Evening star. [volume] (Washington, D.C.) 1854-1972, 1952-02-25
New Clock Misses Time
BY Second In 30 Million
Pendulum 10 the Vibration Of
One Atom Of Rare Element
BY Themes r, Henry

by Themes +, Henry
The hFst modal Of 0 "elock' Whlch
holds forth tho possibility Of meaauTlng
time with on accuracy Of one Aseend In
10000 10000, OF approximately 30
years, has been e0natFuCted At the
National Bureau Of Standards,
To pendulum u the vibration Of On
atom Of the rare element, CesiuFi,
Az present itA accuracy Ia one second
IN 10000 900, but q 60.fold increase In
this ID In sight and there Ia reason 70
believe even this can DO greatly In.
creased,
Probably tho most important event In
this history OF tlinekeeplng was the
construction at the Bureau Of Standards
OF the hrst atomic clock about two
years ago. This kept time with an
accuracy OF only one second In
100000. 10 pendulum was the vibfas
tlen Of On atom In the Fioieoule OF
gas, ammonia,
Before tho introduction OF this
ammonia eleek by Or, Harold Lyons Of
tho bureau stan and his associates tho
best standard OF time available was the
rotation OF the earth, checked by daily
observations, There was always the pose
ability OF ebseFVatienal errors. Also
this speed Ia not constant. Thus the
length OF each ~ hours varied by
fraction OF O second, u was Well.knewn,
besides, that the eaFth's speed OF Fetas
ton ID becoming progressively slower
because OF the tidal drag Of shallow
seas and several other reasons,
Besides Ito extreme accuracy, tho
ammonia clock provided for tho AFst
time q completely independent standard
of time which would remain essentially
constant forever, within the limits Of
any human measuring capacity. The
vibrations would DO going on OF precisely
the same rate even when the earth
ID not rotating,
But this was only start. Two other
models OF the same clock now have been
built. The second has an accuracy more
than twice % great % the flrst--on0
second In B0,000,000. This ID really an
unfair statement, DR.. Lyons says, and
leans over backwards In regard TO the
clocks real capacity. This 10 closer 10
one second In 100000. During this
period many errors will cancel out each
other
The third model ID designed % Q
"reaily working clock" which can DO used
especially In astronomical observatorles.
Plans are now under way by the British
government 10 build q clock based on
this model.
nut one second error In 100000. 900
seeonds--Df. Lyons and his associates
don't expect 10 do much better with fus
ture models OF the ammonia elock-le
altogether too great for some anticipated
future scientific requirements. In any
gas the molecules are In rapid motion.
They ore constantly humping into each
other and the cumulative effect OF this
probably results In q small random error.
u was recognized from the fifst that this
difficulty would DO avoided II the VibFAs
ton waves from the atom OF O pure eles
ment could DO used, The two most
favored were eesium and thaliiuEn.
There was little choice between them, A
thalliuM clock may DO constructed later.
One vibration frequency Of the 90.
SUM atom Is used-that which results
This Is far below the frequency OF light
waves. but considerably above that Of
radio waves, The beam can DO very
sharply focused. It can be used auto
matically to control the vibrations OF Q
crystal which In turn can be used to turn
the hands Of finely made conventional
clock.
Compared to the ammonia clock the
cesium time-keeper is cumbersome and
complicated but, the designers believe.
these difficulties may be overcome to Q
considerable extent with experience.
Preliminary calculations now are I'm.
der way for the construction Of an
oxygen clock which may keep time just
about as well as either cesium or thai
lium and will have all the advantages Of
a gas clock.