The Mirror Has Two Speakers

In the early 1900's England, if a tree fell in the woods or an oncoming enemy plane was approaching a military stronghold on the coast, chances are someone would know it. However, it wasn't due to the Brits bionic hearing. It was more likely due to “sound mirrors;” these concrete parabolic monoliths and design ancestors to the satellite dish were used to trap sound waves and hear incoming enemy airplanes before you could see them. While practical back in the day, the reliance on radar made them obsolete. Fortunately for anyone who finds themselves on the British Isles many of them still stand today as an impressive monument to a technology gone the way of the dodo. Thanks to the good folks at Core77 and deputy dog for the heads up.