The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1899-09-27

ones, caused by an actual motion of the
observer on the earth. The observer
turns with the earth on its axis, and is
thus carried past the sun and stars.
These, then, seem to rise. pass over the
observer and set again, much as houses
and fields seem in motion to d person
seated in a fast railroad train.
This daily turning of the earth,
then, takes place about the axis of ro-
tation. Now, it so happens that all
kinds of astronomical observations for
the determination of latitude lead to
values based on the rotation axis of
the earth, and not on its axis of figure.
We have seen how the earth's equator,
from which we count our ATTITUDES, is
everywhere ninety degrees distant from
the pole. But this pole is the pole of
rotation, or the point at, which the ro
tation pierces the earth'S surface. 1t is
not the pole of figure. Now, it is clear
that the latitude of any observatory
will remain constant if only the pole
of figure and the rotation pole MAIN
tain absolutely the same positions rela-
lively one to the other. These two
poles are actually very near together,
their distance apart being as small as
fifty feet. Indeed, it was supposed for
a very long time that they were abso-
lutely coincfdent. so that there could
not be any variations of latitude. But
it now appears that they are separated
slightly. And, strange to say, one of
them is revolving about the other in a
little curve. The pole of figure is trav
cling around the pole of rotation. The
distance between them varies a little,
never becoming greater than about,
fifty feet, and it takes about fourteen
months to complete a revolution. There.
are some Slight irregularities in the
notion but, in the main, ii takes place,
in the manner here stated. In conse-
quence of this rotation of the one pole
about the other, the pole of figure is
now on one side of the rotation pole
and now on the opposite side, but it
never travels continuously in one direc-
ton. Thus. as we have seen already,
the sort of continuous motion required
to explain the observed geological pIle-
nomena has not yet been found by as
tronomers.
Observations for the study of 1ati-.
tude variations have been made very
extensively within recent years both
in Europe and the United States 1t has.
been found practically most advan
tageouS to carry out simultaneous SER
les of observations al two obseryatories
situated in widely different parts of the
earth, but having very nearly the same
latitude. It is then possible TO, employ
the same stars for observation in both
places. whereas it would be necessary
to use different sets of stars if there
We're much difference in the ATTITUDES.
Now, the advantage of using just the
same stars in both places is quite Pc
culiar. 1t makes possible the determi-
nation OF the small difference in Iati-
tude between the two participating OBJ
selvatories in a manner which will
make it quite free from any uncer-
tainty in CUR knowledge of the posi-
tions on the sky of the stars observed.
For, strange as it may seem, our star
catalogues do not give us absolutely ac-
curate results. Like all other data de-
pending on fallible human observation,
they are affected with small errors.
But if we can determine simply the
difference in latitude of the two obser-
vatories we can discover from@its var
iation the path in. which the pole is
moving. If, for instance, the obserYa-s
tories are separated by one-quarter of
the circumference of the globe, the
pole will. be moving directly toward
one of them, when 1t is not changing its
distance from the other one at all. This
method has been in use for the last six
years with good effect at the observa-
tories of Columbia university in New
York and the Royal observatory at
Naples Italy For obtaining its most.
complete advantages, it would be bet
ter to establish four observing stations
on about the same parallel of latitude.
This isto be done soon by the Interna-
tional Geodetic association. Two of the
stations will be in the United States.
one in Japan and one in Sicily. If
they are all put in successful operation
we can hope confidently that our
knowledge as to more than one puz-
cling problem will soon receive very
material advancement.
HAROLD JACOBY.
Columbia University.