Gheorghe Ţiţeica and the origins of affine differential geometry

We describe the historical and ideological context that brought to the fore the study of a centro-affine invariant that subsequently received much attention. The invariant was introduced by Ţiţeica in 1907, and this discovery has been viewed by many as a consequence of Klein's Erlangen program. We thus present the starting point of affine differential geometry, as it was discovered by Ţiţeica after his years in the Ph.D. program in Paris (1896–1899) under the guidance of Gaston Darboux.

RezumatDescriem în prezenta notă contextul istoric şi istoria ideilor care au condus la descoperirea invariantului centro-afin introdus de Gheorghe Ţiţeica în 1907. Studiul acestui invariant poate fi considerat o consecinţă a programului de la Erlangen. Prezentăm aici originea geometriei diferenţiale afine, aşa cum a fost concepută de Ţiţeica după anii lui de studii doctorale la Paris (1896–1899) sub conducerea lui Gaston Darboux.