THE STORY OF NINETEENTH-CENTURY SCIENCE 



rules to which they are subject, have remained invaria- 

 bly the same." 



But, on the other hand, Hutton and Playfair, and in 

 particular Ly ell, drew inferences from this principle 

 which the modern physicist can by no means admit. 

 To them it implied that the changes on the surface of 

 the earth have always been the same in degree as well 

 as in kind, and must so continue while present forces 

 hold their sway. In other words, they thought of the 

 world as a great perpetual-motion machine. But the 

 modern physicist, given truer mechanical insight by the 

 doctrines of the conservation and the dissipation of en- 

 ergy, will have none of that. Lord Kelvin, in particular, 

 has urged that in the periods of our earttrs infancy and 

 adolescence its developmental changes must have been, 

 like those of any other infant organism, vastly more 

 rapid and pronounced than those of a later day ; and 

 to every clear thinker this truth also must now seem 

 axiomatic. 



Whoever thinks of the earth as a cooling globe can 

 hardly doubt that its crust, when thinner, may have 

 heaved under strain of the moon's tidal pull whether 

 or not that body was nearer into great billows, daily 

 rising and falling, like waves of the present seas vastly 

 magnified. 



Under stress of that same lateral pressure from con- 

 traction which now produces the slow depression of the 

 Jersey coast, the slow rise of Sweden, the occasional 

 belching of an insignificant volcano, the jetting of a 

 geyser, or the trembling of an earthquake, once large 

 areas were rent in twain, and vast floods of lava flowed 

 over thousands of square miles of the earth's surface 

 perhaps at a single jet ; and, for aught we know to the 



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