[Illustration: Fig. 12. The Schichallion Rocks. The dotted line and weight A represent the ordinary position of a plumb line, whilst the line of the weight B indicates (of course, with some exaggeration) the attractive power of the mass of the rock drawing it from the perpendicular.] This truly wonderful power of attraction pervades all masses; and being, as before stated, proportional to the quantity of matter, if a man could be transported to the surface of the sun, he would become about thirty times heavier: he would be attracted, or impelled, to the sun with thirty times more gravitating force than on the surface of the earth, and would weigh about two tons. Of course, nursing a baby on the sun's surface would be a very serious affair with our ordinary strength; whilst on some of the smaller planets, such as Ceres and Pallas, we should probably gravitate with a force of a few pounds only, and with the same muscular power now possessed, we should quite emulate the exploits of those domestic little creatures sometimes called "the industrious fleas," and our jumping would be something marvellous. [Page 12] There is no very good lecture-table experiment that will illustrate gravitation, although attention may be directed to the fact of a piece of potassium thrown on the surface of water in a plate generally rushing to the sides, and, as if attracted, attaching itself with great force to the substance of the pottery or porcelain; or, if a model ship, or lump of wood, be allowed to float at rest in a large tank of water, and a number of light chips of wood or bits of straw be thrown in, they generally collect and remain around the larger floating mass. [Illustration: Fig. 13. A. The centre ball, representing the earth's centre of gravity. W W W W. Four wires fixed into centre ball, and passing through and secured in the hoop, projecting about one foot from the circumference. B B B B. Two balls--a model ship and toy--working on the wires like beads, with vulcanized India-rubber straps attached to them and the circumference of the hoop.] A very good idea, however, may be afforded of the universal action of gravity maintaining all things in their natural position on the earth by [Page 13] taking a hoop and arranging in and upon it balls, or a model ship, or other toy, and wires, as depicted in our diagram. With this simple apparatus we may illustrate the upward, downward, and sideway movement of bodies from the earth, and the counteraction by the force of gravitation of any tendency of matter to fall away from the globe, which is represented in the model by the india-rubber springs pulling the balls and toys back again to the circumference of the hoop.