Curves of the Periodic Law. 75 



As disintegration proceeds and atomic weight falls the steady 

 component of cohesion begins to rise in importance, in those 

 elements having an atomic weight below 180. The atoms 

 are then changing from a condition of constant volume, but 

 the steady force coming into play is sufficient to delay the 

 change to the opposite condition of constant minimum 

 density at n, fig. 2. There is in fact a return to the 

 minimum of volume at p, from which the oscillation of force 

 proceeds regularly. 



It is remarkable that this region of variation is that of the 

 rare earths, and it is now suggested that the reason for their 

 comparative fewness is that the forces under which atoms 

 are formed are modified by the rise in importance of the 

 steady central force, so that there is here in a sense in- 

 stability of type of structural formation, and permanent 

 elements are rare. 



6. So far as it is permissible to draw inferences from the 

 shape of the curves, it may be predicted that the atomic 

 volumes of elements between 150 and 180, such as gadolinium 

 and neoytterbium, will be found to be low, probably between 

 9 and 10. The corresponding densities are about 16 

 and 17. 



The atomic volumes of cerium (21) and samarium (19*3) are 

 relatively higher than those of elements in corresponding 

 positions in the other series, and elements having atomic 

 weights between 155 and 170 should have relatively lower 

 atomic volumes, those from 170 to 185 rather higher volumes 

 than would be obtained from a smooth curve similar to those 

 of the lower periods. 



7. On the degradation theory of atomic formation some 

 form of retarding action is necessary, otherwise matter would 

 slip without resistance to its lowest elements. In the con- 

 secutive loss of nuclear units from the outer ring the forces 

 controlling the size of an atom rise and fall in a regular 

 manner, and because of this periodic change retardation 

 takes the form of cyclic hysteresis. An atom about to lose a 

 unit of mass must be supersaturated, which is a lag of state 

 behind controlling force. 



