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Nature
(Thursday, November 4, 1869)

Lockyer, J. Norman
The recent total eclipse of the sun,   pp. 14-15


Page 14


NA TURE
[Nov. 4, I 869
THIE RECENT TOTAIL ECLIPSE OF THE SUN
I F our American cousins in general hesitate to visit our
    little island, lest, as some of them have put it, they
should fall over the edge; those more astronomically in-
clined may Xvcry fairly decline, on the ground that it is a
spot where the sun steadily refuses to be eclipsed. This
is the more tantalising, because the Americans have just
observed their third eclipse this century, and already I
have been invited to another, which will be visible in
Colorado, four days' journey from Boston (I suppose I
am right in reckoning from Boston ?) on July 29, 1878.
  Thanks to the accounts in Sillimnn's 70ournal and
the Philosothical AMagazine, and to the kindness of
Professors Winlock and Morton, who have sent me some
exquisite photographs, I have a sufficient idea of the
observations of this third eclipse, which happened on the
7th of August last, to make me anxious to know very much
more about them-an idea sufficient also, I think, to
justify some remarks here on what we already know.
  A few words are necessary to show the work that had
to be done.
  An eclipse of the sun, so beautiful and yet so terrible to
the mass of mankind, is of especial value to the astronomer,
because at such times the dark body of the moon, far out-
side our atmosphere, cuts off the sun's light from it, and
round the place occupied by the moon and moon-eclipsed
sun there is therefore none of the glare which we usually
see-a glare caused by the reflection of the sun's light by
the sun was eclipsed, and did not travel with the moon-
that the red prominences really do belong to the sun.
  The evidence, with regard to the corona, was not quite
so clear; but I do not think I shall be contradicted when I
say, that prior to the Indian eclipse last year the general
notion was that the corona was nothing more nor less
than the atmosphere of the sun, and that the prominences
were things floating in that atmosphere.
  While astronomers had thus been slowly feeling their
way, the labours of Wollaston, Herschel, Fox Talbot,
Whcatstone, Kirchhoff, and Bunsen, were providing them
with an instrument of tremendous power, which was to
expand their knowledge with a suddenness almost startling,
and give them previously undreamt-of powers of research.
I allude to the spectroscope, which was first successfully
used to examine the red flames during the eclipse of last
year. That the red flames were composed of hydrogen,
and that the spectroscope enabled us to study them day
by day, were facts acquired to science independently by
two observers many thousand miles apart.
  The red flames were " settled," then, to a certain
extent; but what about the corona?
  After I had been at work for some time on the new
method of observing the red flames, and after Dr. Frank-
land and myself had very carefully studied the hydrogen
spectrum under previously untried conditions, we came to
the conclusion that the spectroscopic evidence brought
forward, both in the observatory and in the laboratory, was
against any such extensive atmosphere as the corona had
Vtolet end.
Red erd.
IrL
       FiG. r, -  i ng- the so'Iar spectnim with the principal Fraunhofer
lines, and above it the bright-line spectrum of a prominence containing
                                        magnesium, sodium, and iron vapour
at its base.
our atmosphere. If, then, there vere anything surrounding
the sun ordinarily hidden from us by this glare, we ought
to see it during eclipses.
  In point of fact, strange things are seen. There is a
strange halo of pearly light visible, called the corona, and
there are strange red things, which have been called red
flames or red prominences, visible nearer the edge of the
moon-or of the sun which lies behind it.
  Now, although we might, as I have pointed out, have
these things revealed to us during eclipses if they be-
longed to the sun, it does not follow that they belong to
the sun because we see them. Halley, a century and a
half ago, was, I believe, the first person to insist that
they were appearances due to the moon's atmosphere,
and it is onl) within the last decade that modern
science has shown to ev'erybody's satisfaction-by photo-
graphing them, and showling that they were eclipsed as
been imagined to indicate; and wce communicated our
conclusion to the Royal Society. Since that time, I con-
fess, the conviction that the corona is nothing else than an
effect due to the passage of sunlight through our own
atmosphere near the moon's place has been growing
stronger and stronger; but there was always this consider-
ation to be borne in mind, namely, that as the spectro-
scopic evidence depends mainly upon the brilliancy of the
lines, that evidence was in a certain sense negative only,
as the glare might defeat the spectroscope with an un-
eclipsed sun in the coronal regions, where the temperature
and pressure are lower than in the red-flame region.
  The great point to be settled then,'in America, was,
What is the corona? and there were many less ones. For
instance, by sweeping round the sun with the spectroscope,
both before and after the eclipse, and observing the pro-
minences with the telescope merely during the eclipse, we


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