NO. 17]. 



BAROMETRICAL DEPRESSIONS AND THEIR MOTION. 



581 



The number of cyclonic systems within whose sphere of influence the 

 Fram has come, her barometer faUing as much as 10 mm. and upwards, 

 amounts to at least 73 in 3 years. The frequency of depressions has a clearly- 

 defined annual period. It has its maximum (4 per month) in January and 

 February, and its minimum (0'7 per month) in June. The mean duration of 

 the passage of a depression does not vary much in the several months or 

 seasons; it is about 4 days. 



In the course of 3 years we find 73 depressions with a fall or rise of 

 the pressure of upwards of 10 mm., or about 24 per annum. Their passage has 

 lasted 290 days, which gives 97 cyclonic days of the above-mentioned force. 



The lowest atmospheric pressure at the Fram's station during the passage 

 of a depression varies from 771-7 mm. to 724-1 mm., both in February. The 

 distribution is as follows: 



