288 Correspondence — R. IT. Deeley. 



the equinox which is in aphelion is cool for hoth hemispheres. It 

 appears to me that Croll has correctly stated the conditions of climate 

 of the hemisphere the winter of which is in aphelion, but has over 

 estimated the effect produced by the conditions favouring warmth in 

 the hemisphere the winter of which is in perihelion. 



The whole problem turns on the probability of the collection of 

 sufficient ice during the ten thousand years of cold winters to resist 

 appreciable melting during the succeeding ten thousand years of hot 

 summers. It appears to me that when a large area has become ice- 

 bound it will take a very long time for the sun's heat falling on that 

 area during times of eccentricity to clear away the ice. 



The edge of the Great Barrier is about 800 miles from the South 

 Pole, and Scott found that the ice was moving northward at the rate 

 of about 600 yards per annum. South of the Great Barrier edge 

 there seems to be very little actual wasting of the ice due to melting, 

 so, independent of evaporation, ice formed near the South Pole would 

 take about 2400 years to reach the Barrier edge. It is clear, there- 

 fore, that when once a large area has become ice-bound the clearing 

 away of the ice would be a very slow process, especially as the 

 precipitation of snow never ceases. 



Just as the coldest time of our winter does not coincide with the 

 shortest day, so during times of great eccentricity the time of 

 maximum cold will not coincide with the time of greatest eccentricity, 

 nor would the periods of greatest warmth coincide necessarily with 

 the moment of least eccentricity. 



Croll calculated that during the next twenty-five thousand years 

 the earth's orbit would become more and more circular, and then, in 

 a similar period of time, having regained about its present eccentricity, 

 it would remain nearly constant for another fifty thousand years. 

 From the fact that the ice is shrinking on both hemispheres, the 

 physical conditions resulting from the present degree of eccentricity 

 are favourable to future warmer conditions concurrently in both frigid 

 zones. 



I do not assert that the distribution of sea and land with reference 

 to the poles is of no importance from a climatic point of view. If 

 there were no Antarctic land and the south polar area were covered 

 by deep water, the ice formed on the sea near the pole would float into 

 warmer latitudes and readily melt, and thus enable the sea to retain 

 the heat of the summer sun. 



Although there is deep water in the Arctic Sea, the sea is so land- 

 locked that the collection of snow and ice formed during the winter 

 cannot fully escape south during the summer, and a great part of the 

 sun's heat is reflected from it into space. 



It is possible that at remote periods of the earth's history the 

 distribution of the land and sea may have been so favourable that 

 during periods of small eccentricity very genial climatic conditions 

 may have existed at times at one or other of the poles. 



R. M. Deelet. 

 Melbourne House, 



OsMASTON Egad, Derby. 

 March 27, 1909. 



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