Evening star. [volume] (Washington, D.C.) 1854-1972, 1905-04-02

human being. And II VIII as greatly as
tonish many more people TO know that
within less than five miles OF this city there
IS a region which in all probability never
viii be visited 10y a human being. Yet each
of these statements is absolutely true. for
the region in each instance is that part of
the earth lying beneath its surface.
1t is true that the work OF exploration of
the earth has been carried on so thoroughly
that, IN the opinion of most people, it is
practically completed. This. however, while
true as regards the surface of the earth. is
far from true in respect to that vast region
beneath its surface.
Undoubtedly. it is reasonable to suppose
that the five miles Immediately below the
earth's surface are filled with rocks or
earth not essentially different from those
found a the surface but il is less easy TO
make reasonable speculations as to the state
faffairs 100 miles deep, or 900 miles deep,
and yet a thousand miles is but fourth of
the way to the center Of the earth. The
possibility of the occurrence. Of course, of
gold and other valuable minerals is a real
one, but. in the absence Of definite knowl-
edge. speculation about the interior of the
earth can but furnish vast field for the
free play of the ina gination, as it did to
Jules Verne in one of his most interesting
romanCes.
Nevertheless. II has been possible to OBJ
tain by indirect means "A certain amount of
real knowledge of the remote depths of the
earth, and careful study of the specuatious
and theories regarding the interior of the
earth has enabled scientists to separate
those which are reasonable probate from
those which are unreasonable or impossible.
One of the most important and best estab-
lished facts in this connection is that the
interior of the earth Is much heavier, per
cubic foot, than most of the materials found
upon the surface of the earth. 1t is possible
to measure the weight of the earth, as
whole, and, from such measurement, it has
been found that the average weight per
cubic foot of the materials below the earth
surface is about $50 pounds. Now, the
weight of a cubic foot of most substances
found at the surface Of the earth is much
less: ordinary earth. for instance, weighing
from 10 to 10 pounds per cubic foot; ClaNS,
about 100 pounds; sands, from 12u to 40
pounds; limestone about 100 pounds: gran
| ite about 100 pounds; sandstone, from 40
to leo pounds; slate, about $50 pounds, and
sea water, only "a pounds. Metallic ores
are of course, much heavier, but they form
4 comparatively small proportion of the
earthS crust, and we see from these figures
| that the average weight per cubic foot OF
| the materials within reach of the surface
| of the earth is somewhere in the neighbor-
| hood of 10 pounds, or less than one-half of
| the weight, per cubic foot, of the earth as
| a whole. 1t follows necessarily, therefore,
| that the materials at great depths must be
| heavier than those near the surface.
| The manner which the weight of the
| EARTH as a whole, is ascertained depends
on the theory of graVitation, according TO
which every piece OF matter attracts every
| other piece, the force with which a
! given piece of matter is attracted by
various bodies being exactly proportional to
| the weights of those bodies, provided they
are all situated at the same distance from
the given piece of matter. The force OF
attraction is so small that II is ordinarily
| quite imperceptible, except when the at
| tracing body Is the earth itself, in which
case the force of attraction is just the same
| All, iOIf Of a
| But it is possible to construct instru-.
ments of such extreme delicacy that the
| minute force of attraction eNerted by any
heavy body like a large ball of lead can be
detected and measured with considerable
accuracy. The weight of the whole earth
| is to the weight of the ball of lead as the
| force of attra ctiOn of the earth Is to the
| force of attraction of the ball of lead, and
| from this PROPORTION, using the data OBJ
| tanned from experiment. the weight OF the
earth can be worked out. So worked ont,
| the weight Of the earth is about six thou
| sand million million tons (6,0UO,pou .OoOo
| coo 600 600. Going further, since surveyors
have measured the size and shape of the
earth. we can readily work out the num-
Der of cubic feet in it, and so, dividing the
number of pounds by the number of cubic
feet the average pounds per cubic foot of
the earth, as a whole. is obtained.
The great heaviness of the materials in
the interior of the earth may very likely
Though not necessarily, will be eN
planned later on) indicate that the core of
the earth consists of some substance of
greater specific gravity than the rocks at
the surface. This substance may be iron,
or even lead or gold or platinum. If this Is
the case, 1t fits in very well with the fact,
now generally regarded as proved. that the
earth was at one time in a molten state;
for in a molten liquid. the heaviest sub
stances would have to sink to the bottom.
That is to say, to the center of the earth.
1t would also accord with the idea, appar-
ant raaSnna HE that the N1TolS uapetS
including the earth, consist of the same in
gradients, in approximately the same pro-
portions. Now, we have no means of know
ing the proportions in which different sub
stances are contained in Mars or Jupiter,
but sometimes meteorites fall upon the
earth. and ahey are nothing more or less
than planets-of course, on very small
scale. MeteOriteS are found to consist
very largely of iron, the iron being in very
much greater proportion to the other in
gradients than is the case with the crust
of the earth. This fact has led Prof. Vie
ebert, of the University of Gottingen. Ger
many. to advance the theory that the earth
consists of a core Of iron tcalled the cen
trosphere'D, like that found in meteorites.
surrounded by a shell Of rocks Called the
'lithosphere'D, similar in nature to those at
the actual surface.
Except as regards the heaviness of the
materials in the interior of the earth, We
have practically no definite certain
knowledge as TO their nature. But
in possession of a few important facts about
the physical conditions under which they
exist. For instance, it SIS easy to see that
these materials, whatever may be their
exact nature must be under enormous pres
sure, for each layer has to support the
weight of all layers above it. A column of
earth one foot square and one mile deep
weighs about 800 600 pounds, so that at Il
depth of one mile every square foot has TO
support q weight of half a million pounds,
or every square inch a weight of about
$500 pounds. At two miles depth twice
as much earth has to be supported and the
pressure there is 1000 pounds per square
inch. At 100 miles, it must be aboue $50 600
pounds per square inch and at the center
of the earth, 1900 miles deep, the pressure
must be enormous, enormous. indeed,
that ii is beyond the powers of human
imagination. However, some idea of the
magnitude of the pressure at moderate
depths may be obtaind when it is borne III
mind that the pressure stream in the pow
erful engines which do most of the work
of civilized countries is ordinarily only
about 200 pounds per square inch.
1t Is we'll known that the properties of all
substances are affected by pressure. as is
we'll illustrated in the production of liquid
air by compressors. Therefore, there can
be no doubt that the stupendous pressure
in the interior of the earth causes the ma
terials there to have properties very differ
ent from those of the same materials at