The San Francisco call., 1909-09-30

cal observations taken and what m
he observer position sEhen near the
lorth pole?
but the above are all that is necessary
for locating position They should
be made as light as possible and Sc
cured in a water tight box. 50 that,
although the sledge may be completely
upset or immersed in water. no dam
age can come to the Instruments
A chart of some sort is desirable. but
as it covers field entirely unsurveyed
it may be composed of a blank sheet
of paper with dot in the center rep
resenting the pole
The drawbacks to determining ones
position in the arctic do not lie in the
computations. but in the great diff
Guilty of securing accurate observations.
The lenses and mirrors of the in
struments are covered with frost from
the warmth of the body or the breath,
the lubricating oil freezes in the joints,
the silver backing of the mirrors crack
and granulate in the cold. and the arti-
fetal horizons freeze if liquid ana re-
fuse to stay horizontal if solid.
should there be fog or the heavens
be overcast no observations are pos
sible.
During the six months Of summer
daylight the stars are not visible, al
though the brightest planets might be
seen under especially favorable cireum-
stances. The pole star, even if visible
in winter. is of no practical utility
After the observation is taken GER
tain corrections must be applied to the
observed altitude to convert it to the
true altitude. OF these the correction
for refraction is the most subject TO
variation
The irregular appearance OF the disk
of the sun near the horizon when ris-
ing or setting is well known In the
arctic the sun is always close TO the
horizon, and its rays in traversing the
atmosphere are strongly refracted-
This. if not allowed for, is sufficient to
cause an error of from to ss miles,
hut as its amount is known and taou-
lated for ordinary conditions such er-
rors are not very likely to occur
AS the pole is approached the OBJ
servations become very simple At the
pole the altitude of any heavenly
body-the sun, for instances the
same as its declination or distance
north of the equator as given In the
astronomical tables. An explorer then,
approaching the pole. need only take
an observation of the sun at noon. and
for errors of Instruments. refraetion,
etc, compare this correct altitude with
the declination given in the tables. The
difference between the declination and
the altitude is the distance he is from
the pole. As he draws nearer to the
pole it becomes of continually lessen
ing Importance that his observation be
taken exactly at noon. and when at the
pole it may be taken at any time and
will be the same as the given declina-
tion at that time.
It thus becomes a very simple matter
to determine ones position at the
pole. AS ones distance from the pole
increases, the computation requires
slightly more time, but still remains
very simple. The following method can
be employed at any time. but various
other methods are equally available.
The time of the observation is taken
by the pocket chronometer, and by a
comparison with the other cfronom-
eters the exact time of Greenwich is
determined. To this is applied the lon
gitude (approximate). and the differ
erce between watch time and sun time
equation of time). which gives the
time as shown by the sun; that is, it's
angle from the meridian at the OBJ
servation. With this hour angle (t),
and the declination and approximate
latitude. the suns altitude is computed
by the following formula
sin = Cos IL = ID = sin2 y
Cos I Cos
The altitude of the sun (h), thus OBJ
tained. is then compared with the OBJ
served altitude after correction, and
the difference is the distance in miles
the observer is from the assumed po-
sition given by the latitude and longi-
tude used in the computation.
His direction from the assumed posi-
tion is toward or away from the sun,
according to whether his observed alti-
tude was greater or less than the alti-
tude obtained by computation BY
marking on the chart the assumed po-
sition in the latitude and longitude
used. and drawing line through this
point in the direction of the suns
bearing (the direction which would be
indicated by the shadow of an upright
staff), the correct position can be
found by measuring OFF on this line.
away from the assumed position. dis
tance equal to the difference between
the observed and the calculated alti-
tudes.
f