Evening star., 1899-04-10
Important Investigations That Are
Now Going On,
PENDULUM PLAYS PRINCIPAL PART
Would Move Faster at the Poles
Than at the Equator.
ACCURATE CALCULATIONS
Written for The Evening Star.

III a man had the extreme misfortune to
fail from a balloon he would reach the
earth much more quickly if the balloon
were near the north pole than if it were
near the equator. An Austrian man-of-
| war, the Donar which stopped at New
| York recently, is making tour of inves-
tigation for the purpose of establishing the
accuracy of this statement. 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 simply to give Lieut.. Rodler
an opportunity to work his instruments.
While in New York Lieut. Rodler expert
mented in subbasement of Columbia Col
lege. His operations were of much inter-
est to the professors of the institution. The
United States survey officials also thought
enough of the matter to send a representa-
tive to Columbia with American instru-
ments 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.. Roder.
1t is part of a great international gravity
survey which has been agreed upon and is
being carried out by the various govern
mentS. 1t was made necessary by a pecu-
liar existing condition. Although nearly
every cne knows that the earth cXerts
strong force of gravity in all it's parts, yet
it 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 equator. That is to
say, the distance from the exact center of
the earth to the surface of the trODic
zone is much greater than is the distance
from the center TO the frigid zone. Now, as
the attraction of gravtation grows stronger
as the center of the earth is approached,
it is plain that the force of gravity of the
| frigid zone must be stronger than that of
the tropic zone.
How the Work is Done.
The earth as a whole exhibits this phe-
nCmenon, but there are certain spots which
seem to take on an individuality of their
own These spots affect testing instru-
ments in such a way that the general law
| might seem to be set at defiance We're it
not that certain local conditions serve as an
explanation The determination of this
varying force of gravity is not accomplish
ed, might be supposed, by dropping q
weight from a height and noting the rate of
its fall This might and indeed has been
accomplished, and chronograph records
have been obtained. But there is another
method of obtaining records which is much
more simple. The trick is accomplished
with a 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
taken toward the north or south poles, the
faster it 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 whatnot.
| carry a pendulum apparatus. lnaSmuch as
| the pendulum swings exactly in proportion
| to it's distance from the exact center of the
| earth, the observer can compute his dis
| tance away from the equator or from the
| north pole, other conditions being uniform.
| Hence a small island near Japan was found
| to be several thousand yards nearer the
| equator than had been supposed before the
observation was made. On the other hand,
| when the exact latitude and longitude of
| spot is known to certainty, any variation
| from the ordinary in the swing of the
pendulum will serve to indicate the char
| acter or the composition of the earth di-
rectly beneath the instrument. 1t is queS-
! ton of specific gravity.
Studying Mountains.
| Two sides of a mountain may affect the
! pendulum differently. By comparing the
| swing on each side and the swing on top
of the mountain. the scientist can tell very
accurately Of what material the mountain
| is made. One pSeudo-scentiSt has face
| tiously observed that man lost in the
| woods, by dropping out of a tree and OBJ
| serving the exact rate of his fall, could de-
| termine his distance from the equator.
| But very accurate calculations not only
| of geographical situation but of the char
acter of the surrounding country beneath
| the surface, may be made. Thus the vol
canic nature of some Of the South Sea Is
| lands has been determined by pendulum
| Ascension Island, for instance. is really
| nothing more than great cinder heap
| which resulted from some volcanic up-
| heaval in the remote past Its specific
gravity determined by the pendulum,
| and it is known therefrom that even to a
| very remote depth its cinder-like character
| ic p1aip Mt cd of ln ,a,o1l
| lum is further borne out by the manner in
| which the island rocks under the influence
| of the very peculiar waves which sometimes
| roll upon Ascension from the northwest
| These terrific combers periodic in ap-
| pearance, and are often over 30 feet high
| They follow one another in rapid success
| sion, and continue for several days, and
| under their influence Ascension Island rocks
| back and forth as though struck by earth
! quakes in manner which it could not do
! if made of firmer material than cinders
| The verdict of the pendulum is thus borne
| out.
| Lieut.. ROdIer's Work.
The mechanics of this pendulum swing
| ing highly Interesting. In the subcel-
! lar of Columbia College, Lieut.. Rodler
| swung the pendulum and noted by means
| of a chronograph and a chronometer just
| how long. even to the slightest fraction of
| a second, it required for the weight to
| ns.vel back and forth. In order to be still
| more accurate, DR.. Davis of the astronGm-
| iCal department made calculations of the
! transits of certain stars, that any de-
| ficiency of the time calculations on the
| earth might be in measure checked up.
| The pendulum itself was Il small affair
| y eighing bur couple of pounds 1t was
| not more than ten inches in length. The
| pendulum was hung from T-shaped bar.
| The under side of this 7 ground down
| u a knife edge. The edge rested on two
| small pieces of agate. Hence as the pen
| du!um swung 1t encountered almost no
| friction and ii slight touch or impulse given
| to il was sufficient to set it going for a
| whole day. In the top of the pendulum bar
J was small square mirror. Near by was
placed candle and the pendulum