known about the decay of the emanation, but one thing is absolutely certain, having first been discovered by Ramsay and Soddy and subsequently confirmed by independent experiment by Madame Curie. It is this: After being kept three or four days the emanation becomes, in part at least, converted into helium--the light gas (second only in the list of elements to hydrogen), the gas found twenty-five years ago by Lockyer in the sun, and since obtained in some quantities from rare radio-active minerals by Ramsay! The proof of the formation of helium from the radium emanation is, of course, obtained by the spectroscope, and its evidence is beyond assail (see fig. 11). Here, then, is the partial conversion or decay of one element, radium, through an intermediate stage into another. And not only that, but if, as seems probable, the presence of helium indicates the previous presence of radium, we have the evidence of enormous quantities of radium in the sun, for we know helium is there in vast quantity. Not only that, but inasmuch as helium has been discovered in most hot springs and in various radio-active minerals in the earth, it may be legitimately argued that no inconsiderable quantity of radium is present in the earth. Indeed, it now seems probable that there is enough radium in the sun to keep up its continual output of heat, and enough in the earth to make good its loss of heat by radiation into space, for an almost indefinite period. Other experiments of a similar kind have rendered it practically certain that radium itself is formed by a somewhat similar transformation of uranium, so that our ideas as to the permanence and immutability on this globe of the chemical elements are destroyed, and must give place to new conceptions. It seems not improbable that the final product of the radium emanation after the helium is removed is or becomes the metal lead! [Illustration: FIG. 11. A { Tube containing { Helium gas derived { from the { mineral Clevelandite. B { Tube of Radium { emanation, a { year old. C { Tube of Hydrogen { gas for { comparison. Photographs of the “spark” spectra of A, Helium as extracted from the mineral Clevelandite of B, the Radium “emanation” after a year’s enclosure in the tube used and of C of Hydrogen gas: copied from the paper by Mr. F. Giesel in the _Berichte der Deutschen Chemischen Gesellschaft_, vol. xxxix, part 10. The three photographs are accurately super-imposed so as to show the coincident lines.