Evening star., 1897-03-27
THE EARTH'S INTERIOR.
Reason for Believing That the GIoba
is Solid to the Core.

Until very recent years the fact had hard
ly been questioned that 10y far the greater
part of the earth's interior was in the con-
dition of a fluid or molten mass. the vol
canic manifestations exhibited and the sur
face, the rapid rise of temperature that is
found as we proceed from the exterior to
the interior. and other considerations point
ing almost irresistibly to such a conclusion.
Indeed. a common belief was that all that
was solid centered in a crust of some ,0-
100 miles thickness Heating the fiery
n agma of the interior. 1t is true that
sCme physicists, as Hopkins. had reasoned
out probability that this crust, 10 with
stand the strains that We're imposed upon
it, could not have thickness of much less
than 500 or 1.ooo miles. bat his arguments
had comparatively little effect toward dis
pelling the notions that had so long existed.
At the present time, after the brilliant
mathematical eNpositlons OF Sir William
Thomson Uord Kelvin, of Prof. George
Darwin, of Prof. Simon Newcomb and of
Mr.. Rudski this doctrine of terrestrial
fiuidity is hardly longer taught. few
there who yet linger with the old
theory, but the great mass of educators
and their pupilS-eNcept in regions where
text books bear the impress of manufac-
ture in the mental power of a quarter or
century age or more-haNe settled down
to the comfortable conviction that our
planet is as solid rigid hall of glass
or steel-in fact. twice as rigid according
to the determinations of NJ. Rudskl. The
doctrine of Solidity does not, however, in
yolve the assumption of equal, but of aver
age rigidty. Again, it is not implied that
because the earth is virtually solid TO the
core local areas of liquidity or huidity DO
not exist. 1t is upon these pockets or
areas of molten material theoretically as
sumed to exist that the geologist largely
relies to harmoniZe his facts concerning
earth movements, etc.D with those OF the
mathematical physicist; they are to the
entire mass of the earth what the air
spaces are to a block of ice. Assuming the
virtual solidity Of the earth, the interest
ing question suggests itself: W nat Is the
nature of the rock masses that COMPOSE
the interior? An answer to this question
is largely one Of inference only. We Know
the rocks of the exterior. and We know
the rocks of the interior to limited depth.
Can our knowledge Of these rocks be made
to answer the inquiry as TO the nature OF
the rocks of the deep interior?
1t is, perhaps. too early to give reply to
this inquiry, but the interesting fact has
long been known that the average density
of the earth is nearly or quite double that
of ordinary rock, such as limestone. sand
stone or granite. and il Is assumed that Its
greatest density cannot easily be less than
from five to ten times that of its super
fetal materials or twenty times the dem
sity of water. This being So the rocks Of
the interior are either compressed TO pro-
digious degree to give them this weight.
or they are of a different character from
those of the surface possibly containing
great quantities of metal In relation to
this inquiry a knowledge OF the exact dem
sty of the earth becomes of first import
ance, and il is of special interest to note
that an extended series of recalculations,
made by Richarz and Kriger-Menzel. ex-
tending back to the year 1854 and with
final results recently announced 10 the
Berlin Academy of Sciences. confirm with
in a very narrow margin the earlier results
obtained with less refined instruments. by
Cavendish and his SUCCESSORS, through a
period OF upward = aundrei years. these
latest determinations Tx the density CT our
planet at 5.505 compared with wateD.