or RHETIUS, the surname which George Joachim derived, from having been a native of that part of the Tyrol which was anciently the territory of the Rheti. This eminent scholar was born at Feldkirch in 1514, and was appointed professor of elementary mathematics at Wittenberg in 1537. His first appearance before the public was in the character of an enthusiastic convert to the newly-broached opinions of Copernicus. No sooner had he adopted these opinions than, resigning his chair, he repaired to Frauenberg to sit at the feet of their great promulgator. All his energy was forthwith devoted to the new system. His aid was given in completing it. His pen was employed in advocating it. His power of persuasion was used to get its founder to lay it before the public. Nor did he desist when it was ready for the press. Receiving the manuscript he superintended the printing, and placed the new work in the hand of the expiring author. Rheticus now commenced his great treatise, Opus Palatinum de Triangulis. It exacted from him the most arduous and the most patient labour. He continued to work at it, while he occupied his old chair at Wittenberg, while he taught mathematics at Leipzig, and while he travelled over different parts of the Continent. His toil was not yet over when he died in Hungary in 1576. The Opus Palatinum of Rheticus was published by Otho in 1596, and was found to contain the most extensive trigonometrical table that had hitherto appeared. This table was rendered still more complete by Pitiscus, the learned philologist, and published under the name of Thesaurus Mathematicus, folio, 1613.