Kansas City daily journal., 1896-12-27
GREENWICH'S GREAT CLOCK.
THE CONSTANT CARE INVOLVED IN
OBTAINING THE CORRECT TIME.
Description of the Wonderful Instrus
ment Found In the Famous OBJ
servatory-Is Aided by
Great Stars.

From the n. 7. Commercial Advertiser
Twenty-one miles from London, in the
county of Kent. is the parliamentary bor-
ough of Greenwich. The census folk give
it population Of about 10000. but it has
none Of the bustlins activity OF an Ameri-
can city of the same size Yet II has Its
share of fame, but not as great a portion
as it should have, considering that 1t en-
tiers into the minute affairs OF every man,
woman and child In the civilized world
This is a pretty broad statement. but It il
the truth, as will speedily be shown.
Ask any resident of Greenwich TO point
out the most prominent feature OF the
town, and it is 10 to that he will Indicate
the historic Greenwich hospital. Ask him
about the second most important feature,
and IL he be particularly shrewd he may
say the Royal observatory. Locally, the
hospital is a thing of tremendous impor-
tance, while the observatory is seldom
thought of.
While much time is given to the study ot
the moon and other planets, the main
business OF the observatory is to secure the
correct time. To detail all of the labors
regarding the latter would be an endless
task. and a dry one to the reader. so mere
ly an outline will be given. The mean tina
standard clock, which gives the time OF
day TO the world. is connected by electric
action with the mean solar clock, and iS
further kept correct by calculation and
comparison with the standard sidereal
clock, whose error is determined by OBJ
servations of the stars. The sidereal clock
Is considered the most wonderful instru-
ment in the observatory. This marvellous
instrument Is in an underground room,
called the magnetic basement. where It
stands like a sentinel with its back against
the wall, ticking its seconds, as prescribed
by the CLOCK stars"
This reference to the "clock stars"-hxed
stars, slightly over 200 in number, which
are used for determining sidereal time
brings US to the transit circle, the most i'm
portant instrument in the observatory, and
one of the most interesting. It consists or
a large telescope, the outside of which Is
not unlike great cannon, as 1t is of solid
iron This instrument is supported by
trunnions. which allow the telescope to be
elevated or depressed to point north or
south, and, in fact, to make a complete
revolution, but never TO diverge from the
north and south line. The magnifying
power of this instrument is not very great,
but Its field of view is large. so that 1t
admits plenty of light. for 1t is not intend
ed as a searcher after or for gazing at
celestial objects, but for noting the exact
time at which stars and planets pass south
and north of Greenwich.
Upon looking through this telescope ths
Observers eye is first arrested by vertical
row of what seem to be iron bars, placed
at equal distances from each other. They
are, however, neither more nor less than
spiders webs, the center one passing
through the focus of the object glass being
the meridian line. By observing the time
at which the ''clock stars pass over these
web lines. or wires" as they are called, IS
sidereal time regulated. The adjustment OF
the instrument has to be extremely exace
in order to obviate error. The slightest
thing will put 1t out, even so small a mat
ter as too much sunshine. On one occasion
| the correction for a level error in the in
luty having hacOUna incOnVarlentIY
| large owing apparently to a subsidence OF
eastern support, about ton weight or
| stone was placed on the western pier.
But this having no effect, the stones werG
| removed and a sheet of very thin paper
was placed under the support on the east
| ern side by which means the error was
corrected. This will give some idea Of the
| delicacy Of adjustment necessary for the
| perfect working of this ponderous tnstru-
| ment.
The hands of the sidereal clock are SAID
| to be at zero when the first point OF the
/ constellation of Aries. or that point
where the ecliptc and equator cross. is on
| the meridian, and. II the clock does not vary
in time its hands will mark four minutes
| OF time, and every fifteen degrees VIII
mark one hour. and so on, In proportion
with the twenty-four hours and the $50 de-
grees of the great circle.
An astronomical clock will beat $500
seconds in twenty-four hours, when going
| to its utmost exactitude, but al no mechan-
ism is absolutely perfect, Il may be either
a second under or a second over this num-
| Der, and 1t is this variation which the as
| tronomer has to discover and allow for.
All of the chronometers used in the Brit
| ish navy are first tested IN the observatory,
| the test lasting eight months. From jan
uary to August are the best months for
| making the test. Those intended for use In
| the tropics are placed for weeks at time
| In ovens heated by gas, and II takes first
class chronometer to Withstand this ordeal
Prior to 1883 each country had its own
meridian of time-France at Paris. the
| United States at Washington. and the 9TH
ers at their capitals. This led to serious
differences In navigation, and compro-
| mise was effected by which the Greenwich
meridian was settled upon, with uniform
| allowances for the distances Of various
| countries.