SOME PHYSICAL PROBLEMS 



These parts gradually becoming collected around con- 

 densed centres have formed what we know as the 

 atoms of elements, the atom thus becoming like an 

 extinct sun of the solar system. From this point of 

 view the radio-active atoms represent an interme- 

 diate stage between nebulae and chemical atoms, 

 the process of contraction giving rise to the heat 

 emissions. 



Lord Kelvin has called attention to the fact that 

 when two pieces of paper, one white and the other 

 black, are placed in exactly similar glass vessels of 

 water and exposed to light, the temperature of the 

 vessel containing the black paper is raised slightly 

 higher than the other. This suggests the idea that in 

 a similar manner radium may keep its temperature 

 higher than the surrounding air by the absorption of 

 other radiations as yet unknown. 



Professor J. J. Thompson believes that the source of 

 energy is in the atom] itself and not external to it. 

 " The reason," he says, " which induces me to think that 

 the source of the energy is in the atom of radium itself 

 and not external to it is that the radio-activity of sub- 

 stances is in all cases in which we have been able to 

 localize it a transient property. No substance goes 

 on being radio-active very long. It may be asked, 

 how can this statement be reconciled with the fact that 

 thorium and radium keep up their activity without any 

 appreciable falling off with time. The answer to this 

 is that, as Rutherford and Soddy have shown in the 

 case of thorium, it is only an exceedingly small frac- 

 tion of the mass which is at any one time radio-active, 

 and that this radio-active portion loses its activity in a 



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