Regiomontanus, Or Johann Muller, a German mathematician, born at Königsberg, Franconia (whence his Latin name), June 6, 1436, died July 6, 1476. He completed his studies under Purbach at Vienna, whom he succeeded in 1461 as professor of mathematics. Subsequently he lectured on astronomy at Padua, spent some time at the court of Matthias Cor-vinus in Hungary, and resided at Nuremberg from 1471 to 1474, when Pope Sixtus IV. alled him to Rome to reform the calendar, and not long before his death appointed him bishop of Ratisbon. According to some authorities, he was assassinated by the sons of George of Trebizond, in whose translations Regiomontanus had detected grave errors; according to other accounts, he died of the plague. He was the first in Europe to publish an astronomical almanac, improved the knowledge of algebra, introduced decimal fractions, greatly promoted the science of trigonometry, and was the most eminent astronomer that Europe had produced. His works include Calendarium (in Latin and German, Nuremberg, about 1473); Ephemerides from 1475 to 1506, continued by Bernhard Walther and published in 1544 by Schonerus; De Befor-matione Calendarii (Venice, 1489); De Come-toe Magnitudine, Longitudineque (Nuremberg, 1531); De Triangulis (1533); and Tabuloe Di-rectionum Profectionumque in Nativitatibus multum utiles (Venice, 1585). - See Regiomontanus als geistiger Vorläufer des Columbus, by Alex. Ziegler (Langensalza, 1874).