
Caesium Atomic Clock, 1955.
1955
1955
1963
1956
1839 (original); circa 1988 (replica)
1969
1961
circa 1955
1960
1955-1965
1960
1960
1968
1964
1955; 1830
1965
1955
1959
1954-1955
1968
1961-1962
circa 1969
1955
1957
1960
1962
1955
1957
1962
1969
1955-1965
circa 1960
(1962); 1982
1969
2000-100 BCE
1962
1967
1960
1965
1954
1960
1958
1964
1964
1954
circa 1955
circa 1964
1957
1955
1962
1958