Grégoire de Saint-Vincent - in Latin : Gregorius a Sancto Vincentio, in Dutch : Gregorius van St-Vincent - (8 September 1584 Bruges – 5 June 1667 Ghent) was a Flemish Jesuit and mathematician. He is remembered for his work on quadrature of the hyperbola. Grégoire gave the "clearest early account of the summation of geometric series." He also resolved Zeno's paradox by showing that the time intervals involved formed a geometric progression and thus had a finite sum. Life Gregoire was born in Bruges 8 September 1584. After reading philosophy in Douai, he entered the Society of Jesus 21 October 1605. His talent was recognized by Christopher Clavius in Rome. Gregoire was sent to Louvain in 1612, and was ordained a priest 23 March 1613. Gregoire began teaching in association with François d'Aguilon in Antwerp from 1617 to 20. Moving to Louvain in 1621, he taught mathematics there until 1625. That year he became obsessed with squaring the circle and requested permission from Mutio Vitelleschi to publish his method. But Vitelleschi deferred to Christoph Grienberger, the mathematician in Rome. On 9 September 1625, Gregoire set out for Rome to confer with Grienberger, but without avail. He returned to the Netherlands in 1627, and the following year was sent to Prague to serve in the house of Emperor Ferdinand II. After an attack of apoplexy, he was assisted there by Theodorus Moretus. When the Saxons raided Prague in 1631, Gregoire left and some of his manuscripts were lost in the mayhem. Others were returned to him in 1641 through Rodericus de Arriaga. From 1632 Gregoire resided with The Society in Ghent and served as a mathematics teacher. The mathematical thinking of Sancto Vincentio underwent a clear evolution during his stay in Antwerp. Starting from the problem of trisection of the angle and the determination of the two mean proportional, he made use of infinite series, the logarithmic property of the hyperbola, limits, and the related method of exhaustion. Sancto Vincentio later applied this last method, in particular to his theory ducere planum in planum, which he developed in Louvain in the years 1621 to 24. Ductus plani in planum The contribution of Opus Geometricum was in making extensive use of spatial imagery to create a multitude of solids, the volumes of which reduce to a single construction depending on the ductus of a rectilinear figure, in the absence of [algebraic notation