188 
ISLAND LIFE. 
[part I. 
hemisphere, and, passing everywhere over a wide ocean, they 
supply the moisture necessary to produce the enormous quantity 
of snow which falls in the Antarctic area. During the period we 
are now discussing, however, this state of things would have 
been partially reversed. The south polar area, having its 
winter in perihelion, would probably have had less ice, while 
the north-temperate and Arctic regions would have been largely 
ice-clad ; and the north-east trades would therefore be stronger 
than they are now. The south-westerly anti-trades would also 
be stronger in the same proportion, and would bring with them 
a greatly increased quantity of moisture, which is the prime 
necessity to produce a condition of glaciation. 
But this is only one-half of the effect that would be produced, 
for the increased force of the trades sets up another action which 
still further helps on the accumulation of snow and ice. It is 
now generally admitted that we owe much of our mild climate 
and our comparative freedom from snow to the influence of the 
Gulf Stream, which also ameliorates the climate of Scandinavia 
and Spitzbergen, as shown by the remarkable northward cur- 
vature of the isothermal lines, so that Drontheim in N. Lat. 62° 
has the same mean temperature as Halifax (Nova Scotia) in 
N. Lat. 45°. The quantity of heat now brought into the North 
Atlantic by the Gulf Stream depends mainly on the superior 
strength of the south-east trades. When the north-east trades 
were the more powerful, the Gulf Stream would certainly be of 
much less magnitude and velocity ; while it is possible, as Dr. 
Croll thinks, that a large portion of it might be diverted south- 
ward owing to the peculiar form of the east coast of South 
America, and so go to swell the Brazilian current and ameliorate 
the climate of the southern hemisphere. 
That effects of this nature would follow from any increase of 
the Arctic, and decrease of the Antarctic ice, may be considered 
certain ; and Dr. Croll has clearly shown that in this case cause 
and effect act and react on each other in a remarkable way. 
The increase of snow and ice in the northern hemisphere is the 
cause of an increased supply of moisture being brought by the 
more powerful anti-trades, and this greater supply of moisture 
leads to an extension of the ice, which reacts in still further 
