POLAR SEA. 
545 
The influences of congelation too, aided by the diminished intensity and the 
withdrawal of the solar ray, increase the atmospheric precipitation, and proba- 
bly diminish the compensating evaporation. Yet this position calls for further 
investigation to establish it absolutely ; for recent experiments show that even 
in the dark hours of winter, and at temperatures of fifty degrees below zero, 
evaporation goes on at a rapid rate. That it holds, however, in general terms, 
is evident from the inferior specific gravity of the Arctic waters. They are less 
salt than those of more equatorial regions. Their average specific gravity 
(1.0265) indicates about 3.60 per cent, of saline matter. 
The atmospheric precipitation extending to the adjacent land slopes, the melt- 
ing of the snows and accumulated glacial material, and the floods of the great 
Siberian rivers, are sutflcient to account for this. 
With such sources of supply, it is evident that this surcharged basin must 
have an outlet, and its contents a movement independent of the laws of cur- 
rents generally operative, which would determine them toward the equator. 
The avenues of entrance to and egress from the polar basin are but three ; 
Behring's Straits, the estuaries of Hudson's and Baffin's Bays, and the interval 
between Greenland and Norway, upon the Atlantic Ocean, known as the Green- 
land Sea. In Behring's Straits, it is probable, from imperfect observations, that 
the surface current sets during a large portion of the year from the Pacific into 
the Arctic Sea, with a velocity varying from one to two and a half knots an 
hour. Neither the soundings nor the diameter of this strait indicate any very 
large deep-sea discharge in the other direction. 
The Gulf Stream, after dividing the L-abrador current, has been traced by Pro- 
fessor Dove to the upper regions of Nova Zembla ; so that Baffin's Bay, and 
the Hudson, and Greenland Seas, constitute the only uniform outlet to the polar 
basin. 
It is by these avenues, then, that the enormous masses of floating ice, with 
the deeply-immersed bergs, and the stdl deeper belt of colder water, are convey- 
ed outward. Underlying the Gulf Stream, whose waters it is estimated at least 
to equal in volume, the vast submerged icy river flows southward to the regions 
of the Caribbean. The recent labors of the United States Coast Survey and 
Nautical Observatory have, as the society is aware, developed and confirmed 
the previously-broached idea of a compensating system of polar and tropical 
currents ; and we are prepared to consider these colder streams as equahzers 
to the heated areas of the tropical latitudes, and analogous in cause and effect 
to the recognized course of the atmospheric currents. 
In fact, Dove, Berghaus, and Petermann, three authorities entitled to the high- 
est respect, recognize for the Arctic Ocean a system of revolving currents, 
whose direction during summer is from north to south, and during winter the 
reverse, or from the south to the north. The isotherms of Lieutenant Maury 
(projected by Professor Flye) point clearly to the same interesting result. Con- 
trasting these great movements of discharge and supply with the surface ac- 
tions, we find during the summer months a movement along the northern coasts 
of Russia, clearly from east to west, from Nova Zembla westwardly and south- 
westwardly to Spitzbergen, where, after an obscure bifurcation, it is met by a 
great drift from the north, and carried along the coast of Greenland, in a large 
body known as the East Greenland current. The observations collected by 
Lieutenant Commanding De Haven show that this stream is deflected around 
Mm 
