https://en.m.wikipedia.org/wiki/Carrington_Event

(http://www.autoadmit.com/thread.php?thread_id=5280809&forum_id=2#45862447)

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Main article: Wigwag (flag signals)

Wigwag is a form of flag signalling using a single flag. Unlike most forms of flag signalling, which are used over relatively short distances, wigwag is designed to maximise the distance covered—up to 32 km (20 mi) in some cases. Wigwag achieved this by using a large flag—a single flag can be held with both hands unlike flag semaphore which has a flag in each hand—and using motions rather than positions as its symbols since motions are more easily seen. It was invented by US Army surgeon Albert J. Myer in the 1850s who later became the first head of the Signal Corps. Wigwag was used extensively during the American Civil War where it filled a gap left by the electrical telegraph. Although the electrical telegraph had been in use for more than a decade, the network did not yet reach everywhere and portable, ruggedized equipment suitable for military use was not immediately available. Permanent or semi-permanent stations were established during the war, some of them towers of enormous height and the system was extensive enough to be described as a communications network.[33][34]

(http://www.autoadmit.com/thread.php?thread_id=5280809&forum_id=2#45862458)