Because the attractive power of a large body is greater than that of a small one. As each atom of matter has inherent power of attraction, it follows that a large aggregation of particles must attract in proportion to the number of those particles.
782. Why do clouds gather around mountain tops?
Because they are attracted by the mountains.
783. Why would a piece of lead tied to a string, and let down from a church steeple, incline a little from the perpendicular towards the church?
Because the masses of stone of which the church is built would attract the lead.
784. How can man weigh the earth?
By observing what is called the deflection of small bodies when brought within given distances of larger bodies, the degree of attraction exercised by the large body upon the smaller one becomes known. This attraction of the large body exercised over the smaller body is an opposing influence, acting against the earth's attraction of the small body, which is drawn out of its course: it constitutes a natural balance between the influence of the earth and another body, acting in opposition to it. Founded upon these, and some other data, man can weigh the earth, and give a morally certain result!
Deflection.—The act of turning aside.
785. How can man weigh the planets?
The planets exercise as certain an influence upon each other as do two pieces of wood floating upon a basin of water. As the planetary bodies fly through their prescribed orbits, and approach nearer to, or travel further from, each other, they are observed to deviate from that course which they must have pursued but for the increase or the decrease of some influence of attraction. By making observations at various times, and by comparing a number of results, it is possible to weigh any planetary body, however vast, or however distant.