154 PLEASANT WA YS IN SCIENCE. 



volcanic heat The modern theory of heat as a form of 

 motion here comes into play. As the solid crust closes in 

 upon the shrinking nucleus, the work expended in crushing 

 down and dislocating the parts of the crust is transformed 

 into heat, by which, at the places where the process goes 

 on with greatest energy, " the materials of the rock so 

 crushed and of that adjacent to it are heated even to fusion. 

 The access of water to such points determines volcanic 

 eruption." 



Now all this is not mere theorising. Mr. Mallet does 

 not come before the scientific world with an ingenious 

 speculation, which may or may not be confirmed by obser- 

 vation and experiment He has measured and weighed 

 the forces of which he speaks. He is able to tell precisely 

 what proportion of the actual energy which must be de- 

 veloped as the earth contracts is necessary for the pro- 

 duction of observed volcanic phenomena. It is probable 

 that nine-tenths of those who have read these lines would 

 be disposed to think that the contraction of the earth must 

 be far too slow to produce effects so stupendous as those 

 which we recognize in the volcano and the earthquake. 

 But Mr. Mallet is able to show, by calculations which can- 

 not be disputed, that less than one-fourth of the heat at 

 present annually lost by the earth is sufficient to account for 

 the total annual volcanic action, according to the best data 

 at present in our possession. 



As I have said, I do not propose to follow out Mr. 

 Mallet's admirable theory into all its details. I content 

 myself with pointing out how excellently it accounts for 

 certain peculiarities of the earth's surface configuration. 

 Few that have studied carefully drawn charts of the chief 

 mountain-ranges can have failed to notice that the arrange- 

 ment of these ranges does not accord w4th the idea of 

 upheaval through the action of internal forces. But it 

 will be at once recognized that the aspect of the moun- 

 tain-ranges accords exactly with what would be expected 

 to result from such a process of contraction as Mr. Mallet 



