Evening star. [volume] (Washington, D.C.) 1854-1972, 1895-09-28
WHAT IS A sEIsMOGRAPHs
Description of One Mt the Weather
bureau and It's Recent Record.

Description of One Mt the Weather
bureau and It's Recent Record.
The earthquake which this month shook
the whole Of the eastern coast between
New York and this city was automatically
observed and recorded by seismograph in
the instrument room of the weather bureau
at exactly eight minutes thirty-nine sec
onds after am, on the LIST Of the month.
This interesting fact has been unknown
until recently to any except those scientists
who made the observation.
Since this was the only seismic observa-
ton made in the country at the time, by
aid of an instrument, and since 1T was the
first satisfactory experiment of the kind
ever accomplished in America, news of it
will excite great interest The results OBJ
tai1 ed have not been announced before, due
to the fact that the specialists having the
detailed diagram, showing the exact cor
rections applied to their clock.
The observers only regret that another
seismograph was not set either at New
irg, in which event it would have been pos
sble to estimate the exact time occupied by
the wave in its journey south. Other seis-
mcgraphs were formerly set in the old
naval observatory, but these have never
been adjusted since the removal Of that in
stitution to it's new quarters.
The weather bureau possesses two kinds
of seismoscopes. That which observed the
the two. In the basement of the main
building of the bureau is a small room,
whose floor Is heavy slab of cement, ex-
tending foot or more into the ground.
The lately used seismescope rests upon this
foundation, which cannot be shaken except
by CULVER of the earth ITSELF The prin-
cipie of this instrument is that of the PEN
dulum, which will move in sympathy with
every change of position of the mass upon
which it rests A hollow cylindrical weight
hangs on a long metallic link fastened in
side of 1t. The upper end of this link is at
tached to the bottom of a vertical steel
needle, very delicate. about foot in length
The needle is balanced to the pedestal by a
pivot allowing it to swing in all directions,
and fixed near its lower end, SO that every
slight tremor of the weight is greatly mag
whole instrument Is placed under q glass
case, to prevent its disturbance by a cur
rent of air or any other force otherwise
than a movement Of the earth.
The extreme point of the long needle,
which is tipped with platinum, passes
through a small round hole in a horizontal
sheet of metal. So carefully is the needle bal
anced that it does not touch the rim of this
hole, which Is also of platinum. One pole
of an electric battery is connected with the
needle, and the other with the metal plate
containing the platinum-lined opening.
Now, when the earthquake shook the
ground under the building, likewise the slab
foundation, the weight and the needle, the
platinum point of the latter vibrated
against the rim of the round hole and
closed the circuit, sending a message to the
recording instrument every time a wave
passed through Washington, on its way
from New York.
The seismograph which records the shock
Is kept in the instrument room, building
separate from the main structure. The
principle parts of the seismograph are a
regulator clock and a revolving chrono-
graph. This latter instrument is a large
cylinder. turned by clock work. making one
revolution exactly every six hours. Fitted
to this cylinder is a covering of paper,
graduated into fine black lines running
lengthwise.
The distance between each of these lines
indicates five minutes of the revolution. AS
the cylinder automatically revolves small
metallic arm holding pen traces spiral
around 1t, like the chisel of a turning lathe.
The regular clock is so connected with this
arm as to make 1t give sudden hitch back
and forth every five minutes, making small,
sharp points along the line the same dis
lance apart as the graduationS of the pa
per.
The electric wires leading from the seis-
mcscope are connected with this arm, as
well as is this circuit from the clock. Every
throb of electricity coming from the seis-
moscope makes the little arm twitch ard
make similar points on the paper. Hence
when the recent earthquake closed the cir
cult, as before described, the only indica-
ton of the disturbance was small point
between the regular five minute points
By counting off the number of five minute
lires checked off since the arm passed the
midnight mark on the paper, the time of
the shock was figured out in five-minute
mutiples of the day. In other words, it
was between five and ten minutes after G.
By applying carefully graduated scale,
under a magnifying glass, the exact posi-
ton of the earthquake mark was located
even to fractions of seconds. In this man.
ner the shock was found to have occurred
at six hours, eight minutes and thirty mine
seconds ante meridlem, or after midnight.
no no nP