Evening star., 1948-11-19
Stars, Men and Atoms !
Ultimate Is Approached
In Precision Measuring

i'll IESSISIOII IVtSOSUt III4
Incomprehensible Accuracy Possible
Due to Oak Ridge Experiments
By Thomas X. Henry
The ultimate in precision measurement Ii
being approached at the United States Bureau
of Standards to within .O00, 900 ,000,.
0O0005 Of nillimeter.
millimeter is approximately twenty-fifth
OF an inch.
Such incomprehensble precision has been
made possible by use of the new standard
Of length-a green wave length Of light emitted
by q form of mercury made out of gold in
the Atomic Energy Commissions uranium pills
at Oak Ridge, Tenn.
Proposals to make this an oficial world
length standard now are being discussed before
a world weights and measures conference in
Paris
While accuracy of the above order already
has been reached under special circumstances
in the Bureau of Standards laboratory, the
official claim to date is for precision of meas
urement only tenth as great, which still Il
by far the finest ever achieved In the world.
Standard Since 1885,
Since 1889 the worlds standard of length has
been a meter bar made of a composition Of
platinum and iridium which Is kept at the
International Bureau of Weights and Meas.
ures In France. For more than a generation.
however, this has not afforded SUFFICIENT preci.
sion for many scientific purposes and use has
been made OF q red wave length of light
emitted by the element cadmium when heated
to q luminescent vapor. This made possible
however, only about half the accuracy now
possible.
The goal was single wave length of light
which could be distinguished easily This was
achieved only just before the war when an
1nvisibly minute amount of the new kind Of
mercury was made by transmutation from
gold in the cyclotron of the University of
California.
In 1942 the Bureau of Standards purchased
40 ounces of absolutely pure gold and arranged
with the University Of California to expose it to
neutron bombardment for one or two years,
IN the hope that 1t would be possible to secure
at least microscopic amounts of the new SUBJ
stance. The experiment was stopped by the
war and prospects looked discouraging when
late in the war, states bureau announcement,
there were rumors OF a secret source of neu.
irons thousands Of times more effective than
the largest cyclotron." The gold was trans
ferred from California to Tennessee, and with.
in year the bureau received 40 milligrams
OF the new mercury.
Process Remains Secret
The process of transmutation remains secret.
The Atomic Energy Commission now is at.
tempting to produce one or more grams year,
anticipating an eventual worldwide demand
for the material.
The meter unit, the present unit of length,
was created about 1870 to represent one ten
millionth Of the earth's quadrant In 1927
some natural philosophers meeting in Paris
agreed that the meter could not be reproduced
If the form of the earth were changed by COL
Ision with comet and proposed light wave
in a vacuum as natural unit of length in.
dependent Of the earths dimensions. Little
was done about it, however, until 1885, when .
meter bar was reconstructed using the red
wave length Of cadmium.
The new standard of measurement will make
possible the absolutely accurate reconstruction
of the meter at any time 1t also provides the
precision Of measurement essential in attempts
to determine the absolute speed of light and
reactions within the atomic nucleus,