Girard Desargues
Gérard Desargues, Girard Desargues also, ( born February 21, 1591 in Lyon, † October 1661 ) was a French architect and mathematician, the geometry is considered one of the founders of Projective.
Life and work
Desargues came from a distinguished family of lawyers in Paris and in Lyon, where the family owned several houses and an estate. His father was a royal notary and had high offices in Lyon. Desargues was the third of six children. His two older brothers were lawyers at the Parliament in Paris. About his life little is known. In 1621 he is shown as a silk merchant in Lyon. 1626 he undertook a journey to Flanders and requested the City of Paris for a patent for the construction of wells. In 1628 he applied for the family inheritance after the death of his two elder brothers. Maybe he took part in the siege of La Rochelle (1627-1628), but this is not proven. Richelieu is said to have appreciated his talent as an engineer and René Taton suspected that he ( was his heritage is not very large ) for most of his livelihood earned as an engineer on behalf of the Cardinal.
Among his acquaintances during his time in Paris from around 1630 included, among others, René Descartes, Gassendi, Marin Mersenne, Étienne Pascal (the father of Blaise Pascal ) and Blaise Pascal ( to which he had 1639 contacts and it to our previous work in projective geometry encouraged ). Mersenne was in Paris a kind of academy that Desargues regularly visited in 1635. In his letters to Mersenne in 1634 mentions a treatise on perspective of Desargues (but that only two years later appeared ). In the 1640s an assassination attempt on Desargues, and to escape the turmoil of that time ( the Fronde ) he goes back to Lyon in 1648. As an architect he worked until about 1645 in Paris and Lyon. His works include the facade of Lyon's town hall. He is said to have also designed a novel spiral staircase and a pump, which was built near Paris, and was based on the epicyclic. From about 1657 he was back in Paris ( demonstrated for example, is the residence in 1660 in a letter by Christian Huygens ), where he works as an architect. He was also in the Academy of Montmor 1660 active.
He wrote about perspective ( Paris 1636), stone carvings (1640) and sundials (1640), but his writings are often difficult to understand (some he uses the language of craftsmen ), which already criticized Descartes. In particular, the for the font, which is known as Brouillon Projet, which appeared in 1639 in Paris and in which he developed the foundations of a new, beyond the classical Euclidean geometry of the Greeks beyond the form of geometry, projective geometry, for from considerations perspective emerged. He treats points at infinity ( which, however, already looked at Kepler ) on the same level, led for the first time a duality of points and lines and gave a theory of projective conics from view.
The set of Desargues projective geometry states that the points of intersection of corresponding sides of two triangles lie on a straight line when the straight line connecting corresponding vertices intersect at one point (and vice versa). It is not found in Brouillon Projet, but was first published in 1648 by the engraver Abraham Bosse in his work on perspective. The set plays an important role in the foundations of projective geometry, particularly as David Hilbert worked out the end of the 19th century. Bosse also published another important set of Desargues, the projective invariance of the cross ratio. Bosse was a friend and student (from about 1641) of Desargues and presented his ideas in a more comprehensible form is by permission of Desargues. Desargues taught from about 1639 different private craftsmen and artists in his doctrine of perspective.
The projective geometry of Desargues and Pascal fell behind again in the background and was only revived by Gaspard Monge and his students in France in the late 18th century and early 19th century.
About his teaching of perspective and other of his writings came Desargues in dispute with the mathematician and royal secretary Jean de Beaugrand ( 1584/88-1640 ), who criticized him in 1636 several tracts, and with Jacques Curebelle, 1644, the treaty examination of the Oeuvres du Sieur Desargues published. The dispute with Curebelle, which also included a bet and went to court, was one reason why Desargues again went back to Lyon. Even bosses, who represented the teaching of Desargues was therefore exposed to attacks and allowed the teaching at the Royal Academy neither present nor defend.
From Brouillon Projet only one copy of the original pressure is obtained. He was discovered in 1951 and published by René Taton. Before that, the book was only ( since 1845, by Michel Chasles ) known from a manuscript copy of Philippe de la Hire.
1964 was named after him by the IAU, the moon crater Desargues.