148 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
basin, nevertheless bears out vast quantities of salt, which is fur- 
nished neither by the rivers nor the rains. 
283. These salts are supplied by the under current ; for as 
much salt as one current brings in, other currents 252) must take 
out, else the polar basin would become a basin of salt ; and where 
the under current transfers its waters to the surface, there is, it is 
supposed, a basin in which the waters, as they rise to the surface, 
are at 30°, or whatever be the temperature of the under current, 
which we know must be above the freezing- point, for the current 
is of water in a fluid, not in a solid state. 
An arrangement in nature, by which a basin of considerable 
area in the frozen ocean could be supplied by water coming in at 
the bottom and rising up at the top, with a temperature not below 
30°, or even 28° — the freezing point of sea water — would go far 
to mitigate the climate in the regions round about. 
284. And that there is a warmer climate somewhere in that in- 
hospitable sea, the observations of many of the explorers who 
have visited it indicate. Its existence may be inferred also from 
the well-known fact that the birds and animals are found at cer- 
tain seasons migrating to the north, evidently in search of milder 
climates. The instincts of these dumb creatures are unerring, 
and we can imagine no mitigation of the climate in that direction, 
unless it arise from the proximity or the presence there of a large 
body of open water. It is another furnace 60) in the beauti- 
ful economy of Nature for tempering climates there. 
285. Relying upon a process of reasoning like this, and the de- 
ductions flowing therefrom, Lieutenant De Haven, when he went 
in command of the American expedition in search of Sir John 
Franklin and his companions, was told, in his letter of instruc- 
tions, to look, when he should get well up into Wellington Chan- 
nel, for an open sea to the northward and westward. He looked, 
and saw in that direction a " water sky." Captain Penny after- 
ward went there, found open water, and sailed upon it. 
286. The open sea in the Arctic Ocean is probably not always 
in the same place, as the Gulf Stream 54) is not always in one 
place. It probably is always where the waters of the under cur- 
rent are brought to the surface ; and this, we may imagine, would 
depend upon the freedom of ingress for the under current. Its 
-course may, perhaps, be modified more or less by the ice on the 
