Madame [Marie] Curie, working with her distinguished husband, isolated and first traced to its true origin the source of the marvellous power which has thus commenced to revolutionise our philosophy of physics. This new element has appropriately been named "Radium;" but it has also been shown that there are many other, though less powerful, radio-active elements, details of which are recorded in the sequel. To be precise, radium, per se, has not yet been isolated as a metal, but only in the form of salts,—chlorides and bromides. … It is supposed that the molecules of radium (composed of similar atoms) during their decomposition into those of the gas helium, are also frittered down into heat and, in part, are liberated as radio-activity.