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, liowever, 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 almosplieric 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 sufficient 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 indi'pcndcnt of the laws of cur- 
rents generally operative, wfliich would determine them toAvard 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 veJocity varying from one to two and a half knots an 
hour. Neither the soundings nor the diameter of this strait indicate any very 
large deei>-sea fliscliarge in the other direction. 
The Gulf Stream, after dividing the Labrador current, has been traced by Pro- 
fessor Dove to the upper regions of Nova Zembla ; so that Baffin’s Bay, and 
ttie Hudson, and Greenland Seas, constitute the only uniform outlet to the polar 
basin. 
It is by these avenues, then, that the enormous masses of floatiug ice, with 
the deeply-immersed bergs, and the still deeper belt of colder water, are convey- 
ed outward. Underlying the Gulf Stream, wiiose waters it is estimated at least 
to equal in volume, the vast submerged icy river flows southward to the rc'gions 
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 Iroprcai 
currents; and we are prepared to consider these colder streams as equalizers 
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 tlu' 
reverse, or from the south to tlic nortfi. The isotherms of Lieutenant Maury 
(projected by Professor Five) 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 Ironi east to west, from Nova Zembla westwardly and south- 
westwardly to Spitzbergen, wffiere, after an obscure bifurcation, it ^ met by a 
great drift from the north, and carried along the coast of Greenland, in a larger 
body known as the East Greenland current, The observations collected by 
ifieutenant Commanding De Haven show that this stream is deflected around, 
M M 
