CHAPTER II 



THE DEPTH OF THE OCEAN 



Archdeacon J. H. Pratt, the mathema- 

 tician, in discussing the pendulum investi- 

 gations among the Himalaya mountains, 

 appears to have believed that the great 

 Pacific Ocean could only be explained on 

 the assumption of " some excess of matter 

 in the solid parts of the earth between the 

 Pacific Ocean and the earth's centre, which 

 retains the water in its place, otherwise 

 the ocean would flow away to other parts 

 of the earth." According to this view 

 the existence of the oceans in their present 

 positions is referred to an excess of density 

 in the sub-oceanic portions of the globe. 

 In one sense this is confirmed by recent 

 geodetic and gravity observations, but 

 in all probability the sub-oceanic heavi- 

 ness does not extend to depths greater than 

 thirty miles. The great centrosphere of the 

 earth is inferred to be more or less homo- 

 geneous in structure and composition, and 

 also as rigid as steel, whatever the nature 

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