After returning from a visit to
Degen and other mathematicians in
Copenhagen, Abel applied for economic support in order to visit top mathematicians in Germany and France. Instead, he was given funds to stay in Cristiania for two years, and he learned German and French in those years. While learning languages, Abel published his first notable work in
1824, Mémoire sur les équations algébriques ou on démontre l'impossibilité de la résolution de l'équation générale du cinquième degré (Memoir on algebraic equations, in which is proved the impossibility of solving the general equation of the fifth degree). While others were questioning ‘what is the solution’, Abel asked ‘is there a solution’ and he proved impossibility of solving quintic equation in radicals in 1823 (see
Abel–Ruffini theorem). This work was in abstruse and difficult form, in part because the page count was severely restricted in order to save money on printing. A more detailed proof was published in
1826 in the first volume of
Crelle's Journal. In 1825, he was given a government scholarship that enabled him to travel abroad. During the travel, Abel visited the astronomer
Heinrich Christian Schumacher in
Altona near Hamburg. He spent six months in Berlin, where he became well acquainted with
August Leopold Crelle, who was then about to publish his mathematical journal. This project was warmly encouraged by Abel, who contributed much to the success of the venture. From Berlin he passed to Freiburg, and here he made his brilliant researches in the theory of functions:
elliptic, hyperelliptic, and a new class now known as
abelian functions being particularly intensely studied.
In
1826 Abel moved to
Paris, and during a ten-month stay he met the leading mathematicians of France; but he was poorly appreciated, as his work was scarcely known, and his modesty restrained him from proclaiming his research. Pecuniary embarrassments, from which he had never been free, finally compelled him to abandon his tour, and on his return to Norway he taught for some time at Christiania.