OUR MOLTEN GLOBE 43 



interior of the earth to be solid, or at least to have a crust 

 not much less than one thousand miles thick. This view 

 was supported by Sir William Thomson and other eminent 

 mathematicians, and so great was the faith of geologists in 

 these calculations that for nearly forty years the theory of 

 the earth's internal liquidity was almost wholly aban- 

 doned. But this argument has now been shown to be 

 erroneous by the more complete investigations of Pro- 

 fessor George Darwin, while Sir William Thomson (now 

 Lord Kelvin) has recently shown experimentally that a 

 rotating liquid spheroid behaves under stresses as if it 

 were a solid. Another difficulty arises from the phe- 

 nomena of the tides. It has been argued that, if the 

 interior of the earth is liquid tides will be formed in it 

 which will deform the crust itself, and thus, by lifting the 

 water up with the land, do away with any sensible tides 

 in the ocean. But Mr. Fisher has pointed out that this 

 conclusion rests on the assumption that the liquid interior, 

 if it exists, is not an expansible fluid ; and he shows that 

 if this assumption is incorrect it is quite possible that little 

 or no deformation would be caused in the crust by tides 

 produced in the liquid interior ; and he further maintains, 

 as we shall see presently, that all the evidence goes to 

 prove that it is expansible. Moreover, in a late paper, he 

 claims to have proved that even the deformation of the 

 crust itself would not obliterate the ocean tides, but would 

 diminish them only to the extent of about one-fifth.^ 



There remain the geological objections founded on the 

 behaviour of volcanoes, which is supposed to be incon- 

 sistent with a liquid interior as their effective cause. We 

 have, for instance, the phenomenon of a lofty volcano like 

 Etna pouring out lava from near its summit, while the 

 much lower volcanoes of Vesuvius and Stromboli show no 

 corresponding increase of activity ; and the still more 

 extraordinary case of Kilauea, on the lower slopes of Mauna 

 Loa, in the Sandwich Islands, at a height of about 3,800 

 feet, whose lake of perennial liquid lava suffers no altera- 

 tion of level or any increased activity when the parent 

 mountain is pouring forth lava from a height of 14,000 

 ^ Proceedings of the Cambridge Philosophical Society ^ 1892. 



