ow-covered peak of a
mountain shines out upon a moonlit night from among the darker hills and
dales and rocks and forests of the landscape. But Herschel considered
that the occasional brightness of the crater Aristarchus could not be
thus explained. The spot had been seen before the time of Herschel's
observations by Cassini and others. It has been seen since by Captain
Kater, Francis Baily, and many others. Dr. Maskelyne tells us that in
March 1794 it was seen by the naked eye by two persons.

Baily thus describes the appearance presented by this lunar crater on
December 22, 1835: 'Directed telescope to the moon, and pointing it to
the dark part in the vicinity of Aristarchus, soon saw the outline of
that mountain very distinctly, formed like an irregular nebula. Nearly
in the centre was a light resembling that of a star of the ninth or
tenth magnitude. It appeared by glimpses, but at times was brilliant,
and visible for several seconds together.'

There can be little doubt, however, that the apparent brightness of this
lunar crater, or rather of its summit, is due to some peculiar quality
in the surface, which may perhaps be covered by some crystalline or
vitreous matter poured out in the far distant time when the crater was
an active one. Prof. Shaler, who examined the crater when it was
illuminated only by earthshine, with the fine 15-inch telescope of the
Harvard Observatory (Cambridge U.S.), says that he has been able to
recognise nearly all the craters over 15 miles in diameter in the dark
part. 'There are several degrees of brightness,' he says, 'observable in
the different objects which shine out by the earth-light. This fact
probably explains the greater part of the perplexing statements
concerning the illumination of certain craters. It certainly accounts
for the volcanic activity which has so often been supposed to be
manifested by Aristarchus. Under the illumination by the earth-light
this is by far the brightest object on the dark part of the moon's face,
and is visible much longer and with poorer glasses than any other object
there.'

Here my record of astronomical myths must be brought to a close. It will
be noticed that in every instance either the illusion has affected the
actual observations of eminent and skilful astronomers, or has caused
such astronomers to put faith for a while in illusory observations. Had
I cared to include the mistakes which have been made by or have misled
observers of less