CLAVIO, CHRISTOPH. — Celebrated Jesuit mathematician, born in Bamberg in 1538, died in Rome on 6 February 1612. Having entered the Society in Rome in 1555, he studied at Coimbra in Portugal and subsequently held the chair of mathematics at the Roman College almost without interruption from 1565 until his death. He took an active part in preparing the Ratio studiorum of the Society and strongly influenced the vigorous development then undertaken by the mathematical sciences within the Order. His works, intended principally for teaching, went through numerous reprints: In sphaeram Ioannis de Sacro Bosco commentarius (Rome 1570); Gnonomicae libri VIII (there 1581); Epitome arithmeticae practicae (there 1583); Astrolabium (there 1593); Computus ecclesiasticus (there 1597); Geometria practica (there 1604); Algebra (there 1608). The most renowned, Euclidis elementorum libri XV (there 1574, with a sixteenth book by C.), also exerted a broad influence outside Europe; it was translated, for example, into Chinese by Fr. Matteo Ricci, formerly C.’s pupil. A fine collected edition was produced: Opera mathematica (5 vols. in-fol., Mainz 1612). C. earned the name “the Euclid of the sixteenth century,” not through originality of discoveries or theories, but through the marvelous gift of synthesis by which he clarified and unified the entire body of mathematical knowledge of his time. He was also an incomparable teacher and maintained scientific correspondence not only with his former pupils, but with the leading scientists of his time. His relations with Galileo are well known: he followed and benevolently supported Galileo’s early discoveries.
C. was one of the principal collaborators in the Gregorian reform of the calendar (1577–82), and it seems that he was responsible for its final drafting. He was subsequently commissioned by Gregory XIII and Clement VIII to explain the new calendar and disseminate it in opposition to Protestant attacks: Novi calendarii romani apologia adversus Michaelem Maestlinum (Rome 1588); Romani calendarii a Gregorio XIII P. M. restituti explicatio S. D. N. Clementis VIII P. M. iussu edita (there 1595); he wrote other apologies against Scaliger (there 1595 and 1609) and against Giorgio Germano (there 1610). A monograph on C., such as he deserves, is still lacking.