CONTEMPORARY ADVANCES IN PHYSICS 



63 



of only 1/1850 of a unit of mass, which is quite inappreciable.^ Hence 

 in a transmutation of the former sort, the point representing the 

 element in the graph moves four units downward as well as two to the 

 left; in one of the latter sort, the point simply slides horizontally to the 

 right. The meaning of Fig. 1 will now be clear. 



238 



234 



230 



22fc 



222 



218 



214 



210 



20& 



202 



80 



82 



83 



84 



85 8fe 67 88 



ATOMIC NUMBER 



89 



90 



32 



Fig. 1. Genealogies of the radioelenients 



(The actinium series is plotted some distance above the others for legibility, 

 but should almost certainly lie lower.) 



The lines in Fig. 1 which represent the family trees of the radio- 

 elements descend in zigzags, which signifies that the "decline and fall" 



^ These masses are given in terms of the unit of mass in which atomic weights are 

 measured, of which 16 constitute the mass of an oxygen atom. Were the mass of an 

 electron appreciable in these measurements, we should have to allow for the electrons 

 added to or lost from the circumnuclear family to balance the change in the nucleus- 

 charge. But then we should also have to make decisions about the mass to be 

 assigned to the energy carried away by the particles and the waves. 



