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