As King Louis XVI faced execution by guillotine on January 21, 1793, he reportedly inquired about the fate of Jean-François de Galaup, the count of Pérouse, a French naval officer and explorer dispatched by the king in 1785 on a scientific expedition around the world. Pérouse’s mission aimed to rival the discoveries of the British explorer Captain James Cook and to advance France’s maritime knowledge and colonial ambitions. The two ships leading the voyage, La Boussole and L’Astrolabe, vanished in 1788 after departing Botany Bay, Australia, and their wreckage was only positively identified in 2005, leaving many questions about their fate.

Recently, a collection of rare and deeply personal letters written by Jean-André Mongez, a scientist and member of the expedition who died in 1788, has come to light. These documents, described as veiled love letters addressed to Louise Victoire Le Cloustier, the married daughter of a minor noble family from Rouen, Normandy, were discovered hidden inside an unassuming 19th-century book of engravings. The letters are scheduled to be auctioned in Paris on November 17.

Ludovic Miran, an expert in books and manuscripts involved in the sale, characterized the discovery as extraordinary, noting that most surviving records from the Pérouse expedition are scientific in nature, making these personal correspondences especially rare. The letters reveal Mongez’s emotional turmoil, expressing regret over his strained relationship with Le Cloustier and hinting that this personal conflict partly motivated his decision to join the perilous voyage.

Miran explained that Mongez frequently promised to return as a changed man and reflected on his unhappy state during the journey. The letters provide insight into the crew’s hardships, including an incident at Samoa where the captain of L’Astrolabe and eleven men were killed. Mongez’s final letter, written shortly before his death, conveys a sense of despair, noting that the expedition’s challenges outweighed its scientific gains and expressing a strong desire to return home.

The La Pérouse expedition itself was launched against the backdrop of intense Anglo-French rivalry over colonial expansion. France aimed to establish new trade routes and verify intelligence that Britain intended to create a permanent presence at Botany Bay, a location the British had reached just days before the French. La Boussole and L’Astrolabe, carrying about 225 crew members, scientists, and officers, made several stopovers globally before disappearing near Vanikoro, east of the Solomon Islands, where they are believed to have been wrecked in a cyclone.

Auctioneer Benoît Derouineau, who identified the letters, noted their careful preservation and the secrecy surrounding them, suggesting that Le Cloustier may have hidden the correspondence from her husband. The discovery sheds new light on one of France’s most significant 18th-century scientific and exploratory endeavors and offers a poignant glimpse into the personal lives entwined with this historic voyage. The letters are expected to fetch between €30,000 and €50,000.