RADIO-ACTIVITY 203 



of the alchemist. But it is easier to destroy than 

 to build up, and it does not follow that, because 

 we can knock to pieces one atom in a million, we 

 shall ever be able to put together a more complex 

 atom from simpler ones. 



Moreover, the number of atoms affected is 

 almost infinitesimally small. About two a particles 

 in a million dislodge hydrogen nuclei. If all the 

 a particles from a gram of radium were steadily fired 

 into aluminium, only about the one-thousandth 

 part of a cubic millimetre of hydrogen would be 

 produced in a year. The modern philosopher's 

 stone falls far short of medieval requirements. 



By investigating radio-active changes, we can 

 trace the transmutation of the elements ; we can 

 watch the disintegration of matter ; we can even 

 knock to pieces a few atoms of certain elements ; 

 but we are far from bringing these processes fully 

 under our control. It would be rash to predict 

 that our impotence will last for ever. It is con- 

 ceivable, too, that some means may one day be 

 found for inducing radio-active change in elements 

 which are not normally subject to it — means more 

 effective than bombardment by the comparatively 

 few a particles which have yet been used. 

 Sir Ernest Rutherford once playfully suggested 

 to the writer the disquieting idea that, could a 

 proper detonator be discovered, an explosive wave 

 of atomic disintegration might be started through 

 all matter which would transmute the whole mass 

 of the globe, and leave but a wrack of helium 

 behind. Such a speculation is, of course, only a 

 nightmare dream of the scientific imagination, but 

 it serves to show the illimitable avenues of thought 

 opened up by the study of radio-activity. 



