landscape. The speed is really somewhat greater than that observed, since the observer is himself carried in the same direction, though at a slower speed, by the rotation of the Earth on its axis.
At the surface of the Earth it is known that bodies fall sixteen feet in the course of a second, owing to the force of gravitation. The same force causes the Moon to drop one-fifth of an inch toward the Earth in the same time. A deflection of one-fifth of an inch in 3,350 feet does not seem a very large amount, but it is sufficient to deflect the Moon's course out of a straight line into a closed orbit around the Earth.
It is singular that gravitation, the most predominant and all-pervading force in the universe, should be the one least understood. No satisfactory hypothesis has as yet been advanced to explain it, excepting that we know it must be a stress of some sort transmitted through the ether and affecting all bodies alike. Yet, when we consider what a tremendous power it is, it is impossible to conceive how it can be transmitted through a material so impalpable as to offer no resistance whatever to the enormously rapid motions of the heavenly bodies, and to be capable of transmitting such vast stores of energy in the form of light and heat with such almost inconceivable velocity.
In order to comprehend the total amount of attractive force existing, for instance, between the Earth and Moon—two comparatively insignificant bodies in the universe — let us imagine all the ether removed, and that in its place we substitute a steel rod a quarter of a million miles in length and having no weight. In order that the rod may properly take the place of the ether, and not be broken by the strain placed upon it, it must be at least 225 miles in diameter. If it were less than this it would be snapped like a pipe-stem by the gigantic force that the invisible, weightless ether transmits without our even noticing it.
The mass of the Moon—that is, the amount of matter it contains—is one-eightieth that of the Earth. Bodies on its surface, therefore, are much lighter than they are here, notwithstanding the smaller size of the Moon. The ratio is almost exactly one-sixth; consequently a man weighing 180 pounds on the Earth, if transported to the Moon, would find that he only weighed 30 pounds there, and could carry two men at once on his back for twenty miles much more easily than he could walk that distance without a load here. He could throw a stone six times as far as on the Earth, and jump six times as high. Indeed, jumping over a moderate-sized house or tree would be a gymnastic feat scarcely worth mentioning upon the Moon.
