The mathematician Fourier (who had beens Napoleon’s Governor in Upper Egypt) set Champollion on the road to the decypherment of hieroglyphs. Champollion met Fourier aged 11, became his protégé, and when shown hieroglyphs by him, decided what his life’s work was to be. Young and he were in correspondence when he started working on the Rosetta Stone; while they feuded over Young’s relative achievement (unsurprisingly, given English/French rivalry of the time), Champollion did later invite Young to research in the Louvre. Humboldt, also a philologist, maintained a lively learned correspondence with Champollion.
The polymath Young corresponded with Arago and Fresnel about scientific matters in general and the wave theory of light in particular. Arago visited Young in 1816 to tell him of experiments in polarisation he and Fresnel had conducted. Malus and Banks were among his scientific correspondents. Watt, Wilkinson and Young were members of a panel convened to select the design for a new London Bridge. Cavendish and Wollaston were among his friends.