Manchester Memoirs, Vol. xlviii. (1904), No. 8. 15. 



metabolon, whether it is long or short, it behaves like an 

 ordinary atom. No indication whatever seems to be given 

 of its approaching end, but suddenly by some internal 

 cataclysm, the cause of which is at present almost beyond 

 conjecture, it flies into pieces and so ceases to exist as 

 such. Radio-activity is a property contributed by a 

 few atoms only in any given instant. The vast majority 

 are for the time being ordinary inactive atoms with a 

 specific and characteristic material nature which is not 

 affected by, or does not exert any influence on, the 

 character of the additional set of properties contributed 

 by the fraction disintegrating. For many purposes how- 

 ever a property which is contributed by a constant fraction 

 of the total is indistinguishable from a property possessed 

 by each atom in common. Thus Mme. Curie in her 

 earlier researches described each atom of a radio-active 

 body as behaving as a constant source of energy. The 

 discovery of the transition-forms has shown otherwise. 

 The question at issue between the two views is in reality 

 nothing short of a question between a discrete and a con- 

 tinuous structure of matter. The whole phenomena of 

 radio-activity would be an absolute enigma on the latter 

 view. A step-by-step change in which there is a sudden 

 break in properties at each step, and yet which proceeds 

 gradually in the mass of the matter, demands an atomic 

 hypothesis, and the radial expulsion of matter into space 

 is only intelligible if the projected manner is in the form 

 of discrete particles. These are generalities. The facts of 

 radio-activity throw new light on the nature of these atoms, 

 the effect having been to confirm in a most remarkable 

 manner the theory first propounded by Dalton to this 

 Society one hundred years ago. We know more about 

 the atoms to-day than Dalton did. From the very 

 immensity of the phenomena which attend its birth and 



