Now clearly here is a fact, if fact it be, of prodigious importance. Undoubtedly the measurements require confirmation, but for myself I see no reason to doubt them, at least as regards their order of magnitude. The atomic weight of radium being say 225, and that of the projected portion being say 2, the residue must represent by its atomic weight the difference between the heavy atom of the original substance and that of the light atom or atoms which have been flung away: unless indeed it be assumed, as it will almost certainly be assumed by some sceptical chemists, those who derided argon and other chemical discoveries when made in a physical manner, that the substance flung away is some foreign ingredient or impurity—a hypothesis, I venture to say, already strongly against the weight of available evidence.
The substance left behind in the pores of the radio-active substance has been examined even more completely than the projected portion: it is volatile, it slowly diffuses away, and it behaves like a gas. It can be stored in gas-holders when mixed with air, for in amount it is quite imperceptible to all ordinary tests; and yet it can be passed through pipes and otherwise dealt with. It condenses not far above the temperature 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
