The Wheeling daily intelligencer. [volume] (Wheeling, W. Va.) 1865-1903, 1886-09-03

AllIbhlhNhN"
In connection with the recent shocks oil
earthquake tho definition OF the phenom'
euon, as given by the Encyclopedia br''a"'
Mica, will be read With interest
Whatever may be the real origin Of the
earthquake shock, it ia convenient 10 re-
gard its effects az proceeding from aeon
custom or sudden blow delivered under
ground at some definite centre. This cen
ira OF impulze is called the seismic focus
It must DO borne in mind, however, that
such centre, so far from being anything
like mathematical point, Is i'll nature a
subterrauean region, which in many cases
ia no doubt OF very large dimensions
measuring perhaps some milesin diameter
From the seiamic centre waves SrepIop'
agsted in all directions through the solid
materials Of the esrth's crust; aud II the
focus be situated beneath the sea, the
vibrations Of the ground will be accom-
panied by undulatioRD OF tho water
Those waves which pass through the
elastic materials OF tho earth consist Tor
the moat part, Of longitudinal vibrations,
like that Of atmospheric sound'wavea, and
consequently not like ordinary water
waves. In the Gound.wave the air Is
alternately condemned and rariaed, the
molecules advancing and retreating In the
line Of direction in which the wave Is
travelling. III water-wave, on the con-
trary, the molecules OF liquid rise and fall,
or rather describe closed curves In planes
which are transverse to the direction in
which tho undulation or wsve.form ad-
yancOs. According TO Mr.. Hopkins, both
orders Of vibration-longiludinal and
transversal-Coexist in the earthquake
wave, and call for investigation. When,
for example tho molecules Of an iron bar
are disturbed by a blow delivered at one
end, both kinds Of vibration arc generally
excited and hence two waves are sent
through the bar-the longitudinal, how.
ever, having much greater velocity than
the transyersal wave. But it may be
doubted whether the seismologist need
concern himself with any but longitudinal
vibrations. For, admitting that small
transyeral vibrations are generated at the
seismic focus, 1t is probable that they
would DO cut OF 10 great extent during
transmission from stratum TO stratum.
Indeed, the planes Of Junction between
the several beds in stratiled deposita
would hinder the transmission OF trans
versal vibrations travelling in direction
normal to tho strata. Hence Mr.. Mallett
maintains, that in studying the effects OF
an earthquake, attention may be restrict
ed, without danger Of error, to the longi-
tudlnal or normal vibrations, the trans
versal or tangental. vibrations being neg
leCted.
Around the seismic centre, or mean
focal point, the molecules Of the rock will
first be squeezed together by the conCus.
sion, and then separated by virtue Of the
elasticity Of tho solid medium; the onward
motion is then rapidly taken up by the
next set Of molecules, which in like man.
ner are pushed against each other, and
then spring apart. In this way the pulse,
or form OF tho wave, may be propagated
IN an enormous distance, whilst the In.
cursions Of the individual particles are
confined within very narrow limits.
1t is therefore Of great Importance
to distinguish between the transit
Of the wave and the movement
Of the material particles. Each molecule
may move only through few inches, but
the unduIation may travel for hundreds Of
miles. The distance through which the
individual particles oslllate Is called the
amplitude Of tho wave. After the Neapoll'
tan earthquake Of 1867 Mr.. Malet found
from actual observation at q place called
Polls, situated nearly above the seismic
center, that the amplitude Of wave
which caused certain fractures In mason.
ry could not havo been more than q
inches. He is thus led TO believe, con.
trary to the opinion Of most geologists,
that earthquakes are not great agents Of
permanent elevation. That elevation has
been frequently observed after an earth.
quake Is fact beyond question; thus,
Captain Fitzroy found, after the South
American earthquake Of 1885, that q part
Of the lSle Of Santa Maria, In the Bay Of
Conception, had been raised upwards Of
ten feet, and, although this elevation was
followed by aBlow subsistence, II ls belisv.
cd that tho land was permanently left
considerably higher than lie level before
the occurrence Of the catastrophe. Mr..
Mellet, however, would refer such Altera.
ton Of levOl 10 the action Of elsvatofy for.
COS accompanying the earthquake, but not
to tho direct transit Of thoearth.wRvO.
From the density and the modulus Of
elasticity Of a given rock, Il 10 possible to
calculate the velocity with which ylbra.
ton would travel through such medium.
But the rate deduCed BY calculation usual.
y exceeds very greatly that actually OBJ
served In an earthquake, To determine
The rate Of transit through various rocks,
Mt. Mallet aud bic son Dr.. ]. ". Mallet
conducted many years ago q series Of ex'
pstlmsnts, at the instance Of the British
Association. Annie was carefully level.
led and measured on sand In KilllnOy
Bay, near Dublin, and by explosion Of
Am i,A,uhnt LhA NnlnniiY Of LtAnaminalnn J