tireless enthusiasm of Madame Curie knew nothing of insurmountable obstacles, and soon drew her husband into the search with her. Her first discovery was that of the substance polonium--so named by Madame Curie after her native country, Poland. This proved to be another of the radio-active substances, differing from any other yet discovered, but still not the sought-for element. In a short time, however, the two Curies made the great discovery of the element radium--a substance which, according to their estimate, is some one million eight hundred thousand times more radioactive than uranium. The name for this element, _radium_, was proposed by Madame Curie, who had also suggested the term "radio-activity." The bearing of the discovery of radium and radioactivity upon theories of the atom and matter will be considered in a moment; first the more tangible qualities of this wonderful substance may be briefly referred to. The fact that radio-active emanations traverse all forms of matter to greater or less depth--that is, pass through wood and iron with something the same ease that light passes through a window-glass--makes the subject one of greatest interest; and particularly so as the demonstration of this fact is so tangible. While the rays given out by radium cannot, of course, be seen by the unaided eye, the effects of these rays upon certain substances, which they cause to phosphoresce, are strikingly shown. One of such substances is the diamond, and a most striking illustration of the power of radium in penetrating opaque substances has been made by Mr. George F. Kunz, of the American Museum of Natural History. Mr. Kunz describes this experiment as follows: "Radium bromide of three hundred thousand activity was placed in a sealed glass tube inside a rubber thermometer-holder, which was tightly screwed to prevent any emanation of any kind from passing through the joints. This was placed under a heavy silver tureen fully one-sixteenth of an inch in thickness; upon this were placed four copper plates, such as are used for engraving; upon these a heavy graduated measuring-glass 10 cm. in diameter; this was filled with water to a depth of six inches. A diamond was suspended in the water and immediately phosphoresced. Whenever the tube of radium was drawn away more than two or three feet the phosphoresce ceased; whenever it was placed under the tureen the diamond immediately phosphoresced again. This experiment proves that the active power of the radium penetrated the following substances: "Glass in the form of a tube, sealed at both ends; the rubber thermometer-holder; silver tureen; four copper plates; a glass vase or measuring-glass one-quarter of an inch in thickness; three inches of water. There is no previously known substance or agent, whether it be even light or electricity, that possesses such wonderfully penetrative powers."*5* THE NATURE OF EMANATIONS FROM RADIO-ACTIVE BODIES