118 Mr Scoresby on the Fogs of the Polar Seas, 
copper in four different places. Thus, the principal design of 
tlie experiment being frustrated, I could only ascertain the quan- 
tity of impregnation. The weight of the mahogany, when dry, 
was 155 grains ; the weight gained in the experiment 90 grains. 
Increase of bulk equal to 8 grains of water. 
II. 071 the Fogs to which the Polar Seas are subject 
The great prevalence of foggy weather in the polar seas, du- 
ring the summer months, is a fact which, though well known, 
has not, that I am aware of, been explained. In the present year 
(1821), from the 11th of July until the 21st of August, we only 
had three days of clear weather. During this interval, we na- 
vigated a sea embarrassed with an accumulated quantity of ice ; 
the whole of the ice that so remarkably disappeared in the years 
1817 and 1818 having been replaced, and a body above 240 
miles in width, having collected on the eastern coast of Green- 
land. As the fog to which the icy seas are subject, frequently 
rests on the surface of the water, and extends only perhaps to the 
height of 150 to 200 feet, the sky above being often perfectly clear, 
it occurred to me, that the cause of these low fogs might be 
found, perhaps, in the temperature : that the cold, during such 
fogs, might be greater at the surface than at considerable eleva- 
tions, though the contrary is usually the case. Some observa- 
tions made on the 23d July, during a very thick fog, with a 
clear sky and bright sunshine above, seemed to confirm this 
opinion. 
The temperature about 11 a. m. at the mast-head, 100 feet 
above the level of the sea, was 35° ; on the level of the deck, by 
the same thermometer, 33|° ; near the water’s edge 34° ; and of 
tlie water at the surface 34°. Hence, it would appear, that 
the fog is occasioned by the damp air, near the surface, be- 
coming chilled by contact with, or radiations from, the ice: for, 
at other seasons, I have almost invariably found the tempera- 
ture aloft tw^o or three degrees lower than at the surface ; while 
in fogs with a clear air above, it seems to be higher. 
