St. Tammany farmer. [volume] (Covington, La.) 1874-current, 1899-09-30

One Of the duties of astronomers Is 10
give ms the correct time. Every day 81
noon an electric signal is flashed from
the national observatory at Washing
ton. or from some other observatory to
which this ..time service" has been as
signed, to all the business centers OF
the country. and all clocks and watches
are set directly or indirectly BY this
signal. This il a matter OF common
knowledge, but the way in which ehe
astronomer sets his own clock - NOT
sksown so generally. - Fsa
Most persons have Vague notion
that our standard time is obtained
from observation of the sun. They have
in mind the old sun dial, which indi-
Gated the hour at noon BY a mark that
showed when the sun vas on The
meridian, or, in other words. was ex-
actly south, and their idea is that the
astronomer can fix the hour of noon
with greater precision because he has
the means of determining with greater
exactness the instant at which the suns
meridian passage takes place.
The truth is the sun has nothing
whatever to do or to say in this mat.
ter of setting the clock. The sun II it
self one Of the poorest of timekeepers.
1t. is almost always either fast Or slow,
sometimes to the extent Of full quar-
ter of an hour. and IS fright" Oh OILY
four days in the year. It Is from the
stars, not from the sun, that the a.
tronomer gets the time. s2-s,.ls !.
The stars perform their nightly
march through the heavenA As4m east
to west, with perfectly reeAat move
ment, never hastenisg and neysr slack
ening their pace. weh tsonly another
way oaNsaying. that the earth turns on
its axis at m uivarying rate of speed.
A star crosses the meridian, and in 3
hours and Sc minutes, about. it will
Iagain cross the meridian, and 1t will
cross this imaginary line in the heavens
again and again. day after day, year in
and year out, with always the same in
| terval between two successive passages.
| The times at which all of the brighter
stars cross the meridian have been As
certained from long and careful OBJ
servation to within a small fraction OF
q second, and catalogues have been pre-
pared in which these times Of meridian
passage or transit" are given.
The astronomer charged with the
duty of setting our clocks has. only to
observe the meridian passage of one OIL
| more of these stars in order to obtain
the exact time. The observation is
i r. - ~~-hn - BALLAD n
meridian circle, a. small telescope Sc
j mounted on a horizontal axis that II
can only point to the meridian. The OBJ
server looking through this instrument
can tell the time at which the stat
crosses that line to within less than ont
second. He uses the observation fol
correcting the observatory clock. OF
rather for determining how much it !!
in erprs N<e&emple, to 4iSlt me ~
tronomer m Washington Wflf observ,
a certain star cross the meridian ut II
hours 81 minutes i2.5 Seconds. we viii
say, according to his clock. From hi
catalogue he will learn that the tru'
time of the stars transit is 10 hours 2
minutes S4.37 seconds Tie 6bsersa
tory clock will thus be found to be 4S.1
seconds fast. He will make note o
the fact, which will enable him to-mor
, row at noon to set by telegraphic sigma
. all the clocks within his range of serv
. ice. -
As to the observatory clock. it viii
Enot be disturbed. 1t may be gaining
slowly. for no clock yet made is abso
lutely faultless, but it will be permitte,
to run on. 1t serves its purpose SO it i
. not too far out of the way, and its erro
!. Il checked regularly by the stars
/ Philadelphia Record.