3i8 POPULAR LECTURES AND ADDRESSES. 



" believe that the height is only two-fifths of what 

 " it would be if, as has been universally assumed in 

 " tidal theories, the earth was perfectly rigid. It 

 " seems, therefore, nearly certain, with no other 

 " evidence than is afforded by the tides, that the 

 " tidal effective rigidity of the earth must be greater 

 " than that of glass." This is the result taking the 

 earth as a globe uniformly rigid throughout. That 

 a crust fifty or a hundred miles thick could possess 

 such preternatural rigidity, as to give to the mass, 

 part solid and part liquid, a rigidity, as a whole, 

 equal to that of glass or steel is incredible ; and we 

 arc forced to the conclusion that the earth is not a 

 mere thin shell filled with fluid, but is on the whole 

 or in great part solid. 



