anoes, three of which he
declared to be in a state of ignition; two of them apparently on the
decline, the third still active. He was so convinced of the reality of
the phenomenon, that on the 20th of April 1787 he wrote:--"The volcano
burns with greater violence than it did last night." The real diameter
of the volcanic light he estimated at 16,400 feet. Its intensity he
described as superior to that of the nucleus of a comet then flashing
across our system. The objects situated near the crater were fully
illuminated by the glare of its burning matter.

It may seem strange that, after observations so exact and minute, few
astronomers now admit the existence of active volcanoes in the Moon. The
reasons for their incredulity are thus stated:--

The various parts of the Moon do not all reflect with the same
intensity. Here, that intensity may be dependent on the form;
elsewhere, on the nature of the materials. Those persons who have
examined the lunar orb with telescopes, know how very considerable the
difference arising from these two causes may be,--with how much keener
and stronger a radiance one point of the Moon will sometimes shine than
those around it. Well, it would seem to be obvious that the ratio of
intensity between the brilliant parts and the faint parts must always be
the same, whatever the origin of the illuminating light. In that portion
of the lunar sphere which receives the glow and glory of the sun, we
know that some points exist, the brightness of which is extraordinary
compared with the feeble flickering gleam of those around them. And
these same points, when seen in the dim reflection of the Earth, will
still predominate in intensity over the neighbouring regions. In this
way Arago and others explain the observations of Herschel, without
admitting the existence of active volcanoes in the Moon. That volcanoes
there are, is a familiar fact; but they would seem to have exhausted
their activity in long-past ages. The lunar surface is now a dreary
waste of rugged lava and ashes, covered with the matter ejected from
craters once in a state of furious eruption. The Moon, in fact, is a
world which has burned itself out. How strange the thought that in a
far-back period the inhabitants of Earth, had Earth then been inhabited,
might have seen the glare of countless volcanoes diffused, lurid and
threatening, over the face of their satellite! How strange the thought
that the once active fires should all have di