s 79 days to travel round
Saturn. In the following year he discovered another; and twelve years
later, in 1684, still two more; thus making a total of five satellites
to this planet.

[Illustration: Fig. 68.--Transit of Titan and its Shadow, by F. Terby
Louvain, 12th April, 1892.]

The complexity of the Saturnian system had now no rival in the heavens.
Saturn had five satellites, and Jupiter had but four, while at least one
of the satellites of Saturn, named Titan, was larger than any satellite
of Jupiter.[28] Some of the discoveries of Cassini had been made with
telescopes of quite monstrous dimensions. The length of the instrument,
or rather the distance at which the object-glass was placed, was one
hundred feet or more from the eye of the observer. It seemed hardly
possible to push telescopic research farther with instruments of this
cumbrous type. At length, however, the great reformation in the
construction of astronomical instruments began to dawn. In the hands of
Herschel, it was found possible to construct reflecting telescopes of
manageable dimensions, which were both more powerful and more accurate
than the long-focussed lenses of Cassini. A great instrument of this
kind, forty feet long, just completed by Herschel, was directed to
Saturn on the 28th of August, 1789. Never before had the wondrous planet
been submitted to a scrutiny so minute. Herschel was familiar with the
labours of his predecessors. He had often looked at Saturn and his five
moons in inferior telescopes; now again he saw the five moons and a
star-like object so near the plane of the ring that he conjectured this
to be a sixth satellite. A speedy method of testing this conjecture was
at hand. Saturn was then moving rapidly over the heavens. If this new
object were in truth a satellite, then it must be carried on by Saturn.
Herschel watched with anxiety to see whether this would be the case. A
short time sufficed to answer the question; in two hours and a half the
planet had moved to a distance quite appreciable, and had carried with
him not only the five satellites already known, but also this sixth
object. Had this been a star it would have been left behind; it was not
left behind, and hence it, too, was a satellite. Thus, after the long
lapse of a century, the telescopic discovery of satellites to Saturn
recommenced. Herschel, as was his wont, observed this object with
unremitting ardour, and discovered that it was much nearer to Saturn
t