Bernard Forest De Belidor, a French military engineer and author, born in Catalonia in 1693, died in Paris, Sept. 8, 1761. He was employed by Cassini and La Hire in their measurements of an arc of the meridian; and they recommended him to the duke of Orleans, regent of France, who appointed him professor of the newly established artillery school of La Fere, which institution acquired great celebrity under his management About 1740, however, he lost the position through the jealousy of superior officers, and became aide-de-camp of Gen. de Segur in Bavaria and Bohemia, and was captured at Linz, but exchanged after two months of confinement, after which he joined the statff the duke d'llarcourt as lieutenant colonel. In 1744 he served under the prince de Conti in Italy, where his skill in reducing strongholds without risking an engagement with the enemy was conspicuous; and subsequently he distinguished himself at the capture of Charleroi, and was promoted to a colonelcy. In 1758 he became director of the arsenal of Paris, and afterward inspector general of engineering.

Among his publications are: Cours de mathematiques, comprising his lectures at La Fere on the application of mathematics to military engineering (1725; enlarged and revised ed. by Mauduit, 1759); La science des ingenieurs dans la conduite des travaux de fortification et d' architecture civile (1729; 2d ed., Paris, 1749, and the Hague, 1753; new illustrated and annotated edition by Navier, Paris, 1837); Le bombardier frangais, ou nourelle methodc de jeter les bombes axec precision (1731; Amsterdam, 1734); and Traite des fortifications (2 vols., 1735). The first volume of a new edition of his greatest work, Architecture hydraulique (4 vols., illustrated, 1737-'53), which continues to rank as a great authority, was published in 1819 by Navier, who died in 1836 without finishing the remaining 3 volumes. A German translation appeared at Augsburg (2 vols., 1764-'66). He was among the first to demonstrate the utility of compression globes, two of his memoirs on this subject having been published in the annals of the academy of sciences (1750).