In 1634 he went to Paris, Florence, and Rome with his pupil, returning to England in 1637. He now, at 55, began to reckon himself as a philosopher in a kind of metaphysics, and physics about which he did not know much. An unfortunate accident had led him to read "Euclid," Book I, proposition 47. "Begad," said Hobbes, "this is impossible!" He pursued his studies, found out that it was possible, and became convinced that it is also possible to square the circle. Easy as it seems, this feat has never been accomplished with pedantic accuracy, and Hobbes, from about 60 to 80, was engaged in controversy on the subject. Oxford mathematicians, annoyed by his attacks on the University, replied with scientific precision, and such banter as mathematicians enjoy when they would be merry among themselves. In this long war, Hobbes was mercilessly handled, partly by way of discrediting his ideas in politics and religion. He had laid out for himself a system of the Universe, "Of the Body," "Of the Man," "Of the Citizen". In the political storm and stress of the Great Rebellion he wrote, in Latin, his book of "The Citizen," "De Cive," much of which he had already done, with other such work, in English. These papers had been circulated; Hobbes thought himself in danger--it was "time for him to go," and in 1640 he fled to Paris. He hated Puritans without loving Bishops. In 1642 he published "De Cive"; he then turned to philosophy, and next worked at his great work on the relations of rulers and ruled, and on religion, called "Leviathan". In 1646-1647 he tutored Charles, Prince of Wales, in Jersey, and Charles always liked him as a witty companion. In 1647, believing himself to be on the point of death, he behaved in an orthodox manner. To the witness, Dr. Cosin, later Bishop of Durham, he always referred when his orthodoxy was doubted. When Charles I had been slain, in 1649, Hobbes, who in 1650 had published his "Human Nature," the briefest Statement of his general view of mankind, thought of returning home, for now a Government, that of Cromwell, was firmly seated, and Hobbes's main political principle was "settled government". By 1651 he had "Leviathan" fairly written out as a present for Charles II in Paris. But the King's advisers thought it a most unholy book (not that Charles himself cared, or had a bad opinion of Hobbes); he was rebuffed; he was afraid of being murdered for his religion (which, says De Quincey, "is a high joke; Tom Hobbes afraid of suffering for his religion!") and he fled back to England.