Christoph Clavius, 1538-1612
A professor at the Roman College, German-born mathematician Christoph Clavius was known for his writings on arithmetic and algebra and for his work on Gregorian calendar reform. He was a friend of Galileo, but in his commentary on medieval mathematician and astronomer Joanes de Sacro Bosco Clavius condemns the Copernican theory of a sun-centered solar system as both physically impossible and as contrary to the Scripture.
Works on measurement and instrumentation were another common feature of early Jesuit science. Textbooks, like the ones by Clavius on sundials and astrolabes, were particulary popular since the use of sundials and astrolabes were taught as part of the science curriculum in many Jesuit colleges.