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and measure, so we ought to be able to measure the amount 
of heat produced by the contracting of the earth’s crust, al- 
though we cannot measure that contraction with a plummet. 
As we go down through the crust we ought to meet with 
evidence that the pressure of the strata has increased the 
temperature, and this we in fact do. In going down towards 
the centre of the earth we find an increase of temperature 
so wonderfully constant in all latitudes that we are con- 
strained, if we accept the nebular hypothesis, to argue that 
this results, as it ought theoretically to result, from the 
pressure of tlie strata, i. e., from the force of gravity. In 
some letters that I have recently written to “Nature,” I have 
tried to show how the areas of upheaval and subsidence on 
the earth are distributed, my conclusion being that the areas 
of depression are distributed about the Equator, while the 
areas of upheaval have their foci at the Poles, that the earth 
is being strictured about the Equator, and thrust out in the 
direction of its shortest axis ; in other words, is shrinking 
in the region where the temperature is the highest, the 
tropics, and is stretching out in the regions of cold, or the 
Polar regions. 
Now let us see how far we have travelled. We have 
postulated that all shrinking matter is giving out heat. We 
have shown that the a iwiori evidence is conclusive that 
the earth is a shrinking mass. We have also adduced evi- 
dence which shows that the earth is in fact hot where it 
should be hot, and cold where it should be cold, in accord- 
ance with the law of contraction ; and it seems to me to 
follow necessarily that the earth is giving out heat, — is in 
fact a furnace, a heat producing substance. This seems 
to be inevitable. 
I need not stay to argue that both popularly and also 
among scientific men it is held as a cardinal doctrine that 
O 
the earth receives a large quantity of its heat directly from 
the sun, and elaborate calculations have been made to show 
