perature of liquid air, and it is itself radio-active, but in such a way that its power decays rapidly with time. Its radio-activity seems to consist likewise in throwing away part of itself and leaving yet another residue, likewise radio-active; and one of the residues so left seems ultimately to pitch away electrons simply instead of atoms of matter. It is not to be supposed that thorium and radium and uranium all behave alike in details. The emanation of one may lose its activity rapidly, and give rise to another substance which retains its power for some time; the emanation of another element may last some time and generate a substance whose activity rapidly decays; but into these details it is not now the place to go.
12. Assuming the truth of this strange string of laboratory facts, we appear to be face to face with a phenomenon quite new in the history of the world. No one has hitherto observed the transition from one form of matter to another: though throughout the Middle Ages such a transmutation was looked for. The transmutation of elements has been suspected in modern times on evidence vaguely deducible by skilled observers from the spectroscopic details of solar and stellar appearances. The evolution of matter has likewise been suspected by a few chemists of genius: it was perceived, on the strength of Mendelejeff's law, that the elements form a kind of family or related series, and it was surmised that possibly the barriers between one species and the next were not absolutely infrangible, but that temporary transitional forms might occur. All this was speculation; but here in radioactive matter the process appears to be going on before our eyes. Professor Rutherford and Mr. Soddy, who in Canada during the present year have worked hard and admirably at the subject, have adduced facts which point clearly in this direction; and they initially describe what appear to be the first links of a chain of substances, all produced in hopelessly minute quantities reckoned by ordinary tests, but which yet by electrical means can easily be detected, and their boiling-points and other properties investigated. Moreover, the investigators of these strange substances are able to dissolve and precipitate, and perform ordinary chemical operations on, these utterly imponderable and hopelessly minute deposits of radio-active substances, because of the powerful means of detection which their ionizing power puts into our hands—even a few stray atoms being able by their ionizing power to discharge an electroscope appreciably.
13. Thus then it would appear that our theoretical conclusion concerning the inevitable radiation and loss of energy from electrically constituted atoms of matter, a loss which must involve them in necessary change and dissolution, meets with quite unexpectedly rapid confirmation, and it is for that reason that I feel willing to accept tentatively and as a working hypothesis this explanation of radio-activity.
