l is maintained
as well as the comparative smallness of the number allows: the two outer
ones are the largest, and the two inner ones the smallest. According to
the most recent observations made by Mr. Lassell, the like is true of
the four satellites of Uranus. In the case of Saturn, who has eight
secondary planets revolving round him, the likeness is still more close
in arrangement as in number: the three outer satellites are large, the
inner ones small; and the contrasts of size are here much greater
between the largest, which is nearly as big as Mars, and the smallest,
which is with difficulty discovered even by the best telescopes. But the
analogy does not end here. Just as with the planets, there is at first a
general increase of size on travelling inwards from Neptune and Uranus,
which do not differ very widely, to Saturn, which is much larger, and to
Jupiter, which is the largest; so of the eight satellites of Saturn, the
largest is not the outermost, but the outermost save two; so of
Jupiter's four secondaries, the largest is the most remote but one. Now
these parallelisms are inexplicable by the theory of final causes. For
purposes of lighting, if this be the presumed object of these attendant
bodies, it would have been far better had the larger been the nearer: at
present, their remoteness renders them of less service than the
smallest. To the Nebular Hypothesis, however, these analogies give
further support. They show the action of a common physical cause. They
imply a _law_ of genesis, holding in the secondary systems as in the
primary system.

Still more instructive shall we find the distribution of the
satellites--their absence in some instances, and their presence in other
instances, in smaller or greater numbers. The argument from design fails
to account for this distribution. Supposing it be granted that planets
nearer the Sun than ourselves, have no need of moons (though,
considering that their nights are as dark, and, relatively to their
brilliant days, even darker than ours, the need seems quite as
great)--supposing this to be granted; how are we to explain the fact
that Uranus has but half as many moons as Saturn, though he is at double
the distance? While, however, the current presumption is untenable, the
Nebular Hypothesis furnishes us with an explanation. It enables us to
predict where satellites will be abundant and where they will be absent.
The reasoning is as follows.

In a rotating nebulo