226 Dr. A. Woeikof s Examination of 



the same regions fogs are frequent in autumn during anti- 

 cyclones. The cause of these fogs is the same as that of the 

 London fogs, i. e. the temperature of the river- or lake- water 

 is much higher than that of the air, and thus the vapour is 

 soon condensed. Neither are fogs common in summer over 

 mountain-snow and glaciers, notwithstanding the great amount 

 of melting. But fogs are experienced on the sea in the 

 vicinity of melting ice, because here we have two masses of 

 air, of unequal temperature, both nearly saturated, and their 

 meeting must produce saturation, i. e. fogs. Thus it is easy 

 to see that fogs are not necessary consequences of the melting 

 of snow and ice per se ; but some other conditions are 

 necessary for them ; and Dr. Croll has no right to say about 

 a glaciated country at some distance from the sea, u Fogs 

 prevent, to a great degree, the melting of the snow and ice.'''' 



Mr. A. R. Wallace * has mentioned that in Northern 

 Siberia the powerful sun of June cannot melt the snow until 

 the warm southerly winds bring warm air. In so far as the 

 beginning of melting depends on this, I am quite of the same 

 opinion ; but Dr. Croll is wrong when he too much extends 

 the influence of these southerly winds, and believes them to 

 prevail in summer on the north coast of Siberia. On the 

 contrary, cold winds from the sea prevail in summer and cer- 

 tainly chill the air, while southerly winds prevail in winter. 

 Thus Dr. Croll's hypothesis, " Matters would be still worse if 

 these southerly winds, instead of ceasing, were simply to 

 change from June and July to December and January; for 

 then, instead of producing a melting effect, they would greatly 

 add to the snowfall,"! is realized as far as the winds are con- 

 cerned; but ihe snowfall of winter is exceedingly light, 

 because the southerly winds come from the colder interior of 

 the continent ; and, besides, they are descending winds, and 

 in descending become relatively dry. We know these facts 

 from the observations of Wrangell and Anjou at Nijnekolymsk 

 and Ustjansk ; and they were confirmed by the recent obser- 

 vations of the Russian polar station of Sagastyr at the mouth 

 of the Lena {. 



Dr. Croll returns over and over again to the importance of 

 knowing the temperature of space, as well in ' Climate and 

 Time ' as in his new book; and in the latter he is rather in 

 favour of a lower value for it than that of Herschel and 

 Pouillet, which he admitted in ' Climate and Time.' He thinks 

 this knowledge of the utmost importance for the determina- 



* < Island Life/ p. 135. 



f P. 88. _ 



% Iswestia of the Russ. G-eogr. Soc. 1885, no. 4. 



