Geoscience Reference
In-Depth Information
Fig. 33
François Arago painted by Charles Steuben in 1832, aged 46. © Observatoire de Paris
be destined for the artillery or the engineers; the career of the sciences, of which
you have talked to me, is really too difficult to go through…” It was with these
discouraging words ringing in his ears that Arago took the entrance examination,
unexpectedly coming in first place. He entered the Polytechnic School at the end of
1803, where, according to his immodestly drafted autobiography (
The History of
My Youth
, Arago 1857) he became the head of his class.
Méchain died in Spain in September 1804 and his son, who was Secretary of the
Paris Observatory, resigned. Jean-Baptiste Biot of the Observatory was an examiner
of the Polytechnic School and had noticed Arago's work. So too had Denis Poisson,
professor of the Polytechnic School, who recommended Arago to the Director of the
Observatory to take Méchain's place. With his mathematical ability, Arago was
invited to replace the younger Méchain as the Observatory Secretary. He did not
want to give up a military career for one of science, especially after the discouraging
words of Méchain senior, but nevertheless he took leave from the Polytechnic to take
up the position on a trial basis. He worked with the telescopes in the Observatory as
an observer, measuring star positions, and also began to work with Biot on the
refraction of light through gases, which was a subject of practical importance in
astronomy because of the way that star positions are distorted by the atmosphere.
Part of the work included the accurate weighing of gases held in glass globes, and
this important data was used by the chemist Joseph Louis Gay-Lussac (1778-1850)
in the first steps to derive the atomic weights of carbon and hydrogen.
While Arago worked with Biot they discussed the value of completing the work
in Spain of extending the Paris Meridian which had been interrupted by Méchain's
death. Biot and Arago submitted a plan to complete the southern extension of the
Paris Meridian to Pierre-Simon Laplace, who was then the Director of the Paris
