Studies in Paris (1822–26)[edit]
Dirichlet again convinced his parents to provide further financial support for his studies in mathematics, against their wish for a career in law. As Germany provided little opportunity to study higher mathematics at the time, with only Gauss at the University of Göttingen who was nominally a professor of astronomy and anyway disliked teaching, Dirichlet decided to go to Paris in May 1822. There he attended classes at the Collège de France and at the Faculté des sciences de Paris, learning mathematics from Hachette among others, while undertaking private study of Gauss's Disquisitiones Arithmeticae, a book he kept close for his entire life. In 1823 he was recommended to General Foy, who hired him as a private tutor to teach his children German, the wage finally allowing Dirichlet to become independent from his parents' financial support.[2]
His first original research, comprising part of a proof of Fermat's last theorem for the case n=5, brought him immediate fame, being the first advance in the theorem since Fermat's own proof of the case n=4 and Euler's proof for n=3. Adrien-Marie Legendre, one of the referees, soon completed the proof for this case; Dirichlet completed his own proof a short time after Legendre, and a few years later produced a full proof for the case n=14.[3] In June 1825 he was accepted to lecture on his partial proof for the case n=5 at the French Academy of Sciences, an exceptional feat for a 20 year old student with no degree.[1] His lecture at the Academy has also put Dirichlet in close contact with Fourier and Poisson, who raised his interest in theoretical physics, especially Fourier's analytic theory of heat.