one. It would condense and abandon successive zones, which would ultimately break up and form the satellites. It might be that the ring preserved its equilibrium; and the rings of Saturn form an illustration of this. It might happen, on the other hand, that the globular masses, formed from the disruption of the ring, preserved their identity; and we have a case of this kind in the asteroids between Mars and Jupiter. This hypothesis ingeniously accounts for the points of harmony above enumerated. The planets and satellites revolve nearly in circles and in one plane, because they have been thrown off from the equator of the rotating mass. The direction of rotation is the same as that of revolution, because the outer portion of the ring, having a greater absolute velocity than the inner, would necessarily originate rotation, and rotation in the same direction as that of the ring. By assuming a suitable law of condensation in the nebulous matter, the relative distances, densities, and magnitudes may be accounted for. The assumptions of Laplace regarding the rotating mass, and the law of condensation, are wholly gratuitous; but, admitting these, the results which he deduced from them flow, as a necessary consequence, according to the unerring laws of dynamics.
It has been attempted to support the nebular hypothesis by what is known as "Kirkwood's law " of the rotation of the primary planets. We have seen, that the direction of the rotation of the planets can-
