Rough Ways Made Smooth: A series of familiar essays on scientific subjectsProctor, Richard A. (Richard Anthony)
Science
Rough Ways Made Smooth: A series of familiar essays on scientific subjects
Proctor, Richard A. (Richard Anthony)
Science
Now, in July, 1878, the corona presented an entirely different
appearance. Mr. Lockyer, in a telegram sent to the _Daily News_,
describes it as small, of pearly lustre, and having indications of
definite structure in two places only. Several long rays were seen; but
the inner corona was estimated as extending to a height of about 70,000
miles from the sun's surface. The most remarkable change, however,
was that which had taken place in the character of the corona's
spectrum--or, in other words, in the physical structure of the corona.
The bright lines or bright images of the inner corona (according as
it was examined through a slit or without one) were not seen in July,
1878, showing that no part, or at least no appreciable part, of its
light came from glowing gaseous matter. But also the dark lines seen by
Janssen in 1871 were wanting on this occasion, showing that the corona
did not shine appreciably by reflecting sunlight. The spectrum was, in
fine, a continuous rainbow-tinted streak, such as that given by glowing
solid or liquid matter.
The inference clearly is: 1. That in July, 1878, the gaseous matter
which had been present in the corona in 1871 was either entirely absent
or greatly reduced in quantity; 2. The particles of solid or liquid
(but probably solid) matter which, by reflecting sunlight, produced a
considerable portion of the corona's light in 1871, were glowing with
heat in July, 1878, and shone in the main with this inherent light;
and 3. The entire corona was greatly reduced in size in July, 1878, as
compared with that which formed the 'star-like decoration' around the
black body of the moon in December, 1871.
We cannot, however, accept the theory that such a corona as was seen
in 1871 invariably surrounds the sun in years of great disturbance,
while the corona of last month is the typical corona for years of
small solar disturbance. The generalisation is flatly contradicted
by the evidence which I have presented in the preceding pages. It
may be that such a corona as was seen in 1871 is common in years of
great disturbance, just as spots are then more common, though not
always present; while such a corona as was seen in July, 1878, is more
common in years of small disturbance, just as days when the sun is
wholly without spots are then more common, though from time to time
several spots, and sometimes very large spots, are seen in such years.
On the whole, I think the evidence I have collected favours rather
strongly the inference that an association of this sort really exists
between the corona and the sun-spots. It would, however, be unsafe at
present to generalise even to this extent; while certainly the wide
generalisation telegraphed to Europe from America as the great result
of the eclipse observations in July, 1878, must unhesitatingly be
rejected.
Public-domain text, read in full here on John Shaqi.
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