nts of the Moon, much
better. Against the alternative supposition, that the equality occurred
by accident, the probabilities are, as Laplace says, infinity to one.
But to this arrangement, which is explicable neither as the result of
design nor of chance, the Nebular Hypothesis furnishes a clue. In his
_Exposition du Systeme du Monde_, Laplace shows, by reasoning too
detailed to be here repeated, that under the circumstances such a
relation of movements would be likely to establish itself.

Among Jupiter's satellites, which severally display these same
synchronous movements, there also exists a still more remarkable
relation. "If the mean angular velocity of the first satellite be added
to twice that of the third, the sum will be equal to three times that of
the second;" and "from this it results that the situations of any two of
them being given, that of the third can be found." Now here, as before,
no conceivable advantage results. Neither in this case can the connexion
have been accidental: the probabilities are infinity to one to the
contrary. But again, according to Laplace, the Nebular Hypothesis
supplies a solution. Are not these significant facts?

Most significant fact of all, however, is that presented by the rings of
Saturn. As Laplace remarks, they are, as it were, still extant witnesses
of the genetic process he propounded. Here we have, continuing
permanently, forms of aggregation like those through which each planet
and satellite once passed; and their movements are just what, in
conformity with the hypothesis, they should be. "La duree de la rotation
d'une planete doit donc etre, d'apres cette hypothese, plus petite que
la duree de la revolution du corps le plus voisin qui circule autour
d'elle," says Laplace. And he then points out that the time of Saturn's
rotation is to that of his rings as 427 to 438--an amount of difference
such as was to be expected.[19]

Respecting Saturn's rings it may be further remarked that the place of
their occurrence is not without significance.

Rings detached early in the process of concentration, consisting of
gaseous matter having extremely little power of cohesion, can have
little ability to resist the disruptive forces due to imperfect balance;
and, therefore, collapse into satellites. A ring of a denser kind,
whether solid, liquid, or composed of small discrete masses (as Saturn's
rings are now concluded to be), we can expect will be formed only near
the body of