
Hilger wavelength spectroscope, with camera, London, England, 1919
1919
1919
1899
1928
1900-1905
1919
1918-1920
1910-1948 (estimated)
1930
1900-1910
1900-1905
1900-1905
1900-1905
1900-1905
1920
1948
1939
1900-1980
1950
1920-1930
1930-1932
1905
1905-1915
circa 1875-1941
1930-1932
1920-1930
1920-1929
1926-1936
1940-1950
1938
1932
1922
1947
1910-1920
1919
1920-1929
1919