REPLY TO CRITICS. 51 



But this is owing to the fact that it is on the moist 

 side that by far the greatest amount of snow is preci- 

 pitated. The moist winds of the south-west monsoon 

 deposit their snow almost wholly on the southern side 

 of the Himalayas, and the south-east trades on the east 

 side of the Andes. Were the conditions in every 

 respect the same on both sides of these mountain- 

 ranges, with the exception only that the air on one 

 side was perfectly dry, allowing radiation from the 

 snow to pass without interruption into stellar space, 

 while on the other side the air was moist and full of 

 aqueous vapour absorbing the heat radiated from the 

 snow, the snow-line would in this case undoubtedly 

 descend to a lower level on the dry than on the moist 

 side. Melting would certainly take place at a greater 

 elevation on the moist than on the dry side; and this 

 is what would mainly determine the position of the 

 snow-line. ^__ 



The annual precipitation on Greenland, as we have 

 seen, is very small, scarcely one-half that of the driest 

 parts of Great Britain. This region is covered with 

 snow and ice, not because the quantity of snow falling 

 on it is great, but because the quantity melted is small ; 

 and the reason why the snow does not melt is not that 

 the amount of heat received during the year is unequal 

 to the work of melting the ice, but that, mainly through 

 the dryness of the air, the snow is prevented from rising 

 to the melting-point. The very cause which prevents a 

 heavy snowfall protects the little which does fall from 

 disappearing. The same remarks apply to the Ant- 

 arctic regions. 



In South Georgia and Fuego, where clouds and dense 

 fogs prevail during nearly the whole year, the per- 

 manent snow and ice are due to a different cause. 

 Here the snowfall is great, and the amount of heat cut 



