firmament twenty degrees in diameter, or, in round numbers, forty times
the diameter of the full moon as seen from the earth! It would shed a
great amount of light and heat, and thus would more or less effectively
supply the deficit of solar radiation, for we must remember that Jupiter
and his satellites receive from the sun less than one twenty-fifth as
much light and heat as the earth receives.

The maze of contending motions, the rapid flow and eddying of cloud
belts, the outburst of strange fiery spots, the display of rich, varied,
and constantly changing colors, which astonish and delight the
telescopic observer on the earth, would be exhibited to the naked eye of
an inhabitant of Jupiter's nearest moon far more clearly than the
greatest telescope is able to reveal them to us.

Here, again, the mind is carried back to long past ages in the history
of the planet on which we dwell. It is believed by some that our moon
may have contained inhabitants when the earth was still hot and glowing,
as Jupiter appears to be now, and that, as the earth cooled and became
habitable, the moon gradually parted with its atmosphere and water so
that its living races perished almost coincidently with the beginning of
life on the earth. If we accept this view and apply it to the case of
Jupiter we may conclude that when that enormous globe has cooled and
settled down to a possibly habitable condition, its four attendant moons
will suffer the fate that overtook the earth's satellite, and in their
turn become barren and death-stricken, while the great orb that once
nurtured them with its light and heat receives the Promethean fire and
begins to bloom with life.