The Republican. [volume] (Oakland, Md.) 1877-current, 1888-09-08

in this way COrfecIS Ghe DlS rrOuSHetln
clock which stands in one corner of the
signal loom. This clock is fastened to
pedestal of granite quite free from
contact with the floor or any other part
of the building. Nothing but an earth
quake or some other extraordinary
CONFUSION of nature can shake 1t or IN
terfere in any way with its steady
marking of the minutes and the sec
onds. This clock keeps the local time
or the time of the meridian passing
through the dome of the observatory.
1t is always right within five hun
dredths of second. Its variation Is
amazingly small. Between this clock
and the clock which keeps standard
Eastern time, there should be eight
minutes and 1909 seconds difference.
To the ordinary mind the problem of
comparing two clocks with the idea of
measuring the difference between
them to hundredths of seconds seems
stupendous. The actual plan of opera
tions is simple enough. In the big
Frodsham clock is little cup of mer-
curry. Over this cup of mercury swings
bit of steel attached to the pendulum
The mercury is connected with one
pole of battery; the piece OF steel
with the other. When the two are
brought in contact the circuit is closed.
On the other side of the room stand
two plain clocks, about which there is
nothing to indicate value of 500 or
$500. These clocks were purchased at
the time of the transit of Venus. In
each of them is cogged wheel just
behind the dial which turns with the
second hand As each of the cogs
passes a point in its path it touches a
brass spring which closes an electric
circuit. With each second, therefore,
there is an electric impulse sent forth.
On table between the Frodsham and
the other clocks is q chronograph. 1t
consists of a metal cylinder which is
made to revolve by a hidden spring at
certain uniform rate. The rate being
timed, each revolution of the cylinder
covers certain time-space and the
circumference of the cylinder can be
divided into fractions of that time or
into minutes or fractions of minutes.
The cylinder is covered with paper;
on the paper rests a pen-point. As the
cylinder revolves the pen traces on
the paper a red line. An electric at
tachment to the pen causes it to be de-
Elected from its position at the passage
of an electric impulse. The two clocks
the Frodsham and the transit clock
are put in circuit with the pen on
the chronOgraph. At each second
registered by the Frodsham the pen is
detected, making marked point at
right angles with the straight line it
was drawing along the paper on the
cylinder. At each second-beat of the
transit clock also the pen is dehected.
The distance between these reflections
being measured with prepared gradu-
| ated scale, it can be determined within
a few hundredths of a second what the
difference between the two clocks is.
If it is desired to retard the movement
VI OAIC u ttllolu ClOCh III OluCl w lIldhC
the difference between the clocks
greater, the operator with his lead
pencil checks the pendulum slightly.
If he desires to lessen the difference
between the beatings of the two clocks
he in the same manner acelerates
slightly the motion of the pendulum.
The difference is at once marked even
to the ear, for on top of each clock is
an electric sounder like that attached
to any telegraph instrument.
The transit clock having been cor
rected at three and one-fourth minutes
before noon the clock is switched into
the telegraph circuits leading from the
observatory to the Office of the Western
Union Telegraph Company, the Signal
Service and the fire alarm. The little
wheel which controls the electric i'm
pulse has the cog representing the
twenty-ninth second, and the cOgs rep
resenting the last five seconds of each
minute cut out. In this way any opera
tor who cuts into the signal circuit at
any time after the signaling has begun
is able by the omission of one of the
regular beats to distinguish the next
as marking the half minute and by the
omission of five to know that the next
beat will represent the close of the full
minute. Automatically the clock sends
its pulsatiOns over thousands of miles
of wire thus for three minutes. There
are fifteen seconds to be measured off
before the noon hour. The operator
steps forward and places his hand up
on a switch key. One, two, three, four,
five. the switch is thrown.
1t throws out of play the cog-wheel
which marked off the seconds and
throws into control of the circuit cog
wheel which marks off the minutes For
ten seconds, then, or until the minute
has expired, the circuit will remain I'M
broken, there will be no electric i'm
pulse sent out. The operators listen
ing for the time have counted from the
last break in the beating twenty dis
tinct impulses. When the beating
stops on the twentieth they know that
the next impulse will mark the close
of the fifty-ninth minute of the eleventh