We have
just observed that the moon is characterized by vast mountain rings,
attaining in many cases a diameter exceeding fifty miles. If these are
volcanic craters, it is evident, at a glance, that the mightiest
volcanoes of the earth fall into insignificance beside them. Now, the
slight force of gravity on the moon has been appealed to as a reason why
volcanic explosions on the lunar globe should produce incomparably
greater effects than upon the earth, where the ejected materials are so
much heavier. The same force that would throw a volcanic bomb a mile
high on the earth could throw it six miles high on the moon. The giant
cannon that we have placed in one of our coast forts, which is said to
be able to hurl a projectile to a distance of fifteen miles, could send
the same projectile ninety miles on the moon. An athlete who can clear a
horizontal bar at a height of six feet on the earth could clear the same
bar at a height of thirty-six feet on the moon. In other words, he could
jump over a house, unless, indeed, the lunarians really are giants, and
live in houses proportioned to their own dimensions and to the size of
their mountains. In that case, our athlete would have to content himself
with jumping over a lunarian, whose head he could just clear--with the
hat off.
These things are not only amusing, but important. There can be no
question that the force of gravity on the moon actually is as slight as
it has just been described.
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