advocated by Mr. Grove, not only accords equally well with all the 

 phenomena connected with light, but is also less gratuitous, and 

 altogether more reasonable than the " ether hypothesis," which 

 latter nevertheless is genei ally accepted. 



As condensation gradually went on, we should have an intensely 

 heated world in a molten condition, surrounded by a highly heated 

 atmosphere of vapours and gases, and assuming by its rotation a 

 spheroidal form, and whatever amount of mere theory may still be 

 attributed to the nebular hypothesis, there can be no doubt what- 

 ever about this next stage ; for astronomers, natural philosophers, 

 and geologists, are all agreed, that our globe was at one period in 

 as highly heated a condition, and as luminous, as the sun and stars 

 are still, and that its entire solid contents wei-e in a state of 

 complete liquidity. 



The law of chemical affinity teaches us that when elements are 

 indiscriminately mixed, combination always takes place in a regular 

 manner ; for instance, if such an acid as sulphuric be in the presence 

 of such bases as baryta, potassa, soda, and lime, it will combine 

 with them invariably iu the order I have given them. 



No doubt the intense temperature that existed at this time, a 

 temperature that greatly exceeds anything we can attain to in the 

 laboratory, so far modified the law of affinity, as to render it 

 impossible for chemists to prove by direct experiment what com- 

 pounds were first formed ; still it holds good sufficiently to enable 

 them to speak with considerable certainty. 



As I have said before, the mean specific gravity of the earth is 

 about 5 '4:, and the density of the solid exterior only 2 '75, con- 

 sequently, even after making all due allowance for the effect of 

 increased pressure, there must be a great accumulation of the 

 heavy metals, and their compounds, in the interior of the earth : 

 in other words, as might have been expected, at the time of the 

 earth's cooling, the newly formed compounds would obey the 

 laws of gravity, and range themselves in layers, according to 

 their respective densities : at the centre, we should expect to 

 find the heaviest metals, such as gold, mercuiy, lead and silver ; 

 in the higher zones such metallic oxides as lime, magnesia, 

 alumina, iron oxide and soda, and lastly, an external crust of silica 



