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