Yet another mystery is the corona of the sun. This is something we
should never have known to exist if the sun were not sometimes
totally eclipsed by the dark body of the moon. On these rare
occasions the sun is seen to be surrounded by a halo of soft,
white light, sending out rays in various directions to great
distances. This halo is called the corona, and has been most
industriously studied and photographed during nearly every total
eclipse for thirty years. Thus we have learned much about how it
looks and what its shape is. It has a fibrous, woolly structure, a
little like the loose end of a much-worn hempen rope. A certain
resemblance has been seen between the form of these seeming fibres
and that of the lines in which iron filings arrange themselves
when sprinkled on paper over a magnet. It has hence been inferred
that the sun has magnetic properties, a conclusion which, in a
general way, is supported by many other facts. Yet the corona
itself remains no less an unexplained phenomenon.

[Illustration with caption: PHOTOGRAPH OF THE CORONA OF THE SUN,
TAKEN IN TRIPOLI DURING TOTAL ECLIPSE OF AUGUST 30, 1905]

A phenomenon almost as mysterious as the solar corona is the
"zodiacal light," which any one can see rising from the western
horizon just after the end of twilight on a clear winter or spring
evening. The most plausible explanation is that it is due to a
cloud of small meteoric bodies revolving round the sun. We should
hardly doubt this explanation were it not that this light has a
yet more mysterious appendage, commonly called the Gegenschein, or
counter-glow. This is a patch of light in the sky in a direction
exactly opposite that of the sun. It is so faint that it can be