Page:In the high heavens.djvu/317

 be experienced by the inhabitants of the granite and of the platinum globe respectively. For though the masses of those globes, that is, the quantity of matter they possess, would be the same, yet a denizen of the globe of stone would be twice as far away from the centre of his world as a denizen of the globe of metal would be from the centre of his. So that though the attractions exerted by the two globes at equal distances from their centres would be identical, yet, owing to the law of the inverse square, the inhabitant of the big globe would feel only one-fourth the attraction experienced by the occupant of the small one. It is thus plain that a piece of artillery placed on one of these globes would launch forth its missile under very different conditions from those which would determine the movement if the projection were made from the other globe. As the body left the muzzle the force striving to draw it back to the metallic globe would be no less than four times as great as that which would commence to operate when the missile left the muzzle of the gun on the stone globe. The consequence is that in the latter case the body would ascend to a far greater elevation before its speed was checked and reversed than when it was shot from the platinum world. From this illustration it will be plain that it is necessary to take into account both the mass of a globe and its dimensions when we would determine the height to which a projectile can ascend.

Let us consider the case of a great cannon placed on a globe of comparatively small mass, the density of that globe being about the same as the average density of the worlds which we find in the solar system. It is plain that as the object goes aloft a lessened attractive force will