The Heliograph

The heliograph originates from the Greek word "Helios," meaning "sun." This wireless for of communication was based solely around the sun. A "solar telegraph," if you will, would send signals using flashes of sunlight reflected by a mirror. This was almost like a Morse code of the sky. The sender of the flashes would pivot a mirror, in and out of a direct beam of sunlight, then interrupting the beam with a shutter. Although it sounds more complicated than it seems, the heliograph was a simple, yet effective tool for optical communication. It was used mainly for military, survey and forest protection work. It is said that heliographs were standard issue in the British and Australian armies until the 1960s, and were used by the Pakistani army as late as 1975. Although it's use has almost vanished today, it certainly plays a big part in our technological timeline. This goes to show how much society has changed our form of communication through technological advancement.