224 MODERN VIEWS ON MATTER. 



active substance, i.s very hioh, in each case over two hundred times the 

 atomic weiglit of hydrogen, whereas the atomic weight of the substance 

 flung olf appears to be more nearly of the order one or two; in other 

 words, the suljstance thrown off is more likely to be either hydrogen 

 or helium than it is likely to be radium. It is just possible that the 

 inert chemical elements are b} -products of radio-activity. 



Now, clearly here is a fact, if fact it be, of prodigious importance. 

 Undoubtedl}' the nu^asurements require conflrmation, but for m3\self 

 I see no reason to doubt them, at least as regards their order of magni- 

 tude. The atomic weight of radium being, sa}^, 225, and that of the 

 projoctt'd portion Ix^ing, 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 he assumed, as it will almost certainly be 

 assumed 1)}^ some skeptical 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 

 h^'pothesis, I venture to say, already strongly against the weight of 

 availal)le evidence. 



The su])stance left behind in the pores of the radio-active substance 

 has 1)een examined even more completely than the projected portion; 

 it is volatile, it slowly diffuses awa}^, and it behaves like a gas. It can 

 be stor(»d in gas holders when mixed with air, for in amount it is quite 

 imp(n-ceptible to all ordinary tests; and yet it can be passed through 

 pipes and otherwise dealt with. It condenses not far al)ove the tem- 

 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 anothei" 

 residue, likewise radio-active; and one of the residues so left seems 

 idtimately to pitch away electrons simply instead of atoms of matter. 

 It is not to I)e 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 sulistance 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 wdth a phenomenon quite new in the his- 

 tory of the world. No one has hitherto observed the transition from 

 one form of matter to another, though throughout the Middle Ages 

 such a tr^nsnmtation 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 Men- 

 delejefl''s law, that the elements form a kind of family or related series, 



