Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1896-12-02
,rs DETERMINE THE TINE FOR THE WORLD

,Vt4rpr SCIENTISTS DETERMINE
o5 stars slightly over 200 in number which
are used for determining sidcral time
brings us to the transt-circle. the most
important instrument I'm the observatory
and one of the most interesting
II consists of a large telescope. the out
side of which is not mike great can
non as IL is of solid iron. This in,tru-
ment is supported by trunnions. when
allow the telescope 10 be elevated or ue-
pressed. to point north or south; and IN
fact 10 make "a complete revolution, but
never to diverge from the north ana
south line. The masnifying power OF
this instrument IS not very great but us
field Of view is large. so that u ADMITS
plenty Of light for IL is not INTENDED as
"a searcher after or for gazing al ceie9-
tial objects but for noting the exact time
at which stars and planets pass south
and north of Greenwich.
Upon looking through this telescope the
Observers eye is first arrested by veru-
cal row Of what seem 20 be iron bars
placod as equal distances from each
other. They are however, neither more
nor less than spiders webs. the centre
one. passing through the focus Of the
object glass being the meridian line.
BY observing the time at when the
o'clock stars" pars over these WEB llhes.
or wires" as they are called. Is sidetal
time regulated. The adjustment OF the
instrument has 20 be extremely exact IN
thing VIII put il out even so shidh "
matter az too much sunshine
ITS DELICATE ADJUSTMENT.
on one occasion the correction for a
level error i'm tine instrument having be-
come inconveniently large. owing. APP
parently to a subsistence Of the eastern
support. about ton weight of stone was
placed ON the western pier.
But this having no effect the stones
were removed. and a sheet Of very thin
paper was placed under the support on
the eastern side. by which means the
error was corrected. This VIII give SONIC
idea of the dolicacy OF adjustment ne
cessary for the perfect working oil TINS
ponderous instrument
The hands OF the sldereal clock are
said TO be al zero when the first point
Of the constellation Of Aries. or that
point where the ecliptic and equator
cross. is on the meridian. and, II the
clock does not vary In time its hands
viii indicate exactly the rate or the
diurnal motion Of the heavens Every
degree of the equator viii marx TOUR
minutes Of time. and every fifteen de-
grces will mark one hour, and so on IN
proportion with the twenty-four hours
ana ths $50 degrees Of the great circle.
An astronomical clock viii beat S54D
seconds in twenty-four hours, when
going TO it's utmost eXactitude; but as
no mechanism is absolutely perfect II
may be either a second under or second
over this number and II Is this variation
which the astronomer has TO discover
and allow for
All of the chronometers used In the
British navy ale first tested In the OBJ
seryatory. the testing lasting eight
months From January 10 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 It takes hrst-class
chronometer 20 Withstand this ordeal
Prior 10 1883 each country had us own
meridian Of time-FTance at Paris, the
United states at Washington, ana the
others AT their capitals. This led TO Sc
rious differences in navigation. and
compromise was effected by winch the
Greenwich meridian was settled upon
with uniform allowances for the distances
Of various countries
HORACE HOWELL