"Which the metaphysicians," laughed Zaidie as she rose, "would tell you are not realities at all, or only realities so far as you can think about them. 'Thinks,' in short, instead of real things. But meanwhile I've got the breakfast _things_ to put away, so you can go up on deck and put the telescopes in order." When she joined him a few minutes later in the deck-chamber the three-quarter disc of Jupiter was rapidly approaching the full. Its phases are invisible from the Earth owing to the enormous distance; but from the deck of the _Astronef_ they had been plainly visible for some days, and, since the huge planet turns on its axis in less than ten hours, or with more than twice the speed of the Earth's rotation, the phases followed each other very rapidly. Thus at twelve o'clock noon by _Astronef_ time they might have seen a gigantic rim of silver-blue overarching the whole vault of heaven in front of them. By five o'clock it would be a hemisphere, and by five minutes to ten the vast sphere would be once more shining full-orbed upon them. By eight o'clock next morning they would find Jupiter "new" again. They were now falling very rapidly towards the huge planet, and, since there is no up or down in Space, the nearer they got to it the more it appeared to sink below them and become, as it were, the floor of the Celestial Sphere. As the crescent approached the full they were able to examine the mysterious bands as human observers had never examined them before. For hours they sat almost silent at their telescopes, trying to probe the mystery which has baffled human science since the days of Galileo, and gradually it became plain that Redgrave was correct in the hypothesis which he had derived from Flammarion and one or two others of the more advanced astronomers. "I believe I was right, or, in other words, those that I got the idea from are," he said, as they approached the orbit of Calisto, which revolves at a distance of about eleven hundred thousand miles from the surface of Jupiter. "Those belts are made of clouds or vapour in some stage or other. The highest--the ones along the Equator and what we should call the Temperate Zones--are the highest, and therefore coolest and whitest. The dark ones are the lowest and hottest. I daresay they are more like what we should call volcanic clouds. Do you see how they keep changing? That's what's bothered our astronomers. Look at that big one yonder a bit to the north, going from brown to red. I suppose that's something like the famous red spot which they have been puzzling about. What do you make of it?" "Well," said Zaidie, looking up from her telescope, "it's quite certain that the glare must come from underneath. It can't be sunlight, because the poor old Sun doesn't seem to have strength enough to make a decent sunset or sunrise here, and look how it's running along to the westward! What does that mean, do you think?"