SCIENTIFIC OBSERVATIONS. 
295 
worth, determining, as if that is the case, all altitudes 
taken at sea must require a like correction on that 
account, independent of the correction which may be 
necessary for the refraction in altitude of the object 
observed. It seems probable also, that the refraction 
of the horizon may be liable to variation with the 
state of the atmosphere. 
When the height of the observer above the level of 
the sea is known, the depression of the real terrestrial 
horizon is correctly ascertained on trigonometrical prin¬ 
ciples ; accordingly, by observing the vertical arc con¬ 
tained between two opposite points of the apparent 
horizon, the refraction of the horizon can be deter¬ 
mined, the difference of the observed vertical arc from 
the half circle being the combined effect of dip and 
refraction. 
So much snow fell during the winter, that the 
Hollanders had almost every day to clear the entrance 
of their hut. 
On the 13th of February, a great bear came close 
to their hut, which they shot, and obtained from the 
carcass above a hundredweight of fat or lard. On 
the 8th of March, the sea to the North was observed 
to be quite clear of ice, which made them conjecture 
there was a great extent of open sea in that direction. 
The next day the sea appeared equally open and clear 
to the North and North-East; but more eastward, and 
