See also: Fourier

Joseph Fourier (March 21st, 1768 with Auxerre - May 16th, 1830 with Paris) is a mathematician and French, known physicist for his work on the decomposition of periodic functions in trigonometrical series convergent called Fourier series.

Biography

He makes his studies at the Bénédictin S at the Military academy of Auxerre. Intended for the monastic state, he prefers to devote himself to sciences. He integrates the National university, where he has inter alia as professors Joseph-Louis Lagrange and Pierre-Simon Laplace, to which he succeeds the pulpit into Polytechnique in 1797.

He takes part in the Révolution, lack of little to be made guillotiner during the Terreur, saved accuracy by the fall of Robespierre. In 1798, it takes share with the Campagne of Egypt. It occupies a high post of diplomat and becomes secretary of the Institut of Egypt. On its return in France in 1801, it is named by Napoleon prefect of the Isere, station which it preserves until the Restauration.

In 1817, it is elected member of the Academy of Science, of which he is perpetual secretary for the section of mathematical sciences with died of Jean-Baptiste Joseph Delambre in 1822. In 1826, it is elected member of the French Academy.

Fourier known for his analytical Théorie of heat , is appeared in 1822. One owes him also several memories as well as Rapports on the mathematical advances in knowledge , published in 1822 - 1829, and of the Éloges of Jean-Baptiste Joseph Delambre, William Herschel and Abraham Breguet.

Work

It is with Grenoble that it leads its experiments on the propagation of the heat which will allow him to model the evolution of the Température through trigonometrical series. This work, which makes a great improvement to the mathematical modeling of phenomena, contributed to the bases of the Thermodynamique. They opened the way with the theory of the Fourier series and the transformed of Fourier. However, excessive simplification that these tools propose will be very disputed, in particular by Pierre-Simon Laplace and Joseph-Louis Lagrange.

Fourier is probably one of the first to have proposed, in 1824, a theory according to which the Gaz of the terrestrial atmosphere increase the temperature on its surface - it is a first outline of the Greenhouse effect. Its work on heat pushed it to study energy balances on planets: they receive energy in the form of radiation starting from a certain number of sources - what increases their temperature - but also lose some by infra-red radiation (what it called “obscure heat”) more especially as the temperature is high - what tends to decrease the latter. A balance is thus reached, and the atmosphere supports the higher temperatures by limiting the losses of heat. It could not however determine with precision this balance, since the Loi of Stefan-Boltzmann, who gives the power of the radiation of the black body, will be established only fifty years later.

It was based on the experiment of Mr. de Saussure, consisting in placing a block box under the sunlight. When one places a glass plate above the box, the temperature inside increases. The infra-red radiation was discovered by William Herschel twenty years afterwards.

If Fourier had noticed that the independent source of energy of the Earth was solar radiation - i.e. geothermal energy does not have that little influence - it made the error to allot a major contribution to radiation resulting from interplanetary space.

Homages

• It belongs to the erudite soixante-douze whose name is registered on the Eiffel Tower.

• Its praise was pronounced by François Arago, of the Academy of Science, and by Victor Cousin, of the French Academy.
• the university of Grenoble {{I}} bears its name.