
Caesium Atomic Clock, 1955.
1955
1955
1957
1955
1958
1958
1830 (original); 1967 (model)
circa 1956
1839 (original); circa 1988 (replica)
1956
circa 1955
1955
1954-1955
1955
1955
1957
1957
1955; 1830
1956
1956
1958
1955
1954
1956
1954
circa 1955
1957
1955
1958
1956
1955
1954
1955
1957
1954
1954
1957
1956
1957
1956
1957
1954
1957
1956
2000-100 BCE
1957
1957
1955
1957
1957
1955