206 DISCUSSIONS IN CLIMATOLOGY. 



determined by purely physical and mechanical con- 

 siderations, based, it is true, on data derived from 

 observation. 



It fortunately happens, however, that the very 

 circumstances that render the region so difficult to get 

 at are those which at the same time tend to simplify 

 the problem. The Antarctic region is the most 

 inaccessible on the globe, but of all regions it is the 

 one where the physical conditions are most uniform 

 and least under the influence of contingent circum- 

 stances, such as those resulting from the presence of 

 warm ocean currents in one place and cold currents in 

 another, or of great masses of land in one part and an 

 open sea in another. We have not in the Antarctic, as 

 in the Arctic region, well-marked warm and moist 

 aerial currents and cold and dry winds blowing athwart 

 different areas. Surrounding the South Polar con- 

 tinent lies an unbroken ocean, in an almost uniform 

 climatic condition. This region also, as Sir Wyville 

 Thomson remarks, is " continuously solid, — that is to 

 say, it is either continuous land or dismembered land 

 fused into the continental form by a continuous ice- 

 sheet." In this case we can treat it as one continuous 

 continent. The South Pole being safely assumed to 

 be in the centre of the sheet, we have here what we 

 perhaps never had on the northern hemisphere, even 

 during the Glacial Epoch — a polar ice-cap. We have 

 the pole in the centre of the cap ; therefore, at equal 

 distances from the pole or centre, the conditions in 

 every respect, both as to climate and the thickness of 

 the ice, may be assumed to be the same, for no reason 

 can be assigned for supposing the conditions in separate 

 areas upon the same parallel of latitude to differ. Thus, 

 as a purely physical and mechanical problem, the 

 conditions could hardly be more simplified. 



