Science tourism
National Physical Laboratory – the birthplace of atomic timekeeping. In the 1950s, Louis Essen and John Parry constructed the atomic clock, Caesium Mk. 1. This new clock kept time more accurately. It paved the way for redefining the second in 1967, based on the fundamental properties of CS atoms, rather than the quite irregular Earth rotation. The facilities in Teddington are among the world's most extensive and sophisticated for measurement science. On 20 May 2014, NPL Open House will give people the chance to explore much of the science that goes on at NPL and the facilities that are used to do it: NPL Open House 2014 . While children are allowed, the exhibits are aimed for adults, and children must be kept under adult supervision at all times.