S07 



Meteorology. — ''On the relation hetiveen the cloudiness of the shy 

 and the duration of sunshine". By Dr. J. P. van der Stok. 



(Communicated in the meeting of September 27, 1913). 



1. The subject, mentioned in the title, has but rarely and then 

 cursorily been discussed in meteorological textbooks, periodicals and 

 monographs, and the fact that the sum of degree of cloudiness and 

 duration of sunshine, expressed in percentages and considered for 

 monthly or seasonal means, differs little from 100, is then regarded 

 as a satisfactory result concerning both methods of observing the 

 covering of the sky. 



From observations taken during many years and for three European 

 stations in different climates we find : 



B = Cloudiness, S =r Duration of Sunshine, T =.- B + S. 



In fact it does seem natural that, to a certain extent, the one 

 factor is complimentary to the other ; if the degree of cloudiness is 

 a hundred or zero, the duration must certainly be resp. zero and 

 a hundred, and as in temperate climates these extreme cases often 

 occur, it is natural that the sums do not differ much from 100. 

 From monthly means of cloudiness and duration of sunshine we 

 find for the five Dutch stations the numbers of table I, calculated 

 from or reduced to the period 1900 — 1911. 



From these results it appears that, in general, the sum increases 

 with the sun's height ; in summer the sum is nearly a hundred, in 

 winter not more than 86 and only at Helder it remains considerably 



-) KöNiG. Dauer des Sonnenscheins in Europa. Nova Acta, K. Leip. Gar. D. 

 Ak. d. Naturf. Bd. 67, nO 3, 1896. 



2) FriedemaNxS^ Bewölkung und Sonnenschein des Mittelmeergebietes. Aus dem 

 Arch. d. D. Seewarte. Bd. 36, 1913. 



3) Meiszner. Das Wetter. 1907 en 1910. 



33 

 Proceedings Royal Acad. Amsterdam. Vol. XVI. 



