The exact opposite of speakers - sound mirrors to track aircraft

[d0dja]

What a great story. The Brits were worried about aerial attack after WW1, so they started building a network of sound mirrors in the 20s and 30s to track possible enemy aircraft - giant concrete sound mirrors as big as a house. Then some spoilsport went and invented radar, and so the idea was abandonded.

Full story http://www.spiegel.de/international/zeitgeist/0,1518,765771-2,00.html

 

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[d0dja]

 

[MorneDJ]

 

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[d0dja]