Evening star., 1932-01-28
ATOMS ABOUT SUN
NOW COUNTED BY
STUDY OF SPECTRA.
DR.. Russell of Princeton Tells
Smithsonian Audience How
Elements Are Defined.
LECTURE Is FIRST
IN ARTHUR SERIES
Opacity of Earth's Atmosphere
Hinders Sciences Discovery
of Missing Traces.

OF the Smithsonian 1IlSlltulIOll
Thus. he said, the amount Of any
given element there now can be com
puted by Interpretation of the solar
spectrum. In the past this has revealed
to astronomers what elements were con-
tai.&G in the atmoSphereS of the sun
an6gstars. Now it is possible to deter
mine the correct proportions.
Atomic theory" Prof. Russell said,
enables us to predict how wide line
would be produced by given number
of atoms, per unit area Of surface, In
the atmosphere. In this way it ap-
pears that the very strongest lines N
the solar spectrum, the H and K lines
in the violet due to ionized calcium,
are produced by an amount of material
comparable to a layer OF ordinary air
one-third of an inch thick. The same
was proved in principle so years ago by
Sir Norman Lockyer, who showed by
direct experiment that BunSen flame
one inch thick containing a small
amount of sodium vapor produced
stronger absorption lines of sodium
than the whole atmosphere of the sun.
Theoretical Relations.
For the fainter lines We may utilize
certain theoretical relations between
the intensities of lines belonging to
groups, called multiplets, of which
many houndredS appear in the solar
spectrum. Thus it is found that the
faintest visible lines demand only about
one twenty-millionth as many atoms
for their production as the strongest
by adding up the number Of atoms
which absorb the various lines OF q
given element, we can get an idea o.
the total amount of this element in the
suns atmosphere. 1t is found that the
suns atmosphere must consist mainly
of hydrogen-for its lines are among
the strongest. although they are abb
soTbed only by atoms so highly excited
that at the suns temperature not more
than one hydrogen atom in 10 millions
should be in this state. The permanent
gases, oxygen and probably helium,
are next in abundance. Vapors Of the
metals make up something like l per
cent of the atmosphere by volume. Six
elements, magnesium, iron, silicon.
sodium, potassium and calcium make
up 95 per cent of the metals and six
more account for nine-tenthS OF the
rest.
In general. the composition of the
suns outer layers is strikingly similar
10 the average composition OF the
earth's crust, and still more like a
mixture of terrestrial rocks and meteo-
rites. Why certain elements should be
abundant and others rare is problem
whose solution may lead us far into
the atomic physics of the future and
give a clue to the evolution OF atoms
themselves"
Sixty-two Elements Identified.
Study of the solar spectrum, Prof.
Russell said. now has led to the identi-
fication in the sun of 50 of the elements
and about a dozen chemical compounds.
For some elenents such as iron or
magnesium he said, practically all
the lines which can be produced in the
laboratory are found in the sun. For
others. such as copper, only the stronger
lines appear. and for still others. such
as silver, only the very strongest lines
show up in the sun and these are faint
Some similar elements, such as phos-
phorus. chlorine and neon. do not ap-
pear in the sun at all. The chief rea-
son for this is th& we can observe but
part of the solar spectrum. We are
cut off in the ultraviolet by the opacity
of the earthS atmosphere, due to ozone
in the upper layers, and in the infra-
red by the absence of Photographic ef-
fect-Which gradually is being remedied
by the invention of new sensitizing dyes.
Many of the missing elements have
their strongest lines in the ultraviolet
and we cannot get at them.
"a given element may produce diff
ferent spectra under different condi-
tions. When isolated atoms are present
we get the arc spectrum. When these
atoms are ionized, by the removal OF an
electron from each, they give an en-
tirely different set of lines known as
the spark spectrum. When the atoms
combine with one another to form COM
pounds, each compound has spectrum
of is own.
Effects on Heat.
The sun is so hot that most COM
pounds are decompoSed in its atmos-
phere and the few which resist are
present only in small amountS-yet
more than a dozen compounds have
been identified. Two Of these-oxide of
boron and fluoride of silicon-reveal the
presence of elements which would
otherwise be missed because their
strong lines are out of reach in the
ultraviolet. In the sunspots, which
are cooler than the rest of the surface,
compounds appear which are com
pletely ASSOCIATED over the hotter parts
of the disk.
"In a similar fashion the atoms them
selves are ionized, under the influence
of high temperature and low pressure.
Ionization is less above the spots than
elsewhere. so that the arc lines are
stronger there and the spark lines weak
er. There are three elements, -lithium,
rubidium and indium, whose lines show
only in the sun spot spectrum. At the
higher temperatures of the disk they
are completely ionized and their strong
spark lines are out of reach.
Recent advances in the theory OF
the spectra have informed us just what
change happens in an atom when any
particular spectral line is absorbed.
some lines are absorbed by atoms in
their normal states, others only by
atoms which have been excited" or
loaded with energy. The proportion of
such excited atoms increases steadily
with the temperature. When allow
ance is made for this, and for the
different degrees of ionization of differ
ent elements. the behavior of many
hundreds of lines which alter in inten-
sitv in the sun-spot spectrum can be
fully explained"
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