St. Paul daily globe. [volume] (Saint Paul, Minn.) 1884-1896, 1895-02-12

! their first position, suspended in one
/ plane. The two little gold balls are
| suspended by quartz fbers on either
/ side of tiny oblong mirror to
which they are attached. If any force
were to pull one gold ball a lit
! tie way forward, and at the same
| time to pull the other little gold ball
a little way back, it is obvious that a
! twist, an oscillation, would be i'm
parted to the tiny mirror Now so
beautifully is this mirror with its gold
| balls hung on it's tube that a force
! equal to the hundred-millionth part of
a grain will set it swinging. Put a can
| die outside the tube where that tiny
mirror hangs and the movement of
J air which the candle flame causes will
set the mirror whirling. Nay, the
presence of Prof. Boys, seventy or
eighty yards away, observing it, or the
light which Eliminates his measur-
ing scale, will influence it. With this
degree of SenSitiveness attained, we
begin to get near some means of meas
uring 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 perpen-
dicular plane as the little gold balls
Suppose we move them contempora-
neously and co-equally, so that one
lead ball moves in front of one gold
ball, and the other lead ball moves lex
actly 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 be-
tween the gold balls and the lead balls
will CriUa the mirror n which
/ balls are attached a little twist, and
will set it oscillating. The instrument
is delicate 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 meas
ure 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 constant q,
and knowing G he can determine the
| specific gravity of the earth, and
! knowing the specific gravity of the
| earth he can find it's weight Prof
| Boys, after years of experiment
has found the specific gravity of
the earth to be 5.527 Before
! his time we were content to re-
gard it as 5.5. He has taken five years
or more to establish beyond contro-
versy these other two decimals. Peo-
pie with taste for large figures may be
! interested to hear that taking this as
the basis, the weight of the world
may be taken at 1852, 900, 900. coo. 900, :
| 100000 tons. Some people add 6,490O00-
! 600 of tons to this figure.
| That, as far as the present writer is
| concerned, is the most lucid eXplana-
| ton which can be- given of Prof.
! Boys methods. But it has left untold
| the extraordinary minuteness of the
| observations and the SensitiVeness of
| his instruments. The instrument which
contains the system of gold and lead
! balls is put in the corner of an I'M
foreground crypt in Oxford. There is
! too much tremor of the earth in Lon
/ don. 1t is boxed up in a thick octago-
nal wooden box. 1t is separated from
| the observer by a series of felt cur
tains. He sits eighty feet away and
! examines it's movements by means of a
| telescope through Sits in the felt cur
! tains and in the wooden box. and in
i the metal tube holding the gold ball
/ system. The mirror reflects a nine-foot
! scale with 5000 divisions placed be-
hind the Observers head. In order to
avoid creating currents of air, Prof.
Boys has the scale Illuminated only
by a 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;
I and once an earthquake in Transyl-
vania, on the other side of Europe, was
marked by it. And then as to the
neaSurementS-the distance of the lead
! balls from one another is calculated by
micrometer and microscope to the
300th part of an inch, the distance of
the gold ball quartz fibers in the
10000th part of an inch, and a force
equal to the millionth of a grain would
be sufficient to send the reflection of
the mirror right off the scale.