The Washington times., 1920-01-04

was arranged IN such way rs 70 renect
tiny spot OF light upon the wall, forty feet
distant, It Is easily r1,-
seen that slight twist nm
ing Of the thread which
bore the mirror would
be shown by the move m
ment, greatly Increased III
by the distance, OF the
little spot Of light upon ~
the wall. ~ I'M
The Technology wv
scientists next fxsd \\N
two lead balls, weigh N1)
ing about ten pounds N1
each, upon a frame, SO n
!. !. ! :
that they were immov- ~
able. The frame was N &
placed about the hang WIU
ing balls In such way " WIK'
that each of the lead ~ Win
balls was brought close ~ NV i
to the freely swinging GvWNN
spheres. I EQl| wv
The lead balls, exercis- LuHJ
ing slight but definite Il>AlA
power of attraction over
the hanging brass ones,
moved them slightly, ,Dnsm ohows
almost lmpefcen'ioi'. Size of Atlas and
The supporting thread Earth from the
was twisted, ever SO lit, Knowledge of Mod,
tie. and the spot OF Scene t
light on the wan oppo' the Earth Are Abo,
site moved almost Equal to That of q
wards length as a re- Solid Ball of
suit.
Not a large force Indeed, when deli
cato ca,cu,ations mad estimated its power
II was round to be equal to the weight OF
an atom OF hair just one one-hundredth
1housandth of an inch long. But this
force slight as It was, had been sufficient
IN reveal the earth's weight. From this
mint II was a comparatively simple mat
ter Of mathematics.
The Technology professors knew the
weights Of the two sets OF balls; they
knew the amount of power which the iead
balls exercised over the brass; they knew
the power which the earth exercised over
tbe lead-that was their weight. Also
they knew that the gravitational attrac-
t,on Of one body over another depends di.
rect,v upon the comparative sizes Of the
bodies involved
What then, more simple than to cadcr-
late the earth's mass? II was simple
eonation. of which three parts already
we're known. The scientists calculated the
value of the fourth part and gained the
answer-6. .OO0, ,OOO, ,000, 900 900 ,0Q0,008 tons.
Over and over again the experiment was
tried. Outside influences, the vibration
caused by subway and surface trains, the
ouiveripg of the great Technology build
ing from its own mechanical laboratories,
affected the delicate mechanism some
what.
But when the experiment had been per-
formed n score Of times and the average
of them all was taken Professor Derr knew
that his result was approximately correct
A million tons one way or the other was a
small matter considering the huge figures
involved.
The earth is not the only planet from
which scientists have wrenched the secret
of weight. Other heavenly bodies have
been accurately weighed, through applica'
tion Of the same simple law OF gravitation.
For hundreds OF years 1t was known that
the orbits of the planets were irregular,
changing abruptly in many cases as the We
flying worlds came within the gravitational "
attraction of some other wanderer Of the ."'
skies. Astronomers, after years OF delicate "'''
observation and intricate calculation in
which they considered the forces required vel
to move these bodies from their paths, the
were able to give to the world the approx OF
mate weight of the sun, the moon and ate
few others Of the nearer heavenly bodies. dis
The distant stars alone have dehed the wa
scales Of science. Too far removed from the
us for the power Of attraction to be felt,
too vast to be affected by flying planets, to
their weight cannot be determined. we
Astronomers can tell US the size but not tin
the weight OF these stars. some Of which No
are blazing gases and some molten rock Inn
and metal
Cavendish, tho great English chemist ne,
and physicist, was the first 10 undertake TO oai