graphs that each atom of radium which becomes unstable throws off at least as many as four alpha particles before it again reaches a condition of stability, it is probable that the above lowest possible limit to the life of radium, viz., 9,000 years, should be replaced by 36,000. At the second or minimum rate radium would lose one-hundredth of its activity in about 500 years and in 900,000 years would be no longer measurably active. It appears then that within a period of a million years at most all the radium now in existence will have ceased to be radio-active, i. e., will have ceased to be radium. The life of uranium and thorium would be from one to two million times as much, since they are radiating only about a millionth as actively.
The Transmutation of the Elements.
The discoveries which we have attempted to describe in the preceding pages have seemed to lead to the startling conclusion that in the case of certain elements at least, the dreams of the ancient alchemists are true, for the radio-active elements all appear to be slowly but spontaneously transmuting themselves into other elements. The present indications seem to be that this transmutation which is going on in nature is a change from the heavier atoms to the lighter ones. Whether any other heavy atoms besides those of uranium, thorium and radium are thus slowly disintegrating, we can not say, but probably actinium must be added to the list. If any of the other known heavy elements, like gold, lead, barium, bismuth, mercury, are undergoing such a change, it is too slow to be detected even by the delicate test of radio-activity. But it is interesting to note that the only changes of this kind which have thus far been discovered to be going on among the atoms are in some respects similar to the changes which are going on in the organic world among the molecules. By the ordinary process of decay, all organic compounds, which represent very complex molecular structures, are continually disintegrating into simpler ones, and in so doing are setting free the energy which was put into them when the processes of life built them up into complex forms. Similarly, the studies of the last eight years upon radiation seem to indicate that in the atomic world also, at least some of the heaviest and most complex atomic structures are tending to disintegrate into simpler atoms. The analogy suggests the profoundly interesting question, as to whether or not there is any natural process which does, among the atoms, what the life process does among the molecules, i. e., which takes the simpler forms and builds them up again into more complex ones. It would be rash to attempt to give any positive answer to such a query, yet the fact that radium now exists on the earth, taken in connection with the fact that the life of radium is short in comparison with the ages in which the earth has been in existence, certainly seems to point to an affirmative answer. The only other alternative is to assume that
