Evening star. [volume] (Washington, D.C.) 1854-1972, 1931-01-29
IN QUEST
OF HIGH, DRY SPOT
Smithsonian Representative
Leaves for Cape Verde
Islands and Africa.
BY THOMAS r. HENRY.

Wanted-the highest, dryest spot in
the Eastern Hemisphere.
This is the quest upon which A. F.
Moore of the astrophysical observatory
of the Smithsonian Institution left
Washington yesterday for the Cape
Verde Islands and continental Africa.
He departed with a single new instru-
ment devised at the observatory, which
combines the properties of two of the
most delicate measuring devices known
to man. 1t will measure the amount of
water in the atmosphere, the intensity
of the suns rays and the SKY light"
or radiation scattered in the atmos-
phere by dust Or water particles.
Important Conclusions.
For years the astrophysical observa-
tory under the direction of DR.. Charles
G. Abbot, secretary of the Smithsonian
Institution, has been measuring daily
the amount of solar radiation in diff
ferent parts of the world. This patient
work is beginning to lead to important
conclusions, and eventually may make
it possible to predict weather weeks and
months in advance. But the observa-
tions must be made with the most ex-
IRENE accuracy under the most favor
able circumstances to have any value,
What is measured is the amount of
heat from the sun which falls at any
given time on a hypothetical black OBJ
ject with the dimensions of a cubic
centimeter placed at the edge of the
earth'S atmosphere. The difficulty is
that nobody can get to the limits of
the atmosphere to place and observe
such cube. 1t must be an imaginary
cube, with the amount of heat it alb
serbs measured somewhere on the
earth'S surface. The radiation which
actually comes through to the surface
is far different in amount than that
which would be measured by the by
pothetical black body, because of the
very great complications brought about
by the content of the atmosphere itself.
First, the air is full of water. Wa
ter abSorbS radiation, especially at the
lower edge of the spectrum from the
limits of the visible red far into the
invisible infra-red. 1t is essential to
find a mountain in a comparative des-
ert where the water vapor will be at
a minimum.
Minimum of Dust.
Second, the minute dust particles in
the atmosphere raise havoc with the
radiation, scattering it over the sky.
So it is essential to have a high noun
tain where there is a minimum of dust.
The combination is hard to find in the
Old World. Secretary Abbot himself
set out on the quest several years ago.
He found an almost ideal spot in Gen.
trail Asia, but political conditions in
the surrounding country were so dis
turbed that it was QUITO the question
to put an observatory there. Finally
he hit on the lonely, desolate Mt. Bruk-
karos in South Africa, and the Smith
sonian has maintained an observatory
there ever since.
Mount Brukkaros is dry enough, but
it is so low that the observations are
disturbed by the minute amounts of
dust rising from the African desert.
Now the Astrophysical Observatory has
learned of mountain over 1000 feet
high in the Cape Verde Island which
Mr.. Moore will investigate. 1t is high
enough and reports are that it is very
dry. If this location does not prove
satisfactory he will proceed to the
African continent. Then the search
Africa where political conditions are
stable and there are desert mountains
The high peaks of Central Africa, in a
rain belt and snow covered all the year,
probably are out of the question because
of the moisture.
Hunting such a mountain ordinarily
would be a difficult job because of the
bulk of the equipment necessary to
make the necessary preliminary obser-
vations. In Mr.. Moore's case this has
been reduced to such an extent that
he can carry it all on his back, If
necessary.
Instruments Used.
Some of the most important obserVa-
tons must be made with a SpectroScope
and the new instrument includes one OF
these delicate devices incloSed in a
small, short tube. BY splitting up the
suns radiation into its component wave
lengths this instrument records what
has been absorbed by the water vapor
in the atmosphere and this varies di-
rectly with the amount of water par
ticles. The actual result is read from
the reflections of galvanometer nee
die so that no complicated computations
are required. Thus Mr.. Moore will be
able to determine quickly the depth of
the water over a square centlmeter II
all the moisture in a column a cent?
meter square extending from the earths
surface to the outer limits of the at
mosphere were concentrated at the sur
face,
The second element of the new in
strument Is a specially constructed
pyrheiiometer which will measure not
only the total radiation received from
the sun upon mountain top, but the
amount of sky light. This is the
amount of the suns radiation which
has been scattered and absorbed by
dust particles in the atmosphere-gen-
orally speaking, the brightness of the
sky. 1t Is measured in such extremely