Physics · Nature of Science

Read the excerpt given below: 'French scientist Henri Becquerel was working on phosphorescent materials. He believed that sunlight was the reason that the uranium crystal would burn its image on a photographic plate. On a stormy day in 1896, he decided to leave the experimental setup in a darkened drawer and resume later. A few days later, he noticed that the image burned on the plate was fogged, meaning the crystal had still emitted rays despite the lack of sunlight.' What does this excerpt primarily illustrate about the nature of science?