Fogs of the Polar Seas. — 'Selenium. 317 



Polar Seas, read before the Wernerlan Society (Edin. Ph. 

 Journ. vol. vi.) alludes to their definite elevation, and to the 

 sky above them being perfectly clear. 



It is possible, however, that two icebergs may be situated so 

 near each other, that their reciprocal horizontal radiations will 

 so cool the volume of air between them as to I'educe it to a 

 temperature nearly uniform, and thereby prevent the forma- 

 tion of mist. The cold volume of air so formed, may, how- 

 ever, 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 txw icebergs should exist, in order to form mist ; 

 since the hoi'izontal radiations of one, 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 

 separating 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 tlifference 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 there- 

 fore capable, in conjunction with the constant radiation of the 

 ice, of jiroducing 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. — Qiuirterly Journal of Science. 



Plymouth, July 19th, 1825. 



SELENIUM. 



We translate the following from a notice in Scliweigger's 

 Journal for April last. 



The remarkable substance discovered by Berzelius, called 

 selenium, is still one of the most scarce and expensive ; even 

 the celebrated discoverer con)plains of the smallness of the 



fjiianlity 



