Evening star., 1896-12-01
Interesting Adjunct to Uncle Sans
Weather Bureau.
SElSMOSCOPE AND SElSM0GRAPH
They Record the Exact Time and
Continuation of Earth Shocks.
IN THE BIG WHITE SHAFT

Perhaps no other mach1ne employed by
official savants for making scientific obser-
vations has a more interesting function
than Uncle Sans earthquake trap. 1t is
baited now for the next earthquake, and
the students in charge are hoping that ma
ture may send them the much-sought-for
game before long. 1t Is the only earth
| quake trap in the country, so far as gov
ernment scientists know. 1t Is an adjunct
Of the natiopal weather bureau, although
as yet the meteorologists of that fnstitu-
| ton do not claim any ability to forecast
earthquakes.
Beneath the southwest corner of the main
building Of the weather bureau there Is d
square cell, whose floor is a single slab of
cement, extending a foot or more into the
earth, and said to be so laid that nothing
short of a tremor of the earth itself can
shake it, Upon this slab rests the earth
quake trap, which in the more dignified
| language OF science is known as seismo-
scope. The instrument proper occupies less
| space than ordinary mantel clock. In
| simple words 1t is a pendulum winch
| moves when the earth trembles even to the
| slightest degree, and which at the moment
of each tremOr closes an electric circuit
| and thereby operates a recording mech
anism.
The Machine.
A cylindrical weight hangs upon a long
| link, the latter supported by horizontal
pivot extending through it. From the up
per edge Of the link extends a long delicate
| needle about foot in length which points
directly upward when the weight is at
tached. The slightest movement Of the
weight is greatly exaggerated at the point
of the needle. This Ioint, which Is tipped
with platinum, passes upward through a
small platinum trimmed hole in a fiat piece
Of metal. held stationary with the base of
the instrument. So perfectly is the needle
balanced that its point normally passes
through the center Of this hole. One pole
of electric circuit is attached to the
weight and needle. at the pivot and the
ing the hole. Even the slightest movement
of the earth will cause the suspended
weight to wobble and thereby cause the
point of the needle to touch the rim of the
hole. When this contact takes place the
electric circuit is closed and message is
dspa tched into another building where
recording Instrument is at work.
Making a Record.
The instrument which automatically
writes a record of the earthquakes occur
renee is known as the seismograph. This is
kept IN the instrument room of the weather
bureau, where are installed the wonderful
paraphernalia used in making weather fore
casts and special observations. The seis-
nograph consists principally of a revolving
cylinder, moved by clockwork, and adapted
to make one revolution every six hours.
Wound around the cylinder Is a broad rib
bon Of paper, cross-ruled with parallel lines
The distance between each one of these
lines indicates five minutes of the revolu-
tion. Bearing against the paper-covered
surface of the cylinder is small arm.
which, If held still, would trace a spiral
like the chfsel of a turn-lathe. The end Of
the arm is tipped with a fountain pen,
which makes marks on the paper. A regu-
lator clock, which ticks at standard time,
cGnnnctad q n.
ner that every five mir utes the pen point
will give a sudden jerk back and forth,
making small points in the otherwise
straight line. The points thus traced are
The same distance apart as the rulings of
the paper.
The registering mechanism is in the same
circuit which is closed by the needle Of
the earthquake trap 1t Is so arranged that
points similar to those made ordinarily
every five minutes will be traced upon the
recording paper by the fountain pen every
time the point of the needle touches against
the rim of the hole mentioned. Thus the
earthquake is denoted by a single point or
a series of points falling between those reg
I!arly made. The exact instant Of the
counting off the number of five-minute
marks made since a known time noted
when the record was begun and by apply
ing a carefully graduated scale which will
show how many minutes, seconds and frac-
tionS thereof the instant of the shock ex-
ceeded the last five-minute mark preceding.
Game Already Trapped.
The earthquake trap has already caught
two earthquakes and one hurricane. The
first earthquake caught was that which
shook Philadelphia and vicinity on the 1st
of September, last year. No one in Wash
ington felt the shock and not even the au-
thorties in charge of the instrument sus-
pected that the vibrations had been carried
thus far with sufficient force to be recorded
in any instrument of precision. The earth
quake occurred on Sunday at Oh. Sm 30s.
am, and the record made by the seismo-
graph was not discovered until two days
afterward and when it was not looked for
Shortly after this earthquake second was
ieit IN a few places, but not in Washing
ton. 1t was trapped by this delicate instru-
ment, however, In manner similar to the
recording of the former
Although seismoscopes are not supposed
to make record Of wind phenomena. the
recent tropical hurricane which played Sc
we're havoc in Washington and other points
of the east was recorded by the sesmo-
graph. The indication, at first thought
would naturally be that the wind on that
occasion was sufficiently intense to shake
the very earth itself. But according to the
authorities at the weather bureau, this in
all probability, was not the case. The wind
perhaps shook the weather bureau building
to its foundations, and the inclosed earth
beneath was made to tremble from that
cause
to see accomplished is the placing of ac-
curate seismoscopes and seismographs in
different observatories throughout the
country, as widely distributed as possible.
with a network of such apparatus, care
fully installed, the next phenomena of the
Kind could be accurately observed. on a
broad scale. for the first time in the his
tory of the world.
In the Washington Monument
The largest seismoscope in the world is
owned by Uncle Sam, and is used here in
Washington, but not for the study of
earthquake shocks. This is a copper wire.
five hundred and fifty feet long, hanging
from the extreme top to the bottom of the
interior Of the Washington monument 1t
is protected throughout Its length by a line
of pipe, and holds suspended at its lower
end plummet, which hangs In a vessel of
OIL Two small transits, arranged at right
angles to each other, are kept focused
upon the wire, just above the plummet
Even the slightest movement of the top of
the monument may be observed by the
transits. The rules of the monument re-
quire the custodian to take statement of
the transts every day, and to submit the
same to the War Department at the end of
each month. The records thus drawn as
shown b the writer. reveal the interesting