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Scientific American 1919-05-31

ScientificAmerican1919-05-31.jpg Scientific American 1903-06-20ThumbnailsScientific American 1921-02-26Scientific American 1903-06-20ThumbnailsScientific American 1921-02-26Scientific American 1903-06-20ThumbnailsScientific American 1921-02-26Scientific American 1903-06-20ThumbnailsScientific American 1921-02-26

Locating entombed miners by aid of the geophone.