A heliograph is a mirror mounted on a tripod for solar signaling, usually using Morse code sent either with a tilting mechanism or a shutter (as on an Aldis lamp). They were used, in some form or other, in military campaigning from ancient times up until the advent of wireless. In the history of our nation, they were particularly useful in the Army campaigns against the Apache.
So, what do you think is the distance record for signal received by heliograph? Make your guess. (Answer after the jump.)