Theodorus Moretus, also known as Theodor or Theodore Moretus (1602–1667) was a Flemish Jesuit priest who was also a mathematician, geometer, theologian and philosopher. He spent most of his working life in Prague and Breslau (now Wroclaw) where he taught philosophy, theology and mathematics. He published a number of treatises on these three subjects and also on physics and music theory.
Life
thumb|270px|Illustration of an experiment showing the melting of metals with a glass, from Tractatus physico-mathematicus de aestu mari
Theodorus Moretus was born in Antwerp, the son of Pieter Moretus and Henrica Plantin. Both his parents were from prominent printing families: his mother was a daughter of Christophe Plantin, the founder of the famous Plantin Press in Antwerp while his father was the brother of Jan Moretus who was initially an assistant of Plantin, married another Plantin daughter and, after taking over the Plantin Press from his father-in-law, steered the business to further success well into the 17th century.
Moretus studied mathematics at the Jesuit school in Antwerp founded by François d'Aguilon. He was a student at this school for seven years. He joined the Jesuit order in Mechelen as a novice on 15 November 1618. He took physics in 1622–1623 and studied theology from 1623 to 1627. In 1627–28 Moretus is mentioned as a teacher of syntax in Bruges. His title was Magister, which indicates he had not been formally ordained yet. His aptitude for science (particularly mathematics) was appreciated early on by Father Gregorius van St-Vincent, who had arranged for Moretus to be able to continue his studies in Louvain without first having to spend a few years in colleges. Gregorius van Vincent also arranged for Moretus to send dissertations on mathematical subjects to Christoph Grienberger, the chair of mathematics at the Collegio Romano in Rome who reviewed them. Moretus was possibly ordained as a priest in 1628–29. From 1642 to 1645, Theodorus left his teaching post as he was sent as a preacher and missionary to the home that the Jesuits owned in Brzezenica, a small town in Galicia. In 1646 he was sent back to Prague as a professor, initially, of Holy Scripture and no longer of mathematics. He also was appointed to the office of councilor of the provincial council of Bohemia. It is from Breslau that Moretus sent the Tractatus physico-mathematicus de aestu mari (Physio-mathematical Treatise of the Tides), one of his best-known works, to Antwerp for publication. In this work he explains the tides as a result of the magnetism of the moon.
Work
The scientific work undertaken by Moretus was very successful: he made various discoveries in physics and astronomy, hydraulics and music theory but mainly mathematics. His research in optics brought him even fame among such scientists as was Robert Hooke, Athanasius Kircher, Cornelis Drebbel and Jan Marek Marci.