Evening star., 1950-09-01
Phenomenon at Sunset
Affects Radio Signals
Bureau Experiments Show
Waves Are Attenuuted
By Thomos R. Henry


A curious sunset phenomenon affect,
ing round -the-world radio signals has
been found by United States Bureau Of
Standards observers.
Radio waves for some reason are
greatly attenuated when they pass
through a sunset zone anywhere in their
path, according to report recently
issued by the Bureau. They come back
strongest when it is sunset at their
starting point.
About tenth of a second is required
for radio signal to pass completely
around the world and return to its point
of origin, Bureau experiments show.
The first such signals were detected
by Jack N. Brown Of the Bureau staff
q few months ago, and since then there
has been considerable experimentation.
Signals are sent out from the Naval
radio station at Annapolis and received
at the Bureaus radio propagation field
station at Sterling. Va, about so miles
away.
> Peak in Strength Noted.
During the winter months these round
the-world signals can be observed
throughout the entire day. A sharp
peak in the strength of the returning
signal was noted at 4:30 pm. when the
sun was setting over the foothills Of
the Blue Ridge mountains At any other
time of the day. it was calculated, sig
nal must cross sunset zone somewhere
between the sending and receiving sta
tions.
1t also has been observed that there
is less delay in the return time when the
radio passes through an "ionospheric"
storm on its way around the earth. The
reason for this, it is explained, is that
at such time the ionosphere, the re-
f1ecting layer which bounces radio i'm
pulses back to the earth, is closer to the
planets surface than at ordinary times.
The earth's upper atmosphere is suf-
fused with laughing gas.
It is nitrous oxide, Of the same COM
position as that used in dentists Of
fee, which presumably is formed by the
ultraviolet radiation of the sun falling
on oxygen and nitrogen atoms at high
attitudes.
That there is minute amount OF
laughing gas in the atmosphere has been
known for some years, but that 1t is
confined to extreme high attitudes has
lust been determined with the use Of
6O-inch searchlight by DR.. William
Benesch, Johns Hopkins University
physicist.
On the other hand DR.. Benesch found
that methane, or marsh gas" which is
the simplest of all the carbon-h hydrogen
combinations and probably forms large
part of the atmospheres of the larger
planets, is uniformly distributed through
the earth's atmosphere from the ground
to the greatest heights attainable.
Practical Applications.
The studies have been carried out in
cooperation with the Office of Naval
Research, and the Navy believes discov-
cries about the composition OF the upper
atmosphere eventually will have prac-
tical applications in improved methods
of weather forecasting. 57 .as.. .su
Z In these researches the light from the
sun strikes a spectrometer, an instru-
ment which sorts out the light and auto
matically records the type of gasses
through which it has Travelled on its
way to the earth. This revealed only
the composition of the whole column OF
atmosphere. yae sg
DR.. Benesch then used the 0.000 600
candle-power searchlight to determine
in the same way the gasses in the lower
atmosphere The searchlight beams
showed no trace of the laughing gas.