well as of development than the most
distant Callisto, and older, at all events in years, than Europa and
Io, both of which are nearer. This supposition is corroborated by the
fact that Europa, the smallest of these four, is also the densest,
having a specific gravity of 2.14, its smallness having enabled it to
overtake Ganymede in development, notwithstanding the latter's start.
In the face of the evidence before us we must believe this, or else
that, perhaps, as in the case of the asteroid Hilda, something like a
collision has rejuvenated it. This might account for its size, and for
the Nautical Almanac's statement that there is a 'small and variable'
inclination to its orbit, while Io and Europa revolve exactly in the
plane of Jupiter's equator."

They had about as long a journey before them as they had already made
in going from the earth to Jupiter. The great planet soon appeared as
a huge crescent, since it was between them and the sun; its moons
became as fifth- and sixth-magnitude stars, and in the evening of the
next day Jupiter's disk became invisible to the unaided eye. Since
there were no way stations, in the shape of planets or asteroids,
between Jupiter and Saturn, they kept the maximum repulsion on Jupiter
as long as possible, and moved at tremendous speed. Saturn was
somewhat in advance of Jupiter in its orbit, so that their course from
the earth had been along two sides of a triangle with an obtuse angle
between. During the next four terrestrial days they sighted several
small comets, but spent most of their time writing out their Jovian
experiences. During the sixth day Saturn's rings, although not as much
tilted as they would be later in the planet's season, presented a most
superb sight, while they spun in the sun's rays. Soon after this the
eight moons became visible, and, while slightly reducing the Callisto's
speed, they crossed the orbits of Iapetus, Hyperion, and Titan, when
they knew they were but seven hundred and fifty thousand miles from
Saturn.

"I am anxious to ascertain," said Cortlandt, "whether the composition
of yonder rings is similar to that of the comet through which we
passed. I am sure they shine with more than reflected light."

"We have been in the habit," said Ayrault, "of associating heat with
light, but it is obvious there is something far more subtle about
cometary light and that of Saturn's rings, both of which seem to have
their birth in the intense cold of in