H. MOHN. METEOROLOGY. 



[NORW. POL. EXP. 



The diurnal period comes out very distinctly in all months except Novem- 

 ber, with a minimum in the early morning hours and a maximum some 

 hours after noon. The range is greatest in May and has a second maximum 

 in September. It is least in the dark season, only a few hundredths of a 

 millimetre. 



THE ANNUAL PERIOD. 

 The following Table gives the mean tension of vapour for each month, 



in mm. 



Annual Mean 

 Minimum 

 Maximum 

 Range 



1'56 mm. 



0-22 - - January 21 st 

 4-31 - July 20 th 

 4-09 



The march of the values of the tension of vapour is very regular from 

 month to month. PI. VI. (1 cm. = 1 mm.) 



