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 to project a missile with a speed sufficiently great to carry it to a height which would even be an appreciable fraction of the earth's diameter. Our globe is so massive that any velocity which we were able to impart to the upward movement of the bullet would not suffice to carry it to an altitude that bears the same relation to the diameter of the earth as the thickness of an egg shell bears to the diameter of the egg.

It is, however, interesting to consider the circumstances under which a missile would take flight if projected from a globe differing widely from our earth in bulk or mass or physical constitution. Let us first of all suppose that a piece of artillery was to be transferred to some globe much more massive than the earth. Take, for example, some globe possessing the same mass as the sun, and of like dimensions. Under these circumstances, the attraction by which the speed of the ascending missile would be gradually lessened is much more effective than the corresponding force upon the earth. It follows that, even though the missile might leave the mouth of the cannon with the same pace on the large globe that it had on the small one, yet the upward velocity would be abated much more quickly when the heavier mass was underneath, than when it was only the attraction of the smaller of the two globes that was checking the ascent. From the big globe the projectile could not ascend to anything like the altitude which it would be able to attain on the small one, and the time that would be occupied in its flight would undergo a corresponding diminution. Thus, although a projectile might be discharged by a piece of our modern artillery, with a speed sufficient to carry it to an elevation of several miles, yet a like velocity of projection from the