Belmont chronicle. [volume] (St. Clairsville, Ohio) 1855-1973, 1869-04-29
sutersstiug & snstrnftirs 6afts.
Eathqukes.

The passion for theorizing, without re
gard to facts or data for deduction, ha:
fingered longer in the subject of earth.
quakes than of any other matter of sci.
ence. Long, before Shakespeare repre-.
sented them as caused sby the impris-
oning of unruly wind within the womb
of Nature, Aristotle had enunciated the
same theory. Ne less unsatisfactory
becaused not based on careful examina-
tion of the phenomena of earthquakes
was the chemical theory which poured
water on masses of sodium or potassium,
or the speculations of De Beaumont,
which referred them to the unequal con-
traction of the fluid and solid portions
of the globe. The best study ever yet
made of an earthquake is that made by
Robert Mallet, on the Calabrian earth
quake of 1857. With all the appliances
of modern science he studied on the spot
all its phenomena, examining the bull
din2s overthrown, in order to find out
the exact movements of the earth. He
also produced artificial earthquakes by
exploding charges of powder under
ground, a5tQtserving the oscillations
of the surfae9 odnced at distance by
them. AS nigheAe expected in an earth
quake, the mOvemehtk over the center
of disturbance are nearly vertical; at a
distance the angle Of emergence of the
wave will be inclined, so that walls will
be tOppled over in the same direction
and loose stones tossed uL at given in
clination. A very simple etrigonOmetric-
a statement would show at what depth
these various lines of direction would
meet at the point of disturbance. So il
is easy, by = similar process. to find
what place is over the center of seismic
action by tracing back to tie point of
meeting the lines of direction in which
the earthquake waves have travelled
The waves of motion in earthquakes are
found to travel at a rate of about | 900
feet second, or about II miles minute
But the particles of the wave moved at
far less velecity-being only in the
Calabrian earthquake speed of II feet
in second, or miles an hour. This
last motion is what does the damage
The two motions are as distinct as those
of wave of water where the particles
of water, in the case, for example, of
the tide, move much slower than the
tide-wave. Tracing back 26 wave-paths,
Mr.. Mallet found that they started from
a depth generally of q miles, though
varying from 81 to q miles. This must
rent in the rocks at that
depth below the earth's surface, which
was the cause of the first shock. while |
the filling of the rent with steam was the !
cause of the second shock. This rent
he found to have been three miles in |
vertical extent, and go lines of wave |
paths met so as to show that the rent
was ten miles long. The distance from |
wall to wall in the rent was probably |
very small. How these rents are pro-
duced it is difficult to tell. We can only !
surmise that steam, Which at the max
imum depth of 81 miles would have had
q pressure of 6S4 atmespheres, allowing
an increment of enc degree Fahrenheit
for every go feet in depth, must have had
to do with it. Were the wat
sr to be suddenly flashed into steam on |
the lava at a temperature of
2 900 F. its force would be enormously
increased. The action of earthquakes
may then be thus illustrated. If a fiddle
bow be drawn across the edge of plate
Of glass, any particles of sand upon it
are set dancing up and down. In this
ease heglass is an elastic body, in which
! wave of compressed glass is travelling
onward as it is constantly being started
oy the bow. The wave moves at rate
If several thousand feet per second but
he particles of glass move at velocity
10 much less that the sand is scarcely I
lifted off of the glass. So in an earth
Inake force is somehow exerted on the
elastic rock, by fissure or otherwise,
md this congresses the rock next to it,
md this wave travels onward 1000 feet
second, while the elastic particles of
rock are-moving their short
distance at far less velocity, and are,
ike the glass, shaking whatever rests
lpon them. This destructive move
nent may be less than the II feet per
econd observed in the Calabrian earth
quake, or may be 80 feet second, as
must have been the case in the earth
quake of Riobamba, by which Hum
,oldt says that men mere tossed 100 feet
nto the air.