Related to the initial retrograde rotations of the planets, and in a sense survivals from an earlier state of things, are two of the latest discoveries of motions in the solar system, the retrograde orbital movements of the ninth satellite of Saturn and the eighth of Jupiter. Considered so anomalous as scarcely at first to be believed, it has been stated that they directly contradict the theory of Laplace. This is true; in the same sense and no more in which they directly contradict the contradictor, one of the latest theories. For neither theory has anything to explain them as the result of law. That they cannot be the sport of indifferent chance seems evidenced by their occupying similar external positions in their respective systems. As the product of a law we must regard them, and to find that law we now turn. Suppose the planet originally to have been rotating backward, or in the direction of the hands of a clock. At this time the satellite, which may never have formed a part of its mass, was travelling backward too, according to what we have said. Then under the friction of the tides raised on the planet by the Sun, the planet proceeded to turn over. It continued to do so until it spun direct. During this process there was no passage through zero of its moment of momentum _considered with regard to itself_, and therefore no difficulty on that score of supposing that it successively generated satellites at all degrees of inclination. That its children are of the nature of adopted waifs, Babinet’s criterion (1861) would seem to imply. But it must be remembered that the Sun has been slowing up the planet’s rotation now for æons. As it turned over, its tidal bulges tended to carry over with it such satellites as it already had. This effect was much greater on the nearer ones, both because they were nearer and because they were much larger than the outer. So that the nearer kept with the planet, the others lagged proportionately behind. This suggests itself to account for the facts, but the subject involves so much that is uncertain that I submit the hypothesis with the distrust which Laplace has so eminently bespoken. I advance in its favor only the three striking facts: that a steady progression in their tilts of rotation is observable from Neptune to Jupiter and a substantially accordant one from Mars to Mercury; secondly, that the satellites turn their faces to their primaries, as likewise do Mercury and Venus to the Sun; and, thirdly, that the orbits of the satellites of all the planets are themselves tilted in accordance with what it would require [see NOTE 7].