The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1896-12-26

| dome, and Its four wings adjusted TO the
four points of the compass.
The first thing that strikes the visitor
on entering the gate is the humble aspect
of this temple of science What he sees
gives no evidence of the uses to which
the buildings are put, except what may be
gathered from the Sits covered by shut
tiers, which in two places intersect them,
and the domes that flank them at then
eastern and southwestern extremities.
Indeed, the whole place has a domestic
rather than a scientific look, and this air Of
domesticity is not greatly-if at all-de-
tracted from by the "business' look Of
the time-ball turret in the corner of the
inclosure to the left, adjoining the As
tronomer Royals residence, with its rooms
all on the ground floor.
While much time is given to the study
of the moon and the other planets, the
main business of the observatory is to Sc
cure the correct time. To detail all of the
labors regarding the latter would be an
endless task and dry one to the reader,
SO merely an outline will be given. The
mean time standard clock, which gives the
time of the day to the world, is connected
by electric action with the mean solar
clock, and is further kept correct by cal
culation and comparison with the standard
solar clock, whose error is determined by
observations of the stars.
The sidereal clock is considered the most
| 4 Il.
This marvellous instrument is in an under
ground room, called the magnetic base
ment, where it stands like sentinel with
its back against the wall, ticking its sec
onds as prescribed by the o'clock stars.
This reference to the ''cloek stars =
fixed stars, slightly over two hundred in
number, which are used for determining
sidereal time-brings us to the transit
circle, the most important instrument in
the observatory, and one of the most in
teresting.
1t consists of large telescope, the out
side of which is not unlike a great can
non, as it is of solid iron This instru-
ment is supported by trunnions, which al
low the telescope to be elevated or de-
pressed, to point north or south, and, in
fact, to make complete revolution, but
never to diverse from the north and south
line The magnifying power of this in
strument is not very great, but its field of
view is large, so that it admits plenty of
light, for it is not intended 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 Green
wich.
Upon looking through this telescope the
observers eye is first arrested by verti-
cal row of what seem to be iron bars placed
at equal distance 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.
BIZ observing the time at which the
o'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 exact in
order to obviate error. The slightest thing
will put it out, even so small a matter as
too much sunshine
On one occasion the correction for a
level error in the instrument having be-
come inconveniently large, owing appar-
emily to a subsidence of the eastern sup
port, 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 will give some idea
of the delicacy of adjustment necessary for
the perfect working of this ponderous in
strument. q
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 ecliptic and equator cross, is on the
meridian, and if the clock does not vary
in time, its hands will indicate exactly the
rate of the diurnal motion of the heavens.
Every degree of the equator will mark
four minutes of time, and every fifteen de-
grees will mark one hour, and so on, in
proportion with the twenty four hours and
the three hundred and sixty degrees of
the great circle.
An astronomical clock will beat So, 400
seconds in twenty -four hours, when going
to its utmost exactitude; but as no mechan-
ism is absolutely perfect, it may be
either second under or a second over this
number, and it is this variation which the
astronomer has to discover and allow for.
All of the chronometers used in the
British navy are first tested in the OBJ
servatory, the test lasting eight months.
From January to August are the best
months for making the test. Those in
tended for use in the tropics are placed
for weeks at a time in ovens heated by
gas, and it takes frst-class chronometer
to withstand this ordeal.
Prior to 1888 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.