RHETICUS, or RHIETICUS, a surname given to GEORGE JOACHIM (1514-1576) from his birth at Feldkirch in that part of Tyfol which was anciently the territory of the Ithti. Born in 1514, he was appointed professor of 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, and, as has been mentioned under COPER-NICUS, it was he who superintended the printing of the DC Orbium Revolutione. Rheticus now commenced his great treatise, Opus Palatinum de Trianguhis, and continued to work at it while he occupied his old chair at Wittenberg, while he taught mathematics at Leipsic, while he travelled over different parts of the Continent, and indeed up to his death in Hungary in 1576. The Opus Palatinum of Rheticus was published by Otho in 1596. It gives tables of sines and cosines, tangents, &c., for every 10 seconds, calculated to ten places. He had projected a table of the same kind to fifteen places, but did not live to complete it. The sine table, however, was afterwards published on this scale under the name of Thesaurus Hathematicus(Prankfort, 1613) by Pitiscus, who himself carried the calculation of a few of the earlier sines to twenty-two places.