; 
1884.] On the Evidence that the Earth's Interior is Solid. © 681 
lends no support to the view of terrestrial consolidation at the 
center first, by continual subsidence of such crusts, as imagined 
by Poisson, nor to the notion as to the nature of volcanic action 
which Sir W. Thomson has based on that assumption. * * * 
We * * * may be permitted to conclude that rocks consist- 
ing of acid silicates contract still less than those of basic silicates» 
and that a terrestrial crust of the former is still more capable of 
floating upon the same in fusion beneath.”! However much Mr. 
Mallet’s views may agree with those of the present writer, it is 
but just to point to the fact that the slags experimented upon 
differ essentially from basaltic rocks, and it is not permissible to 
assume that one certainly gives the law for the other, however 
probable it may be that they act alike under similar conditions. 
This also applies in less degree to Mallet’s comparison between 
plate glass and the rhyolites. 
urther studies were made, in 1874, by Mr. Mallet on the 
alleged expansion of various substances on solidification. His 
experiment of filling a conical wrought iron vessel with molten 
iron seemed to show that liquid iron when heated far above its 
‘Melting point has a specific gravity of 6.65, while the same iron 
in the cold state is 7.17. Mallet claims, therefore, that cold cast- 
iron is always heavier than molten iron. It is to be observed that 
no comparison was made between iron near the melting point 
and the same when just above that point. : 
He further tried some experiments regarding the flotation of 
solid iron upon molten iron, which must be regarded as conclu- 
“We upon that point. In all cases the iron either did not sink, or 
if when first immersed it sank, it afterwards rose again. Mallet 
“ys: “ A piece of cold cast-iron which floats on liquid iron of 
its own quality, if forcibly thrust to the bottom and rapidly and 
at once released, rises again rapidly to the surface with all the 
“pearance of a buoyant body, which it certainly cannot be.” 
same experiments made with lead showed that it always 
sank when immersed in the molten lead. In this case when flat 
Pleces were Carefully laid upon the fluid lead they floated until 
S equilibrium was disturbed, so that the fluid could wet the 
“a Surfaces when they sank. This flotation of the lead seems 
to be a case of the same kind as the flotation of a needle upon 
Water, Mr. Mallet endeavored to explain the phenomena in the 
ie + 
Philos, Trans., 1872, pp. 147-227. 
