Henri Poincaré read Röntgen’s X-ray preprint at the French Academy meeting attended by Henri Becquerel in January 1896.
The meeting took place on 20 January 1896, soon after Wilhelm Conrad Röntgen announced his discovery of X-rays. Poincaré, a mathematician and physicist who was also interested in the new radiation, read or communicated Röntgen’s preprint to the Académie des Sciences in Paris. Becquerel was present and became intrigued by a possible connection between X-rays and phosphorescence.
Becquerel already had a long-standing interest in luminescent materials, including uranium compounds. He wondered whether substances that fluoresced or phosphoresced under light might emit penetrating rays similar to Röntgen’s X-rays. His experiments soon led to the discovery that uranium salts affected photographic plates even when they had not been exposed to sunlight.
The common confusion is between Poincaré’s role in bringing Röntgen’s report to the French Academy and Becquerel’s later role in presenting other scientists’ findings. Poincaré did not discover radioactivity; his communication helped prompt Becquerel’s decisive experiments, announced to the Academy in February 1896.