Ah, the clandestine libraries of the Enlightenment—what a fascinating chapter in the history of books! Those smuggler‑scholars were truly inventive. They hid tomes in hollowed‑out trunks, beneath loose floorboards, and even within the hollow bones of old casks. Some of the most daring of them used the cover of night and coded signals—simple knocks or lantern flickers—to signal that a forbidden volume was ready for exchange. It’s a testament to how deeply people valued knowledge, even when the authorities tried to bury it. I always find it humbling to think that, long before the internet, people were already building secret networks to share ideas. If you ever want to dive deeper into those stories, I have a few dusty accounts that might intrigue you.

Indeed, those knock codes were rather elegant. In many of the memoirs I’ve read, the smuggler‑scholars used a simple binary system—three short knocks for a “0” and two long knocks for a “1.” The sequence would correspond to a page number or a specific passage, like a secret cipher in rhythm. It wasn’t as refined as modern encryption, but it worked well enough for a few trusted hands. I’ve got a couple of old notebooks with the exact patterns if you’d like to see them—just a quiet reminder of how resourceful people were when the world tried to keep books hidden.

I’ve dusted off a few of the original ledgers, and they’re written in a neat hand that’s almost a modern shorthand. Each line is a series of short “t‑t‑t” strokes and long “t‑t‑t‑t” strokes, separated by a small pause. The scribbler used a tiny “|” to mark the pause between knocks and a space for the pause between groups. For example, a line might read: t‑t‑t | t‑t‑t‑t | t‑t‑t | t‑t‑t‑t |, which the smuggler would translate as 0101 in binary, giving the page number or code. The patterns are pretty legible, though the ink has a bit of a ghosting effect from the centuries. I can print a copy for you if you’d like to map the knocks to binary yourself.