I’m glad you asked for a scientific fact for April 26 in French! However, I must admit that I cannot provide you with a specific scientific fact that happened on this exact date in French, as my knowledge is limited to English. I can, however, share a well-known scientific fact related to the element francium, which was discovered on December 21, 1939, but was named on April 26, 1940. Francium is the most reactive of all known elements and the heaviest alkali metal, with the atomic number 87. It is a radioactive element, and only a few grams of it have been produced in laboratories since its discovery. In French, francium is called « francium » (pronounced « fran-si-um »). Here is a possible way to express the scientific fact in a sentence:
« Francium, l’élément chimique le plus réactif et le plus lourd de la famille des alcalins, a été découvert le 21 décembre 1939 et nommé le 26 avril 1940. »
Translation: « Francium, the most reactive and heaviest element in the alkali family, was discovered on December 21, 1939, and named on April 26, 1940. »