232 



and finally, 



To find r, we assume that one side of the cubic atom is f <5, 



8 

 or r = — p = 0.577 5o. 



V3 



Hence, substituting numerical values 



= + 1.04 X 10- 40 . 



Now this is of the same sign, and of the same order of magnitude as 

 the value required experimentally to make a plausible change in the 

 value of n. When we are dealing with exponents as high as 40, it 

 would seem that an agreement of order of magnitudes is of considerable 

 significance. Hence we conclude that the Schottky effect must cer- 

 tainly be expected to play an important part (a conclusion also stated 

 by Schottky, although without numerical computation). Considera- 

 tion of the effect makes the value of n required to give the right 

 compressibility larger than it otherwise would be. 



The conclusion to be drawn from all these considerations I believe 

 to be that we are not yet in a position to attach much significance to 

 the precise value of n necessary to give the best value of compressi- 

 bility. 



An interesting suggestion as to the compressibility of solids at 

 extremely high pressures is contained in Schottky 's equation 



