
Caesium Atomic Clock, 1955.
1955
1955
1956
1839 (original); circa 1988 (replica)
1961
circa 1955
1960
1960
1960
1955; 1830
1955
1959
1961-1962
1955
1957
1960
1962
1955
1957
1962
circa 1960
(1962); 1982
2000-100 BCE
1962
1960
1960
1958
circa 1955
1957
1955
1962
1958
1956
1960
1955
1962
1959
1959
1961
1962
1960
1955
1960
1957
1962
1962
1957
1961
1960
1961
1959