Lepaute Dagelet, Joseph (1751–1788)

Joseph Lepaute (or Le Paute) Dagelet (or d’Agelet) was born in 1751 in Thonne-la-Long in Eastern France, near the present French-Belgian border, son of a blacksmith. He took the agnomen Dagelet from the name of a small country lane in his home village. In 1768 young Dagelet was sent up to the capital to stay with his uncle, Jean-André Lepaute, a well-known Paris clockmaker, and his wife, née Nicole Reine Étable, an associate member of the Academy of Béziers and an occasional research assistant to Jérôme Lalande, the future Director of the Paris Observatory. In Paris young Dagelet studied astronomy under Lalande who became his mentor and friend. Dagelet was like an adopted son to the childless Lepautes and Lalande.
He was soon appointed to the Observatory of the Collège Mazarin (today’s Institut de France, Quai Conti) where Lalande had practised previously, and in 1773, after five years at Mazarin, he was selected as one of two astronomers for the 1773–74 Kerguelen expedition in the Indian Ocean. Dagelet acquitted himself admirably in this controversial venture both as an astronomer and in managing difficult human relations: he was in no way responsible for the failure of the expedition.
In 1777 he was appointed Professor of Mathematics at the École militaire in Paris where Napoleon Bonaparte was one of his students. Most of Dagelet’s research was published in the Journal des savans and the Academy’s Proceedings. He also contributed to Lalande’s Connaissance des temps (1779) and his Éphémérides. He excelled in the observation of planets and stars, especially in the identification of previously uncatalogued smaller stars. After his election to the Académie Royale des Sciences in 1785, he was invited to join the Lapérouse expedition as the astronomer on the Boussole, Lapérouse’s ship. Once again he got on well with both his fellow travellers and his commander. Dagelet was Lapérouse’s favourite scientist in the team: he valued his skills as a scientist and appreciated his lack of intellectual pretension.
During the expedition’s six week stay (26 January to 10 March 1788) at Botany Bay, which coincided with the arrival of the First Fleet, initially to Botany Bay and then to Port Jackson, Dagelet set up a temporary observatory on the shores of the bay.  He was delighted to receive the visit from British astronomer Lieutenant William Dawes who at that time was setting up his own observatory at Port Jackson. Having discovered their common interest in astronomy, they exchanged information and ideas on their work, plans and future cooperation. Dagelet intended to return Dawes’ visit to inspect the site of the new observatory, but his state of health prevented him from undertaking what would have been an arduous journey, whether on foot or by sea. Dagelet sent Dawes a three-page letter instead, probably his last, containing his ideas on the development of astronomy in their time and on the most up-to-date methods to use in the setting up of the Port Jackson observatory. Fortunately this most important document has come down to us. Two days earlier he had written to Lalande telling him of his delight at the prospect of future scientific exchanges and cooperation with the Port Jackson astronomer.
This was not to be, as approximately three months later, probably in May or June 1788, both the Boussole and the Astrolabe were shipwrecked in Vanikoro, in the Solomon Islands, and Dagelet and his companions perished, together with all their papers and instruments. Rumours in the early nineteenth century British and French press of sightings of Dagelet in various parts of the Pacific seem to have no factual foundation, and astronomy lost one of its finest practitioners in his prime, at the age of 37.
Image: Joseph Lepaute Dagelet, Collection Josiane Dennaud
Author: Ivan Barko, Professor Emeritus, The University of Sydney, September 2019


Barko, Ivan, ‘Lepaute Dagelet at Botany Bay (26 January–10 March 1788)’, Explorations, no 43, 2007, pp. 21–40.
Morrison, Doug & Ivan Barko, ‘Dagelet and Dawes: Their Meeting, Their Instruments and the First Scientific Experiments on Australian Soil’, Historical Records of Australian Science, vol. 20, no 1, 2009, pp.1–40.
Barko, Ivan & Claude Parent. ‘Dagelet, astronome de Lapérouse: Vie et carrière de Joseph Lepaute Dagelet (1751–1788)’, Neptunia (Paris), no 59, 2010, pp. 21–31.
Keywords: Lepaute Dagelet, astronome de Lapérouse, Dawes, Boussole, Astrolabe