These works I visited the next day, and found myself outside the walls of Paris, near the old Ivry Cemetery, where some unpretentious sheds serve for this important business of radium extraction. One of the head men met me and explained, step by step, how they obtain this strange and elusive metal. First he showed me a lumpy reddish powder, sacks of it, brought from Bohemia by the ton, and constituting the raw material from which the radium is extracted. This powder is the refuse from uranium mines at Jachimsthal; that is, what remains of the original uranite ore, _pitchblende_, after the uranium has been removed. For years this refuse was regarded as worthless, and was left to accumulate in heaps, tons of it, quite at the disposal of whoever chose to cart it away. Now that it is known to contain the rarest, and most precious substance in the world, it goes without saying that the owners have begun to put a price on it. My informant referred with proper pride to the difficulties that had confronted them when they started these radium works in 1901. It was a new problem in practical chemistry to bring together infinitesimal traces of a metal lost in tons of _débris_. It was like searching for specks of dust hidden in a sand heap, or for drops of perfume scattered in a river. Still, they went at it with good heart, for the end justified the effort. If it took a ton of uranite dust to yield as much radium as would half fill a doll's thimble, then the thing to do was to have many tons of this dust sent on from Bohemia, and patiently to accumulate, after months of handling, various pinches of radium, a few centigrammes, then a few decigrammes, and finally some day--who could tell?--they might get as much as a gramme. This was a distant prospect, to be sure, yet with infinite pains and all the resources of chemistry it might be attained. Well, now they had attained it, and at this time, he said, some eight tons of uranite detritus had passed through the caldrons and great glass jars and muddy barrels of the Ivry establishment, had been boiled and filtered and decanted and crystallized, with much fuming of acids and the steady glow of furnaces; and out of it all, for the twenty-four months' effort, there had come just about a gramme of practically pure chloride of radium--enough white powder to fill a salt-spoon. When next I saw M. Curie he had just returned from London, where he had lectured before the Royal Institution. His hands were much peeled, and very sore from too much contact with radium, and for several days he had been unable to dress himself; but he took it good-naturedly, and proceeded to describe some of the experiments he had made before British scientists. [Illustration: M. CURIE EXPLAINING THE WONDERS OF RADIUM AT THE SORBONNE. THIS EXPERIMENT WITH THE RADIUM LIGHT IS DESCRIBED IN THE ARTICLE.]