texture, extending as far as 

 the toes, are now so enveloped as to resemble the feet of a well-furred quadruped ; while 

 the bill is almost hidden. The additional reason of this will speedily be apparent. 



It is well known that colour greatly influences the rate at which bodies either reflect 

 heat, or acquire and ixirt witli it, and that objects which reflect heat the most part with 

 it the least. Reflection takes place most readily in objects of a white colour, and from 

 such, consequent!}', heat will radi&te with difiiculty. If, then, two animals, one of a 

 black colour and the other white, be placed in a higher temperature than that of their 

 own bod}-, the heat will enter the one that is black with the greatest rapidity, and 

 elevate its temperature considerably above the other. But when these animals are 

 placed in a situation the temperature of which is considerably lower than their own, the 

 black animal will give out its heat, by radiation, to every surrounding object colder than 

 itself, and speedily have its temperature reduced ; while the white animal \\-ill part with 

 its heat by radiation at a much slower rate. The winter colour of the ptarmigan, there- 

 fore, combined with its increased fulness of plumage, tends to limit the expenditure of 

 the vital heat generated in the system ; thougli some expenditure must take place. This 

 power of generating heat in the animal system, it may be added, is the principle on 

 which all animals are enabled to withstalid the effect of cold, and to preserve life and 

 health in a low temperature. 



=ts 



i^Ssr-* 



yOOT OF THE rXARJIIGAN l.N WINTER. 



rOOT OF TEIKAO rAUADUXlS. FALLA^. 



The Tcfrao paraiio.ins, the foot of which is represented, inhabits the si eppes of Bucharia 

 and Tartarv. 



