Whether this furnishes a sound reason for assuming that the lunar inhabitants, if any exist or have ever existed, should be preposterous giants is questionable; yet such an assumption receives a certain degree of support from the observed fact that the natural features of the moon are framed on an exaggerated scale as compared with the earth’s.  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.  So, even without calling in imaginary inhabitants to lend it interest, the comparative inability of the moon to arrest bodies in motion becomes a fact of much significance.  It has led to the theory that meteorites may have originally been shot out of the moon’s great volcanoes, when those volcanoes were active, and may have circulated about the sun until various perturbations have brought them down upon the earth.  A body shot radially from the surface of the moon would need to have a velocity of only about a mile and a half in a second in order to escape from the moon’s control, and we can believe that a lunar volcano when in action could have imparted such a velocity, all the more readily because with modern gunpowders we have been able to give to projectiles a speed one half as great as that needed for liberation from lunar gravity.