**Ernest de Jonquières** was a French naval officer who discovered many results in geometry.

- He reached positions of high rank, being made a lieutenant in 1841 and serving on the Admiralty Council from 1848 to 1850.
- De Jonquières' appointment to the Admiralty Council meant that he was living in Paris during this period and he was already interested in mathematical research after reading the works of Poncelet and Chasles.
- his geometric creative faculty developed in an astonishing manner, and it did not take him long to become Chasles' most eminent pupil and the most gifted commentator on his works.
- This was the period when Chasles was collecting material for his Traité de géométrie Ⓣ(Treatise on geometry) (1852) in which he discusses cross ratio, pencils and involutions - all notions which he introduced.
- De Jonquières thrived in this association with Chasles proving results which Chasles conjectured and solving problems which he put forward.
- After the period in Paris, de Jonquières visited several countries as part of his naval duties.
- During 1860-61 he made lengthy sea voyages and this provided him with much time free from distractions during which he could work out many of the mathematical ideas which he was developing.
- The committee which evaluated the entries decided to split the prize, but de Jonquières' entry was considered the best and he received two-thirds of the prize.
- In 1865 de Jonquières was promoted to captain of a naval vessel.
- De Jonquières played an important role in the transformation of the city by the French.
- After his return he was on the Naval Works Council, then on 17 December 1874 he was appointed as Rear Admiral, becoming Vice-Admiral on 1 October 1879.
- He retired in 1885 having been elected an academician by the Institute of France on 24 March 1884.
- He made many contributions many of them extending the work of Poncelet and Chasles.
- An early work, the treatise Mélanges de géométrie pure Ⓣ(Diversions in pure geometry) (1856) contains: an amplifications of Chasles' ideas on the geometric properties of an infinitely small movement of a free body in space; a commentary on Chasles' work on conic sections; the principle of homographic correspondence; and constructions relating to curves of the third order.
- In a final section de Jonquières presented a French translation of Maclaurin's work on curves.
- De Jonquières' paper was not published until 1885 although a summary of it was published in 1864.
- In addition de Jonquières discovered results in the area of Schubert's Abzählende Geometrie Ⓣ(Enumerative geometry) .
- his results form a series of detailed supplements to the work of others and reflect Jonquières's inventiveness in calculating rather than a more profound contribution to the advancement of the field.
- de Jonquières has a right to a distinguished place among the geometers of second rank who flourished in France in the latter half of the nineteenth century.
- In fact, the discontinuities in his researches in pure science produced those gaps in his culture, that inadequate knowledge of the literature of his time, which stand out in a great number of his works.
- But (leaving aside his research in the realm of number in which he followed known and sure paths) the daily battle with the waves of the ocean appears to have endowed him with an admirable courage and valuable initiative; we see him approach with a smile questions capable of frightening consummate mathematicians, and calmly employ dangerous methods, the legitimacy of which is still under discussion.
- One might say that if, as a soldier, de Jonquières belonged to the regular army, as a geometer he presented all the character of a guerrilla, despising antiquated routine and rising to attack by the most dangerous paths.
- Other fearful geometers, preferring the classical roads, did not fail to proclaim the wounds that befell him, which we, as impartial historians, have not hidden; but we can answer that wounds are part of heroes, and that only cowards who never go into battle escape them.

Born 3 July 1820, Carpentras, France. Died 12 August 1901, Mousans-Sartoux (near Grasse), France.

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Topology

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive