The Roanoke times. [volume] (Roanoke, Va.) 1890-1895, 1895-03-29
WEIGHT OF THE WORLD.
How It Is Calculated by an Eng
Gsh Professor.
Figures Which Arc BewiIdcring in Their
Immcnsity = Tho Scientific Gcntlo-
man Is Doubtless Safe from
Contradiction.

w ueH Newton SCI nlmScit to lind the
law by which an apple falls to the
Garth and the planets revolve ut 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 us law
that tho force with which the earth at
tracts the apple or tho 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 tho
square OF the distance between them
the whole multiplied by q constant
called G. G is the Newtonian constant
OF gravitation. 1t is of all the con-
stants the most important to physical
science; it is constant for the moro
accurate determination Of which Prof.
Boys, who lectured upon it 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 be 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 were to hang
couple of fifty-pound lead balls by two
fbers he would find it as impossible to
fibers to one another as to weigh
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 fibers to suspend some
! of the balls he uses. He uses in all
four balls-two gold balls, Il quarter of
an inch in diameter, weighing forty or
fifty grains, and two lead balls, four
and a half inches in diameter, and
weighing each sixteen pounds.
Now, suppose these four balls in
their first position suspended in one
plane. The two little gold balls are
suspended by quartz fbers on either
side of an oblong mirror, to which they
are attached. If any force We're to
pull one gold ball little way forward,
and at the same time to pull the other
little gold ball a little way back, it is
obvious that twist, an oscillation,
would be impaired TO the tiny mirror.
| Now so beautifully is this mirror, with
its gold balls, hung on its tube, that
! force equal to the hundred-millionth
part of grain will set it swinging.
| With this degree of scnSitiycncss at
tanned, 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 imagined
them to be, in the first instance, in the
same perpendicular plane as the little
| gold balls. Suppose we move them
contcmporaneously and cocqually, SO
that one lead ball moves in front of ono
| gold ball and the other lead ball moves,
exactly in the same way, behind the
other gold ball. If the hanging of tho
mirror and its gold balls is delicate
| enough it is obvious then that the force
exertcd by the attraction between the
| gold balls and the lead balls will give
the mirror to which the gold balls are
attached little twist and will set it
oscillating. The instrument is del
| 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 between
them, he can determine the great con-
slant G., and, knowing G, 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 be
5,527. Before this time we were con-
! tent to regard it as SIS. He has taken
five years or more to establish beyond
controversy these other two decimals.
People with taste for large figures
may be interested to hear that, taking
! this as basis, the weight of the world
may be taken as $3.50 1000, 900, 900, oOO,-
| 1000 tons.
That, as far as the present writer Is
| concerned, is the most lucid explana-
tion which can be given Of Prof. Boys
method. But it has left untold the eX-
| traordinary minuteness of the observa-
tions and the constituencies of his in
| struments. The instrument which con-
tains the system of gold and lead balls
| is put in the corner Of an underground
crypt in Oxford. There is too much
| tremor of the earth in London. It Is
boxed up in thick octagonal wooden
box. It is separated from the observer
by series of felt curtains. He sits
eighty feet away and examines its
movements by means of telescope
through Sits in the felt curtains and in
the wooden box, and in the metal tubes
holding the gold ball system.