ag, Scie etal a nn Renee ee 
etre 
composing the Interior of the Barth. ; 463 
Geology, Pfaff’s Grundriss der Geologie, the author gives a 
brief account of the bearing of astronomical and mathematical 
investigations on the internal structure of the earth; and he 
very justly says that the results of observation compel us to 
regard the earth as for the ‘most part fluid, in order to bring 
these results into harmony with calculation. Professor Pfaff 
attributes this conclusion to Hopkins, whereas it is precisely 
that which I had long since enunciated, and is entirely opposed 
to the views of Mr. Hopkins. More recently Sir William 
Thomson and Mr. Darwin have investigated the tidal action of 
an internal fluid nucleus upon its containing solid shell. They 
have both supposed the liquid to be totally incompressible, and 
the containing vessel to be elastic and therefore compressible. 
They have thus given the liquid a property which no liquid in 
existence possesses, and the solid a property which solids pos- 
sess in a much less degree than liquids. Their hypothesis is 
thus totally inadmissible as a part of the problem of inquiry 
into the earth’s structure. I at once admit that a thin elastic 
spheroidal envelope filled with incompressible liquid and sub- 
jected to the attraction of exterior bodies would present period- 
ical deformations, owing to tidal action far surpassing the tides 
of the ocean. But I do not admit that such impossible sub- 
Pressible than its solid envelope. A highly ne pop lors 
a 
ferent from what is performed in the less-compressible water of 
the ocean. Observation has fully verified this result. : 
3. It is admitted that the earth’s density increases from its 
Surface toward its center. If its interior is oceupied by a 
compressible fluid, the law of density of this fluid would result 
rom the compression of its own strata; just as the law of den- 
sity of the atmosphere is produced by the pressure of the upper 
atmospheric layers upon those below. But instead of suppo- 
Sing the interior of the earth to be filled by a fluid thus con- 
