High-sensitivity mirror galvanometer
circa 1920
circa 1920
1924
circa 1890
1895
1930
1910
1955
1925
1925
1888
1938
1935
1910
1930
1924
1910
1920
1911
1930
1936
1920
1955
1928
1924
1920
1890
1897
1920
1920
1943
1910
1955
1959
1941
1920
1916
1940
1930
1904
1930
1932
1940
1911