110 
DECEPTIONS OF FOG. 
off on the level of the decks, every thing was clearly 
discernible at an elevation of forty feet. I saw dis- 
tinctly the surrounding bergs rising above a sea of 
mist. 
One phenomenon, however, struck me as novel : at 
least I have never seen it described. It was this : 
Though the bergs were thus obscured at their bases 
by a dense plain of vapor, the Rescue, at an equal dis- 
tance, was visible throughout her entire extent, encir- 
cled as by an oriole in a clear atmosphere. Repeated 
observations have suggested to me this explanation of 
this phenomenon. 
These fogs, due to local refrigeration, are merely ex- 
ceptional breaks-in upon our pervading sunshiue. They 
are generally temporary, and the stratum of precipita- 
tion is so narrow that the sun is hardly intercepted. 
Evaporation continues as before; the decks are dry 
and heated ; and the radiating influences of the vessel 
while stationary invest it with a sort of dome or halo 
of transparency. I have noticed this effect when look- 
ing at one of our brigs from on board the other, and 
have found that, if the sun was obscured for any length 
of time, the hull disappeared, and the upper rigging 
only protruded from a sea of mist. My sketch at the 
head of this chapter will show some of the curioias 
phases of this phenomenon. 
The effects of fogs upon our estimation of dimension 
and distance are well known : men are magnified to 
giants, and brigs "loom up," as the sailors term it, 
into ships of the line. They are especially interesting 
among the icebergs of this region. Two bergs were 
measured trigonometrically on the 4th, with a careful- 
ly ascertained base-line of four hundred yards. One 
of these, which I had estimated by eye as nearly three 
