1898-1902. No. 4. 



TEMPERATURE. DAILY PERIOD. 



113 



The Table shows that the temperature of the air is lower with a 

 clear than with an overcast sky in the months January to May, and 

 September to December, and higher in the months June and July. The 

 difference is 



It is only in the summer months that the clear sky is favourable 

 to the rise of the temperature by insolation, and that the cloudiness 

 checks it. In all the other seasons a clear sky is favourable to radi- 

 ation from the earth and loss of heat, and an overcast sky checks this 

 radiation. The effect is greatest respectively in February and in July, 

 and has a regular annual period. With a clear sky we find, in the 

 months October to January, the daily minimum of temperature in the 

 day hours, and the maximum in the night hours. This seems to be a 

 not uncommon daily march of the temperature in arctic regions in the 



cold season. 



In all the other months, from February to September, we find, with 

 a clear skv the ordinary daily period with a minimum in the early 



8 



