Sir John Herschel, son of the astronomer, from Kent, invented the term photography in 1839, meaning light writing. and discovered the first photographic fixer, sodium thiosulphate, known as hypo, also in 1839. GLEEP was Britain's first nuclear reactor, in August 1947 at the Atomic Energy Research Establishment (AERE) at Harwell, and would stay operational until 1990; tt was followed by the British Experimental Pile 0 (BEPO) in 1948.