The Chappe Optical Telegraph

Joshua Foer is a guest blogger on Boing Boing. Joshua is a freelance science journalist and the co-founder of the Atlas Obscura: A Compendium of the World's Wonders, Curiosities, and Esoterica, with Dylan Thuras.


Before the telegraph, there was the optical telegraph, a chain of towers topped by large pivoting cross members, and spaced as far apart as the eye could see. Developed by the Frenchman Claude Chappe at the end of the 18th century, optical telegraph lines once stretched from Paris out to Dunkirk and Strasbourg, and were in service for more than half a century:

Chappe created a language of 9,999 words, each represented by a different position of the swinging arms. When operated by well-trained optical telegraphers, the system was extraordinarily quick. Messages could be transmitted up to 150 miles in two minutes.

Several optical telegraph relay stations are still around, including one in Saverne, France that was renovated in 1998.


  1. a vast improvement over the old system wherein a flagman was lashed to each end of the rotating yard.

  2. interesting they realized the angle was the best thing for visibility, it reminds me of an eyechart I saw used in Japan for school children. Just vertical, horizontal and diagonal lines (both ways at 45 degrees) The child held up a finger and used it to indicate which way the line pointed at sloped.

  3. And here I was came with a serious comment, to find myself completely undone by Takuan’s dry wit.

    Oh well, here goes anyway:

    Are you sure about that 9,999 words figure? This article sounds more realistic:
    “This regulator, as it was known, had a 1.8 metre indicator at each end and had four basic positions – horizontal, vertical or at 45-degree angles.

    When not in operation the indicators were left as horizontal extensions of the regulator and these would then be moved in seven combinations of angles at 45-degree tilts.

    All up the Chappe semaphore tower had 196 combinations known as signs and would be worked by a series of pulleys and levers. ”

    Of course if it really was 9,999 words out of 196 signs, does anyone have more info on the coding scheme?

  4. And Takuan returns with a serious comment before I even get mine in. lol.


    “At the same time as Chappe, the Swedish inventor Abraham Niclas Edelcrantz experimented with the optical telegraph in Sweden.”

    “Edelcrantz eventually developed his own system which was quite different from its French counterpart and nearly twice as fast. The system was based on ten collapsible iron shutters.”

    And in the UK:

    “Lord George Murray, stimulated by reports of the Chappe semaphore, proposed a system of visual telegraphy to the British Admiralty. He employed large wooden boards on his towers with six large holes which could be closed by shutters.”

    I’m reasonably certain that presence or absence of an object is easier to perceive than angle.

  5. from the referred wiki:

    The Chappe brothers determined by experiment that it was easier to see the angle of a rod than to see the presence or absence of a panel. Their semaphore was composed of black movable wooden arms, the position of which indicated alphabetic letters. With counterweights (named forks) on the arms, the Chappe system was controlled by only two handles and was mechanically simple and reasonably rugged. Each of the two 2m-long arms showed seven positions, and the 4.6m-long cross bar connecting the two arms had four different angles, for a total of 196 symbols (7x7x4). Night operation with lamps on the arms was unsuccessful.

    To speed up transmission and to provide some semblance of security a code book was developed for use with semaphore lines. The Chappes’ corporation used a code that took 92 of the basic symbols two at a time to yield 8,464 coded words and phrases.

  6. “The pay is twenty five sous per day and he [the signalman] is obliged to be there from day light till dark, at present from half past three till half past eight; there are only two of them and for every minute a signal is left without being answered they pay five sous: this is a part of the branch which communicates with Strasburg and a message arrives there from Paris in six minutes it is here in four.”

    This must have been the most boring job in history

  7. There was also one in UK – went from Holyhead to Liverpool. Was featured on BBC’s “Coast” programme a few weeks ago. The presenter conducted some very unscientific “experiment” comparing time taken for an optical message, and an SMS message, to be sent and received between two points. No – I can’t recall result. Someone else may read this who has seen it. For more details go to BBC website page about that episode and scroll down …

  8. Lol – I’m in too much of a rush. Anyway, there was a study that was done in the 80s by some statistician, where they measured different ways of displaying quantity. (I think it was published in the American Journal of Statistics, but I can’t find the reference now).

    IIRC, they found that length was best, followed by area, followed by things like shade, angle, etc (can’t recall their order).

    But that is quantities, which is why I leaped to the wrong conclusion: Distinguishing between only 3 different angles is quite a different thing from trying to decipher a pie chart.

  9. Oh yeah … they simply transmitted numbers and there was a code book for translating numbers back to messages – various numbers representing words or even whole phrases. Mostly used for standard messages (ships being sighted on way to port of Liverpool etc, pus weather reports perhaps?)

  10. @6: I’m curious as to how fines could be administered. First off, how would you know that a message was late? Secondly, how could you determine which station was the one which had delayed the message?

  11. @3: The coding scheme was likely based off whatever country’s naval signaling scheme used. In fact you could argue that the navy had been doing this for far longer on the water. Words were coded in specific groupings of three flags (“letters”), and individual letters just used the single flags Google “england expects that every man will do his duty” – all the words except duty are in the code book so only duty is spelled out. In fact yacht racing uses these flags to this day, although only about 6 of the flags are used on a regular basis any more.
    In fact this article does a good job of walking you through how someone might encode a message, based on brevity, compactness and information density. With pictures!

    @10: It’s pretty simple to know if a message was late. Transmitting “DOG” from 1 to 2 to 3, station 1 sends “D” and leaves it up until stn.2 puts up a “D” as well. 3 sees the D and so on down the line. As soon as 1 sees the D at 2, stn.1 throws up the “O”. The lag between D and O would be the fine.

  12. Another SF deployment of these kind of land semaphores: Keith Roberts’ alternative-history Pavane, esp “The Signaller”.

    From the review at :

    “”The Signaller” develops one of the most enduring images of the book: a network of semaphore stations spans the country, allowing rapid communication. The network is controlled by the secretive Guild of Signallers, an organisation whose work supports the empire that stretches from Rome. Rome is suspicious of the Signallers, but reliant upon them. As a result, they have more freedom than any other group within this society. “The Signaller” tells the story of Rafe Bigland, from his childhood fascination with the semaphore stations, through his gruelling apprenticeship with the Signallers, and to a final test for him that reveals a mysterious, older facet of England that the Church has not yet been able to vanquish.”

  13. “Pavane” – a wonderful book! My own favourite use of Semaphore as a plot device is in the Count Of Monte Cristo.

  14. Although this was common, there actually was a true optical telegraph that operated between the deployment of telegraphy and the invention of the telephone.

    Although I’m too lazy to go find it, there was a line-of-site optical beam telegraph that transmitted morse code by using light signals which were detected and translated electrically into morse code pulses.

    The light pulses were amplified and used to modulate a carrier current.

    This “optical telegraph” still required humans to read the signals, so it’s really just fancy semaphores.

  15. This is so cool. This is the type of stuff I love finding out about on the ole internet device.

  16. Sean Mcmullen’s “Eyes of the Calculor” also has such a system figuring prominently. An excellent sci fi book although a bit heavy handed at times.

  17. “…transmitted morse code by using light signals which were detected and translated electrically into morse code pulses.

    The light pulses were amplified and used to modulate a carrier current.”

    Pardon me if this comes off as pedantic, but I’m pretty certain detection, amplification, and modulation were all invented after the telephone, so I am sure these things would not have been employed in an optical light telegraph invented in the time period 1837 – 1877 between the invention of the telegraph and the telephone.

  18. @21 I thought I remembered this or something like this from one of Dumas’ books. Thanks for reminding me which one.

  19. @14: That only works if a signaler falls asleep partially through a message. How do you detect that station 2 took ten minutes to even start sending a message if they’re prompt once they begin? The people at the receiving end (presumably the ones administering the fines) will receive the D,O and G in rapid succession and everything will appear fine to them.

    Furthermore, even if you could determine that a message was delayed, how do you determine which station is at fault? (Given that each signaler has a strong incentive to blame someone else.)

  20. Our eyes and brain are very good at noticing line angles. Detecting lines/edges and their directions are built in to some of the earlier stages of vision processing. It’s fundamental to later assembling shapes in the brain but conscious perception of distinctions between the angles of different lines also occurs pretty fast as well.

  21. so if we evolved to take the simplest tool ( a pointy thing) and make a mark with the simplest muscle contraction (a line), what kind of basic biology would an organism have to have to base everything on circles?

  22. #37TAKUAN according to Charles Fort you draw a circle starting anywhere so contract and then spin

  23. Poor old AtlasObscura… every time Boing Boing finds something interesting there, the whole site goes down. I’m going to wait till all you guys have gone to sleep, and check it out.

  24. Epic? You have no idea.

    King Squid to Mobby:
    “Go! Go and bring my message to Ahab. That is the only way our Worlds can meet and cooperate for the salvation of this planet.”

    “Oooohh shit!”

  25. I was just going to recommend the Victorian Internet by Tom Standage, but someone beat me to it. Anyhow there’s a whole bunch on the old French optical telegraph. It’s fascinating.

  26. I used to talk about the system in the introduction to my lectures on telecommunications systems.

    BTW, There was a line of Chappe telegraph between Moscow and then occupied Warsaw. With more than 1200 km it had about 200 stations and about 1,3 k-man to operate :-)
    So Tsars also invested in it !

    The history of the remote communication is fascinating. The revolution the electric telegraph made a bit later, was more dramatic than initial web revolution of early 90s….

  27. My colleague Alex Field at Santa Clara university has written on this subject; see:

    French Optical Telegraphy, 1793-1855: Hardware, Software, Administration
    Alexander J. Field
    Santa Clara University – Leavey School of Business – Economics Department

    Technology and Culture, Vol. 35, pp. 315-347, April 1994

    French optical telegraph represented a highly refined blend of software and hardware generating performance levels in long distance communication which were, given the limitations of the hardware, quite remarkable. Had the electromagnetic telegraph not become available, French optical telegraphy, or a variant, would have served increasingly as an imperfect substitute, particularly in the transmission of price data on commodity, stock, and bond exchanges. This affirmation of the commercial viability of optical telegraphy does not, however, significantly reduce our estimate of the contribution of electromagnetic telegraphy to economic growth. The more substantial economic payoff to the electromagnetic device came from its use by firms to reduce inventory holdings and raise fixed capital utilization rates in sectors with large minimum efficient scales. Here optical telegraphy’s vulnerability to disruption by the weather, limited channel capacity, and restriction to daylight use would have made it a very imperfect substitute in an age of rail speed communication.

  28. I think you meant Dunkerque, and not “Dunkirk”.

    I live near one of these remaining towers, wich has been restored by the legion, near the toswn of Catelnaudary, because it is a military relic.

    For those who say those towers are restricted to daylight use only, it’s false, they can light up at night, with a gas torch on each branch.

  29. Telecustard:

    Dang, you called me on my poor memory. Now I’ll have to look it up, but I know it was quite obscure.

    As for modulation, I’d point out that the telegraph itself was modulated, though by hand. This line-of-site optical beam telegraph I remember reading about in my optoelectronics textbooks years ago was the same: Basically, a human hand caused a light to flash in morse-code fashion (I can’t remember if it was a lightbulb or candles behind a shutter). The “receiver” through some clever mechanism I can’t remember initiated a nonzero current to translate the light flashes back into morse code on a line.

    No “modulation” in the modern sense, though.

    Perhaps it never caught on because it only existed right as telephones were coming into common occurrence. It’s application was also quite “niche” in that where a wire was available that would be preferable due to atmospheric conditions, etc…(ie, no LIDAR yet!).

  30. For Kittler’s lucid analysis of the telegraph English language readers are going to have to wait a little on the transaltion of his lecture “Optische Medien”.

    A must read! (Though hardly nicely translateable, for his ironic post-heidegger style of word play and play with different registers of language, as his mimicry of German public official’s style ((Deutscher Beamter)) which he is, of course, as most of Germany’s Professors.

  31. For anyone interested in the code used by the Chappe system, there’s quite a bit of information here– it’s in French, but there are lots of tables and illustrations, so you should be able to get some idea of how it worked:

    One of the remaining Chappe towers is quite near where I live, so I wandered by and took a few photos this afternoon (I’d been meaning to do so for a while anyway; thanks, BB). I stuck ’em up on my blog– not great pictures but a better look at the mechanism, anyway:

  32. I recently came across a set of signal towers thought to be used by the ancestral Puebloans to send low-bandwidth optical signals from sites in Colorado to the southern reaches of their empire in central New Mexico. I visited an outpost known as Chimney Rock in Southern Colorado but haven’t been to the central site yet.

    “As the spiritual and/or socio-economic center of a large geographic area, Chaco Canyon had need of more than roads to connect it with important outlier great houses. In fact, Alden Hayes and Tom Windes discovered an extensive line of sight communications network, using, perhaps, smoke or mirrors to signal. For example, at one point of Chimney Rock Pueblo in southern Colorado, there is a direct line of sight to Huerfano Mountain south of the San Juan River. From Huérfano Mountain, on which many archaic fire boxes and shrine sites have been found, there is line of sight to Pueblo Alto.”


Comments are closed.