CAUSE OF THE ARCTIC FOGS. l6l 
the height of the mast-head, than on the level of 
a ship’s deck. But this seems to he only the ease 
while the thermometer continues below the freez¬ 
ing point; for the-foggy season generally sets in 
as soon as a thawing temperature occurs, with 
any degree of prevalence. One set of observations 
made during a thick fog, with a bright sunshine 
and clear sky aloft, were in confirmation of the 
opinion suggested above. The temperature about 
11 a. M., at the mast-head, 100 feet above the le¬ 
vel of the sea, was 35°; on the level of the deck, 
by the same thermometer, 33£°; near the water’s 
edge 34°; and of the water at the surface 34°. 
The ice, at the same time, must have been, at the 
highest, 32 degrees. Hence, it would appear, 
that the fog is generally occasioned by the damp 
air, near the level of the sea, being chilled by con¬ 
tact with, or radiation from, the ice, which occa¬ 
sions a condensation of that proportion of mois¬ 
ture, which the diminished temperature prevents 
the air from retaining. 
About 11 a. m. of the 16th, the fog dispersed. 
The sky immediately became quite clear, the sun 
shone with cheering brightness, and formed a most 
striking contrast to the uncongenial and bewil¬ 
dering gloom that had so long prevailed. 
Not seeing any whales, we proceeded under a 
smart breeze from the south-west, all the after- 
L 
