He was no cloistered monk devoting all his time to the study of the heavens, but a cultivated man of affairs, of recognized ability in business and statesmanship, and a leader among his fellow canons. His mathematical and astronomical pursuits were the occupations of his somewhat rare leisure moments, except perhaps during the six years with his uncle in the comparative freedom of the bishop's castle, and during the last ten or twelve years of his life, after his request for a coadjutor had resulted in lightening his duties. In his masterwork _De Revolutionibus_[102] there are recorded only 27 of his own astronomical observations, and these extend over the years from 1497 to 1529. The first was made at Bologna, the second at Rome in 1500, and seven of the others at Frauenburg, where the rest were also probably made. It is believed the greater part of the _De Revolutionibus_ was written at Heilsburg[103] where Copernicus was free from his chapter duties, for as he himself says[104] in the Dedication to the Pope (dated 1543) his work had been formulated not merely nine years but for "more than three nines of years." It had not been neglected all this time, however, as the original MS. (now in the Prague Library) with its innumerable changes and corrections shows how continually he worked over it, altering and correcting the tables and verifying his statements.[105] [Footnote 102: Copernicus: _De Revolutionibus_, Thorn edit., 444. The last two words of the full title: _De Revolutionibus Orbium Coelestium_ are not on the original MS. and are believed to have been added by Osiander. Prowe: II, 541, note.] [Footnote 103: Ibid: II, 490-1.] [Footnote 104: Copernicus: Dedication, 4. (Thorn edit.)] [Footnote 105: Prowe: II, 503-508.]