Who discovered Radioactivity? Every physics student has heard the story of how Henri Becquerel made the chance discovery while studying the effects of light on chemicals using photographic plates in 1896. He normally exposed the chemicals to sunlight and then left them on a photographic plate in a dark drawer to see if they would expose the plate. One day he was trying the experiment with some uranium salts but the sky stayed cloudy, so he put the plates and chemicals in the drawer without the exposure to wait for better light. When he took them out he decided to develop the plates anyway and was surprised to find that they had been darkened despite the lack of light. He had discovered the effects of radioactivity.
Becquerel was awarded the Nobel Prize in 1903. His contribution is further recognised in the modern name for the unit of radioactivity.
What most people don’t know is that the same discovery had been made some four decades earlier by Abel Niepce de Saint-Victor. Like Becquerel he was studying the effects of light on various chemicals and was using photographic plates to test the reaction. He also used uranium salts and found that they continued to blacken the plates long after any exposure to light had been stopped. Fluorescence and Phosphorescence had been known for many years and Niepce knew that this new observation did not conform to either phenomena. He reported his results to the Academy of Sciences in France several times.
A few scientists including Foucault commented on the findings but no-one had a good explanation. Surprisingly no-one seems to have tried to replicate them and it is likely that everyone thought that there was most likely some experimental error. In any case Niepce and his discovery were soon forgotten.
When Becquerel rediscovered the same result as Niepce the situation was very different. By then X-rays were known and physicists were ready to appreciate that another new type of ray could exist. One physicist Gustave Le Bon pointed to the prior work of Niepce de Saint-Victor but he was ridiculed. Any further chance that Niepce might gain some recognition were extinguished when the Nobel Committee awarded the physics prize to Becquerel.
The story of Abel Niepce de Saint-Victor is typical of what happens to scientists who make a discovery whose importance is not recognised at the time. You would expect that when the effect is rediscovered later, people would appreciate the original discoverer, but that is not what happens. Usually the new discoverer gets most or all of the credit and the original scientists contribution is neglected because he failed to grab everybody’s attention, even if he managed to publish the result six times. In this case it is only in recent years that some small amount of appreciation for the work of Abel Niepce de Saint-Victor has finally emerged.