340 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



the vapors coining in contact with the ice and snow ; fogs and clouds 

 are besides formed which absorb heat from the sun, it is true, but ttiey 

 easily lose it again by radiation because of their elevation and their 

 position in a less dense atmosphere. One would suppose that the sum- 

 mer rains were in themselves sufficient to melt the snow accumulated 

 during the winter ; but such is not the case, for eight parts of water, at 

 L0° centigrade, are necessary to melt one part of snow, even when this 

 has commenced to dissolve. Professor Forbes has found that only the 

 fifteenth part of the snow of Norway is melted by the rains of summer, 

 which are there very abundant. 



If, then, at the time of the maximum of eccentricity tbe mean temper- 

 ature of winter fell to a fifth below the present mean, and if the length 

 of the day in winter was increased in proportion, it is probable that the 

 climate of Central Europe would unite all the conditions for producing 

 the extraordinary development of the glaciers, indicated by the traces 

 of their action. The heat of the summer increased a fifth would not 

 prevent the insensible deterioration of the climate, and we have a beau- 

 tiful example in the island of Georgia of the south, of permanent ice in 

 a latitude where in Ireland palms grow in the open air.* Navigators 

 have seen in Terre del Fuego and in the straits of Magellan, snow fall 

 in the middle of summer, and it has been proved that the temperature 

 of this season rarely rises above 6° and almost never above 10°. 



Such would be the condition of our climates, if, after the reaction 

 from great eccentricity, the winters coincided with the aphelion. This 

 state of things would not even be modified by the Gulf Stream ; this 

 would prevent the congelation of the European seas, but not the detach- 

 ment of icebergs from the glaciers which would have attained the level 

 of the sea, and the masses of ice floating around the islands and conti- 

 nents would cool them considerably by their fusion. There are numer- 

 ous examples of a remarkable coincidence between the presence of 

 floating ice in the vicinity of an island or a continent, and the return of 

 cold weather after the mildness of spring. Not long ago the inhabit- 

 ants of Iceland were reduced to the utmost misery by the accumulation 

 of floating ice, which, by the cold it occasioned, destroyed the harvests. 

 Some exceptionally warm years following 1814 were the cause of the 

 breaking up of the ice of Greenland.t The floating ice descended upon 

 the occidental coasts of Europe, which produced great cold, and in con- 

 sequence the glaciers of the Alps increased in a most unusual manner. 



But it is a question whether the Gulf-Stream and other currents will 

 always exist in their present intensity. In seeking the causes of oceanic 

 currents, we find in the unequal temperature of the poles and of the 



* Captain Cook landed on his second voyage upon this melancholy island, and he 

 says of it: " We thought it very extraordinary that an island between the latitude of 

 54° and 55° should, in the very height of summer, be almost entirely covered with 

 snow, in some places many fathoms deep." (Captain Cook's Second Voyage, vol. ii, p. 232.) 



tArago, (Euvres, Rapports, &c, p. 118. 



