**Étienne Bobillier** is best known for his work on polars of curves and of algebraic surfaces.

- Étienne Bobillier showed no interest in mathematics up to the age of 16 but he did show considerable interest in literary studies and won several prizes for his performance at the local lycée.
- At the age of nineteen Bobillier was examined by Charles Louis Dinet, one of the École Polytechnique's admissions examiners.
- Bobillier was placed in first position among those students examiner by Dinet and, in the overall ranked list for entry in that year, he was placed fourth.
- In his first year of study Étienne Bobillier performed very well indeed, completing the year ranked eighth out of the sixty-four students who completed the course that year.
- However, being short of money, Bobillier left the École Polytechnique in 1818 to became a mathematics instructor at the École des Arts et Métiers at Châlons-sur-Marne.
- The position was offered to a student of the École Polytechnique and Bobillier was quick to take up the offer.
- In the Bulletin de Férussac in 1825 Bobillier announced his intention to publish a three volume Principes d'algèbre Ⓣ(Principles of algebra).
- Bobillier did not see much prospect of a good career at the École des Arts et Métiers at Châlons-sur-Marne and indicated that he wanted a university post.
- The theory of centroids by Chasles (1830) was used by Bobillier in his construction of centres of curvature of plane roulettes in 1831.
- Bobillier's demonstration of the principle of virtual velocities consisted in substituting "for any ordinary machine, whose character can be changed in an infinite number of ways, the winch, whose conditions of equilibrium are so well known and that, at least for the infinitely small deviation that we can estimate in its equilibrium, remains, exactly the same." His method is extremely clever.
- In kinematics there seem to be no known traces of the work Bobillier was doing toward the end of his life, although the passages in his book on geometry that treat this subject are still extant.
- Bobillier then went on to pose the problem of how to determine the corresponding centre of curvature in the path of the third vertex, c, when given the centres of curvature at points a and b of the paths described by vertices a and b of triangle abc.
- The construction he gave of this centre is known as the 'Bobillier construction'.
- Bobillier was a member of a number of societies: the Société Industrielle d'Angers; the Société d'Émulation du Jura; the Société d'Émulation des Vosges; and the the Société des Sciences Physiques, Chimiques et Arts Agricoles de France.

Born 17 April 1798, Lons-le-Saunier, France. Died 22 March 1840, Châlons-sur-Marne, France.

View full biography at MacTutor

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