Optical Telegraphy

The Chappe Telegraph Systems

Claude Chappe d'Auteroche (1763-1805)


Les Télégraphes Chappe (in french)
Napoleon's Secret Weapon
The Early History of Data Networks
Chappe Code (local copy)

Synchronous Telegraph Experiments (1790-1791)

"... The brothers Chappe spent the winter of 1790-1791 experimenting with telegraph designs. In March 1791, they were ready for a first public demonstration of the telegraph they had constructed. The telegraph design used in this first experiment was described by the Chappes as a "pendulum system."  It is usually referred to as the Synchronized

"For the first experiments, two telegraphs were used, possibly merely two modified pendulum clocks. One was placed on a terrace at the former location of a castle in Chappe's hometown Brûlon, and the other at the window of a private house in Parcé, a little town at a distance of roughly 16 km (10 miles), and about halfway between Brûlon and La Flèche. ....

"Unfortunately, we do not have an accurate description of the working of the pendulums that were used in the first experiment, and the information we have leaves many questions unanswered. The most reliable record that has survived is a description given by Ignace Chappe, which reads as follows.
The first telegraphic correspondence that we performed was done with two pendulum clocks, that were kept in perfect synchrony; the face of the clocks was divided into ten parts, each part designating a different numeral [French: un chiffre de la numération ordinaire]. When the pointer of one clock passed over the number one wanted to indicate, a sound was made, announcing to the correspondent that the number which also his pointer indicated at the moment that the sound was heard, was significant.  By representing the words in a dictionary with successive numbers one could thus transmit any thought. ..."
 Dubious Representation of the Synchronized System

Panel Telegraph Experiments (1792)

"... Not satisfied with the use of the pendulum system, Chappe had started experimenting with a different design. He built a rectangular wooden frame with five sliding panels (in French persiennes) that could be displayed or obscured individually with pulleys. The five panels trivially produced a five-bit binary code, with 25 or 32 possible combinations, more than three times as many codes as used in the first design...."  (Source)
A relay station on Abraham Edelcrantz's panel or shutter telegraph system. 

Semaphore Telegraph System (1793...)

"... Around this time Claude Chappe concluded that the panel telegraph had been a false start, and he changed designs once more. As Ignace noted:
Some time later [we] established with certainty that elongated objects were better visible than the sliding panels adopted before.
"The semaphore telegraph that Chappe designed next consisted of a large horizontal beam, called a regulator, with two smaller wings, called indicators, mounted at the ends, seemingly mimicking a person with wide-outstretched arms, holding a signal flag in each hand. The angles of the indicators, andindependently also the position of the large regulator beam, could be varied in increments of 45 degrees, sufficient for the encoding of hundreds of symbols, ..." (Source)

Map of semaphore telegraph lines established between 1793 and 1852.  After the Paris-Lille, other lines gradually were built  radiating in a star pattern from Paris.  It is, in fact, the first telecommunication network in Europe! (Source)

Semaphore in the United States: Staten Island Station

This page was prepared and is maintained by R. Victor Jones
Comments to: jones@deas.harvard.edu.

Last updated September 21, 1999