2,136
Saturn 1,033
Uranus 21
Neptune 9

The power of all of them is very feeble, and by acting on different
sides they usually partly neutralize each other's action; but
occasionally they get all on one side, and in that case some
perceptible effect may be produced; the probable effect seems
likely to be a gentle heaving tide in the solar surface, with
breaking up of any incipient crust; and such an effect may be
considered as evidenced periodically by the great increase in the
number of solar spots which then break out.

The solar tides are, however, much too small to appreciably push
any planet away, hence we are not to suppose that the planets
originated by budding from the sun, in contradiction of the nebular
hypothesis. Nor is it necessary to assume that the satellites, as a
class, originated in the way ours did; though they may have done
so. They were more probably secondary rings. Our moon differs from
other satellites in being exceptionally large compared with the
size of its primary; it is as big as some of the moons of Jupiter
and Saturn. The earth is the only one of the small planets that has
an appreciable moon, and hence there is nothing forced or unnatural
in supposing that it may have had an exceptional history.

Evidently, however, tidal phenomena must be taken into
consideration in any treatment of the solar system through enormous
length of time, and it will probably play a large part in
determining its future.

When Laplace and Lagrange investigated the question of the stability or
instability of the solar system, they did so on the hypothesis that the
bodies composing it were rigid. They reached a grand conclusion--that
all the mutual perturbations of the solar system were periodic--that
whatever changes were going on would reach a maximum and then begin to
diminish; then increase again, then diminish, and so on. The system was
stable, and its changes were merely like those of a swinging pendulum.

But this conclusion is not final. The hypothesis that the bodies are
rigid is not strictly true: and directly tidal deformation is taken into
consideration it is perceived to be a potent factor, able in the long
run to upset all their calculations. But it is so utterly and
inconceivably minute--it only produces an appreciable effect after
mi