492 H. MOHN. METEOROLOGY. [norw. pol. exp. 



The mean length of a period of ascending temperature is 200 days, and 

 of a period of descending temperatures 1"93 days. The temperature rises at 

 a slower rate than that at which it falls. We have seen that in the year it 

 rises on 186'5 days and falls on 178"5 days. The lengths of the ascending 

 and descending temperature-periods have an annual period. The periods are 

 shorter than the annual mean both of rise and fall, from May or June to 

 September, and longer in the other part of the year. 



The whole length of a period comprising the rise and the fall of the 

 temperature, is on an average 3'93 days. It is shorter from June to Sep- 

 tember, and longer from October to May, being longest in December, 4'7 days, 

 and shortest in August, 3'1 days. 



THERMAL WIND-ROSES. 



The numbers in the following Tables have been computed in the same 

 manner as the numbers of the dynamic and baric wind-roses. 



