i88i.i 
Some Results of Gravitation. 
703 
pressure on the interior gas would be reduced, and might, in 
time, come to just equal the resistance of this condensed 
gas. That point once reached, compression by weight of 
the solid surface would not continue. The gaseous interior 
might yet contain considerable volumes of sensible heat, the 
result of previous compression. If this existed in regions 
intermediate between surface and centre it must move in 
both directions. It would be conducted upwards, and escape 
by radiation into space. It would be convected downward, 
and tend to increase the rarity of the central gas. There 
must, in fact, be a constant effort to produce uniformity of 
interior temperature. 
The gradual loss of heat by the layer of gas in contact 
with the interior solid surface might act to produce lique- 
faction or solidification of this layer, and the thickness of the 
crust be thus increased. But such a process could be but 
temporary, since it would tend to rarify the remaining 
gaseous contents of the earth’s interior. Such a rarefaction 
would act to convert sensible into latent heat. Hence the 
solidification of a portion of the gas would necessarily reduce 
the temperature of the remainder, and this might continue 
until the general temperature of the interior gas and the 
solid shell became uniform. This condition attained, there 
could be no further solidification of the gas, except as a result 
of a gradual cooling of the whole system. The refrigeration 
of the gas produced by this loss of sensible heat would not 
affeCt its physical condition, since its absolute heat contents 
would remain the same as before. 
Yet the faCt that a rigid solid shell was formed would not 
necessarily hinder a continuance of processes in the interior 
similar to those already considered. The globe of interior 
gas would in some respeCts resemble the original globe of 
nebulous matter, and gravitative compression might go on 
in it independently of the facft that it is surrounded by a 
solid globular shell. But the special conditions surrounding 
this gaseous globe would be markedly different from those 
surrounding the original nebula. The free radiation from 
the surface of the latter would be here checked, and 
reduced to a slow conduction through the solid shell. 
Thus the heat product of compression could be but slowly 
disposed of, and condensation could proceed only very 
slowly. It may be supposed, however, that it would con- 
tinue until gravity had produced its full effecft, and the 
gas had become regularly denser downward to the centre. 
But it must be borne in mind that the aCtion of gravity here 
would also be greatly modified. 
