darting from the ground or the sea to
the clouds. It ended in a deluge of rain, which lasted all night, and
made us augur ill for the solar eclipse next day; and, sure enough, when
I awoke next morning, the sky was darkened by clouds and rain.
Fortunately, it cleared up just as the eclipse began; we were all
prepared for observing it, and we followed its progress through the
opening in the clouds till at last there was only a very slender
crescent of the sun's disc left; its convexity was turned upwards, and
its horns were nearly horizontal. It was then hidden by a dense mass of
clouds; but after a time they opened, and I saw the edge of the moon
leave the limb of the sun. The appearance of the landscape was very
lurid, but by no means very dark. The common people and children had a
very good view of the eclipse, reflected by the pools of water in the
streets.

Many of the astronomers who had been in Sicily observing the eclipse
came to see me as they passed through Naples. One of their principal
objects was to ascertain the nature of the corona, or bright white rays
which surround the dark lunar disc at the time of the greatest
obscurity. The spectroscope showed that it was decidedly auroral, but as
the aurora was seen on the dark disc of the moon it must have been due
to the earth's atmosphere. Part of the corona was polarized, and
consequently must have been material; the question is, Can it be the
ethereal medium? A question of immense importance, since the whole
theory of light and colours and the resistance of Encke's comet depends
upon that hypothesis. The question is still in abeyance, but I have no
doubt that it will be decided in the affirmative, and that even the
cause of gravitation will be known eventually.

At this time I had the pleasure of a visit from Mr. Peirce, Professor of
Mathematics and Astronomy, in the Harvard University, U.S., and
Superintendent of the U.S. Coast Survey, who had come to Europe to
observe the eclipse. On returning to America he kindly sent me a
beautiful lithographed copy of a very profound memoir on linear and
associative algebra. Although in writing my popular books I had somewhat
neglected the higher algebra, I have read a great part of the work; but
as I met with some difficulties I wrote to Mr. Spottiswoode, asking his
advice as to the books that would be of use, and he sent me Serret's
"Cours d'Algebre Superieure," Salmon's "Higher Algebra," and Tait on
"Quaternions;" so