JACQUIER, François. — Philosopher, mathematician, astronomer of the Order of Minims, born at Vitry-les-Français on 7 June 1711, died at Rome on 3 July 1788.
Sent to Rome, he completed his studies at the Convent of the Trinità dei Monti, and in Rome, in collaboration with his confrere Le Seur (q.v.), he carried out his scientific work. He taught philosophy, theology, but especially mathematics at the Trinità de’ Monti, at the Sapienza, and at Propaganda Fide. The opinions of the two scientists were often sought by the supreme pontiffs and by scholars on the most important problems of architecture, statics, hydraulics, etc. In 1746 their project, in collaboration with Fr R. Boscovich (q.v.), for the stability of the Vatican dome, was preferred and executed by encircling Michelangelo’s structure with five iron hoops. Both were members of the principal academies of Europe. Jacquier (after the suppression of the Jesuits) held the chair of mathematics at the Collegio Romano. He also concerned himself with music and aerostatics (cf. G. Boffito, *Una memoria aeronautica del p. J. [1783]*, in *Rivista aeronautica*, 8 [1932], pp. 669-77 and 219-20).
Besides various replies to questions put to him, and a commentary on Newton’s *Principia*, written in collaboration with Fr Le Seur, he composed: *Del calcolo integrale* (Parma 1768); *Institutiones philosophicae ad studia theologica accomodatae* (4 vols., Rome 1749, many editions and translations in Italy and abroad); *Trattato intorno alla sfera* (Parma 1775); *Descrizione di uno strumento per fare orologi solari* (ibid. 1774).