RIIETICUS ((Icemen Joacnim), in bi ography, a noted German astronomer and mathematician, was born at 1'eldkirk, in Tyrol, the 15th of February, 1514. After imbibing the elements of the ma thematics at Tignri, with Oswald Mycone, he went to Wittemberg, where he dili gently cultivated that science. Here he was made master of Philosophy in 1535, and professor in 1537. He quitted this situation, however, two years after, and went to Fruenberg to put himself under the assistance of the celebrated Coperni cus, being induced to this step by his zeal for astronomical pursuits, and the great fame which Copernicus had then acquired. Rheticus assisted this astrono mer for some years, and constantly ex horted him to perfect his work, De Revo lutionibus, which he published after the death of Copernicus, viz. in 1543, folio, at Norimberg, together with an illustra tion of the same in a narration, dedicated to Schoner. Here too, to render astro nomical calculations more accurate, he began his very elaborate canon of sines, tangents, and secants, to fifteen places of figures, and to every ten seconds of the quadrant, a design which he did not live quite to complete. The canon of sines, however, to that radius, for every ten se conds, and for every single second in the first and last degree of the quadrant, com puted by him, was published m folio, at Franckfort, 1615, by Pitiscus, who Ink self added a few of the firs., shies comput ed to twenty-two places of figures. But
the larger work or cation of sines, tan gents, and secants, to every ten seconds, wag perfected and published after death, viz. in 1596, by his disciple, :d entine Otho, mathematician to the Elec toral Prince Palatine.
After the death of Copernicus, Rheti cus returned to Witte, oberg; viz. in 1541 or 1542, and was again admitted to his of fice of professor of mathematics. The same year, by the recommendation of Melancthon, he went to Norimberg, where he found certain manuscripts of Werner and Regiomontanus. He after wards taught mathematics at Leipsic. From Saxony he departed a second time, for what reason is not known, and went to Poland ; and from thence to Cassovia, in Hungary, where he died December the 4th, 1576, near sixty three years of age.
His Narratio de Libris Revolutionum Copernici, was first published at Gedu min, in quarto, 1540, and afterwards added to the additions of Copernicus's work. He also composed and publish ed Ephemerides, according to the doc trine of Copernicus, till the year 1551. Rheticus also projected other works, and partly executed them, though they were never published, of various kinds, astronomical, astrological, geographical, chemical, &c. as they are more parti cularly- mentioned in his letter to Peter Ramos, in the year 1568, which Adrian Romanus inserted in the preface to the first part of his idea of mathematics.