Evening star., 1935-04-25
CAPITAL BECOMES
GRAVITY CENTER
Dr.. HeyI Near Completion
of Work to Fix Abso-
lutte Value.
BY THOMAS r. HENRY.

BY THOMAS H. HENRY.
Washington is now the worlds cen
ter OF gravity"
DR.. Paul r. Heyl, physicist, Of
the Bureau of Standards. an
nounced to the American Geophysical
Union this morning that he is, within
a few days of completion of his six
years of labor to establish the abso-
lutte value Of the acceleration Of
gravity for the latitude and sea level
Of Washington.
His measurements, he said, are
about three times as precise as those
made at Potsdam. Germany, about
30 years ago. Those figures have been
accepted as giving the standard value
up to the present and upon them all
American instruments now are
standardized
DR.. Heyls determinations are accu-
rate to one part in million. 1t Is
probably impossible to make them
more accurate without development
Of new techniques and, he said today.
1t Is very unlikely that there will be
a sufficient accumulation OF these to
warrant a redetermination for at
least another generation. Until that
time, the accepted values of gravity
the world over will be determined by
the fused silica pendulum swinging
in DIR. HeyIs underground laboratory
at the Bureau of Standards and engi-
neers Of other nations will come here
to- check their instruments instead of
going to Germany.
Q NE~-
The Coast and Geodetic Survey sent
an officer to Germany about three
years ago to check its standard PEN
dulum against the Potsdam one
The difference brought about by
these six years of intensive work is
actually very small but of extreme
Importance because of the fundamental
significance OF gravity in surveying.
timekeeping. etc. where the accumula-
tion of small errors results in serious
ones.
DR.. Eeyl finds that a falling body
at Washington will fall toward the
center of the earth at a rate of
eS0.O87 centimeterS per second per
second-that is it will fall approximate
ly 80 feet the first second, "a feet the
next, and so on with the increasing
distance OF the fall. The final PotSdam
value, applied to Washington. is $50 100.
The difference in the two values is
approximately one part in 100000.
This means that the mass Of the earth
Is about one hundred-thousandth less
than has hitherto been calculated. In
another sense, the weight of everything
on the earth may be considered as re-
duced by that amount, since weight
and the pull of gravity on any object
are essentially the same.
Value Will Fit Any Place.
The Washington value can be trans
posed to fit any point on the surface
OF the earth by reference to tables
showing the gravity variation with
latitude and sea level. The value con-
sistently increases with latitude, being
greatest at the poles. 1t is least at the
equator, because there the surface of
the earth is farthest from the center
and because there the centrifugal force
due to the revolution of the earth Is
greatest. 1t also varies with sea level
being greater the nearer the surface
is to the earth's center. THUS con-
siderable variations have been found
in submarine measurements IN the
great depths of the sea.
Actually DR.. Heyl is close to COM
pletion of a 12-year job, that of de-
termining two fundamental values.
When he started work in his under
ground chamber at the Bureau of
Standards he spoke of reweighing the
earth. Weighing the earth depended
on the most precise possible determi-
nation of these values. The first was
the so-called constant Of gravity"
Gravity, according to the first defini-
ton. formulated by Sir Isaac Newton,
IL "the mutual action between masses
OF matter by which every mass tends
towards every other by a force vary
Ing directly as the product OF their
masses and inversely as the square of
their distance apart" Thus the at
traction of any mass in the universe
for any other mass equals the weight
Of the mass divided by the square OF
Its distance from the other mass.
good example was that OF Sir Isaac
and the apple. The mass of the ap-
pie was pulled downward by the mass
Of the earth. The apple, of course,
also was pulling the earth upwards at
the same time, but the difference be-
tween the upward pull and the down.
ward one was essentially that be-
tween the weight of the earth and the
weight of the apple. So the apple fell
and the earth did not rise.
Gravity Also Is Entity.
But there was one other element
essential to the equation-the So
called constant of gravity" Gravity
was not merely relationship between
two masses. 1t was an entity in it
self, always the same everywhere in
creation. The equation of the attrac-
ton of any object for any other OBJ
ject was actually the mass of that
object multiplied by the constant Of
gravity, divided by the square Of the
distance apart.
The redetermination of this con-
slant was the hardest part OF DR..
Heyl's work, in which he was as
sisted by DR.. G. S. Cook Of the Bu-
reau of Standards staff. DR.. Cook
also was his assistant in the deter
limitations of the pull of gravity.
Working year after year with finely
adjusted tortion balance, by which
the pull of the earth was measured
against that of another object of pre-