The sun. [volume] (New York [N.Y.]) 1833-1916, 1900-02-11
THE EARTH'S INTERIOR.
PROF. N. & SMALLER ON THE LATEST
CONCLUSIONs or SCIENCE.
Arguments Against the Old Theory That
the Interior of the Globe IL Fluid-ln-
tense Heat There Certain and Enormous
Pressure-volcanoes Of Superficial Origin
Coppri A.. 1000. ~ ". s. Shakv.

tonse Heat There Certain and Enormous
Pressur.-voicnnoes Of Superficial Origin
Copvr A.. 1900. Nv v. S. Shahr.
Physical science has undoubtedly attained
more than half its total development within the
nineteenth century, though It IN true that The
scientific gains Of the century do not include
such splendid achievements as the Newton theory
Of gravitAtion the Copernican account Of the solar
system, or the primHr ~ concepts of the atomic
hypothesis The rate 81 advance in scientific
knowledge has been more uniform also In the last
hundred years than In the earlier centuries. The
discoveries in each field have served az never he.
lore 10 help on inquiries in adjacent fields, with
the result that the explorers have moved forward
In touch with one another Nearly every branch
OF science has helped and been helped by 'heo,hers.
To this interaction Of Learning a marked feature
Of our age We may in large measure attrib ute
the surprising advance II has won. To II We clear
ly owe the singularly rapid gain which has been
made In all that relates To the explanation Of the
earth Geological science is not a distinct branch
OF learning, IA is chemistry or astronomy. II IL
a body Of varied knowledge, drawn from the stores
Of all the others and no combined as to render an
account Of what has gone on in and upon this
sphere.
The conditions under which the group of sci.
enoes termed geology has developed have set
certain important limits TO its successes. A
hundred years ago the pioneers had Iust fairly be-
gun 10 interpret the tangle Of rocks which make
up the so called crust Of the earth and TO speculate
as to the meaning of the evidence concerning the
condition Of its interior. From the point Of view
Of scientific inquiry. these speculations had ad
vanced but little beyond the position to which they
had been brought a century before. The real
advance In the science was attained in the main
by close study Of the structure and attitude Of the
rocks. together with the organic remains which
those laid down in water so often contain. In this
way the division OF the pas, history Of the earth
into ages. epochs or periods. a task begun in
earlier times, has been carried so far that We now
have a fairly clear idea az TO the way in which
the record is divided into chapters and sec tons
anda general though still very incomplete, knowl.
edge Of the order Of events on those parts Of the
crust which have been lifted above the level Of
the sea. This store Of facts enables us fairly to
interpret so much Of the history OF the earth as is
written in stratifed rocks that have at no time
In their history been buried TO a greater depth than
from twenty to thirty miles below the surface
While the facts revealed in the newer stra,ined
rocks those which commonly lie in a little
changed form near the surface are easy TO be
interpreted, there are difficulties in this work
which increase in rapid measure az they concern
beds that have been deeply buried. The reason
for this IL that, in proportion as the strata are
covered by others subsequently laid down, they
are brought into a region where they are sub
iected to anumberof physical and hemicalactions
concerning which We can know nothing by iii
rect observation We cannot submit this sphere
10 dissection The deepest mining work pene-
ira tea only about Oup fDurthOusanIth nf The XnN
10 the centre. So far as We can ascertain, the
Oldest and for a time deepest buried rocks ha Va
not been more than one or two score miles below
the sea level.
The first and in some ways the most importa nj
point that our century has made as To the depths
Of this sphere consists IN a determination Of the
heat OF it's interior and the origin thereof. The
evidence OF a high temperature in The depths VI
the earth, afforded by hot springs and volcanoes.
Is 80 clear that the Greeks appear To have noted
its meaning and To have coniectured the exist
ence Of some kind Of a central fire, burning after
the manner Of u furnace. This view indeed ap-
pears to have been commonly held by all the
early geologic inquirers who considered the facts.
So, too, II has long been known that there was in
some mines a distinct increase in heat To he noted
in any considerable descent The main gain
in this inquiry has consisted of a Determination
as 10 the rate of increase and the source Of this
high temperature which exists in the depths.
Many careful observations, distributed over all
the continents, show US that for all the distance
We have penetrated with shafts and borings, the
increase is at an average rateo Of onedegrre Fahren-
! melt, hpproNlTnhlfly, lr thCn MY IpPl O1 Geltn.
At this rate the temperature al the centre would
attain to about 400 600 degrees,
But there are various reasons why this intense
heat cannot really exist How, then, can we
account for the error 1t may bs explained by
what We may observe OF compute as taking place
in any cooling body. Iii a perfectly warrantable
supposiiion that the earth, AT a remote period,
was in a state OF igneous huidity; tina, the mass
was long kept at about the same temperature
by a process Of boiling. When the sphere as.
sumed ls present state OF Approximate solidity
| ito further CpplInV Wplli hay lal tn The ghilltnv
Of the outer part, while the central portion re-
manned at near its original heat a little re-
Election will show that l.lder these conditions
We should have a rapid increase of temperature
for perhaps a few score miles downward, while
below a certain level the increase Of heat would
b. al q steadily diminishing rate the greater
part Of the internal mass being at a rather uniform
heat;
rived from volcanoes had advanced beyond the
primitive notion that they We're due To some kind
of subte rranean combustion, such as takes place
in burning coal beds, biologists adopted the view
tina, they proved the interior 10 be in a fluid state.
substantially like molten glass or iron. II did
not seem possible otherwise 10 account for the
ou,pouring VI lavas in such quantities that they
have covered to great depths areas many thous-
sand square miles in extent
Further proof to the same effect seemed to be
afforded by the fact that wherever We have ac-
cess tocrys'alIine rocks, such as granite, which
have been brought into contact with other depOS.
its, they have entered assures in a way that
shows that they were originally fluid The
hypothesis OF internal Hlldlty appeared at the
beginning of this century TO BE- tolerably we'll
approved IL was indeed assumed by most writer's
and was made the basis Of many learned treatises.
Steadily. however within the last half century
the contributions from other bra nches Of science
have served TO bring this view into doubt First
II was noted that any melted rock shrunks In gen.
eral to the amount Of about Is per cent of
its bulk in solidifying and, in consequence
81 this tends to sink as IL fraezas, This tendency
TO settle down into an interior fluid would make
II i'm possible for the crust Of a generally fluid ea nth
TO attain a greater thickness than about half
a mile before 1t would be dragged down by gravi.
tation. As We know the earth is solid for al least
twenty miles downward and probably is in that
state for several times that depth, the idea Of a
thin crust lying as a layer on n liquid int erior
The next attack on the notion Of internal
nuidity came from the astronomers. II had
long been known that the grayitative attraction
Of the moon on the equatorial bullying 81 the earth
or, rather, the difference in this pull on the parts
of that mass near TO and away from our satellite,
caused the polar axis to b. constantly changing
its position. The geological bearing Of The movement
is found in the fact that, II the earth were fluid
except for its crust, the position Of the polar axis
would not b. altered by the attraction. but the
sphere would change SHAPE in the manner If q
tide, as the waters do under a similar impulse.
While the problem IN complicated and the results
not accepted by all students, II seems from this
argument most likely that the earth Is as rigid
as the most solid Of its rocks
In face NJ the evidence MS to the difficulties
Of reconciling the great heat of the interior and
the election Of lavas with the evidence that shows
that IL cannot b. fluid, gnologists " this century
have had to review many opinions which they
inherited from h elaSt To begin with, they have
had To modify their conceptions Of solids and
fluids so az to clear away certain misconceptions
due 10 our eN perience with materials on the sur.