We now come to the fascinating story of the discovery and manufacture of radium. It has long been known that certain substances are phosphorescent; that is, under the proper conditions they glow without apparent heat. Everybody has seen "fox-fire" in the damp and decaying woods--a cold light which scientists have never been able to explain. To M. Henri Becquerel of the French Institute is generally given the credit for having begun the real study of radio-activity, although, as in every great discovery and invention, many other scientists and practical electricians had paved the way by their investigations. In 1896 M. Becquerel was conducting some experiments with various phosphorescent substances. He exposed some salts of the metal uranium to the sunlight until they became phosphorescent, and then tried their effect upon a photographic plate. It rained, and he put the plate away in a drawer for several days. When he developed it he was surprised to find on it a better image than sunlight would have made. And thus, by a sort of accident, he led up to the discovery of the Becquerel rays, so called. Uranium is extracted from a metal or ore called uranite by mineralogists, and popularly known as pitch-blende. Every young college student who has studied geology or chemistry has heard of pitch-blende. Two years after Becquerel's discovery of the radio-activity of uranium Professor Pierre Curie and Madame Curie, of Paris, made the discovery that some of the samples of pitch-blende which they had were much more powerful than any uranium that they had used. Was there, then, something more powerful than uranium within the pitch-blende? They began to "boil down" the waste rock left at the uranium mines, and found a strange new element, related to uranium but different, to which Madame Curie gave the name polonium, after her native land, Poland. [Illustration: Dr. Danlos Treating a Lupus Patient with Radium at the St. Louis Hospital, Paris.] Then they did some more boiling down, and succeeded in isolating an entirely new substance, and the most radio-active yet discovered--radium. Shortly after that Debierne discovered still another radio-active substance, to which he gave the name actinium. Thus three new elements were added to the list of the world's substances, and the most wonderful of these is radium. In a day, almost, the Curies became famous in the scientific world, and many of the greatest investigators in the world--Lord Kelvin, Sir William Crookes, and others--took up the study of radium.