138 



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 wdth 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 Scandiwavia 

 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 



