Lewiston teller. [volume] (Lewiston, North Idaho) 1878-1900, 1891-05-28
WHAT'S O'CLOCK NOW?
READ THE ANSWER IN THE
STARS, WATCHMAN.
An interesting Account of How the Exacs
Zine Is Taken from the Heavens
at Night In a Great OBJ
scrvatOry Dome.

NO time piece is perfect, and there
are no means on earth of keeping cor
rect time. The stars, however furn-
ish the necessary means. At the OBJ
servatorv in Cambridge there are two
principal clocks employed in keeping
the standard time-the standard mean
time-clock, which telegraphs its sig
nal over the surrounding country. and
the normal sidereal clock, which is
the main standard of the observatory,
to which everything is referred. The
side real clock as its name implies.
keeps side real or star time, which
gains about three minutes and five
eighths seconds per day over mean
solar time, with which we are all
familiar.
The clock is of the finest workman
ship, and is kept in brick vault UNI
derneath the observatory. where the
temperature is as nearly constant as
possible.
Every effort is made to protect it
from any influence which might effect
its ..rate, " or in other words the amount
of its gain or loss per day. This is
necessary in order that the crate" may
be depended upon to give the correct
time during spells of cloudy weather,
when no observations can be made.
On every clear morning the error OF
this clock is carefully determined by
observing certain bright stars with an
instrument known as the meridian
circle.
This instrument consists of a tele-
scope mounted on trunnions like a
cannon and supported by apier OF solid
masonry. 1t is so arranged that it
can be directed toward any point on
the meridian, but can not be pointed
away from the meridian line. On
looking into the eyepiece of this tele-
scope one sees series of fine parallel
lines running north and south across
the field of view, the middle line
marking the meridian.
When time observation is to be
made the observer first selects suit
able star from a printed star list, which
gives the exact time at which each of
the principal stars crosses the meri-
dian. He then sets the telescope at
the proper point on the meridian to
intercept the star, and putting his eye
to the eye-piece waits for the star to
appear.
AS the star crosses each of the lines
before mentioned he presses an cleo
trio key which he holds in his hand.
The signals thus given are recorded
electrically on a registering instru-
ment called a chronograph, on which
are also being recorded the seconds of
the sidereal clock. the chronograph
consists of cylinder made to revolve
by clockwork at the rate of about once
a minute.
A paper, wrapped around this cylin-
der, receives the record traced by a
pen, which is connected by an electric
magnet in such a manner that any
signal, made either by the operator or
by the clock, causes the pen to make a
mark on the paper.
BY examining this paper the observ-
or is able to tell within the tenth of a
second the time which the normal clock
indicated when the star crossed the
meridian.
Comparing this with the time taken
from the star list shows the error OF
the clock. A comparison is then made
between the sidereal and mean time
clocks, which, after allowing for the
difference between the mean and sid
ereal times, shows the error of the
mean time clock.
If the clock is slow slight weight
Is placed on the top OF the pendulum
bob, which causes the clock to gair
slightly. If, on the other hand, the
clock is found to be fast correspond
ing weight is removed, making thu
clock lose slowly. In this way thu
standard signals are kept within few
tenths of second of the correct time