THE INTERIOR OF THE EARTH 



THE radius of the earth is about 3950 miles long. 

 Of this enormous thickness a few yards are 

 sufficient for us to live and die in, and we have 

 never penetrated deeper than a mile and a 

 quarter. What is there lower down? Are we 

 resting on a solid block or floating on a raft? 

 It is hardly credible that, after so many centuries 

 of civilisation, we should have progressed so 

 little on this point, that we should know so much 

 about far-off worlds and so little about the 

 interior of our own. But if the earth begins to 

 tremble, or if volcanoes arise, our thoughts turn 

 to the disquieting mystery of the depths and to 

 cosmogonic hypotheses. 



We still retain the conception of Descartes 

 and of Newton which Laplace perpetuated in 

 an admirable synthesis. For us the earth is a 

 fragment of the original solar nebula condensed 

 into a liquid sphere, which, while cooling gradu- 

 ally, has covered itself with a solid crust. But on 

 what experimental basis does this belief rest? 



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