[54 THE FOKMS OF WATER IN 



not only be white hot, but would be passing into the 

 molten condition. 



387. Consider the conclusions at which, we have now 

 arrived. For every pound of tropical vapour, or for 

 every pound of Alpine ice produced by the congelation 

 of that vapour, an amount of heat has been expended 

 by the sun sufficient to raise 5 lbs. of cast iron to its 

 melting-point. 



388. It would not be difficult to calculate approxi- 

 mately the weight of the Mer de Glace and its tribu- 

 taries — to say, for example, that they contained so many 

 millions of millions of tons of ice and snow. Let the 

 place of the ice be taken by a mass of white-hot iron of 

 quintuple the weight ; with such a picture before your 

 mind you get some notion of the enormous amount of 

 heat paid out by the sun to produce the present glacier. 



389. You must think over this, until it is as clear as 

 sunshine. For you must never henceforth fall into the 

 error already referred to, and which has entangled so 

 many. So natural was the association of ice and cold, 

 that even celebrated men assumed that all that is needed 

 to produce a great extension of our gla,ciers is a dimi- 

 nution of the sun's temperature. Had they gone 

 through the foregoing reflections and calculations, they 

 would probably have demanded more heat instead of less 

 for the production of a ' glacial epoch.' What they 

 really needed were condensers sufficiently powerful to 

 congeal the vapour generated by the heat of the sun. 



