Template:POTD/2011-06-21
A World War I Ottoman signaling crew in Huj (1917) with a heliograph (far left), a wireless solar telegraph that signals using Morse code flashes of sunlight reflected by a mirror. The flashes were generated by tilting the mirror with a lever mounted behind it. The heliograph is a simple but highly effective instrument for instantaneous optical communication over long distances. The record is 183 mi (295 km), using a 8"x8" mirror. The depicted device has a 5" diameter mirror, rated for 30 mile range.Photo: American Colony; Restoration: Lise Broer