Nikolaus von Schönberg wrote to Copernicus and urged him to publish his manuscript. In 1539, Georg Joachim Rheticus, a young mathematician from Wittenberg, arrived in Frauenburg (Frombork) to study with him. Rheticus read Copernicus' manuscript and immediately wrote a non-technical summary of its main theories in the form of an open letter addressed to Schöner, his astrology teacher in Nürnberg; he published this letter as the Narratio Prima in Danzig in 1540. Rheticus' friend and mentor Achilles Gasser published a second edition of the Narratio in Basel in 1541. Due to its friendly reception, Copernicus finally agreed to publication of more of his main work—in 1542, a treatise on trigonometry, which was taken from the second book of the still unpublished De revolutionibus. Rheticus published it in Copernicus' name. Under strong pressure from Rheticus, and having seen that the first general reception of his work had not been unfavorable, Copernicus finally agreed to give the book to his close friend, Bishop Tiedemann Giese, to be delivered to Rheticus in Wittenberg for printing by Johannes Petreius at Nürnberg (Nuremberg). It was published just before Copernicus' death, in 1543. Copernicus kept a copy of his manuscript which, sometime after his death, was sent to Rheticus in the attempt to produce an authentic, unaltered version of the book. The plan failed but the copy was found during the 18th century and was published later. It is kept at the Jagiellonian University Library in Kraków, where it remains bearing the library number BJ 10 000. Contents From the first edition, Copernicus' book was prefixed with an anonymous preface which argues that the following is a calculus consistent with the observations, and cannot resolve philosophical truths. Only later was this revealed to be the unauthorized interjection by Lutheran preacher Andreas Osiander, who lived in Nuremberg when the first edition was printed there. This is followed by Copernicus' own preface, where he dedicates his work to Pope Paul III and appeals to the latter's skill as a mathematician to recognize the truth of Copernicus' hypothesis. De revolutionibus is divided into six "books" (sections or parts), following closely the layout of Ptolemy's Almagest which it updated and replaced: Book I chapters 1–11 are a general vision of the heliocentric theory, and a summarized exposition of his cosmology. The world (heavens) is spherical, as is the Earth, and the land and water make a single globe. The celestial