nd the development of the visual telegraph by Claude Chappe in 1794 in France. Chappe's telegraph was a relatively complex system and was based on mechanical and optical technologies, result- ing in much faster rates of message transmissions compared with traditional means. Development of telescopes in the 17th century extended human visual reach and made it possible to view very distant objects. Visual telegraphy could then transmit messages over distances of many kilometres. Chappe's invention was a semaphore system with mechani- cally movable arms constructed over a mast (called a regulator) and used special codes to represent letters and numbers to convey information to a remote station. The arms and regulator had a length of 2 and 4.5 m, respectively, as shown in Figure 2.1, with the whole device constructed on the top of tall buildings such as towers or churches. The angle of arms with respect to each other and to the regulator was the code which represented a letter of the alphabet or a number as shown in Figure 2.2. Chappe named the system télégraphe, a combination of two Greek words meaning 'distance' and 'writer'. To distinguish it from the better known electrical telegraph, Chappe's system is usually referred to as a visual telegraph. The maximum distance between transmitter and receiver was a function of visual range of the telescopes as well as the local topography. For example, the distance between the stations on the first line which connected Lille (a city in the north-east of France) and Paris varied bet- ween 4 km and 15 km. In total 23 relay stations were used to cover the distance of 200 km. A message was relayed from station to station until it reached its final destination. The semaphore's movable arms were large and a telegraph operator could only change the angles once approximately every 2 min. From this, the transmission speed can be calculated to be Figure 2.1 A Chappe telegraph transmitter on top of a cathedral [1, 2]. Source: Chappe telegraph. Illustration published in Les Merveilles 