146 ISLAND LIFE 



shown that the existence of perpetual snow often depends 

 upon it. South Georgia in the latitude of Yorkshire is 

 almost, and Sandwich Land in the latitude of the north of 

 Scotland, is entirely covered with perpetual snow ; yet in 

 their summer the sun is three million miles nearer the 

 earth than it is in our summer, and the heat actually 

 received from the sun must be sufficient to raise the 

 temperature 20° F. higher than in the same latitudes in 

 the northern hemisphere, were the conditions equal — in- 

 stead of Avhich their summer temperature is probably full 

 20° lower. The chief cause of this can only be that the 

 heat of the sun does not reach the surface of the earth ; 

 and that this is the fact is testified by all Antarctic 

 voyagers. Darwin notes the cloudy sky and constant 

 moisture of the southern part of Chile, and in his remarks 

 .on the climate and productions of the Antarctic islands he 

 says : " In the Southern Ocean the Avinter is not so 

 excessively cold, but the summer is far less hot (than in 

 the north),/(9?' the clouded shy seldom alloivs the sun to vjao^m 

 the ocean, itself a bad absorbent of heat ; and hence the 

 mean temperature of the year, which regulates the zone 

 of perpetually congealed under-soil, is low." Sir James 

 Ross, Lieutenant Wilkes, and other Antarctic voyagers 

 speak of the snow-storms, the absence of sunshine, and the 

 freezing temperature in the height of summer ; and Dr. 

 CroU shows that this is a constant j^henomenon accom- 

 panying the presence of large masses of ice in every part 

 of the world.^ 



In rejDly to the objections of a recent critic Dr. Croll 

 has given a new proof of this important fact by comparing 

 the known amount of snow-fall with the equally well- 

 known melting power of direct sun-heat in different 

 latitudes. He says: ''The annual precipitation on 

 Greenland in the form of snow and rain, according to Dr. 

 Rink, amounts to only twelve inches, and two inches of 

 this he considers is never melted, but is carried away in 

 the form of icebergs. The quantity of heat received at the 



^ For numerous details and illustrations see the paper— "On Ocean 

 Currents in Relation to the Physical Theory of Secular Changes of Climate. " 

 — in the Phihso2}hical Magazine, IS 70. 



