equality of the time of the moon's revolution on
her own axis and of her revolution round the earth.
The moon, however, is subject to a slight swinging
motion, called her libration, which brings
sometimes a little piece of one side of the unseen
hemisphere into view, and sometimes a little
piece of the other. The cause of the libration
is thus explained: When the moon passed from
a liquefied, or fused, to a solid state, under the
influence of the earth's attraction, she assumed a
form less regular than would have been if no
powerful attractive body had existed in her
neighbourhood. The moon's equator, which
would have been circular, was pulled into an
ellipse by the action of our globe. The moon
would, therefore, appear to an observer situated
in open space who could look at it transversely,
as an egg-shaped body drawn out in the
direction of the earth—as a sort of pendulum
without a visible string or rod of connexion, the
real rod being the force of gravity. When a
pendulum is pushed out of the perpendicular, its
own weight brings it back again: when the
moon's major axis leaves its usual position, the
earth's attraction in like manner forces it to
return. The human race will never see but one
face of the moon. This strange phenomenon
may be thus accounted for without having
recourse to an almost miraculous coincidence
between the moon's times of rotation and revolution,
which are really quite independent of each
other; we find that it is due to a physical cause,
which is calculable, although it is visible only to
the eyes of the mind—namely, to the lengthening
of one diameter, which took place in consequence
of the earth's attraction, when the moon
cooled down into a solid body. If there had
existed, at the outset, a slight difference
between the moon's movements of rotation and
revolution, the earth's attraction would have
reduced those movements to the strict equality
which we witness now.

And, as the fact of the moon exposed to our
view remains ever unchanged, so does the aspect
of that face. Schröter studied the moon for
years, in order to ascertain whether any alteration
of her surface could be discovered. Maedler,
who began, in 1830, a grand topographical
map of the moon, which, with its accompanying
treatise, was published at Berlin in 1837, was
obliged to come to the conclusion that, as far as
we are permitted to judge, there is no living
thing, nor will there ever be, in the moon. Any
one who could behold the earth from a distance,
would have his view of our continents and
oceans continually intercepted by curtains of
clouds; as one position became unveiled, another
would be shrouded in shifting mists. Spring
would tinge vast tracts of forest land with green;
winter would silver over still wider areas with
white. We see nothing of this in the moon;
not a cloud, not a token of change of season
not an exhalation to betray the presence of
water, not a refracted ray or tinge of varying
colour to give reason to suspect an atmosphere
The moon herself never offers the slightest
obstacle to our minutest inspection; when, we
cannot see her, she is hid only by the happy
mutations to which the terrestrial atmosphere
is subject.

From these circumstances, the conclusion,
perhaps too hasty, has been arrived at, that the
noon is not only dead, but is a mummified dead
body, utterly uninhabitable. Huygens, the first
who stated that the moon had no atmosphere
capable of refracting the light of the stars, more
cautiously expressed his belief that the
inhabitants of the moon, if any, must be quite
differently constituted to ourselves. At present,
there exists a tendency to revise the verdict
of "Found Dead," which preceding centuries
have pronounced on the moon. By a comparison
of old drawings made by careful astronomers
with the most exact sketches that can
be taken now, Mr. Webb believes that notable
hanges have taken place on the moon's surface.
Father Secchi concludes, from experiments, that
the topmost points of the-lofty mountains may
be covered with ice and snow. Mr. Delarue
concludes, from his photographic observations, that
the moon has an atmosphere, which is very
shallow, but relatively very dense, and that the
vast space entitled seas are neither more nor
less than forests.

Apropos of vegetation, there are known on
the surface of the moon some hundred luminous
furrows or grooves, already mentioned, whose
nature remains as yet unexplained. They were
once thought the dry beds of rivers; but that
cannot be. Their length varies from ten to a
hundred and twenty miles; their greatest breadth
is about a mile, but the majority are much
narrower. Their edges are parallel and very steep;
their depth must be great. Some stretch
onwards in straight lines, others are slightly curved,
but all are generally isolated. A few cross, or
branch into, each other, like veins. There are
some which traverse the craters of mountains,
while others terminate at the steep rampart
which surrounds them. They are visible
everywhere, except in the region of the highest
mountains. Many more of these luminous
furrows exist than are laid down in M.
Lecouturiers's map; the small ones were omitted to
avoid confusion.

A German astronomer, M. Schwabe, undertook
the elucidation of the mystery, by studying
the furrows with powerful telescopes. He found
them to be composed, at certain epochs, of fine
parallel dark lines, separated by luminous rays.
In the course of several months, the dark lines
and luminous rays disappear, but not for good
and all; they are afterwards reproduced,
disappearing again, and so on, continually. These
periodical appearances and disappearances are
interpreted by M. Schwabe as a phenomenon of
vegetation. He holds the dark lines to be rows
of green trees, and the bright lines which separate
them to be naked sterile vacant spaces which
acquire the look of luminous stripes from the
contrast of the dark trees fringing them. The
disappearance of the bright and sombre lines is
attributed to the trees' shedding their foliage.
Whether this explanation be correct or not, the