s
by Herschel gave astronomers an excuse for taking for granted the
fulfilment of the condition thus vaguely postulated; and the question
remained in abeyance until once more brought prominently forward by the
discovery of the dusky ring in 1850.

The younger Bond led the way, among modern observers, in denying the
solidity of the structure. The fluctuations in its aspect were, he
asserted in 1851,[1097] inconsistent with such a hypothesis. The fine
dark lines of division, frequently detected in both bright rings, and as
frequently relapsing into imperceptibility, were due, in his opinion, to
the real nobility of their particles, and indicated a fluid formation.
Professor Benjamin Peirce of Harvard University immediately followed
with a demonstration, on abstract grounds, of their non-solidity.[1098]
Streams of some fluid denser than water were, he maintained, the
physical reality giving rise to the anomalous appearance first disclosed
by Galileo's telescope.

The mechanism of Saturn's rings, proposed as the subject of the Adams
Prize, was dealt with by James Clerk Maxwell in 1857. His investigation
forms the groundwork of all that is at present known in the matter. Its
upshot was to show that neither solid nor fluid rings could continue to
exist, and that the only possible composition of the system was by an
aggregated multitude of unconnected particles, each revolving
independently in a period corresponding to its distance from the
planet.[1099] This idea of a satellite-formation had been, remarkably
enough, several times entertained and lost sight of. It was first put
forward by Roberval in the seventeenth century, again by Jacques Cassini
in 1715, and with perfect definiteness by Wright of Durham in
1750.[1100] Little heed, however, was taken of these casual
anticipations of a truth which reappeared, a virtual novelty, as the
legitimate outcome of the most refined modern methods.

The details of telescopic observation accord, on the whole, admirably
with this hypothesis. The displacements or disappearance of secondary
dividing-lines--the singular striated appearance, first remarked by
Short in the eighteenth century, last by Perrotin and Lockyer at Nice,
March 18, 1884[1101]--show the effects of waves of disturbance
traversing a moving mass of gravitating particles;[1102] the broken and
changing line of the planet's shadow on the ring gives evidence of
variety in the planes of the orbits described by those partic