400 Tnnisactions. — Geoloc/y. 



and wbicli revolved round its centre of gravity during the process of conden- 

 sation. That, from time to time, extensive rings of this nebulous matter 

 were left by the central condensing mass at points in the cu-cumference 

 where the centrifugal and gravitating forces became exactly balanced, and 

 that these rings, still circulating round the central nucleus, broke up into 

 masses which became endued with a motion of rotation and assumed a 

 spheroidal form. These masses, acting in tlie same manner as the parent 

 mass, and abandoning similar rings of outlying matter, led to the formation 

 of the satellites of the various principal planets. During this process of con- 

 densation, which, of course, took place in obedience to the all-pervading law 

 of gravitation, the motion of the condensing particles of which each planet 

 was composed, was converted into heat, and that to such a degree as would 

 result in the fusion of the whole into one mass. Meyer, indeed, remarks, in 

 a paper on Celestial Dtjnaiincs (as quoted by Nasmyth and Carpenter in 

 their great work on the m.oon), that " the Newtonian theory of gravitation, 

 whilst it enables us to determine, from its present form, the earth's state of 

 aggregation in ages past, at the same time points out to us a source of heat 

 powerful enough to produce such a state of aggregation, — powerful enough 

 to melt worlds; it teaches us to consider the molten state of a planet as the 

 result of the mechanical union of cosmical masses, and to derive the 

 radiation of the sun and the heat in the bowels of the earth from a common 

 origin." 



Sir Charles Lyell, hov>'"ever, though he did not dispute the opinions 

 of Laplace and others as to the effect of the condensation of cosmical 

 matter, appeared unwilling to admit the continued existence of internal 

 heat to the extent contended for by leading physicists, and inclined 

 rather to the opinion advanced by Poisson, "that in coohng by radiation to 

 the medium AAliich surrounded the earth, the parts which were first solidi- 

 fied sunk, and that by a double descending and ascending current the great 

 inequality was lessened, which would have taken place in a solid body 

 cooling from the surface." I am here quoting directly from Poisson, and 

 not from Sir Charles' work, as I wish to show how completely at variance 

 . Poisson's opinions are with the laws which govern heated matter passing 

 into the solid condition. Nasmyth and Carpenter point out, with special 

 reference to the opinions of Poisson and of those who held similar views, 

 " that fusible substances are (with a few exceptions) specifically heavier 

 whilst in their molten condition than in the solidified state, or, in other 

 words, that molten matter occupies less space, weight for weight, than the 

 same matter after it has passed from the melted to the solid condition," 

 and they point to the remarkable facts, amongst others, that cold iron floats 

 upon molten iron, cold silver upon molten silver, cold slag upon molten 



