One beam, two arms, ninety-eight figures.
Atop each tower stands a regulator — a 4.6-metre timber beam — carrying a 2-metre indicator at either end. For signalling, the regulator takes two working attitudes, vertical or horizontal, while each indicator locks into any of seven angles, forty-five degrees apart; the eighth, folded flat along the beam, vanishes at distance and is excluded. Two attitudes, seven by seven arm angles: ninety-eight distinct figures, of which Chappe's operators kept ninety-two. The oblique attitudes of the regulator were reserved for service signs — start, wait, error, close.
The whole apparatus is counterweighted so finely that a single operator, working cranks in the room below, throws four metres of timber in a couple of seconds. Watch any arm arrive: it overshoots a few degrees and settles back. The counterweights that make it light enough for one pair of hands are the same reason it lands like a pendulum, not a latch. A fixed telescope, trained on the next tower up the line, does the rest.
Ninety-two figures pointed into a codebook. These twenty-six are ours.
Chappe's operators never spelled. Signals travelled in pairs — a page number, then a line — indexing a secret vocabulary of 92 × 92 = 8,464 entries, so the towers could carry words their own operators could not read.
The alphabet below is therefore a reconstruction for the eye, built strictly from the machine's legal geometry: regulator vertical for A–M, horizontal for N–Z, indicators stepped through their seven lawful angles in order. Choose a letter; the practice frame throws it, and every tower on the ridge throws it the same way.
Lille to Paris, fifteen stations, inside the hour.
On 30 August 1794 the new line carried its first dispatch of consequence: Condé-sur-l'Escaut, taken back from the Austrian garrison, announced to the National Convention within the hour — across roughly 230 kilometres that a mounted courier needed a full day to cover. The deputies rose and cheered.
Before nightfall the same towers carried the answer back up the line: the recaptured town would bear a new name, Nord-Libre. For the first time a state could speak across itself faster than rumour. The panorama above frames eight of the line's towers; the real chain ran fifteen stations, each one a telescope, a crank room, and two arms against the sky.