Page:Popular Science Monthly Volume 10.djvu/723

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sixty-five elements. But, however this may be, we know that the atoms, whatever they were, must have been held so far apart that no combinations could possibly have existed. Neither were they drawn more in one direction than another by their mutual attractions, for they are equally diffused through all space. Therefore, heat, the great repulsive force, has overcome all the forces of attraction—cohesion, chemical affinity, and gravity.

Between such mighty contending forces we can hardly imagine a state of perfect equilibrium. Immense currents and world-wide surgings must be the long-continued if not the permanent condition of this state of things, especially if we conceive it brought about by natural causes. More condensed portions of nebulous matter would be formed—sections of space larger or smaller, in which the forces of attraction counterbalanced those of repulsion. Each such section would then have its centre of gravity, around which all the currents within its influence, by the law of the composition of forces, must eventually unite in one. This one flowing ever around and slowly toward the centre, like a ball rolling down an inclined plane, goes faster and faster, until the centrifugal overbalances the centripetal force, and it separates completely from the inner mass. Thus a ring is formed revolving around a central nucleus. Unless perfectly equiposed, and of homogeneous material, this ring would sooner or later break up into a number of globes, which, by the superior attraction of the largest, would ultimately coalesce into one. This globe, still contracting, and the nucleus also contracting, would throw off satellites and other planets, all revolving in nearly the same plane and in the same direction. All these processes are in perfect accord, not only with the conditions of the heavenly bodies so far as discovered, but with known natural laws. Many of them have been successfully imitated on a small scale in experimental illustrations, as in the rapid rotation of oil suspended in water.

We have here given only the simple outlines of the famous "nebular hypothesis" of Laplace. In later years, the discovery of nebulae in the heavens in all stages of world-formation, the evidence of the spectroscope on the unformed material of the universe, and other proofs, have compelled for the proscribed hypothesis a recognized place in science. We do not stop to consider these subjects more fully, because it is the purpose of this article to inquire chiefly concerning the forces that would be engaged in such a process of evolution; and, firstly, how from the preponderance of the repellent forces holding matter in universal diffusion there came the final mastery of the aggregating forces ever concentrating, combining, and working up the materials of the universe.

The first of the operations which have come to our notice in the progress of this evolution is the condensation of the gases. This, according to all experience, ought to evolve heat; but, instead, we