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The “acoustic telegraph” (4th c. B.C.)

It consisted of a giant circularly folded trumpet in a form of a sound horn and hung from a tripod of four metres in height for its easy rotation and signal transmission towards all directions. It was used by Alexander the Great’s army in his famous expedition and it had an action range up to four kilometres. Perhaps, its function was also reverse so as to locate sounds, therefore, being the first acoustic radar in history.

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