"It is hard to realize,"said the professor,"that those mountains must be several hundred miles away,for the reason that they are almost entirely above the horizon.This apparent flatness and wide range of vision is of course the result of Jupiter's vast size.With sufficiently keen sight,or aided by a good glass,there is no reason why one should not see at least five hundred miles,with but a slight elevation.""It is surprising,"said Ayrault,"that in what is evidently Jupiter's Carboniferous period the atmosphere should be so clear.
Our idea has been that at that time on earth the air was heavy and dense.""So it was,and doubtless is here,"replied Cortlandt;"but you must remember that both those qualities would be given it by carbonic-acid gas,which is entirely invisible and transparent.
No gas that would be likely to remain in the air would interfere with sight;water vapour is the only thing that could;and though the crust of this planet,even near the surface,is still hot,the sun being so distant,the vapour would not be,raised much.
By 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 2.55times as much as on the earth.
"It is strange,"said Ayrault,"that,notwithstanding its great speed,the water remains so hot;you would think its motion would cool it.""So it does,"answered the professor."It of course cools considerably more in a given period--as,for instance,one minute--than if it were moving more slowly,but on account of its speed it has been exposed to the air but a very short time since leaving the spring."Just before them the stream now widened into a narrow lake,which they could see was straight for some distance.
"The fact is,"said Bearwarden,"this water seems in such haste to reach the ocean that it turns neither to right nor to left,and does not even seem to wish to widen out."As the huge ferns and palms grew to the water's edge,they concluded the best way to traverse the lake would be on a raft.
Accordingly,choosing a large overhanging palm,Bearwarden and Ayrault fired each an explosive ball into its trunk,about eighteen inches from the ground.One round was enough to put it in the water,each explosion removing several cubic feet of wood.
