Evening star., 1939-05-30
Of Sturs, Men
And Atoms
Notebook Of Science Progress
In Field, Laboratory
And Study
By Thomas r. Henrn.

By Thomas r. Henry.
Observatories scattered around the
earth now are making constant observa-
tions of the calms, storms and other
variations in the blanket of ionized
gasses wrapped around the planet at
great atmospheric heights which pre-
vents radio waves from escaping into
space and makes long distance transmits
sion possible.
The work of these observatories is de-
scribed by DR.. E. o. Hulburt, physicist
of the Naval Research Laboratory, in
the current issue of the Scientific Month";
ly, publication of the American Associa-
ton for the Advancement of Science.
The observations are on the state of
the atmosphere at heights more than go
kilometers above sea level At such high
attitudes, DR.. Hulburt explains, there are
several hundred thousand molecules in
each cubic centimeter which have lost
an electron. The various levels of this
'lonosphere" vary from hour to hour and
from season to season with the forces re-
sponslble for the ionization.
All radio messages to distances greater
than 100 miles, DR.. Hulburt explains. are
by means of radio waves which have
travelled from the transmtter to the
lonosphere and have been reflected down
to the receiver. The waves get around
the curve of the surface Of the earth bv
successive reflections between the earth
and the ionosphere That a complete
understanding Of what is happening
there is of fundamental Importance to
the successful maintenance Of long dis
tance radio circuits is obvious.
The ionosphere can only be studied in
one way, he points out. This is by means
of controlled radio waves bounced"
against the ionized atmospheric surfaces,
From their echos and the time taken for
their return to earth many significant
deductions can be made
An ionosphere station, DR.. Hulburt
says, lis radio weather observat tory and
its data are the weather conditions for
radio traffic"
Since the ionization of the atmospheric
regions increases during the day and d.
mlnlshes at night, says DR.. Hulburt, it is
fairly obvious that the most important
cause OF the ionization is radiation from
the sun, but not the kind of light that
reaches the observer on earth. 1t is be-
neved to be due to very short wave
radiations which are completely absorbed
in the high levels of the atmosphere. In
laboratory observations such radiations
do actually ionize gases.
Physicists now believe. says DR.. HUI
burt, that the observed ionization is
the result OF two opposing factors, one
being the action of solar ultraviolet
light in splitting neutral air molecules
and atoms into negative electrons and
positive ions, and the other being loss
OF lonizaton by reconciliation of the
electrons and ions to form neutral air
particles. The density of ionization
which exists at any place and time
depends on the values of the two rates.
1t is assumed DR.. Hulburt says, that
in levels above about $50 kilometers
there is an expansion of the atmosphere
underneath the sun, due to the effects
OF sunlight in heating the high at
mosphere and in dissociating oxygen
and nitrogen molecules into atoms. In
the tropics, at least, this process starts
IN the morning. In the afternoon the
march Of events is reversed. The total
ionization decreases with the lowering
sun.
AN important type Of ionospheric dis
turbance which occurs only on the day
light side OF the EARTH says DR.. Hulburt,
lis that associated with radio fade
outs. The fade-out is sudden disap-
pearance of radio signals for few
minutes, the complete process Of fading
out and reappearing occupying a time
usually less than an hour.
THE strength OF the radio signal falls
to zero usually in less than a minute,
the effect being simultaneous throughout
the sunlit hemisphere of the earth and
most intense directly under the sun.
BY means Of cooperation with the Mount
Wilson Observatory it was observed that
radio fade-outs occurred at times when
there were unusually bright hydrogen
eruptions on the surface of the sun.
1onospheric observations showed that
the fade-out was caused by sudden
increase in ionization at or slightly be-
low the lowest daytime level Therefore
the evidence is fairly complete that
the ionization which accompanies the
fade-out is produced by sharp burst
OF radiation from a hydrogen eruption
on the surface of the sun which travels
in straight lines from the sun to the
earth with approximately the velocity
OF light. The radiation is, in all proba-
bility, ultraviolet light.
"This is the first instance in which
the cause of definite terrestrial cir
cumstance has been traced almost be-
yond doubt to definite, unusual hap
pening on the sun. The hydrogen oc-
ours usually but not always near an
active sunspot group"