502 



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. 



m mm. 



Annual Mean 1'56 mm. 



„ Minimum 0-22 — January 21^* 

 „ Maximum 4-31 — July 20"^ 

 Range 409 — 



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

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



