executed at Lick in
1894-95,[1113] showed no sensible divergence from them. Hence, much
weight cannot be laid upon Huygens's drawings and descriptions, which
had been held to prove conclusively a partial filling up, since 1657, of
the interval between the ring and the planet.[1114]

The rings of Saturn replace, in Professor G. H. Darwin's view,[1115] an
abortive satellite, scattered by tidal action into annular form. For
they lie closer to the planet than is consistent with the integrity of a
revolving body of reasonable bulk. The limit of possible existence for
such a mass was fixed by Roche of Montpellier, in 1848,[1116] at 2.44
mean radii of its primary; while the outer edge of the ring-system is
distant 2.38 radii of Saturn from his centre. The virtual discovery of
its pulverulent condition dates, then, according to Professor Darwin,
from 1848. He conjectures that the appendage will eventually disappear,
partly through the dispersal of its constituent particles inward, and
their subsidence upon the planet's surface, partly by their dispersal
outward, to a region beyond "Roche's limit," where coalescence might
proceed unhindered by the strain of unequal attractions. One modest
satellite, revolving inside Mimas, would then be all that was left of
the singular appurtenances we now contemplate with admiration.

There seems reason to admit that Kirkwood's law of commensurability has
had some effect in bringing about the present distribution of the matter
composing them. Here the influential bodies are Saturn's moons, while
the divisions and boundaries of the rings represent the spaces where
their disturbing action conspires to eliminate revolving particles.
Kirkwood, in fact, showed, in 1867,[1117] that a body circulating in the
chasm between the bright rings known as "Cassini's division," would have
a period nearly commensurable with those of _four_ out of the eight
moons; and Meyer of Geneva subsequently calculated all such
combinations, with the result of bringing out coincidences between
regions of maximum perturbation and the limiting and dividing lines of
the system.[1118] This is in itself a strong confirmation of the view
that the rings are made up of independently revolving small bodies.

On December 7, 1876, Professor Asaph Hall discovered at Washington a
bright equatorial spot on Saturn, which he followed and measured through
above sixty rotations, each performed in ten hours fourteen minutes
twenty-four se