To meet the need for swift communication between Napoleon's (1769-1821) far-flung armies in the 1790s, the Frenchman Claude Chappe (1763-1805) invented an optical-relay system of visual telegraphs that he called the semaphore. His system consisted of tall vertical posts, each of which supported a movable crossbar with movable arms at each end. Using a system of pulleys and ropes, the semaphore operator would move the crossbeam and its indicator arms into a variety of positions that represented numbers and the different letters of the alphabet. Chappe installed his signalling mechanisms on hilltop towers which allowed an unobstructed view. While such a system would have been possible many centuries earlier, Chappe's made use of both a signalling code and the recently invented telescope to read signals across distances much greater than would previously have been possible.

Giving the name telegraph to his signalling system, Chappe secured a commission from...