Undated Map of Optical Telegraph Stations in France
Courtesy of Low-Tech Magazine via Ecole Centrale de Lyon

E-mail in the 18th Century

Centuries of slow long-distance communications came to an end with the arrival of the telegraph. Most history books start this chapter with the appearance of the electrical telegraph, midway the nineteenth century. However, they skip an important intermediate step. Fifty years earlier (in 1791) the Frenchman Claude Chappe developed the optical telegraph. Thanks to this technology, messages could be transferred very quickly over long distances, without the need for postmen, horses, wires or electricity.

The optical telegraph network consisted of a chain of towers, each placed 5 to 20 kilometres apart from each other. On each of these towers a wooden semaphore and two telescopes were mounted (the telescope was invented in 1600). The semaphore had two signalling arms which each could be placed in seven positions. The wooden post itself could also be turned in 4 positions, so that 196 different positions were possible. Every one of these arrangements corresponded with a code for a letter, a number, a word or (a part of) a sentence.

The other day I found this tremendously enlightening article about optical telegraphs on Low-Tech Magazine. Prior to reading this article I had no idea about this arcane method of communication. The authors supplied a map (above) to really drive home how extensive this system was.

Something that I think few people do when surfing through Wikipedia is to check the articles in other languages. It’s really easy to do and the results tend to be very useful. For words that have equivalent spellings, all one has to do is change the URL’s prefix (fr to en). For words that have different spellings (telegraph vs télégraph) you will have to correct this spelling in order for the entry to show up.

For example, the French entry on telegraphe yields quite a bit more information related to the use of semaphores (the object used to construct the optical telegraphic code) than the English entry on telegraphs.

Below is a carte of the semaphoric number system and an engraving of Mont St. Michel with a semaphore at the top. Both images obtained from the French wikipedia.