Who was the French professor that the Robert brothers built the world's first hydrogen balloon for?
Jacques Charles Jacques Alexandre César Charles (November 12, 1746 – April 7, 1823) was a French inventor, scientist, mathematician, and balloonist.
Henry Marcel Henri-Camille Marcel called Henry Marcel, (25 November 1854 – 6 March 1926) was a 19th–20th-century French senior official, general administrator of the Bibliothèque nationale de France from 1905 to 1913.