on the earth could, with the
same exertion, carry six sacks of corn on the moon. A cricketer who can
throw a ball 100 yards on the earth could with precisely the same
exertion throw the same ball 600 yards on the moon. Hiawatha could shoot
ten arrows into the air one after the other before the first reached
the ground; on the moon he might have emptied his whole quiver. The
volcano, which on the moon drove projectiles to the distance of
thirty-nine miles, need only possess the same explosive power as would
have been sufficient to drive the missiles six or seven miles on the
earth. A modern cannon properly elevated would easily achieve this feat.

[Illustration: Fig. 30.--Formation of the Level Floor by Lava.]

It must also be borne in mind that there are innumerable craters on the
moon of the same general type but of the most varied dimensions; from a
tiny telescopic object two or three miles in diameter, we can point out
gradually ascending stages until we reach the mighty Petavius just
considered. With regard to the smaller craters, there is obviously
little or no difficulty in attributing to them a volcanic origin, and as
the continuity from the smallest to the largest craters is unbroken, it
seems quite reasonable to suppose that even the greatest has arisen in
the same way.

It should, however, be remarked that some lunar features might be
explained by actions from without rather than from within. Mr. G.K.
Gilbert has marshalled the evidence in support of the belief that lunar
sculptures arise from the impact of bodies falling on the moon. The Mare
Imbrium, according to this view, has been the seat of a collision to
which the surrounding lunar scenery is due. Mr. Gilbert explains the
furrows as hewn out by mighty projectiles moving with such velocities as
meteors possess.

The lunar landscapes are excessively weird and rugged. They always
remind us of sterile deserts, and we cannot fail to notice the absence
of grassy plains or green forests such as we are familiar with on our
globe. In some respects the moon is not very differently circumstanced
from the earth. Like it, the moon has the pleasing alternations of day
and night, though the day in the moon is as long as twenty-nine of our
days, and the night of the moon is as long as twenty-nine of our nights.
We are warmed by the rays of the sun; so, too, is the moon; but,
whatever may be the temperature during the long day on the moon, it
seems certain that the