The whole formation is covered
with the same light-reflecting material as the streaks which surround
it."

CHAPTER VI

THE SCENERY OF THE MOON'S SOUTHERN HEMISPHERE

I now directed M'Allister to steer across the lunar equator into the
southern hemisphere, and our attention was soon attracted by a very
large walled plain on the eastward side of our course.

John asked me what it was called, and I explained that it was named
Grimaldi, being also well known to observers as the darkest tinted of
all the large lunar formations. As seen from the earth it appears a
narrow ellipse, but we could see its full width, which is 129 miles, the
length being 148 miles. It is also noteworthy as one of the few plains
which are convex in section, and it is so large that its area is equal
to the combined area of the whole of the counties of England south of
the line of the Thames, including Cornwall.

I showed M'Allister this formation on our map, where it appears only a
narrow ellipse in consequence of the moon's curvature, and pointed out
how very different was its appearance now we could see over its whole
extent. Other formations nearer to the moon's limb appear still more
foreshortened when viewed from the earth.

John here remarked that "these large ring-plains covered immense areas,
and, now that we could actually see them, their magnitude was more
impressive than anything we could have imagined from merely hearing or
reading about them."

"Yes, John," I said, "from our altitude of more than ten miles above the
lunar surface we command a much more extensive view and gain a better
knowledge of details than we could obtain even if we landed on the moon.
For instance, if we could stand down in the centre of one of those very
large rings, we should imagine we were in the midst of a boundless open
plain. The mountains all around us would be so distant that, owing to
the sharp curvature of the lunar sphere, they would all be below the
horizon, notwithstanding the fact that many of them are several
thousands of feet in height. So, for all we could see of them, those
mountains might be non-existent.

"In the case of somewhat smaller rings we might perhaps see, here and
there above the horizon, just the topmost peaks of some of the more
lofty mountains."

M'Allister was now struck with an idea, and exclaimed, "Professor, I
notice that many of these great walled plains are very flat, and I
should think they would make fine