Rapid Messaging Possible In The 18th Century?
Before the electrical telegraph was invented, there was the optical telegraph. Optical telegraph were the “smoke signals” of their day, making it possible to communicate messages over a long distance.
According to an article on optical telegraphs,optical telegraph networks existed all over Europe and North America until the electrical telegraph was invented. They were able to use two semaphores–those dangly arms–to signal a particular character. 196 such symbols were possible and they could be signaled at 1-3 symbols per minute at a distance of 5-20 kilometers per minute.
Given the technology of the day, it was pretty high-tech. However, it had numerous issues. The first, most obvious one is the whole line of sight thing. You had to have a line of sight between each tower in the telegraph network. This means messages could only be sent during daylight hours when there was no obstructions between the nodes on the telegraph network.
Second of all, not only can the intended target see the symbol, anyone else nearby with a telescope could see the message, too. If they could see the communication and figure out how to decipher it, they would know what the message was.
Finally, the network was prone to human error. Each tower required a human to read the symbol, transcribe it, and send it along to someone else. What is to prevent someone from compromising one of the tower operators and causing them to send a different message? Can you say “man in the middle” attacks?
Of course, the electronic telegraph eliminated the first two issues: no line-of-sight issues and no easy way to intercept messages. Human error was the still an issue with electronic telegraphs. Still an issue with email, and every other communication method, too. 
Via Slashdot
