Lagny, Thomas Fantet De

, an eminent mathematician, was born at Lyons in 1660. Being intended for the bar, he was sent to study the law first at the college of Lyons, and next at the university of Thoulouse but having accidentally met with Fournier’s Euclid, and a treatise on algebra, mathematics became his favourite science. In 1686 he came to Paris, was soon after appointed tutor to the duke de Noailles, elected a member of the academy of sciences, and was appointed by Louis XIV, royal hydrographer at Rochefort; but sixteen years afterwards, he was recalled to Paris, and made librarian to the king with a considerable pension. He died April 11, 1734, and in his last moments, when he no longer knew the persons who surrounded his bed, one of them, through a foolish curiosity, asked him “What is the square of 12” to which he replied, as it were mechanically, 144. His works are, 1. “New Methods for the Extraction and Approximation of Roots,” 1692, 4to, 2. “Elements of Arithmetic and Algebra,” 1697, 12mo. 3. “On the Cubature of the, Sphere,” 1702, 12mo. 4. “A general Analysis, or Method of resolving Problems,” published by Richer in 1733, 4to. 5. Several Papers in the Memoirs of the Academy. | Lagny excelled in arithmetic, algebra, and geometry, in which he made many important discoveries. ¹