RADIO-ACTIVITY 187 



million times greater than that involved in the 

 most energetic chemical action known. ^ 



The conclusion is thus forced on us that, 

 in radio-active processes, we are dealing with 

 changes in the atoms themselves, and are watching 

 the phenomena which accompany a true trans- 

 mutation of the elements. The continuity of the 

 problems which present themselves to the human 

 intellect is once more strikingly demonstrated, 

 for surely the imagination must be deficient 

 which does not see in these transformations of 

 matter a partial fulfilment of the dreams of the 

 mediaeval alchemist. 



The strength of any hypothesis lies in its 

 power of co-ordinating observed facts, and of fore- 

 casting intelligently the discoveries of the future. 

 If, then, we accept this new revelation, and in its 

 light reconsider the phenomena we have already 

 discussed, we shall be able to marshal our facts 

 in orderly array, while the few privileged pioneers 

 alone can tell how much assistance they received 

 from it in their brilliant achievements. 



Let us then, in terms of this new theory, re- 

 state the results which we have already described. 

 All radio-active elements have very high atomic 

 weights, the atom of radium, for instance, being 

 226 times as heavy as that of hydrogen. Radio- 

 active atoms are therefore very complex structures, 

 and, on the theory we are considering, are capable 

 of breaking down into simpler and lighter systems. 

 The elements thorium and uranium contain some 

 few atoms which, at any moment, are disintegrat- 

 ing. As we have seen, the activity of the pure 

 separated thorium or uranium consists of a rays 

 only. Thus, the essential process of the radio- 



