Evening star., 1947-12-01
Stars. Men and Atoms
Light Wave Length Held
UItimute in Meusurino
New Standard Declared So Precise
1t Finds Billionths of Meter
By Thomas r. Henry

Ii Flnds blllIOnths OF Meter
By Thomas r. Henry
new measuring rod of creation is proposed
by Bureau of Standards physicist.
1t is, says DR.. William j. Meggers, head OF
the bureaus spectroscopy section, the one unit
in the universe which can be measured with
the most extreme precision and which win
never change
This new unit is 4 wave length Of green
light emitted by q new synthetic mercury
which is made out of gold by atomic lombard
ment. Its length is precisely 5,46l Angstrom
units. An Angstrom unit is about . tenth OF
billionth of meter, which in turn is pre-
cisely 3937 inches.
Present Meter Stick Crude.
For all practical purposes the world stand
ard of length is the finely ruled international
meter stick kept in Paris, . precise duplicate
OF which is at the Bureau of Standards in
Washington. But this, standards experts say,
is only an artifact and q rather crude one.
At best it can be used for measurements of .
few millionths of an inch. insufficient for the
greatest precision required by science.
A wave length of light never changes in
length. From such standard it would be pos
sible to reconstruct all measuring devices on
earth If those now in existence were lost.
This has long been recognized. The standard
adopted to date has been . line Of red light
emitted by the element cadmium when it Ii
made luminous It has been the easiest to
work with, and from 1t several standard meters
have been constructed.
The difficulty has been to get samples of
cadmium all of whose atoms were of precisely
the same weight. The element has eight iso-
topes. Most of these are bound to be mixed
{,. ~n@ d. n~lw
minute variation in the light wave lengths
emitted by each OF them.
Made RED Line" Fuzzy.
t. The effect, DR.. Meggers explains, has been
to make the red line" = trine fuzzy. despite
the fact that 1t was selected because it was
the least fuzzy. Mercury has been impossible
in the past. The element has seven istopes,
the atoms of each of which are slightly differ
ent in weight. They are 50 mixed together
that all the wavelengths of visible light emitted
by luminous mercury are too fuzzy to be dis
tinguished sharply enough to qualify them AZ
ultimate standards of length.
The new mercury, all Of whose atoms have
the same mass, was produced ut the Univer-
sity OF California about two years ago. 1t was
a strange reversal Of the efforts of the alche-
mists of the Middle Ages who tried in vain to
turn mercury into gold. The reverse process,
DR.. Meggers believes, has produced something
of vastly more value to this generation.
Ultimate Standard Reached.
1t was recognized at the time that the new
form of the element which produced this line
Of green light might become = source Of the
ultimate length standard, and the Bureau of
Standards physicists have been at work on 1t
ever since they were able to obtain . sample.
"It is," says DR.. Meggers, "the best standard
In Nature"
The best measurement that can be obtained
with meter bar. he says, is from 10 to II
times the length Of = wave length Of light,
whereas now dimensions can be measured very
accurately in single wave lengths.