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Rh ball. These attendant objects gradually diminished in apparent size, and after two years disappeared altogether, the ring being then edgeways as seen from the earth. This occurs every fourteen years, though naturally the fact was quite unknown to Galileo, and he was very much taken aback at the vanishing of the new objects, which suggested to him a reference to the Greek myth of Saturn swallowing his children. He predicted their reappearance and observed them again as the ring widened out. Later he realised the dark space on each side of the ball between it and the ring, but, as he gave no indication of having grasped the significance of this appearance, it is probable that he did not really understand it. The true explanation was discovered some years after his death, by Huygens, with a telescope of magnifying power of 100 diameters. It is needless to emphasise the additional annoyance caused to the Aristotelians by this new evidence of change in the "immutable" heavens.

To Galileo himself the successive discoveries and the controversies they aroused brought a large increase of students and pupils from all directions, and his teaching work grew to such an extent that he could find very little time for original research. He felt that after twenty years he had had enough of this labour and was desirous of finding more leisure. He had gratefully accepted the life-appointment at Padua, but was only too ready to relinquish it when an opportunity of escape was offered. His great European reputation made it seem desirable to the Tuscan Court to attach him permanently to the Grand Ducal service, and negotiations were opened between Galileo and the Duke's Secretary of State. Galileo stated plainly how irksome he found the necessity of spending so much time on pupils on account of his family expenses, and even the amount of lecturing required,