BoletiÌn mercantil de Puerto Rico. (San Juan, P.R.) 18??-1918, 1902-05-23
SAElJUAN, MAYO %
Cause of Volcanoes.
Theories as to Earthquake
Phenomena.

Theories as to Earthquake
Phenomena.
Sir Robert Balls Nebua Hypothesis
Disturbances That Take Place Under
Extraordinary Presure-The Gradual
Shrinking of the Earth's Crust-Pro-
blems That Battle Scientists.
The cause of volcanoes and earth |
ouakes. like most scientific questions, is
for the most part, only theoretically ex'
planned, that theory gaining currency
which will solve the largest number OF
problems. "The Earth's Beginning is
the title of book by Sir Robert Ball,
the chief astronomer of England, pub
lished by D. Appleton &ss Co. Of New
York. In this book Sir Robert Ball say
that the nebu1a theory, outlined by Kant
and Laplace, will account for all the phe
nomena of earth and heaven. This
theory maintains that the earth, sun
and solar system originated from vast
contracting nebula.
THE internal heat of the earth, de-
rived from the primava1 nebula, is IN
no way more strikingly illustrated than
by the phenomena of volcanoes, says
Sir Robert. The evidence has proved
that under the extraordinary pressure
which prevails in the earth the ma
terials in the central portions of our
globe behave with the characteristic OF
solids rather than of liquids. Many, If
not all, solids may be made to flow like
liquid if only adequate pressure be aP-
piled The fact is that the terms solid
and liquid appear to have no physical
meaning with regard to bodies subject
ed to these tremendous -pressllrzs. But
when the circumstances are such that
the pressure is relaxed, then the heat IS
permitted to exercise its property OF
Transforming the solids into hq lids.
Masses of matter near the earths crust
are thus in certain circumstances trans
formed into the fluid form and issue
from volcano in sluggish currents OF
lava. There has boen much difference
in opinion as to the immediate cause OF
volcanic action, but there can be little
doubt that the energy which is ma
infested in volcanic eruption has been
originally derived in some way from
the contraction of the primaval ne
bula."
Lord Kelvin, says Sir Robert Ball,
has demonstrated that, whatever Its
nature, the earth possesses an intense
rigidity, and this is proved from the
study of earthquake phenomena. AS
to the immediate cause Of earthquakes,
he adds, there is considerable differ
ence of opinion. But l think that an
earthquake is one of the consequences
of the gradual loss Of Internal heat from
the arth. AS this terrestrial heat IS
gradually declining, it folio that the
bulk of the earth mis-! be shrinking,
and, accordingly, the crust of he earth
has from time to time to be OcCommo-
dated to the fact that the whole globe
is .lessening. It follows from these
considerations that the rocks which
form the earth's crust must have les
sening acreage from year to year.
These rocks must, therefore, submit to
compression, and the necessary yield
ing of the rocks will, in general, take
place in those regions where the ma
terials of the earth's crust happen to
have comparatively small bowers Of
resistance. The acts of compression
will often and, perhaps generally, not
proceed with uniformity, but rather
with small successive shifts, and even
thought the displacements of the rocks
in these slips be actually very small
yet the pressures to which the rocks
are subjected are so vast that very
small shift may correspond to very
great terrestrial disturbance. The ef-
feet of such shock would be propagat-
ed in the form of waves through the
globe, and when the effect of this ad-
justment reaches the earth's surface it
will sometimes be great enough to be
perceptible in the shaking it gives that
surface. The shaking may be SO VIC
lent that buildings may not be able to
Withstand it Such is the phenomenon
of an earthquake"
Albert Perry Brigham, professor Of
geology in Colgate University says in
his textbook Geology (a1so published
byD. Appleton and Company "T1eE
great number of earthquakes are prol-
ably due to the shrinking of the earth
crust in cooling. A comparatively stiff
crust over a cooling and shrinking
interior must shrink. J Il. become crack
Cu IL oOAiC pletCSo dhu lO1uCu III OLlS1S.
Stupendous strains are thus set I'd and +
rock masses are liable to move suddenly
upon each other All points to which
the impulse is transmitted exp rience
an earthquake"
Writing on the causes of volcani
action he says NO conclusive word
has been spoken on this subject A
final conclusion may lie beyond the
hounds Of human investigation. Vol.