Evening star., 1951-01-17
5 BiIIionth Of Ounce
Weight Precision Found
Bureau Of Standards Reports
On Tests With New Method
By Thomos R. Henry

By Thomos R. Henry
Objects now can be weighed with q
precision Of about 5 billiontk of an
ounce by United States Bureau Of
Standards physicists.
This represents Is to 20 times
greater accuracy than has been possible
In the past. It is q notable accomplish
ment at the outset Of the atomic age,
where it is necessary to obtain with ex-
treme accuracy the weights Of invisibly
minute bits Of matter. representing some
Of the rarer radioactive isotopes.
The newly developed methods, In
which results are obtained by observing
q finely divided scale with q telescope,
allow an accuracy, says q Bureau an
nouncement, within one or two tenth
millionths of gram" They make pos
sible the weighing Of sample about
one-tenth the mass Of that possible
before. In the field Of radioactive
isotopes the new system makes it pos
sible to handle smaller samples with
greater safety and to obtain small
samples at less cost Of time and labor.
Remote Control Weighings.
For most purposes. however, the
bureau contents itself with an accuracy
of about millionth of an ounce, ac-
complished by balancing the object to
be weighed, usually another standard
weight, against the national standard
of mass-a platinum iridium cylinder
having mass Of almost precisely one
kilogram. 1t is kept in a special, air
conditioned underground vault at the
bureau. It never is touched by human
hands and weighings are always by re-
mote control. Each weight opera
ton requires accurate determination Of
barometric pressure in the vault and
the degree to which the object being
weighed is buoyed up by the air.
Many determinations are made before
the final value is determined and mathe-
matical procedures are essential. This
was good enough for all ordinary
purposes for which objects might have
been weighed in the past but becomes
quite crude in the realm of the
infinitesimally minute. the inside Of
the nucleus OF the atom, an under
standing of which is essential to the
scientific progress Of the future.
The most titanic mathematical Job
in history now Is nearing its conclusion
fixing the precise positions of the five
outer planets Of the solar system at any
second during the next century.
1t has been cooperative job of the
United States Naval Observatory and
Yale University under the sponsorship of
the Office Of Naval Research.
The five outer planets are Jupiter,
Saturn, Uranus, Neptune and Pluto.
The mass Of the other four, including
the earth, is insignificant compared to
them. They are pulling each other with
enormous gravitational forces. They are
pulling the sun and the sun Is pulling
them. 1t is essential to know their
positions with very great accuracy for
purposes OF navigation. Small errors
soon accumulate into big ones which
throw navigational calculations badly
out Of gear.
Tables Getting Out Of Date.
About so years ago a Naval Observa-
tory astronomer worked out formula
by which the position Of Saturn always
could be calculated with reasonable
accuracy. This formula was 30 compli-
Gated that 1t filed seven large pages
printed In small type. Then tables were
worked out for applying the formula
They filed "a similar pages This is
cited by DR.. @. M. Clemence Of the
Naval Observatory and Prof. Dirk
Brewer Of Yale University as an example
OF the enormous complications involved.
Even at that, the tables rapidly are get
ting out Of date.
The new job was possible only by
the use Of one Of the latest model
electronic calculating machines, tho
selective sequence electronic calculator.
which In an hour will accomplish a.
much as man with an ordinary elec-
trio desk calculator in 1000 hours.
Also it Is far less likely to make mis-
takes than a human calculator.
The calculated positions will be
checked regularly by Naval Observatory
observations. The work will make pos
sible a close check on gravity and rela-
tivity. It also will make possible the
determination Of other forces working
to influence the motions of the planets
within the solar system. It is known,
for example, that the vast spaces be-
tween the planets are not entirely
empty. They are filled with matter Of
some sort, very finely diffused. It Is
expected that the astronomers will be
able to determine whether this is thick
enough to retard the progress of the
planets In their revolutions around the
sun.
Questions and Answers
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