OBJECTS AND RESULTS OF POLAR RESEARCH. 639 



another group of phenomena, those of meteorology, which are of 

 interest to the whole earth, and are especially remarkable in the 

 polar regions. An interchange of great wind currents between 

 the equator and the poles is constantly going on, upon which the 

 movements of the atmosphere and the pressure in the interme- 

 diate regions are ultimately dependent, and the study of the at- 

 mospheric phenomena of the polar regions is indispensable to our 

 proper knowledge of them. 



The excess of heat at the equator forces masses of air into the 

 highest regions of the atmosphere ; the congestion at the pole, the 

 necessary consequence of accumulation there, forces them back to 

 the earth. On their way through the higher regions these masses 

 are attenuated and cooled, so that, even when condensed at their 

 sinking, they can not overcome the polar cold ; and as they bring 

 little moisture, and consequently little cloudiness, the radiation of 

 heat goes on continuously during the long polar night ; the more 

 so because snow and ice are extremely good radiators. Hence the 

 extreme cold which Nansen found in Greenland, and which makes 

 that interior a second pole of cold along with that in the interior 

 of Siberia, is fully explained. 



Yet the winds contribute to the warming of the polar sea. 

 They drive the waters from warmer regions in wide superficial 

 currents into the higher latitudes, where, being heavier in conse- 

 quence of their greater content of salt than the fresher water 

 resulting from the melting of the glaciers and the ice and from 

 the outpour of the great Siberian rivers, they sink beneath them 

 to the bottom and keep the temperature of the sea constantly 

 above the freezing point. The colder, lighter water has to give 

 way to these under-sea currents, and flows into the Atlantic 

 Ocean, cooling the American coasts. At the south pole currents 

 flow in from all the seas, and superficial waters spread into all 

 the oceans. 



How shall we account for the masses of polar ice, for the im- 

 mense icebergs, and the glaciation of Greenland ? The snowfall 

 of the polar regions is light. The air is nowhere drier than over 

 the cold glacier ice, as is proved every day in Switzterland by the 

 quickness with which clothes dry when hung over it. At the 

 same time the ice is covered with extremely fine, hardly visible 

 snow crystals. If we boil water in a retort which is connected 

 with another vessel containing a piece of ice, all the steam will 

 pass over on to the ice and deposit itself as ice upon it. The same 

 takes place in a larger degree on the earth, where the retort is 

 the warm evaporating water of the tropical regions, the connect- 

 ing pipe is the upper atmosphere, and the thickening ice is at the 

 pole. Thus, without any rain or snow falling, all the moisture 

 and all the vapor is withdrawn from the atmosphere by this ice 



