Now it is evident that any disturbance in so closely packed a system of small bodies as that constituting Saturn’s rings must result in collisions between the bodies concerned. Particles pulled out or in must come in contact with others pursuing their own paths, and as at each collision some energy is lost by the blow, a general falling in toward the planet results. At the same time, as the blow will not usually be exactly in the plane in which either particle was previously moving, both will be thrown more or less out of the general plane of their fellows, and the ring at that point, even if originally flat, will not remain so. For the ring, though very narrow relatively, has a real thickness, quite sufficient for slantwise collision, if the bodies impinge. [Illustration: _Saturn’s Rings._ _November 1907._] Now the knots or beads on the rings appeared exactly inside the points where the satellites’ disturbing action is greatest, or, in other words, in precisely their theoretic place. We can hardly doubt that such, then, was their origin.[9] [9] Paper by the writer in the _Phil. Mag._, April, 1908. The result must be gradually to force the particles as a rule nearer the planet, until they fall upon its surface, while a few are forced out to where they may coalesce into a satellite,—a result foreseen long ago by Maxwell. It is this process which in the knots we are actually witnessing take place, and which, like the corona about the eclipsed Sun, only comes out to view when the obliterating brightness of the main body of the rings is withdrawn by their edgewise presentation. The reason the out-of-plane particles are most numerous just inside the point of disturbance is not only that there the action throwing them out is most violent, but that all the time a levelling action quite apart from disturbance is all the time tending to reduce them again to one plane, as we shall see further on when we come to the mechanical forces at work. Thus the tore is most pronounced on its outer edge, and falls to a uniform level at its inner boundary. The effect is somewhat as represented in the adjoining cut, in which the vertical scale is greatly magnified:— [Illustration: THE TORES OF SATURN. Not drawn to scale.] With Saturn ended the bounds of the solar system as known to the civilized world until 1781. On March 13 of that year Sir William Herschel in one of his telescopic voyages through space came upon a strange object which he at once saw was not a star, because of its very perceptible round disk, and which he therefore took for a peculiar kind of comet. Nearly a year rolled by before Lexell showed by calculation of its motion that it was no comet, but undoubtedly a new planet beyond Saturn travelling at almost twice that body’s mean distance from the Sun.