reflecting astatic moving iron galvanometer
circa 1920
circa 1920
1955
circa 1932
1905
1885
1883
1930
1905
1910
1945
1930
1945
1920
1930
1904
1910
1930
1905
1925
1920
1910
1896
1890
1915
1950
1890
1905
1910
1945
1920
1910
1910
1904
1940
1895
1901
1935
1941
1925
1907
1920
1940
1905
1940