Year: 1872

There are few subjects less satisfactorily


treated in scientific treatises than tha


which Humboldt calls the Reaction of the


Elrth's Interior We find not merely il
the cont guration of the Elrth's crust, bu
in actual and very remarkable phenomena,
evidence of subterranean forces of great
activity, and the problems suggested seem
in no sense impracticabIe, yet no theory
of the earlh's volcanic energy has yet
gained general acceptance. While the
astronomer tells Us Of the constitution OF
orbs millions Of times farther away than
our own sun, the geoIogist has hitherto
+ been unable to give an account of the
! forces which agitate the crust of the orb
/ on which we live.


\ theory has just been put forward
respecting volcanic energy, however, by
the eminent seismologist Mallet, which
promises not merely to take the place of
all others but to gain degree of accept
/ auce which has not been accorded to any
theory previously enuncated. 1t is, in
principle, exceedingly simple, though many
Of the details onto which we do not pro-
pose to en3er) involve questions of con-
siderable difficulty.


Let Us, in the first place, consider briefly
the various explanations which had been
already advanced There was first the
chemical theory of volcanic energy, the
fayorite theory of Sir Humphrey Davy.
1t is possible to produce on small scale
nearly all the phenomena due to subterra
mean activity, by simply bringing together
certain substances, and leaving them TO
undergo the chemical changes due to their
association. As a familiar instance Of ex-
plosiye action thus occasioned, we need
only mention the results experienced when
any one, unfamiliar with the methods Of
treating lime, endeavors over hastily to
''sake' or ''slack" it with water Indeed,
one Of the strong points 'of the chemical
theory consisted in the circumstance that
volcanoes only occur where water can
reach the subterranean regions-or as
Mallet expresses it, that without water
there is no volcano" But the theory is
disposed of by the fact, now generally ad
mitted, that the chemical energies of our
earth's materials were almost wholly ex-
hausted before the surface was consolida-
ted


Another inviting theory IS that accord





mere shell OF solid matter surrounding a
molten nucleus. There is every reason to
believe that the whole interior Of the earth
is in a state Of intense heat; and if the in
crease of heat with depth (as shown in
our mines) is supposed to continue uniform
ly, we find that at very moderate depths
a degree OF heat must prevail sufficient to
liquety any known solids under ordinary
conditions. But the conditions under
which matter exists a few miles only below
the surface of the earth are not ordinary
the pressure enormously exceeds any which |
our physicists can obtain experimentally. |
The ordinary distinction between solids |
and liquids cannot exist at that enormous
pressure; mass of cold steel could be as
plastic as any of the glutinous liquids,
while the structural change which solid
undergoes in the process of liquefying |
could not take place under such pressure
even at an enormously high temperature.
1t is now generally admitted that, if the
earth really has molten nucleus, the solid
crust must, nevertheless, be far too thick
to be in any way disturbed By changes
affecting the liquid matter beneath.


Yet another theory has found advocates.
The mathematician Hopkins, whose ana
lysis of the molten-nucleus theory was
mainly effective in rendering that theory
suggested that there may be
isolated subterranean lakes of fiery matter,
and that these may be the true seat of /
energy. But such lakes could .
not maintain their heat for ages, if sur /
rounded (as the theory requires) By cooler
solid matter, especially as the theory also
requires that water should have access to