This was a quiet period of his life, spoiled only by occasional fits of illness and severe rheumatic pains, to which the old man was always liable. Many little circumstances are known of this peaceful time. For instance, the convent clock won't go, and Galileo mends it for them. He is always doing little things for them, and sending presents to the lady superior and his two daughters. He was occupied now with problems in hydrostatics and on other matters unconnected with astronomy: a large piece of work which I must pass over. Most interesting and acute it is, however. In 1623, when the old Pope died, there was elected to the papal throne, as Urban VIII, Cardinal Barberino, a man of very considerable enlightenment, and a personal friend of Galileo's, so that both he and his daughters rejoice greatly, and hope that things will come all right, and the forbidding edict be withdrawn. The year after this election he manages to make another journey to Rome to compliment his friend on his elevation to the pontifical chair. He had many talks with Urban, and made himself very agreeable. Encouraged, doubtless, by marks of approbation, and reposing too much confidence in the individual good-will of the Pope, without heeding the crowd of half-declared enemies who were seeking to undermine his reputation, he set about, after his return to Florence, his greatest literary and most popular work, _Dialogues on the Ptolemaic and Copernican Systems_. This purports to be a series of four conversations between three characters. Salviati, a Copernican philosopher; Sagredo, a wit and scholar, not specially learned, but keen and critical, and who lightens the talk with chaff; Simplicio, an Aristotelian philosopher, who propounds the stock absurdities which served instead of arguments to the majority of men. The Aristotelians were furious, and represented to the Pope that he himself was the character intended by Simplicio, the philosopher whose opinions get alternately refuted and ridiculed by the other two, till he is reduced to an abject state of impotence. The infirm old man was instantly summoned to Rome. His friends pleaded his age--he was now seventy--his ill-health, the time of year, the state of the roads, the quarantine existing on account of the plague. It was all of no avail; to Rome he must go, and on February 14th he arrived. His daughter at Arcetri was in despair; and anxiety and fastings and penances self-inflicted on his account dangerously reduced her health. At Rome he was not imprisoned, but he was told to keep indoors and show himself as little as possible. He was allowed, however, to stay at the house of the Tuscan ambassador instead of in jail.