Olry Terquem (16 June 1782 – 6 May 1862) was a French mathematician. He is known for his works in geometry and for founding two scientific journals, one of which was the first journal about the history of mathematics. He was also the pseudonymous author (as Tsarphati) of a sequence of letters advocating radical reform in Judaism. He was French Jewish.
Education and career
Terquem grew up speaking Yiddish, and studying only the Hebrew language and the Talmud. However, after the French Revolution his family came into contact with a wider society, and his studies broadened. He became an assistant there in 1803, and earned his doctorate in 1804.
After finishing his studies he moved to Mainz (at that time known as Mayence and part of imperial France), where he taught at the Imperial Lycée. In 1811 he moved to the artillery school in the same city, in 1814 he moved again to the artillery school in Grenoble, and in 1815 he became the librarian of the Dépôt Central de l'Artillerie in Paris, where he remained for the rest of his life. He became an officer of the Legion of Honor in 1852. After he died, his funeral was officiated by Lazare Isidor, the Chief Rabbi of Paris and later of France, and attended by over 12 generals headed by Edmond Le Bœuf.
240px|thumb|The nine-point circle of a triangle. The three marked points that lie on the circle and interior to the triangle are the ones found by Terquem. The point of convergence of the three red lines through the triangle is its [[orthocenter.]]
In geometry, Terquem is known for naming the nine-point circle and fully proving its properties. This is a circle that passes through nine special points of any given triangle. Karl Wilhelm Feuerbach had previously observed that the three feet of the altitudes of a triangle and the three midpoints of its sides all lie on a single circle, but Terquem was the first to prove that this circle also contains the midpoints of the line segments connecting each vertex to the orthocenter of the triangle. He also gave a new proof of Feuerbach's theorem that the nine-point circle is tangent to the incircle and excircles of a triangle. "the enfant terrible of French Judaism". pushing for reforms that in his view would better assimilate Jews into modern life Terquem rejected the Talmud, proposed to codify intermarriage between Jews and non-Jews,