22 'Tin American Geologist. July, 18W 
melting, it will usually increase the amount of heat .in the 
compressed body. 
The crust of the earth possesses the properties of an arch, 
and. as it is composed of oxidized materials, it possesses a 
lower coefficient of contraction than does the metallic interi- 
or. The contraction of the interior would, therefore, be greater 
than for the crust, for equal decrements of temperature; and 
instead of there being much pressure on the metallic interior, 
the probabilities are there is none, resulting from the weight 
of the crust. 
It is the object of this article to show that, proceeding from 
the nebular hypothesis, the temperature of the interior can- 
not be as much as 3,000° F. at any point, except perhaps, but 
not necessarily, localities in the crust, whence proceed the 
fused materials ejected by volcanoes. 
The nebular hypothesis of the earth's origin is so generall} 7 
accepted, and appears to be so firmly based upon observations 
of celestial phenomena, that we should always consider it in 
our speculations as to the histoiy and present condition of 
the earth's interior. 
When the earth was in its nebulous condition, the temper- 
ature, though high, must have been nearly uniform throughout 
the nehulous mass. Matter in the gaseous form so readily 
diffuses, as shown in the present composition of the earth's 
atmosphere, moving most rapidly from hot to colder points, 
that it seems, even in so large a volume of gaseous matter as 
that of the earth in its nebulous condition, the temperature 
must have been kept nearly uniform, down to the time when 
it was condensed to the liquid state. At what temperature 
liquefaction began is a matter for speculation which I have 
not considered. It seems evident however that the first mol- 
ten mass was mainly composed of the heavier metallic ele- 
ments, while the lighter gaseous, alkali, and alkaline earth 
elements, still remained in their gaseous condition, uneom- 
bined with each other. The lamented Sterry Hunt, in an ad- 
dress before the Royal Institution, in 1807, generalized as 
follows: "The breaking up of compounds, or dissociation of 
elements by intense heat is a principle of universal applica- 
tion, so that we may suppose that all the elements which 
make up the sun. or our planet, would when so intensely 
