CLCUDS AND RIVERS, ICE AND GLACIERS. 21 



there precipitated, falling sometimes as rain, or more 

 commonly as snow. The land near the pole is covered 

 vs itli this snow, which gives birth to vast glaciers in a 

 manner hereafter to be explained. 



62. It is necessary that you should have a perfectly 

 clear view of this process, for great mistakes have been 

 made regarding the manner in which glaciers are related 

 to the heat of the sun. 



63. It was supposed that if the sun's heat were 

 diminished, greater glaciers than those now existing 

 would be produced. But the lessening of the sun's 

 heat would infallibly diminish the quantity of aqueous 

 vapour, and thus cut off the glaciers at their source. 

 A brief illustration will complete your knowledge here. 



64. In the process of ordinary distillation, the liquid 

 to be distilled is heated and converted into vapour in 

 one vessel, and chilled and reconverted into liquid in 

 another. What has just been stated renders it plain 

 that the earth and its atmosphere constitute a vast dis- 

 tilling apparatus in which the equatorial ocean plays 

 the part of the boiler, and the chill regions of the poles 

 the part of the condenser. In this process of distilla- 

 tion heat plays quite as necessary a part as cold, and 

 before Bishop Heber could speak of 6 Greenland's icy 

 mountains,' the equatorial ocean had to be warmed by 

 the sun. We shall have more to say upon this question 

 afterwards. 



