   Although Copernicus received encouragement to publish his book from his close friend, the bishop of Chelmo Tiedemann Giese (1480–1550), and from the cardinal of Capua Nicholas Schönberg (1472–1537), it was the arrival of Georg Joachim Rheticus in Frombork that solved his needs for a supportive and stimulating colleague in mathematics and astronomy and for access to an appropriate printer. Rheticus was a professor of mathematics at the University of Wittenberg, a major center for the student of mathematics as well as for Lutheran theology. In 1538 Rheticus took a leave of absence to visit several famous scholars in the fields of astronomy and mathematics. It is not known how Rheticus learned about Copernicus’s theory; he may have been convinced to visit Copernicus by one of the earlier scholars he had visited, Johann Schöner, though, as Swerdlow and Neugebauer (16) noted, by “the early 1530’s knowledge of Copernicus’s new theory was circulating in Europe, even reaching the high and learned circles of the Vatican.” Rheticus brought with him some mathematical and astronomical volumes, which both provided Copernicus with some important material and showed him the quality of the mathematical printing available in the German centers of  publishing.[10]   Rheticus’s present of the 1533 edition of Regiomontanus’s On all Kinds of Triangles (De triangulis omnimodis), for example, convinced Copernicus to revise his section on trigonometry. But Rheticus was particularly interested in showing Copernicus the work of the Nuremberg publisher Johann Petreius as a possible publisher of Copernicus’s volume.  Swerdlow and Neugebauer (25) plausibly suggested that “Petreius was offering to publish Copernicus’s work, if not advertising by this notice that he was already committed to do so.” Rheticus wrote the Narratio prima in 1540, an introduction to the theories of Copernicus, which was published and circulated.  This further encouraged Copernicus to publish his Revolutions, which he had been working on since he published the Commentariolus.