240 The American Geologist. April, 1892 
to the heat lost to produce 550 feet linear radial contraction in 
a cooling globe. 
Let us now examine the potency of the opposite principle of 
expansion which lies at the foundation of my theory. I have 
shown that if 10 miles of sediment were laid down on the crust 
of the earth, the underlying strata would be raised 1000° Fahy, 
in temperature by the rising of the isogeotherms, and the bottom 
layers of sediment to the same temperature gradually shading off 
to the normal at the surface. I have taken 20 miles in thickness 
of the under crust and overlying sediment combined raised 1000° 
Fahr. as representing my conception of the heating that would 
take place under the assumed conditions. 
I must also ask my readers, to assume that instead of the heat 
being lost, equal to the production of such a contraction of the 
earth it is, by some non-conducting covering over the whole earth 
prevented from escaping into space. Under these conditions the 
heat from the nucleus would flow into the assumed shell 20 miles 
thick, until the temperature of the shell and the nucleus became 
equalized. Let us now consider what would be the effect on this 
shell when it was raised 1000° Fahr. in temperature, intercepting 
the precise amount of heat lost into space in the previous example. 
It is evident, firstly, that if the co-efficient of expansion were 
the same at all temperatures in the shell as in the cooling mass it 
envelopes, the radius of the globe would remain the same, if we 
consider the radius as measured to the mean of the irregularities 
of the surface which would certainly come into being. 
Secondly, though the cubic contents of the globe would remain 
precisely the same, the redistribution of heat within the mass would 
produce certain stresses and strains which we may easily picture 
to ourselves. The shell 20 miles thick, if it were possible for it 
to receive this accession of heat and sustain itself as a spheroidal 
shell, would increase in diameter. Taking the mean diameter of 
the earth, considered as a sphere at 7912.41 miles,* and the ex- 
pansion 2.75 feet per mile per 100° Fahr., the mean diameter of 
the spherical shell would be increased 7912.41 x 27.5=217,591 
feet=41.2 miles. But it is evident that this could not happen, 
but that the shell must adapt itself to the nucleus, so leaving out 
of account for the present the contraction of the nucleus, which 
would be the same as in the first example, there will be a surplus. 
*Herschel. Outlinesof Astronomy. 
