1883.] The Variability of Protoplasm. 931 
free energy is necessary, whether it be derived from a sun or 
from local sources of heat outflow. 
It is, therefore, among the possibilities of chemical action that 
spheres whose temperature is much higher or much lower than 
that of the earth may be abodes of life. In an early period of 
the earth’s history, when the elements which are now solid 
oxides were liquids or gases, some of them may have played the 
part which carbon now plays, and unstable molecules may have 
been produced resembling those of organic life. Perhaps some 
of the complex mineral constituents of the earth’s surface are 
results of such an incipient organic evolution, as the mineral 
substances known as fossils are results of a more advanced evo- 
ution. 
This idea leads us to a conception of a long series of efforts 
towards the evolution of organic life, as the earth gradually 
cooled, and one after another of its atmospheric constituents be- 
came reduced to solidity. Every such substance may, under the 
influence of heat emissions, have been aggregated with others 
into unstable compounds, which is the essential principle of or- 
ganic development. The degree of chemical complexity and 
instability which could be thus produced would depend largely 
on the rate of rapidity of cooling. The advantage which carbon 
has had arises from its coming into play after the cooling of the 
earth had virtually ceased. Hence its period of activity has been 
much longer than that of the elements which may have preceded 
it in this organic process, and the results are immensely superior. 
But if our argument is of any value we seem to perceive tentative 
efforts towards organic evolution during the whole period of cool- 
ing of the earth’s surface, while success in this direction was at- 
tained only after a stable condition of surface temperature was 
reached. In other spheres a long continued stability of tempera- 
ture may have been reached under other chemical relations, and 
living beings composed of other constituents than those of earthly 
Organisms have appeared. 
