The San Francisco call., 1909-09-30

Here is some useful information
pole. 1t Is taken from the Pilot Ci
October, 1909, published by the Unite
authority of the secretary of the M
What are the various astronoml
struments are used for determining
north pole and when actually at the
Answer-In theory there is no
greater difficulty in determining ones
position in the arctic than at any other
portion of tho globe. The observations
of the sun or stars are such as would
be taken elsewhere and may be worked
by the same methods.
The instruments employed are the
same as those used by mariners in all
seas, but special care should be taken
in their construction TO insure ex-
treme lightness and to guard against
possible errors due TO unequal expan-
sion and contraction of the various
metals in the great changes of temper
ature to which they are TO be ex-
posed. In the expedition of the duke
of the Abruzzi some of the sextants
were made of aluminium
All the astronomical observations of
this expedition were made by sextant'
the ordinary type being used on the
ship and the aluminium instruments on
the Journeys over the ice.
Particular care must be taken in the
selection of the chronometers. These
instruments are subject to errors under
the most favorable conditions Of
handling and temperature. 1t is inev-
liable during the hard knocks OF a
sledge journey in a temperature low
enough to CONCEAL the oil with which
they are fabricated that chronometers
can not be considered the instruments
of precision they are under better con-
ditions.
AS their use is principally in deter
mining the longitude. errors in this
direction are of little moment near the
pole. At the pole, where all meridians
converge. one longitude is the same as
another, and every altitude is a me
ridian altitude" which does not require
a chronometer for it's solution.
The greatest difficulty in astronom-
ical work in the arctic lies in getting
suitable horizon. The mariner in the
open sea in clear weather has little
difficulty. in measuring the angle be-
tween any heavenly body and the actual
visible sea horizon. On shore or sur
rounded by a sea of ice in various
forms there Is no such thing as level.
SO Ao
comes necessary to resort to an arti-
fetal horizon of some sort. The usual
method is to use a basin of mercury
which, when sheltered from the wind
by a glass cover, forms perfectly
smooth, horizontal surface in which the
heavenly bodies are brilliantly re-
hected. It is then only necessary to
measure with a sextant the angle be-
tween the body in the heavens and its
reflection in the artificial horizon to
determine it's actual elevation above
the true horizon. 1t must be remem-
bered, however, that mercury freezes
at about 40 degrees Fahrenheit below
zero, and has accordingly very lin
tied field of usefulness in the arctic
For this reason and on account or It's
weight some other form of artificial
horizon is necessary.
Other liquids besides mercury have
been used. as have also glass mirrors
made horizontal by means of screw
legs and spirit levels. These last re-
ouire great care in adjusting, and
there is always more or less error at
tending their use. With the above in
struments one can determine his posi-
ton with sufficient accuracy whenever
the sun, moon or any OF the principal
stars are visible, but. having done so,
it is a matter of no small difficulty to
ascertain what is the proper direction
in which to travel to be sure of always
going north
The compass. to which we are accus-
toned to look for guidance, does not,
as is well known. point to the geo.
graphical pole, but TO a region some
distance south of it called the mag
netic pole. This has been located to
the northwestward of Hudson bay, and
at any place between that and the true
pole the compass Aeeuic Will punt
south instead of north. If to one side
of the magnetic pole it will point more
or less east or west, as the case may
be.
In preparing for a sledge journey in
the arctic it has been found advisable
to have special chest for instruments,
usually secured to the front of the
sledge. This should contain a sextant,
an artificial horizon of nonfreezing
type, one or two chronometers, and the
tables of logarithms and the astronom-
ical data of the sun, moon and stars,
necessary in working out observa-
tions.
1t is advisable that pocket chro-
nometer be carried on the person in
order that it may get the warmth of
the body and be spared the jolting of
the sledge.
Other instruments may be carried for
+be ooIIectiou of scientific information