Ray Essen gives his talk 'The Birth of Atomic Time' in which he describes Louis Essen's work in developing the first atomic clock which paved the way for a new and better definition of the second, based on the fundamental properties of atoms.

Recorded at NPL on 31 January 2014, celebrating NPL being officially declared the birthplace of atomic time by the European Physical Society.

Learn more: NPL named birthplace of atomic timekeeping