At the suggestion of M. Becquerel, M. and Madame Pierre Curie undertook a thorough quest for these effects in a wide diversity of substances. They found that several minerals containing uranium were more radio-active than that element itself. Pitchblende, for instance, consisting mainly of an oxide of uranium, was especially energetic as it approached an electroscope, suggesting the presence of an uncommonly active constituent, thus far not identified. At the end of a most laborious series of separations they came at last to a minute quantity of radium chloride displaying extraordinary properties. Another compound of radium, a bromide, has since been arrived at: radium by itself has not yet been obtained. In radio-activity radium chloride surpasses uranium about one-million-fold. Provided with an electroscope of exquisite sensibility, Professor Ernest Rutherford of McGill University, Montreal, has discovered seven distinct radiations from radium, each with characteristics of its own. Directed upon plates of aluminium he finds its _gamma_ rays to be 100 times more penetrating than its _beta_ rays, and _beta_ rays 100 times more penetrating than its _alpha_ rays. Each radiation has qualities as distinct as those of an ordinary chemical element. _Beta_ rays behave in all respects like cathode rays, so that here a bridge is discerned betwixt the qualities of radium and the long familiar phenomena of the Crookes tube. The substance ranking next in radio-activity to radium is thorium. Professor Rutherford has observed it throwing off a substance he calls Thorium X; this radiates strongly for a time, the parent mass not radiating at all. Gradually Thorium X ceases to radiate and the original thorium resumes an emission of Thorium X. From Thorium X emanates what seems a gas, condensible by extreme cold, which attaches itself to adjacent bodies so as to make them radio-active. This emanation in its turn produces successively three new and distinct kinds of radiation. Professor Charles Baskerville, of the College of the City of New York, has separated from thorium two substances probably elementary, carolinium and berzelium. Other radio-active substances have each several derivatives: actinium has nine, uranium has four. As researchers broaden their range of inquiry they steadily lengthen the list of radio-active substances. Minerals of many kinds, water from springs, especially those of medicinal value, the leaves of plants, newly fallen snow, and even common air, are found to be radio-active, although usually in but a slight degree, so that the doubt may be expressed, Is the observed effect due to a trace of some highly radio-active material diffused in something else which is not radio-active at all? Should it be established that radio-activity is really present in all matter it would be no other than a parallel to what, at another point in the physical scale, presents itself as ordinary evaporation. Solids are not as Solid as They Seem.