48 
REPORT—184/. 
would be composed oJ’ a solid shell, and a solid central nucleus, with matter 
in a state of fusion between them, the fluidity of which, however, would 
necessarily be less than that which miglit exist in the fused mass very near 
the centre in the case previously considered. 
“ With respect to the thickness of the shell which may bo consistent with 
the present appearances of the earth's surface, the same conclusion will hold 
as in the former case, i. e. it may be small compared with the earth's radius. 
What would be the radius of the solid nucleus at the instant of the first in' 
crustatiou of the surface, or that which would correspond to any assigned 
thickness of the exterior shell, it is quite impossible to determine from the 
want of all experimental evidence respecting the tendency of great pressure 
to promote solidification at very Iiigh temperatures, and our ignorance ot 
the temperature at which the supcrfeial incrustation of a large mass would 
begin, when exposed to the temperature of the planetary space, it is, tlieiv* 
fore, manifestly impossible to decide by any such reasoning as the abwe, 
whether the exterior shell and solid nucleus arc now united, or are separaud 
by matter still in a state of fusion*. 
“ Upon the whole, n-usoiiing such as the above can Icail us to nothing 
more definite than tho following conclusions respecting the actual state of 
the earth, assuming it to have once been in a statu of perfect fluidity. 
“(1.) It may consist of u solid fixterior shell utid an internal mass in a 
state of fusion, of which the fluidity is greatest at the centre. It is possible 
that the thickness of the shell may he small compared with its radius, and the 
fluidity at the centre may approximate to that which would admit of cooling 
by convection. 
*' may consist of an exterior shell, and a central solid nucleus, with 
matter m a state of fusion between them. Tlie thickness of the shell, as well 
as the radius of the solid nucleus, may possibly be small compared with the 
m lus o t le earth, flie fluidity of the intervening mass must iipccssariiy 
be considerably more imperfect than that which would iiust admit of cooling 
by circulation. 
?«*>’facc to the centre.” 
nressiirp in^n^* rca^ning I have assumed the possible influence of great 
Sositiie sohdiheation. Wcare unable however, 
ovule,.ce on the suhiect. and hence arises a great p..rt 
in exDer^H.nM?^ *" ^ 'f “•'f^ved at. I trust that tiiis great defect 
a beSfoTo. » ««hjcct whiel. has so immediate and importaot 
Tim *>« allowed to exUt. 
snhip^.» mJcJi 'vhicli 1 recollect as having .anv direct relation to the 
tion is notVrouSed^'^*^ 7 support the conclusion that solidifica* 
fon IS not promoted by pressure. I allude to the celebrated experiments of 
the earm'h^v?ng"commlm-c^S^ advocate the hypolhesis of the soli<li6cation oi 
case, it would pLevd to the *ur7ac.. 7meUw,lems that, in 
P- 428). It ia\u„ifo7 howe7rrro77ir„r^^^ '"V (Tb^oried. laCI»le-‘0 
rally correct, hut that the aolidificailon most that ihi» could not k luc- 
whole internal portion hiuJ become lolid -rl commence at the surface before die 
the object which M. Poisson Imd in view hm ‘f of hltlr consequence as respeew 
to geological speculation, because it sliows’tf.a, importance with refer^nw 
it must be now, or have been nt >>.,«» . i*’ tiic eiirth once to have been fluid, 
know, that this state of the ear hcncalii. It is imporiaut “> 
neccKsarily have pasted in the comae oriu^ -hi ''’T one throoirh which it must 
solidification.” ‘“® ®‘ whatever ini ' ‘ 
might he the process 
ofic 
