The morning news. [volume] (Savannah, Ga.) 1887-1900, 1899-04-09
THE EARTH's ATTRACTION.
Lieut.. ROdIer Measures the Earth's
Pulling Power.

eAttSHe misfortune TO TAN from balloon
he would reach the earth much more
quickly if the balloon were near the North
Pole than If 1t were near the equator An
Austrian man-of-war, the Donar which
stopped at New York recently, is making
a tour of investigation for the purpose of
establishing the accuracy of this state
ment.. One of her officers. Lieut.. Rodler,
has been testing the force of the earth's
gravity at every point which the vessel
has touched, and the captain Of the Donar
has been ordered by his government TO
make several visits at various points sim
ply to give Lieut.. Rodcr an opportunity
to work his Instruments. While In New
York, Lieut.. Rodler experimental in a sub
basement of Columbia College His opera
tons were of much interest to the profess
sors of the institution. The United States
survey officials also thought enough of the
matter 10 send representative TO Column
bia with American Instruments to verify
the computations made by the Austrian.
The action of the United States survey
officials, however, was not meant to cast
doubt on the observations of Lieut.. Rod
Ter. Ii Is part of a great International graV-
is being carried out by the various govern
ments. II was made necessary by a pecu-
fiar existing condition. Although nearly
every one knows that the earth eXerts
strong force of gravity in all its parts,
yet 1t is not so well known that the force
is variable 1t grows much stronger as
either of the poles is approached. This is
because the earth is flattened slightly at
the North and South Poles The North
and the South Poles are much nearer the
exact center of the earth than is the equa-
tor. That is to say, the distance from the
exact center of the earth TO the surface
of the tropic zone is much greater than is
the distance from the center to the frigid
zone Now, as the attraction Of graVitation
grows stronger as the center of the earth
is approached It is plain that the force OF
gravity of the frgid zone must be strong
er than that of the tropic zone. The earth
as a whole exhibits this phenomenon, but
there are certain spots which seem to take
on an individuality of their own. These
spots affect testing instruments in such
way that the general law might seem to be
set at defiance, were it not that certain
local conditions serve as an explanation.
The determination of this varying force
of gravity is not accomplished. as might
be supposed, by dropping weight from a
height and noting the rate of its fan.
This might and indeed has been accom-
plished and chronograph records have been
obtained. But there is another method of
obtaining records which is much more
simple The trick is accomplished with
pendulum, the rate of the swing of which
enables the scientist to tell the exact force
of gravity existing at any particular point.
In short, the nearer the pendulum is taxi
en- towards the North or South Poles, the
faster il will swing, because the attraction
of the earth becomes greater.
All of the great scientific expeditions.
whether of exploration, lunar or solar
eclipse, North pole seeking or whatnot,
carry a pendulum apparatus Inasmuch
as the pendulum swings exactly In pro-
portion Of it's distance from the exact CEN
ter of the earth, the observer can COM
pute his distance away from the equator
or from the North pole, other conditions
being uniform Hence a small island near
Japan was found 20 be several thousand
yards nearer the equator than had been
supposed before the observation was made.
on the other hand, when the exact lau-
tude and longitude of a spot is known to
a certainty, any variation from the or
binary in the swing of the pendulum will
serve to indicate the character or tbs
composition of the earth directly beneath
the instrument 1t is a question of spe.
cific gravity.
Telling what Mountain Is Made Of
Two sides of mountain may affect thu.
pendulum differently. BY comparing the
swing on each side and the swing on top
of the mountain, the scientist can fell
very accurately of what material the
mountain is made One pseudo-scientist
has facetiously observed that a man LOST
in the woods, by dropping out of a tree
and observing the exact rate of his fall,
could determine his distance from the
equator
But very accurate calculations. not only
of geographical situation, but Of the
character of the surrounding country be-
meath the surface, may be made. Thus
the volcanic nature of some of the South
Sea islands has been determined by
pendulum Ascension Island, for instance
is really nothing more than a great cin-
der heap, which resulted from some vol
canic upheaval In the remote past It's
specific gravity was determined by the
pendulum and il Is known therefrom that
even to very remote depth its cinder-
like character is maintained. This YER
diet of the pendulum is further borne out
by the manner in which the island rocks
under the influence of the very peculiar
waves which sometimes roll upon Ascen
sion from the northwest These terrific
combers are periodic in appearance, ard
are often over Htty Ieet high. They fol-
low one another in rapid succession, ana
continue for several days and under their
influence Ascension Island rocks back ard
forth as though struck by earthquakes IN
a manner which Il could not do If made
of frmer material than cinders. The YER
dict of the pendulum is thus borne out
How Lieut.. ROdIer Worked.
The mechanics OF this pendulum swing
ing are highly interesting In the sub
cellar Of Columbia College, Lieut. Rodler
swung the pendulum and noted by means
of a chronograph and chronometer Just
how long, even to the slightest fraction of
a second, 1t required for the weight to
travel back and forth. In order TO be still
more accurate. DR.. Davis Of the astronom-
ical department made calculations OF the
transits Of certain stars, 80 that any de-
hclency Of the time calculations on the
earth might De in measure checked up
The pendulum itself was a small affair."
weighing but couple OF pounds. IL was
not more than ten inches In length. The
pendulum was hung from a T-shaped bar
The under side Of this r was ground down
20 knife edge. The edge rested on two
small pieces OF agate. Hence as the pen
"a