156 ISLAND LIFE part i 



If this argument is valid, then it would follow that, so 

 long as excentricity was high, whatever condition of 

 climate was brought about by it in combination with 

 geographical causes, would persist through several phases 

 of precession ; but this would not necessarily be the case 

 when the excentricity itself changed, and became more 

 moderate. It would then depend upon the proportionate 

 effect of climatal and geographical causes in producing 

 glaciation as to what change would be produced by the 

 changing phases of precession ; and we can best examine 

 this question by considering the probable effect of the 

 change in precession during the next period of 10,500 

 years, with the present moderate degree of excentricity. 



Prdbahle Effect of Winter in Aphelion on the Climate of 

 Britain. — Let us then suppose the winters of the northern 

 hemisphere to become longer and much colder, the 



in summer to the near sun in winter and distant sun in summer, aided by 

 the change in the physical causes which this would necessarily bring about, 

 would certainly be sufficient to cause the snow and ice to disappear." 

 (Climate and Cosmology, p. 106.) But I demur to his ''necessarily." It 

 is not the direct effect of the nearer sun in winter that is supposed to melt 

 the snow and ice, but the "physical causes," such as absence of fogs and 

 increase of warm equatorial currents. But the near sun in winter acting 

 on an ice-clad surface would only increase the fogs and snow, while the 

 currents could only change if a large portion of the ice were first melted, 

 in which case they would no doubt be modified so as to cause a further 

 melting of the ice. Dr. Croll says : *'The warm and equable conditions 

 of climate which would then prevail, and the enormous quantity of 

 intertropical water carried into the Southern Ocean, would soon produce a 

 melting of the ice. " (Loc. cit. p. 111.) This seems to me to be assuming the 

 very point at issue. He has himself shown that the presence of large 

 quantities of ice prevents "a warm and equable climate" however great 

 may be the sun-heat ; the ice therefore would not be melted, and there 

 would be no increased flow of intertropical water to the Southern Ocean. 

 The ocean currents are mainly due to the difference of temperature 

 of the polar and equatorial areas combined with the peculiar form and 

 position of the continents, and some one or more of these factors must 

 be altered before the ocean currents towards the north pole can be 

 increased. The only factor available is the Antarctic ice, and if this 

 were largely increased, the northward-flowing currents might be so 

 increased as to melt some of the Arctic ice. But the very same argument 

 applies to both poles. Without some geographical change the Antarctic 

 ice could not materially diminish during its winter in perihelion, nor in- 

 crease to any important extent during the opposite phase. We therefore 

 seem to have no available agency by which to get rid of the ice over a 

 glaciated hemisphere, so long as the geographical conditions remained 

 unchanged and the excentricity continued high. 



