Operator listening to miner picking on coal rib 600 feet away, as part of the war work and research conducted by the Bureau of Mines during World War One. The Bureau offered use of its experimental mine near Pittsburgh, PA, and trained personnel to develop instruments for detecting enemy mining operations and determining the strength of different sounds in mining operations. Taken on Nov. 4, 1918.

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Photo credit: © piemags/NSC / Alamy / Afripics
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