Year: 1873

| There are few subjects less Satlsfac-


torily treated in scientific treatises than


that which Humboldt calls the Reac-


tion of the Earth's Interior. We find,


not merely in the confguration of the


earth's crust, but in actual and very


remarkable phenomena, evidence Of


subterranean forces of great activity,


and the problems suggested seem in no


sense impracticable, yet no theory of


the earth'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 geologist has
hitherto been unable to give an &C
count of the forces which agftare the
crust of the orb on which we live.


A theory has just been put forward
respecting volcanic energy, however,


by the eminent seismologist Nallet,
which promises not merely to take the
place Of all others, but to gain de-
gree of acceptance which has not been
accorded to any theory previously enun-
ciated. 1t is, in principle, exceeding
ly simple, though many of the details
Onto which we do not propose to enter)
involve questions of considerable diff
Guilty.


Let us, in the first place, consider
briefly the various explanations which
had been already advanced. There
was first the chemical theory of vol
canic energy, the favorite theory of
Sir Humphrey Davy. 1t is possible to
produce on a small scale nearly all the
phenomena due to subterranean activ-
ity, by simply bringing together GER
tain substances, and leaving them to
undergo the chemical changes due to
their association. AS familiar in
stance of explosive action thus occa-
stoned, we need only mention the re-
suits experienced when any one, unfa-
miliar with the methods of treating
lime, endeavors over-hastily to s'slake"
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 admitted, that the chemical
energies of our earth's materials were
almost wholly exhausted before the
surface was consolidated.


Another inviting theory is that ac-
cording to which the earth is regarded
DIS mere shell of solid matter sur
rounding molten nucleus. There is
every reason to believe that the whole
interior of the earth is in a state of in
tense heat; and if the increase of heat
with depth Gas shown in our mines) is
supposed to continue uniformly, we
find that at very moderate depths de-
gree Of heat must prevail sufficient to
liquefy any known solids under ordi-
nary conditions. But the conditions
under which matter exists 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 a solid
undergoes in the process of liquefying
could not take place under such pres
sure even at an enormously high tenn
perature. It is now generally admit
ted that, if the earth really has a mol
ten nucleus, the solid Gust must, never
theless, be far too thick to be in any
way disturbed by changes affecting the
liquid matter beneath.