The Cambria freeman. [volume] (Ebensburg, Pa.) 1867-1938, 1895-05-03
WEIGHT OF THE WORLD.
How It Is Calculated by an Eng
liSh Professor.
ImmensIty The Scientific Gentle
man Is Doubtless safe from
Contradiction

When Newton set himself to find the
law by which an apple falls to the
earth and the planets revolve at vary
ing speeds along their orbits he con-
structed formula which would ex-
plain these phenomena, says the Lon
don Graphic. He laid it down as a law
that the force with which the earth at
tracts the apple or the apple the earth,
or the planets one another, is equal to
the mass of the one multiplied by the
mass of the other. and divided by the
square of the distance between them
the whole multiplied by constant
called &. q is the Newtonian constant
of gravitation. 1t is of all the con-
stants the most important to physical
science; 1t Is Il constant for the more
accurate determination of which Prof
Boys, who lectured upon ii recently at
the London institute, has been willing
to spend five years of the most arduous
and minute observation. 1t Is one hun
dred years since Rev. Mr.. Mitchell first
devised an instrument by which it
would bc possible To obtain, by actual
observation. the attraction which two
bodies have for one another.
Cavendish improved upon Mitchell's
observations, Cornu carried it on. Prof.
Boys has. so to speak, carried it two
decimal places further. Now let us
consider how it would be possible to as
certain, by observation, the attraction
which two bodies have for one an
other. If Prof. Boys We're to hang
couple of fifty-pound lead balls by two
fbers he would find it as impossible To
measure the inclination of the two
fibers to one another as to weigh "a
sunbeam. But there is possible way
of measuring the attraction. and Prof
Boys has made it more poSsible-or, let
us say, more practical-by the employ
ment of quartz tibers to suspend some
of the balls he uses. He uses in all
four ballS-two gold balls, quarter OF
an inch in diameter, weighing forty or
fifty grains. and two lead balls. four
and n half inches in diameter, and
weighing each sixteen bounds.
Now, suppose these four balls in
their first position suspended in one
f.Ianc. The two little gold balls are
suspended by quartz tibers on either
side of an oblong mirror, to which they
are attached. If any force were to
pun one gold ball little way forward,
and At the same time to pull the other
little gold ball a little way back, il is
obvious that twist, an oscillation,
would Toe impaired to the tiny mirror
Now 50 beautifully is this mirror, with
its gold balls, hung ON its tube, that
force equal to the hundrcd-millionth
part of q grain will set it swinging.
with this degree of sensitivencSs at
tained, we begin To get near some
means of measuring influences upon it.
The influence we can measure Is that
of the two lead balls. We lima gined
them to be, in the first instance, i'll the
same perpendicular plane the little
gold balls. Suppose we move them
contemporaneously and coequally, 50
that one lead ball moves in front of one
gold ball and the other lead ball moves,
exactly in the same way. behind the
other gold ball. If the hanging of the
mirror and its gold balls is delicate
enough il i obvious then that the force
eXcrted by the attraction between the
gold balls and the lead balls will give
the mirror To which the gold balls are
attached a little twist and will set ii
oscillating. The instrument Is eel
icate enough.
Seated eighty feet away the observer
can time it He therefore can measure
the force which the lead balls and the
gold balls exert upon one another; he
can measure the distance which the
balls are apart; he can measure the
balls. Therefore, knowing the force,
the masses and the distance betwee-
them. he can determine the great con
stant G.. and. knowing &, he can deter
mine the specific gravity of the earth:
he can find its weight. Prof. Boys.
after years of experiment has found
the specific gravity of the earth To toe
5.521. Before this time we We're con-
tent to regard it as 5.5. He has taken
five years or more To- establish beyond
controversy these other two decimalS.
People with a taste for large figures
may be interested to hear that, taking
this as basis. the weight of the world
may bc taken as 5,SS2, 900, ,O0O, 900, ,OOO,-
OOO. 900 tons.
That. as far as the present writer is
concerned, is the most lucid eXplana-
tion which can lac given of Prof. Boys
method. But it has left untold the eX-
traordinary minuteneSS of the ObScrva
tionS and the senSitivencSs of mis- in
strumentS. The instrument which con
tainS the system of gold and lead balls
is put in the corner of an underground
,rvpt in oxford. There is too much
trcmor of the earth in London. 1t Is
boxed up in thick octagonal wooden
box 1t is separated from the observer
by a series of felt curtains. He sits
eighty feet away and examines Its
movements by means of a telescope
through Sits in the felt curtains and il
the wooden box, and in the metal tubes
holding the gold ball system.
The mirror reflects nine-foot scale
with 1000 div' Sions placed behind tn,
observers head. In order to avoid ere
ating currents of air, Prof. Boys ha:
the scale Illuminated only by little
travelling lamp. In order to avoic
trcmorS of earth he works at dead %
night. for Il train shunting mile away
will move that tiny mirror; and once
an earthquake in Pennsylvania, on the
other side of Europe, was marked 10y
it. And then as to the measurement:
the distance of the lead balls from
one another is calculated by micro
meter and microscope to the 30Oth par
of an inch. the distance of the gold bal
quartz fibers in the 10, ,O0Oth part of al
inch. and a force equal to the milliontl
of a grain would be sufficient to senC
the reflection of the mirror right off th'
scale.