256 SUN'S POWER DURING ARCTIC SUMMERS. 



to warm the chilled atmosphere, once they have been 

 withdrawn from it for ever so short a time. For 

 the greater part of the day however, during the height 

 of the summer season, the power of the northern sun 

 is often felt to be of very considerable intensity, so 

 that it sometimes burns the face and hands with almost 

 tropical power. Very hot days are therefore a thing 

 by no means unknown, even far within the arctic 

 circle provided there is no wind and that the sky is 

 clear, during the height of its short summer: but all 

 strong winds are of course very keen and bitter, their 

 temperature being always low in consequence of 

 the wide expanse of ice and snow over which they 

 generally blow. In connection with this fact it is 

 well to bear in mind, that though snow-clad ground 

 and clear ice have the faculty of reflecting heat, very 

 strongly, they do so without absorbing heat. Hence 

 it comes that on snow-clad mountains, for instance,' 

 while the sun shines brightly, the heat is often most 

 trying, because of the way in which the sun's rays are 

 refracted by the snow, but the moment the genial rays 

 of this the great source of terrestrial life are withdrawn, 

 the cold becomes as severe as the heat appeared to 

 be just before ; the moment of sunset each evening is 

 also immediately followed in these localities by an 

 intense and bitter cold that seems to pierce the very 

 marrow of one's bones. So again, during the winters 

 at highly elevated stations, like St. Moritz in the 

 Engadine Valley, Switzerland, situated 6089 feet over 

 sea level ; the temperatures are frequently quite of an 

 arctic character ; the night temperatures often descend- 

 ing to 30, and even 40 degrees below zero : yet here, 

 during the day (when some hours of bright sunshine 



