THE CUPOLA OF ICE AT THE SOUTH POLE. 405 



M. Adhemar points out, however, that the temperature of 

 each hemisphere does not depend on the quantity of heat 

 received from the sun, but on the difference between the 

 amount received and the amount radiated away into space ; 

 in other words, on the quantity retained. If, he says, in 

 illustration, you burn a given quantity of wood in two iden- 

 tical rooms, and then open the windows in one and not in the 

 other, you will soon have a difference of temperature, though 

 the supply of heat has been the same in both.* 



Now, our northern hemisphere has 186x24 = 4464 hours 

 of day in the year, and 179 x 24 = 4296 hours of night, while 

 the southern hemisphere has 4464 hours of night, and only 

 4296 of day. We may admit that the southern hemisphere 

 will receive as much heat from the sun in its 4296 hours of 

 day, as we do in our 4464, but it is evident that it will retain 

 less, because it will have 168 hours more of night, during 

 which radiation will be going on. Though, therefore, the heat 

 received by the two hemispheres will be equal, the tempera- 

 ture of the two will not, M. Adhemar maintains, be by any 

 means the same ; and though at first this difference may be 

 slight, it will in its nature be to a certain extent cumulative. 



Mr. Croll, however, is of opinion that this difference can, 

 after all, produce little or no effect on climate. However this 

 may be, it is evident that, on account of the much greater 

 accumulation of ice, the southern hemisphere is colder than 

 the northern ; and it is also clear that this very fact tends to 

 aggravate the difference to which it is due. 



Moreover, M. Adhemar affirms that the immense cupola of 

 ice which is known to exist round the South Pole must affect 

 the centre of gravity of the earth, and consequently attract 

 the ocean southwards. In this manner, indeed, he attempts 

 to explain the remarkable preponderance of land in the north, 

 and of sea in the southern hemisphere. A glance at the map 



* Revolutions de la Mer, p. 344, 



