14 SODDY, Evolution of Matter by Radio-active Elements. 



destruction we know that under ordinary circumstances, 

 as for example in the whole sphere of chemistry, the atom 

 is the true unit of change. At the same time a new world 

 has been opened to us by the discovery of radio-activity, 

 in which the atom is not the unit, in which the forces are 

 not chemical, and in which common physical conceptions 

 such as temperature are without meaning. The further 

 we advance into this sub-atomic world we realise how 

 completely it is removed from the plane of molecular 

 and atomic considerations. We can watch, it is true 

 only as spectators without power to interfere, the pro- 

 gress of sub-atomic change, and from the novel character 

 of the phenomena manifested, it is clear that the atom of 

 Dalton represents a very real and distinct stage in the 

 complexity of matter which under all ordinary circum- 

 stances is conserved. The fundamental theory on which 

 Dalton founded modern chemistry may be said to have 

 received a positive proof by the discovery of the nature 

 of sub-atomic change. 



In the papers by Professor Rutherford and myself 

 already alluded to it was our object to show that the facts 

 of radio-activity led without possible alternative to the 

 theory of atomic disintegration. Here a less rigorous 

 treatment of the problem must suffice, and the argument 

 will be inverted. The possibility of atomic disintegration 

 on the lines laid down will be assumed, and the phenomena 

 of radio-activity shown to follow as simple and natural 

 consequences. In the first place, since the process is not 

 affected by any known agency, we must assume that it has 

 proceeded continuously during past ages at the same 

 rate, for any given type of matter, as it is proceeding at 

 present. Hence it follows that the initial process of 

 disintegration must be excessively slow, in order that 

 some of the matter disintegrating should survive to the 



