Evening star., 1923-09-06

yet that volcano showed no special ac-
tivity.
Might there not be many causes, not
all being necessary in all quakes?
many places. biologists call those
cracks faults"
One of the most advanced scientists
of seismography in the world is Fa-
ther Francis A. Tondorf of George
town Observatory. He is equipped
with the most complete seismographs
in America. Speaking of the liability
of earthquakes along the great
faults" he says:
The practical certainty of the dis
location theory calls for a more thor
so that the more unstable areas may
be indicated ON the map. This ac-
complished, more exact interpreta-
tions of the warnings given by lesser
shocks would be useful in places sit
uated along q serious fault line. Had
and San Francisco would have been
better prepared to meet the shocks
that were SO disastrous to them"
x* X
The above suggestion will be ap-
connection with the fact that there
are, almost daily. earth trembles
which are not pei eiceptible except to
the delicate instrument called the
Seismograph. These can be watched
continually at the seismograph, and
interpreted as accurately in prognos-
ticating the approach of serious dis
turbances as. weather bureau scien-
lists forecast storms.
The trembling of the earth is actual
-physical-not merely magnetic. 1t
can, he observed at times without
the delicate seismograph. even upon
the calm surface of "A lake. The Lis
bon earthquake was noted on Loeb
Lomond, Scotland by the rhythmic
waves. not made by the wind. In the
same year GS77i Russian astron-
omer noted oscillations in the level
of his transit instrument. which were
coincident with an earthquake 1000
miles distant.
When the Charleston. S. c., earth
quake was active an astronomer at
the United States Naval Observatory,
stars moving across the web of his
great telescope. He learned next
day that that was because the tele-
scope was being shaken by the vibra-
tions of the earth. Until that expla-
nation had come. through the news
of the earthquake, 1t was most un-
cahny that the very heavens were
apparently no longer stationary.
. X X +
There have been published some in
accurate figures as TO the number Of
earthquakes recorded in Japan. ac-
cording to Father Tondorf. Japan
cannot be. credited with 1900 quak IS
A year. as has been published. On
the highest authority OF Count de
Montessus. director of the seismo-
logical observatory of Chile, there
are 3S30 uuakeS year somewhere
in the world The official figures for
Japan, recorded by DIR. Omori. snow
that that country has had 2,l13 quakes
in twenty-four years-one every lour
days.
How are earthduakes recorded
What is n eismograph? When an
earthquake starts it has two mo-
tions. simultaneously. One is an up
heaval or compression which causes
what are called preliminary trem-
hles" Then there is a twisting or
distortion which causes What are
known as long waves
The preliminary tremhles continue
for awhile on the recording seismo-
graph. the duration depending on
how far the instrument Is from the
seismic focus OF the quake. Then
suddenly the Tong wave" arrives.
The speed of the long waves is
known to be about three miles per
second: the speed of the preliminary
tremble (P. tt is twice 8 fast. The
Up T" travels along the chord of
the arc of the round earth. while the
long wave U. W. comes along the
surface of the earth. The seismo-
graph records the exact instant of
the arrival of both waves and by
noting the span of time between the
two arrivals II is possible to COM
pute the distance from the instru
ment TO where the disturbance oc-
ours. 1t is as simple as it is to
count the seconds between a light
ming flash and the arrival of the
sound of thunder. knowing Gmt
sound travels 1850 feet per second.