into account! Why should the ring-system, 30,000 miles in width,
be thus divided into zones of different material? An arrangement so
artificial is quite unlike all that is elsewhere seen among the
subjects of the astronomer's researches. But when the rings are regarded
as made up of multitudes of small bodies, we can quite readily
understand how the nearly circular movements of all of these, at
different rates, should result in the formation of rings of aggregation
and rings of segregation, appearing at the earth's distance as bright
rings and faint rings. The dark ring clearly corresponds in appearance
with a ring of thinly scattered satellites. Indeed, it seems impossible
otherwise to account for the appearance of a dusky belt across the globe
of the planet where the dark ring crosses the disc. If the material of
the dark ring were some partly transparent solid or fluid substance, the
light of the planet received through the dark ring added to the light
reflected by the dark ring itself, would be so nearly equivalent to the
light received from the rest of the planet's disc, that either no dark
belt would be seen, or the darkening would be barely discernible. In
some positions a bright belt would be seen, not a dark one. But a ring
of scattered satellites would cast as its shadow a multitude of black
spots, which would give to the belt in shadow a dark grey aspect. A
considerable proportion of these spots would be hidden by the satellites
forming the dark ring, and in every case where a spot was wholly or
partially hidden by a satellite, the effect (at our distant station
where the separate satellites of the dark ring are not discernible)
would simply be to reduce _pro tanto_ the darkness of the grey belt of
shadow. But certainly more than half the shadows of the satellites would
remain in sight; for the darkness of the ring at the time of its
discovery showed that the satellites were very sparsely strewn. And
these shadows would be sufficient to give to the belt a dusky hue, such
as it presented when first discovered.[37]

The observations which have recently been made by Mr. Trouvelot
indicate changes in the ring-system, and especially in the dark ring,
which place every other theory save that to which we have thus been led
entirely out of the question. It should be noted that Mr. Trouvelot has
employed telescopes of unquestionable excellence and varying in aperture
from six inches to twenty-six inches, the latter ap