Autograph Letter Signed ‘Becquerel’, to Monsieur Boutigny [Pierre Hippolyte Boutigny, professor of chemistry], discussing his research into the action of hydro-chloric acid in the formation of sulphur of arsenic. 2 pp. 7 x 4½ inches, in good condition, with address leaf, tippped on to part of an old album page. Paris, 26 March 1833. Antoine César Becquerel (1788-1878), French scientist and a pioneer in the study of electric and luminescent phenomena. In 1825 he invented a differential galvanometer for the accurate measurement of electrical resistance. In 1829 he invented a constant-current electrochemical cell, the forerunner of the Daniell cell. In the same year, working with his son A. E. Becquerel, he discovered the photoelectric effect on an electrode immersed in a conductive liquid. In 1837 he became a Fellow of the Royal Society, and received its Copley Medal for his various memoirs on electricity, and particularly for those on the production of metallic sulphurets and sulphur by electrolysis. He was the first to prepare metallic elements from their ores by this method.