12 Mr. George Harvey on the 



diffused, not only by radiations from their upper surfaces to the 

 canopy of the sky above them ; but by horizontal radiations, to 

 the air surrounding their sides. A volume of the atmosphere 

 therefore, between two neighbouring masses of ice, will necessa- 

 rily have its middle portion of a higher temperature than that of 

 either of the portions of air between it and the icebergs * ; and 

 the consequence of such an unequal distribution of temperature 

 must be, to cause the cold air to mingle with that of a higher 

 temperature, and thus to produce mist or fog. The density of 

 such mist or fog will depend on the difference between the tem- 

 peratures of the mingling volumes, and on the quantity of vapour 

 contained in the air. 



The elevation of those mists above the surface of the sea will 

 also be regulated by that of the icebergs, near which they form ; 

 since the cooling influence of the frozen mass, by rapidly dimi- 

 nishing above its summit, will as rapidly destroy all tendency in 

 the portion of the atmosphere above the level of the iceberg, to 

 assume a condition favourable to the formation of mist ; thus 

 prescribing to the mist an elevation dependent on that of the 

 iceberg near which it forms. Captain Ross accordingly remarks, 

 in his Account of the Polar Voyage, " that the fog was extremely 

 thick on the surface of the sea, but at the mast-head, and at the 

 top of the iceberg, it was perfectly clear." Captain Scoresby 

 also, in his Paper on the Fogs of the Polar Seas, read before the 

 Wernerian Society t, 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 reduce it to a tern- 



* If the water in the vicinity of icebergs presents considerable inequalities 

 of temperature, the air which reposes on it must be subject to like variations; 

 and numerous examples of the former are to be met with in the Accounts of 

 the Polar Voyages. Thus Captain Franklin remarks, " the temperature of the 

 surface water was 35° when among the ice, 38° when just clear of it, and 41°, 5 

 at two miles distant." 



f Edinburgh Philosophical Journal, Vol. VI, 



