This phenomenon, it seems to me, ought to account for, and will
possibly satisfy, the spectroscopic conditions observed just before,
during, and after totality; which has probably led to the epithet used
by some leading observers--"the fickle corona." The peculiar
phenomenon observed in the spectroscope, the flickering bands or lines
of the solar spectrum flashing upon and across the coronal spectrum,
has caused no little speculation among observers.
The diffraction or interference bands projected by the passage of a
strong beam of light by a solid body, as discovered long since by
Grimaldi, and investigated later by Newton, Fresnel, and Fraunhofer,
are explained and illustrated in our text books; but the grand display
of this phenomenon in a total solar eclipse, where the sun is the
source of light and the moon the intercepting body, has as yet
received but little attention from observers, and is not mentioned to
my knowledge in our text books.
In the instructions issued from the United States Naval Observatory
and the Signal Office at Washington for the observation of the eclipse
of July 29, 1878, attention was casually directed to this phenomenon,
and a few of the observers at Pike's Peak, Central City, Denver, and
other places have given lucid and interesting descriptions of the
flight of the diffraction bands as seen coursing over the face of the
earth at the speed of the moon's shadow, at the apparent enormous
velocity of thirty-three miles per minute, or fifty times the speed of
a fast railway train.
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