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Powdered graphite microphone, 1878-1890
1878-1890
1878-1890
1878-1890
1878-1890
1878-1890
1878-1890
1872-1880
1896
1879
1934
1878
1879
1886-1887
1898
1899
1894
1895-1900
1899-1901
before 1889
1885-1894
1872
before 1889
About 1890
1890
1884
1892-1900
1880-1890
1898-1899
1876
1891-1900
1872
1872 (original); 1909 (model)
1892
1874-1900
1889
1877-1897
1876
1898
1880-1900
1901
1884
1890
1901
1898
1896
1875
1896
1900
1895-1899
1889
1885