Evening star. [volume] (Washington, D.C.) 1854-1972, 1910-07-21

the low altitude of the sun. Had the
expedition been delayed on the return
until May or June. the theooohte might
have been more convenient In determn-
ing our position than the sextant.
..The method of taking meridian obser-
Wations with a sextant and artihclai
horizon on a polar sledge journey Is as
follows: If there is any wind. semi
circular windguard of snow blocks. two
tiers high is put up, opening TO the
south If there is no wind, this Is not
necessary The instrument box is nrmiy
bedded in the snow, and snow Is packed
around the box. Then something. usually
a skin. is thrown over the snow. partly
to prevent shy possible warmth from the
sun melting the snow ana snlfting the
bearing Of the box; partly 10 protect
the eyes Of the observer from the intense
reflected glare of light from the snow.
The Mercury Trough.
1.-The mercury trough of the artificial
horizon is placed on top of the level box
and the mercury which has been thor
ouphly warmed in the igloo, Is poured
into the trough until it is full. In the
case of the special wooden trough de-
vised and used on the last expeditiOn ~
was possible to bring the surface OF tno
mercury level with the edges OF the
trough, thus enabling us 10 Teao dhsie'
very close to the horizon.
1.-The mercury trough is covered Win
what is called the rOof-a metal frame
work carrying two pieces OF very ecCu-
rately ground glass. set inclined. IKE .ne
opposite sides of the roof of house.
The object of this roof is to prevent any
slightest breath of wind disturbing the
surface CT the mercury and SO oistol.
ing the suns image in 1t, and also 70
keen out any fine snow or frost crystals
that NAV be in the atmosphere. In plac-
ing the trough and the Roof On the top
of the instrument box the trough
placed SO that it's longer diameter VIII De
toward the sun.
between the box and the inner END Oh
the snow shelter. On this the observer
lines down fiat on his stomach, MS neau
to the south. He rests both elbows VI
the snow. holding the sextant nrmiy ha
both hands and moving his head ana the
instrument until the image or part
the image of the sun is seen renecteo
i'm the surface of the mercury.
Figuring Latitude.
THE method by which the latitude OF the
observer is figured from the altitude OF
the sun at noon is very simple. IL IL
this: That the latitude of the observer Is
equal to the distance of the center OF the
sun from. the zenith, plus the dechnalloh
of the sun for that day and hour me
declination of the sun Is, as every schooi-
bow knows, it's distance north or soutn
from the equator, measured In degrees
and minutes, declinatiOn being simply
celestial latitude. 1t is varying guam
titv as the axis of the earth is inclined
to the plane of its orbit The deciina-
ton of the sun for any place at any hour
may be obtained from tables prepared
for that purpose. which give the oechha-
tions for noon OF every day on the Green
wich meridian, and the hourly change in
the declination.
such tables for the months OF FeDruary'
March. April May, June and July. to-
gether with the ordinary tables Tor re
fraction to minus 10 degrees Fahrenhelt,
l had with me on pages torn from the
Nautical Almanac and Navigator
Commander Peary proceeds thereafter
TO describe Just how the sextant is used.
and finally to tell what the north pole
really is, and how on the afternoon OF
Anrii after thirty hours at the pole. he
and his party turned their faces south
ward again for a lonely march OF more
than four hundred miles to land.