The Groundivorh of the Univevfie, &c. 61 



some material which displays radioactivity. Thus niton clearly 

 disintegrates and gives rise to some solid material, Radium A, 

 which is also radioactive like its parent. 



The next question which arises concerns the helium found in 

 the tube. Where does it come from? To discover this we must 

 go back to the alpha-particles which form part of the Bccijuercl 

 rays. These alpha-particles are helium atoms carrying two 

 charges of positive electricity ; and since niton shows very strong 

 alpha-ray activity, it is not hard to deduce that the helium found 

 in the tube by Ramsay and Soddy was simply a collection of the 

 helium atoms ejected fiom the niton in the course of its disin- 

 tegration. Thus we may symbolise the break-down of radium 

 and its descendants in the following way : — 



Table III. 



Solid RADIUM l-> HELIUM Gas 



Gas NITON S»-> HELIUM Gas 



RADIUM ^ 



-* HELIUM 



Atomic Weight 



Atomic Weight 



226 



4 



T 





NITON S»-> HELIUM 



Atomic Weight 



Atomic Weight 



222 



4 



I 





RADIUM-A 





Atomic Weight 





218 





Solid 



Thus the atom of radium, in disintegration, gives rise to an 

 atom of helium and an atom of niton ; and the atom of niton is 

 four units lighter than the radium atom, since the remainder of 

 the weight of the radium appears in the helium atom, with atomic 

 weight 4. In turn, the niton atom throws off four units of 

 weight in the guise of a helium atom and the remainder of the 

 exploded atom is the atom of radium-A, with atomic weight 218. 



The diagram above gives us the idea of a " radioactive 

 series," that is, a series of elements each of which is born from 

 one heavier than itself, and may give rise in its turn to some 



