THE TIDES 321 



dimensions; and perhaps greater than that of a globe of 

 steel of the same dimensions. But that it cannot be less 

 rigid than a globe of glass, we are assured. It is not to be 

 denied that there may be a very large space occupied by 

 liquid. We know there are large spaces occupied by lava ; but 

 we do not know how large they may be, although we can cer- 

 tainly say that there are no such spaces, as can in volume be 

 compared with the supposed hollow shell, occupied by liquid 

 constituting the interior of the earth. The earth as a whole 

 must be rigid, and perhaps exceedingly rigid, probably ren- 

 dered more rigid than it is at the surface strata by the 

 greater pressure in the greater depths. 



The phenomena of underground temperature, which led 

 geologists to that supposition, are explained otherwise than 

 by their assumption of a thin shell full of liquid; and 

 further, every view we can take of underground temperature, 

 in the past history of the earth, confirms the statement that 

 we have no right to assume interior fluidity. 



HC VOL. xxx K 



