PHILIP DE LA, a French mathematician and astronomer of eminence, was born at Paris in the year 1640. His father, who was painter to his majesty, designing to bring him up to the same occupation, taught him drawing and such parts of the mathematics as are intimately connected with it. At the age of 20 he took a journey into Italy, to enlarge his knowledge of his favourite art, in which country he resided for about four years. The study of the mathematics afterwards occupied all his attention, which he continued to prosecute on his return to his native city; and the publication of some works having procured him so high a reputation, he was chosen a member of the Academy of Sciences in the year 1678.

When the celebrated minister Colbert conceived the design of constructing a better map of France than any at that time to be met with, De la Hire was nominated in conjunction with Picard, to make the necessary observations, which engaged his attention for some years in different provinces. But besides the chief object of his journeys, he philosophized upon every thing that occurred to him, in a particular manner on the variations of the magnetic needle, on refractions, and the height of mountains as ascertained by the barometer.

In the year 1683 he was employed in continuing the meridian line which had been begun by Picard in 1669. He continued it from Paris towards the north, and Cassini carried it on towards the south; but on the death of Colbert, which happened the same year, the work was laid aside in an unfinished state. He was afterwards employed, in conjunction with other eminent philosophers, in taking the necessary levels for the grand aqueducts which Louis XIV. was about to make.

The works which have been published by De la Hire are very numerous; and as he was professor of the Royal College and Academy of Architecture, he must have been constantly employed. He had the politeness, circumspection, and prudence of Italy, which made him appear too reserved in the estimation of his versatile countrymen, yet he was regarded by all as an honest, disinterested man. He died in the year 1718, at the great age of 78.

He published Traité de Mechanique; Nouvelle Méthode en Géométrie pour les Sections des Superficies Coniques et Cylindriques; De Cycloide; Nouveaux Elements des Sections Coniques; les Lieux Géométriques; la Construction ou Effection des Equations; La Gnomonique, and several others of less importance. That which gained him the greatest reputation all over Europe, was his Sectiones Conicae in novem libros distributae, considered by the best judges as an original work.