In 1892, he became the third in his family to occupy the physics chair at the [[Muséum National d'Histoire Naturelle]]. In 1894, he became chief engineer in the Department of Bridges and Highways. During the later half of his career Becquerel stayed in Clifton, Bristol while undergoing his investigations into the phosphorescence of uranium salts which was one of his most renowned discoveries.
In 1896, while investigating [[phosphorescence]] in [[uranium]] salts, Becquerel accidentally discovered [[radioactivity]]. Investigating the work of [[Wilhelm Conrad Röntgen]], Becquerel wrapped a fluorescent substance, potassium uranyl sulfate, in [[photographic plate]]s and black material in preparation for an experiment requiring bright sunlight. However, prior to actually performing the experiment, Becquerel found that the photographic plates were already exposed, showing the image of the substance. This discovery led Becquerel to investigate the spontaneous emission of [[nuclear radiation]].
Describing his method to the [[French Academy of Sciences]] on 24 January 1896, he said: