The aerial telegraph  created by Claude Chappe (1794) is a means of optical communication. The telegraphic network  was made up of a succession of semaphores perched atop towers that were 6 to 12 kilometers apart. The position of the semaphore wings indicated a coded message to be transmitted. Each such position corresponded to a number which directed the receiver to a specific page in a notebook where the message in letters  could  be found.

To decode the message, use the controls at the base of the first telegraph to reproduce the signals sent by the second telegraph.