France’s 100-year sealed science letters

For almost 300 years, inventors and researchers have been entrusting their secrets to one of France’s most prestigious scientific institutions.

The Académie des Sciences began receiving plis cachetés – sealed letters – in 1735. Each envelope contained a description of a discovery, experiment, invention or hypothesis.

Depositing one established the date of the work and could later support a claim that its author had thought of the idea first. It was not a patent and conferred no commercial rights. Instead, it acted as a scientific time stamp, protected by a seal and the Académie’s authority.

“It was a way of attesting to the priority of a discovery, an invention, or sometimes even just a hypothesis,” says Marc Kefer, an archivist at the Académie, to The Connexion.

Authors could request that their letter be opened or withdrawn. Today, heirs may also request an opening.

Otherwise, the Académie generally waits 100 years.

More than 18,700 letters have been deposited. They are stored in the archives at the Institut de France on Paris’s Quai de Conti, where Kefer prepares batches for examination by the Comité des plis cachetés.

Meetings are held as required rather than to a fixed timetable. Kefer opens the envelopes beforehand, taking care not to damage the documents, then sorts them by subject so specialists can assess them.

“You never know what you are going to come across,” he said. “It can be completely ordinary, or something very unusual.”

The contents range from serious industrial processes, mathematical arguments and technological designs through to impossible machines and eccentric theories.

Among the best-known examples are three sealed letters that were from Antoine Lavoisier.

One concerned coloured fireworks; two others set out hypotheses he feared might emerge during discussions with colleagues before he could verify them.

Two letters deposited in 1857 by Édouard-Léon Scott de Martinville described a system for recording sound graphically. Related material included an 1860 recording of Au clair de la lune, later reconstructed by researchers.

Letters from the 1920s include plans for a portable telephone, television systems and unusual aircraft.

Others reflect the post-World War One fascination with weapons and military machines.

The collection brings together established science, abandoned ideas and highly speculative theories.

“What makes it remarkable is that you find very famous names, such as Lavoisier, Buffon and Pasteur, alongside a multitude of little-known scientists – and sometimes people who were not scientists at all,” Kefer says.

“It is extremely eclectic, both in its contents and its quality.”

Yet the moment of opening still carries weight.

“It always makes one think: I am opening a letter that was closed a century ago,” he says. “I am the first to open it. There is always a little pang.”