
Caesium Atomic Clock, 1955.
1955
1955
1956
1839 (original); circa 1988 (replica)
circa 1955
1955; 1830
1955
1955
1955
2000-100 BCE
circa 1955
1955
1956
1955
1955
1956
1956
1956
1956
1956
1955
1955
1955
1955
1955
1955
1955
circa 1956
1956
1955
1956
1956
1955
1955
1955
1955
1830 (original); 1967 (model)
1903 (original); 1982 (model)
circa 1955
circa 1956
1990-96
circa 1955
1955
4000-2001 BCE
1955
1956
1955-08
1956-07-15
1956-05-08
1956
1956