Evening star., 1942-10-03
Of Stars, Men i
And Atoms
Notebook Of Science Progress
In Laboratory, Field
And Study
By Thomas r. Henry.

By Thomas r. Henry.
An invisibly minute speck of greenish-
yellow gas, made by transmitting gold
into mercury, may become the immutable
basis of all measurements on earth.
United States Bureau of Standards
physicists, aided by the gigantic atom
smashing cyclotron at the University of
California, now are at work on this gas
inch" with high hopes that it will be-
come the universal standard of meas
urement.
If they succeed-and all that stands in
the way Of success is obtaining enough
OF the peculiar form of mercury neces-
sary-they will have established the
meter forever, safe from all cataclysms
OF man or nature.
The practical standard of measure
ment, up to two years ago, was a plat
mum iridium bar exactly one meter long,
kept in vault at the International Bu-
reau of Weights and Measures in Paris.
There, every few years, all the civilized
nations used to send their own stand
ards of measurements for comparison
under the most exacting conditions. The
best meter sticks-or yard, foot or inch
stlcks-varled from year to year a few
fractions of millionth part due to wear,
expansion, etc. So, probably, did the bar
at Paris, but there was international
agreement that it should constitute the
final judgment from which there could
be no appeal.
so every measurement of length and
derivatively of weight and time on earth
has depended ultimately on the Paris
bar. Governments always have worried
lest something happen to it, and now it
may wantonly have been destroyed by
the Germans in favor of a pure Aryan
inch, or something of the sort.
There has been long search for some
thing in nature whose length never
changes, which is easily available and
measurable, from which the bar could
be reconstructed exactly as it was before,
There Is only one thing which satisfies
this requirements wave-length of light.
Each OF the 90 elements, when made
luminous, emit light composed of a series
OF wave-lengths ranging from extreme
red to extreme violet. There is never
any duplication. Iron, for example,
when it is heated until it becomes a gas.
gives out light made up of a few hun
dred wave-lengths and whenever one of
these is detected, even in the farthest
star, it is indisputable evidence that
iron Is present.
But Wave-lengths are messy" They
are so close together that they get mixed
up. They vary with pressure and
temperature. 1t was essential to find
one that was sharp, easily observed,
and not much affected by external con-
dltions. About 20 years ago the late DR..
Albert A. Nicholson of the University of
Chicago, after an extensive search. hit
upon a single wave-length of red light
from the heavy element cadium as the
most practical.
1t was exactly 6438 1896 angstrom units
in length. An angstrom unit is a bill
lionth of millimeter. A thousand mil
llmeters make meter. From the meter
can be derived the yard, the inch or any
other length measure.
So ever since 6438 1896 angstrom units
has been the worlds unofficial standard
of length from which it was planned to
rebuild the standard meter stick if it
should be destroyed, and otherwise to
correct it every few years. Actually, Bu-
reau of Standards physicists have re-
constructed the meter from this stand
ard.
But this unit never has been entirely
satisfactory. 1t is apt to get messed up
with other wave-lengths and it is not
seen as clearly as might be by the eye.
A few years ago DR.. William F. Meggers
of the Bureau of Standards recognized
that one of the lines of greenish-yellow
light emitted by the element mercury in
gaseous form would be ideal.
1t came, however, only from one
rare form of mercury which could not
be separated by any known means from
several other forms with which it oc-
CURED in combination. Now, it is found
that when pure gold is bombarded with
slow neutrons an incredibly minute
amount of it is changed into this one
type of mercury-and this one type only
To get enough of the element to be
OF any use 20 ounces of gold now are
being bombarded constantly with slow
neutrons in the University of California
cyclotron. This will be kept up for six
months. Even then it is not expected
that enough will be obtained to be more
than barely visible to the naked eye. But
even that will be enough to constitute a
permanent standard of length for the
world and will make possible a meter
stick with at least 100000 subdivisions
Offers Correction of Definitions
OF Diplomatic Agents.
To the Editor of The Star: