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 the vicinity of the globe on which it was placed. A cannon, for instance, which was strong enough to impart to the projectiles that issued from it a velocity double as great as that which our missiles receive here, would send the body entirely away from the moon. On globes still smaller a speed correspondingly less would suffice. Thus in the case of some of the minor planets where the diameters are not expressed in thousands, but only in hundreds of miles, the necessary projectile force would be quite within the range of modern artillery. Indeed, on some of the still smaller globes like the satellites of Mars, where the diameter is a score of miles or less, it is quite likely that velocities comparable with those with which a cricket ball is thrown would suffice to transcend the critical amount. The arm of a vigorous cricketer would cause the ball to ascend with a speed sufficient to make it go on further and further until at last it gradually sank away into the heavens never more to tumble back again to the globe from which its way was sped.

Provided with these considerations, let us now seek to determine the source of meteorites from an astronomical point of view. It is plain that if these objects had been shot as bombs from volcanoes, those volcanoes must have had a potency sufficient to discharge fragments of the solid crust of the globe aloft with such speed that they did not presently return in consequence of that globe's attraction. The great difficulty which we encounter in the consideration of this question arises from the high velocity which would be necessary to set the missiles free from the obligation of immediate return to the parent globe. As the speed of seven miles a second is undoubtedly far in excess of any speed which is attained in terrestrial