218 DISCUSSIONS IN CLIMATOLOGY. 



is considerably below the freezing-point. A wind, a 

 few degrees below the freezing-point, blowing on the 

 icy surface would probably re-freeze the ice as rapidly 

 as the sun's rays could melt it. These conditions differ 

 entirely from those that obtain in the Arctic regions. 

 In the latter the air in summer is above the freezing- 

 point, and consequently assists the sun in melting the 

 ice, whereas in the Antarctic regions it is below the 

 freezing-point, and tends to prevent the sun from 

 melting the ice. This circumstance explains the fact, 

 which so much surprised Sir James Ross, that no 

 streams of water flow off the Antarctic ice, similar to 

 those that escape from the great ice-fields of Greenland. 



Such water as formed on the surface could not 

 penetrate to any considerable depth, for the ice, as we 

 shall presently see, being much below the freezing- 

 point, the water would be re-frozen before it could 

 descend to any great depth. 



It therefore follows that the great mass of ice, up 

 to within a short distance of the surface, can be very 

 little affected by heat transmitted either by conduc- 

 tion, or by radiation, or by water from ice melted at 

 the surface. 



Heat derived from Work of Compression and 

 Friction. — I shall now consider the third and last 

 source from which the ice can obtain heat, viz., Work 

 of Compression and Friction. We are fortunately 

 able to come to a pretty definite conclusion in regard 

 to the total amount of heat derivable from this source. 

 The force employed is Gravity, and we can thus 

 determine with certainty the greatest amount of work 

 which that can possibly perform on the ice. Mere 

 pressure, however great, cannot of course generate 

 heat unless it perform work, and the heat thus 

 generated is not proportionate to the pressure, but to 



