De Groot, Jan Cornets

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De Groot, Jan Cornets

also known as Johan Hugo De Groot or Janus Grotius (b near Delft, Netherlands, 8 March 1554; d. Delft, 3 May 1640)


The son of Hugo Cornelisz and of Elselinge Van Heemskerck, De Groot (or perhaps a namesake) entered the University of Leiden on 5 February 1575, its opening day. He was a master of liberal arts and philosophy at Douai. Belonging to the Delft patriciate, he was a councillor, and from 1591 to 1595 was one of the mayors. From 1594 to 1617 he was a curator of the University of Leiden, which in 1596 awarded him the doctorate of law. After 1617 he served as adviser to the Count of Hohenlohe.

In 1582 De Groot married Alida Borren, from Overschie. One of their five children was the jurist known as Hugo Grotius.

De Groot was a distinguished amateur scientist, acquainted with the best minds in the Netherlands. Stevin, with whom he collaborated in the construction of windmills, praised him as a man well versed in the whole of philosophy, mentioning Euclid, Alhazen (Ibn al-Haytham), Witelo, music, and poetry. De Groot is best known through the experiment he performed with Stevin, in which they proved that lead bodies of different weights falling on a board traverse the same distance in the same time. This anti-Aristotelian experiment, published by Stevin in his Waterwicht (1586, p. 66), anticipated Galileo’s famous, but apocryphal, experiment at the Leaning Tower of Pisa. De Groot also befriended Ludolph Van Ceulen, on whose behalf he translated Archimedes’ Measurement of the Circle from the Greek into Dutch and who submitted to him his approximation of to π 20 decimal places (1586). Van Roomen, in his Ideae mathematicae(1593), praises De Groot as one of the better mathematicians of his time.


Only some Latin and Greek poems, correspondence with his son Hugo—Hugonis epistolae (Amsterdam, 1607)—and some MS letters in the library of the University of Leiden are extant.

Secondary literature is C. de Waard, “Groot, J. H. de,” in Nieuw Nederlandsch biographisch Woordenboek, II (1912), cols. 528, 529, with bibliography; and The Principal Works of Simon Stevin (Amsterdam, 1955–1966), esp. vols. I, V.

Dirk J. Struik

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De Groot, Jan Cornets

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