Concave Rowland-type diffraction grating on speculum metal
1926, April
1926, April
1898
1825-1835
1899
1882-1899
1882, Nov 6
1876
1879
1926, May
1913, 14 November
circa 1930
1907-05
1910-1948 (estimated)
1881
1910-1920
1895-1909 (estimated)
1960-1969 (estimated)
1894
1950-1974 (estimated)
1882-1909 (estimated)
1975-1979
1957
1894
1910-1915
1905-05-26
1960-1970
1960-1969 (estimated)
1984
1878
1890
1964
1905-1907
1934
1964
1945-1955
1984
1964