CLAVIO, CHRISTOPH. - Celebrated Jesuit mathematician, b. at Bamberg in 1538, d. at Rome on 6 Feb. 1612. He entered the Society in Rome in 1555, studied at Coimbra in Portugal, and then held the chair of mathematics at the Roman College almost uninterruptedly from 1565 until his death. He took an active part in the preparation of the Ratio studiorum of the Society and strongly influenced the flourishing development that the mathematical sciences then experienced within the Order. His works, intended mainly for teaching, went through numerous reprints: In sphaeram Ioannis de Sacro Bosco commentarius (Rome 1570); Gnomonica libri VIII (ibid. 1581); Epitome arithmeticae practicae (ibid. 1583); Astrolabium (ibid. 1593); Computus ecclesiasticus (ibid. 1597); Geometria practica (ibid. 1604); Algebra (ibid. 1608). The most renowned, Euclidis elementorum libri XV (ibid. 1574, with a 16th book by C.), exerted a wide influence even outside Europe; it was translated, for example, into Chinese by Fr. Matteo Ricci, a former pupil of C. A fine collected edition of his works appeared: Opera mathematica (5 vols. fol., Mainz 1612). He earned the name of the “Euclid of the 16th century,” not for originality of discovery or theory, but for the marvelous gift of synthesis with which he clarified and unified all the achievements of the mathematical sciences 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 day. Well known are his relations with Galileo, whose early discoveries he followed and supported with benevolence.
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 then entrusted by Gregory XIII and Clement VIII with explaining the new calendar and defending it against Protestant attacks: Novi calendarii romani apologia adversus Michaelem Maestlinum (Rome 1588); Romani calendarii a Gregorio XIII P. M. restituiti explicati S. D. N. Clementis VIII P. M. iussu edita (ibid. 1595); he wrote other defenses against Scaliger (ibid. 1595 and 1609) and against Giorgio Germano (ibid. 1610). A monograph worthy of him is still lacking.