22 J. Croll— Cause of Mild Polar Climates. 
means of aerial currents is trifling, and that, consequently, the 
transference must be referred to the currents of the ocean. I 
became obvious then that the influence of ocean-currrents in 
the distribution of heat over the globe had been enormously 
under-estimated. In order to ascertain with greater certainty 
that such had been the case, I resolved on determining, if pos- 
sible, in absolute measure the amount of beat actually being 
co onveyed from the equator to temperate and polar regions by 
means of ocean-currents. 
The only great current whose volume and temperature had 
been ascertained, with any degree of certainty was the Gulf- 
stream. On sorepulng,| tos absolute amount of heat conveyed 
by that stream, it was to be more than equal to all the 
heat received from stipe sun wis 32 miles on each side of the 
equator. Theamount of equatorial heat carried into pine 
and polar regions by this stream alone is therefore equa 
one-fourth of all the heat received from the sun by the North 
Atlantic from the tropic of Cancer up to the Arctic Circle.* 
Although Be Renee pone of the Gulf-stream had long been 
known, yet no one had imagined that the warmth of our cli- 
mate was Bi to such an enormous extent, to the heat con- 
veyed by that stream. The amount of heat received by an 
equatorial zone 64 miles in breadth represents, be it olner vets 
merely the amount conveyed by one current alone. Ther 
are several other great currents some of which convey as ei 
heat polewards as the Gulf-stream. On taking into account 
the influence of the whole system of oceanic circulation, it was 
not surprising that the difference of temperature between the 
equator and the poles should be reduced from 200° to 80°. 
m these considerations, the real cause of former compar- 
atively aaa climates in Arctic regions became now apparent. 
All that was necessary to confer on, say Greenland, a condition 
of climate which would admit of the growth of a luxuriant 
vegetation was simply an increase in the amount of heat trans- 
lue to ‘he eho effect of the permanent snow and ice as to 
an actual want of heat. An increase in the amount of warm 
water entering the Arctic Ocean, just sufficient to prevent the 
formation of permanent ice, was all that was really necessary ; 
or biol i not for the presence of ice ne summers of Green- 
land w be as warm as those of 
Won - whole of the warm Bitse of the Gulf-stream at 
present to flow into the Arctic Ocean, it would probably 
* Climate and Time, pp. 34, 35; Phil. Mag., February, 1870. 
eae ay 
pe Et Ae ne, jini 
