Floquet obtained his mathematics agrégation on 15 September 1875 and a week later he was named as professor of elementary mathematics at the Lycée d'Angers. On 8 November of the following year Floquet was appointed to the position of professor of special mathematics at the Lycée de Clermont-Ferrand. On 13 February 1878 he was appointed maître de conférences at the Faculty of Science at Nancy. As a result of the Franco-Prussian war which had proved disastrous for France, some French territory had been annexed by Germany and this increased the importance of Nancy. It was situated near the border, and when Floquet arrived there it was a city full of barracks. It also contained many industrialists who had left the annexed territory refusing to become German nationals.
Floquet submitted his doctoral thesis Sur la théorie des équations différentielles linéaires Ⓣ to the Faculty of Science in Paris on 8 April 1879. Much of the work he did over the next few years was based on the ideas which were incorporated in his thesis. For example he published three papers with the title Sur les équations différentielles linéaires à coefficients périodiques Ⓣ , two in 1881 and the third in 1883. In 1884 he published Addition à un mémoire sur les équations différentielles linéaires Ⓣ and Sur les équations différentielles linéaires à coefficients doublement périodiques Ⓣ. The two 1881 papers and the second mentioned paper of 1884 appeared in Comptes Rendus while the others appeared in the Annals of the École Normale Supérieure.
In November 1879 Floquet was given a temporary appointment as a professor at Nancy and in the following year he was put in charge of the mathematics course there. In July 1880 he was given a permanent chair and by the end of the year he was holding the chair of pure mathematics and analysis. He was appointed as head of the Faculty of Science at Nancy in October 1905. He was a very successful head, creating a number of Institutes which helped to make Nancy the leading scientific research centre outside Paris. He continued to publish high quality papers on mathematics and astronomy in Comptes Rendus and in various journals associated with Nancy. For example he published Sur une classe d'équations différentielles linéaires non homogènes Ⓣ (1887), Sur une propriété de la surface xyz = l3Ⓣ (1888), Sur le mouvement d'un fil dans un plan fixe Ⓣ (1889), Sur l'équation de Lamé Ⓣ (1895), Sur le mouvement d'un point ou d'un fil glissant sur un plan horizontal fixe lorsqu'on tient compte de la rotation de la terre et du frottement Ⓣ (1898), Sur les équations intrinsèques du mouvement d'un fil et sur le calcul de sa tension Ⓣ (1901), and L'astronome Messier Ⓣ (1902).
World War I broke out in 1914 and Nancy was heavily shelled. Floquet remained in Nancy during the war, never once leaving the city during the four years to 1918.
Article by: J J O'Connor and E F Robertson