Evening star. [volume] (Washington, D.C.) 1854-1972, 1936-12-16
NEW WEIGHT BASE
FOR EARTH FOUND
Six Years of Work on Gravity
Measurement Sets Figure
Lower.
nv THOMAS r. HENRY.


Finding of new absolute value Tor
the acceleration of gravity-and hence
q new basis for determining the
weight of the earth-waS announced
today at the Bureau of Standards.
The result was obtained by six
years Of work with delicate instru-
ments, mostly in an underground
vault, by DR.. Paul r. Heyl and DR..
G. 8. Cook. It shows that the speed
OF q falling body Is accelerated 980.08
centimeters per second as 1t drops
10 the earth-a value which Is lower
by two parts in 10000 than the hith-
erto accepted value obtained at Pots
dam, in Germany, 80 years ago.
= This indicates that the earth Is
considerably lighter than the weight
calculated in the past-but it is only
the second step in obtaining an &C
curate figure for the mass OF the
planet. DR.. Heyl, in a specially con-
structed circular hut in the woods
near Albemarle street and Connectl-
cut avenue, is about to start work on
the third step, which will require sew
eral years.
Everybody Weighs Less.
The result also indicates that the
weight of every person on earth is
trife less-approximately 10000, 0o0ths
less, which is far too minute a dill
ference for any scale-than it would
have been considered yesterday.
Gravity is the force of attraction
between two bodies, which varies dl-
rectly as their masses and inversely
as the square Of their distance apart.
Thus, if the weight of any object
Is accurately known, the weight OF
any other object could be deduced
from it by the attraction between the
two, If 1t could be measured. 1t is
the force which pulls all falling bodies
toward the earth. The falling body,
of course, also is pulling the whole
earth towards itself, but the relative
mass OF the earth is so enormous
that the contrary pull cannot be de-
tected.
Three Requisites.
In order to obtain an accurate
measure of the earth's weight, DR..
Heyl explains, it is necessary to know
three things to fit into the gravita-
tional attractions formula. First is
the actual radius of the earth. Sec
ond is the so-called Newtonian con-
slant of gravitation, which DR.. Heyl
refers to as big c. Third is the &C
celeration of gravity-his little g."
the determination of which he has
Just completed.
The earth's radius is known with
considerable precision. The second
value, postulated by Sir Isaac Newton
and first determined by the English
physicist Cavapdish about $50 years
ago, was predetermined by DR.. Heyl
himself a few years ago. 1t is ex-
tremely small-about 6.670 times 10
10 the minus 8 power. DIR. Hey1
at the conclusion of his work in 1880
found that Ii was slightly smaller than
the accepted value, and Immediately
started his measurement of small g."
Square Vault Discarded.
He was by no means satisfied, how
ever, with his value for the constant
of sravitation. First, the work was
carried on in square vault where
there was some variation in the dis
lance between the tortion balance
which he used and the walls The
new laboratory has circular walls, and
Is far enough removed from Con-
necticut avenue to be away from the
disturbing influence of automobiles
.d ht,ec ba Ho~
instrument of much greater precision
which, he believes, will make it pos
sible to carry the determination to
one more decimal point This rede-
termination will be the third step in
weighing the earth"
The earth weighs small g" divided
by big G" times its radius.
DR.. Heyl's work has been designated
as "the symphony in g minor and
the symphony in @ major"
The planet, on the basis of present
calculations, weighs approximately
5000, 900, ooO, o0o. 900 600, 900 tons.
Animal Life Negligible.
The mass is so great, Dr. Heyl says,
that If all the men and all the ami
mails on earth were suddenly trans
ported to the moon the loss in weight
would be so trif1ing that it would
be impossible to detect it with any
existing instruments.
The determination Of the gravity
constants, he stresses, has q much
more practical Importance. For ex-
ample. the small g" which he has
5ust determined enters into the cali
culation of some of the fundamental
constants of electricity. The house,