Michèle Audin, writing for Oulipo, tells the history of les plis cachetés:
[THIS IS A MACHINE TRANSLATION:] “Let me begin by reminding you (or tell you) the ancient practice (and a tad outdated) sealed envelopes. Suppose you make a discovery you deem worthy of interest. You want while you posterity attributed maternity (or paternity, if you are a man) of the thing. But for one reason or another, you do not want to publish it. You will then go to the Academy of Sciences and you drop a fold (ie a letter, a piece of paper), which shall seal (with wax, yes) under your eyes (it is this operation that transforms the fold ‘sealed envelope’), which is assigned a serial number and is preserved.You have certainly noticed that, during this series of operations, one has knowledge of the content of your fold.
Even if it seems a bit absurd way of doing science, this practice has been used once or another, by serious scientists…. Well, and that happens next? Well, the sealed envelope can be opened as soon as the author on request. Otherwise, it must be open after a hundred years….”
The tradition arose with, and is carried on by, l’Académie des sciences.