The mathematician who decoded heat also first imagined the greenhouse effect
Joseph Fourier was an orphaned tailor's son who survived the Terror, sailed with Napoleon to Egypt and governed a French province. In his spare hours he studied how heat spreads, and ended up inventing a way to break any wave into simple sines, plus the first idea of what we now call the greenhouse effect.
Born in Auxerre, Burgundy, on 21 March 1768, Fourier lost both parents by the age of nine. The bishop's patronage got him an education with Benedictine monks, but army science posts were reserved for the well-born, so he took a job lecturing on mathematics instead. He threw himself into revolutionary politics in his district, was jailed briefly during the Terror, and in 1795 joined the new École Normale, later succeeding Lagrange at the École Polytechnique.
In 1798 he went with Napoleon to Egypt as a scientific adviser and secretary of the institute founded in Cairo. When the British fleet cut the army off, he organised the workshops that supplied its munitions. After the French surrendered in 1801 he came home, only for Napoleon to make him prefect of Isère, based in Grenoble, where he oversaw road building and helped assemble the vast Description de l'Égypte.
Grenoble is where he began experimenting on heat. His paper on heat propagation in solids reached the Paris Institute on 21 December 1807, and his Analytical Theory of Heat followed in 1822. It made three leaps. He claimed any function, even a discontinuous one, could be written as a sum of sines; that is not true without extra conditions, and Dirichlet later supplied a rigorous version, but it laid the groundwork for the Fourier transform. He insisted equations must balance their physical dimensions. And he wrote down the heat equation, now taught to every student of mathematical physics.
In the 1820s he calculated that sunlight alone should leave a planet like Earth much colder than it is. He wondered whether the atmosphere acts as an insulator, citing a glass-paned box built by Horace-Bénédict de Saussure, though he noted that real air also moves heat by convection. He never used the phrase greenhouse effect. He became permanent secretary of the Academy of Sciences in 1822, died in Paris on 16 May 1830 after a fall on the stairs, and lies under an Egyptian-style tomb at Père Lachaise.
Source: Joseph Fourier
