Castelli, Benedict

, an Italian mathematician, the particular friend of Galileo, was born of an ancient and noble family at Brescia, in the year 1577. In 1595, he entered into a monastery of the order of St. Benedict in his native city, but afterwards studied at Padua and at Florence, where he became a disciple of Galileo, and assisted him in his astronomical observations, and afterwards maintained a regular correspondence with him. Galileo, not only had the highest esteem for his talents, but reposed the utmost confidence in his friendship. Under his name the apology of Galileo against the censures of Ludovico delle Colombe and Vincent di Grazia appeared, though it was principally written by Galileo himself. From 1615 to 1625, he occupied the mathematical chair at Pisa. In 1625, Castelli was invited to Rome by pope Urban VIII. and made mathematical professor in the college della Sapienza. The subject of his particular attention, and in the investigation | of which he chiefly excelled, was the motion of water, on which subject as connected with the health of the cities of Venice, &c. he was frequently consulted, and suggested many important improvements. In 1628, he published on the mensuration of running waters, “Delia misura dell' acque correnti,” Rome, 4to, and “Dimostrazioni geometriche clella misura dell acque correnti,” ibid. 4to. These have been inserted in the collection of the author’s works on similar topics, printed at Florence, with other treatises, on the laguna of Venice, on the improvement of the Pontine, Bolognese, Ferrarese, and Romagnese marshes, &c. in 1766. Guglielrnini, though in other things he impugns Castelli, allows him the honour of having first applied geometry to the motion of water; and Montucla calls him “The Creator of a new part of Hydraulics.” His defence of Galileo, “Riposta alle opposizioni del Sig. Ludovico delle Colombe, &c.” was published at Florence, 1615, 4 to. He deeply lamented the death of this great man, and it is supposed to have hastened his own in 1644. Duke Leopold ordered his bust to be placed beside that of Galileo. ¹