h awful magnitude would be something so enormous
that no materials we know of would be capable of bearing it. Were the
ring formed of the toughest steel that was ever made, the pressure would
be so great that the metal would be squeezed like a liquid, and the
mighty structure would collapse and fall down on the surface of the
planet. It is not credible that any materials could exist capable of
sustaining a stress so stupendous. The law of gravitation accordingly
bids us search for a method by which the intensity of this stress can be
mitigated.

One method is at hand, and is obviously suggested by analogous phenomena
everywhere in our system. We have spoken of the ring as if it were at
rest; let us now suppose it to be animated by a motion of rotation in
its plane around Saturn as a centre. Instantly we have a force developed
antagonistic to the gravitation of Saturn. This force is the so-called
centrifugal force. If we imagine the ring to rotate, the centrifugal
force at all points acts in an opposite direction to the attractive
force, and hence the enormous stress on the ring can be abated and one
difficulty can be overcome.

We can thus attribute to each ring a rotation which will partly relieve
it from the stress the arch would otherwise have to sustain. But we
cannot admit that the difficulty has been fully removed. Suppose that
the outer ring revolve at such a rate as shall be appropriate to
neutralise the gravitation on its outer edge, the centrifugal force will
be less at the interior of the ring, while the gravitation will be
greater; and hence vast stresses will be set up in the interior parts of
the outer ring. Suppose the ring to rotate at such a rate as would be
adequate to neutralise the gravitation at its inner margin; then the
centrifugal force at the outer parts will largely exceed the
gravitation, and there will be a tendency to disruption of the ring
outwards.

To obviate this tendency we may assume the outer parts of each ring to
rotate more slowly than the inner parts. This naturally requires that
the parts of the ring shall be mobile relatively to one another, and
thus we are conducted to the suggestion that perhaps the rings are
really composed of matter in a fluid state. The suggestion is, at first
sight, a plausible one; each part of each ring would then move with an
appropriate velocity, and the rings would thus exhibit a number of
concentric circular currents with different velocities. The