508 



TABLE I. 



Sums of cloudiness and duration of sunshine, Monthly means. 



behind the full peroentcage in every month. However, it is well known, 

 (as an inspection of the hourly values given in annals also proves) 

 that the sunshine-recorders do not register until some time after 

 sunrise and leave off registering before sunset, so that all average 

 values (but mostly those of the winternionths when the total amount 

 of sunshine is small) must be too low and that to a considerable extent. 



Monthly means therefore are certainly not likely to give a proper 

 idea of the relation between cloudiness and duration of sunshine so 

 that in order to come to a better understanding we employ observ- 

 ations taken at a time when we are sure of the undisturbed influence 

 of the sun ; as the cloudiness is observed at 8 a.m., 2 p.m and 

 7 p.m., it is the afternoon observation which is indicated for this 

 investigation. 



As shown by tables II and III, the sum is then considerably 

 higher than lOOVo for all five stations with the exception of winter 

 for Helder and of December for all stations. 



From the fact that in June and July, when the sun is highest, 

 the sums are almost equal for all stations, we may conclude that 

 individual conceptions in estimating the cloudiness play a subordinate 



