REGIOMONTANUS (1436-1476)  , German astronomer, was born at Konigsberg in Franconia on the 6th of June 1436 . The son of a miller, his name originally was Johann Muller, but he called himself, from his birthplace, Joh. de Monteregio, an appellation which became gradually modified into Regiomont anus . At Vienna, from 1452, he was the pupil and associate of George Purbach (1423—1461), and they jointly undertook a reform of astronomy rendered necessary by the errors they detected in the Alphonsine Tables . In this they were much hindered by the lack of correct translations of Ptolemy's works; and in 1462 Regiomontanus accompanied Cardinal Bessarion to Italy in search of authentic manuscripts . He rapidly mastered Greek at Rome and Ferrara, lectured on Alfraganus at Padua, and completed at Venice in 1463 Purbach's Epitome in Cl . Ptolemaei magnam compositionem (printed at Venice in 1496), and his own De Triangulis (Nuremberg, 1533), the earliest work treating of trigonometry as a substantive science . A quarrel with George of Trebizond, the blunders in whose translation of the Almagest he had pointed out, obliged him to quit Rome precipitately in 1468 . He repaired to Vienna, and was thence summoned to Buda by Matthias Corvinus, king of Hungary, for the purpose of collating Greek manuscripts at a handsome salary . He also finished his Tabulae Directionum (Nuremberg, 1475), essentially an astrological work, but containing a valuable table of tangents . An outbreak of war, meanwhile, diverted the king's attention from learning, and in 1471 Regiomontanus settled at Nuremberg . Bernhard Walther, a rich patrician, became his pupil and patron; and they together equipped the first European observatory, for which Regiomontanus himself constructed instruments of an improved type (described in his posthumous Scripta, Nuremberg, 1544) . His observations of the great comet of January 1672 supplied the basis of modern cometary astronomy .

At a

printing-press established in Walther's house by Regiomontanus, Purbach's Theoricae planetarum novae was published in 1472 or 1473; a series of popular calendars issued from it, and in 1474 a volume of Ephemerides calculated by Regiomontanus for thirty-two years (1474–1506), in which the method of " lunar distances," for determining the longitude at sea, was recommended and explained . In 1472 Regiomontanus was summoned to Rome by Pope Sixtus IV. to aid in the reform of the calendar; . and there he died, most likely of the plague, on the 6th of July 1476 .