Manchester Memoirs, Vol. xlviii. (1904), No. 8. 19 



the parent-element by chemical means does not in any 

 way affect the course of the disintegration. Left to 

 itself the parent-element _^ steadily accumulates a fresh 

 crop of the transition-forms separated, while the quan- 

 tities originally separated disappear as such by further 

 change. As the activity of the parent-element recovers 

 to its maximum or equilibrium value, that of the 

 transition-forms decays to zero, and the sum total is 

 always the same as if the separation had not been 

 effected. 



Radio-activity, as the manifestation of atomic disin- 

 tegration, has thus introduced us to a whole series of new 

 unstable elements which at present find no place in the 

 periodic table, and of which, except in the single case of 

 radium, we possess but little chemical knowledge. 

 They are the products of a material evolution, the 

 initial stage of which is so slow that the ages that 

 have elapsed since it started have not yet sufficed for its 

 -completion. But after the initial stage is passed the 

 evolution proceeds rapidly, and passes from stage to stage 

 so quickly that almost all we know at present of the 

 intermediate forms is derived from the energy-phenomena 

 which mark their appearance and destruction. Yet these 

 phenomena, viz., the expulsion of rays, are so character- 

 istic and so fitted for exact study that our knowledge is 

 iby no means necessarily scanty, although it is of a kind 

 not usually associated with ordinary matter. We are in 

 a new science, and its correlation to other sciences must 

 be held secondary to its own development. This 

 appears at once when the means of identifying and 

 distinguishing the different types of metabolons from one 

 another are compared with those employed in the case 

 of the stable atoms. For the latter, atomic weight, 

 spectrum reaction, and general chemical and physical 



