Étienne Bobillier

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Étienne Bobillier showed no interest in mathematics up to the age of 16. After his brother was admitted to the École Polytechnique he decided that he wanted to emulate him. He found mathematics books which his brother had left behind and began to study on his own.

At the age of 19 Bobillier sat the entrance examinations of the École Polytechnique. He passed well and in his first year of study he also performed very well indeed. However, being short of money, he left the École Polytechnique in 1818 to became an instructor at the École des Arts et Métiers at Châlons. He immediately displayed a remarkable talent for teaching mathematics.

In 1829 Bobillier was recommended by Poisson for the post of professor of mathematics at the Collège Royal in Amiens. However he was sent as director of studies to the École in Angers. He served in the National Guard during the 1830 revolution, then in 1832 his post was abolished. This was a time of great uncertainty in France and there was little stability anywhere.

After returning to Châlons he was soon promoted to professor there in 1832.

Bobillier corresponded with Poncelet during the years 1828-29 and worked on geometric problems. He followed Monge in treating geometric problems in an analytic and projective way. He was the first to use z → 1/z in the study of conic sections.

Bobillier is best known for his work on polars of curves and of algebraic surfaces. He showed that the tangents drawn from a point to a plane curve of order m have their points of contact on a curve of order m - 1 which he called the polar of the point.

The post at Châlons was to be his last since in 1836 he became ill. Refusing to take time to recuperate from a recurring illness, he continued to teach. This hastened his death at the early age of 42. At the time of his death he was working on problems in kinematics, having earlier studied statics and in particular the catenary.

After his death Poncelet, who did know him personally wrote:-

Bobillier had an intelligent and singularly active mind.

Chasles, who did not know Bobillier personally and in fact made a serious mistake in the date of his death, wrote:-

We owe remarkable researches to Bobillier, a distinguished geometer who gave hopes of great achievements for mathematical sciences.

Article by: J J O'Connor and E F Robertson

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Lunar features	Crater Bobillier

JOC/EFR © December 1996 Copyright information	School of Mathematics and Statistics University of St Andrews, Scotland
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