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A Journey in Other Worlds

avoiding low places near hot springs, we shall doubtless have very nearly as clear an
atmosphere as on earth. What does surprise me is the ease with which we breathe. I can
account for it only by supposing that, the Carboniferous period being already well
advanced, most of the carbonic acid is already locked up in the forests or in Jupiter's coal-
beds."
"How, asked Bearwarden, "do you account for the 'great red spot' that appeared here in
1878, lasted several years, and then gradually faded? It was taken as unmistakable
evidence that Jupiter's atmosphere was filled with impenetrable banks of cloud. In fact,
you remember many of the old books said we had probably never seen the surface."
"That has puzzled me very much," replied Cortlandt, "but I never believed the
explanation then given was correct. The Carboniferous period is essentially one of great
forest growth; so there would be nothing out of the way in supposing the spot,
notwithstanding its length of twenty-seven thousand miles and its breadth of eight
thousand miles, to have been forest. It occurred in what would correspond to the
temperate region on earth. Now, though the axis of this planet is practically straight, the
winds of course change their direction, and so the temperature does vary from day to day.
What is more probable than that, owing perhaps to a prolonged norther or cold spell, a
long strip of forest lying near the frost line was brought a few degrees below it, so that
the leaves changed their colours as they do on earth? It would, it seems to me, be enough
to give the surface a distinct colour; and the fact that the spot's greatest length was east
and west, or along the lines of latitude, so that the whole of that region might have been
exposed to the same conditions of temperature, strengthens this hypothesis. The strongest
objection is, that the spot is said to have moved; but the motion--five seconds--was so
slight that it might easily have been an error in observation, or the first area affected by
the cold may have been enlarged on one side. It seems to me that the stability the spot
DID have would make the cloud theory impossible on earth, and much more so here,
with the far more rapid rotation and more violent winds. It may also have been a cloud of
smoke from a volcano in eruption, such as we saw on our arrival, though it is doubtful
whether in that case it would have remained nearly stationary while going through its
greatest intensity and fading, which would look as though the turned leaves had fallen off
and been gradually replaced by new ones; and, in addition to this, the spot since it was
first noticed has never entirely disappeared, which might mean a volcanic region
constantly emitting smoke, or that the surface, doubtless from some covering whose
colour can change, is normally of a different shade from the surrounding region. In any
case, we have as yet seen nothing that would indicate a permanently clouded
atmosphere."
Though they had walked a considerable distance, the water was not much cooled; and
though the stream's descent was so slight that on earth its current would have been very
slow, here it rushed along like a mountain torrent, the reason, of course, being that a
given amount of water on Jupiter would depress a spring balance 2.55 times as much as
on the earth.
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