268 The Evolution of the Solar System. May, 
is a marked distinction between the state of condensation of 
the solid and gaseous surfaces. As globes increase in gravi- 
tative vigour this distinction decreases. It is much less 
declared in the earth than in the moon. In Jupiter, or in 
the Sun, it may be so reduced that no real distinction con- 
tinues to exist. The atmosphere of the sun may be, or may 
become, so dense through gravity and pressure, and through 
chemical integration, that in this orb the three states of 
matter — the solid, the liquid, and the gas — may eventually 
shade into each other with no marked line of demarcation. 
If, again, the earth cannot absorb its atmosphere, and 
remain denuded of an atmospheric covering, neither is it 
probable that it can dispose finally of its liquid covering. 
For the absorption of the water surrounding the earth must 
aCt to decrease the density of the atmosphere, by depriving 
it of its aqueous vapour. In such a case the tendency of 
the remaining atmosphere to greater condensation might 
bring the possible hydrogen which exists in contiguity with 
oxygen above their combining level to a lower level, and 
produce a new production of atmospheric water vapour. It 
is certainly conceivable that any loss of water at the surface 
might be thus compensated, and even that such a production 
of water vapour may occasionally occur now ; balanced, 
perhaps, by a reverse aCtion, as now hydrogen descends 
below the limiting level, now water vapour ascends 
above it. 
In faCt, the process of formation of the solid surface of 
the earth may have been through successive stages of deve- 
lopment similar to that above described. As density increased 
the atmosphere partly became liquefied. Further condensa- 
tion solidified this liquid, and a new liquid replaced it. The 
solids became more and more complex and dense, while 
successively new liquids appeared. Finally only the most 
volatile elements remained in the atmosphere, and these, in 
their turn, partly condensed into the liquid called water. 
This is also, by the slow process of refrigeration, approaching 
its solidifying point, and would long since have passed it 
but for the external heating influence of the sun. This 
liquid is also being slowly exhausted through absorption 
into the solid surface ; but as it is composed of two of the 
lightest elements, which are likely long to continue abundant 
in a gaseous state, all such loss by absorption will probably 
be replaced by new production. We have water on the sur- 
face, water vapour in the atmosphere extending to a certain 
height, and beyond that height free hydrogen. Thus hydro- 
gen as well as oxygen may extend through all levels, but 
