Middletown transcript., 1899-07-22
HOW THE CLOCK IS SET
Old Sol No Longer Regarded as the
Worlds Timekeeper

Old Sol No Longer Regarded as the
Worlds Timekeeper
One Of the duties of astronomers is
to give us the correct time. Every day
at noon an electric signal is flashed
from the National Observatory at
Washington, or from some other OBJ
servatory to which this "time service"
has been assigned, to all the business
centres Of the country, and all clocks
and watches are set directly or indi-
rectly by this signal. This is matter
of common knowledge, but the way in
which the astronomer sets his own
clock is not known so generally.
Most persons have a vague notion
that our standard time is obtained from
observation of the sun. They have in
mind the old sun dial, which indicated
the hour of noon by mark that show
ed when the sun was on the meridian,
or, in other words, was exactly 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 SUMS meridian
passage takes place.
The truth is the sun has nothing
whatever to do or to say in this matter
of setting the clock. The sun is itself
one of the poorest of timekeepers. tt
is almost always either fast or slow,
sometimes to the extent of full quart,
or of an hour, and is fright on only
four days in the year. 1t is from the
stars, not from the sun, that the astro-
nomer 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
slackening their pace, which is only
another way of saying that the earth
turns on its axis at an unvarying rate
of speed. A star crosses the meridian,
and in % hours and 56 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 interval between two successive
passages. The times at which all of
the brighter stars cross the meridian
have been ascertained from long and
careful observation to within a small
fraction of second, and catalogues
have been prepared 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 q
meridian circle, q small telescope so
mounted on horizontal axis that it
can only point to the meridian. The
observer looking through this instru-
ment can tell the time at which the
star crosses that line to within, less
than one second. He uses the observa
tion for correcting the observatory
clock, or rather for determining how
much it is in error, For example. to-
night the astronomer in Washington
will observe a certain star cross the
meridian at 10 hours, 27 inmates, 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 observatory clock will
thus be found to be 4S.13 seconds fast.
He will make a note Of the fact,
which will enable him tomorrow at
noon to set by telegraphic signal all the
clocks within his range of service.
As to the observatory clock, it will
not be disturbed. It may be gaining
slowly or losing slowly, for no clock
yet made is absolutely fautless. but it
will be permitted to run on. 1t serves
its purpose, SO it is not too far out Of
the way, aud its error is checked regu.
larry by the stars.