Observer Egy using geophones to detect sounds produced by mining machines. He listens to the sounds through clay, with the geophones placed firmly on the clay. A closed telephone booth protects the observer from external noises like wind. This technology was developed by the Bureau of Mines for detecting enemy mining operations during World War I.

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Size: 8448px × 5862px
Photo credit: © piemags/NSC / Alamy / Afripics
License: Licensed
Model Released: No

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