360 Dr. T. Sterry Hunt's Lecture - 



at one time have been a gaseous mass ; it must at one time have 

 been a mass so intensely heated, that this process of consolidation 

 was only going on at the surface. It was once a self-luminous body, 

 such as the sun is at the present day, but being very much smaller, 

 the process of cooling has gone on with a very much greater rapidity. 

 Now there comes up another question, — whether, in this process 

 of concretion, or agglomeration, or separation, which has gone on n 

 this nebulous mass, all the masses — all the subordinate masses — 

 have the same composition, — whether this great mass of vapor was 

 homogeneous or not. That we cannot certainly decide, but from our 

 present knowledge it would seem extremely probable that it was so. 

 But let us consider this cooling to go on, and, as in the case of the 

 sun, a condensation taking place at the surface. This mist-like 

 matter, as it became solid or liquid, having a certain weight, would 

 fall down toward the centre of the sun, or of the planet which 

 was then like the sun, and undergo the process of heating again, 

 From the constant contraction going on in this mass, the process of 

 losing heat, and of gradual condensation, would be going on until 

 you arrived at the point of liquefaction, that is to say, at the point 

 where there were certain compounds which could exist without 

 decomposition even at the centre, in other words, until you had 

 cooled it below the decomposing, the dissociating point of certain 

 compounds. Let us suppose that certain of the metals are capable 

 of combining with oxygen and forming compounds so condensed and 

 so fixed that they resist the decomposing action ; then, and then 

 only, would commence the formation of a liquid nucleus. That 

 once begun, a process of condensation would go on until in each one 

 of these planets — in our earth for example — you would have even- 

 tually a great liquid globe, an igneous fluid mass, surrounded by 

 intensely heated vapours. 



Now as to the composition of this mass. Whether it would be 

 homogeneous or not becomes a question. I think it extremely 

 probable that in such a mixture as this yoti would have toward 

 the centre a progressive condensation and accumulation of matters 

 denser than at the surface. This idea has been a favourite one with 

 many who have speculated upon the density of the earth, for you 

 are well aware that the earth, weighed as a whole, has a specific 

 gravity of something over five, — five three-tenths, as was determined 

 by Maskelyne, — that being, in fact, about twice the density of the 

 superficial parts. Hence, I think it extremely probable that we 

 have at the centre metallic or metalloid masses of elements, grouped 

 in different proportions from any that we have at the surface, and in 

 that way we have explained the great density of the earth con- 

 sidered as a whole. 



But next with regard to this central mass. Would it remain 

 fluid, or would it become solidified ? And here I am aware of a 

 notion very widely entertained and very generally taught in our 

 text-books on geology, that the earth's centre is a liquid mass, and 

 has only a crust of from fifteen to twenty or twenty-five miles in 

 thickness, a crystalline solid rock which beai's us upon its surface. 



