Evening star., 1938-07-19
OF STARS
MEN AND ATOMS
Notebook of Science PROGRESS
in Field, Laboratory
and Study.
BIZ THOMAS r. HENRY.


Measurements of the temperature and
density of the atmosphere to heights of
nearly 40 miles above the surface of
the earth, region hitherto almost COM
pletely inaccessible, now are being made
at the Naval Research Laboratory at
Anacostia by DR.. E. o. Hulburt, using
the rotating earth itself as one of his
experimental instruments.
The quality of sunlight passing
through air varies observably with the
thickness Of the atmospheric particles
and the temperature. The differences
can be determined by spectra of the
light. AS the sun sets the earth's
shadow above the observer moves up
ward and the region of the atmosphere
Illuminated by direct rays of the sun
goes to continuously higher levels. This
is the natural consequence of the rota-
ton Of the earth taken advantage of by
DR.. Hulburt. At sunrise the process is
reversed, the highest regions of the at
mosphere being the first traversed by
the returning light of day.
He is making measurements each clear
day of the brightness of the sky at the
zenith, directly overhead, for one hour
rise. Once the measurements have been
attained a complicated mathematical
procedure Is necessary before they mean
anything. The intensity Of the sunlight
itself is known. Corrections must be
made for the known scattering of light
by air particles and the secondary scat
terlng which results in the brilliant
gloWS OF sunrise and sunset DR.. HUI
burt must make precise observations of
the intensity Of the light just over the
western and eastern horizons to get this
last correction.
His calculations show that from about
to 40 miles above the surface the
temperatures range from approximately
80 to 60 degrees below freezing and that
the change is roughly constant with al
tituoe. From the temperatures the pres
sures can be determined since the loss
OF heat with increasing height is due
to the fact that each particle of air. it.
self even hotter than it would be at the
earth's surface, is further away from
its nearest neighbor and thus has a
larger area to keep warm.
DR.. Hulburt has just reported to the
Optical Society of America the results
OF his observations from October to
April. No noteworthy changes were
found from day to day and he now is
engaged IN determining whether the
same holds true for the summer r,orths.
He emphasizes that his results may not
hold true other than for the latitude Ct
washington and that many such obser-
VatlonS from many stations will be
necessary to obtain a comprehensive
map OF the upper air. For attitudes
above approximately 40 miles he found
the method useless. The light of the
twilight sky is very weak at the yerv
great heights and the corrections re-
quired for secondary scattering are so
large that no validity can be attached
to the results
Methods available for measuring this
region in the past have been verv un-
satisfactory. About all scientists have
known OF the high atmosphere was that
IT existed and very, very attenuated
That 1t extended for at least 70 miles
ABOVE the earth was determined from
the fact that shooting stars are OBJ
served at such heights. These do not
begin to glow until they enter the al
mosphere and are subjected to the fric-
ton OF the extremely attenuated par
ticles.
Radio investigations of the United
States Bureau of Standards and the
carnegie Institution of Washington have
shown that at heights of about 60
miles there are layers which are ionized
py the ultra violet radiation of the sun
a fortunate circumstance because IT.
confines radio impulses to the earth.
setting up an electrical wall through
which they cannot escape into outer
space.
But the sum total of this information
about a region which eventually will be
very significant for human welfare has
oeen scant indeed. Direct observations
OF the upper atmosphere from mar
carrying balloons extend only a little
over Is miles. Free balloons CARVING
raolometeorographs may go about 10
miles higher. Their results show that
temperature decreases with altitude up
TO about miles and then changes very
httle Tor the next or 10 miles, which is
as high as they are able to make obser-
Vatlons. Ihey also show that the gas
eous composition of the atmosphere re-
mains relatively constant, regardless of
altitude.
Dr. Hulburt's observations apparently
have carried him clear through the
stratosphere to the point where the
temperature begins to change once more
with altitude and to become slightly
warmer instead of colder.
HIS first efforts were made last year
oy olrectlng straight upward the beam
OF powerful searchlight. He was able
TO photograph the beam to a verti,le
helght OF almost 20 miles, but above IS
miles the light was so faint that il was
impossible to deduce valid measurements
from the plates.
Eventually he hopes to obtain meas
urements for this new region opened to
intestlgatlon 1or an entire year and to
determine the changes which take nIsce
with the seasons-if there actually are
seasons In these far depths of the air
ocean on the floor of which man is a
crawling creature, as were the first living
organisms on the floor of the water