Fogs of the Polar Seas. 13 



perature nearly uniform; and thereby prevent the formation of 

 mist. The cold volume of air so formed, may, however, pass from 

 between the icy masses, and by mingling with the air reposing on 

 the warmer water, beyond the icebergs, produce mist at a distance 

 from them. Nor is it absolutely necessary that two icebergs 

 should exist, in order to form mist ; since the horizontal radia- 

 tions of owe, by cooling the portion of air in contact with it, will 

 cause it to mingle with the warmer air beyond the last-mentioned 

 stratum, and thus create fog. The density of a mist when formed 

 under the latter conditions, will be of a more variable character, 

 than when it is formed between adjacent icebergs. 



The general diffusion of fogs over the Northern Seas may also 

 be satisfactorily accounted for, from the scattered icebergs sepa- 

 rating the water into detached portions ; and thereby creating, 

 in innumerable directions, volumes of air, possessed of unequal 

 temperatures. The cold air near the icebergs being blended, 

 therefore, with the warmer air reposing on the middle portions 

 of the broken intervals of water, must form, between most of the 

 floating masses of ice, visible volumes of vapour, having their 

 density dependent on the relative difference of heat between the 

 mingling portions of air, and on the degree of humidity possessed 

 by each. 



The cause here referred to, for the production of the Polar 

 fogs, is also one likely to promote their continuance for a con- 

 siderable time ; it being known, that the sea continues for many 

 months relatively warmer than the icebergs ; and therefore 

 capable, in conjunction with the constant radiation of the ice, of 

 producing that almost constant succession of fogs which cover 

 the Arctic Seas during the greater part of the summer months ; 

 and which increase, in so considerable a degree, the difficulties of 

 Polar navigation. 



Plymouth, July }9th t 1825. 



