The Columbian. [volume] (Bloomsburg, Pa.) 1866-1910, 1898-05-19
3here are two somewhat dif.erer

Uses in which the meridian OF Green
9ch Is che standard meridian of near.
9 fhe entire world. 1t constitutes thu
ndamental line whence distance.
Est and west are measured; and Il
8YslVes the time to the world.
1t will be interesting to note how
time is found.
The great telescope, already de.
scrlbed as occupying the center of the
transit room, is very solidly mounted
lts plVots are supported by the pair oI
great stone pillars. whose foundations
go deep down under the surface of the
hill; and 1t turns but in one plane
that Of Longitude Naught." On the
west side Of the telescope, and rigidly
connected with it, is a large wheel
with number Of wooden handles fas.
tened to it, like the steering-wheel O,
q large steamer. This wheel carries
the setting circle, which is engraved
on band of silver LEI into the face and
back OF the wheel Lear its circumfer.
ence. Eleven microscopes penetrate
through the pier, and are directed al
the circle on the vack of the wheel
These are the Instruments used in
finding time.
Time is usually a:ermined by the
watching of passing stars. The stars
are used for this purpose, because they
are many and the sun is but one. Ii
clouds hide the sun at noon, the only
time when 1t can be observed to de.
terEine time, a day is lost; but IL one
star Is covered by a cloud there are
still many others than can be oh.
served. Star translts can be taken a,
various times throughout the day and
night, while the sun can lie used onl,
once day.
About two minutes before the m.
pointed time the operator takes his
place at the eye-piece of the telescope
AS he looks in he sees a humber n,
vertical lines across his field of view
These are spider-threads placed in tbs
focus Of the eye-pierce. Presently a
bright point of silver light comes NOV.
ing quickly. steadily onward. This
watchers hand now seeks the side n,
sns te's.tcpe till HIS finger finds a little
button, over which 1t rests ready tc
strike. On comes the star "withoui
haste, without rest" till 1t reaches ona
of the cleaning threads. Tap! The
irser falls sharply on the button. In
three or four seconds later the star has
reached another thread. Tap! Again
the button is struck; and SO on until
the ten threads have been passed and
the transit Is over.
Now what Lave the finger taps donei
Each tap completed, for an instant, an
electric circuit and recorded a mark
on the "chGonometer." This Is o
large metal cylinder covered with pa.
per, and turned by carefully regu.
lated clock once in every two minutes
A similar mark is made once in every
two seconds by a current sent by
means of the standard siderial cloch
of the Observatory. II, then, one Of
the clock dots and one of the Observer
dots come exactly side by side, 1t 1,
known ct what precise second the sta,
was on one Of the wires, as the spider
threads are called. II the cbserv.
er's dot comes between two clock dots
1t is easy, by measuring its distance
from them with dividing scale, to tel
the instant the star was on the wire td
the tenth part of second. Since the
transit was taken over ten wires ane
the distance of each wire from the
center of the field of view is known
practically ten separate observations