Just before World War II in 1939, Marguerite Perey succeeded in discovering the long-sought element 87 while working at the Institut du Radium in Paris. The existence of the heaviest alkali metal, eka-caesium, had been predicted by Mendeléev long before and intensively pursued by a large number of chemists and physicists since the beginning of the 20th century.
One of the scientists participating in the search was Dr. G.A. Aartovaara from Helsinki. The events leading to the discovery of francium are discussed and the career of Marguerite Perey is outlined.