French mathematician, architect and theorist. He settled at an early age in Paris, where he associated with such intellectuals as Marin Mersenne and Etienne Pascal; the latter's son, Blaise Pascal, claimed to be Desargues's disciple and was interested in his geometry of conic sections. Desargues was particularly interested in building techniques that involved the application of scientific knowledge, for example for the draught of chimneys, on which he corresponded with Mersenne and René Descartes, and lifting pumps, the subject of a proposal approved by the city of Paris in 1626, in which a series of fountains to clean the streets was planned. In 1636 he published a treatise on perspective, but he subsequently concentrated on architecture, including a design proposal for the Hôtel de Ville, Lyon. He also became interested in stonecutting (stereotomy), publishing a treatise on the subject in 1640. He used this specialized knowledge when building staircases, which were greatly admired by his contemporaries. Examples (all destroyed) include the stairs of the north wing in the courtyard of the château of Vizille, Isère (1653), interior staircases at the Palais Cardinal, the Hôtel de Turenne and the Hôtel de L'Hôpital (all Paris), and the staircases in the house he built on the Rue de Cléry for a M. Roland and in another on the Rue des Bernardins. Two of these staircases are recorded in plan in François Blondel's Cours d'architecture (1675-98). The skill of these designs derived from Desargues's mastery of perspective effects. In the Rue de Cléry house, for example, he sited the staircase in a square stairwell, which the first flight traversed diagonally to reach a landing located in the corner opposite that of the entrance, the ascent then continuing to the right or left, following the walls of the stairwell. //