288 POPULAR LECTURES AND ADDRESSES. 



hour or 70 miles per four days, flowing towards 

 the pole across the arctic circle. The area of the 

 arctic circle J is 700 square miles for each mile of 

 its circumference. Hence 40 fathoms deep of such 

 a current would carry in, per twenty-four hours, a 

 little more than water enough to cover the whole 

 area to a depth of I fathom: and this, if 7'! 

 Cent, above the freezing point would bring in 

 just enough of heat to prevent freezing, if in 

 twenty-four hours as much heat were radiated 

 away as taken from a tenth of a fathom of ice- 

 cold water would leave it ice at the freezing point. 

 This is no doubt much more than the actual 

 amount of radiation and the supposed current is 

 probably much less than would be if the water 

 were ice-cold at the pole and f Cent, at the 

 Arctic circle. Hence, without any assistance from 

 air, we find in the convection of heat by water 

 alone a sufficiently powerful influence to prevent 

 any free/ing up in polar regions at any time of 

 Hut the air also must carry much heat 

 .quantities of heat considerable in comparison with 



1 I Sung approximately plane, and of 1400 miles radius. 



