changes would take place in each of its component substances, and how
much the whole would shrink in bulk.

The earth and all its various substances have at present a certain
volume in consequence of the temperature which actually exists.
When, then, we find that its matter and that of the associate planets
was at one time diffused throughout the whole space, now
circumscribed by the orbit of Uranus, we cannot doubt, after what we
know of the power of heat, that the nebulous form of matter was
attended by the condition of a very high temperature. The nebulous
matter of space, previously to the formation of stellar and planetary
bodies, must have been a universal Fire Mist, an idea which we can
scarcely comprehend, though the reasons for arriving at it seem
irresistible. The formation of systems out of this matter implies a
change of some kind with regard to the condition of the heat. Had
this power continued to act with its full original repulsive energy,
the process of agglomeration by attraction could not have gone on.
We do not know enough of the laws of heat to enable us to surmise how
the necessary change in this respect was brought about, but we can
trace some of the steps and consequences of the process. Uranus
would be formed at the time when the heat of our system's matter was
at the greatest, Saturn at the next, and so on. Now this tallies
perfectly with the exceeding diffuseness of the matter of those elder
planets, Saturn being not more dense or heavy than the substance
cork. It may be that a sufficiency of heat still remains in those
planets to make up for their distance from the sun, and the
consequent smallness of the heat which they derive from his rays.
And it may equally be, since Mercury is twice the density of the
earth, that its matter exists under a degree of cold for which that
planet's large enjoyment of the sun's rays is no more than a