t within certain limits, which
must widen as our knowledge of the facts of their substance and surface
becomes greater, what have been and what are the developments of
Vulcanicity which have taken place or are occurring in or upon them.
Looking to our own satellite, we see for the first time a sufficient
physical cause for the enormous display of volcanic energy there which
the telescope divulges to us; one which is not to be explained alone by
the commonly made statement of the small density of the moon, but by
the fact that as the rate of her cooling from a given temperature, as
compared with that of our earth (apart from questions of the chemical
nature of the two bodies, or of their specific heats, etc.), has been
inversely as their respective masses, and directly as their surfaces, so
has the rate of cooling of the moon been vastly greater than that of the
earth, and the energy due to contraction by cooling more intense and
rapidly developed in our satellite than upon our globe.

We have thus traced, in meagre and broken outline only--because space
admitted no more--the progress of Science to its existing state as
respects Vulcanicity, in its two branches of Vulcanology and of
Seismology, and pointed out their more intimate relations and points of
connection, and been at length able to refer them, on the sure basis of
physical laws, to one common cause, and that one derived from no
hypothesis, but simply from the postulate of our world as a terr-aqueous
globe cooling in space.

What I have here advanced with reference to volcanic energy, which
appertains to my own researches, I do not conceal from myself, nor from
the reader, has yet to await the reception generally and the award of
the true men of science of the world.

That, like every new line of thought which has attempted or succeeded in
supplanting the old, it will meet with opposition, I make no doubt.

My belief, however, is that in the end it will be found to have added a
fragment to the edifice of true knowledge.

The interpretation which I have given of the nature and origin of
volcanic activity points at once to the function in the Cosmos which it
is its destiny to fulfil. It is the instrument provided for the purpose
of continually preserving the earth's solid shell in a state to follow
down after the descending nucleus. It does this by an apparatus or play
of mechanism whereby the material of the solid shell, locally or along
certain lines, is no