e. Solitary peaks rise from the level plains and cast their
long narrow shadows athwart the smooth surface. Vast plains of a dusky
tint become visible, not perfectly level, but covered with ripples,
pits, and projections. Circular wells, which have no surrounding wall
dip below the plain, and are met with even in the interior of the
circular mountains and on the tops of their walls. From some of the
mountains great streams of a brilliant white radiate in all directions
and can be traced for hundreds of miles. We see, again, great fissures,
almost perfectly straight and of great length, although very narrow,
which appear like the cracks in moist clayey soil when dried by the
sun."[14]

But interesting as these views may be, it was not for such discoveries
as these that astronomers examined the surface of the moon. The
examination of mere peculiarities of physical condition is, after all,
but barren labour, if it lead to no discovery of physical variation. The
principal charm of astronomy, as indeed of all observational science,
lies in the study of change--of progress, development, and decay, and
specially of systematic variations taking place in regularly-recurring
cycles. And it is in this relation that the moon has been so
disappointing an object of astronomical observation. For two centuries
and a half her face has been scanned with the closest possible scrutiny;
her features have been portrayed in elaborate maps; many an astronomer
has given a large portion of his life to the work of examining craters,
plains, mountains, and valleys, for the signs of change; but until
lately no certain evidence--or rather, no evidence save of the most
doubtful character--has been afforded that the moon is other than "a
dead and useless waste of extinct volcanoes." Whether the examination of
the remarkable spot called Linne--where lately signs were supposed to
have been seen of a process of volcanic eruption--will prove an
exception to this rule, remains to be seen. The evidence seems to me
strongly to favour the supposition of a change of some sort having taken
place in this neighbourhood.

The sort of scrutiny required for the discovery of changes, or for the
determination of their extent, is far too close and laborious to be
attractive to the general observer. Yet the kind of observation which
avails best for the purpose is perhaps also the most interesting which he
can apply to the lunar details. The peculiarities presented by a