Evening star., 1926-06-13
BY ROALD AMUNDSEN AND
LINCOLN ELLSWORTH.
No. VII.
By Wireless So and Cable to The Star.

June 1.-THE principles of navigation
used in transpolar flights are in many
ways different from those used in
erdinnry navigation. Hjalmar Risen
Larsen of the Norwegian navy, our
second in command, was the navi
gator, as he was on the 1925 eXpedi'
ton. The way he performed his diff
cult task may be understood by the
fact that he could announce to us,
after the ship had covered the I'm.
mense distance of between 2,100 and
1900 miles between Kings Bay and
Alaska, that we had reached Point
Barrow at just the point we had
steered for all the way from SpitZ-
bergen, even though during a great
part of the flight the ship went
through fog and snow, making II
very difficult to take observations.
The Goerz sun compass was his
chief aid in navigation. 1t was OF
the same type as the one we used on
the 1925 expedition. 1t was mounted
outside the pilot cabin close 20 the
side rudder wheel. We had brackets
for it on each side in order to get
noon observations from the sun. The
compass had to be shifted from one
side to the other every II hours-a
cold job for the navigator. who had
to hang for quite time with half
his body out Of the cabin.
How it Works.
The principal of the sun compass
is as follows: A picture of the sun
is reflected through a periScope down
on a glass plate lsing before the
rudder1nan. Connected to the peri
scope is a clockwork mechanism
which turns the periscope 26O degrees
in the same time the sun uses for
the same movement. When once
correctly set your bow is pointing IN
the same direction. as long as the
picture of the sur. is kept on the
same spot. Corrections must be
made for declination and also for
change in latitude, as the axis of the
periscope must be parallel to the axis
of the world. To this must be added
a correction for the ships drift on
account of winds.
We also had periodic steer
ing compass and periodic STAN
dard compass, both of English type.
Besides these we had one ball aero
plane compass of the German Ludoff
type. Both types behaved very well
and it is impossible to say which
was the best. We had the same COM
bination on the 1925 expedition and
found then that it was safest to have
both types.
Shadow Helps Calculation.
For measuring drift and speed we
had the GoerZ instruments, through
which the speed is measured by a
four points bearing of an object on
the snow underneath the ship. Inc
distance passed over in measured
time is equal to the height OF the
ship above the ground. This requires
the correct altitude for exact measure
ment. Our altimeters were the ordl'
nary aneroid barometers. AS these
are set according to the barometrlc
pressure at the place of departure,
they are wrong when the pressure
changes. We had different methods,
however, of checking the sight TOR
corrections in the altimeter. We car
ried instruments for this, but they
could not be used under the special
circumstances existing in the polar
basin.
Ordinarily the speed also can be
checked by the time the shadow OF
the ship, the length OF Whlca Is
known, takes to travel over cef.alii
object on the ground. But this method
could not be used on our flight, as
the low height Of the sun gave d
shadow too far away from the snip
for sharp contours. We tried to use
these methods, but they gave, as II
proved afterward, too great a speed.
Because of the blurred outline the
shadow did not give the full length
of the shin The speed obtained IN
this way corresponded very well with
the speeds found by the other lnstru-
ments. Therefore we relied upon
them until the midnight height OF the
sun gave us the correct latitude
not as high as we had calculated.
Sextants and ChrOnOmeters.
The speed had been less parity
because the barometric pressure had
changed, and the altlmeter thus gave
a false altitude, and partly because
1he measured speed will always be 100
high. due to the fact that the rudder-
men steer a straighter course tnan
usuaI while the observations are DelhS
taken. ,a .
Among other instruments we had q
snlendid German bubble SeNtant ana
three nocket chronometerS when iiau
been checked daily for long perioo
before we left. They were kept uhuel
a constant temperature during tiie
flight. Wireless time signals were
also taken. ,,d
n Norwegian Fisherman t4iilti ,i,'a
on the trip, the latter giving aZimuihS
fo,, high latitudeS. For charts we
used Mercator Projections up TO 81
degrees north on the Spitzbergen Slae
and n degrees north on the Alasha
Side For the rest of the trip we
used n gnomonic chart with an Amerl-
con man based on deviation curves
in the polar basin.
TO Aid the Layman.
For the laymans better understand
ing here is a short description Oh one
side of the astronomic Navigation WIN
respect to the special Navigation con
1itions in the polar basin. -.
Bv taking one observation on'S ol
Srr moon. planets or stars one ooeS
~ ,at ones exact position in GER
-, no;nt Such an observation tens
80, nnlv that YOU stand somewhere
-, tbp socalled position line. by
,,,aons of this line, which corresponds
80 nornnndicular in the direction ol
tbe sun. the azimuth can be Drawn
80 tho chart TO get your exact
,,nsition if is necessary to get sec
IA nosition line. which crosses your
first line at quite big angie, u W.
tain a sharp crossing. .ho
THAT is. YOU must either at the
same time take an observation or a
second astral body, far to the sioe Oh
the first one, or if you get only the
sun you can wait until the direction
OF this orb has altered. If you have
Seen standing still between the oo-
sefvations it is very easy; but II you
have been moving between the obser-
vstions another calculation comes IN.
You must then do what is done in
maritime navigation, move the nrst
position line parallel to itself to cor.
respond to the distance you yourself
have moved between the observation.
Then you draw also your second po-
sition line and the crossing of these
lines is your exact position at the
time of the second observation.