Page:Popular Science Monthly Volume 13.djvu/358

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will show how planets and satellites are formed from rotating nebulous masses:

As radiation still continued, the repulsive force between the particles diminished, which allowed them to approach nearer to each other; and this tendency to agglomeration resulted in the formation of small centres of local attraction near the surface of the ring, where radiation was most rapid.

As condensation continued, new centres of local attraction were formed within, while the outer and older nodules continued to increase in size, and to coalesce into larger masses; till, finally, the outer edge of this ring had changed from an homogeneous and continuous nebulous disk to a multitude of nebulous planetoids of great volume, but of small mass; while the succeeding interior particles, as fast as they were left out by the contracting spheroid, were preparing to undergo a like change.

Now, as these planetoids have various periods of revolution, they will occasionally come into conjunction, and then, on account of the great volume and small mass of each, they should coalesce without crash; till, finally, some preponderating mass should collect all the little ones exterior to its orbit into itself, together with as many of those within its orbit as its gravitating force could control.

In like manner will all succeeding rings be collected into nebulous planets; and, if the masses of these planets be sufficiently large, they too, in a like manner, will develop nebulous secondaries after their own likeness, both in form and motion.

It is the satellites so formed of the out-left rings of the condensing nebulous planets in our system that have been under discussion in this paper.

That the nebulous planet thus formed will be given a motion of rotation in the same direction as that of its primary is due to the fact that the exterior planetoids have a greater virtual velocity than the interior ones have. This will become evident from the following considerations:

Let us consider, first, the effect produced on its rotation by one of the outer planetoids as it coalesces with this preponderating mass. As the two bodies approach conjunction, the small one will be drawn inward to meet the larger one, and this contraction of its orbit so increases its orbital velocity that, at the time of meeting, this velocity is greater than that of the controlling mass, and on striking it will give the latter an impulse to rotate in the direction of its orbital motion; while, on the other hand, one of the interior planetoids, by being drawn outward, will have its motion diminished to such a degree that, on meeting, it will give the larger one an impulse to rotate in the same direction as that which the outer one gave to it.

Now, if this nebulous globe be not disturbed by some external force, it will form the outer planet of the then future solar system.