This is a short "fly-around" of a British WWII Mance Mark V heliograph set up in the "duplex" (two mirror) configuration. The heliograph signaled long distances using reflected sunlight and Morse code. It was used by many nations from the 1870s to the 1940s. The Wikipedia article "Heliograph" is a good summary. The references to that article provide information in much greater depth. Today I signaled 22 miles, which is short range for this heliograph. My receiver today used his naked eye. Military heliograph teams used 30x telescopes as standard issue. Mance began his publicity campaign for his heliograph in London in 1875, and it was issued to British and Commonwealth troops until the end of WWII. The messages were transmitted by Morse Code created by briefly tilting the mirror to interrupt the beam. When the sun was on the opposite side of the signaler than the target, two mirrors were used, as shown here, causing the light to travel in a zigzag path through the instrument. Before signaling, the heliograph was aligned with the target. This was done by looking in the main (gimbaled) mirror at the sight (in the duplex setup, the crosshairs on the paper on the center of the secondary mirror), and moving the heliograph arm and the sight until the three points lined up: the target, the unsilvered hole in the main mirror, and the sight crosshairs. When one mirror was used, a crosshairs ring sight served as the aimer. Once aligned, the sunbeam was brought in alignment by using the azimuth and elevation screws on the main mirror to cast the tiny shadow spot from the unsilvered hole in the center of the main mirror on the crosshairs. At that point, transmission began by using the broad collar on the rod behind the main mirror as a telegraph key, briefly tilting the beam off the target line. Due to the motion of the sun, the shadow spot had to be realigned with crosshairs every 15 seconds or so. The aiming and signaling process for a Mark V heliograph in single mirror mode is shown in the longer YouTube video: "VMARS Heliograph Demonstration 2". If you own a heliograph, get the 1922 manual. I posted it on Google Docs as a free 55mb .pdf here: https://docs.google.com/open?id=0Bxca... The manual is: "Signal Training, Volume III, Pamphlet No. 2. Heliograph, 5-inch, Mark V, 1922, published by His Majesty's Stationery Office, London, Crown copyright reserved. My understanding is that the Crown copyright lapsed in 1972 (50 years), so it should be freely distributable.
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