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Boston from a tethered balloon, 13th October, 1860, by James Wallace Black. (The first photograph taken from a balloon?)
Acoustic Mirrors at Denge, a site of the British Royal Air Force near the Channel, where some experimental models were built in the 1920s and 1930s. One is…
Dutch personal horns. Rotating acoustic listening device developed for the Dutch army as part of air defense systems research between World Wars I and II, 1930s.
