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.