Perpignan, where he began to study mathematics in preparation
for the entrance examination of the polytechnic school. Within two years
and a half he had mastered all the subjects prescribed for examination,
and a great deal more, and, on going up for examination at Toulouse, he
astounded his examiner by his knowledge of Lagrange. Towards the close
of 1803 he entered the polytechnic school, with the artillery service as
the aim of his ambition, and in 1804, through the advice and
recommendation of S.D. Poisson, he received the appointment of secretary
to the Observatory of Paris. He now became acquainted with Laplace, and
through his influence was commissioned, with J.B. Biot, to complete the
meridional measurements which had been begun by J.B.J. Delambre, and
interrupted since the death of P.F.A. Mechain (1744-1804). The two left
Paris in 1806 and began operations among the mountains of Spain, but
Biot returned to Paris after they had determined the latitude of
Formentera, the southernmost point to which they were to carry the
survey, leaving Arago to make the geodetical connexion of Majorca with
Ivica and with Formentera.

The adventures and difficulties of the latter were now only beginning.
The political ferment caused by the entrance of the French into Spain
extended to these islands, and the ignorant populace began to suspect
that Arago's movements and his blazing fires on the top of Mount Galatzo
were telegraphic signals to the invading army. Ultimately they became so
infuriated that he was obliged to cause himself to be incarcerated in
the fortress of Belver in June 1808. On the 28th of July he managed to
escape from the island in a fishing-boat, and after an adventurous
voyage he reached Algiers on the 3rd of August. Thence he procured a
passage in a vessel bound for Marseilles, but on the 16th of August,
just as the vessel was nearing Marseilles, it fell into the hands of a
Spanish corsair. With the rest of the crew, Arago was taken to Rosas,
and imprisoned first in a windmill, and afterwards in the fortress of
that seaport, until the town fell into the hands of the French, when the
prisoners were transferred to Palamos. After fully three months'
imprisonment they were released on the demand of the dey of Algiers, and
again set sail for Marseilles on the 28th of November, but when within
sight of their port they were driven back by a northerly wind to Bougie
on the coast of Africa. Transport to Algiers by sea f