Williston graphic. (Williston, Williams County, N.D.) 1895-1919, 1899-09-28
HOW THE CLOCK IS SET.
Old Sol II No Longer Regarded ms the
Worlds Most Reliable Time.
keeuer.

One of the duties of astronomers is to
noon an electric signal is flashed from
the national observatory at Washing
ton, or from some other observatory to
which this 'time service" has been as
signed, to all the business centers of
the country, and all clocks and watches
are set directly or indirectly by this
signal. This is a matter OF common
knowledge, but the way in which the
astronomer sets his own clock is not
known so generally.
Most persons have vague notion
that our standard time is obtained
from observation of the sun. They have
in mind the old sun dial, which indi-
Gated the hour at noon by mark that
showed when the sun was on the
meridian, or, in other words, was ex-
actly south, and their idea is that the
astronomer can fix the hour of noon
with greater precision because he has
the means of determining with greater
exactness the instant at which the suns
meridian passage takes place.
The truth is the sun has nothing
whatever to do or to say in this mat
ter of setting the clock. The sun is it.
self one of the poorest of timekeepers.
1t is almost always either fast or slow,
sometimes to the extent of full quar-
ter of an hour, and is fright" on only
four days in the year. 1t is from the
stars, not from the sun, that the as
tronomer gets the time.
The stars perform their nightly
march through the heavens, from east
to west, with perfectly regular move
ment, never fastening and never slack
ening their pace, which is only another
way of saying that the earth turns on
it's axis at an unvarying rate of speed.
A star crosses the meridian, and in 20
hours and Sc minutes, about, it will
again cross the meridian, and it will
cross this imaginary line in the heavens
again and again, day after day, year in
and year out, with always the same in
terval between two successive passages.
The times at which all of the brighter
stars cross the meridian have been as
certained from long and careful OBJ
servation to within small fraction of
second, and catalogues have been pre-
pared in which these times of meridian
passage or transit" are given.
The astronomer charged with the
duty of setting our clocks has only to
observe the meridian passage of one or
more of these stars in order to obtain
the exact time. The observation is
made by means of what is called a
meridian circle, small telescope so
mounted on horizontal axis that it
can only point to the meridian. The 90
server looking through this instrument
can tell the time at which the star
crosses that line to within less than one
second. He uses the observation for
correcting the observatory clock, or
rather for determining how much it is
in error. For example, tonight the as
tronomer in Washington will observe
a certain star cross IT,, meridian at 10
hours ~ minutes 42.5 seconds, we will
say, according to his clock. From his
catalogue he will learn that the true
time of the stars transit is 10 hours 26
minutes 54.37 seconds. The observa-
tory clock will thus be found to be 4S.13
seconds fast. He will make a note of
the fact, which will enable him to-mor-
row at noon to set by telegraphic signal
all the clocks within his range of serv-
ice.
AS to the observatory clock, it will
not be disturbed. 1t may be gaining
slowly, for no clock yet made is abso-
lutely faultless, but it will be permitted
to run on. 1t serves its purpose so it is
not too far out of the way, and it's error
is checked regularly by the stars
Philadelphia Record.