Heliograph
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A heliograph is a solar telegraph system that signals by flashes of sunlight reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shut
Fig. 1: Signaling with a Mance heliograph; Alaska–Canada border, 1910.
Fig. 2: A German heliograph made by R. Fuess in Berlin, on display at the Museum of Communication in Frankfurt
Fig. 3 A Turkish / Ottoman Empire heliograph military crew at Huj during the First World War, 1917
Fig. 4: A U.S. Army Signal Corps heliograph instrument, 1898
Heliotrope (instrument)
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The heliotrope is an instrument that uses a mirror to reflect sunlight over great distances to mark the positions of participants in a land survey. The heliotrope was invented in 1821 by the German ma
Heliograph
…a side. The German professor Carl Friedrich Gauss (1777–1855), of the University of Göttingen developed and used a predecessor of the heliograph (the heliotrope) in 1821. His device directed a controlled beam of sunlight to a distant station to be used as a marker for geodetic survey work, and was suggested as…
Heliotrope (c. 1878): B.A. Colonna collection (NOAA). This may be the very one Colonna surveyed from 192 miles away.
Gauss's Heliotrope (c. 1822)
Wurdemann's Heliotrope (1866)
Coast Survey, Steinheil, and simple heliotropes c. 1898