The Bennington evening banner. (Bennington, Vt.) 19??-1961, 1921-12-12
IS WORLDS TIME CENTER
Elaborate System by Which observa-
, tions Are Made at Greenwich, Eng
land, and Made Public.

: The astronomical, wind and rain In
Btrnments on the roof of the chrome
logical building at Greenwich, Eng.
make the scene an interesting one.
Here, In this building. is the time
center of the world. Time is usually
determined by watching the stars.
The stars are used for this purpose
becaase they are many and the sun Is
but one, Star transits can be taken
at various times throughout the day
and night, while the sun can be used
but once day.
This is how observations are made
at Greenwich: About two minutes
before the appointed time the operator
takes his place at the eye piece Of the
telescope. AS he looks he sees mum
Der of vertical lines. These are spider
threads placed In the focus of the eye
piece. Presently bright point Of sill
yer light comes moving quickly on
ward. The watchers hand now seeks
the side of the telescope until his fin.
ger finds little button, over which
II rests ready to strike. On comes the
star without haste, without rest" un-
I'll II reaches one OF the cleaning
threads, Tap! The finger falls sharp.
ly on the button. In three or four sec
onds 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 let us consider what the finger
taps have done. Each tap completed.
for an instant, an electric current and
recorded mark on the "chronometer."
This is large metal cylinder covered
with paper, and turned by carefully
regulated clock once 10 every two min
utes. A similar mark is made once In
every two seconds by a current sent by
means Of the standard sldereal clock
OF the observatory. II then one OF
the clock dots and one OF the observ-
er's dots come exacatly side by side,
II Is known at what precise second the
star was on one Of the wires, as the
spider threads are called. II the OBJ.
servers dot comes between two clock
dots, 1t Is easy, by measuring its dis.
tnnce from them with dividing scale,
to tell the instant the star was on the
wire TO the tenth part Of second.
Since the transit was taken over ten
wires and the distance OF each wire
from the center of the field OF view
is known, practically ten separate oh,
servatlons have been made, and the
average Of these gives the time OF
transit.
AT the observatory there is great
clock, called the sidereal clock, which
registers 81 hours In the precise time
that the earth rotates once on its
axis, or the time when a given star
would again appear on fixed meri.
dian. Hence, since the exact time is
known when the star ought to be on
the meridian, this clock can be readily
checked by the observations Of star
trausits.
BY this admirable method the error
Of the clock is determined twice a
day, shortly before 10 o'clock in the
morning and shortly before one o'clock
in the afternoon. These two times
are chosen because at 10 and 1 o'clocl;
signals are sent to all the great provln.
cl0l centers. Also at one o'clock the
time ball at Greenwich and at Deal
are dropped, so that the captains of
ships within sight of the dropping
mast may set their chronometers.
Thus is time found and regulated
at the great observatory,