The Moon | Page 3

were either
coming into or passing out of sunlight; and though his method was
incapable of accuracy, and his results consequently untrustworthy, it
served to demonstrate the immense altitude of these circumvallations,
and to show how greatly they exceed any mountains on the earth if the
relative dimensions of the two globes are taken into consideration.
Before the close of the century when selenography first became
possible, Hevel of Dantzig, Scheiner, Langrenus (cosmographer to the
King of Spain), Riccioli, the Jesuit astronomer of Bologna, and
Dominic Cassini, the celebrated French astronomer, greatly extended
the knowledge of the moon's surface, and published drawings of
various phases, and charts, which, though very rude and incomplete,
were a clear advance upon what Galileo, with his inferior optical means,

had been able to accomplish. Langrenus, and after him Hevel, gave
distinctive names to the various formations, mainly derived from
terrestrial physical features, for which Riccioli subsequently substituted
those of philosophers, mathematicians, and other celebrities; and
Cassini determined by actual measurement the relative position of
many of the principal objects on the disc, thus laying the foundation of
an accurate system of lunar topography; while the labours of T. Mayer
and Schroter in the last century, and of Lohrmann, Madler, Neison
(Nevill), Schmidt, and other observers in the present, have been mainly
devoted to the study of the minuter detail of the moon and its physical
characteristics.
As was manifest to the earliest telescopic observers, its visible surface
is clearly divisible into strongly contrasted areas, differing both in
colour and structural character. Somewhat less than half of what we see
of it consists of comparatively level dark tracts, some of them very
many thousands of square miles in extent, the monotony of whose
dusky superficies is often unrelieved for great distances by any
prominent object; while the remainder, everywhere manifestly brighter,
is not only more rugged and uneven, but is covered to a much greater
extent with numbers of quasi-circular formations, differing widely in
size, classed as walled-plains, ring-plains, craters, craterlets,
crater-cones, &c. (the latter bearing a great outward resemblance to
some terrestrial volcanoes), and mountain ranges of vast proportions,
isolated hills, and other features.
Though nothing resembling sheets of water, either of small or large
extent, have ever been detected on the surface, the superficial
resemblance, in small telescopes, of the large grey tracts to the
appearance which we may suppose our terrestrial lakes and oceans
would present to an observer on the moon, naturally induced the early
selenographers to term them Maria, or "seas"--a convenient name,
which is still maintained, without, however, implying that these areas,
as we now see them, are, or ever were, covered with water. Some,
however, regard them as old sea-beds, from which every trace of fluid,
owing to some unknown cause, has vanished, and that the folds and
wrinkles, the ridges, swellings, and other peculiarities of structure

observed upon them, represent some of the results of alluvial action. It
is, of course, possible, and even probable, that at a remote epoch in the
evolution of our satellite these lower regions were occupied by water,
but that their surface, as it now appears, is actually this old sea-bottom,
seems to be less likely than that it represents the consolidated crust of
some semi- fluid or viscous material (possibly of a basaltic type) which
has welled forth from orifices or rents communicating with the interior,
and overspread and partially filled up these immense hollows, more or
less overwhelming and destroying many formations which stood upon
them before this catastrophe took place. Though this, like many other
speculations of a similar character relating to lunar "geology," must
remain, at least for the present, as a mere hypothesis; indications of this
partial destruction by some agency or other is almost everywhere
apparent in those formations which border the so-called seas, as, for
example, Fracastorius in the Mare Nectaris; Le Monnier in the Mare
Serenitatis; Pitatus and Hesiodus, on the south side of the Mare
Nubium; Doppelmayer in the Mare Humorum, and in many other
situations; while no observer can fail to notice innumerable instances of
more or less complete obliteration and ruin among objects within these
areas, in the form of obscure rings (mere scars on the surface), dusky
craters, circular arrangements of isolated hills, reminding one of the
monoliths of a Druidical temple; all of which we are justified in
concluding were at one time formations of a normal type. It has been
held by some selenologists --and Schmidt appears to be of the
number,--that, seeing the comparative scarcity of large ring-plains and
other massive formations on the Maria, these grey plains represent, as it
were, a picture of the primitive surface of the moon before it was
disturbed by the operations of interior forces; but this view affords no
explanation of the