The Irish standard., 1895-03-09

Otner. 1t FrOl. BOYS were 10 tldHS d.
couple Of 6fty-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 a possible way
of measuring the attraction, and Prof.
Boys has made it more possible-or, let
us say, more practically the employ
ment Of quartz 6bers to suspend some
of the balls he uses. He uses in all
four balls-two gold balls, a 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 were 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
it's gold balls, hung on it's tube, that
force equal to the hundred-milliont
part of a grain will set it swinging.
With this degree of constituencies 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
contemporaneously and coequaAy, 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 it's 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 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 it's 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
NAV be interested to hear that, taking
this as a basis, the weight Of the world
NAV be taken as 5,882, ZOO, 00O, 200, 000,-
GOO, 900 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-
tons and the sensitiveness 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 ii Oxford. There is too much
trernor Of the earth in London. It is
boxed up in thick octagonal wooden
box. It is separated from the observer
by q 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 ID the metal tubes
holding the gold ball system.
The mirror reflects q nine-foot scale
with 5, 900 divisions placed behind the
observers head. In order to avoid Gre
ating currents Of air, Prof. Boys has
the scale Illuminated only by little
travelling lamp. In order to avoid
tremors Of earth he works at dead Of
night, for train shnnting q mile away
will move that tiny mirror; and once
an ear thquake in Transylvania, on the
other side Of Europe, was marked by
1T And then as TO the measurements
HE distance of the lead balls from
one another Is calculated by micro
meter and microscope to the 300th part
81 an inch, the distance ftha gold ball
quartz hbers Is the Il, 000th part Of an
inch, and i force equal TO the mill ionth
81 8 grain would 10 sufficient to send
the reflection of the mirror right Oh Tho.
3scaie. } E5sa!