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Keywords: Heliotrope6.jpg Heliotrope used for directing sun's rays to distant observer Used to illuminate station site so far distant observer could measure angles NOAA's http //www photolib noaa gov/cgs/index html Historic C GS Coast and Geodetic Survey Collection Image ID http //www photolib noaa gov/htmls/theb3904 htm theb3904 http //www noaa gov/ US National Oceanic and Atmospheric Administration PD-USGov Heliotrope |