The Optical Telegraph: Semaphore Networks Before Electricity
How 18th-century semaphore towers relayed coded messages hundreds of kilometers in minutes — the first practical telecommunications network, and its brief dominance.
A century before the electric telegraph, France moved information across hundreds of kilometers in under an hour using nothing but towers, pivoting shutters, and telescopes. Claude Chappe's optical telegraph, adopted by the French state from 1794, was the first practical long-distance rapid communication network — a physical relay race of visible signals that prefigured every later network, down to its congestion and its failures.
How it worked
Stations stood on hilltops 10–15 km apart (the limit of the telescopes used to read them). Each tower had three articulated wooden arms whose positions, read through a telescope, encoded one of 92 or more symbols — digits, letters, and codes for common words. An operator read the previous tower's arm positions through a telescope, set his own arms to match, and the next tower read his. A coded message moved from Paris to Lille (about 200 km, ~15 towers) in roughly 10–20 minutes in good weather — faster than any rider, faster than news traveled anywhere in human history to that point.
The network and its limitations
By the 1840s the French network ran over 5,000 km of lines with hundreds of towers, and other countries (Sweden, England) built smaller systems. It was a government monopoly: private messages were forbidden, and the network served military and administrative traffic. The signal could not travel at night, in fog, or in heavy rain; towers were expensive; and capacity was tiny — a few symbols per minute per line.
The replacement
Samuel Morse's electric telegraph (1844) carried messages at any hour, in any weather, over wires that cost a fraction of tower chains, and the optical networks were decommissioned within a decade — a classic case of a technology rendered obsolete not by failure but by a cheaper successor. Related reading: the printing press for the earlier information-speedup, and the Internet era's reflection on latency.
Tags
communication history technology telegraph