The morning news. [volume] (Savannah, Ga.) 1887-1900, 1895-02-17
FINDING THE EARTHs WEIGHT.
An English Professors Calculations
by Means of n Delicate Device.
From the London Granhic.

by Means of "A Delicate Device.
From the London Graphic.
When Newton set himself to md the law
by which an apple falls to the earth and
the planets revolve at varying speeds
along their orbits, he constructed a for
mula which would explain these phenom-
ena- He laid it down as a law that the
force with which the earth attracts the
apple or the apple the earth, or the plan
cts one another. is equal to the mass Of
the one multiplied by the mass Of the 9th
er' and divided by the square of the dis
lance between them-the whole multiplied
by constant called G. G is the Newton
ian constant Of gravitation. 1t is Of all
the constants the most important to physi-
cal science; it is constant for the more
accurate determination of which Prof.
Boys who lectured upon it recently at the
London Institute, has been willing to spend
hve years of the most arduous ana minute
observation. 1t is 100 years ago 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.
Cavedish improved upon MftchelTs OBJ
80 NotivAos 1oInu carried IL on. Prof.. Bows
has, so to speak, carried il two decimal
places further. Now let us consider how
IL would be possible to ascertain, by obser-
walton, the attraction which two bodies
nave for one another. If Prof. Bows were
TO hang couple of 50-pound lead balls
by two fbers, he would find it as impos-
slble TO measure the inclination of the two
hbers to one another as to weigh a sun
beam. But there is a possible wav of
measuring a
has made it more possible or let us say
more practical, by the employment of
quartz hbers to suspend some of the balls
ne 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, AZ inches in diameter, and
weighing each Is pounds.
Now suppose these four balls in their
first position suspended in one plane. The
two little gold balls are suspended by
quartz tbers on either side of a tiny OBJ
long mirror, to which they are attached
II any force were to pull one gold ball a
little way forward and at the same time
to pull the other little gold ball a little way
back, ii is obvious that a twist, an osciIIa-
ton, would be impaired to the tiny mir
ror. Now, so beautifully is this mirror
with its gold balls hung on it's tube that
force equal to the hundredth millionth
part of grain will set it swinging. With
this degree of sensitiveness attained, we
begin to get near some means of measur-
ing influences upon it. The influence we
can measure is that of the two lead balls
We imagined them to be, in the first in
stance, in the same perpendicular plane
as the little gold balls Suppose we move
them contempOraneously and co-equally,
so 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,
it is obvious then that the force exerted
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 it oscillating.
The instrument is delicate enough. Seat
ed 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. There
fore, knowing the force, the masses and
the distance between them, he can de-
termine the great constant c. and, know
ing G.. he can determine the specific crawl
ty of the earth, and, knowing 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 5.5270. Before his time we We're content
to regard it as So. He has taken five years
or more to establish beyond controversy
these other two decimals. People with a
taste for large figures may be inter-
ested to hear that. taking this as the basis,
the weight of the world may be taken as
:, SS2 900, 900 900, 900 600 600 tons.
That, as far as the present writer is con-
cerned, is the most lucid explanation
which can be given of Prof. Boys meth
DDS. But it has left untold the extraordi-
nary minuteness of the observations and
the sensitiveness of his Instruments The
instrument which contains the systems 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.
1t is boxed up in a. thick octagonal wooden
box. 1t is separated from the observer
by a series of felt curtains. He sits eighty
feet away and examines it's movements by
means of a telescope through Sits in the
felt curtains and in the wooden box, and
in the metal tubes holding the gold ball
system. The mirror reflects a nine-foot
scalt with 5000 divisions placed behind the
observers head. In order to avoid Great
ing currents of air. Prof. Boys has the
scale illuminated only by little travelling
lamp. In order to avoid tremors of the
earth he works at dead of night for a
train shunting a mile away will move
that tiny mirror; and once an earthquake
in Pennsylvania, on the other side of Eu-
rope, was marked by it. And then, as to
the measurements-the distance of the
lead balls from one another is calculated
by micrometer and microscope to the 3OOth
part of an inch, the distance of the gold
ball quartz fibers in the 10,000th part of an
inch, and force equal to the millionth of
a grain would be sufficient to send the
reflection of the mirror right off the
scale.
A GOOD DOG STORY.