INTRA-ATOMIC ENERGY. 175 



one of which is accompanied by the expulsion of an alpha 

 particle. Therefore, four is the very least number pro- 

 duced from any one atom of disintegrating radium. On 

 this basis, calculation leads to the conclusion that in every 

 mass of radium, however great or however small, not more 

 than thirteen trillionths of it is undergoing change per sec- 

 ond, and all its radiated energy is due to this infinitesimal 

 portion of it. Knowing the amount of radium undergoing 

 change per second, it is possible to deduce the average 

 life of the radium atom. This life is about 2,450 years as 

 a minimum estimate. It is obvious from this that the radium 

 at present existent in the world has not always been with 

 us. It has come into existence since the formation of the 

 world. It is also obvious that in the course of a few thou- 

 sand years all the radium at present existing will be re- 

 duced to practically nothing. What we have in the world 

 to-day has come to be, and will cease to be, within the 

 time of man. We may ask, then, is it an unprecedented 

 substance, the phenomenon of a day in all time? 



Not likely. Certain indications point to the conclusion 

 that radium is itself a disintegration product from the 

 heavier, and more slowly changing, radio-active element 

 uranium. It turns out that the relative proportion of 

 radium to uranium in the different radio-active minerals 

 from which radium is extracted is a constant quantity. 

 This is just as it should be if uranium were the parent of 

 radium. But there is contrary evidence. If uranium is 

 the parent of radium, the actual genesis of the radium 

 ought to be capable of detection. Soddy has tested this 

 point by carefully extracting all the radium from a mass of 

 uranium nitrate and testing the uranium for the growth of 

 radium at frequent intervals throughout a year. He has 

 been able to show that if radium is generated its quantity 



