In 1617 Sylvius accompanied Malapert on his return to the Southern Netherlands, where they both spent twelve years at the University of Douai. They performed observations of sunspots with better astronomical instruments. These Sylvius invented and constructed himself.
In 1630, Malapert was called to Spain to occupy a newly created chair in the Jesuit Colegio Imperial de Madrid. However, he fell ill during the journey and died shortly after entering Spain. Sylvius continued on, and subsequently taught at the Colegio Imperial, building the university a planetarium in 1634.
Sylvius left Spain for the Southern Netherlands in 1638, where he stayed in the Benedictine monastery at Anchin, for which he may have constructed its planetarium.
Sylvius was in Poland by 1649. In 1651, he published a work on calendariography.
