to have taken place in the planets. The experiment has since been several times repeated. When the rotation becomes very rapid, the figure becomes more oblately spheroidal, then hollows out above and below round the axis of rotation, stretches out horizontally until finally the outside layer of oil abandons the mass and becomes transformed into a perfectly regular ring. After a little while the ring of oil, losing its own motion, gathers itself once more into a sphere. As often as the experiment is repeated the ring thrown off immediately takes the globular form. These are seen to assume at the instant of their formation a movement of rotation upon themselves, which takes place in the same direction as that of the ring. Moreover, as the ring at the instant of its rupture had still a remainder of velocity, the spheres to which it has given birth tend to fly off at a tangent; but, as on the other side, the disk, turning in the alcoholic liquor, has impressed on the liquor a movement of rotation, the spheres are carried along and revolve for some time round the disk. Those which revolve at the same time upon themselves "present the curious spectacle of planets revolving at the same time on themselves and in their orbit." Another curious result is almost always exhibited in this experiment. Besides three or four large spheres into which the ring resolves itself, there are almost always two or three very small ones which may thus be compared to satellites. The experiment presents, therefore, an image in miniature of the formation of the planets, according to the hypothesis of Laplace, by the rupture of the cosmical rings attributable to the condensation of the solar atmosphere.
Modern discoveries carry the matter on much further. Recent investigations into the doctrine of the conservation of energy have shown the generation of cosmical heat. The amount of force comprised in the universe, like the amount of matter contained in it, is a fixed quantity, and to it nothing can either be added or taken away. It is, therefore, constantly undergoing change from one form to another. If it ceases in one form it is not destroyed, it is converted. The blow of a hammer on an anvil sets a certain amount of energy in motion. The anvil stops the blow, but the force changes into heat. Hammer a nail, and it will burn your fingers. Apply a brake to a wheel, and you will stop the motion, but the force will be changed, into heat, which will burn you if you touch the brake. Measure the hammered nail, and you find that it has expanded by the vibration of its particles; heat it still more, and the particles will overcome the attraction of cohesion and revolve about each other, that is, they will become molten; heat them still more, and they will assume the vaporous or gaseous form. Now, seeing that motion was convertible into heat, and heat into motion, it became an object of inquiry what was the exact relation between the two. Dr. Mayer, in Germany, and Dr. Joule, in England, set themselves to the solution of this problem. By
