Page:Popular Astronomy - Airy - 1881.djvu/149

Rh in the way and retards its motion. Many persons suppose that, in consequence, the planet would fall into the sun.

No such thing will happen; the only effect it would have is this: it would cause the planet to describe a different orbit, such as is shown by the dotted line Lprm. Its velocity would be diminished by the interruption at L, and it would consequently be more bridled in by the attraction of the sun there, and the planet would then describe a new orbit of such a nature as to have a greater curvature at L; but if nothing disturbed it again, it would then go on continually describing that new orbit over and over again. Whenever the series of disturbances ceases, whatever orbit the planet is then moving in, it will continue to go on moving in that orbit. The planet's orbit is changed by any sudden disturbance, but the orbit so changed will continue, and the planet will be no nearer destruction than if it had not been disturbed at all.

There is only one more point regarding the law of gravitation, on which I shall here speak; it is the velocity, or the change of motion, which an attracting body produces on another body. I have spoken of attraction as if it was directed towards the sun; but we shall find that experiments of various kinds lead us to this conclusion: that every particle of matter attracts every other particle of matter; and that every planet attracts every other planet, that every planet attracts the sun, that the sun attracts