Nicholas Copernicus was born February 19, 1473, in Poland. He entered the University of Krakow in 1491, then in 1495 went to Padua and studied medicine. In 1500 he was called to Rome and took the chair of mathematics there. He began to believe that the earth went round the sun about 1507 and from that time until his death worked, more or less intermittently, on his exposition of his theory. He delayed the publication of this exposition because of fear of being accused of heresy. Copernicus died May 24, 1543, just as his book was published. The knowledge of the time was not sufficient to prove his theory; his great argument for it was from its simplicity as compared to the epicycle hypothesis. In 1514, Copernicus privately circulated an outline of his thesis on planetary motion, but actual publication of De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) containing his mathematical proofs did not occur until 1543, after a supporter named Rheticus had impatiently taken it upon himself to publish a brief description of the Copernican system (Narratio prima) in 1541. Most of De revolutionibus requires a great deal of the modem reader, since sixteenth century methods of mathematical proofs are quite foreign to us; this is evident in the section of Book VI that is included. However, Book I and Copernicus' preface are more readily accessible. It must be noted that the foreword by Andreas Osiander was not authorized Copernicus, and that Osiander, who oversaw the book's printing, included it without the author's knowledge and without identifying Osiander as its author.