r pictures would have led directly to the
detection of the dark ring, had not this appendage been exceedingly
faint. Thus, while the observation of the dark belt across the planet's
face proves the dusky ring to have existed in some form long before it
was perceived, the same fact only helps to render us certain that the
dark ring has changed notably in condition during the present century.

The discovery of this singular appendage, an object unique in the solar
system, naturally attracted fresh attention to the question of the
stability of the rings. The idea was thrown out by the elder Bond that
the new ring may be fluid, or even that the whole ring-system may be
fluid, and the dark ring simply thinner than the rest. It was thought
possible that the ring-system is of the nature of a vast ocean, whose
waves are steadily advancing upon the planet's globe. The mathematical
investigation of the subject was also resumed by Professor Benjamin
Pierce, of Harvard, and it was satisfactorily demonstrated that the
stability of a system of actual rings of solid matter required so nice
an adjustment of so many narrow rings as to render the system far more
complex than even Laplace had supposed. 'A stable formation can,' he
said, 'be nothing other than a very great number of separate narrow
rigid rings, each revolving with its proper relative velocity.' As was
well remarked by the late Professor Nichol, 'If this arrangement or
anything like it were real, how many new conditions of instability do we
introduce. Observation tells us that the division between such rings
must be extremely narrow, so that the slightest disturbance by external
or internal causes would cause one ring to impinge upon another; and we
should thus have the seed of perpetual catastrophes.' Nor would such a
constitution protect the system against dissolution. 'There is no escape
from the difficulties, therefore, but through the final rejection of the
idea that Saturn's rings are rigid or in any sense a solid formation.'

The idea that the ring-system may be fluid came naturally next under
mathematical scrutiny. Strangely enough, the physical objections to the
theory of fluidity appear to have been entirely overlooked. Before we
could accept such a theory, we must admit the existence of elements
differing entirely from those with which we are familiar. No fluid known
to us could retain the form of the rings of Saturn under the conditions
to which they are exposed