New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1900-04-29
HOW THE EARTH WABBLES.
EFFORTS OF PROFESSOR REEFS AND OTHERS TO
MEASURE THE MOVEMENT

MEASURE THE MOVEMENT.
There several popular misapprehensions
regarding the relations existing between the
North Pole of the earth and that point in the
sky which may be designated by a similar name.
In the first place. 1t is not true that the Pole
Star is situated exactly at the pole of the
heavens. 1t is d trife to side. and revolves
around the true pole. Hence, when a surveyor
wishes to ascertain the extent to which his
magnetic needle deViates from true north he
must compare the Indications of that instru-
ment with the position of the Pole Star only at
a particular minute of a given day.
1t is also a mistake to suppose that the
North Pole of the earth continues to point faith
fully to the pole of the heavens 1t does not.
1t wabbes around appreciably. To be sure, the
amount of this variation, though constantly
changing in degree, is never great. In fact,
when one considers that the globe has a diam
eter of about eight thousand miles and a cir
conference of nearly twenty-five thousand. one
may well wonder at the skill which has enabled
the astronomers to detect this curious perform
ance at al. However, the general fact has been
well established within the last few years A
number of astronomers engaged in
measuring the extent and time of the oscilla-
ton, and diagram which was to be seen at
the exhibition of the New-York Academy of
of one laborious and beautiful investigation of
this kind.
For a period of nearly seven years-from early
In 1893 to the close of 1S99-Professor j. X Rees
of Columbia University, and two of his asso-
ciates-Messrs. JacOby and Davis-carried on a
series of observations to determine the ''varia-
ton of latitude" of this city. 1t is easy to I'M
derstand that if the North Pole of the earth
shifts its aim TO any rema rkable degree the po-
sitlon of a star seen i'll our latitude would seem
to change in elevation above the southern hori-
zon from time to time. And even though the
wabbling of the terrestrial axis be small the
change in the apparent position of the stars
must correspond precisely. Hence an astrono-
mer who was studying this problem would
fully observe few stars when they passed the
meridian every night for a number of successive
nights, and try to perceive to what degree if at
all, they crossed that line higher up or lower
down than at other times. This is what Pro
fessor Rees and his assistants did
An effort made to secure four observations
each half month. OF course as the season changed
new stars would come into eligible position
and the ones first studied would disappear. Dur
ing year fifty-eight different stars used
for this work, and the observation always in
cluded pair of stars. During the seven years
covered by the Columbia University research no
less than 6,j1S measurements of pairs were
made. OF these Professor Rees conducted over
one-half. 500 Messrs Davis and Jacobv are
credited with the others While this work was
in progress Columbia moved from it's old site to
a new one This change did not vitiate the re-
suits obtained, because a careful survey was
made to determine the exact amount of differ
epce in latitude between the two sites, and
proper allowance was made in the subsequent
calculations.
To form just idea of the delicacy of such a
task this few figures necessary. The
complete circle of the heavens through the
North and South poles includes 360 degrees each
made up of 800 seconds of are There are
129 600 seconds of are. then, to start with. one
of these is very small angle to measure. But
the Columbia observers were not satisfied with
any such rough calculation this. They
sought to detect differences in the elevation of
the stars above the southern horizon of a hun
dredth part of a second. or Of a thirteen mill