Evening star. [volume] (Washington, D.C.) 1854-1972, 1927-07-31
1,(l)OTHOF SECOND
FOUND IMPORTANT
Standard Clocks, Never Set,
Found Slightly Wrong at
Each Test.
~ THOMAS II. HENRY.

Such an evanescent atom of time
fails to register on the Photographic
plate of the normal human conscious
ness as it crosses the hairline of the
present from the impenetrable future
into the equally impenetrable past.
Yet it is not altogether an imaginary
unit of duration. of consequence only
tn mvstics and philosophers. Much of
,~lNs:e@.l reality can happen in such
a fleeing instant. A wave of light,
or a radio wave, can travel nearly 200
miles. The earth, turning on it's axis,
moves almost an inch. An even
slighter diff renee means success or
failure for delicate scientific expert
mentS. Moreover, it represents about
a trillionth of Il human life. calculated
on the ,ihlical span Of three score and
teu.
Seek to Reduce Error
An accuracy closely approaching
ttIs i2ure is attained by the time sec
ten OF the United States Naval OBJ
serVatC"y, which furnishes the stand
ard by which the clocks and watches
of the Nation are set. One-thousandth
of a second is Il span of no incon-
siderable Importance to Paul Solien-
berger, associate astronomer, who is
in charge of this work, and the con-
stant effort of the observatory staff
is to reduce still further the probable
error inherent in the dclicacy of their
observations.
Absolutely correct time is unattain-
able, of course, by any mechanisms
available to human beings. But, year
after year, as instruments Of increas-
ing delicacy are cor: ucted. the
mystical borderline betw time and
timeleSSneSS, which never can be
crossed on earth. grows narrower.
The Naval Observatory scientists,
indeed. have a clock of almost abso.
Lutte accuracy upon which to check
their calculations-the face of the sky
studded with stars. All the stars, like
the sun which is one of them, move
across the sky from East to West. ris-
ing. reaching their high noon and set
ting This movement, of course, is
only apparent. The stars themselves,
for all practical purposes are motion
less with respect to the position of the
earth. but their positions change for
the human observer, due to the rapid
rotation of this planet.
Stars Change Little.
A selected star is due to pass over
the meridian of Washington-the
north and south line across the sky
directly above the Naval Observatory
at a definitely known instant From
year to year this changes very little
Some actual change of position, not
connected with the rotation of the
earth, has been observed among the
fixed stars, but it is too slight to be
taken into consideration in the cal
culations from day to day.
For the purpose of observing the
stars the Naval Observatory uses
Ill FOL L.
scopes. The 26-inch equatorial tele-
scope. which remained for many years
the largest in the world, has no place
in time observations. These transit
telescopes are mounted with great
ffgIdity and pivoted so that they can
be rotated from north to south but
not from east to west. Thus a star is
visible through such a glass only
When it is on the celestial meridian.
Stars are selected for observation
which cross this meridian near the
washington zenith-that is the point
directly overhead from which. If q
plumb line were dropped, it would
hit the telescope. The observers
nave a list of approximately $50
stars, different ones of which are used
as the star map changes from sea-
son to season. The observer operates
a mlcrometer apparatus which causes
interruptions in an electric circuit as
the star passes certain points in the
field. The exact time at which these
Interruptions should occur is known
In advance. They are recorded
graphically by an instrument known
as the chronograph on the same sheet
which records the ticks of a standard
clock, another important instrument
in keeping time for the United States.
Clock Never Right.
BY making measurements on this
sheet the exact times, according to
the clock, when the stars crossed the
meridian can be determined. If
they are at variance, as they always
are, with the known time when the |
stars actually did cross the difference
represents the inaccuracy of the
clock, because the star cannot be in
accurate. In making these calcula-
tons. however it is necessary to APP
ply several corrections fer possible
errors in the telescope and for other
reasons which involve higher mathe-
matics.
There are three standard clocks at
the observatory, maintained in an
underground vault under uniform
temperature and air pressure. These
clocks are set, in the first place, by
oNdA AaAliC. A1CiiiS uChlSCSJ
with friction to overcome, they do not
remain long absolutely accurate, al
though. of course. their errors are far
less than those of the finest watches.
But they are left undiSturbed and
never reset or interfered with in any
manner except when repairs are nee
eSsary. The necessary corrections
are made on paper.
Thus the observers are able to give
the correct time. within the allow
able error of three one -hundredths Of
a second. at any instant of the day.
The time shown by the standard clock
needs only TO be corrected by the
amount indicated by the last star OBJ
servation. A new correction figure Is
obtained every night. The observa
tions usually are taken just before
10 pm, when the time signals are
sent out from the Government radio
station ut Arlington, so that the Citi
zen actually is setting his watch just
before he goes TO bed by the very
latest reading Of the sky.
Clocks Usually Fast.
But the standard clocks lose or
gain very little in the course Of "a
hours. They are protected from many
az 10 ills TO which ordinary time
pIccC3 are heir. Their pendulums, for
example. are of invar, an alloy OF
nickel and steel which does not change
in length because Of temperature va
riations. They also have Il rather uE
usual form of escapement, or clock
motive mechanism, in which nothing
touches the pendulum rod directly, the
driving impulse being impaired
through the pendulum suspension
springs These clocks, however, gen
orally tend to run faster as Time
passes, During the first year after
cleaning their daily rates are apt TO
increase by as much as a hundrcdth
Of a second a month, after which they
run with a more constant rate. The
IL l. --A.-