in the Franz Joseph Land region, since the average number of freezing degree-days in that 

 region is 5625 . 



Assuming that the ice thickness would decrease 100 cm during the summer, i.e , that it 

 would become 109 cm thick, he calculated that by the end of the second winter, the ice would be- 

 come 234 cm thick due to the effect of another 5625 freezing degree-days on ice 109 cm thick. 



Thus, considering the further increase of ice thickness, Wejrprecht found that for Franz 

 Joseph Land where, on the average, the number of freezing degree-days was 5625 with a summer 

 decrease of 100 cm, the maximum thickness would be 260 cm. With this ice thickness, as much 

 ice would melt in summer as would accrete in winter . 



We have seen that ice accretion, as a function of the number of freezing degree-days, can 

 be determined with adequate approximation, by my formula 



r"+50i = 8R. (1) 



From this formula , we get 



(A/)2+(50-l-2/o)A/ — 8A/? = 0. (2) 



From figure 72, we see, e.g. , that if there were no ice at the initial moment, after 6000 

 freezing degree-days the ice would become 196 cm thick, while if the ice were 400 cm thick at the 

 initial moment, after 6000 freezing degree-days, the ice thickness would increase only 53 cm. 

 This, then, is Weyprecht's concept of the maximum accretion of perennial ice. 



Transforming formula (2) , we get 



4AR A/ 

 /i = ^^-^-25. (3) 



In this formula, let us assume that: A J is the decrease of ice thickness during summer due 

 to melting and Ai? is the number of freezing degree-days during the winter in a given region. 



In this case, J, will be the maximum ice thickness during the autumn, before ice formation 

 begins . 



If we assume that all the ice which has formed in the given region during the winter, melts 

 during the summer, 



then from (3) we get 



8A/? = (A/)3-l-50A/. (4) 



If the number of freezing degree-days is greater in a given region than that obtained by for- 

 mula (4), the ice which had formed during the winter would last through the summer and would 

 then be classified as perennial ice. If it is less, not only the ice which had formed in a given re- 

 gion, but also ice of any thickness which had been carried into the given region from another region 

 would eventually be destroyed by melting. 



226 



