Henri Becquerel

Henri Becquerel stands at a heavy wooden bench beside a large electromagnet, its two thick coils taking up most of the tabletop, with more apparatus on the shelves behind him. The picture's period caption calls it the experiment with the magnet. In 1896 Becquerel found that uranium salts fog a photographic plate wrapped in black paper, the discovery that opened the study of radioactivity, and magnets became one of his tools for finding out what those invisible rays were made of.