Chappe Optical Telegraph Tower, Ste-Foy
I didn't have my camera with me that day, so I made a mental note to come back and take a few pictures the next time I was in the area. This weekend I read a post on BoingBoing about the Chappe Optical Telegraph system, and that provided the impetus to actually go and do it.
The tower is only open to the public on the afternoon of the first Sunday of the month, but there's a small schematic on the plaque that provides some idea of the working of the control apparatus [photo].
Here's what the rest of the plaque says (translation errors mine):
"Chappe Telegraph: Paris-Lyon-Toulon Line
Put into service in 1793, Claude Chappe's telegraph was for 50 years the means of the most rapid transmission of government messages (Paris to Lyon in less than 30 minutes in good conditions). The signals of a secret code were transmitted from one station to another by means of vast mobile arms visible with a spyglass at more than 10km. 535 stations were distributed across the entirety of France.
The well-preserved St-Foy-les-Lyon tower is one of the rare witnesses of this part of the history of communications. The mast and its mechanism [photo: mast with arms stowed] were reconstructed in 1994 by the Centre de Lyon du Conservatoire National des Arts et Metiers (CNAM) for the bicentennial of the CNAM and the telegraph."
It appears from the plaque that though the network dates to 1793, this particular tower wasn't built until 1821-- though it would have been there in plenty of time to send the news to Paris of the Canut (silkworker) uprisings a decade later.
I imagine that at the time, the trees in the small park below the tower, and the one immediately behind it, would have been considerably smaller, allowing better sightlines, but you can imagine the kind of vantage point one would have had here at the time, even from such a relatively small tower [last photo].
There's quite a bit more information en francais at this site, including a lengthy explanation of how the code worked (lots of pictures even if you don't parlez) and other remaining signal towers in the area.