Manchester Memoirs^ Vol. xlviii. (1904), No. 8. ir 



Rutherford and myself to denote unstable atoms of this 

 character, and the name indicates the essential feature 

 which characterises them, and the means employed in 

 their investigation. A metabolon is an atom with a 

 limited life. While it exists it is a normal atom, possess- 

 ing the ordinary attributes of matter. At the moment of 

 its disruptive change it exhibits the property of radio- 

 activity. 



An obvious criticism may be anticipated. It may be 

 objected that the word atom means ' indivisible,' and 

 that a disintegrating atom is a verbal absurdity ; the 

 argument being that if the particle does change it ipso 

 facto cannot be an atom. This argument, of course, 

 involves the assumption that an unchangeable thing is 

 also necessarily unchanging. The weather, for example,, 

 is unchangeable in the same sense as the atom is, for both 

 have defied our active efforts to change them. The line 

 must be sharply drawn between personal inability and 

 natural impossibility. So far as the former is concerned, 

 the metabolon accords with the experience of chemistry 

 with regard to the atoms. It changes, but we are power- 

 less either to stop it changing or to affect its rate of 

 change. The cause of the change is beyond our control. 



The above view of radio-activity explains at once 

 what may be termed the dual character of radio-active 

 matter, according as its ordinary material properties or 

 its radio-active properties are under consideration. There 

 is nothing abnormal in the chemistry of uranium or 

 thorium which can be connected with their radio-activity. 

 Radium from its atomic weight, spectrum reaction and 

 chemical behaviour is a completely normal heavy element 

 of the alkaline-earth family. The recent examination of 

 its spectrum by Runge and Precht has revealed in a 

 remarkable way how closely radium resembles barium,. 



