Caesium Atomic Clock, 1955.
1955
1955
1926, May
circa 1950
1940-1960
1918
1915
1932-05-06
1943-1944
1943-1944
1954
1950-1958
1949
1958-1967
1932-05-06
1932-05-06
1943-1944
1905-1911
1943-1944
1950
1899
1964-1965
20th Century
1940-1960
circa 1934
1965-1968
1911
1970-1972
1901-1927
1912-1930
circa 1948
1924
1916