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.