They passed Io and Europa, which changed from new to full moons as they sped by towards the Sun, and then the golden yellow crescent of Ganymede also began to fill out to the half and full disc, and by the tenth hour of Earth-time, after they had risen from its surface, the _Astronef_ was once more lying beside the gate of the Crystal City. At midnight on the second night after their return, the ringed shape of Saturn, attended by his eight satellites, hung in the zenith magnificently inviting. The _Astronef's_ engines had been replenished after the exhaustion of their struggle with the might of Jupiter. They said farewell to their friends of the dying world. The doors of the air-chamber closed. The signal tinkled in the engine-room, and a few moments later a blurr of white lights on the brown background of the surrounding desert was all they could see of the Crystal City under whose domes they had seen and learnt so much. CHAPTER XVII The relative position of the two giants of the Solar System at the moment when the _Astronef_ left the surface of Ganymede, was such that she had to make a journey of rather more than 340,000,000 miles before she passed within the confines of the Saturnine System. At first her speed, as shown by the observations which Redgrave took with the instruments which Professor Rennick had designed for the purpose, was comparatively slow. This was due to the tremendous pull of Jupiter and its four moons on the fabric of the vessel. The backward drag rapidly decreased as the pull of Saturn and his system began to overmaster that of Jupiter. It so happened, too, that Uranus, the next outer planet of the Solar System, 1,700,000,000 miles away from the Sun, was approaching its conjunction with Saturn, and so assisted in producing a constant acceleration of speed. Jupiter and his satellites dropped behind, sinking, as it seemed to the wanderers, down into the bottomless gulf of Space, but still forming by far the most brilliant and splendid object in the skies. The far-distant Sun, which, seen from the Saturnian System, has only about a nineteenth of the superficial extent which it presents to the Earth, dwindled away rapidly until it began to look like a huge planet, with the Earth, Venus, Mars, and Mercury as satellites. Beyond the orbit of Saturn, Uranus, with his eight moons, was shining with the lustre of a star of the first magnitude, and far above and beyond him again hung the pale disc of Neptune, the Outer Guard of the Solar System, separated from the Sun by a gulf of more than 2,750,000,000 miles.