Page:Popular Science Monthly Volume 17.djvu/635

Rh to be measured by 15,000,000 of our unit-bars, together making a bar of solid steel whose section would cover 15,000,000 square miles, more than four times the area of the United States. The wires, such as we supposed to hold the moon, would, in the case of the earth and sun, be almost as close as the blades of grass on a lawn.

Without going any further into calculations, it is enough to say of the other planets, that Mercury is held to its duty by 6,590,000 of our unit-bars; while Venus, being nearly as large as the earth, and so much nearer the sun, requires the united strength of nearly 23,000,000. Mars is smaller, and more remote, and therefore needs only some 811,500 such bands to hold it to its course; for, strange as it may appear, and however unlike other sovereigns, the sun holds its subjects in obedience the more easily, the greater their distance from the center of the system, provided, of course, that their importance otherwise is the same. But still, distant as it is, Jupiter's immense mass demands incomparably the strongest measures to keep it in check; nothing less than 170,000,000 of those bands of steel will overcome its wandering tendencies. Saturn, being a lighter weight, is more easily guided—15,000,000 suffice for that. Uranus and Neptune are of little account as compared with Jupiter; 588,000 for the one and 282,000 for the other are all that are needed to restrain their vagaries.

If, now, we turn to the planets, and study their influence, we shall find them pulling and tugging at each other with forces that, but for compensations planted in the system itself, would tear it to pieces; but, like the armed men of Cadmus, these forces destroy each other.

However difficult it may be to conceive of such an amount of power as the sun puts forth, we are so accustomed to regard that body as the governing center of our part of the universe, and have heard so much of its vast size, that we are prepared to accept almost any statement in regard to it. But as to the planets we do not realize their size, and we seldom think of their exerting any influence on the earth or on one another. That they do exert such an influence we know, for astronomers have told us of perturbations thus produced; but, then, very few of us connect such statements with the tiny specks which we see in the heavens. Yet their influence is no trifle. Mercury, which is too small and too near the sun for most of us to have seen, draws the earth when in mean perigee with a force small indeed when compared with those which we have been considering, but large enough to break 232,390,000 bars one foot square; Venus pulls with a force of 11,175,000,000; Mars pulls enough to overcome the united strength of 590,680,000; while Jupiter draws away with a steady tug of nearly 23,000,000,000; and even Neptune, 2,700,000,000 miles away, and utterly invisible to the naked eye, still has sufficient energy to drag our earth toward it with force able to snap 27,000,000 such bars. Besides these, which are only the interplay of forces between our