Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-11-24

ences observed between Arctic and
Antarctic magnetic phenomena are due
to the different distribution of land and
water in the two regions. The Arctic
is an ocean surrounded by the great
land masses of the globe the Antarctic
is a continent surrounded by great
stretches of ocean in all directions
How far this fact influences magnetic
and auroral phenomena is not known
1t Is one of the problems that cannot De
solved until more data are obtained
from the Antarctic.
The Variometer Hut.
Two hundred yards from the radio
towers of Little America and 20 yards
south of the main tunnel is the nom
magnetic hut. Here iron is taboo.
Chips Gould, when he built the frame.
removed all iron from the timberS and
used only brass and copper nails. Iron
affects the needles used In magnetic
work. so the greatest care has to be
taken that no iron is left near the hut.
Martin Rome made a brown canvas
tent to At the frame.
A hole was dug deep enough 70
swallow the hut and snow was packed
around. it to a depth of foot above
the roof. The hut has to be dark, as
the recording apparatus is Photographic.
Also it is important to keep the tenn
perature as constant as possible and
the best way to do this in Little Amer
lea is to dig down into the snow.
In view of the experience OF other
expeditions IN blizzards, it was de-
cided to make a tunnel from the mag
netic observatory to the main tunnel.
The labor battalion under Capt. Mac
Mckinley turned out and dug this
tunnel. although the men had already
shoveled more snow than any of us
had dreamed existed. 1t has proved a
go6send to this poor magnetician and
has made 1t possible to continue the
magnetic work through the Winter.
The Instruments Used.
The magnetic and electrical instru-
ments and laboratory equipment were
provided by the department of terres-
trial magnetism of the Carnegie Insti-
tuition of Washington. To prevent jar
ring, the instruments were mounted on
tables which rest on wooden piers frozen
two feet into the floor. At first small
Gil stove was used to heat the hut, but
it brought more trouble than benefit.
Frost forming on the mirrors and lenses
has to be removed continually, but this
became much worse when the stove was
used. Since the first trial of heating
the hut work has been carried on with
out it. -,
In this hut the three elements are
MISUNDERSTANDING the horizontal
intensity and the vertical intensity. All
three vary according to the season OF
the year and also have daily variations.
some of which are periodic and others
Of storm nature.
One instrument records the direction
of magnetic needle allowed to swing
Iu fc =
ometer. The declination is the degree in
which the magnetic needle varies from
true north. To make this instrument
more sensitive the needle is suspended
| from a very fine quartz fiber, which
| looks like a thread in a spiders web.
1t is strong enough to support the
needle and also a small mirror that
moves with the needle, though it is a
dificult matter TO adjust the needle and
mirror in the cold without breaking the
| fiber
| Light from a small electric bulb Is
reflected in the mirror and falls On a
Photographic sheet When the needle
moves the mirror moves also, and the
| spot of light on the sheet travels a con-
1 siderable distance. Thus an angular
| motion of the needle is recorded as a
straight line motion on the sheet and
angles too small to be measured accu-
/ rately can De measured by means OF
the exaggerated movement of the re-
flected light. The sheet is wound on a
drum, which revolyes once day and Is
driven by elockwork.
PhotOgraphing "Wiggles."
The horizontal intensity variometer
works in similar way, throwing spot
of light on the Photographic sheet. This
| spot moves as changes occur in tho
component of the earth's magnetic field
| parallel to the ground. In Little Amer
| lea this is much weaker than the YER
| tical intensity, which is recorded by a
| third instrument.
The vertical intensity variometer OPP
crates in different way. Its needle IA
pivoted to swing vertically. If it were
allowed to swing freely it would point
almost straight down, as the angle of
| dip here is SO 1-3 degrees. A weight is
hung on the needle to bring it to hori-
zontal position. 1t also carries a mirror
| and reflects a light on to the same
Photographic sheet. An extra mirror IS
used in this case to produce a horizontal
motion in place of the vertical, thus