502 
MR. HENNESSY’S researches IN TERRESTRIAL PHYSICS. 
the process of its solidification. It is now proposed to commence the investigation 
of these geological consequences. 
Before proceeding to the purely mathematical portions of this investigation, it 
seems necessary that some preliminary remarks should be made on the nature of the 
solidification of the globe. It seems the more necessary that these remarks should 
be now given, as they will not probably be found to agree entirely with those which 
have been made on the same subject by an eminent geologist and geometer*. It 
is, however, satisfactory to reflect that even if my views respecting the solidification 
of the earth should be more correct than those of Mr. Hopkins, the real value of that 
gentleman’s researches will still remain unaltered. 
Although until now no allusion has been made to the probable cause of the pri- 
mitive fluidity of the earth, it becomes necessary in order to proceed with the geolo- 
gical portion of these investigations that this cause should be assigned. Intense 
heat is that which is generally supposed to be the cause, and which the advocates of 
the earth’s central heat seem to support by numerous facts. The solidification of this 
heated mass of fluid is so connected with its refrigeration, that some remarks on the 
latter subject must accompany or precede any investigations about the former. 
If the whole earth from the action of a high temperature were reduced to that 
state of fluidity which forms the groundwork of the hypothesis upon which the theory 
of its figure is founded, it appears probable that the fluid mass would be extremely 
heterogeneous chemically, as well as mechanically. New chemical combinations 
would be formed, of whose physical properties it would be difficult to form an accu- 
rate idea. After the most energetic combining tendencies of the different substances 
composing the fluid Avould have been satisfied, the mass may be supposed to have 
arrived at a state of comparative chemical stability. Such properties of the different 
compounds as density and compressibility, would then exert a direct influence upon 
the nature of their arrangement around the centre of gravity of the spheroid. Every 
portion of the fluid, denser than the stratum, in which from any cause it may happen 
to be, would sink until it would meet a stratum of equal density. The light portions 
of the fluid which may happen to be in heavier strata than themselves, would on the 
contrary ascend until equilibrium would be obtained. The fluid mass would thus 
arrive at length at such a state, that it would consist of a series of spheroidal strata, 
each of uniform density throughout its own mass, and having that density expressible 
as a function of its axes. 
At some time after the arrival of the fluid at this state, and perhaps before it, por- 
tions of its heat would radiate in space. The exterior portions of the fluid would cool 
first, until they would acquire, according to the particular circumstances which may 
influence their cooling, certain densities. If the effect of refrigeraiion be in general 
an increase in density of the matter cooled, then the cooled portions of the fluid will 
sink. The higher temperature of the matter yet unexposed to cooling influences, 
* Hopkins, Philosophical Transactions, 1839, 
