Jean-Paul MARAT (1743-1793) revolutionary orator and pamphleteer. L.A.S., "Rue du Vieux Colombier" January 25, 1788, to Abbé Rochon; 1 1/2 pages in-4 (slight foxing). Very rare letter as a physicist. Marat has just published his Mémoires académiques, ou nouvelles découvertes sur la lumière. [Abbé Alexis de Rochon (1741-1817), astronomer and physicist, was guard of the Cabinet de physique et d'optique du Roi and member of the Institut]. He was not unaware that Rochon was "the first one who attacked, with knowledge of the cause, the doctrine of the different refrangibility", and Marat was able to work on facts allowing to overthrow this doctrine, "and although we still differ in principles, the love of the truth unites us". He sends his work to him "as a mark of esteem", and engages him to examine it: "noted the little known facts which it contains, weighed the new proofs which are developed there; and if it deserves your sufrage, deign to concur in the triumph of the truth; with the generous zeal of a true scrutinizer of the nature"...