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Rh complimentary sentences to Tycho, and the book is the earliest in which the words secant and tangent are proposed, while several new fundamental formulæ of trigonometry occur in it for the first time, so that the author must have been a man of considerable ability. The mission of the two professors was no doubt caused by some disturbances at Hveen, which, perhaps, had more to do with Tycho's departure than we are aware of, and it is much to be regretted that we do not possess any account of these transactions except Tycho's own. Gassendi thinks that the report of the professors was the cause of Tycho's chemical experiments being forbidden; but this cannot have been the case, as the expedition of the two learned professors must have taken place after the 2nd June, and Tycho must have left Copenhagen either on that date or immediately after it, as he arrived at Rostock during the first half of June.

After having spent two or three months at Copenhagen, Tycho must have felt that there was nothing to be obtained by delaying his departure from Denmark any longer, and early in June 1597 he sailed for Rostock with his family, some students and attendants, about twenty persons in all, taking his instruments, printing-press, &c., with him. His principal assistant of late years, Longomontanus, who wished to study at German universities, had obtained his discharge with a kind testimonial from Tycho, dated at Copenhagen on the 1st June. Among those who