A History of Science — Volume 5Williams, Henry Smith
History
A History of Science — Volume 5
Williams, Henry Smith
Science -- History
Another important result of Professor Lockyer's very recent studies has
come about through observation of the sun in eclipse. A very interesting
point at issue all along has been the question as to what layers of the
sun's atmosphere are efficient in producing the so-called reverse lines
of the spectrum. It is now shown that the effect is not produced, as
formerly supposed, by the layers of the atmosphere lying just above the
region which Professor Lockyer long ago named the chromosphere, but by
the gases of higher regions. Reasoning from analogy, it may be supposed
that a corresponding layer of the atmosphere of other stars is the
one which gives us the reverse spectrum of those stars. The exact
composition of this layer of the sidereal atmosphere must, of course,
vary with the temperature of the different stars, but in no case can
we expect to receive from the spectroscope a full record of all the
substances that may be present in other layers of the atmosphere or in
the body of the star itself. Thus, for example, the ordinary Freuenhofer
spectrum of the sun shows us no trace of the element helium, though
through other observations at the time of eclipse Professor Lockyer had
discovered that element there, as we have seen, some thirty years before
anything was known of it on the earth.
In a recent eclipse photographs were taken of the spectra of the lower
part of the sun's atmosphere by itself, and it was found that the
spectrum of this restricted area taken by itself gave the lines which
specialize the spectra of so different a star as Procyon. "I recognize
in the result," says Professor Lockyer, "a veritable Rosetta Stone which
will enable us to read the celestial hieroglyphics presented to us in
stellar spectra, and help us to study the spectra and to get at results
much more distinctly and certainly than ever before."
But the most striking confirmation which the meteoritic hypothesis has
received has come to hand through study of the spectrum of the new star
which appeared in the constellation Perseus in February, 1901, and which
was so widely heralded everywhere in the public press. This star was
discovered on the morning of February 22d by star-gazers in Scotland,
and in America almost simultaneously. It had certainly not been
visible a few hours before, and it had blazed up suddenly to a greater
brilliancy than that of a first-magnitude star. At first it was
bluish-white in color, indicating an extremely high temperature, but
it rapidly subsided in brilliancy and assumed a red color as it cooled,
passing thus, in the course of a few days, through stages for which
ordinary stars require periods of many millions of years.
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