Joseph Lepaute Dagelet, astronomer and mathematician, was born on 25 November 1751 in Thonne-la-Long in northern Meuse, near the Belgian border. He was the son of Pierre Lepaute, a blacksmith, and Martine Demouzon. He was the nephew of the famous watchmakers who supplied sovereigns (from Louis XV to Napoleon III). At the age of 16, Joseph Lepaute left his native village and was called to Paris by his uncle Jean-André Lepaute and his aunt Reine Etable de la Brière Lepaute. They entrusted his education to Jérôme de LaLand, who ran the observatory at Mazarin College.
The young astronomy student quickly established himself as a brilliant pupil, with a keen sense of observation and scientific reasoning. In 1773, aged just 22, he was chosen to take part in Tremarec’s Kerguelen expedition to the Southern Lands. In recognition of his excellent work, he was appointed professor of mathematics and astronomy at the Royal Military School in Paris. In fact, he became the teacher of a certain Napoleon Bonaparte! In 1780, he presented his observations of the planets and stars to the Académie des Sciences. He was now the leading specialist in small stars. Three years later, he published his memoirs on the aphelion of Venus (the point in its orbit furthest from the Sun), and took an interest in eclipses of the Sun and the passage of comet Halley. Elected to the Académie in 1785, he became the youngest academician in France.
Dagelet was chosen from among the elite of French scientists to take part in Lapérouse’s expedition. He embarked on the frigate La Boussole, alongside Lapérouse, becoming one of his favourite collaborators. During this long and difficult voyage, he made numerous astronomical observations, the results of which are mentioned in his correspondence, but which perished with him and his companions on the island of Vanikoro in the Pacific, around May 1788.
A bachelor, he refused to marry his cousin Henriette Lapaute shortly before boarding his ship. And yet… There are now more than 3,875 individuals listed. The Nivromont, Choltus and Rollin families are the genealogically and genetically closest to Joseph Lepaute Dagelet, who is on the list of those presumed to be the “Vanikoro unknown”, due to the numerous astronomical instruments found around the skeleton discovered twenty years ago.
In Thonne-la-Long, a stele commemorates the Lepaute family, in particular Joseph Lepaute, whose birthplace can still be seen. The last bearer of the name is Nicolas Henry Lepaute, a company executive in Nice.